Dissertationen zum Thema „Locked dynamics“

External cavity semiconductor mode-locked lasers can produce pulses of a few picoseconds. The pulses from these lasers are inherently chirped with a predominant linear chirp component that can be compensated resulting in sub-picosecond pulses. External cavity semiconductor mode-locked lasers can be configured as multiwavelength pulse sources and are good candidates for time and wavelength division multiplexing applications. The gain medium in external cavity semiconductor mode-locked lasers is a semiconductor optical amplifier (SOA), and passive and hybrid mode-locked operation are achieved by the introduction of a saturable absorber (SA) in the laser cavity. Pump-probe techniques were used to measure the intracavity absorption dynamics of a SA in an external cavity semiconductor mode-locked laser and the gain dynamics of a SOA for the amplification of diverse pulses. The SOA gain dynamics measurements include the amplification of 750 fs pulses, 6.5 ps pulses, multiwavelength pulses and the intracavity gain dynamics of an external cavity multiwavelength semiconductor mode-locked laser. The experimental results show how the inherent chirp on pulses from external cavity semiconductor mode-locked lasers results in a slow gain depletion without significant fast gain dynamics. In the multiwavelength operation regime of these lasers, the chirp broadens the temporal pulse profile and decreases the temporal beating resulting from the phase correlation among wavelength channels. This results in a slow gain depletion mitigating nonlinearities and gain competition among wavelength channels in the SOA supporting the multiwavelength operation of the laser. Numerical simulations support the experimental results.
Ph.D.
Department of Physics
Optics and Photonics
Optics

As a type of nonlinear system with complexity, mode-locked fiber lasers are known for their complex behaviour. It is a challenging task to understand the fundamental physics behind such complex behaviour, and a unified description for the nonlinear behaviour and the systematic and quantitative analysis of the underlying mechanisms of these lasers have not been developed. Here, we present a complexity science-based theoretical framework for understanding the behaviour of mode-locked fiber lasers by going beyond reductionism. This hierarchically structured framework provides a model with variable dimensionality, resulting in a simple view that can be used to systematically describe complex states. Moreover, research into the attractors' basins reveals the origin of stochasticity, hysteresis and multistability in these systems and presents a new method for quantitative analysis of these nonlinear phenomena. These findings pave the way for dynamics analysis and system designs of mode-locked fiber lasers. We expect that this paradigm will also enable potential applications in diverse research fields related to complex nonlinear phenomena.

Doctor of Philosophy
Department of Physics
Brian R. Washburn
Mode-locked lasers that produce short optical pulses in the mid-infrared wavelength region have been sought out for a wide range of applications such as free space communication, molecular spectroscopy, medical diagnostics, and remote sensing. Here, a thulium and holmium (Tm/Ho) co-doped fiber laser that mode-locks in both the solitonic and stretched-pulse regimes is used to produce ultra-short pulses in the 2 [mu]m region. Nonlinear polarization rotation technique is used where fiber nonlinearity is responsible to mode-lock the laser. The anomalous group velocity dispersion of both the single mode and gain fibers used limit the laser operation in the solitonic regime where spectral bandwidth is 10 nm and hence the pulse duration is limited to 996 fs. In order to increase the spectral bandwidth and hence get the shorter pulses the anomalous dispersion of these fibers has to compensate using normal group velocity dispersion fiber in the laser cavity. High numerical aperture fibers, which have normal group velocity dispersion around 2 [mu]m due to its large and positive waveguide dispersion, can be used to compensate the anomalous dispersion of the gain and single mode fibers. We used a high numerical aperture fiber called UHNA4 in the laser cavity in order to compensate the anomalous dispersion of other fibers and mode-locked the laser in stretched pulse regime. The spectral bandwidth of the laser increased to 31 nm with corresponding pulse duration of 450 fs measured from the interferometric autocorrelation. The laser dynamics of the Tm/Ho co-doped fiber laser is also studied while going from the stretched-pulse to solitonic regime by fiber cut-back measurements of normal dispersion fiber. It was clearly observed that both the spectral bandwidth and the pulse duration changed significantly going from one region to the other.

Vertical external-cavity surface-emitting lasers are ideal testbeds for studying the influence of the non-equilibrium many-body dynamics on mode locking. As we will show in this thesis, ultra short pulse generation involves a marked departure from Fermi carrier distributions assumed in prior theoretical studies. A quantitative model of the mode locking dynamics is presented, where the semiconductor Bloch equations with Maxwell’s equation are coupled, in order to study the influences of quantum well carrier scattering on mode locking dynamics. This is the first work where the full model is solved without adiabatically eliminating the microscopic polarizations. In many instances we find that higher order correlation contributions (e.g. polarization dephasing, carrier scattering, and screening) can be represented by rate models, with the effective rates extracted at the level of second Born-Markov approximations. In other circumstances, such as continuous wave multi-wavelength lasing, we are forced to fully include these higher correlation terms. In this thesis we identify the key contributors that control mode locking dynamics, the stability of single pulse mode-locking, and the influence of higher order correlation in sustaining multi-wavelength continuous wave operation.

Cette thèse de doctorat porte principalement sur la dynamique et la robustesse d’un nouveau concept de verrouillage de mode dans les nanolasers semi-conducteurs ultracompacts. Un tel nanolaser présente des modes ermites-gaussiens créés par une cavité photonique harmonique pour confiner la lumière. Cela permet de mapper la cavité optique en oscillateur harmonique de mécanique quantique, avec des fréquences propres régulièrement espacées, une condition essentielle pour le verrouillage de mode. La période de verrouillage de mode est contrôlée par la conception du potentiel photonique, et non par la longueur de la cavité. Les régimes non linéaires possibles sont décrits par l’équation de Gross-Pitaevskii avec un potentiel parabolique et des termes non linéaires décrivant le gain et l’absorption. Pour étudier ces comportements dynamiques, des simulations numériques directes sont principalement mises en œuvre. Tout d’abord, la compétition de mode pour le gain entre les modes ermites et gaussiens en l’absence d’absorption saturable est étudiée. Deuxièmement, on prévoit que le verrouillage des modes se produira avec une saturation instantanée du gain et de l’absorption sur un large éventail de paramètres, correspondant à l’émergence d’une soliton dissipative. Troisièmement, dans le régime de saturation non instantanée du gain et de l’absorption, différents comportements dynamiques du nanolaser sont obtenus en faisant varier le gain et l’absorption. Ces différents régimes, y compris la commutation Q, le verrouillage de mode à commutation Q et le verrouillage de mode CW, sont décrits en détail. L’influence du facteur Henry sur le verrouillage de mode est également abordée. Quatrièmement, la robustesse du verrouillage de mode des modes ermite et gaussien au désordre de la cavité harmonique est étudiée en détail, y compris l’effet de la non-parabolicité du potentiel et les erreurs aléatoires dans la forme du potentiel
This PhD thesis mainly addresses the dynamics and the robustness of a novel concept of mode locking in ultracompact semiconductor nanolasers. Such a nanolaser exhibits Hermite-Gaussian modes created by a harmonic photonic cavity to confine light. This maps the optical cavity into quantum mechanical harmonic oscillator, with evenly spaced eigenfrequencies, an essential requirement for mode locking. The possible nonlinear regimes are described by the Gross-Pitaevskii equation with a parabolic potential and nonlinear terms describing gain and absorption. To investigate these dynamical behaviors, direct numerical simulations are mainly implemented. Continuation calculations are also performed using pde2path.First, the mode competition for gain among Hermite-Gaussian modes in the absence of saturable absorption is investigated and shown to be very different from usual resonators.Second, mode locking is predicted to occur with instantaneous saturation of gain and absorption over a broad range of parameters, corresponding to the emergence of dissipative soliton and multisoliton solutions. The mode locking period is controlled by the design of the photonic potential, and not by the cavity length. The dissipative soliton is well described by the coherent state of a quantum mechanical oscillator, namely a Gaussian envelope oscillating without deformation.Third, in the regime of noninstantaneous gain and absorption saturation, different dynamical behaviors of the nanolaser are obtained by varying the gain and the absorption. These different regimes, including Q-switching, Q-switched mode locking, and CW mode locking, are described in detail, illustrating the rich physics of this nonlinear system. The influence of the Henry factor on the mode locking is also discussed. Moreover, similar dynamical behaviors using spatially separated gain and absorber sections inside the cavity are obtained.Fourth, the robustness of mode locking of the Hermite-Gaussian modes to the disorder of the harmonic cavity is investigated in details. It includes the effect of non-parabolicity of the potential and the random errors in the shape of the potential

It is relatively straightforward to establish equilibrium inmagnetically confined plasmas, but the plasma is frequentlysucceptible to a variety of instabilities that are driven bythe free energy in the magnetic field or in the pressuregradient. These unstable modes exhibit effects that affect theparticle, momentum and heat confinement properties of theconfiguration. Studies of the dynamics of several of the mostimportant modes are the subject of this thesis. The studies arecarried out on plasmas in the reversed field pinch (RFP)configuration.

One phenomenon commonly observed in RFPs is mode walllocking. The localized nature of these phase- and wall lockedstructures results in localized power loads on the wall whichare detrimental for confinement. A detailed study of the walllocked mode phenomenon is performed based on magneticmeasurements from three RFP devices. The two possiblemechanisms for wall locking are investigated. Locking as aresult of tearing modes interacting with a static field errorand locking due to the presence of a non-ideal boundary. Thecharacteristics of the wall locked mode are qualitativelysimilar in a device with a conducting shell system (TPE-RX)compared to a device with a resistive shell (Extrap T2). Atheoretical model is used for evaluating the threshold valuesfor wall locking due to eddy currents in the vacuum vessel inthese devices. A good correlation with experiment is observedfor the conducting shell device.

The possibility of succesfully sustaining discharges in aresistive shell RFP is introduced in the recently rebuiltdevice Extrap T2R. Fast spontaneous mode rotation is observed,resulting in low magnetic fluctuations, low loop voltage andimproved confinement. Wall locking is rarely observed. The lowtearingmode amplitudes allow for the theoretically predictedinternal nonresonant on-axis resistive wall modes to beobserved. These modes have not previously been distinguisheddue to the formation of wall locked modes. The internal andexternal nonresonant resistive wall modes grow on the timescale of the shell penetration time. These growth rates dependon the RFP equilibrium. The internal nonresonant resistive wallmodes dominate in Extrap T2R, especially for shallow reverseddischarges. The external nonresonant modes grow solely in deepreversal discharges.

KeywordsNuclear fusion, reversed field pinch, resistiveinstabilities, wall locked modes, tearing modes, resistiveshell modes, field errors, EXTRAP-T2, EXTRAP-T2R, TPE-RX

Systeme mit Zeitverzögerung sind von großem Interesse in Nichtlinearer Dynamik und allgegenwärtig in den Naturwissenschaften. Gegenstand dieser Doktorarbeit ist die raumzeitliche Dynamik räumlich-ausgedehnter, nichtlinearer Systeme mit Zeitverzögerung, mit besonderem Augenmerk auf deren lokalisierte Lösungen. Die betrachteten Systeme werden beschrieben durch partielle Differentialgleichungen und gekoppelte Systeme von gewöhnlichen Differentialgleichungen mit verzögerter Rückkopplung. Hinsichtlich der partiellen Differentialgleichungen untersucht diese Arbeit die Existenz und Stabilität der ebenen Wellenlösungen ebenso, wie die Existenz und Stabilität der lokalisierten Lösungen der eindimensionalen, komplexen, kubischen und kubisch-quintischen Ginzburg-Landau Gleichung mit verzögerter, optischer Rückkopplung. Das erste Ergebnis dieser Arbeit ist die vollständige Beschreibung der Menge der ebenen Wellenlösungen und ihre Stabilität für lange Verzögerungszeiten. Aufgrund der Symmetrie der Ginzburg-Landau Gleichung bildet diese Menge eine eindimensionale Familie, die zum Auftreten einer „Tube“ in Parameter-Koordinaten führt. Das zweite, neuartige Ergebnis ist die Beschreibung der Modulationsinstabilität dieser lokalisierten Strukturen. Diese Instabilität kann zu einer periodischen und chaotischen Zickzackbewegung der Lösung führen. Das dritte Resultat ist die Charakterisierung gebundener Impulsfolgen in einem System von gekoppelten gewöhnlichen Differentialgleichungen mit Zeitverzögerung, das zur Beschreibung einer Anordnung von modengekoppelten Lasers herangezogen wird. In diesem Regime interagieren die modengekoppelten Impulse in verschiedenen Lasern lokal über die Balance von Abstoßung und Anziehung. Resultierend daraus entstehen Cluster von Impulsen, die in einzelnen modengekoppelten Lasern nicht möglich sind. Sämtliche genannte Phänomene wurden analytisch und numerisch behandelt.
Systems with time-delay are ubiquitous in nature and attract significant interest in the field of nonlinear dynamics. The scope of this Thesis is the spatiotemporal dynamics in spatially extended nonlinear systems with time-delay, with a focus on the dynamics of localized structures. The systems under consideration are described by partial differential equations with delayed feedback and coupled systems of delay differential equations. For the partial differential equations, the existence and stability of plane wave solutions as well as localized structures are investigated in one-dimensional complex cubic and cubic-quintic Ginzburg-Landau equation with delayed feedback. The first result of this Thesis is the complete description of the set of plane wave solutions and their stability in the limit of large delay time. Due to the symmetry of Ginzburg-Landau equation, this set forms a one-dimensional family which leads to the appearance of the “tube” in parameter coordinates which is filled densely with plane wave solutions with the increase of the delay time. The second novel result is the description of modulational instability of localized structures in spatially extended systems with time-delay which can lead to periodic and chaotic zigzagging movement of the solution. The third result is the description of bound pulse trains in coupled delay systems depicting an array of mode-locked lasers. In this regime mode-locked pulses in different lasers interact locally via the balance of their repulsion and attraction. As a result, clusters of pulses emerge which can not exist in a solitary mode-locked laser. All of the aforementioned phenomena were described analytically and the results are supported by path continuation methods as well as direct numerical simulations with a specially designed software tool.

Inicialmente, apresentam-se características de dispositivos eletrônicos conhecidos como PLLs (phase-locked loops). PLLs são amplamente empregados para se extrair sinais de tempo em canais de comunicação e em aplicações nas quais se deseja controle automático de freqüência. O objeto principal é estudar PLLs analógicos descritos por uma equação diferencial ordinária de terceira ordem. Assim, deduzem-se condições de estabilidade assintótica e identifica-se um regime de caos conservativo, que ocorre sob certas combinações de valores de parâmetros. Três métodos de controle não-linear/caótico são então apresentados e aplicados. Os métodos são os seguintes: o Método de Pyragas via realimentação de variável de estado; o Método de Pyragas com atraso temporal na realimentação; e o Método de Sinha, o qual efetua o controle perturbando um parâmetro do sistema. Simulações numéricas são levadas a cabo a fim de ilustrar o comportamento dinâmico do sistema quando sujeito à ação desses métodos. Este trabalho termina com um estudo de uma rede formada por uma cadeia de PLLs. Condições para soluções síncronas, periódicas e caóticas (dissipativas e conservativas) são deduzidas para tal rede.
Firstly, features of electronic devices known as PLLs (Phase-Locked Loops) are presented. PLLs are widely employed to extract time signals in communication channels and in applications where automatic control of frequency is desired. The main goal is to study analog PLLs described by a third-order nonlinear ordinary differential equation. Thus, conditions for asymptotic stability are derived and a regime of conservative chaos occurring under certain combinations of parameter values is identified. Then, three methods of control of nonlinear/ chaotic dynamics are presented and applied. The methods are the following: the Pyragas method via feedback of state variable; the Pyragas method with time delay in the feedback; and the Sinhas method, which performs the control by disturbing a parameter of the system. Numerical simulations are accomplished in order to illustrate the dynamical behavior of the system when subjected to the action of these methods. This work ends with a study of a single-chain PLL network. Conditions for synchronous, periodic and chaotic (dissipative and conservative) solutions are derived for such a network.

Nous présentons une étude expérimentale des effets d'anisotropie des joints interphase sur la dynamique de croissance lamellaire en solidification directionnelle d'alliages eutectiques Al-Al2Cu en échantillons minces. La croissance couplée (accrochée ou flottante) est observée optiquement en temps réel, ce qui permet le suivi in situ de régimes stationnaires et la maîtrise des stades initiaux. J'ai utilisé la diffraction de rayons X et l'EBSD pour identifier les relations d'orientation (ORs) entre la solution solide α (cfc) et l'intermétallique θ (tétragonal) dans des grands grains eutectiques. De plus, la microdiffraction Laue synchrotron (ESRF/BM32) a été utilisée pour la première fois avec succès dans ce domaine. Dans des échantillons hypoeutectiques, nous avons identifié une nouvelle famille (type-C) d'ORs mettant en jeu la coïncidence entre les plans {123}α et {100}θ, favorisée par la germination de θ sur α. Dans des échantillons hypereutectiques, la formation de grains eutectiques présentant des ORs dites Beta-6 et Alpha-4 est liée à la germination de α sur θ. Les lamelles ont tendance à s'accrocher sur un plan de coïncidence ou sur un plan (100)α. Nous avons également observé qu'une faible mosaïcité, négligeable dans θ mais pouvant atteindre 5° dans α, engendrée probablement en cours de solidification, peut présenter un caractère propagatif en fonction de l'OR. Les premières expériences de solidification directionnelle en rotation nous ont permis d'obtenir des informations sur la forme du diagramme de Wulff du joint interphase d'un grain d'OR de type-C
We present an experimental study of the effects of the anisotropy of the interphase boundaries on the lamellar growth dynamics during directional solidification of eutectic Al-Al2Cu alloys in thin samples. The coupled growth (locked or floating) is observed optically in real time, allowing the in situ monitoring of steady-state regimes and the control of initial stages. X-ray diffraction and EBSD were used to identify the orientation relationships (ORs) between the solid solution α (fcc) and the intermetallic θ (tetragonal) in large eutectic grains. In addition, synchrotron Laue microdiffraction (ESRF/BM32) has been successfully used for the first time in this field. In hypereutectic samples, we have identified a new family (type-C) of ORs involving a coincidence between a {123}α and a {100}θ planes, favored by the nucleation of θ on α. In hypereutectic samples, eutectic grains with so-called Beta-6 and Alpha-4 ORs arise via the nucleation of α on θ. The lamellae tend to lock onto a coincidence plane or a (100)α plane. We also observed that a weak mosaicity, negligible in θ but up to 5° in , was probably generated during solidification, and may present a propagative feature depending on the OR. The first experiments of rotational directional solidification allowed us to gain new information on the shape of the Wulff diagram of the interphase boundary in a type-C OR grain

Extremsökande reglering (ESC) är en modellfri adaptiv reglermetod som kan användas för att lokalisera den optimala arbetspunkten i olinjära processer. Det har nyligen visats att det finns problem med traditionell ESC om det reglerade systemet är dynamiskt. I den här avhandlingen behandlar vi en ny metod för extremsökande reglering som är applicerbar för både statiska och dynamiska system. Metoden är baserad på att reglera processens arbetspunkt tills det lokala fasskiftet hos processen når ⇡/2. Resultatet är baserat på det faktum att fasskiftet hos processer generellt förändras kraftigt kring optimum, och för låga frekvenser motsvarar optimum ett fasskift på ⇡/2radianer. Regulatorstrukturen som används liknar en faslåst slinga (PLL). Ett olinjärt Kalmanfilter används för att estimera fasen och en integrerande regulator används för att justera arbetspunkten tills fasen når det önskade fasskiftet. Resultaten är illustrerade i ett exempel där den nya regulatorstrukturen används för att optimera produktionen i en kemisk reaktor.
Extremum Seeking Control (ESC) is a model-free adaptive control method to locate and track the optimal working point for nonlinear plants. However, as shown recently, traditional ESC methods may not work well for dynamic systems. In this thesis, we consider a novel ESC loop to locate the optimal operating point for both static and dynamic systems. Considering that the phase-lag of the system undergoes a large shift near a steady-state optimum and reaches the value of ⇡/2attheoptimaloperatingpoint, thenovelESC applies the phase-lag of the target system to track the optimum. An ex-tended Kalman filter is used to ensure the accuracy of the phase estimation. The structure of a phase locked loop (PLL) is employed in combination with an integral controller to lock the phase near ⇡/2, such that the target system will operate near the optimal working point. The controller is demonstrated by application to optimization of the substrate conversion in a chemical re-actor.

Pavement roughness has been found to have an effect on the coefficient of friction measured with the Locked-Wheel Skid Tester (LWT) with measured friction decreasing as the long wave roughness of the pavement increases. However, the current pavement friction standardization model adopted by the American Society for Testing and Materials (ASTM), to compute the International Friction Index (IFI), does not account for this effect. In other words, it had been previously assumed that the IFI's speed constant (SP), which defines the gradient of the pavement friction versus speed relationship, is an invariant for any pavement with a given mean profile depth (MPD), regardless of its roughness. This study was conducted to quantify the effect of pavement roughness on the IFI's speed constant. The first phase of this study consisted of theoretical modeling of the LWT using a two-degree of freedom vibration system. The model parameters were calibrated to match the measured natural frequencies of the LWT. The calibrated model was able to predict the normal load variation during actual LWT tests to a reasonable accuracy. Furthermore, by assuming a previously developed skid number (SN) versus normal load relationship, even the friction profile of the LWT during an actual test was predicted reasonably accurately. Because the skid number (SN) versus normal load relationship had been developed previously using rigorous protocol, a new method that is more practical and convenient was prescribed in this work. This study concluded that higher pavement long-wave roughness decreases the value of the SP compared to a pavement with identical MPD but lower roughness. Finally, the magnitude of the loss of friction was found to be governed by the non-linear skid number versus normal load characteristics of a pavement.

Gravity currents, which are also known as density currents, are established when one fluid flows into another of different density, and the density difference between the two drives the flow. They are widespread and vital phenomena that occur within numerous natural systems (Lemckert and Imberger, 1993a, b; Lemckert et al., 2002; Yu et al., 2013; Zigic et al., 2002). While the majority of commonly occurring gravity currents have received significant attention by researchers, crystalline gravity currents have not been studied extensively yet, and there is very little fundamental knowledge about their behavior. Crystalline and particle-driven gravity currents are suspensions of dense particles that spread into an ambient fluid due to the difference between the density of suspension and that of the ambient fluid (Sparks et al., 1997; Simpson, 1997). Studies have been conducted in laboratories analyzing gravity currents mainly on lock exchange phenomenon (Huppert and Simpson, 1980; Hallworth et al. 1996; Lemckert et al., 2002; Rottman and Simpson, 1983; Shin et al., 2004) and continuous inflow phenomenon (Ellison and Turner, 1959; Garcia, 1993; Maxworthy, 1983; Middleton, 1966b; Zhang et al., 2008). In Lock exchange mechanism, two fluids of varying density are kept separate by a lock gate. The fluid with higher density is known as the lock fluid and it has significantly lower volume than the second fluid. When the lock gate is removed, gravity current forms because of the density difference between the fluids. During the evolution of the current, the particles continually deposit or dissolve, thus reducing the excess density of suspension and the driving buoyancy force (e. g. during the late stages of turbidity currents, Parker et al., 1986). While the non-dissolving kind (sediment-laden) is well studied by many researchers (Fragoso et al., 2013; Garcia, 1994; Hallworth et al., 1996; Kuenen, 1937; Parker et al., 1986; Simpson and Britter, 1979; Shin et al., 2004;), the crystalline gravity currents are not being looked at. The focus of this study was on these currents produced by lock release inflow of highly saline solution with suspended salt crystals to understand their behavior, and the impact they may have on the receiving environment. The results were then compared with those of unsaturated gravity currents under the same experimental conditions. Data were also extracted from the literature for sediment-laden lock release gravity currents under similar experimental conditions and compared with the findings of this study focusing on the self-similar phase. The outcomes of this experimental study showed that dynamics of crystalline gravity currents are entirely different from those of unsaturated and sediment-laden gravity currents. The temporal change in the driving buoyancy affects its characteristics. The research and outcomes of this study will assist in providing first-hand knowledge of the progress of gravity currents with initially suspended salt crystals in lock release condition into a receiving environment.
Thesis (Masters)
Master of Philosophy (MPhil)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text

The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle. The atomic nucleus is comprised of the protons and the neutrons which possess a spin each. The composite object- the atomic nucleus is therefore a tiny magnet itself. In the presence of an external bias like a magnetic field, the nucleus therefore evolves like a magnetic moment and attains a characteristic frequency in its evolution called the Larmor frequency given by, (formula) where η is the magnetogyric ratio of the particle and B is the applied magnetic field. The existence of a natural frequency presents the possibility of a resonance behaviour in the response of the system when probed with a driving field. This is the basic principle of magnetic resonance, which in the context of the atomic nucleus, was discovered independently by Purcell [2] and Bloch [3]. From its conception, the technique and the associated understanding of the involved phenomena have come a long way. In its original form the technique involved the study of the steady-state response of the nuclear magnetic moment to a driving field. This continuous wave NMR had the basic limitation of exciting resonances in a given sample, serially. In due course of time, this technique was replaced by the Fourier transform NMR (FTNMR) [4]. This technique differed from the continuous wave NMR in its study of the transient response of the system in contrast to the steady-state response in the former. The advantage of this method is the parallel observation of all the resonances present in the system ( within the band-width of the excitation). In addition to the bias created by the external field, other internal molecular fields produce additional bias which in turn produce interesting signatures on the spectrum of the system, which are potential carriers of information about the molecular state. The fact that the spins are not isolated from the molecular environment, produces a striking effect on the ideal spectrum of the system. These effects contain in them, the signatures of the molecular local environment and are hence of immense interest to physicists, chemists and biologists.

The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle. The atomic nucleus is comprised of the protons and the neutrons which possess a spin each. The composite object- the atomic nucleus is therefore a tiny magnet itself. In the presence of an external bias like a magnetic field, the nucleus therefore evolves like a magnetic moment and attains a characteristic frequency in its evolution called the Larmor frequency given by, (formula) where η is the magnetogyric ratio of the particle and B is the applied magnetic field. The existence of a natural frequency presents the possibility of a resonance behaviour in the response of the system when probed with a driving field. This is the basic principle of magnetic resonance, which in the context of the atomic nucleus, was discovered independently by Purcell [2] and Bloch [3]. From its conception, the technique and the associated understanding of the involved phenomena have come a long way. In its original form the technique involved the study of the steady-state response of the nuclear magnetic moment to a driving field. This continuous wave NMR had the basic limitation of exciting resonances in a given sample, serially. In due course of time, this technique was replaced by the Fourier transform NMR (FTNMR) [4]. This technique differed from the continuous wave NMR in its study of the transient response of the system in contrast to the steady-state response in the former. The advantage of this method is the parallel observation of all the resonances present in the system ( within the band-width of the excitation). In addition to the bias created by the external field, other internal molecular fields produce additional bias which in turn produce interesting signatures on the spectrum of the system, which are potential carriers of information about the molecular state. The fact that the spins are not isolated from the molecular environment, produces a striking effect on the ideal spectrum of the system. These effects contain in them, the signatures of the molecular local environment and are hence of immense interest to physicists, chemists and biologists.

The Northeastern Atlantic Forest of Brazil contains thousands of forest fragments at different stages of regeneration, some recovering from abandoned agricultural fields, while others recovering from chronic disturbances such as fire, logging, and poaching. Some of these fragments kept protected for several reasons: corporate responsibility, compliance with the forest code, preservation of biodiversity, among others. Although these fragments are far from having the same species richness of plant and animal, they can perform important ecosystem services, such as protection of water bodies, reservoir of important nutrients and carbon (C). This is especially important if we consider that there are global initiatives such as REDD + with the objective of assessing secondary forests and forests in recovery process as important C pools. On the other hand, the management and preservation of these fragments depends on a solid knowledge about their structure and nutrient cycle. There is a relatively rich literature on the loss of biodiversity in these Northeastern forest fragments. Much less is available, however, about the structure and function of these fragments. This work intends to contribute to fill this gap, providing solid scientific information on four forest areas and a secondary forest, where a restoration program was implemented in the State of Alagoas, Northeast of Brazil. After a brief introduction, chapter one discusses the structure of these fragments through a complete forest inventory, where individuals density, height and diameter at breast height (DBH) were measured for each tree with DBH >= 10 cm. With these allometric data, we estimated the basal area and aboveground live biomass (AGLB), comparing these attributes with other estimates available in the literature. In chapter two, we investigated the distribution of nutrients in the forest fragments, where we measured the foliar concentration of C, nitrogen (N) and phosphorus (P). At the same time, we measured the litterfall mass in each fragment and its nutrient content for a one year period of sampling. With this information we were able to establish how these areas cycled their main limiting nutrients and C. Finally, in the last chapter we approached the partition of C and nutrient stocks, above and belowground, in order to evaluate the importance of C pools and nutrients in the forest fragments and understand the role of these fragments in a world that urgently needs to store C in a sustainable reservoir.
A Floresta Atlântica do Nordeste do Brasil contém milhares de fragmentos de florestas em diferentes estágios de regeneração, alguns se recuperando de campos agrícolas abandonados, enquanto outros se recuperam de distúrbios crônicos como incêndio, extração de madeira e caça furtiva. Alguns desses fragmentos ficaram protegidos por várias razões: responsabilidade corporativa, cumprimento do código florestal, preservação da biodiversidade, entre outros. Embora estes fragmentos estejam longe de ter a mesma riqueza de espécies vegetais e animais, podem desempenhar importantes serviços ecossistêmicos, como proteção de corpos d\'água, reservatório de importantes nutrientes e carbono. Isso é especialmente importante se considerarmos que há iniciativas globais como o REDD+ que visam avaliar florestas secundárias e de recuperação como importantes reservatórios de carbono (C). Por outro lado, a gestão e preservação destes fragmentos dependem de um conhecimento sólido sobre a sua estrutura e ciclo de nutrientes. Há uma literatura relativamente rica sobre a perda de biodiversidade nestes fragmentos florestais do Nordeste. No entanto, muito menos está disponível sobre a estrutura e o funcionamento destes fragmentos. Este trabalho pretende contribuir para o preenchimento desta lacuna, fornecendo informações científicas sólidas sobre quatro áreas florestais e uma floresta secundária, onde foi implantado um programa de restauração no Estado de Alagoas, Nordeste do Brasil. Após uma breve introdução, o capítulo um discute a estrutura desses fragmentos através de um inventário florestal completo, onde a densidade indivíduos, sua altura e diâmetro à altura do peito (DAP) foram medidos para cada árvore com DAP >= 10 cm. Com esses dados alométricos, estimamos a área basal e a biomassa viva acima do solo (AGLB), comparando esses atributos com outras estimativas disponíveis na literatura. No capítulo dois, investigamos a distribuição de nutrientes nos fragmentos florestais, onde medimos a concentração foliar de C, nitrogênio (N) e fósforo (P). Ao mesmo tempo, medimos durante um ano a massa da serapilheira em cada fragmento e seu teor de nutrientes. Com essas informações pudemos estabelecer como essas áreas ciclam seus principais nutrientes limitantes e C. Finalmente, no último capítulo abordamos a partição dos estoques de C e nutrientes, acima e abaixo do solo, com o objetivo de avaliar a importância dos pools de C e nutrientes nos fragmentos de floresta e entender qual o papel desses fragmentos em um mundo que necessita urgentemente estocar C em um reservatório sustentável.

The major part of mountain drainage networks is formed by high gradient channels and their nature and dynamics affect the features of sediment delivered to downstream channels, determining the quantity, timing and size of material transported by lowland rivers. Bedload is the transport process that regards the coarser particles, that are mobilized by rolling, sliding and saltating on the channel bed. In mountain environments, the analysis and quantification of bedload transport is of fundamental importance for hazard assessment, understanding the morphodynamics of higher order channels, planning and designing reservoir sedimentation. The importance of this phenomenon contrasts with the fact that it is difficult and impractical to monitor, especially in small, steep mountain basins, due to its high-energy and impulsive nature. Moreover, in mountain streams the particle motion is strongly affected by the bed structures as well as by the highly heterogeneous channel-bed material, acting especially through the hiding/exposure, consolidation and embedding effects. These issues are reflected in the use of bedload equations that, being calibrated on data from laboratory flume experiments or from specific study areas, generally show low performances. Different direct and indirect methods can be used to monitor the bedload in the field but generally require either expensive structures (i.e. permanent monitoring stations) or extensive and perilous surveys (i.e. tracers, bedload traps). Consequently, field bedload data are relatively scarce, and monitoring programs maintained continuously over long-term periods are particularly rare. Thanks to the assumption that bedload transport may be understood as the result of random individual particle displacements, the sediment tracing method was widely employed in the last years. Such method allow to obtain precious data concerning sediment dynamic in mountain streams, improving the results obtainable by samplers, traps and permanent monitoring stations. This thesis aims to investigate the sediment dynamics in two study areas: the Rio Cordon (Alps) and Estero Morales (Andes), focusing particularly on the bedload. The Rio Cordon (northeast Italy) is a typical alpine channel characterized by step-pool and riffle-pool morphology and by a mean slope equal to 13%. The catchment extended 5 km2 exhibits a nivo-pluvial runoff regime. The second study site is the Estero Morales, a high-gradient stream located in the Metropolitan Region (central Chile). The channel bed exhibits boulder-cascade, step-pool and plane bed morphologies while the average slope is of about 9.5%. The basin (27 km2) hosts the San Francisco glacier (1.8 km2) that strongly affects the hydrological regime. In particular during the melt period (December-March) the glacier ensures daily discharge fluctuations with highly variable associated bedload transport rates. These study areas were investigated because different in terms of extent, geology, morphology, altitude, vegetation, climate, precipitation and flow regime. This dissimilarity allowed to carry out a comparative analysis. First, nearly 30 years of monitoring of sediment fluxes in the Rio Cordon instrumented basin were analyzed. The collected bedload and suspended sediment transport data allows sediment dynamics to be analyzed at different time scales, ranging from short- (single event) to long-term (three decades). The Rio Cordon monitoring station has been operating since 1986, continuously recording water discharge, bedload and suspended load (at 1 hr intervals, and 5 min intervals during floods). At the flood event scale, a good relationship was found between peak (Qpeak) and sediment load. The annual trend of sediment fluxes was analyzed as well as the single floods contribution to the total sediment yield. The annual suspended load contribution ranges from 10 to 2524 t y-1, while the bedload varies from 0 to 1543 t y-1. The higher annual yields were recorded in the years when large floods occurred, highlighting that the sediment budget in the Rio Cordon is strongly controlled by the occurrence of high magnitude events. Investigation of the seasonal suspended load contribution demonstrated that from 1986 to 1993 most sediments were transported during the snowmelt/summer seasons, whilst autumn and snowmelt were the dominant seasons contributing to sediment yield in the periods 1994-2004 and 2004-2014, respectively. The mean annual sediment yield from 1986 to 2014 is equal to 103 t km-2 y-1, and overall, bedload accounts for 21% of the total sediment yield. The ratio between the amount of sediment transported by the floods and the effective runoff of the events allowed the temporal trends of transport efficiency to be inferred, highlighting the existence of periods characterized by different sediment availability. In particular, a period with high transport efficiency appears to have occurred after an exceptional event registered in September 1994 (RI > 100 years). The 1994 flood affected the sediment availability at the basin and channel bed scales, and provided a legacy influencing the sediment dynamics in the basin over the long-term by increasing the transport efficiency for approximately a decade. The achieved results update the sediment budget assessed in the Rio Cordon, shedding further light on the long-term and recent behavior of sediment dynamics in a high gradient mountain basin. Once assessed the quantity and timing of sediment yield, the sediment entrainment conditions were investigated. For this purpose, the tracing method was used in either study areas. Specifically, on the channel bed of Rio Cordon and Estero Morales creeks were seeded 250 and 429 PITs (i.e Passive Integrated Transponder), respectively. In the Rio Cordon, the tracers are monitored since the 2010, analyzing the displacement over a study reach 320 m long. The Estero Morales creek was equipped with tracers since the austral summer 2014, and the displacements over a reach of approximately 700 m were monitored. Overall, 25 PIT surveys were performed in the two study areas, using a mobile antenna to detect the position of the tracers. In the Estero Morales and Rio Cordon the average recovery rate was 50% and 70%, respectively. These values are in line with the recoveries obtained by similar works concerning the tracing of bedload using PIT tracers. In terms of peak of water discharge (Qpeak), in the Alpine channel the monitored floods range between 0.44 m3 s-1 to 2.10 m3 s-1, while in the Andean stream Qpeak varies among 3.44 m3 s-1 and 4.68 m3 s-1. In either study cases, the influence of particle size and hydraulic forcing conditions on the sediment entrainment were investigated. In both channels, the size-selective transport appears the prevalent transport dynamic during the relative low-moderate magnitude floods while equal mobility conditions were triggered by the higher magnitude events. Notwithstanding the similar dynamics, the relationship between the grain size distribution of tracers mobilized and Qpeak seems to suggest that in the Rio Cordon the sediment entrainment is strongly affected by particle size, while in the Estero Morales such relationship is poorly defined. In order to compare the hydraulic forcing conditions, the unit stream power (ω) is derived from discharge measurement. Additionally for each displacement, the flow duration curve was realized and consequently the 25th (ω25), 50th (ω50) and 75th (ω75) percentiles of unit stream power were calculated. These significant percentiles, with the ωpeak, are used in order to test their capacity to explain the relationship among hydraulic forcing and tracers displacement. In both study areas, the mean transport distances are better correlated with the ωpeak of individual transport events, which appears the most relevant descriptor as regards the sediment entrainment. In this sense, the Estero Morales showed a persistent high transport capacity, while the Rio Cordon exhibited similar conditions only above a threshold ( ~ 400 W m-2). Over such threshold the Alpine stream exhibits higher transport efficiency compared to the Andean channel. This thesis benefited by two monitoring programs. First, the long-lasting monitoring program undertaken on the Rio Cordon thanks to the experimental station active since 1986, that permitted to produce long-term data series, very precious in order to analyze the sediment dynamics over long-term. Secondly, the use of PIT tracers in the Estero Morales and Rio Cordon creeks allowed to obtain interesting results concerning the sediment entrainment in this two study areas, permitting to perform a comparative analysis. In this sense, the PIT tracers have proved to be a very fitting method to monitoring the bedload without disturbing the channel bed and avoiding empirical assumptions regarding the sediment transport.
La maggior parte della rete idrografica montana è costituita da collettori ad elevata pendenza (torrenti montani). La natura e la dinamica di tali collettori influenzano le caratteristiche del materiale solido rilasciato a valle, determinando aspetti quali quantità, temporalità e caratteristiche fisiche del sedimento trasportato ai fiumi pedemontani e vallivi. Col termine trasporto di fondo (bedload) si definisce la mobilitazione del materiale grossolano presente in un collettore, materiale che viene mobilitato lungo il letto tramite rotolamento, strisciamento e saltazione. In ambiente montano, l’analisi e la quantificazione del trasporto di fondo è di fondamentale importanza per diversi aspetti, come ad esempio poter meglio comprendere le condizioni morfo-dinamiche dei collettori montani, valutare il pericolo connesso al trasporto solido, pianificare e progettare opere di trattenuta. L’importanza di questo fenomeno contrasta però col fatto che esso è di difficile monitoraggio, soprattutto nei piccoli bacini montani, a causa della sua natura puramente impulsiva. Inoltre, nei torrenti montani la mobilità del sedimento è fortemente influenzata dalla presenza di forme di fondo e dal materiale altamente eterogeneo costituente il letto del collettore, aspetti che si traducono negli effetti di nascondimento/esposizione (hiding/exposure), consolidamento (consolidation) e incorporamento (embedding). Tali condizioni rendono difficile la valutazione del trasporto di fondo e si riflettono, ad esempio, nelle equazioni predittive. Esse, infatti, sono perlopiù sviluppate tramite esperimenti di laboratorio (flume) o calibrate in specifiche aree studio, e quindi forniscono generalmente basse performance se applicate ad altri siti di studio. Diversi metodi diretti ed indiretti possono essere utilizzati in campo al fine di monitorare il trasporto di fondo. Generalmente tali metodi richiedono la realizzazione di dispendiose strutture (es. stazioni di monitoraggio permanenti) o estese e perigliose indagini di campo (es. tracers, bedload traps). Come conseguenza, i dati di campo riguardanti il trasporto di fondo sono relativamente scarsi, ed in particolare i programmi di monitoraggio mantenuti nel lungo periodo sono particolarmente rari. Grazie all’assunzione che il trasporto di fondo può essere inteso come il risultato di singoli movimenti casuali di particelle, negli ultimi anni il metodo dei traccianti (tracers) è stato largamente impiegato in campo. Tale metodologia consente di ottenere preziosi dati riguardanti le dinamiche di trasporto solido, affinando i risultati ottenibili tramite samplers, traps e stazioni di monitoraggio permanenti. L’obiettivo principale del lavoro di tesi è stato quello esaminare le dinamiche di trasporto solido in due aree studio, il Rio Cordon (Alpi) e l’Estero Morales (Ande), focalizzandomi in particolare nell’indagine del trasporto solido di fondo. Il Rio Cordon (NE Italia) è un tipico torrente alpino, caratterizzato da una prevalente configurazione step-pool/riffle-pool e da un pendenza media pari al 13%. Il bacino esteso 5 km2 mostra un regime dei deflussi dominato da scioglimento nivale e da precipitazione piovose. In questo bacino è in funzione dal 1986 una stazione di monitoraggio, realizzata al fine di registrare in continuo le portate liquide ed il trasporto solido (di fondo e in sospensione). Il secondo sito è l’Estero Morales, torrente montano situato nella Región Metropolitana de Santiago (Cile centrale). Il collettore presenta una morfologia mista, in cui prevalgono le configurazioni a boulder-cascade, step-pool e plane bed, mentre la pendenza media è pari al 9.5%. Questo bacino andino ospita il ghiacciaio San Francisco (1.8 km2), il quale influenza notevolmente il regime idrologico dell’area studio. Durante il periodo di scioglimento (Dicembre-Marzo), il ghiacciaio assicura fluttuazioni giornaliere nelle portata idriche con un ampio variabilità nei tassi di trasporto solido. Queste aree studio sono state esaminate in quanto diverse in termini di geologia, morfologia, vegetazione, clima, precipitazioni e regime delle portate. Tale diversità ha permesso di poter eseguire un’analisi comparativa tra le due aree studio. Grazie ai dati prodotti dalla stazione di monitoraggio situata nel Rio Cordon, sono stati analizzati i flussi di sedimento registrati dal 1986 ad oggi. I dati raccolti riguardanti sia il trasporto solido di fondo che in sospensione hanno permesso di analizzare le dinamiche di trasporto solido a diverse scale temporali, spaziando dal breve (eventi di piena) al lungo periodo (tre decenni). A scala di evento, una buona relazione è stata trovata tra picco di portata (Qpeak) e le quantità di sedimento trasportate. Il trend annuale nei flussi di sedimento è stato esaminato così come il contributo dei singoli eventi alla produzione totale di sedimento da parte del bacino. In questo senso, il contributo annuale in sospensione varia tra 10 e 2524 t y-1 mentre il trasporto di fondo varia tra 0 e1543 t y-1. In termini di quantità trasportate, i maggiori apporti annuali sono stati registrati negli anni in cui si sono verificati eventi ad elevata magnitudo, evidenziando come il budget di sedimento nel Rio Cordon sia controllato dal verificarsi di tali fenomeni. L’analisi del trasporto in sospensione stagionale ha dimostrato che tra il 1986 e il 1993 la maggior parte del materiale fine è stato mobilitato durante lo scioglimento nivale e durante la stagione estiva. L’autunno ed il periodo di scioglimento nivale sono stati invece le stagioni che hanno principalmente contribuito nei periodi 1994-2004 e 2004-2014, rispettivamente. Il bacino del Rio Cordon, nel periodo 1986-2014, è stato caratterizzato da una produzione media annuale di sedimento pari a 103 t km-2 y-1, con il trasporto di fondo che ha contributo per il 21% al totale trasportato. Il rapporto tra la quantità di sedimento trasportato da ciascun evento ed il volume d’idrogramma che ha contribuito a tale evento di trasporto, ha permesso di ottenere un trend temporale riguardante l’efficienza di trasporto. Tale trend ha evidenziato l’esistenza di periodi caratterizzati da una diversa disponibilità di sedimento. In particolare, un periodo ad elevata efficienza di trasporto sembra essersi verificato successivamente ad un evento eccezionale registrato nel Settembre 1994 (RI > 100 years). Tale evento ha influenzato le disponibilità di sedimento sia a scala di bacino che di collettore, e la sua magnitudo ha influenzato le dinamiche di trasporto solido nel lungo periodo, incrementandone l’efficienza per circa un decennio. I risultati ottenuti aggiornano il budget di sedimento riguardante il Rio Cordon, facendo inoltre luce sulle quelle che possono essere nel lungo periodo le dinamiche di trasporto in un bacino alpino. Una volta affrontata la questione della quantità e la temporalità con cui un collettore montano può trasportare sedimento, la tesi si è focalizzata nell’esaminare le condizioni di mobilità che caratterizzano il trasporto di fondo. A questo scopo, il metodo dei traccianti e stato utilizzato in entrambi i siti di studio. Nello specifico 250 PITs (Passive Integrated Transponders) sono stati installati nel Rio Cordon, mentre 429 sono stati posizionati nell’Estero Morales. Nel collettore alpino i tracers sono stati monitorati a partire dal 2010, indagandone gli spostamenti lungo un tratto di studio esteso 320 m. L’Estero Morales è stato equipaggiato con i traccianti a partire dall’estate australe 2014 ed utilizzando un tratto di studio esteso circa 700 m. Complessivamente nelle aree di studio sono stati eseguiti 25 monitoraggi PIT, avvalendosi di un’antenna mobile per determinare la posizione dei traccianti. Nelle campagne di misura effettuate nell’Estero Morales e nel Rio Cordon sono stati raggiunti dei tassi di recupero dei traccianti pari al 50% e 70%, rispettivamente. Tali valori sono in linea con i tassi ottenuti da lavori simili riguardanti il monitoraggio tramite tracers. In termini di portata al picco, nel Rio Cordon sono stati monitorati eventi compresi tra 0.44 m3 s-1 e 2.10 m3 s-1, mentre nell’Estero Morales QPEAK varia tra 3.44 m3 s-1 e 4.68 m3 s-1. In entrambi i siti, è stata esaminata l’influenza sia della dimensione del sedimento sia delle condizioni idrologiche sulle distanze di trasporto. In entrambi i casi, il trasporto selettivo appare la dinamica di trasporto prevalente durante gli eventi a bassa e media magnitudo; mentre condizioni di equimobilità sono state innescate dagli eventi ad elevata magnitudo. Nonostante queste dinamiche simili, la relazione tra granulometria dei traccianti mobilitati e Qpeak sembra suggerire che nel Rio Cordon il trasporto è fortemente influenzato dalle dimensioni della particella, mentre nell’Estero Morales tale relazione appare alquanto debole. Al fine di confrontare i casi studio, lo stream power (ω) è stato utilizzato in entrambi i siti per descrivere le condizioni idrologiche. Per ciascun movimento PIT, è stata realizzata la relativa curva di durata potendo così calcolare anche il 25° (ω25), 50° (ω50) e 75° (ω75) percentile di unit stream power a cui è stato sottoposto ciascun tracciante. In entrambi i siti la distanza media è positivamente correlata con ωpeak, il quale appare il descrittore più rilevante per quanto riguarda la mobilità dei traccianti. In questo senso, nell’Estero Morales è stata riscontrata durante l’intero periodo di studio una elevata capacità di trasporto. Nel Rio Cordon condizioni comparabili sono state osservate solo oltre una specifica soglia ( ~ 400 W m-2), oltre cui il collettore alpino mostra capacità di trasporto superiori rispetto a quanto osservato nel torrente andino. Questa tesi beneficia di due programmi di monitoraggio dedicati al trasporto di fondo. Il primo è rappresentato dal monitoraggio a lungo termine in corso nel Rio Cordon e svolto dal 1986 dalla stazione sperimentale. Tale programma ha prodotto una serie di dati estesa quasi tre decenni, permettendo di analizzare le dinamiche di trasporto solido nel lungo periodo. Oltre a ciò, il monitoraggio intrapreso nell’Estero Morales e nel Rio Cordon tramite l’uso di traccianti PIT ha consentito di ottenere interessanti risultati riguardanti la mobilità del sedimento in queste due aree studio, permettendo di effettuare un analisi comparativa. In questo senso, i traccianti PIT si sono dimostrati un metodo particolarmente adatto al monitoraggio del trasporto di fondo, il quale non causa disturbi al letto del collettore ed evita di doversi avvalere di assunzioni empiriche riguardanti un fenomeno così complesso come il trasporto solido.

The Seattle District wants to better manage the Ballard Locks and structures along the Lake Washington Ship Canal (LWSC) in a way that will maintain the environmental sustainability and biodiversity in the area. Due to strict salt water intrusion regulations in the LWSC, the Seattle District is working on upgrading their management practices such that they will resolve two inter-related problems. First, to improve the fish passage conditions for migrating salmon; and second, to learn how to better manage the salt wedge that forms and intrudes upstream. Based on the hydrodynamic and water quality results that are produced by this research, the Engineer Research and Development Center (ERDC) Portland Office will use their Eulerian-Lagrangian-Agent-Model (ELAM) to analyze fish patterns, looking for the most beneficial management schemes that assist salmon in migrating upstream. This research implemented CFD engineering techniques to help better understand the effectiveness of the hydraulic structures in the area, as well as come up with management practices that both mitigate the salt water intrusion from Puget Sound, and improve the migrating passages for salmon.

This work deals with the impact of selected electronic chassis systems of modern vehicles, their driving dynamics. The general aim of this work is to create the basic methodology for assessing casualties of the influence of these systems. The thesis is describing functions and effects antilock and stability systems on vehicle dynamics. Below are possible methods and systems for determining the influence on accident plot. As part of the study was performed measuring the impact of anti-lock system on the vehicle. The result of this work is the basic methodology to the analysis of road accidents involving vehicles with electronic chassis systems.

Abstract

With the Introduction of the internet and human technological advancement, our everyday lives have changed dramatically over the past 20 years and because of this, how we communicate, form social networks and purchase or sell goods have also developed.

In the light of this, we have completed this thesis which concerns the influence of the internet and the possibilities of forming long lasting relationships between businesses and customers through what we have described as ‘Locking in’ the customer. This is done by forming ‘Psychological Switching Costs’ that make the cognitive process of switching too expensive or un-wanted by the customer. In order to develop an understanding of this we saw it as prudent to interview senior managers of businesses that operate mainly on the internet to discover if they attempt such strategic moves in, ‘Locking in’ customers. Thus forming the research question; How are Companies based on the internet using Psychological Switching Costs as a strategy to Lock in the customers?

The process by which the information was collected was through a qualitative method and semi-structured interviews. We found from the respondents that were interviewed that when it comes to operating a business on the internet it is important to consider, Transparency, Two-way communication, Simplicity, Agility and Flexibility in creating a loyal customer who is positively locked in. These were the strategies considered by the respondents to have an effect on customers.

One of the most interesting points that were made was that if the customer was locked in to the business, the business did not have to be as dynamic. Thus, according to the respondents, Psychological Switching Costs do have an influence on how they form strategy to Lock In customers. In that it can be beneficial to attempt to Lock in customers rather than develop other Dynamic Capabilities. This factor seems very relevant when considering communication, agility and flexibility, in that by forming relationships and strategies directly to the customer these companies are creating something that is difficult to substitute, un-imitable for their competitors and convenient to the customer.

Bayou St. John (BSJ) and City Park Lakes and Lagoons (CPLL) are urban waterways in New Orleans, Louisiana. I studied habitat selection of red drum in BSJ, and fish assemblage change in BSJ and CPLL over 40 years. Temperature was found to be the best predictor of red drum habitat selection in Bayou St. John, while salinity and change in depth also were found to be good predictors for certain sites. Potential prey item abundance did not appear to influence habitat selection. Using data from 1971 – 2010, nearshore habitats in CPLL were affected by Hurricane Katrina, but have sense recovered and nearshore habitats in BSJ were found to have decreased diversity. Pelagic habitats in both areas were found stable across 40 years. Since 2006, nearshore assemblages were similar for CPLL and BSJ with a decrease in fishes from Order: Cyprinodontiformes and an increase in other fishes seen across years.

This doctoral thesis deals with design aspects of a reconfigurable frequency synthesizer for flexible radio transceivers in future cognitive multi-radios. The frequency bandwidth to be covered by this multi-radio synthesizer corresponds to the frequency bands of the most diffused wireless communication standards in the frequency band 800 MHz to 6 GHz. Since multi-standard operation is required, the synthesizer must fulfil the most stringent and sometimes conflicting requirements. Given these requirements, a novel approach for multi-mode frequency synthesis has been conceived. A hybrid phase locked loop based frequency synthesizer has been proposed and a novel switching protocol has been presented and validated on an experimental evaluation board. This approach combines fractional-N and integer-N modes of operation with switched loop filter topology. Compared to standard PLL techniques, the hybrid configuration provides a great flexibility in terms of reconfiguration and moreover, it offers relatively low circuit complexity and low power consumption. This architecture provides reconfiguration of the loop bandwidth, frequency resolution, phase noise and settling time performance and hence, it can adapt itself to diverse requirements given by the concerned wireless communication standards. Corresponding analyses, simulations and measurements have been carried out in order to verify the performance and functionality of the proposed solution. A part from the design of the multiband frequency synthesizer, a set of regional measurements of the radio spectrum utilization has been carried out in the framework of this dissertation research. These measurements are based on the energy detection principle and provide a close look at the degree of radio spectrum utilization in different regions, namely in the city of Brno in the Czech Republic and in the city of Paris and one of its suburbs in France. The goal of the experimental measurement campaign has been to estimate the degree of radio spectrum usage in a particular environment and to point out the fact that a new approach for radio spectrum management is inevitable

Neste trabalho, são estudados os problemas de sincronismo de fase nas redes mestre-escravo de via única (OWMS), nas topologias Estrela Simples, Cadeia Simples e mista, através da Teoria Qualitativa de Equações Diferenciais, com ênfase no Teorema da Variedade Central. Através da Teoria das Bifurcações, analisa-se o comportamento dinâmico das malhas de sincronismo de fase (PLL) de segunda ordem que compõem cada rede, frente às variações nos seus parâmetros constitutivos. São utilizadas duas funções de excitação muito comuns na prática: o degrau e a rampa de fase, aplicadas pelo nó mestre. Em cada caso, discute-se a existência e a estabilidade do estado síncrono. A existência de pontos de equilíbrio não-hiperbólicos, não permite uma aproximação linear, e nesses casos é aplicado o Teorema da Variedade Central. Através dessa rigorosa técnica de simplificação de sistemas dinâmicos é possível fazer uma aproximação homeomórfica em torno desses pontos, preservando a orientação no espaço de fases. Desse modo, é possível determinar, localmente, suas estabilidades.
This work presents stability analysis of the syncronous state for three types of one-way master-slave time distribution network topologies: single star, single chain and both of them, mixed. Using bifurcation theory, the dynamical behavior of second-order phase-locked loops employed to extract the syncronous state in each node is analyzed in function of the constitutive parameters. Two usual inputs, the step and the ramp phase pertubations, are supposed to appear in the master node and, in each case, the existence and stability of the syncronous state are studied. For parameter combinations resulting in non hyperbolic synchronous states, the linear approximation does not provide any information, even about the local behaviour of the system. In this case, the center manifold theorem permits the construction of an equivalent vector field representing the asymptotic behaviour of the original system in the neighborhood of these points. Thus, the local stability can be determined.

Quantifying the impacts of restoration on coastal waterways is crucial to understanding their effectiveness. Here, I look at the impacts of multiple restoration projects on urban waterways within the city limits of New Orleans, LA, with an emphasis on the response of fishes. First I report the effects of two projects designed to improve exchange down estuary on the hydrologic characteristics of Bayou St. John (BSJ). Within BSJ, flow is dominated by subtidal wind driven processes. Removal of an outdated flood control structure did not appear to alter exchange in BSJ, but removal combined with sector gate openings did. I also refined a three dimensional hydrodynamic model of this system to have accurate predictions of velocity and elevation. Temperature and salinity were difficult to constrain with this model. Solutions of this model were used to compare flow metrics, along with linearly interpolated temperature, and other variables to Red Drum (Sciaenops ocellatus) activity and movement patterns. Relationships between Red Drum activity and velocity suggested a response to subtidal, wind driven flow. Overall, high Sedentariness, a measure of inactivity, was found suggesting high levels of site fidelity. Higher mean Sedentariness during the night was also found. I also used a pseudo-BACI design to analyze the fish assemblage response to removal of an outdated flood control structure and the impacts of sector gate openings on fish guild species richness in BSJ. Limited differences were found when comparing fish assemblages before and after removal, but these differences were likely due to a decrease in salinity not restoration efforts. No significant differences in Freshwater or Estuarine fish guild species richness was observed for any of the control or impact sites. Marine fish species richness was found to be higher immediately following sector gate openings at the site closest to the structure, suggesting an initial pulse of young marine organisms is provided via these events. The findings here can be used to optimize management of exchange flow in coastal impounded waterways.

Outsourcing attracted much attention in 1989 when Kodak outsourced its data center operation to IBM (International Business Machines Corp.). Nowadays, this strategy has become more popular. At the beginning of this century, the ASP (Application Service Provider) model was considered one of the typical solutions of Internet-based IT (Information Technology) outsourcing. Although this model has been transformed and renamed (e.g. SaaS - Software as a Service), the principle concept of providing IT service through the Internet or wide area network is still there. This study attempts to explore the determinants of customer perception of Internet-based IT outsourcing by obtaining a comprehensive understanding of the ASP model. The research dimensions not only include factors affecting users' perception of service quality but also ASP business position (i.e. the firm origin of ASP and its provider type) and services utilized by the customers. Through the study of firm history, two important theoretical themes of this research - path-dependence and Ansoff's product/ market growth matrix - are taken account of in exploring the influence of the determinants. Web-based questionnaire survey research is conducted together with a documentation study to collect data. Targeting the customers of the top 50 ASPs selected by ASPnews.com during the period 2001-2004, the researcher contacted 597 potential respondents, and 196 responses were returned. The valid sample consisted of 175 responses, and 124 of them not only provided full information for satisfaction evaluation but also the information for tracking their ASP vendors' business position. The GLM (General Linear Model) and the Pearson correlation coefficient were the major statistical approaches used to evaluate the survey data for developing a structural model. The research findings indicated that the factors associated with service competitiveness, such as capability and performance, reliability and trustworthiness, affordability, integration and customization, have positive effects on customer perceived satisfaction; whereas lock-in has a negative effect. More specifically, the origin of the ASP firm has a direct effect on capacity and performance, and also directly influences the use of IT adoption services. Based on this finding, a descriptive analysis and qualitative research shows that two mechanisms for path-dependence - existing expertise and perceived expertise - can affect the satisfaction level of capacity and performance of ASP services. On the other hand, provider type has a direct effect on affordability and also directly influences the use of facility supporting services. On this basis, another two mechanisms for path-dependence - transaction cost and standardization - can indirectly impact customer's perception of this business model via affordability. In addition to those major findings, some other determinants (e.g. software applications, brand of applications, and intensity of service used) were also identified in this study. The study result can be used for theoretical understanding about the determinants of ASP customer's perception. It not only indicates a new perspective to enhance the current body of research on this topic, but can also be more broadly applied to any fast-growth firm, rapid-change business, or technology intensive industry. Acknowledgements I would like to sincerely thank the following people for their contribution to this research project. Dr. Scott Koslow, my chief supervisor, for his continued encouragement, patience and guidance to ensure the completion of this project. His speciality in statistics has provided appropriate and valuable guidance in the data analysis for my research. Dr. Steven Lim, my second supervisor, for his advice, coherence, and support over the years. I also appreciate his constructive comments on my drafts and the shaping of my research. Dr. Bob McQueen and Dr. Jim Corner, for their assistance and advice in the early stages of my study. My parents, Yu-Ho and Lee-Chiung Liang, and my brother Ken, my sisters Annie, Eva, and Nancy, my brothers-in-law, J.C. and Chen, and Alice, my sister-in-law, for their emotional support throughout the length of my study. I also thank Bessie, my best friend for her assistance in data collection and her loving support, as well as Ted, Kevin, Mark, Frank, and Shirley, my study mates for their encouragement and friendship. Special thanks goes to Dr. Kuang-Ya Wang, the principal of Yu Da High School of Commerce and Home Economics, Taiwan, and also to the staff over there for their concern and assistance in data collection. Most importantly, my heartfelt appreciation goes to Warren, my husband. I am deeply grateful to him for his understanding, patience, and practical help. Without his enduring support I could not have done this study. Finally, my thanks and gratitude goes to those people who patiently answered my survey questionnaire as their kind assistance made it possible to complete this research.

Une écoulement de cavité ouverte tridimensionnel saturé non-linéairement est étudié par une approche spatio-temporelle utilisant des données expérimentales résolues à la fois en temps et en espace. Ces données ont été acquises dans deux plans longitudinaux, respectivement perpendiculaire et parallèle au fond de la cavité, dans le régime incompressible, en air ou en eau. À l'aide de multiples méthodes de décompositions globales en temps et en espace, les ondes et les structures cohérentes constituant la dynamique dans le régime permanent et pouvant être produites par des mécanismes d'instabilités différents sont identifiées et caractérisées.Tout d'abord, on approfondit la compréhension de l'effet des non-linéarités sur les oscillations auto-entretenues de la couche cisaillée impactante et leurs interactions avec l'écoulement intra-cavitaire. En particulier, l'analyse spectrale d'une portion de l'espace des paramètres permet de mettre en évidence un lien entre l'accrochage des modes d'oscillations auto-entretenues, la modulation d'amplitude au niveau du coin impactant et l'intermittence de ces modes. De plus, l'observation des basses fréquences intéragissant fortement avec les oscillations de la couche de mélange démontre l'existence d'une dynamique tridimensionnelle intrinsèque à l'intérieur de la cavité malgré les perturbations causées par la couche cisaillée instable.Les analyses de stabilité linéaire ont montré que des instabilités centrifuges peuvent résulter de la courbure induite par la recirculation. L'étude de la dynamique après saturation révèle de nombreuses structures cohérentes dont les propriétés sont quantifiées et classées en s'appuyant sur la forme des instabilités sous-jacentes: des ondes transverses progressives ou stationnaires. Enfin, certains comportements des structures saturées suggèrent que les mécanismes non-linéaires gouvernant le développement de l'écoulement une fois sorti du régime linéaire pourraient être étudiés dans le cadre des équations d'amplitude
A space-time study of a three-dimensional nonlinearly saturated open cavity flow is undertaken using time-resolved space-extended experimental data, acquired in both cross-stream and spanwise planes, in incompressible air and water flows. Through use of multiple modal decompositions in time and space, the waves and coherent structures composing the dynamics in the permanent regime are identified and characterised with respect to the instabilities arising in the flow.Effects of nonlinearities are thoroughly investigated in the impinging shear layer, regarding the self-sustained oscillations and their interactions with the inner-flow. In particular, the analysis conducted throughout the parameter space enlightens a global connection between the selection of locked-on modes and the amplitude modulation at the impingement and the mode switching phenomenon. Furthermore, observations of low frequencies interacting drastically with the shear layer flapping motion underline the existence of intrinsic coherent three-dimensional dynamics inside the cavity in spite of the shear layer disturbances.Linear stability analyses have demonstrated that centrifugal instabilities are at play along the main recirculation. The present investigation of the dynamics after onset of the saturation reveals numerous space-time coherent structures, whose properties are quantified and classified with respect to the underlying instabilities: travelling or standing spanwise waves. Finally, some patterns exhibited by the saturated structures suggest that the nonlinear mechanisms governing the mutations of the flow after the linear regime could gain more insight in the frame of amplitude equations

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Instituto Presbiteriano Mackenzie
Recognition of patterns can be performed by using neural networks built with oscillators, like phase-locked loops (PLLs). These networks are modeled with differential equation systems and can be studied by using Dynamical System Theory, which is used in this work in order to investigate the dynamical behavior related to a synaptic configuration of a neural network. As a result of such an investigation, two methods (Brute Force and Algebric) that help to build neural networks formed by PLLs are presented. These methods aim to relate the synaptic configuration of the network to the corresponding basin of attraction of fixed points, which represent the stored patterns on the network. Also general properties of synaptic configuration are presented in order to generate other useful configurations. Then a model of an image recognition machine able to store in its memory a monochromatic image and able to determine if other image is similar to the memorized one is proposed.
Reconhecimento de padrões pode ser feito usando redes neurais construídas com osciladores, como malhas de sincronismo de fase (PLLs). Essas redes são modeladas por sistemas de equações diferenciais e podem ser estudas pela Teoria de Sistemas Dinâmicos, que é usada neste trabalho para investigar o comportamento dinâmico associado a uma configuração sináptica de uma rede neural. Como resultado dessa investigação, são apresentados dois métodos (Força Bruta e Algébrico) que auxiliam na construção de redes neurais formadas por PLLs. Esses métodos têm como objetivo relacionar a configuração sináptica da rede às respectivas bacias de atração de pontos atratores, os quais representam os padrões memorizados na rede. Também são apresentadas propriedades gerais da configuração sináptica que podem ser usadas para compor outras configurações de interesse. Por fim, é proposto um modelo de máquina reconhecedora de imagem capaz de armazenar em sua memória uma figura monocromática e determinar se uma imagem qualquer apresentada a ela é semelhante à memorizada.

L'objet de la thèse est l'étude des dynamiques industrielles, en particulier des biais cognitifs qui conduisent au blocage de ces dynamiques. Si les processus d'innovation dépassant le cadre de l'entreprise ont fait l'objet de diverses recherches, les dynamiques industrielles sont restées peu étudiées sous l'angle du blocage cognitif dans les activités de conception. Pour approfondir cette question, la thèse se focalise sur l'étude d'une phénoménologie nouvelle, l'innovation orpheline, définie comme une innovation très attendue par la société, mais qu'aucun acteur ou consortium d'acteurs n'est capable de générer, alors que les conditions traditionnelles pour favoriser son émergence sont réunies. L'enjeu de la thèse est de répondre à trois questions: Quelle modélisation pour cerner les facteurs causaux de l'innovation orpheline ? ; Quel outil pour diagnostiquer les biais cognitifs dans une situation empirique ? ; Quelles modalités organisationnelles pour sortir de l'innovation orpheline ?Cette démarche a permis de dégager trois résultats principaux :1) un modèle de la fixation cognitive collective, soulignant l'impact fort que peut avoir l'interaction entre les imaginaires singuliers au sein d'un collectif.2) un outil, le référentiel C-K pour identifier la fixation collective et pour diagnostiquer l'innovation orpheline.3) un modèle d'action pour un nouvel acteur, baptisé l'architecte de l'inconnu, en charge de stimuler les capacités de conception innovante de l'écosystème d'acteurs
The purpose of the thesis is the study of industrial dynamics, in particular cognitive biases that lead to the lock-in of these dynamics. If innovation processes beyond the scope of the firm have been the subject of various studies, little has been done on the study of industrial dynamics from the perspective of cognitive lock in design activities. To explore this question, the thesis focuses on the study of a new phenomenology, orphan innovation, which is defined as orphan innovation as an innovation highly expected by society, but one which no actor or consortium of actors can manage to process with their current innovation capabilities, although all of the institutional conditions to foster it are gathered. The aim of the thesis is to answer three questions: How to model industrial dynamics and to identify causal factors of orphan innovation? How to build a tool to diagnose cognitive biases and orphan innovation in empirical situations? What are the organizational levers to overcome orphan innovation situations?The thesis then is based on three main results:1) a model of collective cognitive fixation, underlying the impact of imaginaries and their interactions among a collective action.2) a methodology to identify collective fixation and therefore to diagnose orphan innovation.3) a model of action for a new actor, called the architect of the unknown, in charge of stimulating innovative design capacities of the actors among the industry

Afin de réduire les émissions de gaz à effet de serre et le coût du transport maritime, l'utilisation des cerfs-volants comme système de propulsion auxiliaire des navires est prometteuse. Pour estimer les performances et l’opérabilité d’un navire tracté par cerf-volant, une modélisation dynamique du système est alors mise en oeuvre. Une modélisation analytique de cerf-volant est utilisée. Ce modèle néglige la masse du cerf-volant et suppose que les lignes sont droites et indéformables. Ces hypothèses conduisent à un modèle cinématique dépendant du coefficient de portance et de la finesse aérodynamique. Une évolution linéaire des coefficients aérodynamiques en fonction de la courbure de la trajectoire de vol est proposée. Par ailleurs, en développant un modèle quasi analytique de ligne, il est montré qu’à partir de 2 m.s-1 de vent relatif que l’hypothèse de ligne droite est raisonnable. En se basant sur un modèle de ligne, un critère analytique de vitesse de vent minimum permettant un vol quasi-statique est présenté. Dans le but de résoudre l’ensemble des termes d’interaction entre le cerf-volant et le navire, un modèle linéarisé de tenue à la mer temporelle est développé. Le produit de convolution de la réponse impulsionnelle du navire est calculé avec des systèmes d’états. Cependant comme celle-ci représente mal les mouvements horizontaux des navires, le modèle développé est alors couplé à un modèle de manoeuvrabilité. Pour étudier les interactions entre le cerf-volant et le navire un couplage monolithique et un couplage dissocié sont comparés. Le couplage dissocié néglige l’influence des mouvements du navire sur le vol du cerf-volant. En cas de mer calme, les résultats obtenus par les deux types de couplage sont très proches. En cas de houle régulière les mouvements du navire sont principalement causés par la houle. Le couplage monolithique montre qu’un réseau de sous-harmoniques basse fréquence apparait alors dans le spectre d’excitation du navire. La fréquence fondamentale des sous-harmoniques est donnée par la différence entre la fréquence de vague et la fréquence de l’harmonique la plus proche de l’excitation du kite. Quand cette différence est suffisamment petite, un phénomène d’accrochage apparait. Ce phénomène est bénéfique pour le cerf-volant et le navire quand le décalage des harmoniques d'excitation correspond à une augmentation. Par ailleurs, une étude de la stabilité de route montre qu'il est nécessaire de contrôler activement le safran
In order to reduce greenhouse gas emissions and shipping costs, the use of kites as an auxiliary propulsion device for ships is promising. In order to estimate the performance and the operability of a kite-towed vessel, a dynamic modeling of the system is implemented. A classical kite modeling is used. This model neglects the mass of the kite and assumes straight and inelastic tethers. These assumptions lead to a kinematic model depending on the lift coefficient and the aerodynamic lift to drag ration angle. A linear evolution of these aerodynamic coefficients as a function of the curvature of the flight path is proposed. In addition, by developing a quasi-analytical line model, it is shown that from 2 m.s-1 of relative wind the straight tether assumption is reasonable. Based on the tether model, an analytical criterion assessing the minimum wind speed to enable a quasi-static kite flight is developed. To solve all the interaction terms between the kite and the ship, a time domain seakeeping model based on the linearized ship equation of motion assuming a potential flow is developed. The convolution product of the impulse response of the ship is computed with state-space systems. However, since horizontal ship motions are not well represented by such theories, a coupling with a maneuvering model is presented.Comparisons to experimental data tests show good agreements. To study the interactions between the kite and the ship, a monolithic coupling and a dissociated coupling are compared. The dissociated coupling neglects the influence of ship motions on the kite flight. In a calm water case, results obtained by the two types of coupling are very close. In regular waves, ship motions are dominated by the wave influence. Thus, with the monolithic coupling, a network of low frequency subharmonic appears in the kite excitation spectrum. The fundamental frequency of the subharmonic is given by the difference between the wave frequency and the frequency of the nearest kite excitation harmonic. When this difference is small enough, a lock-in phenomenon appears. This phenomenon is a benefit for the kite and the ship when the shift of the excitation harmonics corresponds to an increase. Furthermore, a course keeping stability study shows that the rudder needs to be actively controlled

As Diretrizes da Política Nacional de Transporte Hidroviário apresentam metas ambiciosas para os próximos anos quanto à construção de eclusas e ao aumento da participação do transporte aquaviário de carga na matriz brasileira. A bibliografia expõe que os custos são otimizados quando um desnível é transposto com a construção do menor número eclusas, o que resulta na busca pela transposição de desníveis significativos com a execução de eclusas com uma única câmara. No entanto, problemas hidráulicos encontrados junto às comportas de enchimento e esvaziamento estão entre as principais limitações para o aumento da altura de queda das eclusas. Os diferenciais de pressão entre as faces de montante e jusante das comportas e a variação do seu grau de abertura durante as operações de enchimento e esvaziamento de eclusas de navegação de média e alta queda geram escoamentos turbulentos, com velocidades e pressões capazes de produzir danos às estruturas. Com o objetivo de analisar os parâmetros hidráulicos do escoamento médio a jusante de comportas dos sistemas de enchimento e esgotamento de eclusas, do tipo segmento invertida, e as pressões instantâneas ao longo do teto e da base do conduto, de forma a identificar e caracterizar padrões de comportamento que auxiliem na elaboração de projetos e no aperfeiçoamento dessas estruturas, foram conduzidas duas investigações complementares, a experimental e a numérica. A investigação experimental, desenvolvida no Laboratório de Obras Hidráulicas do Instituto de Pesquisas Hidráulicas da Universidade Federal do Rio Grande do Sul, proporcionou a geração de dados discretos de pressão instantânea ao longo do teto e da base do conduto para 53 condições de abertura e vazão, para escoamento em regime permanente. A investigação numérica, realizada com o software Flow-3D®, de Dinâmica de Fluidos Computacional, viabilizou a geração de dados do escoamento médio no interior do conduto para 12 condições de abertura e vazão, que reproduziam as simulações experimentais. Os resultados das simulações realizadas no Flow-3D® com modelo de turbulência k- e demonstraram a sua aplicabilidade no estudo do escoamento médio a jusante de comportas de sistemas de enchimento e esvaziamento de eclusas. O modelo numérico reproduziu os dados experimentais de pressão a montante da comporta e os formatos das curvas de pressão ao longo da base e do teto do conduto a jusante da comporta, apresentando resultados mais aderentes para a base. Para as condições operacionais com a comporta parcialmente aberta, as menores pressões ocorreram no teto do conduto próximo à comporta, região de recirculação do escoamento, e junto ao terminal da comporta. A partir da análise dos dados foi possível a caracterização do comportamento das pressões médias, das flutuações de pressão e das pressões máximas e mínimas ao longo da base e do teto do conduto por meio da relação entre coeficientes adimensionais de posição e de pressão.
Brazilian Waterways Policy has ambitious goals for constructing navigation locks and increasing the participation of the cargo transport through waterways in the national transport matrix. Literature states that costs are optimized by the construction of fewer locks for the transposition of water levels by vessels, which results in the search for transposition of significant lifts by using navigation locks with single camera. However, the hydraulic problems in the filling and emptying systems, especially close to the valves, are among the major limitations to increase the lock lift. During filling and emptying operations of medium and high-lift locks, the pressure difference between upstream and downstream sides of lock valve and its opening generate turbulent flows with associated flow velocities and pressures capable of damaging the structures. In the current research, experimental and numerical investigations were conducted in order to analyze the mean flow through lock culvert valves and the instantaneous pressures behavior along the culvert roof and base, and to identify and to characterize hydraulic parameters which could be useful for project development and improvement of these structures. The experimental research was conducted at the “Laboratório de Obras Hidráulicas” of the “Instituto de Pesquisas Hidráulicas” of the “Universidade Federal do Rio Grande do Sul” and provided the generation of discrete data of instantaneous pressure along the culvert roof and base for 53 conditions of flow and valve opening. Experimental simulations were performed with steady state flow. Numerical investigation applied the Computational Fluid Dynamics software Flow-3D® and produced information for the mean flow inside the culvert for 12 valve opening and flow conditions, which reproduced the experimental simulations. valve opening and flow conditions, which reproduced the experimental simulations. The numerical results, obtained by using the k-e turbulence model, demonstrated the applicability of Flow-3D® in the study of the mean flow downstream of lock culvert valves. The numerical model was able to reproduce the experimental data of pressure along the culvert base and roof presenting more accuracy to base data. For partially open gate conditions, the lowest pressures were verified next to the valve lip and at the downstream culvert roof close to the valve, which correspond to the recirculating flow region. From data analysis it was possible to characterize the behavior of the mean pressure, pressure fluctuations and extreme pressures along the culvert base and roof by the relationship between dimensionless coefficients of position and pressure.

A park lock is a mechanism used to prevent unintentional movement of the vehicle. A failure in the proper function of this mechanism can lead to the safety concerns of an automobile. The main focus of this thesis is to understand the reason behind the failure of the park lock mechanism by FEM analysis in ANSA. For this, temperature build up during the park lock engagement has been studied in a dynamic explicit analysis. The FE results are compared to results from experiments on park lock. The modelling has been done in ANSA, ABAQUS was used as a solver for simulation and the results have been studied in META. The results indicate that there is a rise in the temperature. This is due to the friction between the contact surfaces and the oscillations generated in the vehicle. Based on the observations, discussions and conclusions are formulated and the research questions are answered.

This project was a step forward in improving the voltage profile of traditional low voltage distribution networks with high photovoltaic generation or high peak demand. As a practical and economical solution, the developed methods use a Dynamic Voltage Restorer or DVR, which is a series voltage compensator, for continuous and communication-less power quality enhancement. The placement of DVR in the network is optimised in order to minimise its power rating and cost. In addition, new approaches were developed for grid synchronisation and control of DVR which are integrated with the voltage quality improvement algorithm for stable operation.

The design of microprocessors is undergoing radical changes that affect the performance and reliability of hardware and will have a high impact on software development. Future systems will depend on a deep collaboration between software and hardware to cope with the current and predicted system design challenges. Instead of higher frequencies, the number of processor cores per chip is growing. Eventually, processors will be composed of cores that run at different speeds or support specialized features to accelerate critical portions of an application. Performance improvements of software will only result from increasing parallelism and introducing asymmetric processing. At the same time, substantial enhancements in the energy efficiency of hardware are required to make use of the increasing transistor density. Unfortunately, the downscaling of transistor size and power will degrade the reliability of the hardware, which must be compensated by software. In this thesis, we present new algorithms and tools that exploit speculative and asymmetric execution to address the performance and reliability challenges of multicore architectures. Our solutions facilitate both the assimilation of software to the changing hardware properties as well as the adjustment of hardware to the software it executes. We use speculation based on transactional memory to improve the synchronization of multi-threaded applications. We show that shared memory synchronization must not only be scalable to large numbers of cores but also robust such that it can guarantee progress in the presence of hardware faults. Therefore, we streamline transactional memory for a better throughput and add fault tolerance mechanisms with a reduced overhead by speculating optimistically on an error-free execution. If hardware faults are present, they can manifest either in a single event upset or crashes and misbehavior of threads. We address the former by applying transactions to checkpoint and replicate the state such that threads can correct and continue their execution. The latter is tackled by extending the synchronization such that it can tolerate crashes and misbehavior of other threads. We improve the efficiency of transactional memory by enabling a lightweight thread that always wins conflicts and significantly reduces the overheads. Further performance gains are possible by exploiting the asymmetric properties of applications. We introduce an asymmetric instrumentation of transactional code paths to enable applications to adapt to the underlying hardware. With explicit frequency control of individual cores, we show how applications can expose their possibly asymmetric computing demand and dynamically adjust the hardware to make a more efficient usage of the available resources.

Die Assoziation kleiner Moleküle (Liganden) in hydrophobe Bindungstaschen spielt eine fundamentale Rolle in der Biomolekularerkennung und den Selbstassemblierungsprozessen der physikalischen Chemie wässriger Lösungen. Während der Einfluss des Wassers auf die freie Energie der Bindung (die Bindungsaffinität) im thermischen Gleichgewicht in den letzten Jahren auf immer stärkere Aufmerksamkeit stößt, ist die Rolle des Wassers in der Kinetik und der Bestimmung der Bindungsraten noch weitestgehend unverstanden. Welche nanoskaligen Effekte des Wassers beeinflussen die Dynamik des Liganden in der Nähe der Bindungstasche, und wie lassen sie sich durch die chemischen Eigenschaften der Tasche steuern? Neuste Forschungen haben mithilfe von molekularen Computersimulationen eines einfachen Modells gezeigt, dass Hydrationsfluktuationen in der hydrophoben Bindungstasche an die Dynamik des Liganden koppeln und damit seine Bindungsrate beeinflussen. Da die Wasserfluktuationen wiederum durch die Geometrie und Hydrophobizität der Bindungstasche beeinflusst werden, entsteht die Möglichkeit, kontrollierte Fluktuation zu kreieren, um die Bindungsraten des Liganden zu steuern. In dieser Arbeit wird diese Perspektive mithilfe eines theoretischen Multiskalenansatzes für prototypische Schlüssel-Schloss-Systeme aufgegriffen. Wir untersuchen den Einfluss der physikochemischen Eigenschaften der Bindungstasche auf die Diffusivität und die Bindungsraten des Liganden, und wie die Orientierung eines anisotropen Liganden an die Hydrationsfluktuationen der Tasche koppelt. Damit stellen wir fest, dass kleine Änderungen der Taschentiefe eine extreme Beschleunigung der Bindungsraten bewirken kann und, dass gleichzeitig die Bindung in konkave Taschen vorteilhaft für die Reorientierungsdynamik des Liganden ist. Die Resultate dieses Projekts sollen somit helfen, maßgeschneiderte Lösungen für funktionale „Host-Guest“-Systeme sowie pharmazeutische Moleküle in biomedizinischen Anwendungen zu entwickeln.
The association of small molecules (ligands) to hydrophobic binding pockets plays an integral role in biochemical molecular recognition and function, as well as in various self-assembly processes in the physical chemistry of aqueous solutions. While the investigation of water contributions to the binding free energy (affinity) in equilibrium has attracted a great deal of attention in the last decade, little is known about the role of water in determining the rates of binding and kinetic mechanisms. For instance, what are the nanoscale water effects on ligand diffusion close to the hydrophobic docking site, and how can they be steered by the chemical composition of the pocket? Recent studies used molecular simulations of a simple prototypical pocket-ligand model to show that hydration fluctuations within the binding pocket can couple to the ligand dynamics and influence its binding rates. Since the hydration fluctuations, in turn, can be modified by the pocket’s geometry and hydrophobicity, the possibility exists to create well-controlled solvent fluctuations to steer the ligand’s binding rates. In this work, we pick up this appealing notion employing a theoretical multi-scale approach of a generic key-lock system in aqueous solution. We explore the influence of the physicochemical properties of the pocket on local ligand diffusivities and binding rates and demonstrate how the orientation of a (non-spherical) ligand couples to a pocket’s hydration fluctuations. We find that minor modulation in pocket depth can drastically speed up the binding rate and that, concurrently, binding to molded binding sites is advantageous for the rotational dynamics of the ligand. The results and discussion of this work shall, therefore, imply generic design principles for tailored solutions of functional host-guest systems as well as optimized drugs in biomedical applications.

Cette thèse porte sur la conception, la réalisation et la caractérisation de diodes lasers de puissance, faible bruit à 1.5 µm sur InP pour des applications d’optique hyperfréquence, notamment pour des liaisons optiques analogiques de grande dynamique pour les systèmes radar. La première partie du travail a consisté à modéliser et concevoir des structures laser DFB ayant de faibles pertes internes. Ces structures, appelées lasers à semelle, incorporent une couche épaisse de matériaux entre la zone active et le substrat pour agrandir et délocaliser le mode propre optique des zones dopées p. La complexité de la conception résidait dans le bon compromis à trouver entre les performances statiques et dynamiques. Nous avons réalisé des diodes-lasers DFB avec une puissance > 150 mW, un rendement de 0.4 W/A, un niveau de bruit de 160 dB/Hz et une bande passante de modulation à 3 dB de 7.5 GHz. Les composants ont ensuite été caractérisés puis évalués dans des liaisons analogiques. Nous avons démontré des performances de gain de liaison, de dynamique et de point de compression à l’état de l’art mondial. En bande L (1-2 GHz) par exemple, nous avons montré des liaisons avec 0.5 dB de gain, un point de compression de 21 dBm et une dynamique (SFDR) de 122 dB.Hz2/3.En utilisant la même méthodologie de conception, la dernière partie du travail de thèse a été consacrée à la réalisation et à la caractérisation de lasers de puissance à verrouillage de modes pour la génération de train d’impulsions ultra-courts et la génération de peignes de fréquences. Ces structures présentent de très faibles largeurs de raie RF (550 Hz) et de très fortes puissances optiques (> 18 W en puissance crête)
This work focuses on the design, realization and characterization of high power, low noise 1.5 µm diode lasers for microwave applications and more particularly for high dynamic optical analog link for radar systems. The first part of this study deals with modeling and design of low internal losses DFB laser structures. These specific structures are called slab-coupled optical waveguide lasers, and are composed of a thick layer between the active layer and the substrate. The aim of this waveguide is to enlarge the optical eigenmode and to move the optical mode away from p-doped layers. The main difficulty was to find the good trade-off between laser static performances (optical power, efficiency) and dynamic performances (RIN and modulation bandwidth). We have succeeded in developing high efficiency (0.4 W/A), low noise (RIN ≈ 160 dB/Hz) DFB lasers with more than 150 mW and a 3 dB modulation bandwidth up to 7.5 GHz. We have then characterized our components on wide band and narrow band analog links. We have demonstrated state of the art gain links, dynamic and 1 dB compression power. In the L band (1-2 GHz) for example, we have obtained an optical link with a gain of 0.5 dB, a compression power of 21 dBm and a dynamic (SFDR) of 122 dB.Hz2/3.Finally we have applied the methodology and the design of slab-coupled optical waveguide structures to develop high power mode-locked lasers for ultra-short pulses generation and for optical and electrical comb generation. We have demonstrated narrow RF linewidth (550 Hz) lasers with very high power (continuous power > 400 mW and peak power > 18 W)

An understanding of compartment fire behaviour is important for fire protection engineers. For design purposes, whether to use a prescriptive code or performance based design, life safety and property protection issues are required to be assessed. The use of design fires in computer modelling is the general method to determine fire safety. However these computer models are generally limited to the input of one design fire, with consideration of the complex interaction between fuel packages and the compartment environment being simplified. Of particular interest is the Heat Release Rate, HRR, as this is the commonly prescribed design parameter for fire modelling. If the HRR is not accurate then it can be subsequently argued that the design scenario may be flawed. Therefore the selection of the most appropriate fire design scenario is critical, and an increased level of understanding of compartment behaviour is an invaluable aid to fire engineering assumptions. This thesis details an experimental study to enhance the understanding of the impact and interaction that the size and location of pool fires within an enclosure have upon the compartment fire behaviour. Thirty four experiments were conducted in a reduced scale compartment (½ height) with dimensions of 3.6m long by 2.4m wide by 1.2m high using five typical ventilation geometries (fully open, soffit, door, window and small window). Heptane pool fires were used, located in permutations of three evenly distributed locations within the compartment (rear, centre and front) as well as larger equivalent area pans located only in the centre. This thesis describes the experimental development, setup and results of the experimental study. To assist in the classification of compartment fire behaviour during the experiments, a ‘phi’ meter was developed to measure the time dependent equivalence ratio. The phi meter was developed and configured to measure O₂, CO₂ and CO. The background development, calibration, and experimental results are reported. A review of compartment fire modelling using Fire Dynamics Simulator, has also been completed and the results discussed. The results of this experimental study were found to have significant implications for Fire Safety Engineering in that the size of the fire is not as significant as the location of the fire. The effect of a fire near the vent opening was found to have a significant impact on compartment fire behaviour with the vent located fuel source increasing the total compartment heat release rate by a factor of 1.7 to that of a centrally placed pool fire of the same total fuel area. The assumption that a fire located in the centre of the room provides for the highest heat release rate is not valid for post-flashover compartment fires. The phi meter was found to provide good agreement with the equivalence ratio calculated from total compartment mass loss rates, and the results of FDS modelling indicate that the use of the model in its current form can not be applied to complex pool fire geometries.

Data Handover est une librairie de fonctions adaptée aux systèmes distribués à grande échelle. Dho offre des routines qui permettent d'acquérir des ressources en lecture ou en écriture de façon cohérente et transparente pour l'utilisateur. Nous avons modélisé le cycle de vie de Dho par un automate d'état fini puis, constaté expérimentalement, que notre approche produit un recouvrement entre le calcul de l'application et le contrôle de la donnée. Les expériences ont été menées en mode simulé en utilisant la libraire GRAS de SimGrid puis, en exploitant un environnement réel sur la plate-forme Grid'5000. Par la théorie des files d'attente, la stabilité du modèle a été démontrée dans un contexte centralisé. L'algorithme distribué d'exclusion mutuelle de Naimi et Tréhel a été enrichi pour offrir les fonctionnalités suivantes: (1) Permettre la connexion et la déconnexion des processus (ADEMLE), (2) admettre les locks partagés (AEMLEP) et enfin (3) associer les deux propriétés dans un algorithme récapitulatif (ADEMLEP). Les propriétés de sûreté et de vivacité ont été démontrées théoriquement. Le système peer-to-peer proposé combine nos algorithmes étendus et le modèle originel Dho. Les gestionnaires de verrou et de ressource opèrent et interagissent mutuellement dans une architecture à trois niveaux. Suite à l'étude expérimentale du système sous-jacent menée sur Grid'5000, et des résultats obtenus, nous avons démontré la performance et la stabilité du modèle Dho face à une multitude de paramètres
Data Handover is a library of functions adapted to large-scale distributed systems. It provides routines that allow acquiring resources in reading or writing in the ways that are coherent and transparent for users. We modelled the life cycle of Dho by a finite state automaton and through experiments; we have found that our approach produced an overlap between the calculation of the application and the control of the data. These experiments were conducted both in simulated mode and in real environment (Grid'5000). We exploited the GRAS library of the SimGrid toolkit. Several clients try to access the resource concurrently according the client-server paradigm. By the theory of queues, the stability of the model was demonstrated in a centralized environment. We improved, the distributed algorithm for mutual exclusion (of Naimi and Trehel), by introducing following features: (1) Allowing the mobility of processes (ADEMLE), (2) introducing shared locks (AEMLEP) and finally (3) merging both properties cited above into an algorithm summarising (ADEMLEP). We proved the properties, safety and liveliness, theoretically for all extended algorithms. The proposed peer-to-peer system combines our extended algorithms and original Data Handover model. Lock and resource managers operate and interact each other in an architecture based on three levels. Following the experimental study of the underlying system on Grid'5000, and the results obtained, we have proved the performance and stability of the model Dho over a multitude of parameters

碩士
國立交通大學
光電工程系所
96
Asynchronous mode-locked fiber soliton lasers have some interesting properties including slow periodic variation of the pulse parameters and excellent low noise performance. They may find applications in high speed optical communication, ultrafast optical processing, and other scientific researches. The study of the thesis is focused on how to characterize the slow periodic variation of the pulse timing position and the pulse center frequency by directly analyzing the RF spectra of the laser output pulse train. The measured results are compared with theoretical results to enhance our understanding on the laser dynamics of asynchronous mode locked fiber soliton lasers. This will also help to develop the applications of this new laser source.

碩士
國立交通大學
光電工程學系
99
Asynchronous Harmonic Mode-Locked Ytterbium Doped Fiber Lasers have many characteristics which are of great application potentials in the fields of long-distance optical communication, bio-photonics and ultrafast optics. These advantages include higher super-mode suppression ratios and the capability of generating ultrahigh repetition rate and ultra-short pulse trains. In this thesis, we demonstrate for the first time an asynchronous harmonic mode-locked ytterbium doped fiber laser with the hybrid mode-locking technique. This is the first observation of the asynchronous harmonic mode-locking in a normal dispersion fiber cavity. The deviation frequency of the laser is 94 kHz and the super-mode suppression ratio is around 60 dB at the 10 GHz asynchronous harmonic mode-locked state. The super-mode suppression ratio increases around 40 dB than the ordinary harmonic mode-locked state. The output power is around 20 mW operating at 1050 nm, a useful wavelength in many applications including bio-photonics.

碩士
國立臺灣海洋大學
光電科學研究所
105
In this thesis,we study the relationship between different input powers and polarization state of Nd: YAG crystal. So we made a series of experiments and inferences. I use Nd:YAG crystal to achieve mode-locked laser. And observe whether its polarization states will change with different input powers and crystal positions. Changing the different crystal positions will have different polarization modes, so the pumping source irradiate in different crystal positions will have different polarization states. I had been successful in the experiment. So I analyzed and discussed the polarization characteristics of the Nd: YAG mode-locked laser experiment.