Dissertations / Theses on the topic 'Stability to noise'
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Grein, Matthew Edward 1970. "Noise and stability of actively modelocked fiber lasers." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29237.
Full textIncludes bibliographical references (leaves 162-174).
The timing jitter of a modelocked laser is fundamentally limited by the amplified spontaneous emission in the laser cavity. While one cannot, even in principle, remove this source of noise, one does have control over the pulse timing by using filtering and modulation. In this thesis, we report on the advances made in developing the understanding of timing jitter and stability in actively modelocked soliton fiber lasers. The main achievements reported here are: the development of a theory for quantum-limited timing jitter for the cases of amplitude and phase modulation (AM and PM, respectively); identification of a set of characteristic coefficients governing the physics of pulse retiming that depend on the laser parameters; construction of an apparatus-including the development of harmonically modelocked soliton fiber lasers in both a ring and a sigma configuration-to measure the predicted coefficients; and residual phase-noise measurements of the quantum-limited timing jitter using homodyne detection. The measurements of the characteristic coefficients and the timing jitter were found to be in good agreement with the theory. In addition, a theory for the case of harmonic modelocking was developed, and it is shown that the supermodes reveal pulse-to-pulse correlation statistics and must be included in measurements and calculations of the timing jitter. For the case of uncorrelated timing jitter between different pulses in the laser cavity, the supermodes are predicted to have the same timing jitter spectrum as the baseband mode, and this is confirmed by measurements.
(cont.) A scheme for reducing the timing jitter of a pulse train outside of the laser cavity using group-velocity dispersion and phase modulation is described, and it is shown theoretically that a reduction in the timing jitter is possible, but only at the expense of the carrier-frequency fluctuations. It is also shown that two-photon absorption in a semiconductor mirror structure prevented pulse dropouts in a short harmonically modelocked soliton fiber laser producing picosecond pulses at 2 GHz.
by Matthew Edward Grein.
Ph.D.
Bandla, Atchaiah. "Highly Linear 2.45 GHz Low-Noise Amplifier Design." Thesis, Linköpings universitet, Fysik och elektroteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-119982.
Full textAnanthaganeshan, Kanapathipillai Arunachalam. "Stability and performance of active vibration isolation systems." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273915.
Full textSalgado, Adriana M. "Jet hydrodynamic and noise calculations using the parabolized stability equations." Thesis, University of Southampton, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.560810.
Full textGruman, Fredrick S. (Fredrick Steven). "Stability analysis of the optical reference gyro discrete noise eliminator." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36459.
Full textSiakalli, Michailina. "Stability properties of stochastic differential equations driven by Lévy noise." Thesis, University of Sheffield, 2009. http://etheses.whiterose.ac.uk/15019/.
Full textWang, Shaokang Jerry. "Analysis of Stability and Noise in Passively Modelocked Comb Lasers." Thesis, University of Maryland, Baltimore County, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10840412.
Full textThe search for robust, low-noise modelocked comb sources has attracted significant attention during the last two decades. Passively modelocked fiber lasers are among the most attractive comb sources. The most important design problems for a passively modelocked laser include: (1) finding a region in the laser’s adjustable parameter space where it operates stably, (2) optimizing the pulse profile within that region, and (3) lowering the noise level. Adjustable parameters will typically include the cavity length, the pump power, and the amplifier gain, which may be a function of the pump power, the pump wavelength, and both the material and geometry of the gain medium.
There are two basic computational approaches for modeling passively modelocked laser systems: the evolutionary approach and the dynamical approach. In the evolutionary approach, which replicates the physical behavior of the laser, one launches light into the simulated laser and follows it for many round trips in the laser. If one obtains a stationary or periodically-stationary modelocked pulse, the laser is deemed stable and, if no such pulse is found, the laser is deemed unstable. The effect of noise can be studied by using a random number generator to add computational noise. In the dynamical approach, one first obtains a single modelocked pulse solution either analytically or by using the evolutionary approach. Next, one finds the pulse parameters as the laser parameters vary by solving a root-finding algorithm. One then linearizes the evolution equations about the steady-state solution and determines the eigenvalues of the linearized equation, which we refer to as the equation’s dynamical spectrum. If any eigenvalue has a positive real part, then the modelocked pulse is unstable. The effect of noise can be determined by calculating the noise that enters each of the modes in the dynamical spectrum, whose amplitudes are described by either a Langevin process or a random walk process.
The evolutionary approach is intuitive and straightforward to program, and it is widely used. However, it is computationally time-consuming to determine the stable operating regions and can give ambiguous results near a stability boundary. When evaluating the noise levels, Monte Carlo simulations, which are based upon the evolutionary approach, are often prohibitively expensive computationally. By comparison, the dynamical approach is more difficult to program, but it is computationally rapid, yields unambiguous results for the stability, and avoids computationally expensive Monte Carlo simulations. The two approaches are complementary to each other. However, the dynamical approach can be a powerful tool for system design and optimization and has historically been undertilized.
In this dissertation, we discuss the dynamical approach that we have developed for design and optimization of passively modelocked laser systems. This approach provides deep insights into the instability mechanisms of the laser that impact or limit modelocking, and makes it possible to rapidly and unambiguously map out the regions of stable operation in a large parameter space. For a given system setup, we can calculate the noise level in the laser cavity within minutes on a desktop computer.
Compared to Monte Carlo simulations, we will show that the dynamical approach improves the computational efficiency by more than three orders of magnitude. We will apply the dynamical approach to a laser with a fast saturable absorber and to a laser with a slow saturable absorber. We apply our model of a laser with a slow saturable absorber to a fiber comb laser with a semiconductor absorbing mirror (SESAM) that was developed at National Institute of Standards and Technology (NIST), Boulder, CO. We optimize its parameters and show that it is possible to increase its output power and bandwidth while lowering the pump power that is needed.
Lanaria, Lois. "The Effects of Vibratory Noise on Responses to Postural Stability." Master's thesis, Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/203894.
Full textM.S.
Our human balance system is critical for preventing falls. The system consists of a complex set of sensorimotor controls that includes integration of sensory inputs including sight, touch and vestibular to produce motor output. Tactile afferents from the plantar surface contribute to the human balance and movement control system. Loss of sensory information could lead to impaired balance primarily because of impaired detection of changes in upright position, delayed postural reflexes, or failure to realize how far one's center of mass has been displaced thus increasing the probability of falls. Somatosensory and visual information must be integrated to interpret complex sensory environment. Sensory pathways that are simultaneously feeding inputs into the system exhibit non-linear behavior and it is unlikely that the role of a single pathway can be characterized in a static environment. As the sensory environment changes, the need to re-weight the relative dependence on each senses is essential for maintaining stability. Thus, attention also plays an important role in postural control. Attention can be defined as the individual's capacity for information processing. Performing two or more tasks at the same time may require more than an individual's attention capacity and thereby may weaken performance in the other task. Stochastic resonance phenomena has been shown to enhance sensory information processing and perception. This series of studies sought to analyze the effects of vibrotactile noise on human postural responses using a sub-threshold vibration (SV) and above-threshold vibration (AV). The vibrotactile noise was applied at the soles of both feet with six DC vibrator disks embedded in open-type footwear. Twenty one healthy adults wearing the vibrating footwear stood quietly on a compliant surface for 90 seconds inside a three-wall virtual environment. The visual conditions were either eyes closed, eyes open or a continuous visual flow field in a pitch-up direction at constant velocity of 30°/sec. A dual task paradigm was presented as a computation task, the Fibonacci sequence. The first 30 seconds of the 90 seconds trial had no vibration followed by 30 seconds of either sub-threshold or above-threshold vibration. Vibration was removed for the final 30 seconds. Root mean squares (RMS) and approximate entropy (ApEn) of center of mass (COM) and center of pressure (COP) excursions were calculated in the anterior-posterior (AP) and medio-lateral (ML) directions for each 30 second time period and normalized to each subject's initial position. Approximate entropy (ApEn) was used to detect movement variability in a time series to determine the unpredictability of the postural responses. COP and COM data were tested for statistical significance using repeated measures analysis of variance (ANOVA) with within-subject factors of vision (3 levels: eyes closed, eyes open and pitch-up), task (2 levels: single task and dual task), and vibration level (2 levels: sub-threshold vibration and above-threshold vibration) at a 95% confidence level (p<0.05). Results supported the hypothesis that the application of SV and AV affected COP regularity and variability differently when subjected to different visual conditions (eyes closed, eyes open and pitch-up). COM randomness increased (higher ApEn) when attention was diverted from postural control which is in agreement with previous studies. The decrease in COM AP randomness (lower ApEn) with vibration suggested that the application of vibration increased the amount of attention invested in postural control or balance when performing an attention demanding cognitive task. The SV increased the COP-AP regularity (lower ApEn) during eyes-closed and eyes-open conditions while AV increased COP-AP variability (increased RMS) during the pitch-up visual condition. In conclusion, posture and balance were affected by the application of vibration noise. The vibration noise enhanced the amount of attention invested in postural control while performing an attention demanding cognitive task and sensory-motor learning was achieved by increasing COM sway structure regularity (lower ApEn) but not the sway magnitude. These results suggest that the interaction between vibration noise and an attention demanding task resulted in the temporal re-structuring of the postural control system without affecting the equilibrium region for the COM sway excursion. Vibration noise appears to facilitate postural control by altering postural response regularity (lower ApEn). For COM, only postural response regularity but not sway variability was affected by vibration noise in relation to vision regardless of the vibration level (SV or AV). For COP postural responses, the effect of SV and AV differs. Due to the perception of self-motion from the pitch-up visual condition, COP postural response most likely arise from cortical level. Since AV only affected COP responses during pitch-up visual condition and not SV, this study suggests that AV applied affected the cortical level of postural control. Effects of SV on postural responses between the eyes-open and eyes-closed vision conditions suggests that SV may affect a subcortical level of postural control. Understanding the effects and mechanism of vibratory noise may help in the design of effective interventions to prevent falls and rehabilitation. These results provide the scientific basis for development of a SR-based rehabilitation device for people with sensory information and processing deficiency as occurs with aging or stroke. The finding of after effects of vibratory noise can be used to determine dosage of vibrotactile stimulation in the design of vibrating footwear.
Temple University--Theses
Wan, Kin Wa. "Advanced numerical and digital techniques in frequency stability analysis." Thesis, University of Portsmouth, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237843.
Full textHo, Yenpo. "Dynamic stability margin analysis on SRAM." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2722.
Full textTabatabaei, Ardekani Iman. "Stability analysis of adaptation process in FxLMS-based active noise control." Thesis, University of Auckland, 2012. http://hdl.handle.net/2292/12430.
Full textKeerthi, Rajasekhar. "STABILITY AND STATIC NOISE MARGIN ANALYSIS OF STATIC RANDOM ACCESS MEMORY." Wright State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=wright1195600920.
Full textFosas, De Pando Miguel Ángel. "Tonal noise generation in flows around aerofoils : a global stability analysis." Palaiseau, Ecole polytechnique, 2012. https://theses.hal.science/tel-00816987.
Full textThe generation of discrete acoustic tones in the compressible flow around an aerofoil is addressed in this thesis by means of nonlinear numerical simulations and global stability analyses. To this end, a nonlinear simulation code featuring a novel technique for gaining access to the linearized direct and adjoint dynamics has been developed and applied to the flow around an aerofoil. The nonlinear simulations confirm the appearance of discrete tones in the acoustic spectrum, and for the chosen flow case, the global stability analyses of the mean-flow dynamics reveal that the linearized operator is stable. However, the flow response to incoming disturbances exhibits important transient growth effects that culminate into the onset of aeroacoustic feedback loops, involving instability process on the suction- and pressure-surface boundary-layers together with their cross interaction by acoustic radiation at the trailing edge. The features of the aeroacoustic feedback loops and the appearance of discrete tones are then related to the features of the least stable modes in the global spectrum: on the one hand, the spatial structure of the direct modes display the growth of hydrodynamic instabilities on the suction surface and the near wake; on the other hand, the associated adjoint modes display increased receptivity of the flow on the pressure surface. Finally, the analysis of the wavemaker region highlights, in agreement with previous experimental investigations, the sensitivity of the flow to the pressure-surface boundary layer
Perrault-Joncas, Dominique C. "Linear stability of coaxial jets with application to aeroacoustics." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112343.
Full textHáněl, Petr. "Měření frekvenční stability oscilátorů v časové oblasti." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220360.
Full textWittrock, Steffen. "From noise & stability to synchronization & complex dynamics in spin torque nano-oscillators." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS088.
Full textSpin torque nano-oscillators (STNOs) present unique potential functionalities for rf-communications, energy harvesting or next-generation computing. Therewith, they unify hardware multifunctional key capabilities in the framework of Industry 4.0 and emphasize the potentialities of spintronics, even beyond the paradigm of CMOS. Along with the STNO’s nano-size, radiation-hardness, frequency tunability, low energy consumption and CMOS compatibility, their key characteristics is their strong nonlinearity, which opens up the path to various interesting physical phenomena. However, their nonlinearity also causes the oscillators’ poor spectral coherence, which so far limits their applicability in real practical devices. This PhD thesis aims at providing a deeper understanding of the STNO’s noise in the framework of nonlinearity. Generalizable to all types of spintronic oscillators, we experimentally and theoretically study the contribution of 1/f flicker noise at low frequency offsets in vortex based STNOs. We discuss the influence of this type of noise on the oscillation’s spectral shape and demonstrate potential means for efficient coherence improvements. Moreover, this PhD thesis is also dedicated to the coupling and synchronization of several STNOs, since these capabilities facilitate different applicational schemes in prospective technologies. Indeed, beyond synchronization, novel complex phenomena are experimentally demonstrated and studied, such as the emergence of exceptional points in the coupled system. In summary, the obtained results open up new perspectives not only for the fundamental research on STNOs, but also for novel types of future applications
Lapeyre, Corentin. "Numerical study of flame stability, stabilization and noise in a swirl-stabilized combustor under choked conditions." Phd thesis, Toulouse, INPT, 2015. http://oatao.univ-toulouse.fr/14493/1/Lapeyre.pdf.
Full textRajendran, Aravind. "Noise Margin, Critical Charge and Power-Delay Tradeoffs for SRAM Design Space Exploration." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1307667225.
Full textBouyrie, Raphaël. "Influences, stabilité au bruit et déficit isopérimétrique pour des modèles continus et discrets." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30078/document.
Full textThe general topic of this Ph.D thesis is functional and geometrical inequalities, in both continuous and discrete setting. In particular, we make use of the monotone property along the heat flow, which had led to important developments in analysis, geometry and probability since the pioneer work of Bakry and Émery. More recently, this principle has been used in the analysis of Boolean functions in view of application in theoretical computer science. In the first part, we present some multiple integrals inequalities and geometric type inequalities obtained by monotonicity along the heat flow. We characterize, for most of them, equality cases and we put forward rigidity phenomenon in the setting of Riemannian manifolds. In particular, we study rigidity for the Bakry-Ledoux isoperimetric comparison theorem using their semigroup proof. This proof has been exploited by Mossel and Neeman to derive robust dimension free bounds for the Gaussian isoperimetry. We simplify their proof an in particular remove most of Gaussian-specific parts. This gives hope to derive robust estimates to more general log-concave measures or on high dimensional Euclidean spheres. The second part is devoted to analysis of Boolean functions. The principal contribution in this field is the extension of a criterion of Benjamini, Kalai and Schramm linking noise sensitivity and influences of a Boolean function. Such a criterion has been extended recently in continuous setting via the concept of geometric influence. We give a new, semigroup, proof of a quantitative version of it previously established in the discrete cube and in the Gaussian space. This quantitative version generalizes both to various models of Schreier graphs and more general continuous spaces. In particular, the quantitative version over the slices of the Boolean cube has consequences in percolation theory. In the last chapter, we link this quantitative criterion with a generalization over graph products of the "Junta" theorem of Friedgut
黃毅 and Ngai Wong. "Signal processing: linearized noise analysis of delta-operator based filters and nonlinear stability study ofsigma-delta modulators." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31244920.
Full textCheung, Lawrence C. "Aeroacoustic noise prediction and the dynamics of shear layers and jets using the nonlinear parabolized stability equations /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full textGhanbarnejad, Fakhteh. "Perturbations in Boolean Networks." Doctoral thesis, Universitätsbibliothek Leipzig, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-96825.
Full textZhou, Limin. "ASSESSING AND MITIGATING AIRBORNE NOISE FROM POWER GENERATION EQUIPMENT." UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/22.
Full textFerrara, Marco Ph D. Massachusetts Institute of Technology. "Axisymmetric equilibrium and stability analysis in Alcator C-Mod, including effects of current profile, measurement noise and power supply saturation." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53265.
Full textCataloged from PDF version of thesis.
Includes bibliographical references (p. 147-150).
The vertical position of elongated tokamak plasmas is unstable on the time scale of the eddy currents in the axisymmetric conducting structures. In the absence of feedback control, the plasma would drift vertically and quench on the wall, a situation known as Vertical Displacement Event (VDE), with serious consequences for machine integrity. As tokamaks approach reactor regimes, VDE's cannot be tolerated: vertical feedback control must be robust against system uncertainty and the occurrence of noise and disturbances. At the same time, adaptive routines should be in place to handle unexpected events. The problem of robust control of the vertical position can be formulated in terms of identifying which variables affect vertical stability and which ones are not directly controlled/controllable; identifying the physical region of these variables, and the corresponding most unstable equilibria; and designing the control system to stabilize all equilibria with sufficient margin. The margin should be enough to allow the system to tolerate realistic scenarios of noise and disturbances. A set of metrics is introduced to characterize the problem of vertical stability: the stability margin describes the plasma-wall interaction and the open-loop growth rate; the maximum controllable displacement looks at the vertical stabilization power supplies and their ability to handle noise and off-normal events; the gain and phase margins quantify the linear stability of the feedback control loop.
(cont.) The dependence of these metrics on relevant plasma parameters is proven with analytic calculations and numerical simulations: in particular, it is shown that the stability margin is a decreasing function of the plasma internal inductance, for a given plasma elongation. An upper bound of the value of the internal inductance is derived and validated with database analysis, which describes the most unstable equilibrium for given values of the external elongation and the edge safety factor. The stability metrics are evaluated for typical and ITER-like C-Mod plasmas to give an example of the C-Mod operational space and of feasible control conditions. The vertical stabilization system should be able to tolerate realistic scenarios of noise and disturbances. The main sources of noise and pick-ups in Alcator C-Mod are identified and their effects on the measurement and control of the vertical position are evaluated. Broadband noise may affect controllability of C-Mod plasmas at limit elongations and may become an issue with high-order controllers, therefore two applications of Kalman filters are investigated. A Kalman filter is compared to a state observer based on the pseudo-inverse of the measurement matrix and proves to be a better candidate for state reconstruction for vertical stabilization, provided adequate models of the system, the inputs, the intrinsic and measurement noise and an adequate set of diagnostic measurements are available. A single-input single-output application of the filter for the vertical observer rejects high frequency noise without destabilizing high-elongation plasmas, however does not match the performance of an optimized low-pass filter.
(cont.) Aggressive control targets and large off-normal events can cause a control current to rail. The magnetic topology is consequently perturbed and the plasma might become uncontrollable. An adaptive anti-saturation control routine is demonstrated which avoids an impending saturation by interpolating in real-time to a safe equilibrium. This approach becomes necessary when poor redundancy of control coils may require mid-shot pulse rescheduling, as opposed to an adaptation in control.
by Marco Ferrara.
Ph.D.
Eklund, Anders. "Microwave Frequency Stability and Spin Wave Mode Structure in Nano-Contact Spin Torque Oscillators." Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188546.
Full textDagens snabba utveckling inom informationsteknik drivs på av ständigt växande informationsmängder och deras samhällsanvändning inom allt från resursoptimering till underhållning. Utvecklingen möjliggörs till stor del hårdvarumässigt av miniatyrisering och integrering av elektroniska komponenter samt trådlös kommunikation med allt större bandbredd och högre överföringshastighet. Det senare uppnås främst genom utnyttjande av högre radiofrekvenser i teknologiskt tidigare oåtkomliga delar av spektrumet. Frekvensutnyttjandet har det senaste årtiondet ökat markant i mikrovågsområdet med typiska frekvenser runt 2.4 GHz och 5.2-5.8 GHz. I den spinntroniska oscillatorn (STO:n) möjliggörs frekvensgenerering i det breda området från 0.1 GHz upp till över 65 GHz av en komponent med mikrometerstorlek som kan integreras direkt i CMOS-mikrochip. Till skillnad från i konventionella radiokretsar med oscillatorer konstruerade av integrerade transistorer och spolar, genereras mikrovågsfrekvensen direkt i STO:ns magnetiska material och omvandlas därefter till en elektrisk signal genom komponentens magnetoresistans. Dessa materialegenskaper möjliggör ett tillgängligt frekvensband med extrem bredd i en och samma STO, som därtill kan frekvensmoduleras direkt genom sin styrström och på så sätt förenklar konstruktionen av sändarsystem. STO:ns icke-linjära egenskaper kan potentiellt också användas för att i en och samma komponent blanda ned mottagna mikrovågssignaler och på så sätt förenkla konstruktionen även av mikrovågsmottagare. STO:ns signalegenskaper bestäms av det magnetiska materialets fysik i form av magnetiseringsdynamik driven av elektriskt genererade spinnströmmar. I denna avhandling studeras denna dynamik experimentellt med särskilt fokus på frekvensstabiliteten i den hittills mest stabila STO-typen; nanokontakts-STO:n. Genom mätningar i tidsdomän av STO:ns elektriska signaler runt 25 GHz har frekvensstabiliteten funnits hänga samman med den typ av icke-linjärt beteende som också funnits vara utmärkande för tillverkningsvariationen i komponenterna. Mikroskopiska undersökningar av materialet visar att en trolig källa till denna variation är den magnetiska metallens uppbyggnad i form av korn i storleksordningen 30 nm, och datorsimuleringar av en sådan materialstruktur har visats kunna reproducera de experimentella resultaten. Därtill har en metod utvecklats för att med röntgenstrålning direkt mäta de små, magnetiska mikrovågsrörelserna i materialet. Denna röntgenteknik möjliggör detaljerade experimentella studier av magnetiseringsdynamiken och kan användas för att verifiera och vidareutveckla den existerande teorin för mikrovågsspinntronik. Sammantaget förs STO-teknologin genom denna studie ett steg närmare sina tänkbara samhällsbreda tillämpningar inom snabb, trådlös kommunikation för massproducerade produkter med integrerad sensor- och datorfunktionalitet.
QC 20160620
Rodarte, Milena Domingos de Oliveira. "Exposição e reatividade do prematuro ao ruído intenso durante o cuidado em incubadora." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/22/22133/tde-14112007-141101/.
Full textIntroduction: The sound levels found in incubators and the additional noise generated during the manipulation of them reveal that the preterm and high-risk newly born babies (RN) are exposed to a noisy environment and are kept for long periods in this environment without chance to have auditive rest. Objectives: To evaluate the exposition of premature babies and their reactivity to the incubator noise during the care delivered in the intermediate care neonatal unit of a school hospital in Ribeirão Preto - SP, Brazil. Method: Prospective observational study performed in the intermediate care neonatal unit of a school hospital in Ribeirão Preto. A total of 35 premature babies participated in the evaluation of noise levels and sources. The analysis of the physiological (cardiac frequency and oxygen saturation) and behavioral (reflexive, bodily, facial activities and sleep and awake pattern) responses to intense noise was also performed in 20 of the babies studied. The noise levels were measured through the sound pressure level meter (NPS), dosimeter Quest-400, fixed inside the incubator for two hours during the care delivered to the newly born baby. The noise sources as well as the physiological and behavioral responses were investigated when Lmax above 65dBA was identified. These responses were filmed using four cameras connected to a video card installed in a computer. Results: The Leq was around 47.6 to 88.7dBA, and all of them were exposed to Leq above the limit 45dBA recommended by international organizations. More than half were exposed to average Leq above 60dBA, allowed in incubators by the Brazilian norms. The Lmin varied from 46.9 to 61.6dBA, the Lmax from 49 to 97.2dBA and the Lpeak from 87 to 135.7dBA. The main sources of intense noise were: chat in the unit and around the incubator, balcony handling, the RN vocalization, opening and closing the portholes and moving chairs in the unit. The differences in the cardiac frequency and in the oxygen saturation were not significantly different in the previous and post periods to the intense noise. When exposed to intense noise, 63.2% of the RN reacted with the cochleopalpebral and 20% with the startle reflex, 42.1% presented facial expressions, 55% body activities and 60% changed their sleep and wake pattern. There were statistically significant differences between the periods analyzed. Conclusion: The sound levels measured were intense and from several sources: team and family chatting, the own baby?s manifestations, direct care to the RN, handling the incubator and external environment around it and in the nursing ward of the neonatal unit. It is believed that the noise from these sources can be minimized by changes in the professionals\' attitudes. It is evidenced that the noise to which the babies are exposed in the incubators during the care delivery constitutes a stressing event because it modifies the RN\'s behavior, eliciting reflexive, bodily responses, facial manifestations and changing their sleep and wake states when facing intense and abrupt noises.
Brenes, Alexis. "Modélisation des phénomènes non-linéaires dans un capteur MEMS résonant pour l'optimisation de ses performances et de sa fiabilité." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC072/document.
Full textThe use of MEMS technologies in navigation measurements faces two main challenges.On the one hand, reliability improvement requires a deep understanding of MEMS failure mechanisms. These components are meant for long-term use and are subject to harsh mechanical and thermal constraints during their expected lifetime, usually longer than a decade. On the other hand, the replacement of macroscopic navigation sensors by MEMS components remains impossible as long as the performances of MEMS sensors do not match those of their macroscopic equivalents. With respect to these two challenges, the nonlinear behavior of MEMS resonators is usually seen as an obstacle, if not an insurmountable barrier to technological progress.However, nonlinear phenomena are actually a rich source of potential improvements. At the cost of increased mathematical complexity and specific design efforts, a precise model of MEMS nonlinear behaviors gives access to valuable information about the internal structure of the device. This information may then be used for failure detection and performance optimization.In this thesis, a linear and nonlinear characterization method is developed and experimentally-demonstrated. The knowledge of such nonlinear characteristics allows the determination of optimal operating points in terms of frequency stability and, hence, measurement accuracy
Razavi, Sabah. "Channel Estimation Error, Oscillator Stability And Wireless Power Transfer In Wireless Communication With Distributed Reception Networks." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-dissertations/508.
Full textSingh, Navrag B. "Functional competency of lower limb musculature in the elderly." Doctoral thesis, Humboldt-Universität zu Berlin, Philosophische Fakultät IV, 2013. http://dx.doi.org/10.18452/16772.
Full textUndertaking activities is fundamental throughout daily living. In order to successfully perform these activities, continuous involvement of the human sensori-motor system (HSMS) is required. The HSMS involves feedback mechanisms to control numerous afferent and the efferent subsystems to ensure maintenance of balance and stability during both static and dynamic activities. Despite such control and stabilizing mechanisms, the kinematic and kinetic output of a task is not constant; instead variability occurs during continuous performance of both global tasks such as standing and walking, as well as local force production. The interpretation of variability during output task performance remains controversial, with larger levels of variability not always indicating deficits in human-motor performance. The aim of this dissertation was to assess variability during local as well as global task performance in static and dynamic settings. Furthermore, the association between the level of variability during local force production and variability during global tasks such as standing and walking was also investigated. The results within this dissertation showed that variability during task performance is modified in magnitude as well as in structure after perturbation due to fatigue, changes in environmental conditions, and aging, as well as in fall-prone elderly individuals. Furthermore, both high as well as low levels of variation constitute a key functional deficit among elderly individuals. This dissertation highlights the importance of considering trial-to-trial variations during continuous task performance as a key functional biomarker for motor-related pathologies. Effective assessment of such measures of variability in clinical settings could effectively complement current clinical practice for both early and effective identification of individuals with motor-related pathology, designing subject-specific rehabilitation programs, and evaluating therapy efficacy.
Ansaldi, Tobias. "Compressible single and dual stream jet stability and adjoint-based sensitivity analysis in relationship with aeroacoustics." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17505/13/Ansaldi_Tobias.pdf.
Full textSchmid, Robert L. "Design of a reconfigurable low-noise amplifier in a silicon-germanium process for radar applications." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/47642.
Full textAndersson, Peter. "Implementering av digitalt vågfilter av Richardstyp i FPGA." Thesis, Linköping University, Department of Electrical Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-1267.
Full textEtt digitalt vågfilter av Richardstyp har implementerats i en FPGA på ett utvecklingskort. Sampel kan skickas till filtret och mottas från filtret via serieporten på en dator. Metoden som användes är att en modell av filtret konstruerades i Simulink. Filtret har modifierats med avseende på skalning, brus och stabilitet. VHDL-koden till filtret genererades i Simulink genom att bygga modellen av Xilinx Blockset. Ytterligare VHDL-kod konstruerades för att kunna skicka sampel mellan filter och minnet på utvecklingskortet. För kommunikation mellan minnet på utvecklingskortet och dator utnyttjades färdiga lösningar.
Filtrets funktion efter implementeringen var samma som modellens byggd i Simulink. A Richards’ structure wave digital filter has been implemented on an evaluation board in an FPGA. Samples can be sent to the filter and received from the filter using the serial port of a computer. The method used is that a modell of the filter has been created in Simulink. The filter has been modified with respect to scaling, noise and stability. VHDL for the filter has been generated in Simulink by using Xilinx blockset to build the modell. Also, VHDL has been constructed to be able to send samples between the filter and the memory on the evaluationboard. For communication between the memory on the evaluationboard and the computer, existing solutions have been used. The functionality of the filter after implementation was the same as in the modell built in Simulink.
IKI, MASAYUKI. "VIBRATION-INDUCED WHITE FINGER AS A RISK FACTOR FOR HEARING LOSS AND POSTURAL INSTABILITY." Nagoya University School of Medicine, 1994. http://hdl.handle.net/2237/16062.
Full textGhosh, Santunu. "Study on the origin of 1/f in bulk acoustic wave resonators." Thesis, Besançon, 2014. http://www.theses.fr/2014BESA2046/document.
Full textSince a few decades, frequency control technology has been at the heart of modern day electronics due to its huge areaof applications in communication systems, computers, navigation systems or military defense. Frequency controldevices provide high frequency stabilities and spectral purities in the short term domain. However, improvement of theperformance of these devices, in terms of frequency stability, remains a big challenge for researchers. Reducing noise inorder to increase the short term stability and avoid unwanted switching between channels is thus very desirable. It iscommonly admitted that the fundamental limitation to this short-term stability is due to flicker frequency noise in theresonators. In this manuscript, a first chapter recalls some basic facts about acoustic, crystallography and definitions oftime and frequency domain needed to explore ultra-stable resonators and oscillators. The second chapter is devoted to asummary of the literature on flicker frequency noise. Then, the third chapter concerns our studies on Handel’s quantum1/f noise model, which although criticized by many, is still the only one that provides an estimation of the flooramplitude of 1/f noise that is not invalidated by experimental data. In the fourth chapter, another approach, based on thefluctuation-dissipation theorem, is used in order to put numerical constraints on a model of 1/f noise caused by aninternal (or structural) dissipation proportional to the amplitude and not to the speed. The last chapter is devoted toexperimental results. An ultra-stable resonator used during this study is described. Phase noise measurements on severalbatches of resonators are given. Measurements of resonator parameters have been done at low temperature in order tocorrelate them with noise results. Another approach with a procedure that use transient pseudo periodic oscillations andput to their limits the capacities of presently available digital oscilloscopes, is presented, in order to assess rapidly thequality of various resonators. Finally, conclusions and perspectives are given
Cichon, Dominick [Verfasser], and Undagoitia Teresa [Akademischer Betreuer] Marrodán. "Liquid xenon detector physics with XENON1T and HeXe: electric noise stability, background discrimination studies and measurements of the scintillation pulse shape / Dominick Cichon ; Betreuer: Teresa Marrodán Undagoitia." Heidelberg : Universitätsbibliothek Heidelberg, 2021. http://d-nb.info/1225868521/34.
Full textBenites, Ayala Ivan Alejandro. "Nízkošumový zesilovač pro pásmo S." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2019. http://www.nusl.cz/ntk/nusl-400532.
Full textGonzalez, de Cossio Francisco. "Synthèse d’observateur robuste pour les systèmes non linéaires." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1273.
Full textEstimating the state of a nonlinear system is an essential task for achieving important objectives such as: process monitoring, identification and control. Observers are algorithms that estimate the current state by using, among other information, sensor measurements. The problem of observer design for nonlinear systems has been a major research topic in control for many decades. Recently, there has been an increasing interest in the design of observers for more realistic models, which can include disturbances, sensor nonlinearities and discrete outputs. This thesis concerns the design of robust observers for selected classes of nonlinear systems and we can distinguish three main parts. The first part studies state-affine systems affected by noise, and analyses the state estimation via the so-called high-gain Kalman filter. The convergence properties of this observer are strongly influenced by two variables: its tuning parameter and the properly excited system input. We present a new optimization algorithm, based on Lyapunov analyses, that adapts these variables in order to minimize the effect of both dynamic and output disturbances. The novelty of this approach is that it provides a systematic method of simultaneous tuning and input selection with the goal of improving state estimation in the face of disturbances, and that it avoids the use of trial-and-error based methods. The second part studies the problem of observer redesign for general nonlinear systems whose outputs are transformed by nonlinear functions. Indeed, a given observer might not estimate the system state properly if it does not take into account sensor nonlinearities and, therefore, such an output mismatch needs to be addressed. We present an observer redesign that consists in the interconnection of the original observer with an output estimator based on a dynamic inversion, and we show its asymptotic convergence via small-gain arguments. We illustrate our method with two important classes of systems: state-affine systems up to output injection and systems with additive triangular nonlinearity. Finally, the third part extends our redesign method to systems whose outputs are not only transformed but also discretized in time. This added assumption introduces important challenges; we now implement sample-and-hold techniques leading to an observer gain based on linear matrix inequalities. The main feature of our redesign methods is the possibility to adapt a large number of observers from the literature to more realistic scenarios. Indeed, classical sensors in engineering applications are often nonlinear or discrete, whereas a recurrent assumption in observer design is the linearity or continuity of the output
Denimal, Enora. "Prédiction des instabilités de frottement par méta-modélisation et approches fréquentielles : Application au crissement de frein automobile." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC039/document.
Full textBrake squeal is a noise nuisance that represents significant costs for the automotive industry. It originates from complex phenomena at the frictional interface between the brake pads and the disc. The stability analysis remains the preferred method in the industry today to predict the stability of a brake system despite its over- and under-predictive aspects.In order to build a robust brake system, it is necessary to find the technology that limits instabilities despite some uncertain parameters present in the system. Thus, one of the main objectives of the PhD thesis is to develop a method to treat and propagate the uncertainty and variability of some parameters in the finite element brake model with reasonable numerical costs.First, the influence of a first group of parameters corresponding to contacts within the system was studied in order to better understand the physical phenomena involved and their impacts on the squealing phenomenon. An approach based on the use of a genetic algorithm has also been implemented to identify the most unfavourable set of parameters in terms of squeal propensity on the brake system.In a second step, different meta-modelling methods were proposed to predict the stability of the brake system with respect to different parameters that may be design parameters or uncertain parameters related to the environment of the brake system.In a third step, a non-linear analysis method complementary to the stability analysis was proposed and developed. It is based on the tracking of the stability of an approximate vibrational solution and allows the identification of unstable modes present in the dynamic response of the system. This method was applied to a simple academic model before demonstrating its feasibility on the complete industrial brake finite element model under study
Gudmundson, Sara. "Stabilizing factors in spatially structured food webs." Thesis, Linköping University, Linköping University, Theoretical Biology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-18657.
Full textEcological models have problems showing the positive relationship between diversity and stability found in nature. Theory states that complex food webs have high extinction risks and low stability. However, persistent food webs found in nature are large and complex containing many interconnections between species. There are many possible mechanisms enabling persistent food webs such as; complex interaction patterns, asynchronous fluctuations of species densities, environmental fluctuations and spatial distribution. These factors have not been used in classical models. In this study, coloured environmental 1/f noise and dispersal between subpopulations were incorporated into a diamond shaped food web based on a model by Vasseur and Fox 2007. Contradictions between theoretical and empirical results regarding food webs can be resolved by detailed analyses of models, withholding stabilizing mechanisms. Weak environmental 1/f noise generated an increased coefficient of stability but the stabilizing effect of noise can be questioned because of a decreased mean food web biomass and reduced stabilizing effect when reddened. However, detailed studies of the food web revealed that noise can redistribute density proportions between species, evading lowest species density and thereby increase food web resistance to demographic stochasticity and catastrophes. Noise induced density proportion shifts imply that large population sizes are no insurance towards future increase in environmental variance. Synchrony of species environmental responses and dispersal between subpopulations can both have major influences on stability and extinction risk of smaller food webs indicating that spatial structure could be one of the dominating factors stabilizing complex food webs found in nature.
Itasse, Maxime. "Effet sur le bruit de jet de l'excitation de modes instables : rôle des interactions non linéaires." Thesis, Toulouse, ISAE, 2015. http://www.theses.fr/2015ESAE0028/document.
Full textThis study is part of the effort to reduce aircraft noise during take-off. Jet noise is oneof the main contributors, of which lower frequency component can be attributed to thedirective acoustic field generated by the large-scale coherent structures arising from jetmixing-layer instabilities. The development of these instability waves can be describedusing Parabolized Stability Equations (PSE). A first objective was to determine if inthe case of a natural turbulent jet, nonlinear interactions between instability waveshave a significant impact on its dynamic and acoustic behaviour. For this purpose,a nonlinear PSE model has been developed and applied to a realistic configuration.Then, the possibility to manipulate these instability waves by means of nonlinearity wasinvestigated with a view to reduce noise. To this end, a PSE analysis has been carried outto assess the impact on jet noise of exciting one or more unstable modes. The findingsof this doctoral work demonstrate a minor impact of nonlinearities on the dynamics ofinstability waves for natural turbulent jets on the one hand, and the possibility to makethe initially dominant instability acoustically ineffective using nonlinear interactions onthe other hand
Elmer, Michael James. "Improved Methods for Phased Array Feed Beamforming in Single Dish Radio Astronomy." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3340.
Full textIvica, Milanović. "Мерење стабилности фреквенције у фреквенцијском домену." Phd thesis, Univerzitet u Novom Sadu, Fakultet tehničkih nauka u Novom Sadu, 2018. https://www.cris.uns.ac.rs/record.jsf?recordId=107278&source=NDLTD&language=en.
Full textDisertacija istražuje najprihvatljivije metode merenja stabilnosti frekvencije ufrekvencijskom domenu, odnosno merenje vrednosti veličine „fazni šum“, prilikomprocesa etaloniranja merne opreme. Kada se govori o mernoj opremi koja je predmetetaloniranja, disertacija je, pre svega, okrenuta ka etaloniranju vrhunskihkomercijalnih standarda (etalona) frekvencije. Prikazana istraživanja su bila osnovza pokretanje i realizaciju istraživačko-razvojnog projekta u okviru Ministarstvaodbrane, koji je imao za cilj osposobljavanje metrološke laboratorije Tehničkogopitnog centra Vojske Srbije za potpuno etaloniranje merne opreme iz oblastivremena i frekvencije. Različite metode merenja podrazumevaju i različite mernemogućnosti, kao i vrlo širok spektar etalonske i merne opreme koja se koristi prinjihovoj realizaciji. U disertaciji se prikazuju različiti načini merenja faznog šumai opisuju metode realizovane na osnovu dostupne merne opreme. Kako se radi ometodama uporedne analize referentnog i merenog signala, posebno kritična pozicijaje odabir reference, odnosno referentnog etalona. Istraživanje je dovelo dozaključaka kojima je predložen metod merenja potrebne i dovoljne merne nesigurnostikao i način realizacije izabrane metode, odnosno odabir etalonske merne opreme. Ucilju uvođenja merne metode u upotrebu, izvršena su i prikazana merenja narazličitim tipovima i vrstama merne opreme. Validacija metode je ostvarenabilateralnim poređenjem sa Direkcijom za mere i dragocene metale, Grupa za vreme,frekvenciju i distribuciju vremena. Da je moguće realizovati metodu merenja faznogšuma prilikom etaloniranja najkvalitetnijih oscilatora je postavljena hipotezadisertacije, koja je istraživanjem dokazana i praktično sprovedena. Krajnji rezultatistraživanja je doveo do uvođenja priznate metode etaloniranja faznog šuma, prvi put
The dissertation examines the most acceptable methods for measuring the frequency stabilityin the frequency domain, that is, measuring the value of the "phase noise", during the processof measuring equipment calibration. When it comes to measuring equipment as a subject ofcalibration, the dissertation is, first of all, oriented towards the calibration of the highestcommercial frequency standards. The presented researches were the basis for initiation andrealization of the research and development project within the Ministry of Defense, which wasaimed at training the metrology laboratory of the Technical Test Center of the Serbian Armyfor complete calibration of measuring equipment in the area of time and frequency. Differentmeasurement methods also involve different measurement possibilities, as well as a very widerange of calibration and measuring equipment used in their realization. Different methods ofmeasuring phase noise are described in the dissertation and they describe realized methodsbased on available measuring equipment. As for methods of comparative analysis of thereference and measured signal, a particularly critical position is the selection of the reference,that is, the reference oscillator. The research led to conclusions suggesting the method ofmeasuring the necessary and sufficient measurement uncertainty, as well as the method ofrealization of the chosen method, i.e. selection of the standard measuring equipment. In orderto put the measurement method into practice, measurements were performed on differenttypes of measuring equipment. Validation of the method was achieved by bilateralcomparison with the Directorate of Measures and Precious Metals, Group for time, frequencyand time dissemination. The possibility to realize the method of phase noise measurementduring the calibration of the highest quality oscillators is a hypothesis of the dissertation thathas been set up, and has been proven and practically carried out by the research. The finalresult of the research led to the introduction of a recognized calibration method of the phasenoise, for the first time in the Republic of Serbia.
Godeme, Jean-Jacques. "Ρhase retrieval with nοn-Euclidean Bregman based geοmetry." Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMC214.
Full textIn this work, we investigate the phase retrieval problem of real-valued signals in finite dimension, a challenge encountered across various scientific and engineering disciplines. It explores two complementary approaches: retrieval with and without regularization. In both settings, our work is focused on relaxing the Lipschitz-smoothness assumption generally required by first-order splitting algorithms, and which is not valid for phase retrieval cast as a minimization problem. The key idea here is to replace the Euclidean geometry by a non-Euclidean Bregman divergence associated to an appropriate kernel. We use a Bregman gradient/mirror descent algorithm with this divergence to solve thephase retrieval problem without regularization, and we show exact (up to a global sign) recovery both in a deterministic setting and with high probability for a sufficient number of random measurements (Gaussian and Coded Diffraction Patterns). Furthermore, we establish the robustness of this approachagainst small additive noise. Shifting to regularized phase retrieval, we first develop and analyze an Inertial Bregman Proximal Gradient algorithm for minimizing the sum of two functions in finite dimension, one of which is convex and possibly nonsmooth and the second is relatively smooth in the Bregman geometry. We provide both global and local convergence guarantees for this algorithm. Finally, we study noiseless and stable recovery of low complexity regularized phase retrieval. For this, weformulate the problem as the minimization of an objective functional involving a nonconvex smooth data fidelity term and a convex regularizer promoting solutions conforming to some notion of low-complexity related to their nonsmoothness points. We establish conditions for exact and stable recovery and provide sample complexity bounds for random measurements to ensure that these conditions hold. These sample bounds depend on the low complexity of the signals to be recovered. Our new results allow to go far beyond the case of sparse phase retrieval
Maury, Rémy. "Réponse d'un jet rond subsonique à une excitation fluidique stationnaire et instationnaire." Thesis, Poitiers, 2012. http://www.theses.fr/2012POIT2272.
Full textThis work investigates the response of an axisymetric turbulent jet to steady and unsteady fluidic florcing where the azimuthal wavenumber-frequency (!,m) content of the perturbation is well known. The control setup is composed of 16 round microjets azimutally distributed around the nozzle lip. Such actuation can lead to a decrease in the acoustic energy radiated by the jet (especially for the steady case). The aerodynamic fied is investigated using hotwire measurements and time-resolved stereoscopic PIV. Using the unsteady forcing, phase-averaging is possible, and this allows the implementation of a triple decomposition of the measurements. Examination of the cyclic component of the flow response shows that a non-negligible phase-locked fluctuation is obtained over a large spatial extent, in other words, the actuation has good deterministic control authority over the flow. Furthermore, comparison of the cyclic component of the flow response with Linear Stability Theory supports the idea that the jet response comprises linear hydrodynamic instability waves. Subsequent analysis of jets controlled by steady fluidic actuation shows how the control effect can be explained by a mean-flow modification that leads to the reduction of instability-wave growth rates ; the mean flow modification is argued to be due to the introduction of azimuthal wavenumber-frequency pairs to which the mean flow is stable. The response is therefore turbulent, and involves Reynolds stresses which deform the mean-field such that the most unstable modes have lower growth rates
Léon, Olivier. "Étude du rayonnement acoustique d'instabilités hydrodynamiques de jets double-flux par les équations de stabilité parabolisées (PSE)." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/9138/1/leon_partie_1_sur_2.pdf.
Full textLozi, Julien. "Caractérisation du banc stabilisé d'interférométrie en frange noire PERSÉE." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00690642.
Full textLozi, Julien. "Caractérisation du banc stabilisé d’interférométrie en frange noire PERSÉE." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112047/document.
Full textThere are two problems with the observation of exoplanets: the contrast between the planet and the star and their very low separation. One technique solving these problems is nulling interferometry: two pupils are recombined to make a destructive interference on the star, and their base is adjusted to create a constructive interference on the planet. However, to ensure a sufficient extinction of the star, the optical path difference between the beams must be around the nanometer, and the pointing must be better than one hundredth of Airy disk, despite the external disturbances.To validate the critical points of such a space mission, a laboratory demonstrator, PERSÉE, was defined by a consortium led by CNES, including IAS, LESIA, ONERA, OCA and Thales Alenia Space and integrated in Meudon Observatory. This bench simulates the entire space mission (interferometer and nanometric cophasing system). Its goal is to deliver and maintain an extinction of 10^-4 stable at better than 10^-5 over a few hours in the presence of typical injected disturbances.My thesis work consisted in integrating the bench in successive stages and to develop calibration procedures. This helped me to characterize the critical elements separately before grouping them. After having implemented the control loops of the cophasing system, their precise analysis helped me to reduce down to 0.3 nm rms the residual OPD, and 0.4 % of the Airy disk the residual tip/tilt, despite disturbances of tens of nanometers, consisting of several tens of vibrational frequencies between 1 and 100 Hz. This has been achieved by the implementation of a linear quadratic Gaussian controller, parameterized by the preliminary measurement of the disturbance to minimize. Thanks to these excellent results, I obtained on the band [1.65 – 2.45] µm a record null rate of 8.8x10^-6 stabilized at 9x10^-7 over a few hours, a decade better than the original specifications. An extrapolation of these results to the case of a space mission shows that the expected performance is achievable if the available flux is sufficiently important. With telescopes of 40 cm and a control frequency around 100 Hz, stars brighter than magnitude 9 should be observable
Barbagallo, Alexandre. "Model reduction and closed-loop control of oscillator and noise-amplifier flows." Palaiseau, Ecole polytechnique, 2011. https://pastel.hal.science/docs/00/65/49/30/PDF/Barbagallo_PhDThesis.pdf.
Full textCe travail est consacré au contrôle en boucle fermée des perturbations se développant linéairement dans des écoulements laminaires et incompressibles de types oscillateurs et amplificateurs de bruit. La loi de contrôle, calculée selon la théorie du contrôle LQG, est basée sur un modèle d'ordre réduit de l'écoulement obtenu par projection de Petrov-Galerkin. La stabilisation d'un écoulement de cavité de type oscillateur est traitée dans une première partie. Il est montré que la totalité de la partie instable de l'écoulement (les modes globaux instables) ainsi que la relation entrée-sortie (action de l'actionneur sur le capteur) de la partie stable doivent être captées par le modèle réduit afin de stabiliser le système. Les modes globaux, modes POD et modes BPOD sont successivement évalués comme bases de projection pour modéliser la partie stable. Les modes globaux ne parviennent pas à reproduire le comportement entrée-sortie de la partie stable et par conséquent ne peuvent stabiliser l'écoulement que lorsque l'instabilité du système est initialement faible (nombre de Reynolds proche de la criticité). En revanche, les modes POD et plus particulièrement BPOD sont capable d'extraire la dynamique entrée-sortie stable et permettent de stabiliser efficacement l'écoulement. La seconde partie de ce travail est consacrée à la réduction de l'amplification des perturbations sur une marche descendante. L'influence de la localisation du capteur et de la fonctionnelle de coût sur la performance du compensateur est étudiée. Il est montré que la troncature du modèle réduit peut rendre le système bouclé instable. Finalement, la possibilité de contrôler une simulation non-linéaire avec un modèle linéaire est évaluée
Corradi, Grégoire. "Approches numérique et expérimentale pour des structures à interfaces frottantes : Application au crissement de frein." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC044.
Full textBrake systems are sometimes prone to squeal noise, which is due to friction-induced self-sustained vibrations, characterized by a set of frequencies above 1kHz. Those vibrations and resulting noises are a source of perturbations for car occupants, which can be nowadays considered as a health issue.This thesis deals with a global strategy to better understand this phenomenon from an experimental point of view and to propose the prediction of squeal noise by numerical approaches. Moreover, experimental observations of squeal occurrences are analyzed to lead to assumptions about the modelisation of numerical finite element models for squeal prediction. A Double Modal Synthesis is also applied to reduce the size of the discrete finite element model of brake system and to save computational time and ressources. The proposed numerical approach starts with a stability analysis with the classical CEA method. Then the determination of nonlinear self-excited vibrations are performed for the unstable cases detected via the CEA method. Finally the acoustic field emitted by the brake system is computed to predict squeal noise.Specific tools are applied for each computational step to assess the efficiency of reduced model versus the reference model: criteria based on the mean error on eigenvalues and the Modal Assurance Criterion analysis (MAC) are used for the stability analysis; comparisons of the limit cycles, spectrograms and the modal contributions of unstable modes are undertaken for the transient responses; patterns of the acoustic intensity are computed on several observations surfaces and a decomposition based on the theory of 2D wavelets is introduced and applied to assess the convergence of patterns
Paes, Torquato Luciane. "Modélisation de la stabilité dimensionnelle et des propriétés mécaniques du bois d’épinette noire." Doctoral thesis, Université Laval, 2021. http://hdl.handle.net/20.500.11794/68341.
Full textBending strength, stiffness, and dimensional stability of wood are determining properties fortheir potential use in building structure and added-value products. A detailed knowledge of the variation patterns of the properties inside a tree is essential to optimize the use of this renewable resource and to develop high-performance products. This PhD project’s goal is to characterize and model the variation pattern for bending strength, stiffness, and dimensional stability within the tree as a function of different parameters (radial distance, the height ofthe stem, the ring width) and taking into account the history of the stands. This general objective was pursued by the means of the specific objectives to : 1) describe the variation pattern of the physico-mechanical properties from pith to the bark (i.e. as a function ofcambial age) and in the longitudinal axis of the stem; 2) model the effect of the radial growth rate on the physico-mechanical properties; 3) model the effect of the basic specific densityon the physico-mechanical properties and examine the differences between the two types of stand structures (regular and irregular). The study focused on black spruce (Picea mariana[Mill.] B.S.P.), a species of high commercial importance in Canada. Sixty trees were sampled in twelve stands located north and south of the North Shore region, thirty trees in six standsin Abitibi-Témiscamingue and forty-two trees from Lac Saint-Jean. This study used astatistical modelling approach to relate flexural strength, stiffness and dimensional stability parameters to variables such as cambial age and annual growth rate. The stands were sampled with a known time since the last fire because this is known to influence stand structure and tree growth. The results confirmed that cambial age is clearly the most important source ofradial direction variation in wood properties, which could be used as a predictive variable. The ring width had a small additional influence to explain the variations in mechanical and dimensional stability properties. The fast-growing wood in regular stands had superior mechanical properties and were less dimensionally stable. Slow-growing trees from unevenaged, irregular stands may produce less dense late wood, which would tend to reduce mechanical properties and increase the dimensional stability of the material. Thus, these properties may be affected by the patterns of intra-ring variation in wood density. The effect of stand type on the wood physico-mechanical properties may also be due to the presence of mild compression wood, which can occur in trees of layer origin or in trees subjected togreater or more complex mechanical stimuli. Analyses also indicate that wood density and cambial age measurements can be used to estimate dimensional stability and mechanical properties. In addition, prediction indices have shown that it is preferable to predict dimensional stability from MOE and cambial age measurements rather than opting for the opposite case, i.e., estimating mechanical properties from dimensional stability. These results could have practical implications for decision-making in forest management and wood allocation. The selection of forest stands to produce black spruce wood for either high dimensional stability or high mechanical properties may be an interesting option that emerges from our results. In general, the modelling results were able to clearly characterize the differences between the two types of stand structures. However, further fundamental researchis needed to elucidate the mechanisms of wood formation that are responsible for differences in properties related to the growth environment in these two types of stand, including the internal structure of growth rings and the ultrastructure and chemical composition of the cell wall of wood tracheids, in order to obtain a more complete tool of simulation of wood qualityfor black spruce.