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1
Jain, Bhuvnesh. "The evolution of cosmological density fluctuations". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28060.
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Lumsden, Stuart Leonard. "The statistics and evolution of cosmological density fluctuations". Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/28460.
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Durham, Laura M. (Laura Marie) 1977. "A density evolution analysis of turbo product codes". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/87208.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (leaves 112-113).
by Laura M. Durham.
S.M.
4
Arsenlis, Athanasios 1975. "Modeling dislocation density evolution in continuum crystal plasticity". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/36679.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 221-229).
Dislocations are the singly most important material defects in crystal plasticity, and although dislocation mechanics has long been understood as the underlying physical basis for continuum crystal plasticity formulations, explicit consideration of crystallo- graphic dislocation mechanics has been largely absent in working constitutive models. In light of recent theoretical developments in dislocation dynamics, and the introduc- tion of geometrically necessary dislocation (GND) density in continuum formulations through plastic strain gradients, a single crystal plasticity model based on dislocation density state variables is developed. The density state variables evolve from initial conditions according to equations based on fundamental concepts in dislocation me- chanics such as the conservation of Burgers vector in multiplication and annihilation processes. Along with those processes that account for bulk statistical dislocation evolution, the evolving polarity due to dislocation species flux divergences may be in- cluded to detail the length-scale dependence of mechanical properties on the micron level. The full dislocation density description of plasticity allows a simple evaluation of the role of GND density in non-homogeneously deforming bodies. A local version of the constitutive model, which captures the bulk processes of dislocation multiplication and annihilation during plastic deformation, is implemented within a finite element framework to investigate the poly-slip behavior of aluminum single crystals under tension.
(cont.) A non-local version of the constitutive model using an idealized planar double slip system geometry is implemented within a finite element framework to investigate the length-scale dependence observed in the bending of thin single crystal beams. The results not only capture the mechanical stress/strain response of the material, but also detail the development of underlying dislocation structure responsible_ fr: the plistic behavior of the crystal.
by Athanasios Arsenlis.
Ph.D.
5
Cross, Nicholas James Geraint. "The bivariate space density of galaxies". Thesis, University of St Andrews, 2002. http://hdl.handle.net/10023/12935.
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The luminosity function of galaxies, the measurement of the space density as a function of luminosity, is an important test of cosmology, galaxy formation and evolution. Unfortunately, there is a factor of two variation in recent measurements of the luminosity function. Most of this variation is due to systematic errors, caused by various selection effects. With two large new surveys, the Two degree Field Galaxy Redshift Survey and the Sloan Digital Sky Survey, underway it is important to recognise and eliminate these selection effects if we are going to improve our measurement of the luminosity function and fully utilise these surveys. By measuring the space density of galaxies as a function of surface brightness as well as luminosity, a bivariate brightness distribution, we can comprehend many of the selection effects such as light loss, incompleteness and the visibility of galaxies. Since galaxies have a variety of shapes and sizes, a distribution in luminosity and surface brightness helps to separate out different types of galaxy. Correlations between the luminosity and surface brightness place extra constraints on models of galaxy formation and evolution. When we analyse our results, we find that recent surveys that have not taken into account surface brightness selection effects underestimate the luminosity of the bright end by 5-10%. Using the bivariate brightness distribution, we can constrain the luminosity density to a range that varies by < 20% rather than by a factor of 2. We find that the luminosity function is flat over the range -19.5 < M < -17 and then rises sharply as late-type spiral galaxies begin to dominate. The space density does not vary with surface brightness with the result that low surface brightness galaxies are at least as common as normal galaxies. However, low surface brightness galaxies are also intrinsically faint, following the luminosity-surface brightness correlation for spirals, so they do not contribute significantly to the luminosity density.
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Percival, Will. "Cosmological structure formation and its link to quasar evolution". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325786.
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Borch, Andrea. "Evolution of the stellar mass density of galaxies since redshift 1.0". [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972022481.
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Lane, Jennifer M. (Jennifer Marie) 1977. "A fundamental study of feature evolution during high density plasma etching". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80245.
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Thesis (M.Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaves 91-94).
by Jennifer M. Lane.
M.Eng.and S.B.
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Benage, Mary Catherine. "The thermal evolution and dynamics of pyroclasts and pyroclastic density currents". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53962.
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The thermal evolution of pyroclastic density currents (PDCs) is the result of entrainment of ambient air, particle concentration, and initial eruptive temperature, which all impact PDC dynamics and their hazards, such as runout distance. The associated hazards and opaqueness of PDCs make it impossible for in-situ entrainment efficiencies or concentration measurements that would provide critical information on the thermal evolution and physical processes of PDCs. The thermal evolution of explosive eruptive events such as volcanic plumes and pyroclastic density currents (PDCs) is reflected in the textures of the material they deposit. A multiscale model is developed to evaluate how the rinds of breadcrust bombs can be used as a unique thermometer to examine the thermal evolution of PDCs. The multiscale, integrated model examines how bubble growth, pyroclast cooling, and dynamics of PDC and projectile pyroclasts form unique pyroclast morphology. Rind development is examined as a function of transport regime (PDC and projectile), transport properties (initial current temperature and current density), and pyroclast properties (initial water content and radius). The model reveals that: 1) rinds of projectile pyroclasts are in general thicker and less vesicular than those of PDC pyroclasts; 2) as the initial current temperature decreases due to initial air entrainment, the rinds on PDC pyroclasts progressively increase in thickness; and 3) rind thickness increases with decreasing water concentration and decreasing clast radius. Therefore, the modeled pyroclast’s morphology is dependent not only on initial water concentration but also on the cooling rate, which is determined by the transport regime.
The developed secondary thermal proxy is then applied to the 2006 PDCs from the Tungurahua eruption to constrain the entrainment efficiency and thermal evolution of PDCs. A three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model is coupled to topography and field data such as paleomagnetic data and rind thicknesses of collected pyroclasts to study the entrainment efficiency and thus the thermal history of PDCs at Tungurahua volcano, Ecuador. The modeled results that are constrained with observations and thermal proxies demonstrate that 1) efficient entrainment of air to the upper portion of the current allows for rapid cooling, 2) the channelized pyroclastic density currents may have developed a stable bed load region that was inefficient at cooling and 3) the PDCs had temperatures of 600-800K in the bed load region but the upper portion of the currents cooled down to ambient temperatures. The results have shown that PDCs can be heterogeneous in particle concentration, temperature, and dynamics and match observations of PDCs down a volcano and the thermal proxies. Lastly, the entrainment efficiencies of PDCs increases with increasing PDC temperature and entrainment varies spatially and temporally. Therefore, the assumption of a well-mixed current with a single entrainment coefficient cannot fully solve the thermal evolution and dynamics of the PDC.
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Mahorowala, Arpan P. (Arpan Pravin) 1970. "Feature profile evolution during the high density plasma etching of polysilicon". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50514.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1998.Includes bibliographical references (p. 185-191).
This thesis work deals with one of the critical steps in the manufacturing of modem integrated circuits - the plasma etching of thin polysilicon films used to form the metaloxide- semiconductor transistor gate. The etching of very small features (-0.25 jim) in the -2500 A thick films, performed at low operating pressures (-10 mTorr), must be accompanied with minimal etching artifacts that can degrade device performance. This thesis aims to understand the causes for the etching artifacts observed during the etching of polysilicon line-and-space features in C12 and HBr plasmas so that better etching recipes can be developed. The second goal of this work was to develop a generalized simulator capable of predicting the feature profile evolution for the above plasma etching system as well as systems involving other materials and chemistries. The 2V2-dimensional simulator developed used Monte Carlo techniques to compute the transport and surface kinetics combined with a cellular representation of the feature. Using the Monte Carlo algorithm permitted the incorporation of all dominant physical and chemical mechanisms of the etching process such as angle-dependent ionenhanced etching, physical sputtering, ion scattering, surface recombination, plasma deposition, and line-of-sight re-deposition without encountering numerical difficulties. The technique allowed the calculation of surface kinetics rates based on the surface composition; simultaneous composition-dependent etching and deposition could be handled easily. A modification of the cellular representation of the feature was developed to determine neutral species interactions with the surface correctly. A surface normal calculation algorithm involving least-squares fitting of the surface was developed to handle specular ion scattering. Designed sets of plasma etching experiments were performed on photoresist masked and silicon oxide-masked polysilicon samples using C12 and HBr chemistries varying the inductive power (controls the ion density, radical concentrations), the rf biasing power (controls the ion energy) and the gas flowrate (controls the reactant and product concentrations). The interesting features exhibited in the experimental profiles included: 1) the increased sidewall deposition associated with photoresist-masking and isolated features, 2) the greater curvature of the sidewalls associated with the combination of photoresist and Cl2 plasmas, 3) the more vertical sidewalls achieved with HBr, 4) the double faceting of the feature sidewalls under etching conditions accompanied by significant deposition, 5) the delay in the onset of microtrenching at the feature bottom while etching photoresist-masked samples with C12, 6) the greater microtrenching exhibited with silicon oxide-masking and C12 plasmas, and 7) the lack of microtrenching for the HBr etching. The experimental results suggested strong dependencies of microtrenching, tapered sidewall profiles and photoresist-mask faceting on the feature aspect ratio, product formation rate and product residence time in the etching chamber. The etching artifacts were explained using the profile evolution simulator. The microtrenching was associated with two mechanisms - ion scattering from tapered sidewalls and the focussing of directional ions by bowed sidewalls onto the feature bottom. The former mechanism led to trenching initially while the latter mechanism gained importance midway during the etching. The absence of tapered sidewalls initially and the relatively straight sidewall profiles developed during the etching explained the non-occurrence of microtrenches when using HBr. Under processing conditions accompanied by significant deposition, facets at two distinct angles were predicted. The top facet depended on the composition of the material on the photoresist-mask line and its etching angular dependence. The lower facet angle and the polysilicon sidewall profile were governed by the feature aspect ratio, the sticking probabilities and fluxes of the depositing material, and the depositing material etching angular dependence. The phenomenon of feature charging was incorporated in the Monte Carlo simulator to understand its role in the profile evolution. Two electrical approximations were made for the feature - the perfectly insulating and a novel resistive approximation. With an insulating feature, the potential profiles were obtained by determining the space charge on the feature surface and solving Poisson's equation over the entire simulation domain. Calculation of the potential profiles with the resistive feature representation involved treating the feature as a large resistive network, determining the steady-state currents to the feature surface and solving the conductivity equation and Laplace's equation in the solid and gas, respectively. The role surface and bulk conductivities played on the potential profiles were studied. The potential profile in a completely etched polysilicon (conducting) feature with a silicon oxide (insulating) feature bottom was generated. Higher ion currents were calculated at the lower part of the polysilicon sidewall. These currents can etch the passivating material deposited at lower portion of the sidewall enabling spontaneous etching of the sidewall, and cause notching of the sidewall.
by Arpan P. Mahorowala.
Ph.D.
11
Smith, Alyson Rae. "Designing density". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28147.
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Malgesini, Giusseppe. "Evolution of submarine sediment density flows deduced from long distance bed correlations". Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/351356/.
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Submarine flows can transport huge volumes of sediment across the large submarine fans that dominate many parts of the deep ocean floor. Active flow events are notoriously difficult to monitor directly, and therefore our understanding of such flows still strongly relies on the analysis of the deposits they leave behind. This thesis aims to investigate the transport and depositional processes, the stacking patterns and the time frequency distribution of turbidites and debrites deposited in the Miocene Marnoso Arenacea Formation (Italian Apennines). This location is unique because deposits from individual flow events (beds) can be traced for long distances, allowing the lateral and down flow evolution of single flow events to be analyzed in detail. Lateral changes in individual flow deposits are documented through extensive correlation of beds deposited in a stratigraphic interval below the most prominent Contessa Marker bed. The observed transitions in facies, and the external shape of different types of deposit, are used as an independent test of models that capture our understanding of submarine flow processes. This work highlights how deposits of submarine density flows can be complex, even in relatively simple basin plain settings. A single event can comprise different flow types, and transformations can occur between these flow types. The initial volume, sediment concentration and grain size (including the proportion of fine cohesive mud) control the external shape of the deposits. Low density turbidity currents deposit clean sandstone beds with an exponentially tapering shape, while coarser grained high density turbidity currents produce massive or parallel laminated layers that maintain their thickness for longer (10’s of kilometers) distances. Cohesive debris flows form istinctive ungraded mud-rich sandstone that can either pinch-out abruptly or gradually taper. Liquefied debris flows with elevated pore pressures can deposit clean (mud-poor) sand over large areas (up to 30 km) of the Marnoso Arenacea basin plain. This is suggested by the distinctive swirly, patchy fabric of a particular type of clean sandstone, that records pervasive liquefaction during the late stages of the flow, and confirmed by the rapid pinch-out geometry of flow deposits at their margins. Such debris flows most likely form through transformation from an initial high density turbidity current. A similar flow process may characterize the distal, rapid pinch out of sandstone lobes in Fan 4 of the Skoorsteenberg Formation (Karoo basin, South Africa). The observed stacking pattern of turbidite beds in a 530 meters thick stratigraphic section indicates a long-term clustering. Debrite intervals however occur randomly, and bed correlation suggest that almost every large volume flow deposited clean or muddy debrite (or both) intervals in different positions of the basin. Hemipelagic marl thickness is used as a proxy for time between flow events. The distribution of time between events is exponential, therefore related to a Poisson Process. This indicates that flow events (most likely triggered by submarine slope failures) occur independently one from the other through time.
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Dlamini, Simthembile. "Evolution of matter density perturbations in viable f (R) theories of gravity". Master's thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31500.
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In the ΛCDM model, the late-time accelerated expansion of the Universe is explained via a dark energy fluid in the form of a cosmological constant. Such a cosmological constant dominates the energy budget of the Universe today, and yet, it is still a poorly understood species because it is not observed yet. A competitive theoretical approach to understand this is via the so-called f (R) extended theories of gravity, which explain the late acceleration epoch of the Universe resorting to a geometrical modification of the field equations. We illustrate how f (R) theories are constructed and how both the analysis of the cosmological expansion and the growth of matter density perturbations in these theories may differ from the standard Einsteinian results. We study the evolution of matter density perturbations in a viable f (R) model (Hu-Sawicki model) and explain why the Hu-Sawicki model is indeed a viable alternative to ΛCDM by discussing the Dynamical System approach as a method used to obtain the cosmological background solutions. A complete comparison of density perturbations in both the ΛCDM model and Hu-Sawicki model is presented.
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Tejeda, Abiezer. "Correcting Errors Due to Species Correlations in the Marginal Probability Density Evolution". DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1472.
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Synthetic biology is an emerging field that integrates and applies engineering design methods to biological systems. Its aim is to make biology an "engineerable" science. Over the years, biologists and engineers alike have abstracted biological systems into functional models that behave similarly to electric circuits, thus the creation of the subfield of genetic circuits. Mathematical models have been devised to simulate the behavior of genetic circuits in silico. Most models can be classified into deterministic and stochastic models. The work in this dissertation is for stochastic models. Although ordinary differential equation (ODE) models are generally amenable to simu- late genetic circuits, they wrongly assume that a system's chemical species vary continuously and deterministically, thus making erroneous predictions when applied to highly stochastic systems. Stochastic methods have been created to take into account the variability, un- predictability, and discrete nature of molecular populations. The most popular stochastic method is the stochastic simulation algorithm (SSA). These methods provide a single path of the overall pool of possible system's behavior. A common practice is to take several inde- pendent SSA simulations and take the average of the aggregate. This approach can perform iv well in low noise systems. However, it produces incorrect results when applied to networks that can take multiple modes or that are highly stochastic. Incremental SSA or iSSA is a set of algorithms that have been created to obtain ag- gregate information from multiple SSA runs. The marginal probability density evolution (MPDE) algorithm is a subset of iSSA which seeks to reveal the most likely "qualitative" behavior of a genetic circuit by providing a marginal probability function or statistical enve- lope for every species in the system, under the appropriate conditions. MPDE assumes that species are statistically independent given the rest of the system. This assumption is satisfied by some systems. However, most of the interesting biological systems, both synthetic and in nature, have correlated species forming conservation laws. Species correlation imposes con- straints in the system that are broken by MPDE. This work seeks to devise a mathematical method and algorithm to correct conservation constraints errors in MPDE. Furthermore, it aims to identify these constraints a priori and efficiently deliver a trustworthy result faithful to the true behavior of the system.
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Oda, Takeshi. "The cosmic evolution of supernova rate density : implications for the galaxy evolution and the origin of type 1a supernova". 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136885.
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Ferguson, Jane A. "Fiber optic chemical sensors : the evolution of high-density fiber-optic DNA microarrays /". Thesis, Connect to Dissertations & Theses @ Tufts University, 2001.
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Thesis (Ph.D.)--Tufts University, 2001.Adviser: David R. Walt. Submitted to the Dept. of Chemistry, Includes bibliographical references (leaves 197-208). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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Sandfeld, Stefan. "Evolution of dislocation density in a higher-order continuum theory of dislocation plasticity". Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/11367.
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Lu, Peizhen. "Microstructural evolution and macroscopic shrinkage in the presence of density gradients and agglomeration /". The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488194825665703.
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Watkins, Aaron Emery. "A New Perspective on Galaxy Evolution From the Low Density Outskirts of Galaxies". Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1499354382030385.
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Larsdotter, Mellström Helena. "Life history evolution in a bivoltine butterfly". Doctoral thesis, Stockholms universitet, Zoologiska institutionen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-81399.
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Evolution is not always straight-forward, as selection pressures may differ between different generations of the same species. This thesis focuses on the evolution of life history of the model species, the Green-veined White butterfly Pieris napi. In central Sweden P. napi has two generations per year. The directly developing summer generation is short-lived and time stressed, compared to the diapausing generation. In paper I polyandry, defined as female mating rate, was shown to differ between generations but was unaffected by environmental factors. In paper II both males and females of the direct developing generation were shown to eclose more immature than the diapausing generation, indicating larval time constraints. Consistent with this, diapausing males mated sooner than direct developers. Directly developing females, however, mated sooner after eclosion than diapausing females, even though they are more immature. This was shown to negatively affect fecundity, but can pay off when the season is short. Paper III shows that directly developing males have less sex pheromones at eclosion than diapausers, and the differences in sex pheromone production is consistent with developmental time constraints and the differences in mating system. In P. napi and other polyandrous butterflies, males transfer a large, nutritious ejaculate at mating. Large ejaculates confer advantages under sperm competition, but as they are costly, males should adjust ejaculate size to the risk of sperm competition. In paper IV we found that males transfer on average 20% larger spermatophores under high male competition than at low competition. The same effect could be observed if we added male sex pheromone to the air in a mating cage without male-male competition. Paper V shows that males of the two generations respond differently to an increase in male-male competition, with diapausing males transferring larger spermatophores than direct developers at high male competition risk.At the time of the doctoral defence the following paper was unpublished and had a status as follows: Paper 5: Submitted manuscript.
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Casavecchia, Benedetta. "Studying synthetic column density maps and absorption spectra from galactic wind models". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25361/.
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Galactic winds are multi-phase outflows that probe how feedback regulates the mass and metallicity of galaxies. Their cold phase, mainly observable with absorption lines, is often detected hundreds to thousands of pc away from the galactic plane and with velocities of hundreds of km $\rm s^{-1}$. To understand observations, it is important to theoretically study how such lines are produced via numerical simulations of cloud systems exposed to winds and starburst UV backgrounds. In this thesis we study the thermodynamics, ion populations, and ion absorption lines of cold and warm radiative clouds evolving from magnetised wind-cloud systems and an unmagnetised shock-multicloud model. We account for radiative cooling with two different cooling floors and magnetic fields with two different orientations.
In our wind-cloud simulations, cold clouds survive the interaction with the wind for longer, since they are less exposed to instabilities, than warmer clouds. Magnetic fields have a larger influence on warm clouds than in cold clouds. If transverse to the wind direction, the field creates a shield that confines the expansion of the cloud, delaying its evaporation. In our shock-multicloud simulation, cold gas at large distances is not accelerated by ram-pressure, but, instead, precipitates from mixed gas out of thermal equilibrium. To study ion populations and create synthetic spectra, we developed a flexible python interface to link our PLUTO simulations to TRIDENT via the YT-package infrastructure and CLOUDY. Our ion population analysis reveals that setting different cooling floors and magnetic fields affect the column densities of several ions. H\,{\sc i}, O\,{\sc vi}, Mg\,{\sc ii}, C\,{\sc iii}, and Si\,{\sc iv} are more sensitive to the cooling floors, and H\,{\sc i}, Mg\,{\sc ii}, C\, {\sc iii}, and Si\, {\sc iv} can also trace the initial magnetic field direction, making them good candidates for comparisons with observations.
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Graur, Or, K. Decker French, H. Jabran Zahid, James Guillochon, Kaisey S. Mandel, Katie Auchettl y Ann I. Zabludoff. "A Dependence of the Tidal Disruption Event Rate on Global Stellar Surface Mass Density and Stellar Velocity Dispersion". IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626532.
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The rate of tidal disruption events (TDEs), R-TDE, is predicted to depend on stellar conditions near the super-massive black hole (SMBH), which are on difficult-to-measure sub-parsec scales. We test whether R-TDE depends on kpc-scale global galaxy properties, which are observable. We concentrate on stellar surface mass density, Sigma M-*, and velocity dispersion, sigma(nu), which correlate with the stellar density and velocity dispersion of the stars around the SMBH. We consider 35 TDE candidates, with and without known X-ray emission. The hosts range from star-forming to quiescent to quiescent with strong Balmer absorption lines. The last (often with post-starburst spectra) are overrepresented in our sample by a factor of 35(-17)(+21) or 18(-7)(+8), depending on the strength of the H delta absorption line. For a subsample of hosts with homogeneous measurements, Sigma M-* = 10(9)-10(10) M-circle dot/kpc(2), higher on average than for a volume-weighted control sample of Sloan Digital Sky Survey galaxies with similar redshifts and stellar masses. This is because (1) most of the TDE hosts here are quiescent galaxies, which tend to have higher Sigma M-* than the star-forming galaxies that dominate the control, and (2) the star-forming hosts have higher average Sigma M-* than the star-forming control. There is also a weak suggestion that TDE hosts have lower sigma(nu) than for the quiescent control. Assuming that R-TDE infinity Sigma M-*(alpha) x sigma(beta)(nu), and applying a statistical model to the TDE hosts and control sample, we estimate (alpha) over cap = 0.9 +/- 0.2 and (beta) over cap = -1.0 +/- 0.6. This is broadly consistent with RTDE being tied to the dynamical relaxation of stars surrounding the SMBH.
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Sandfeld, Stefan [Verfasser]. "The Evolution of Dislocation Density in a Higher-order Continuum Theory of Dislocation Plasticity / Stefan Sandfeld". Aachen : Shaker, 2011. http://d-nb.info/1084535742/34.
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Lim, Wen Jun. "Analysis and design of analog fountain codes for short packet communications". Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29277.
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Channel coding is at the heart of any communications systems and plays a key role in meeting the requirements of current and future wireless standards. The services defined by the 3rd Generation Partnership Project (3GPP) for fifth generation (5G) new radio, in particular ultra-reliable low-latency communication (URLLC) and massive machine type communication (mMTC), have very stringent requirements in terms of latency and reliability. Short packet communication is proved to be one of the solutions to achieve the latency requirement of future wireless communication systems due to shorter transmission-time interval. Therefore, designing robust and efficient short channel codes for URLLC and mMTC is of critical importance to design sustainable and efficient mobile communication systems.
Traditional channel coding methods are not able to fulfil the requirements for Beyond 5G (B5G) or 6th generation (6G) mobile standards, which have a strong emphasis on bit-level granularity and flexibility. Rateless codes have been considered as viable candidates for short packet communication in URLLC and mMTC due to their rate-adaptive nature. Furthermore, the fact that rateless codes do not rely on channel state information (CSI) makes them stand out from traditional channel codes, which is an important characteristic to reduce transmission overhead.
Analog fountain code (AFC) is a newly introduced rateless code, which has linear complexity in terms of encoding and decoding, and a capacity-approaching performance for a wide range of signal-to-noise ratios (SNRs). The code structure is simple; that is, the modulated information symbols are directly generated from information symbols in a linear manner. In this thesis, I will take a step forward to provide a comprehensive analysis and design of AFC for short packet communications. I first propose a density evolution (DE)-based framework, which tracks the evolution of the probability density function of the messages exchanged between AFC’s variable and check nodes in the belief propagation (BP) decoder. Based on the proposed DE framework, I formulate an optimisation problem to find the optimal weight set for AFC in order to minimise the bit error rate at a given SNR. Simulation results show the superiority of the AFC code design with optimised weight set compared to existing AFC designs in the literature.
Next, I focus on the design of AFC in a short block length regime. In order to guarantee the performance of AFC in these conditions, a proper precoder is required. Therefore, the optimised weight set obtained from the proposed DE framework can be directly applied in the short block length regime with the aid of a precoder with powerful error correcting capability. Specifically, I use Bose, Chaudhuri, and Hocquenghem (BCH) codes with an ordered statistics decoder (OSD) and low-density parity check (LDPC) codes with the BP decoder. Simulation results show that low rate precoders offer better reliability across a wide range of SNRs compared to high-rate precoders. Additionally, the precoded AFC performs close to the normal approximation benchmark in the short block length regime over a wide range of SNRs. I also discuss the complexity of the AFC decoder and propose a threshold-based decoder to reduce it.
Finally, I focus on the analysis and design of AFC in a multiple access channel. I present two encoding schemes, i.e., superposition coding and joint encoding, and two decoding schemes, i.e., successive interference cancellation and joint decoding, for multiple access AFC (MA-AFC). The process of joint encoding and the updating rules for joint decoding are explained in detail. I propose different combinations of encoding and decoding schemes for MA-AFC and evaluate their performance in terms of block error rate (BLER) to determine which combination has the best performance. Next, I propose a DE-based framework to track the evolution of messages exchanged between check nodes and variable nodes of MA-AFC under the joint decoding scheme. With the proposed DE framework, I formulate optimisation problems to find the optimal AFC code parameters, specifically the weight-set, which minimise the bit error rate at a given SNR. Simulation results show that the optimised AFC code outperforms the existing AFC code design in multiple access scenarios.
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Bjartnes, Erik. "Oxygen evolution on La1-xSrxCoO3 Pellet-Electrodes in alkaline Solution : Charge Carrier density dependence of electrocatalytic activity". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18901.
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Alkaline water electrolysis need a catalyst with low overpotential and high current densitiy for oxygen evolution in order to be a commercial viable hydrogen source in the future. Finding and establishing a correlation between electrocatalytic activity and charge carrier density will help towards finding an optimum catalyst for this purpose. Such comparisons have been made using theoretical values for charge carrier density, but the aim of this work is to use charge carrier data from experimental values.Five powders of La<sub>1-x</sub>Sr<sub>x</sub>CoO<sub>3</sub> (with compositions x = 0, 0.25, 0.5, 0.75, 1) were synthesized by solid-state synthesis and sintered to pellets. The pellet surfaces were investigated in alkaline solution (pH = 13) by cyclic voltammetry, polarization and impedance measurements. Polariza- tion curves with Tafel lines and Mott-Schottky plots were established. The powders and pellet surfaces were investigated by XRD, SEM, EDS, AFM and light microscope.The polarization curves revealed a volcanic behavior with an increase in catalytic activity from x = 0 up to x = 0.75 and then decreasing. The charge carrier density increased with increasing strontium doping. The resulting comparison gave figure 34. Surface investigation revealed much porosity. Because of corrosion, the surface area increased with measuring, and finding the real surface area and the roughness proved to be problematic.A volcanic behavior of the charge carrier density and electrocatalytic activity relationship were observed. Finding roughness factor values by measuring double layer capacitance measured by the cyclic voltammetry method and dividing by the nominal capacitance for a flat surface proved to be unsuccessful. Better synthesis and sintering procedures of pellets are needed to increase the density of the samples in order to decrease the roughness and the effect of corrosion.
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Wilkins, Stephen Matthew. "Comparing the evolution of the stellar mass density with that predicted from the cosmic star formation history". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608736.
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Gómez, Jenny Marcela Rodríguez. "Evolution of the electron density, temperature distribution in the solar corona during solar cycles 23 and 24". Instituto Nacional de Pesquisas Espaciais (INPE), 2017. http://urlib.net/sid.inpe.br/mtc-m21b/2017/02.16.21.15.
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The present thesis aims at the study of the plasma parameters in the solar corona, using a flux transport model, force free-field extrapolations, a model of emission and optimization algorithm. The physical-model is based on the assumption that the variation of the irradiance and plasma parameters is due to the evolution of the solar magnetic field. The goal is to reconstruct electron density and temperature distributions in the solar corona and the emission in four different wavelengths during the last two solar cycles (large scale) and also the emission, electron density and temperature profiles from Active Region NOAA 11855 (small scale). The relation between photospheric dynamics, emission, and plasma parameters in different time scales are reviewed. These characteristics are important in the Astrophysical and Geophysical fields, because they can help to understand physical phenomena such as coronal heating and eruptive events.Esta tese tem como objetivo principal o estudo dos parâmetros de plasma na coroa solar, usando um modelo de transporte de fluxo, extrapolações de campo livre de forças, um modelo de emissão e um algoritmo de optimização. O modelo esta baseado na ideia que as variações da irradiância e os parâmetros de plasma estão relacionados com a evolução do campo magnético solar. O objetivo é reconstruir as distribuições de densidade e temperatura na coroa solar e a emissão em quatro comprimentos de onda diferentes durante os dois últimos ciclos solares e também a emissão, perfis densidade eletrônica e temperatura usando a região ativa NOAA 11855. A relação entre a dinâmica, emissão e parâmetros de plasma em diferentes escalas de tempo são revisadas. Estas características são importantes em astrofísica e geofísica, porque podem ajudar a entender fenômenos físicos como o aquecimento coronal e eventos eruptivos.
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Munger, Emily LaRee. "Alteration to Astrocyte Density and Morphology across Mammalia with Specific Attention to Primate Brain Evolution and Aging". Kent State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=kent1594638449298271.
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Reynolds, Eric W. "Laboratory observation of evolution of IEDD-wave-modified equilibrium and density-gradient effects on SMIA wave propagation". Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10471.
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Thesis (Ph. D.)--West Virginia University, 2009.Title from document title page. Document formatted into pages; contains xxviii, 307 p. : ill. Includes abstract. Includes bibliographical references (p. 118-131).
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Knoche, Krysti Lynn. "Density gradient films, lanthanide electrochemistry, and magnetic field effects on hydrogen evolution, oxygen reduction, and lanthanide electrochemistry". Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/3124.
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Electroanalytical techniques are used to investigate mass transport through density gradient films; lanthanide triflate reduction and oxidation in a Nafion/acetonitrile matrix; and magnetic field effects on hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and lanthanide electrochemistry.
Graded density films are more dense at the electrode surface and become less dense out into solution due to a brush polymer structure. Fick's second law expands to account for a diffusion coefficient that varies with distance x normal to the electrode surface. Confocal microscopy, cyclic voltammetry, and computer simulations are used to investigate density graded Ficoll® films. Mass transport approaches steady state (scan rate independence) at slow scan rates where the diffusion length samples the entire film. The use of Ficoll to template an ion exchange polymer is explored by casting Nafion® Ficoll composites.
Lanthanide electrochemistry is enabled in acetonitrile at a Nafion modified platinum electrode in the presence of triflate ligands. Formal potentials are shifted into the voltage window of acetonitrile accessible due to triflate complexation. The Nafion further solubilizes the compounds. The mechanism (ECEC) is studied with cyclic voltammetry and x-ray photoelectron spectroscopy.
Magnetic field effects on electrochemical systems have been of interest to researchers for the past 65 years. Mass transport effects, such as magnetohydrodynamics and magnetic field gradient effects have been reported, but the Leddy group focuses on electron transfer effects. Electrode surfaces are modified with composite films of magnetic microparticles suspended in ion exchange polymer Nafion. Effects are verified to be electron transfer related and due to the magnetization of chemically inert microparticles. The magnets catalyze the rates of important electron transfer reactions such as hydrogen evolution and oxygen reduction.
Magnetic field effects on HER at various noncatalytic metal electrodes are explored with linear scan voltammetry. There is a correlation between the magnetic susceptibility of the electrode metals and the HER exchange currents (reaction rates). Exchange currents are 103× larger for a paramagnetic metal electrode than a diamagnetic one with the same work function. The overpotential at diamagnetic electrodes is decreased by modification with a Nafion + magnetic microparticle composite film. A decrease in overpotential of ∼70 % for all electrodes except platinum is observed. The overpotential decrease correlates with the magnetic susceptibility of the particles.
Magnets can enhance differences between lanthanide cyclic voltammograms by shifting current densities at a given potential and enhancing current based on the number of 4f electrons and magnetic moment of each lanthanide ion.
Magnetic field effects on ORR in acetonitrile are investigated with cyclic voltammetry. In aprotic solvents, ORR proceeds by a one electron transfer reaction to paramagnetic O2.–. Enhanced reversibility and electron transfer kinetics are observed as well as a decrease in overpotential of ∼100 mV. Magnetic field effects on ORR in a lanthanide triflate solution are also examined. Electron transfer kinetics and reversibility are further enhanced in the presence of lanthanide triflate.
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Libois, Quentin. "Evolution des propriétés physiques de neige de surface sur le plateau Antarctique. Observations et modélisation du transfert radiatif et du métamorphisme". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU026/document.
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Le bilan d'énergie de surface du Plateau Antarctique est essentiellement contrôlé par les propriétés physiques des premiers centimètres du manteau neigeux. Or l'évolution de cette neige de surface est complexe car elle dépend de processus fondamentalement imbriqués: vitesse de métamorphisme, profils de température, pénétration du rayonnement solaire, précipitations, transport de neige par le vent, etc. L'objectif de ces travaux de thèse est d'étudier ces diverses composantes et leur couplage afin de simuler l'évolution de la densité de la neige et de la taille de grain (surface spécifique) sur le Plateau Antarctique. Pour représenter de manière physique l'absorption de l'énergie solaire à l'intérieur du manteau, un modèle de transfert radiatif à fine résolution spectrale (TARTES) a été implémenté dans le modèle de manteau neigeux détaillé Crocus. TARTES permet de calculer le profil vertical d'absorption d'énergie dans un manteau stratifié dont les caractéristiques sont connues. Parmi elles, la forme des grains, explicitement prise en compte dans TARTES, a été peu étudiée jusqu'à présent. C'est pourquoi une méthode de détermination expérimentale de la forme optique des grains est proposée et appliquée à un grand nombre d'échantillons de neige. Cette méthode, basée sur des mesures optiques, des simulations TARTES, et l'inférence bayésienne, a permis de déterminer la forme la plus adéquate pour simuler les propriétés optiques de la neige, et a mis en évidence le fait que représenter la neige par un ensemble de particules sphériques conduisait à surestimer la profondeur de pénétration du rayonnement d'environ 30%. L'impact de l'absorption en profondeur du rayonnement sur les profils de température dans le manteau et son métamorphisme est ensuite étudié par des approches analytique et numérique, mettant en valeur la sensibilité des profils aux propriétés de la neige proche de la surface. En particulier, la densité de la neige sur les premiers centimètres est cruciale pour le bilan d'énergie du manteau car elle impacte à la fois la profondeur de pénétration du rayonnement et la conductivité thermique du manteau. Puisque le modèle Crocus tient compte de ce couplage entre propriétés optiques et physiques du manteau, il est utilisé pour estimer l'influence des conditions météorologiques sur la variabilité temporelle des propriétés physiques de la neige de surface à Dôme C. Ces simulations sont évaluées au regard d'un jeu de données collectées lors de missions de terrain et de mesures automatiques de l'albédo spectral et de la pénétration du rayonnement dans la neige. Ces observations mettent en évidence le rôle primordial des précipitations dans les variations rapides de taille de grain en surface et l'existence d'un cycle saisonnier de cette taille de grain. Ces variations sont bien simulées par Crocus lorsque le forçage atmosphérique qui lui est imposé est adéquat. En particulier, l'impact du vent sur l'évolution du manteau est fondamental car il contrôle la densité de surface par le biais du transport de neige. Ce transport est aussi à l'origine de la variabilité spatiale des propriétés de la neige observée à Dôme C. C'est pourquoi une modélisation stochastique de l'érosion et du transport de neige dans Crocus est proposée. En plus d'expliquer la variabilité spatiale de la densité et de la taille de grain, elle permet de reproduire celle de l'accumulation annuelle ainsi que les variations rapides de hauteur de neige liées à des épisodes de vent. Ces travaux ont permis une meilleure représentation des processus physiques qui contrôlent les variations des propriétés de la neige de surface à Dôme C, tout en soulignant le rôle primordial du vent, dont l'impact sur le manteau est particulièrement complexe à simulerThe surface energy balance of the Antarctic Plateau is mainly governed by the physical properties of the snowpack in the topmost centimeters, whose evolution is driven by intricated processes such as: snow metamorphism, temperature profiles variations, solar radiation penetration, precipitation, snow drift, etc. This thesis focuses on the interactions between all these components and aims at simulating the evolution of snow density and snow grain size (specific surface area) on the Antarctic Plateau. To physically model the absorption of solar radiation within the snowpack, a radiative transfer model with high spectral resolution (TARTES) is implemented in the detailed snowpack model Crocus. TARTES calculates the vertical profile of absorbed radiation in a layered snowpack whose characteristics are given. These characteristics include snow grain shape, a parameter that has been seldom studied. For this reason, an experimental method to estimate the optical grain shape is proposed and applied to a large number of snow samples. This method, which combines optical measurements, TARTES simulations and Bayesian inference, is used to estimate the optimal shape to be used in snow optical models. In addition, it highlights that representing snow as a collection of spherical particles results in overestimation of the penetration depth of solar radiation. The influence of the penetration of solar radiation on the snow temperature profiles is then investigated with analytical and numerical tools. The results point out the high sensitivity of the temperature profiles to surface snow physical properties. In particular, the density of the topmost centimeters of the snowpack is critical for the energy budget of the snowpack because it impacts both the effective thermal conductivity and the penetration depth of light. To simulate the evolution of snow physical properties at Dome C by taking into account their interdependence with snow optical properties, the model Crocus is used, driven by meteorological data. These simulations are evaluated against a set of data collected during field missions as well as automatic measurements of snow spectral albedo and penetration depth. These observations highlight the influence of weather conditions on the temporal variability of surface snow properties. They show the existence of a slow decrease of snow grain size at the surface during summer. Rapid changes are also observed, essentially due to precipitation. These variations are well simulated by Crocus when forced by an appropriate atmospheric forcing. In particular, the impact of wind on the evolution of the snowpack is crucial because it controls the surface density through snow transport. This transport is also responsible for the spatial variability of snow properties observed at Dome C. That is why a stochastic representation of snow erosion and transport in Crocus is proposed. It explains well the observations of the spatial variability of density and grain size, and reproduces the variability of the annual accumulation as well as rapid changes in snow height resulting from drift events. This study improves our understanding of the physical processes which drive the properties of snow close to the surface on the Antarctic Plateau, and also points out the critical role of wind, the impact of which is very difficult to account for in models yet
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Zhang, Tianyu. "DENSITY FUNCTIONAL THEORY STUDIES ON THE STRUCTURAL EVOLUTION AND CATALYTIC REACTIVITY OF MOLYBDENUM-BASED CATALYSTS FOR METHANE CONVERSION". OpenSIUC, 2019. https://opensiuc.lib.siu.edu/dissertations/1768.
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Methane is an abundant resource existing in the form of natural and shale gas, and molybdenum-based catalysts, including molybdenum oxides and carbides, are the commonly used components in catalysts for converting methane to value-added chemicals. Therefore, understanding the catalytic mechanism underlying the methane conversion over molybdenum-based catalysts is key to designing highly efficient catalysts and optimizing the operating conditions. In this dissertation, I focus on the structural evolution from oxide to carbides and catalytic reactivity of the molybdenum-based catalysts for methane conversion based on the result from density functional theory (DFT) computational studies.First, the surface chemistry and reactivity of α-MoO3 toward C-H bond activation of methane by breaking the first C-H bond on the MoO3 (010) surface were used to evaluate various functionals of the DFT method. Our results indicate that surface reduction of α-MoO3 (010) occurs preferably through releasing the terminal oxygen atoms, generating oxygen vacancies while exposing the reduced Mo centers. These oxygen vacancies tend to be separated from each other at a higher density due to the repulsive interactions. Furthermore, the reduced α-MoO3 (010) surface promotes methane activation kinetically and thermodynamically by reducing the activation barrier for the first C-H bond breaking and stabilizing the product state as compared with those on the stoichiometric surface. There is a synergy between the reduced Mo active site and surface lattice oxygen for C-H bond cleavage. In addition, the performance of different functionals, including the pure-GGA PBE functional with the semi-empirical vdW correction and the meta-GGA SCAN functional, has been investigated. With the meta-GGA functional, we can predict the bulk structure of α-MoO3 more accurately while reproducing the thermal chemistry of MoO3. On the other hand, the reactivity based on the PBE functional is qualitatively consistent with that from the SCAN functional.We then conducted a systematic study of methane activation and conversion over the Mo-terminated surfaces derived from different phases of Mo2C carbides, i.e. the (001) surface of α-Mo2C and the (100) surface of β-Mo2C. The results show that Mo-terminated Mo2C with lower carburization in its subsurface (β-Mo2C) possesses a superior reactivity toward methane activation, resulting in a complete dissociation of methane to carbon adatom on the surface. This carbon adatom causes further carburization of the surface, lowering the reactivity toward methane activation. Moreover, the carburization occurs more easily in the near surface layers of Mo2C than in the bulk. Although carburization lowers the activities for methane activation, it promotes C-C coupling for dimerization of the (CH)ad species, resulting in (C2H2)ad on the Mo-terminated surfaces. On the deep carburized molybdenum carbide (MoC) surfaces, we mapped out the elementary steps of CH4 dissociation and possible mechanisms for forming the C2 species. The results indicate that the Mo-terminated MoC surfaces derived from different bulk phases (α- and δ-) of MoC possess a similar mechanism to that on the noble-metal surfaces for methane dissociation, i.e., CH4 dissociates sequentially to (CH)ad with both kinetic and thermodynamic feasibilities while breaking the last C-H bond in (CH)ad is highly activated. As such, C-C coupling through dimerization of the (CH)ad species occurs more readily, resulting in (C2H2)ad on the Mo-terminated surfaces. Such (C2H2)ad species can dehydrogenate easily to other C2 adsorbates such as (C2H)ad and (C2)ad. Consequently, these C2 species from CH4 dissociation will likely be the precursors for producing long chain hydrocarbons and/or aromatics on molybdenum carbide based catalysts.
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Luna, Ricardo y Hrishikesh Tapse. "An Analysis on the Coverage Distance of LDPC-Coded Free-Space Optical Links". International Foundation for Telemetering, 2008. http://hdl.handle.net/10150/606240.
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ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, CaliforniaWe design irregular Low-Density Parity-Check (LDPC) codes for free-space optical (FSO) channels for different transmitter-receiver link distances and analyze the error performance for different atmospheric conditions. The design considers atmospheric absorption, laser beam divergence, and random intensity fluctuations due to atmospheric turbulence. It is found that, for the same transmit power, a system using the designed codes works over much longer link distances than a system that employs regular LDPC codes. Our analysis is particularly useful for portable optical transceivers and mobile links.
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Whitaker, Katherine E., Rachel Bezanson, Dokkum Pieter G. van, Marijn Franx, der Wel Arjen van, Gabriel Brammer, Natascha M. Förster-Schreiber et al. "Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5 < z < 2.5". IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623862.
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In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at 0.5. <. z. <. 2.5 selected from 3D-HST. We confirm that star-forming galaxies are larger than quiescent galaxies at fixed stellar mass (M*). However, in contrast with some simulations, there is only a weak relation between star formation rate (SFR) and size within the star-forming population: when dividing into quartiles based on residual offsets in SFR, we find that the sizes of star-forming galaxies in the lowest quartile are 0.27. +/-. 0.06 dex smaller than the highest quartile. We show that 50% of star formation in galaxies at fixed M. takes place within a narrow range of sizes (0.26 dex). Taken together, these results suggest that there is an abrupt cessation of star formation after galaxies attain particular structural properties. Confirming earlier results, we find that central stellar density within a 1 kpc fixed physical radius is the key parameter connecting galaxy morphology and star formation histories: galaxies with high central densities are red and have increasingly lower SFR/M., whereas galaxies with low central densities are blue and have a roughly constant (higher) SFR/M. at a given redshift. We find remarkably little scatter in the average trends and a strong evolution of > 0.5 dex in the central density threshold correlated with quiescence from z.similar to. 0.7-2.0. Neither a compact size nor high-n are sufficient to assess the likelihood of quiescence for the average galaxy; instead, the combination of these two parameters together with M* results in a unique quenching threshold in central density/velocity.
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Whitaker, Katherine E., Rachel Bezanson, Dokkum Pieter G. van, Marijn Franx, der Wel Arjen van, Gabriel Brammer, Natascha M. Foerster-Schreiber et al. "Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5 < z < 2.5". IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623944.
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In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at 0.5. <. z. <. 2.5 selected from 3D-HST. We confirm that star-forming galaxies are larger than quiescent galaxies at fixed stellar mass (M*). However, in contrast with some simulations, there is only a weak relation between star formation rate (SFR) and size within the star-forming population: when dividing into quartiles based on residual offsets in SFR, we find that the sizes of star-forming galaxies in the lowest quartile are 0.27. +/-. 0.06 dex smaller than the highest quartile. We show that 50% of star formation in galaxies at fixed M. takes place within a narrow range of sizes (0.26 dex). Taken together, these results suggest that there is an abrupt cessation of star formation after galaxies attain particular structural properties. Confirming earlier results, we find that central stellar density within a 1 kpc fixed physical radius is the key parameter connecting galaxy morphology and star formation histories: galaxies with high central densities are red and have increasingly lower SFR/M., whereas galaxies with low central densities are blue and have a roughly constant (higher) SFR/M. at a given redshift. We find remarkably little scatter in the average trends and a strong evolution of > 0.5 dex in the central density threshold correlated with quiescence from z.similar to. 0.7-2.0. Neither a compact size nor high-n are sufficient to assess the likelihood of quiescence for the average galaxy; instead, the combination of these two parameters together with M* results in a unique quenching threshold in central density/velocity.
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Hjelm, Vivien. "Optimizing a Single Atom Catalyst for theOxygen Evolution Reaction using DensityFunctional Theory". Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-259703.
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The growing interest of renewable fuel and energy sources has steadily increased over time due to climate changes. Research is being made around the world to find solutions for the different problems; one possible solution is to produce hydrogen gas to help phase out the usage of fossil fuels. So far, the technology for the hydrogen gas production is expensive for various reasons, one of the challenges is to minimize the energy usage for the production. Hydrogen could be used in fuel cells which can be used to fuel an electric car. In a fuel cell, hydrogen and oxygen gas are mixed to produce electrical energy as the main product, but it also forms thermal energy and water. Hydrogen gas can be produced from the reversed reaction; by electrolysis of water. This reaction requires energy and one way to minimize the energy usage for this is by using acatalyst. The goal with this master thesis was to see how the reaction rate of the oxygen evolution reaction can be affected by different single atom catalyst systems. The main structure for this catalyst in this thesis is aporphyrin molecule where different transition metals were tried as the active site. Different modifications on the structure were also made by exchanging some of the structures atoms and by adding different ligands.The purpose of this is to see how these modifications change the activity of the catalyst. The catalysts were optimized and calculated in a computational chemistry program called Gaussian 16. The calculations was made by using the DFT functional PBE0 and the basis sets Def2svp and Def2tzvpp. The results show that different modifications do affect the activity of the catalyst. The biggest variations in activity are from placing ligands under the active site while exchanging hydrogens to other substituents on the outer radial position can fine tune the results. The best active sites for this system came by using iridium, rhodium and cobalt which are all elements in group 9 of the periodic table. The lowest overpotential of 0.513 V was given by an iridium based system with four hydrogens exchanged by fluorides.Runt om i världen finns ett ökat intresse för förnyelsebara energi och bränslekällor för att tackla klimat förändringarna. Stor del av forskningen som görs idag har i syfte att hitta nya lösningar för att minska klimatpåverkan i olika områden. Ett av forskningsområderna är hitta vägar till en miljövänligare vätgasproduktion där vätgasen skulle kunna användas i bränsleceller. Dessa celler kan sättas i elbilar och på så sätt fasa ut användingen av fossila bränslen. En av utmaningarna för vätgasproduktionen är att den idag är kostsam och kräver mycket energi. Forskare försöker hitta olika katalysatorer som kan minska energiåtgången som krävs vid elektrolys av vatten där syrgas och vätgas produceras. Målet med det här examensarbetet är att se hur en single atom catalyst kan påverka reaktionskinitiken för den syrgasbildande reaktionen vid elektrolys av vatten. Huvudstrukturen för katalysatorn som beräkningarna är gjorda på är en porphyrinmolekyl där olika övergångsmetaller kommer testas som det aktiva sätet i katalysatorn. Olika ligander kommer även tillsättas systemet samt utbyte av några väteatomer till olika substituenter i porfyrinstrukturen. Katalysatorn optimerades i det kvantkemiska beräkningsprogrammet Gaussian 16 med funktionalen PBE0 med basset Def2svp och Def2tzvpp. Resultaten visade att olika modifikationer på systemet hade en påverkan på katalysatorns aktivitet. Den största påverkan hade de olika liganderna som placerades under det aktiva sätet jämfört med de olika substituenterna. De bästa metallerna för katalysatorn var iridium, rhodium och kobolt vilket alla ligger i grupp nio i det periodiska systemet. Den lägsta överpotentialen på 0.513 V gavs av iridium systemet med fyra utbyta väten till fluor.
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Hui, Lam. "The evolution of density fluctuations through reheating in the inflationary universe and gravitational instability in the non-linear regime". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38413.
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Miao, Sha Ph D. Massachusetts Institute of Technology. "Mechanistic study of slug formation and evolution in high-viscosity-liquid/High-density-gas multiphase flows in channels/pipes". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118725.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 165-176).
Rapidly rising global energy demand coupled with dwindling conventional oil resources has pushed unconventional oil, such as heavy oil, to become one of the most important future energy resources. However, design and operation of pipelines to transport heavy-oil/gas flows have raised new challenges associated with remarkably different flow regime transitions compared to conventional low-viscosity-oil/low-density-gas flows. Many traditional flow regime models for these oil/gas flows result in O(1) prediction errors when applied to high-viscosity-oil/high-density-gas flows because they fail to account for the complex change in physics and scales that occur as the fluid properties substantially change. Therefore, understanding the mechanisms that cause flow-regime transition for these types of flows is of critical importance to the development of physics-based models allowing for the creation of more robust and cost effective designs. The work described in this thesis focuses on investigating the fundamental mechanisms governing the initial growth and nonlinear evolution of interfacial waves leading to slugging in concurrent high-viscosity (laminar) liquid/high-density(turbulent) gas two-phase flows in horizontal channels/pipes. We first develop a Fully-Coupled Immersed Flow (FCIF) solver for the three-dimensional simulation of fluid-fluid interaction by coupling two distinct flow solvers using an Immersed Boundary (IB) method. The FCIF solver captures dynamic interactions between two fluids with disparate flow properties, while retaining the desirable simplicity of non-boundary-conforming grids. For the application of slug development with turbulent gas and laminar liquid, we couple an IB-based unsteady Reynolds Averaged Navier Stokes (uRANS) simulator with a depth-integrated (long-wave) solver in FCIF. We perform a series of validations on this method. The results demonstrate that the FCIF solver effectively captures the essential physics of gas-liquid interaction and can serve as a useful tool for the mechanistic study of slug generation in two-phase gas/liquid flows in channels and pipes.
by Sha Miao.
Ph. D.
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Hodgkinson, Jonathan. "Sedimentary evolution, hydrogeology and geochemistry of a back-barrier sand island : Toorbul, Southeast Queensland". Thesis, Queensland University of Technology, 2008. https://eprints.qut.edu.au/16686/1/Jonathan_Hodgkinson_Thesis.pdf.
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Small back-barrier sand islands are poorly known in terms of hydrogeology and have been overlooked in more extensive studies of coastal groundwater systems that include larger barrier island complexes. This study employs a three-fold sequential approach to aquifer characterisation in a back-barrier sand island. A three-dimensional stratigraphic model forms the foundation framework, being derived from a multidisciplinary approach to sedimentary analysis and the construction of a depositional chronology. A conceptual hydrostratigraphic model is formulated based on the translation of sedimentary facies to hydrofacies, combined with density dependent flow calculations and tidal oscillation measurements. Groundwater hydrochemical data and mineral geochemistry are integrated with the resulting hydrogeological model to examine water-rock interaction and solute transport mechanisms.
The study area is Toorbul Island, a small back-barrier sand mass of ~5 km2 with a maximum surface elevation of ~3.5 m AHD, located in the Pumicestone Passage of Southeast Queensland. The island hosts a dual aquifer system consisting of an unconfined island freshwater lens, underlain by a semi-confined palaeovalley-fill aquifer. Groundwater in the semi-confined aquifer is hyper-saline, carrying high concentrations of dissolved metals, with iron, in particular, ranging from 40 to < 200 mg l-1. This is of significant interest for both human health and environmental management, because iron is an important nutrient source for toxic algal bacteria such as Lyngbya majuscula.
Conceptual modelling demonstrates that iron oxides and hydroxides are the main source of iron in the semi-confined aquifer, with a contribution from ferruginous chlorite dissolution. Aqueous manganese and a proportion of the aqueous iron are derived from the dissolution of manganoan ilmenite. Ferric iron minerals also contribute a significant proportion of dissolved iron in the deeper regions of the unconfined aquifer. Aqueous iron in the shallow unconfined groundwater is limited by iron sulphides, which also regulate acidity and indirectly limit dissolved aluminium concentrations. Groundwater redox state governed by seasonal climatic fluxes is the most significant control on iron-bearing mineral phase stability. Transport of dissolved metals to the surrounding estuary and the adjacent barrier island groundwater system is limited by the rate of ion diffusion across transition zone boundaries.
The overall conclusions derived from this research show that back-barrier islands should be evaluated as discrete hydrogeological entities. The stratigraphic complexity that may be apparent within these island landforms should not be underestimated and the model domain should not necessarily be treated as a homogeneous system. This complexity is exemplified by the relationship between the upper and lower aquifers on Toorbul Island and the associated distribution of groundwater compositional heterogeneity. The complex stratigraphy within the sedimentary pile is derived from the presence of a sub-surface palaeovalley and the sedimentary response to changing sea-level over time. Considering the current widespread distribution of estuarine systems, complex hydrogeology as exhibited by Toobul Island, may be common in many small back-barrier island groundwater systems. The aquifer characteristics and their influence on solute transport and delivery can have significant ramifications for the exploitation of the adjacent coastal plain and barrier island aquifers. The potential influence on the latter is of particular concern due to the pressure imposed on potable groundwater supplies by increasing population densities in coastal areas.
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Hodgkinson, Jonathan. "Sedimentary evolution, hydrogeology and geochemistry of a back-barrier sand island : Toorbul, Southeast Queensland". Queensland University of Technology, 2008. http://eprints.qut.edu.au/16686/.
Texto completoResumen
Small back-barrier sand islands are poorly known in terms of hydrogeology and have been overlooked in more extensive studies of coastal groundwater systems that include larger barrier island complexes. This study employs a three-fold sequential approach to aquifer characterisation in a back-barrier sand island. A three-dimensional stratigraphic model forms the foundation framework, being derived from a multidisciplinary approach to sedimentary analysis and the construction of a depositional chronology. A conceptual hydrostratigraphic model is formulated based on the translation of sedimentary facies to hydrofacies, combined with density dependent flow calculations and tidal oscillation measurements. Groundwater hydrochemical data and mineral geochemistry are integrated with the resulting hydrogeological model to examine water-rock interaction and solute transport mechanisms. The study area is Toorbul Island, a small back-barrier sand mass of ~5 km2 with a maximum surface elevation of ~3.5 m AHD, located in the Pumicestone Passage of Southeast Queensland. The island hosts a dual aquifer system consisting of an unconfined island freshwater lens, underlain by a semi-confined palaeovalley-fill aquifer. Groundwater in the semi-confined aquifer is hyper-saline, carrying high concentrations of dissolved metals, with iron, in particular, ranging from 40 to < 200 mg l-1. This is of significant interest for both human health and environmental management, because iron is an important nutrient source for toxic algal bacteria such as Lyngbya majuscula. Conceptual modelling demonstrates that iron oxides and hydroxides are the main source of iron in the semi-confined aquifer, with a contribution from ferruginous chlorite dissolution. Aqueous manganese and a proportion of the aqueous iron are derived from the dissolution of manganoan ilmenite. Ferric iron minerals also contribute a significant proportion of dissolved iron in the deeper regions of the unconfined aquifer. Aqueous iron in the shallow unconfined groundwater is limited by iron sulphides, which also regulate acidity and indirectly limit dissolved aluminium concentrations. Groundwater redox state governed by seasonal climatic fluxes is the most significant control on iron-bearing mineral phase stability. Transport of dissolved metals to the surrounding estuary and the adjacent barrier island groundwater system is limited by the rate of ion diffusion across transition zone boundaries. The overall conclusions derived from this research show that back-barrier islands should be evaluated as discrete hydrogeological entities. The stratigraphic complexity that may be apparent within these island landforms should not be underestimated and the model domain should not necessarily be treated as a homogeneous system. This complexity is exemplified by the relationship between the upper and lower aquifers on Toorbul Island and the associated distribution of groundwater compositional heterogeneity. The complex stratigraphy within the sedimentary pile is derived from the presence of a sub-surface palaeovalley and the sedimentary response to changing sea-level over time. Considering the current widespread distribution of estuarine systems, complex hydrogeology as exhibited by Toobul Island, may be common in many small back-barrier island groundwater systems. The aquifer characteristics and their influence on solute transport and delivery can have significant ramifications for the exploitation of the adjacent coastal plain and barrier island aquifers. The potential influence on the latter is of particular concern due to the pressure imposed on potable groundwater supplies by increasing population densities in coastal areas.
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Roucher, Clémentine. "Evolution de l'épidémiologie et des critères diagnostiques du paludisme clinique à Dielmo de 1990 à 2010". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM5062.
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En Afrique tropicale, là où le paludisme est fortement endémique, la plupart des individus sont semi-immuns et les infections asymptomatiques sont très répandues. Ainsi la détection de parasites dans le sang de malades fébriles n'est pas un critère suffisant pour distinguer le paludisme des autres causes de fièvre. A Dielmo, un village du Sénégal d'environ 500 habitants en 2010, un suivi épidémiologique continu très étroit du paludisme a débuté en 1990. Dans ce village où la transmission est pérenne, la mise en place de moyens de lutte et de prévention contre le paludisme de plus en plus efficaces a profondément transformé l'épidémiologie du paludisme. Dans ce travail, nous analysons l'impact de ces interventions sur les prévalences parasitaires, les densités parasitaires et les critères diagnostiques du paludisme et nous mesurons l'évolution du paludisme clinique à Plasmodium falciparum, P. malariae et P. ovale de juin 1990 à décembre 2010. Les données parasitologiques et cliniques ont été analysées par régression logistique à effet aléatoire pour étudier la relation entre les densités parasitaires et le risque de fièvre. Les prévalences parasitaires des trois espèces plasmodiales ont considérablement diminué lors de l'abandon de la chloroquine en traitement de première ligne et de son remplacement par des combinaisons thérapeutiques, puis sont devenues presque nulles après la mise en place de moustiquaires imprégnées d'insecticides à longue durée d'action. Les seuils pyrogéniques calculés nous ont permis de mesurer la densité d'incidence des accès palustres et d'étudier l'impact des mesures de lutte sur la morbidité palustre dans la populationIn tropical Africa, where malaria is highly endemic, most people are semi-immune and asymptomatic infections are widespread. Thus, the detection of malaria parasites in the blood of febrile patients is not a sufficient criterion for distinguishing malaria from other causes of fever. In Dielmo, a Senegalese village of about 500 inhabitants in 2010, a very closely continuous epidemiological monitoring of malaria began in 1990. In this village where the transmission is perennial, the establishment of more effective means of control and prevention against malaria have profoundly changed the epidemiology of malaria. In this work, we analyze the impact of these interventions on the parasite prevalences, the parasite densities and the malaria diagnostic criteria and we measure the evolution of Plasmodium falciparum, P. malariae and P. ovale clinical malaria from June 1990 to December 2010 in Dielmo. Parasitological and clinical data are analyzed in a random effect logistic regression to investigate the relationship between parasite density and fever risk. The prevalence of the three Plasmodium species decreased dramatically with the abandonment of chloroquine as first line treatment and his replacing with the combination therapies and became almost zero after the introduction of long lasting insecticidal nets. Pyrogenic thresholds calculated enabled us to measure the incidence density of malaria and to study the impact of intervention methods on malaria morbidity in the population
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Decarli, Roberto, Fabian Walter, Manuel Aravena, Chris Carilli, Rychard Bouwens, Cunha Elisabete da, Emanuele Daddi et al. "ALMA SPECTROSCOPIC SURVEY IN THE HUBBLE ULTRA DEEP FIELD: CO LUMINOSITY FUNCTIONS AND THE EVOLUTION OF THE COSMIC DENSITY OF MOLECULAR GAS". IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/623950.
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In this paper we use ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field in band. 3 and band. 6, to place blind constraints on the CO luminosity function and the evolution of the cosmic molecular gas density as a function of redshift up to z similar to 4.5. This study is based on galaxies that have been selected solely through their CO emission and not through any other property. In all of the redshift bins the ASPECS measurements reach the predicted "knee" of the CO luminosity function (around 5 x 10(9) K km s(-1) pc(2)). We find clear evidence of an evolution in the CO luminosity function with respect to z similar to 0, with more CO-luminous galaxies present at z similar to 2. The observed galaxies at z similar to 2 also appear more gas-rich than predicted by recent semi-analytical models. The comoving cosmic molecular gas density within galaxies as a function of redshift shows a drop by a factor of 3-10 from z similar to 2 to z similar to 0 (with significant error bars), and possibly a decline at z > 3. This trend is similar to the observed evolution of the cosmic star formation rate density. The latter therefore appears to be at least partly driven by the increased availability of molecular gas reservoirs at the peak of cosmic star formation (z similar to 2).
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Kameni, Ngassa Christiane. "Décodeurs LDPC opérant sur des circuits à comportement probabiliste : limites théoriques et évaluation pratique de la capacité de correction". Thesis, Cergy-Pontoise, 2014. http://www.theses.fr/2014CERG0735/document.
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Ces dernières années ont vu naitre un intérêt grandissant pour les décodeurs correcteurs d'erreurs opérant sur des circuits non fiables. En effet, la miniaturisation croissante des composants électroniques ainsi l'échelonnage agressif de la tension d'alimentation ont pour conséquence la diminution de la fiabilité des systèmes. Par conséquent, les futures générations de circuits électroniques seront intrinsèquement non fiables. En outre, les décodeurs correcteurs d'erreurs sont indispensables non seulement pour assurer une transmission fiable de l'information mais aussi pour concevoir des systèmes de stockage performants.Nous nous intéressons, dans cette thèse, plus particulièrement aux décodeurs à précision finie Min-Sum (MS), Self-Corrected Min-Sum (SCMS) et Stochastiques.Nous commençons par effectuer une analyse statistique du décodeur Min-Sum opérant sur des circuits à comportement probabiliste. Pour ce faire nous introduisons des modèles d'erreurs probabilistes pour les composants logiques et les opérateurs arithmétiques du décodeur et étudions leurs propriétés de symétrie. Puis nous effectuions une analyse asymptotique rigoureuse et en déduisons les équations d'évolution de densité du décodeur Min-Sum bruité. Nous mettons ainsi en évidence l'effet positif, dans certains cas, du bruit issu du circuit sur la capacité de correction du décodeur. Nous révélons ensuite l'existence d'un phénomène de seuil particulier que nous nommons seuil fonctionnel. Ce dernier peut être considéré comme la généralisation du seuil classique pour les décodeurs non fiables. Nous corroborons ensuite les résultats asymptotiques par des simulations Monte-Carlo.Nous implémentons des décodeurs LDPC bruités pour plusieurs paramètres de bruit et montrons que les décodeurs LDPC bruité ont des résultats très proches de ceux des décodeurs non bruités. Nous pouvons par conséquent considérer le circuit d'autocorrection comme un patch bruité appliqué au décodeur MS bruité afin d'améliorer la robustesse du décodeur face au bruit issu des composants non fiables. Nous évaluons par railleurs l'impact de l'ordonnancement et montrons qu'un ordonnancement série dégrade fortement la robustesse des décodeurs bruités MS et SCMS qui ne parviennent plus à atteindre une capacité de correction acceptable.Pour finir nous étudions les performances des décodeurs stochastiques pourvus de mémoires d'arêtes et opérant sur des circuits non fiables. Nous proposons deux modèles d'erreurs décrivant le comportement probabiliste des composants du décodeur. Nous montrons que, dans certains cas, le bruit issu du circuit non fiable permet de réduire le plancher d'erreur. Nous en déduisons alors que le décodeur stochastique est intrinsèquement tolérant aux fautesOver the past few years, there has been an increasing interest in error correction decoders built out of unreliable components. Indeed, it is widely accepted that future generation of electronic circuit will be inherently unreliable, due to the increase in density integration and aggressive voltage scaling. Furthermore, error correction decoders play a crucial role both in reliable transmission of information and in the design of reliable storage systems. It is then important to investigate the robustness of error correction decoders in presence of hardware noise.In this thesis we focus on LDPC decoders built out of unreliable computing units. We consider three types of LDPC decoders: the finite-precision Min-Sum (MS) decoder, the Self-Corrected Min-Sum (SCMS) decoder and the Stochastic decoder.We begin our study by the statistical analysis of the finite-precision Min-Sum decoder with probabilistic components. To this end, we first introduce probabilistic models for the arithmetic and logic units of the decoder and discuss their symmetry properties. We conduct a thorough asymptotic analysis and derive density evolution equations for the noisy Min-Sum decoder. We highlight that in some particular cases, the noise introduced by the device can increase the correction capacity of the noisy Min-Sum with respect to the noiseless decoder. We also reveal the existence of a specific threshold phenomenon, referred to as functional threshold, which can be viewed as the generalization of the threshold definition for noisy decoders. We then corroborate the asymptotic results through Monte-Carlo simulations.Since density evolution cannot be defined for decoders with memory, the analysis of noisy Self-corrected Min-Sum decoders and noisy Stochastic decoders was restricted to Monte-Carlo simulations.We emulate the noisy SCMS decoders with various noise parameters and show that noisy SCMS decoders perform close to the noiseless SCMS decoder for a wide range of noise parameters. Therefore, one can think of the self-correction circuit as a noisy patch applied to the noisy MS decoder, in order to improve its robustness to hardware defect. We also evaluate the impact of the decoder scheduling on the robustness of the noisy MS and SCMS decoders and show that when the serial scheduling is used neither the noisy MS decoder nor the noisy SCMS decoder can provide acceptable error correction.Finally, we investigate the performance of stochastic decoders with edge-memories in presence of hardware noise. We propose two error models for the noisy components. We show that in some cases, the hardware noise can be used to lower the error floor of the decoder meaning that stochastic decoders have an inherent fault tolerant capability
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WANG, YANXIA. "HIGH SPEED TURBO TCM OFDM FOR UWB AND POWERLINE SYSTEM". Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3198.
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Turbo Trellis-Coded Modulation (TTCM) is an attractive scheme for higher data rate transmission, since it combines the impressive near Shannon limit error correcting ability of turbo codes with the high spectral efficiency property of TCM codes. We build a punctured parity-concatenated trellis codes in which a TCM code is used as the inner code and a simple parity-check code is used as the outer code. It can be constructed by simple repetition, interleavers, and TCM and functions as standard TTCM but with much lower complexity regarding real world implementation. An iterative bit MAP decoding algorithm is associated with the coding scheme. Orthogonal Frequency Division Multiplexing (OFDM) modulation has been a promising solution for efficiently capturing multipath energy in highly dispersive channels and delivering high data rate transmission. One of UWB proposals in IEEE P802.15 WPAN project is to use multi-band OFDM system and punctured convolutional codes for UWB channels supporting data rate up to 480Mb/s. The HomePlug Networking system using the medium of power line wiring also selects OFDM as the modulation scheme due to its inherent adaptability in the presence of frequency selective channels, its resilience to jammer signals, and its robustness to impulsive noise in power line channel. The main idea behind OFDM is to split the transmitted data sequence into N parallel sequences of symbols and transmit on different frequencies. This structure has the particularity to enable a simple equalization scheme and to resist to multipath propagation channel. However, some carriers can be strongly attenuated. It is then necessary to incorporate a powerful channel encoder, combined with frequency and time interleaving. We examine the possibility of improving the proposed OFDM system over UWB channel and HomePlug powerline channel by using our Turbo TCM with QAM constellation for higher data rate transmission. The study shows that the system can offer much higher spectral efficiency, for example, 1.2 Gbps for OFDM/UWB which is 2.5 times higher than the current standard, and 39 Mbps for OFDM/HomePlug1.0 which is 3 times higher than current standard. We show several essential requirements to achieve high rate such as frequency and time diversifications, multi-level error protection. Results have been confirmed by density evolution. The effect of impulsive noise on TTCM coded OFDM system is also evaluated. A modified iterative bit MAP decoder is provided for channels with impulsive noise with different impulsivity.Ph.D.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering
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Tripsanas, Efthymios. "Evolution of depositional and slope instability processes on Bryant Canyon area, Northwest Gulf of Mexico". Texas A&M University, 2003. http://hdl.handle.net/1969.1/1627.
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Bryant and Eastern Canyon systems are located on the northwest Gulf of Mexico, and they are characterized by a very complex sedimentological history related to glacioeustatic cycles, river discharges, and interactions of depositional and halokinetic processes. Both canyon systems were active during the low sea-level stand of Oxygen Isotope Stage 6, and provided the pathways for the transport of enormous amounts of sediments on the continental slope and abyssal plain of the northwest Gulf of Mexico. Right after their abandonment, at the beginning of Stage 5, salt diapirs encroached into the canyons, and resulted in their transformation into a network of intraslope basins. The transformation of the canyons resulted in the generation of massive sediment failures.
The mid-shelf (Stages 4 and 3) to shelf edge (Stage 2) lowering of the sea-level during the last glacial episode resulted in: 1) extensive river-sourced deposits on the outer shelf and/or upper continental slope that contributed in a seaward mobilization of the underlying salt masses, and 2) the generation of numerous gravity flows and turbidity currents on the outer shelf/upper continental slope. The seaward mobilization of the salt masses resulted in the oversteepening of the flanks of the basins, and consequently in the generation of numerous and massive sediment failures. The turbidity currents were confined on the intraslope basins of the upper continental slope, depositing their coarsest material. However, their most diluted upper and end members were able to continue their downslope propagation depositing characteristic fine-grained turbidites. The frequency of the turbidity currents was highly increased during the last glacial maximum (Stage 2), and three short melt-water pulses centered at 30.5, 36, and 52 ky B.P.
The last deglaciation event is characterized by the development of a major melt water event that resulted in the deposition of distinct organic rich sediments, similar to the sapropels of the Eastern Mediterranean. At about 11 ky B.P. the melt water discharges of the North America switched from Mississippi River to St Lawrence Seaway, causing the domination of hemipelagic sedimentation on the continental slope of the northwest Gulf of Mexico.
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Lee, Bomee, Mauro Giavalisco, Katherine Whitaker, Christina C. Williams, Henry C. Ferguson, Viviana Acquaviva, Anton M. Koekemoer et al. "The Intrinsic Characteristics of Galaxies on the SFR–M ∗ Plane at 1.2 < z < 4: I. The Correlation between Stellar Age, Central Density, and Position Relative to the Main Sequence". IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/627039.
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We use the deep CANDELS observations in the GOODS North and South fields to revisit the correlations between stellar mass (M-*), star formation rate (SFR) and morphology, and to introduce a fourth dimension, the mass-weighted stellar age, in galaxies at 1.2 < z < 4. We do this by making new measures of M-*, SFR, and stellar age thanks to an improved SED fitting procedure that allows various star formation history for each galaxy. Like others, we find that the slope of the main sequence (MS) of star formation in the (M-*; SFR) plane bends at high mass. We observe clear morphological differences among galaxies across the MS, which also correlate with stellar age. At all redshifts, galaxies that are quenching or quenched, and thus old, have high Sigma(1) (the projected density within the central 1 kpc), while younger, star-forming galaxies span a much broader range of Sigma(1), which includes the high values observed for quenched galaxies, but also extends to much lower values. As galaxies age and quench, the stellar age and the dispersion of Sigma(1) for fixed values of M* shows two different regimes: one at the low-mass end, where quenching might be driven by causes external to the galaxies; the other at the high-mass end, where quenching is driven by internal causes, very likely the mass given the low scatter of Sigma(1) (mass quenching). We suggest that the monotonic increase of central density as galaxies grow is one manifestation of a more general phenomenon of structural transformation that galaxies undergo as they evolve.
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Vermeulen, Stephanie. "an architecture of daily life: the continuing evolution of Toronto's residential fabric". Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2889.
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This thesis envisions a new way of living in the city of Toronto. It is a vision that evolves not from the ideologies on which Toronto was founded, set out over 100 years ago when all multi-family dwellings were called tenements and tenements were considered, among other things, immoral. Instead, it is a vision founded on a city that has seen immense change over the last century, and faces an even greater rate of change over the next. Our city prides itself on its cultural and social diversity, yet, architecturally, we still struggle to adapt within a fabric of single-family homes. The Dutch provide an edifying example of an architecture of daily life, embodied by their attitude toward issues of privacy, toward traffic, toward work and play. Based on a case study of housing in the Netherlands, a country that has successfully and creatively adapted to the demands of housing in a climate of rapid immigration and a diversifying population, this thesis proposes new, high density urban housing typologies for the city of Toronto. This new vision for the city serves not only to add the necessary density to our existing neighbourhoods, but to foster a strong community life and to provoke new ideas about urban living.
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Champollion, Nicolas. "Evolution de la surface de neige sur le plateau Antarctique : observation in situ et satellite". Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00934480.
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La surface de neige sur le Plateau Antarctique joue un rôle important dans l'étude du bilan de masse et d'énergie de surface. Ses caractéristiques dépendent des interactions entre les conditions atmosphériques et le haut du manteau neigeux, à travers notamment les précipitations, la redistribution de neige par le vent et le métamorphisme. L'ensemble des aspects de la surface, i.e. le type de cristaux, la rugosité, la densité, l'albédo ..., sont regroupés sous la formule état de surface. L'objectif de cette thèse est l'étude de l'état de surface et de son évolution, en fonction des conditions atmosphériques, à l'aide d'observations in situ et satellite. L'analyse conjointe d'observations in situ, essentiellement à partir de photographies infrarouges de la surface (développement d'un algorithme examinant la texture des images), et satellite, principalement l'émission micro-onde du manteau neigeux (utilisation du rapport de polarisation sensible à la densité proche de la surface), a permis de montrer une dynamique rapide de la surface à Dôme C. En particulier, des périodes où le givre recouvre entièrement la surface sont observées et représentent environ 45% du temps. Cette dynamique est aussi caractérisée par des élévations rapides et importantes de la surface, pouvant être largement supérieures à l'accumulation annuelle moyenne de 8 cm (jusqu'à 20 cm en 2 heures). Le vent est déterminant dans l'évolution de la surface. Plus particulièrement, ces travaux ont montrés l'importance de la direction du vent pour la disparition du givre (perpendiculaire à la direction dominante, i.e. le sud-ouest). Enfin, la corrélation entre présence de givre et rapport de polarisation a permis d'étendre ces résultats sur les 10 années d'observation du satellite et ouvre la voie à la détection des précipitations par télédétection. La modélisation de l'émission micro-onde à 19 et 37 GHz a ensuite été menée à Dôme C à l'aide d'un modèle de transfert radiatif (DMRT-ML). Les propriétés du manteau neigeux (taille des grains, densité et température), utilisées en entrée du modèle, ont été mesurées durant la campagne d'été 2010 - 2011. Les résultats des simulations montrent que la densité de la neige proche de la surface est principalement responsable des variations du rapport de polarisation. Cette densité a ainsi été " inversée " à Dôme C sur 10 ans. Elle montre une tendance pluriannuelle à la baisse de 10 kg m-3 a-1, superposée à un cycle annuel et à des variations journalières / hebdomadaires. La mesure in situ de la densité et l'observation du givre coïncident avec les variations rapides de la densité estimée. L'évolution pluriannuelle conséquente mérite d'être prise en compte pour l'étude du bilan de masse de surface, les causes probables étant une hausse des précipitations ou une baisse de l'intensité du vent. Suivant une méthodologie similaire, l'évolution de la densité de surface a été déduite pour l'ensemble de l'Antarctique. Les variations spatiales mettent en évidence une tendance claire à la diminution de la densité sur une grande région entre Dôme C et Vostok et une région à l'est de Dôme C où elle augmente. À plus grande échelle, le rapport de polarisation moyen montre de grandes variations, signatures de la stratification en densité du manteau neigeux. L'étude de l'altimétrie satellite permettrat de corroborer ces résultats.
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Almutairi, Alanoud. "Electronic band structure equations and Fermi surface evolution from 2D materials to 3D layered superconducting compounds". Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134414/1/Alanoud%20Mulfi%20Z_Almutairi_Thesis.pdf.
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A simple approach for extracting the superconducting gap of materials from trendline fittings of key sections of their Electronic Band Structures (EBS), calculated using Density Functional Theory (DFT), is presented. The proposed approach works well for very different compositions, structure types and superconducting transition temperatures, indicating that it is robust, reliable and versatile. This approach provides many advantages in terms of required computational time and power, compared with similar information extracted from phonon dispersion calculations, making it accessible to wider DFT-computational chemistry and physics communities. The approach also identifies requirements for superconductivity and indirectly contributes towards understanding of superconductivity mechanisms.
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Gonzalez-Pena, Omar Israel. "Mass Transport Enhancement in Copper Electrodeposition due to Gas Co-Evolution". Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1439826379.
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