Bibliografie tematiche / Dispersion

Letteratura scientifica selezionata sul tema "Dispersion"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 30 luglio 2024

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Articoli di riviste sul tema "Dispersion"

Mohammad Hadi, Mohammad Hadi, Farokh Marvasti Farokh Marvasti e and Mohammad Reza Pakravan and Mohammad Reza Pakravan. "Dispersion compensation using high-positive dispersive optical fibers". Chinese Optics Letters 15, n. 3 (2017): 030601–30605. http://dx.doi.org/10.3788/col201715.030601.

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Thonglerth, P., P. Sujaridworakun e O. Boondamnoen. "Preparation of ZnO Nanoparticles Water-based Dispersion". Journal of Physics: Conference Series 2175, n. 1 (1 gennaio 2022): 012029. http://dx.doi.org/10.1088/1742-6596/2175/1/012029.

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Abstract In this work, an attempt was made to stabilize ZnO NPs as water-based dispersion. The dispersing agents used are 3-glycidoxypropyltrimethoxysilane (GPTMS), polyvinyl alcohol (PVA) and oleic acid (OA). These dispersing agents were combined with sodium dodecyl sulfate (SDS) to facilitate better dispersion stability. Different wt% content of modified ZnO NPs such as 0.2, 0.4, 1 and 3% w/v was used at a fixed ratio of ZnO NPs:SDS:dispersing agent. The highest dispersion stability was achieved at 1% w/v content of modified ZnO NP, whereas some precipitate was observed at 3% w/v. The result reveals that sonication at 30 minutes produced the highest dispersion stability whereas extended sonication led to re-agglomeration of ZnO NPs. The optimum ratio of ZnO NPs:SDS:dispersing agent which produced about 98% dispersion stability was at 1:0.25:0.2. The zeta potential (ZP) values of ZnO NPs/GPTMS, ZnO NPs/PVA, and ZnO NPs/OA dispersions are -51, -29 and -15 mV, respectively. The ZP values was influenced by the electrical charge surrounding the particles which was also caused by the functional group of the dispersing agents. However, the stabilization mechanisms of modified ZnO NPs in water was complicated. It did not only depend on the electrostatic value but also on electrosteric stabilization caused by the steric effects hindering the dispersing agents. Interactions between the dispersing agents and ZnO NPs was confirmed through FTIR analysis.

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Mavko, Gary, e Diane Jizba. "The relation between seismic P‐ and S‐wave velocity dispersion in saturated rocks". GEOPHYSICS 59, n. 1 (gennaio 1994): 87–92. http://dx.doi.org/10.1190/1.1443537.

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Seismic velocity dispersionin fluid-saturated rocks appears to be dominated by tow mecahnisms: the large scale mechanism modeled by Biot, and the local flow or squirt mecahnism. The tow mechanisms can be distuinguished by the ratio of P-to S-wave dispersions, or more conbeniently, by the ratio of dynamic bulk to shear compliance dispersions derived from the wave velocities. Our formulation suggests that when local flow denominates, the dispersion of the shear compliance will be approximately 4/15 the dispersion of the compressibility. When the Biot mechanism dominates, the constant of proportionality is much smaller. Our examination of ultrasonic velocities from 40 sandstones and granites shows that most, but not all, of the samples were dominated by local flow dispersion, particularly at effective pressures below 40 MPa.

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Khatry, Sadhna, Neha Sood e Sandeep Arora. "Surface Solid Dispersion – A Review". International Journal of Pharmaceutical Sciences and Nanotechnology 6, n. 1 (31 maggio 2013): 1915–25. http://dx.doi.org/10.37285/ijpsn.2013.6.1.1.

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Preparation of an effective formulation of poorly water-soluble drugs is a key challenge in pharmaceutical technology. Dissolution rate and solubility are the rate- limiting steps for increasing the bioavailability of poorly water‐soluble drugs. Solid dispersion is an efficient technique for improving dissolution rate and subsequently, the bioavailability of poorly water‐soluble drugs. Surface sSolid dDispersion is a novel technique of solid dispersion for dispersing one or more active ingredients on a water insoluble carrier of high surface area in order to achieve increased dissolution rates and bioavailability of insoluble drugs. The Vvarious polymers used in this technique are Avicel, Crosspovidone, sSodium starch glycolate, pPregelatinized starch, Cab-o-sil, Ac-di-sol, KyronT-314, Primojel and pPotato sStarch. This article reviews the various methods of preparation and characterization of surface solid dispersion and compiles some of the drugs formulated as surface solid dispersions. Some of the practical aspects to be considered for preparing surface solid dispersion are selection of a suitable carrier and method of preparation of surface solid dispersion.

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Perumal, Suguna, Raji Atchudan e In Woo Cheong. "Recent Studies on Dispersion of Graphene–Polymer Composites". Polymers 13, n. 14 (20 luglio 2021): 2375. http://dx.doi.org/10.3390/polym13142375.

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Graphene is an excellent 2D material that has extraordinary properties such as high surface area, electron mobility, conductivity, and high light transmission. Polymer composites are used in many applications in place of polymers. In recent years, the development of stable graphene dispersions with high graphene concentrations has attracted great attention due to their applications in energy, bio-fields, and so forth. Thus, this review essentially discusses the preparation of stable graphene–polymer composites/dispersions. Discussion on existing methods of preparing graphene is included with their merits and demerits. Among existing methods, mechanical exfoliation is widely used for the preparation of stable graphene dispersion, the theoretical background of this method is discussed briefly. Solvents, surfactants, and polymers that are used for dispersing graphene and the factors to be considered while preparing stable graphene dispersions are discussed in detail. Further, the direct applications of stable graphene dispersions are discussed briefly. Finally, a summary and prospects for the development of stable graphene dispersions are proposed.

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Ben Basat, Moran, e Noa Lachman. "Development of Quality Control Methods for Dispersibility and Stability of Single-Wall Carbon Nanotubes in an Aqueous Medium". Nanomaterials 11, n. 10 (5 ottobre 2021): 2618. http://dx.doi.org/10.3390/nano11102618.

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The attractive properties of single-wall carbon nanotubes (SWCNT) such as mechanical strength and high electrical and thermal conductivity are often undercut by their agglomeration and re-agglomeration tendencies. As a result, the application of SWCNT as additives in advanced composite materials remain far from their potential, with proper dispersion being the major inhibitor. This work presents a dispersion quality control approach for water-based SWCNT dispersions (dispersed by a unique combination of physical and chemical methods), using complementary and easily scalable, characterization methods. UV-Vis spectroscopy, rheological measurements, and precipitant sheet resistance were used to understand the properties of the initial solution through processing and application. From an industrial perspective, these methods are fast and easy to measure while giving a repetitive and quick indication of dispersion quality and stability. The methods were correlated with microscopy and Raman spectroscopy to validate dispersion and SWCNT quality under various dispersing energies. The protocol was then applied to estimate the stability of SWCNT solutions, as well as the effectiveness of different surfactants in aiding dispersion. The simple, fast, and scalable combination of different characterizations provides good SWCNT dispersion and can be used as a quality control system for industrial production and usage.

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Borja, Katerine, Jaime Mercado e Enrique Combatt. "Methods of mechanical dispersion for determining granulometric fractions in soils using four dispersant solutions". Agronomía Colombiana 33, n. 2 (1 maggio 2015): 253–60. http://dx.doi.org/10.15446/agron.colomb.v33n2.47236.

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Sieve analysis studies depend on obtaining suspensions of fully-dispersed and stable samples to facilitate the quantification of the fractions of soil aggregates. The aim of this study was to compare the percentage of fractions obtained with four chemical dispersants and two methods of mechanical dispersion. To carry out this investigation, nine soils were selected from the departments of Cordoba and Sucre and four methodologies using chemical dispersions: ((NaPO3)6 + Na2CO3), (NaOH) 1M, (Na4P2O7) 0.1M pH 10, and CH3COONa 1M, and two methodologies of mechanical dispersion were evaluated: a slow one at 60 rpm for 6 hours and another at 4,000 rpm for 15 minutes. The results were analyzed using a correlation test and contrasts. It was verified that the highest content of clay in the soil samples was found when using the 60 rpm agitation methodology, due to greater dispersion of the granulometric fractions. Likewise, when comparing the different methods of chemical dispersion, it was determined that NaOH had the highest dispersing ability and sodium acetate presented a low efficiency in the separation of soil particles.

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Ramos, Héctor M., e Miguel A. Sordo. "Dispersion measures and dispersive orderings". Statistics & Probability Letters 61, n. 2 (gennaio 2003): 123–31. http://dx.doi.org/10.1016/s0167-7152(02)00341-3.

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Jin, J., W. Kaewsakul, J. W. M. Noordermeer, W. K. Dierkes e A. Blume. "MACRO- AND MICRO-DISPERSION OF SILICA IN TIRE TREAD COMPOUNDS: ARE THEY RELATED?" Rubber Chemistry and Technology 94, n. 2 (1 aprile 2021): 355–75. http://dx.doi.org/10.5254/rct.20.80365.

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ABSTRACT The dispersion of rubber fillers, such as silica, can be divided into two categories: macro- and micro-dispersion. Both dispersions are important; however, to achieve the best reinforcement of rubber, micro-dispersion of silica is crucial. The common view is that these filler dispersions are strongly related. The micro-dispersion is understood as the consequence of the continuous breakdown of filler clusters from macro-dispersion. Yet, a large problem is that an objective unequivocal direct measurement method for micro-dispersion is not available. In this study, a set of parameters is defined that are anticipated to have an influence on the micro- as well as the macro-dispersion. Mixing trials are performed with varying silanization temperature and time, different amounts of silane coupling agent, and by using silicas with different structures and specific surface areas. The degrees of micro- and macro-dispersion are evaluated by measuring the Payne effect as an indirect method for micro-dispersion and using a dispergrader for quantitative measurement of macro-dispersion. The results show that the filler dispersion processes happen simultaneously but independently. These results are supported by earlier work of Blume and Uhrlandt, who stated as well that micro- and macro-dispersion are independent. The major influencing factors on micro- and macro-dispersion of silica are also identified.

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Opaynych, Iryna Ye, e Zenovii M. Yaremko. "Aqueous Dispersions of High-dispersion Polystyrene". NIP & Digital Fabrication Conference 21, n. 1 (1 gennaio 2005): 628. http://dx.doi.org/10.2352/issn.2169-4451.2005.21.1.art00075_2.

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Tesi sul tema "Dispersion"

Mietka, Colin. "Ondes périodiques dans des systèmes d’ÉDP hamiltoniens : stabilité, modulations et chocs dispersifs". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1031/document.

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La première partie de cette thèse concerne l'étude du problème de Cauchy pour l'équation de KdV quasi-linéaire.On établit un théorème d'existence locale obtenu grâce à des propriétés structurelles et des techniques de jauge qui permettent de compenser les pertes de dérivées apparentes dans les estimations a priori.Dans la seconde partie, les propriétés de stabilité orbitale co-périodique et modulationnelle sont explorées numériquement en exploitant des critères algébriques tous établis à partir d'une même intégrale d'action et de ses dérivées secondes. Notre méthode utilise des quadratures numériques suivies de différences finies afin de calculer la matrice hessienne de l'intégrale d'action. Le comportement asymptotique de cette matrice nous pousse à prêter beaucoup d'attention à l'étude des ondes de grande période ou de faible amplitude. Les résultats numériquesprésentés fournissent de nombreuses informations en lien avec des questions ouvertes.On effectue également des simulations directes sur le système d' ÉDP original pour étudier à la fois le comportement des ondes périodiques sous différents types de perturbations, et les solutions de problèmes de Cauchy avec donnée initiale discontinue. Pour ces derniers, on s'attend à observer des chocs dispersifs, dont la compréhension est basée sur le problème de Gurevich-Pitaevskii, où les équations modulées à la Whitham sont utilisées pour approcher la zone oscillante des chocs. On compare des simulations directes aux solutions idéales du problème de Gurevich-Pitaevskii, en commençant par la célèbre équation de KdV
The first part of this manuscript presents a well-posedness result for a quasilinear version of the KdV equation.The proof takes advantage of structural properties and gauge techniques to deal with apparent loss of derivativesin a priori estimates.In the second part, we investigate the modulational and orbital coperiodic stability of periodic waves by computingalgebraic criteria involving the same abbreviated action integral and its second order derivatives. Our methoduses numerical integrations followed by finite differences to compute the Hessian matrix of the action integral.We pay attention to the asymptotic behavior of this matrix in the large period and small amplitude limits. Thenumerical results about stability give some new insight on several analytical open questions.Finally, direct numerical computations are done on the original system of PDEs to study the behavior of periodictraveling waves under various kinds of perturbations and the solutions of Cauchy problem with discontinuousinitial data. For the latter, we expect dispersive shock waves to arise. The building block for understandingdispersive shocks is known as the Gurevich-Pitaevskii problem, in which modulated equations 'a la Whitham'are used as an approximate model for the oscillatory zone. We compare direct numerical simulations to idealizedsolutions of Gurevich-Pitaevskii problems, starting with the famous KdV equation

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Wongsangpaiboon, Natee. "Variational Calculation of Optimum Dispersion Compensation for Nonlinear Dispersive Fibers". Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/32973.

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In fiber optic communication systems, the main linear phenomenon that causes optical pulse broadening is called dispersion, which limits the transmission data rate and distance. The principle nonlinear effect, called self-phase modulation, can also limit the system performance by causing spectral broadening. Hence, to achieve the optimal system performance, high data rate and low bandwidth occupancy, those effects must be overcome or compensated. In a nonlinear dispersive fiber, properties of a transmitting pulse: width, chirp, and spectra, are changed along the way and are complicated to predict. Although there is a well-known differential equation, called the Nonlinear Schrodinger Equation, which describes the complex envelope of the optical pulse subject to the nonlinear and dispersion effects, the equation cannot generally be solved in closed form. Although, the split-step Fourier method can be used to numerically determine pulse properties from this nonlinear equation, numerical results are time consuming to obtain and provide limited insight into functional relationships and how to design input pulses. One technique, called the Variational Method, is an approximate but accurate way to solve the nonlinear Schrodinger equation in closed form. This method is exploited throughout this thesis to study the pulse properties in a nonlinear dispersive fiber, and to explore ways to compensate dispersion for both single link and concatenated link systems. In a single link system, dispersion compensation can be achieved by appropriately pre-chirping the input pulse. In this thesis, the variational method is then used to calculate the optimal values of pre-chirping, in which: (i) the initial pulse and spectral width are restored at the output, (ii) output pulse width is minimized, (iii) the output pulse is transform limited, and (iv) the output time-bandwidth product is minimized. For a concatenated link system, the variational calculation is used to (i) show the symmetry of pulse width around the chirp-free point in the plot of pulse width versus distance, (ii) find the optimal dispersion constant of the dispersion compensation fiber in the nonlinear dispersive regime, and (iii) suggest the dispersion maps for two and four link systems in which initial conditions (or parameters) are restored at the output end. The accuracy of the variational approximation is confirmed by split-step Fourier simulation throughout this thesis. In addition, the comparisons show that the accuracy of the variational method improves as the nonlinear effects become small.
Master of Science

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Mattsson, Rosa. "AKD sizing - dispersion colloidal stability, spreading and sizing with pre-flocculated dispersions /". Licentiate thesis, Luleå tekniska universitet, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17236.

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Alkylketene dimer, AKD, dispersions are used in the paper industry to obtain paper grades with a hydrophobic character i.e. resistance to sorption of water. AKD is used in neutral to alkaline internal sizing, pH in the interval of 6-9. AKD dispersions consist of wax particles emulsified in water. The particles are electrostatically and in most cases also sterically stabilized by cationic polyelectrolytes. The size of the particles is usually in the range of 0.5-2 µm in diameter. The idea of having cationic particles is that they are supposed to be deposited onto the negatively charged fiber surfaces, heterocoagulation. An increased usage of recycled pulp and a closure of the wet-end circuits of the paper machine will lead to increasing levels of dissolved and colloidal substances. These substances could be detrimental by affecting the AKD deposition onto the fiber material and the colloidal stability i.e. induce flocculation of sizing particles. Flocculation could lead to an inhomogeneous distribution of the sizing agent. The aims addressed in this thesis were the following: to investigate if high levels of shear, electrolyte concentration, anionic polymers and surfactants could affect the colloidal stability and induce flocculation of differently designed AKD dispersions to study the migration of AKD and the influence of extractives on the migration to study the sizing efficiency and retention using flocculated dispersions The colloidal stability of the dispersions was tested under shear by measuring the particle size distribution and the microelectrophoretic mobility. The migration of AKD through paper sheets with defined thickness and through paper sheets impregnated with extractives was analyzed with contact angle measurements on stored samples. The sizing efficiency of flocculated AKD was determined by measuring 60-second Cobb and contact angles on laboratory sheets. The retention of AKD was determined by quantitative analysis of the AKD content in the laboratory sheets using alkaline hydrolysis followed by solvent extraction and quantification with capillary gas chromatography. It was shown that anionic polymers and surfactants could seriously affect the colloidal stability of the dispersions, while shear and electrolyte concentration had a small influence. Dispersions with a high surface charge flocculates easier than dispersions with a low surface charge in process water from the wet-end of a linerboard paper machine. The flocculation rate is fast and occurs on the same time scale as deposition onto fines and fibers. The AKD agglomerates could be up to 30 µm in diameter even at high levels of shear. The AKD diffusion coefficient in paper sheets was estimated to be 10-11 m2/s at a temperature above the melting point of the wax. The results indicate that extractives do not interfere with the AKD migration. A reasonable explanation is that migration occurs via the vapor phase. It was also shown that sizing with flocculated AKD improved the sizing efficiency significantly due to increased retention. This clearly indicates that migration is efficient and that agglomerates can be used for internal sizing provided that the flocculation process is controlled. The conventional picture that the sizing agents must be very evenly distributed to achieve efficient sizing could, from the viewpoint of these results, be questioned. The process of sizing with pre-flocculated AKD dispersions is the subject of a patent application. Even if this thesis is focused on AKD dispersions, the obtained knowledge should be possible to transfer to other sizing systems. The emulsification process for rosin and ASA is based on the same principles as for AKD.
Godkänd; 2002; 20070222 (ysko)

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Wong, Samuel Tin Bo 1979. "Dispersion-managed solutions in the path-average normal dispersion regime". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86745.

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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.
Includes bibliographical references (leaves 83-87).
by Samuel Tin Bo Wong.
M.Eng.

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Komaki, Ghorbanmohammad. "PORTFOLIO SELECTION AND RISK DISPERSION BASED ON GEOMETRIC DISPERSION THEORY". Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1512232304419177.

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Sadofyev, Andrey, e Srimoyee Sen. "Chiral anomalous dispersion". SPRINGER, 2018. http://hdl.handle.net/10150/627127.

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The linearized Einstein equation describing graviton propagation through a chiral medium appears to be helicity dependent. We analyze features of the corresponding spectrum in a collision-less regime above a flat background. In the long wave-length limit, circularly polarized metric perturbations travel with a helicity dependent group velocity that can turn negative giving rise to a new type of an anomalous dispersion. We further show that this chiral anomalous dispersion is a general feature of polarized modes propagating through chiral plasmas extending our result to the electromagnetic sector.

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Farzaneh, Mohamadreza. "Modeling Traffic Dispersion". Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29757.

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The dissertation studies traffic dispersion modeling in four parts. In the first part, the dissertation focuses on the Robertson platoon dispersion model which is the most widely used platoon dispersion model. The dissertation demonstrates the importance of the Yu and Van Aerde calibration procedure for the commonly accepted Robertson platoon dispersion model, which is implemented in the TRANSYT software. It demonstrates that the formulation results in an estimated downstream cyclic profile with a margin of error that increases as the size of the time step increases. In an attempt to address this shortcoming, the thesis proposes the use of three enhanced geometric distribution formulations that explicitly account for the time-step size within the modeling process. The proposed models are validated against field and simulated data. The second part focuses on implementation of the Robertson model inside the popular TRANSYT software. The dissertation first shows the importance of calibrating the recurrence platoon dispersion model. It is then demonstrated that the value of the travel time factor β is critical in estimating appropriate signal-timing plans. Alternatively, the dissertation demonstrates that the value of the platoon dispersion factor α does not significantly affect the estimated downstream cyclic flow profile; therefore, a unique value of α provides the necessary precision. Unfortunately, the TRANSYT software only allows the user to calibrate the platoon dispersion factor but does not allow the user to calibrate the travel time factor. In an attempt to address this shortcoming, the document proposes a formulation using the basic properties of the recurrence relationship to enable the user to control the travel time factor indirectly by altering the link average travel time. In the third part of the dissertation, a more general study of platoon dispersion models is presented. The main objective of this part is to evaluate the effect of the underlying travel time distribution on the accuracy and efficiency of platoon dispersion models, through qualitative and quantitative analyses. Since the data used in this study are generated by the INTEGRATION microsimulator, the document first describes the ability of INTEGRATION in generating realistic traffic dispersion effects. The dissertation then uses the microsimulator generated data to evaluate the prediction precision and performance of seven different platoon dispersion models, as well as the effect of different traffic control characteristics on the important efficiency measures used in traffic engineering. The results demonstrate that in terms of prediction accuracy the resulting flow profiles from all the models are very close, and only the geometric distribution of travel times gives higher fit error than others. It also indicates that for all the models the prediction accuracy declines as the travel distance increases, with the flow profiles approaching normality. In terms of efficiency, the travel time distribution has minimum effect on the offset selection and resulting delay. The study also demonstrates that the efficiency is affected more by the distance of travel than the travel time distribution. Finally, in the fourth part of the dissertation, platoon dispersion is studied from a microscopic standpoint. From this perspective traffic dispersion is modeled as differences in desired speed selection, or speed variability. The dissertation first investigates the corresponding steady-state behavior of the car-following models used in popular commercially available traffic microsimulation software and classifies them based on their steady-state characteristics in the uncongested regime. It is illustrated that with one exception, INTEGRATION which uses the Van Aerde car-following model, all the software assume that the desired speed in the uncongested regime is insensitive to traffic conditions. The document then addresses the effect of speed variability on the steady-state characteristics of the car-following models. It is shown that speed variability has significant influence on the speed-at-capacity and alters the behavior of the model in the uncongested regime. A method is proposed to effectively consider the influence of speed variability in the calibration process in order to control the steady-state behavior of the model. Finally, the effectiveness and validity of the proposed method is demonstrated through an example application.
Ph. D.

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Nisa, Khoirin. "On multivariate dispersion analysis". Thesis, Besançon, 2016. http://www.theses.fr/2016BESA2025.

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Cette thèse examine la dispersion multivariée des modelés normales stables Tweedie. Trois estimateurs de fonction variance généralisée sont discutés. Ensuite dans le cadre de la famille exponentielle naturelle deux caractérisations du modèle normal-Poisson, qui est un cas particulier de modèles normales stables Tweedie avec composante discrète, sont indiquées : d'abord par fonction variance et ensuite par fonction variance généralisée. Le dernier fournit la solution à un problème particulier d'équation de Monge-Ampère. Enfin, pour illustrer l'application de la variance généralisée des modèles Tweedie stables normales, des exemples à partir des données réelles sont fournis
This thesis examines the multivariate dispersion of normal stable Tweedie (NST) models. Three generalize variance estimators of some NST models are discussed. Then within the framework of natural exponential family, two characterizations of normal Poisson model, which is a special case of NST models with discrete component, are shown : first by variance function and then by generalized variance function. The latter provides a solution to a particular Monge-Ampere equation problem. Finally, to illustrate the application of generalized variance of normal stable Tweedie models, examples from real data are provided

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Slater, Geoffrey Reginald. "Welding fume plume dispersion". Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20050307.120815/index.html.

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Nokes, Roger Ian. "Problems in turbulent dispersion". Thesis, University of Canterbury. Civil Engineering, 1985. http://hdl.handle.net/10092/7711.

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Solutions to a number of turbulent dispersion problems, involving a contaminant issuing from a steady source into uniform, steady open channel flow, are presented. These problems include the two and three-dimensional dispersion of a neutrally buoyant contaminant and the two-dimensional dispersion of buoyant particles and are modelled with the diffusion equation incorporating turbulent diffusion coefficients. In order to ensure that the solutions simulate the physical processes as accurately as possible the experimentally determined logarithmic velocity profile and the theoretically deduced parabolic diffusivity are used. The solutions take the form of one or two eigenfunction expansions, the eigenfunctions and eigenvalues of which are governed by Sturm-Liouville theory. Generally the power series method for solving ordinary differential equations is employed to derive the eigenfunctions and eigenvalues and in nearly all cases this method is found to be accurate, straightforward in its use and efficient with computing resources. Much useful information is deduced from the eigenfunctions and eigenvalues. The rate at which equilibrium conditions are approached and the ideal source position, that from which the contaminant is most rapidly mixed, come naturally from these quantities. An experimental programme, with the aims of verifying the theoretical solution for vertical dispersion of a neutrally buoyant contaminant and measuring the lateral turbulent diffusion coefficient, is described. The two-dimensional results for vertical mixing strongly support the theoretical predictions, using the measured logarithmic velocity profile and the deduced parabolic diffusivity in the turbulent diffusion equation, and indeed confirm the location of the ideal source derived from theory. The values of the depth-averaged lateral diffusivity obtained from the experiments lie at the lower end of the range of values obtained by other experimentalists. A reanalysis of these previously published results demonstrates that, provided the natural turbulence of a wide channel is the only mixing mechanism present, the depth-averaged lateral diffusivity, non-dimensionalised by the flow depth and shear velocity, is in fact independent of all flow parameters, except when the friction factor is small. The dependence of the rate of lateral spreading on height in the flow and the location of the source demonstrates, at least qualitatively, that the vertical dependence of the lateral diffusivity is in essence the same as the velocity distribution. Verification of the theoretical solution for dispersion of buoyant particles is achieved with the experimental results of Jobson and Sayre (1970) which indicate that the theoretical model is valid for fine particles dispersing in strongly turbulent flow.

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Più fonti

Libri sul tema "Dispersion"

Stanfield, R. Dispersion and dispersion equipment. Wembley: Oil & Colour Chemists' Association, 1993.

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Buhmann, Stefan Yoshi. Dispersion Forces II. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-32466-6.

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Buhmann, Stefan Yoshi. Dispersion Forces I. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-32484-0.

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Visscher, Alex De. Air Dispersion Modeling. Hoboken, NJ: John Wiley & Sons, Inc, 2013. http://dx.doi.org/10.1002/9781118723098.

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Galtarossa, Andrea, e Curtis R. Menyuk, a cura di. Polarization Mode Dispersion. New York: Springer-Verlag, 2005. http://dx.doi.org/10.1007/b137385.

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Acemoglu, D. Efficient wage dispersion. London: Centre for Economic Policy Research, 1997.

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Amerasinghe, Anojie. Matara: Structuring dispersion. A cura di European Union. Leuven: European Union, 2007.

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Acemoglu, Daron. Efficient wage dispersion. Cambridge, Mass: Dept. of Economics, Massachusetts Institute of Technology, 1996.

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Acemoglu, Daron. Efficient wage dispersion. Cambridge, Mass: Dept. of Economics, Massachusetts Institute of Technology, 1997.

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Doubrovsky, Serge. La dispersion: Roman. Paris: Mercure de France, 1990.

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Capitoli di libri sul tema "Dispersion"

Cercignani, Carlo, e David H. Sattinger. "Dispersion". In Scaling Limits and Models in Physical Processes, 91–99. Basel: Birkhäuser Basel, 1998. http://dx.doi.org/10.1007/978-3-0348-8810-3_3.

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Shive, John N., e Robert L. Weber. "Dispersion". In Ähnlichkeiten in der Physik, 163–74. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-642-76110-2_13.

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Upchurch Sweeney, C. Renn, J. Rick Turner, J. Rick Turner, Chad Barrett, Ana Victoria Soto, William Whang, Carolyn Korbel et al. "Dispersion". In Encyclopedia of Behavioral Medicine, 606–7. New York, NY: Springer New York, 2013. http://dx.doi.org/10.1007/978-1-4419-1005-9_1004.

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Gooch, Jan W. "Dispersion". In Encyclopedic Dictionary of Polymers, 980. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-6247-8_15222.

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Bettini, Alessandro. "Dispersion". In Undergraduate Lecture Notes in Physics, 125–74. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-48329-0_4.

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Turner, J. Rick. "Dispersion". In Encyclopedia of Behavioral Medicine, 677–78. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-39903-0_1004.

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Kalmijn, Wim. "Dispersion". In Encyclopedia of Quality of Life and Well-Being Research, 1668–70. Dordrecht: Springer Netherlands, 2014. http://dx.doi.org/10.1007/978-94-007-0753-5_759.

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Fiedler, Johannes. "Dispersion". In Urbanisation, unlimited, 33–49. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-03587-1_4.

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Godin, Biana, Elka Touitou, Rajaram Krishnan, Michael J. Heller, Nicolas G. Green, Hossein Nili, David J. Bakewell et al. "Dispersion". In Encyclopedia of Nanotechnology, 577. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-90-481-9751-4_100182.

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Aksel, Murat. "Dispersion". In Encyclopedia of Estuaries, 201. Dordrecht: Springer Netherlands, 2015. http://dx.doi.org/10.1007/978-94-017-8801-4_195.

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Atti di convegni sul tema "Dispersion"

Knox, W. H. "Femtosecond Intracavity Dispersion Measurements". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/up.1992.mc18.

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In the new class of CW-pumped widely tunable femtosecond solid-state self-modelocked lasers [1], dispersive phenomena represent an important limit. We present the first complete measurements of intracavity dispersion in a "live" femtosecond modelocked laser. These measurements illustrate the importance of higher order dispersion and its effects on the modelocking physics in the operating laser, and show for the first time the dispersive behavior of a complete operating system.

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Qiao, Haigeng, Chuanfeng He, Jinlong Yu, Jufeng Dai e Enze Yang. "New dispersion-decreasing dispersion management". In Lasers and Applications in Science and Engineering, a cura di Kenneth L. Schepler e Dennis D. Lowenthal. SPIE, 2004. http://dx.doi.org/10.1117/12.527644.

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Knox, W. H. "Femtosecond intracavity dispersion measurements". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.thoo1.

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In femtosecond mode-locked lasers, dispersion plays a critical role in the mode-locking physics. With the advent of new broad bandwidth solid-state gain media that could support pulses of less than 10 fs duration in principle, dispersive effects are becoming more important and represent a barrier for further progress. Previously, dispersion in individual cavity elements has been measured with femtosecond accuracy. In this talk, we discuss a new technique for measurement of intracavity dispersion in operating mode-locked femtosecond lasers. Using a frequency-domain technique, we measure the frequency dependent group delay with ±0.65 fs accuracy. We discuss limits imposed by the high order dispersion in such lasers and also extend the technique to cover intracavity spectroscopy and nonlinear effects.

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Fedulova, Elena, Kilian Fritsch, Jonathan Brons, Oleg Pronin, Tatiana Amotchkina, Michael Trubetskov, Ferenc Krausz e Vladimir Pervak. "New Levels of Dispersion of Highly Dispersive Mirrors". In Advanced Solid State Lasers. Washington, D.C.: OSA, 2015. http://dx.doi.org/10.1364/assl.2015.atu3a.8.

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Pervak, Vladimir. "Highly-dispersive Mirrors Reach New Levels of Dispersion". In Optical Interference Coatings. Washington, D.C.: OSA, 2016. http://dx.doi.org/10.1364/oic.2016.td.1.

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Franson, J. D. "Nonlocal cancellation of dispersion". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.thr1.

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Two classical, coincident light pulses propagating through two different dispersive media will become broadened and their degree of coincidence will be reduced. The width of the coincidence curve can be shown to be proportional to ( β 1 2 + β 2 2 ) x 2 , where β1, and β2 are the dispersion coefficients in the two media and x is the distance traveled. When entangled photon pairs from parametric down conversion are considered instead, it is found that the width of the coincidence curve is then proportional to (β1 + β2)2x2, which gives an interference term of 2β1β1. If β1 = β2, the dispersion experienced by one photon can exactly cancel the dispersion experienced by the other in such a way that their coincidence is maintained.

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Lei, Ting, Daniel Al Choboq, Josselin Kherroubi, Lin Liang e Romain Prioul. "Sonic Data Classification Using Supervised Machine-Learning Approach". In 2022 SPWLA 63rd Annual Symposium. Society of Petrophysicists and Well Log Analysts, 2022. http://dx.doi.org/10.30632/spwla-2022-0105.

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Cross-dipole sonic data have been widely accepted in the industry to characterize shear slowness measurements using borehole flexural modes. The borehole flexural mode is dispersive and sensitive to many factors such as tool structure, borehole shape, drilling fluid and formation properties. These sensitivities further enable us to characterize anisotropy, drilling features, and logging conditions. From wide-frequency-band dispersions, one can evaluate the cross-dipole dispersions to identify zones with intrinsic anisotropy, stress-induced anisotropy, or fracture-induced anisotropy. One can also check the dispersions to identify drilling features such as break-out and gas leak, and logging conditions such as tool decentralization. A good understanding of dispersion types is an essential step to guide petrophysical and geomechanical applications. Traditionally, the classification is often carried out manually through visual inspection on a depth-by-depth basis. This is mainly because the dispersion data are represented by scattered and noisy points. Consequently, such a process is time-consuming and requires knowledge on sonic dispersion signatures. To automate sonic data classification, we have developed an algorithm using a supervised machine-learning approach. A neural network classifier was trained using a large volume of synthetic dispersions. The training data are generated using randomly sampled input physical parameters covering effective borehole ovality model, anisotropic model and an alteration model for near wellbore concentration effects. The training datasets are labeled with these physical models. Excellent accuracy was achieved with neural network training. We then applied the classifier to field prediction, where scattered dispersion points are first reconstructed as smooth curves using a recently developed automatic dispersion interpretation algorithm. We tested the new algorithm to real field data where we observe different formation types that are dominant. The testing results show that the developed workflow is accurate in predicting dispersion types with noisy data, and efficient in handling large volume wells. The machine-learning based workflow provides a more natural way for classification than a criteria-based algorithm, thanks to the rich physical information brought by training datasets. The outputs of the classification give ‘soft flags’ in the sense they are represented by prediction probabilities between 0 to 1 using the concept of entropy, which further enable us to evaluate co-existing dispersion signatures. This workflow serves as a key step in the quality control of sonic data and guides further applications in geomechanics where features such as stresses, intrinsic anisotropy and breakouts are key inputs. This paper will describe the methodology, including the construction of the training library, and illustrate the classification with several field examples.

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Schneider, Thomas, Cheng Feng e Stefan Preussler. "Dispersion engineering with stimulated Brillouin scattering and applications". In Steep Dispersion Engineering and Opto-Atomic Precision Metrology XI, a cura di Selim M. Shahriar e Jacob Scheuer. SPIE, 2018. http://dx.doi.org/10.1117/12.2299175.

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de Sousa, Mayra H., e Mario F. S. Ferreira. "Dispersion-managed solitons with average normal dispersion". In Asia-Pacific Optical and Wireless Communications Conference and Exhibit, a cura di Chongcheng Fan e Norman S. Kwong. SPIE, 2001. http://dx.doi.org/10.1117/12.445029.

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Evangelides, Stephen G., e J. Nathan Kutz. "Dispersion-managed solitons with average normal dispersion". In Nonlinear Guided Waves and Their Applications. Washington, D.C.: Optica Publishing Group, 1998. http://dx.doi.org/10.1364/nlgw.1998.nwc.5.

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As a result of their excellent performance characteristics, dispersion-managed communications systems have become increasingly important in recent years. Consequently, a growing research effort has focused on understanding the nonlinear dynamics observed in experiment1,2 and numerical simulation3-7. In particular, many studies have been made of so-called dispersion managed solitons: RZ signals propagating in periodic dispersion maps. These investigations have focused on dispersion maps with a path-average dispersion in the anomalous regime where solitons are expected based on perturbative theories. Using the variational approach, we show that over a small range near the mean-zero dispersion point, there exist stable periodically fluctuating soliton like pulses for dispersion maps with a normal average dispersion. This work confirms recent observations by Nijhof et al8 and explains the mechanism which allows the propagation of these pulses.

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Rapporti di organizzazioni sul tema "Dispersion"

Kehrig, Matthias, e Nicolas Vincent. Good Dispersion, Bad Dispersion. Cambridge, MA: National Bureau of Economic Research, giugno 2019. http://dx.doi.org/10.3386/w25923.

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Pérez Pérez, Jorge, e José G. Nuño-Ledesma. Workers, Workplaces, Sorting, and Wage Dispersion in Mexico. Banco de México, giugno 2024. http://dx.doi.org/10.36095/banxico/di.2024.06.

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Between 2004 and 2018, the spread of wages in Mexico's private labor sector remained stable. Nonetheless, the underlying factors behind salary dispersion underwent significant shifts. To uncover these changes, we analyze an employer-employee dataset comprising the near-universe of Mexico's formal employment. We estimate log wage models and decompose earnings dispersions into worker, workplace and sorting components. At the national level, we find that sorting increased its importance over time. While worker-level factors were the main contributors to salary variability in the 2004-2008 period, workplace factors became as important as worker-level factors in the 2014-2018 time segment. The influence of workplace factors on wage dispersion correlates negatively with per capita GDP at the regional level.

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Feddersen, Falk. Dispersion in the Surfzone: Tracer Dispersion Studies. Fort Belvoir, VA: Defense Technical Information Center, settembre 2011. http://dx.doi.org/10.21236/ada557187.

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Ghosh, Subir, e Eric S. Lagergren. Dispersion Models and Estimation of Dispersion Effects in Replicated Factorial Experiments. Fort Belvoir, VA: Defense Technical Information Center, marzo 1988. http://dx.doi.org/10.21236/ada194695.

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Blaskiewicz, Michael. Dispersion and electron cooling. Office of Scientific and Technical Information (OSTI), gennaio 2019. http://dx.doi.org/10.2172/1494049.

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Hofman, G. L. High density dispersion fuel. Office of Scientific and Technical Information (OSTI), settembre 1996. http://dx.doi.org/10.2172/373920.

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Drazen, Allan, e Daniel Hamermesh. Inflation and Wage Dispersion. Cambridge, MA: National Bureau of Economic Research, gennaio 1986. http://dx.doi.org/10.3386/w1811.

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Garren, A. Dispersion suppressors with bending. Office of Scientific and Technical Information (OSTI), ottobre 1985. http://dx.doi.org/10.2172/93779.

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Cooper, Russell, e Özgen Öztürk. TFPR: Dispersion and Cyclicality. Cambridge, MA: National Bureau of Economic Research, dicembre 2020. http://dx.doi.org/10.3386/w28174.

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Watson, Thomas. Urban Dispersion Virtual Workshop: Designing the Next Generation Urban Dispersion Field Programs. Office of Scientific and Technical Information (OSTI), aprile 2018. http://dx.doi.org/10.2172/1469782.

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