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Robust control applied to power flow control in single-phase inverter with LCL filter, using droop control and D-stability

Sampaio, Leonardo P.; De Brito, Moacyr A. G.; Alves, Marcos G.; E Melo, Guilherme A.; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
35.85%
This paper proposes a new methodology to control the power flow between a distributed generator (DG) and the electrical power distribution grid. It is used the droop voltage control to manage the active and reactive power. Through this control a sinusoidal voltage reference is generated to be tracked by voltage loop and this loop generates the current reference for the current loop. The proposed control introduces feed-forward states improving the control performance in order to obtain high quality for the current injected to the grid. The controllers were obtained through the linear matrix inequalities (LMI) using the D-stability analysis to allocate the closed-loop controller poles. Therefore, the results show quick transient response with low oscillations. Thus, this paper presents the proposed control technique, the main simulation results and a prototype with 1000VA was developed in the laboratory in order to demonstrate the feasibility of the proposed control. © 2012 IEEE.

Controle do regime fluidodinâmico estável durante o processo de umedecimento de inertes em leito de jorro utilizando análise espectral; Control of fluid dynamics regime in spouted bed wetting process using spectral analysis

José Júnior Butzge
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/08/2012 PT
Relevância na Pesquisa
35.82%
A técnica do leito de jorro têm sido utilizada em diversos processos industriais e com maior ênfase nos setores químico, alimentício e farmacêutico, visto que apresenta como principais vantagens excelentes taxas de transferência de calor e massa. Contudo, tais características estão diretamente condicionadas à manutenção do regime de jorro estável, sendo, portanto, um ponto crítico de controle e objetivo operacional que deve ser satisfeito. Em geral, as condições operacionais executadas durante a secagem de pastas em leito de jorro produzem uma atmosfera interna com elevado conteúdo de umidade devido à aspersão de líquidos, promovendo notória dificuldade de operação e manutenção do regime fluidodinâmico desejado neste tipo de processo. Uma forma de superar os problemas efetivos associados à dificuldade de manutenção do regime de jorro estável é através da engenharia de controle e automação de processos. Dentro deste contexto e objetivando a manutenção do regime dinâmico estável durante o processo de umedecimento de inertes em leito de jorro, utilizou-se a metodologia de análise espectral dos sinais de flutuação de queda de pressão no leito para estudar o comportamento dos regimes fluidodinâmicos e implementar uma estratégia de monitoramento e controle do processo. Como partículas inertes foram utilizadas microesferas de vidro...

Model-based strategies for computer-aided operation of recombinant E. coli fermentation

Rocha, I.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em //2003 ENG
Relevância na Pesquisa
45.73%
Tese de Doutoramento em Engenharia Química e Biológica; The main objectives of this thesis were the development of model-based strategies for improving the performance of a high-cell density recombinant Escherichia coli fed-batch fermentation. The construction of a mathematical model framework as well as the derivation of optimal and adaptive control laws were used to accomplish these tasks. An on-line data acquisition system was also developed for an accurate characterization of the process and for the implementation of the control algorithms. The mathematical model of the process is composed of mass balance equations to the most relevant state variables of the process. Kinetic equations are based on the three possible metabolic pathways of the microorganism: glucose oxidation, fermentation of glucose and acetate oxidation. A genetic algorithm was used to derive the kinetic structure and to estimate both yield and kinetic coefficients of the model, minimizing the normalized quadratic differences between simulated and real values of the state variables. After parameter estimation, a sensitivity function analysis was applied to evaluate the influence of the various parameters on model behavior. Sensitivity functions revealed the sensitivity of the state variables to variations in each model parameter. Thus...

Motion of a magnetic flow follower in two-phase flow : application to the study of airlift reactor hydrodynamics

Klein, Jaroslav; Godó, Stefan; Teixeira, J. A.
Fonte: Wiley Periodicals Publicador: Wiley Periodicals
Tipo: Artigo de Revista Científica
Publicado em /11/2006 ENG
Relevância na Pesquisa
35.81%
A low-cost and simple magnetic particle tracer method was adapted to characterize the hydrodynamic behavior of an internal- and an external-loop airlift reactor (ALR). The residence time distribution of three magnetic particles differing in diameter (5.5, 11.0 and 21.2mm) and with a density very close to that of water was measured in individual reactor sections. The measured data were analyzed and used to determine the velocity of the liquid phase. Validation of the experimental results for liquid velocity was done by means of the data obtained by an independent reference method. Furthermore, analysis of the differences found in the settling velocity of the particle in single-liquid and gas-liquid phases was carried out, using a simplified 3D momentum transfer model. The model considering particle-bubble interaction forces resulting from changes in the liquid velocity field due to bubble motion was able to predict satisfactorily the increase in the particle settling velocity in the homogeneous bubbly regime. The effective drag coefficient in two-phase flow was found to be directly dependent on particle Reynolds number to the power of - 2 but independent of gas flow-rate for all particle diameters studied. Based on the experimental and theoretical investigations...

Injetor multicanal com válvulas de estrangulamento para análise em fluxo

Palgrossi,Fabiano S.; Pedrotti,Jairo J.; Gutz,Ivano G. R.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2001 PT
Relevância na Pesquisa
35.74%
An important component for the automation of flow injection analysis (FIA) systems is the sample injection valve. A simple and inexpensive commutator with 16 pinch valves (8 normally open and 8 closed) was developed and configured as a multichannel injection valve. It is activated by a single solenoid of 3 Kgf, powered by a pulsed driver circuit, controlled by a microcomputer or a switch. FIA with spectrophometric detection of potassium dichromate solution was used for the evaluation of the new injection valve and its comparison with other valves, for sample loops of 50, 100, 200, 300 and 500 muL. The repeatability was favorable (RSD 1.0% for 15 injections at each loop volume) compared to a manual injector, an electropneumatic injector and an injector configured with three mini solenoid valves (RSD 1.1, 1.3 and 1.0%, respectively, for15 injections at each loop volume).

Determinação enzimática de dopamina em formulações farmacêuticas utilizando sistema de análise por injeção em fluxo com extrato bruto de abacate (Persea americana)

Lupetti,Karina Omuro; Ramos,Luiz Antônio; Fatibello-Filho,Orlando
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2003 PT
Relevância na Pesquisa
45.86%
In this work, a spectrophotometric flow injection analysis system using a crude extract of avocado (Persea americana) as a source of polyphenol oxidase to dopamine determination was developed. The substrates and enzyme concentrations from 2.4x10-7 to 5.3x10-4 mol L-1 and 28 to 332 units mL-1 were evaluated, respectively. In addition, the FIA parameters such as sample loop (50 to 500 µL), flow rate (1.4 to 4.3 mL min-1) and reactor length (100 to 500 cm) were also evaluated in a 0.1 mol L-1 phosphate buffer solution (pH 7.0). Dopamine solution concentrations were determined using 277 units mL-1 enzyme solution, 400 mL enzyme loop, 375 µL sample loop, 2.2 mL min-1 flow rate and a reactor of 350 cm. The analytical curve showed a linearity from 5.3x10-5 to 5.3x10-4 mol L-1 dopamine with a detection limit of 1.3x10-5 mol L-1. The analytical frequency was 46 h-1 and the RSD lower than 0.5% for 5.3x10-4 mol L-1 dopamine solution (n=10). A paired t-test showed that all results obtained for dopamine in commercial formulations using the proposed flow injection procedure and a spectrophotometric procedure agree at the 95% confidence level.

Indirect Determination of Ethanol in Drinks Using a Capacitance Flow-through Detector

Liu,Shan-jun; Tubino,Matthieu
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/1999 EN
Relevância na Pesquisa
35.75%
A flow procedure based on a metallic capacitance flow-through detector is described for the analysis of water vapour. The capacitance detector consists of two stainless steel tubes and is located in the loop of a sampling valve. The logarithm of the capacitance signal correlates linearly with the concentrations of water vapour in the 1705 to 2197 Pa range. A sampling frequency of about 55 h-1 can be achieved. The flow system was applied to the indirect determination of the ethanol concentration in drinks based on the analysis of water vapour content above the liquid sample, without any pre-treatment of the sample. The colour of the drinks has no effect on the measurements.

Characterization of gas-liquid parameters in a down-flow jet loop bubble column

Mandal,Ajay
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2010 EN
Relevância na Pesquisa
35.76%
In order to characterize the gas-liquid parameters of a down-flow jet loop reactor, experiments were carried out to study the gas holdup, bubble sizes and their distribution, mass transfer area and mass transfer coefficient. The experiments were performed in the bubbly flow regime because of its stability and uniformity. Analysis of experimental data showed an unambiguous relationship between gas holdup, bubble size, bubble size distribution and interfacial area. It has also been found that gas holdup and interfacial area is a strong function of slip velocity. The variation of interfacial area and mass transfer coefficient were also analyzed and expressed as a function of operational and geometric parameters.

Specific In Vivo Labeling of Cell Surface-Exposed Protein Loops: Reactive Cysteines in the Predicted Gating Loop Mark a Ferrichrome Binding Site and a Ligand-Induced Conformational Change of the Escherichia coli FhuA Protein

Bös, Christoph; Lorenzen, Dirk; Braun, Volkmar
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /02/1998 EN
Relevância na Pesquisa
35.74%
The FhuA protein of Escherichia coli K-12 transports ferrichrome, the antibiotic albomycin, colicin M, and microcin 25 across the outer membrane and serves as a receptor for the phages T1, T5, φ80, and UC-1. FhuA is activated by the electrochemical potential of the cytoplasmic membrane, which probably opens a channel in FhuA. It is thought that the proteins TonB, ExbB, and ExbD function as a coupling device between the cytoplasmic membrane and the outer membrane. Excision of 34 residues from FhuA, tentatively designated the gating loop, converts FhuA into a permanently open channel. FhuA contains two disulfide bridges, one in the gating loop and one close to the C-terminal end. Reduction of the disulfide bridges results in a low in vivo reaction of the cysteines in the gating loop and no reaction of the C-terminal cysteines with biotin-maleimide, as determined by streptavidin-β-galactosidase bound to biotin. In this study we show that a cysteine residue introduced into the gating loop by replacement of Asp-336 displayed a rather high reactivity and was used to monitor structural changes in FhuA upon binding of ferrichrome. Flow cytometric analysis revealed fluorescence quenching by ferrichrome and albomycin of fluorescein-maleimide bound to FhuA. Ferrichrome did not inhibit Cys-336 labeling. In contrast...

A versatile injection system for flow-injection analysis

Sollacaro, M.; Dittmar, A.; Later, R.
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em //1992 EN
Relevância na Pesquisa
45.74%
Analyser injection systems based on the principle of flow-injection analysis depend on the technique used. They generally take the form of an injection loop valve; the injected sample volume is determined by the volume of the valve. Injection systems are seldom designed with a time factor to define this volume. The authors report on an original injection system, which enables the two techniques to be used. The paper describes the evaluation of this system using both injection techniques and the comparison between them. The results show good linearity (r = 0.999 to 1.000) and an average precision (CV = 1.04 to 1.51%) for the volume-based injection technique; (ii) good linearity (r = 1.000) and better precision (CV = 0.73 to 1.30%) for the time-based injection technique. The system can be used equally well by the loop and by the clock; however, the latter is preferable because of its practicability.

Cine Computed Tomography Angiography Evaluation of Blood Flow for Full Face Transplant Surgical Planning

Sisk, Geoffroy C.; Kumamaru, Kanako K.; Schultz, Kurt; Bueno, Ericka M.; Diaz-Siso, J. Rodrigo; George, Elizabeth; Redjaee, Marta M.; Mitsouras, Dimitrios; Steigner, Michael L.; Pomahac, Bohdan; Rybicki, Frank J.
Fonte: Open Science Company, LLC Publicador: Open Science Company, LLC
Tipo: Artigo de Revista Científica
Publicado em 18/12/2012 EN
Relevância na Pesquisa
35.75%
Objective: Screening for full face transplantation candidates includes computed tomographic vascular mapping of the external carotid distribution for potential arterial and venous anastomoses. The purpose of this study is to illustrate the benefits and drawbacks of cine computed tomographic imaging for preoperative vascular mapping compared with best arterial and venous phase static images. Methods: Two image data sets were retrospectively created and compared for diagnostic findings. The first set of images was the clinical cine computed tomographic acquisition including all phases. The second set of images was composed of the best arterial and best venous phases extracted from the cine loop and determined by the quality of contrast enhancement. For each patient, the benefits and drawbacks of the cine loop were documented in consensus by a plastic surgeon and a radiologist. Results: Cine loop analysis identified retrograde arterial filling not illustrated on the static images alone. Cine assessment identified most of the major vessels necessary for surgery, whereas the static images depicted small vessels more clearly, particularly in the crowded vessel takeoffs. Conclusions: Cine computed tomographic images provide data on direction of blood flow...

Spatial and temporal variations of microbial community in a mixed plug-flow loop reactor fed with dairy manure

Li, Yueh-Fen; Chen, Po-Hsu; Yu, Zhongtang
Fonte: BlackWell Publishing Ltd Publicador: BlackWell Publishing Ltd
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.77%
Mixed plug-flow loop reactor (MPFLR) has been widely adopted by the US dairy farms to convert cattle manure to biogas. However, the microbiome in MPFLR digesters remains unexplored. In this study, the microbiome in a MPFLR digester operated on a mega-dairy farm was examined thrice over a 2 month period. Within 23 days of retention time, 55–70% of total manure solid was digested. Except for a few minor volatile fatty acids (VFAs), total VFA concentration and pH remained similar along the course of the digester and over time. Metagenomic analysis showed that although with some temporal variations, the bacterial community was rather stable spatially in the digester. The methanogenic community was also stable both spatially and temporally in the digester. Among methanogens, genus Methanosaeta dominated in the digester. Quantitative polymerase chain reaction (qPCR) analysis and metagenomic analysis yielded different relative abundance of individual genera of methanogens, especially for Methanobacterium, which was predominant based on qPCR analysis but undetectable by metagenomics. Collectively, the results showed that only small microbial and chemical gradients existed within the digester, and the digestion process occurred similarly throughout the MPFLR digester. The findings of this study may help improve the operation and design of this type of manure digesters.

Determinação eletroquímica de glicerol em biodiesel por amperometria de múltiplos pulsos com eletrodo de ouro

Barbosa, Tatielli Gonçalves Gregório
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
45.71%
O biodiesel é o combustível derivado de óleos vegetais ou gorduras animais que pode substituir parcial ou totalmente o diesel de petróleo. Além de ser obtido de fontes renováveis, é menos poluente que diesel de petróleo e biodegradável. Uma desvantagem do biodiesel é o coproduto da reação de transesterificação da matéria prima, o glicerol, que pode causar danos aos motores de combustão e, por isso, é limitado a 0,25 % (m/m) como glicerol total, e 0,02 % (m/m) como glicerol livre, por regulamentações técnicas como a ANP 7, ASTM D 6751 e EN 14214. Este trabalho propõe um método de determinação amperométrica de glicerol livre em biodiesel utilizando eletrodo de ouro como detector, em meio básico, acoplado a sistema de análise por injeção em fluxo (FIA). A caracterização voltamétrica do glicerol foi realizada de -0,8 a 0,5 V, verificando o perfil eletroquímico típico concordante com a literatura. Para a determinação de glicerol no sistema FIA, foi empregada a amperometria de múltiplos pulsos sendo aplicados três pulsos de potencial sequenciais: -0,2; 0,25 e 0,7 V, cada um aplicado por 100 ms. O glicerol livre foi extraído para a fase aquosa analisada por meio de agitação em vortex seguida por centrifugação. O sistema FIA foi avaliado em função da obtenção do maior sinal de corrente para a detecção de glicerol. As melhores condições foram 150 μL de alça de amostragem e vazão de 4...

A preliminary estimate of genetic diversity of Pelteobagrus fulvidraco (Yellow Catfish) and Silurus meridionalis (Southern Catfish) along the Yangtze River at the mitochondrial D-Loop and ND5/6 gene regions.

Silva, Anthony
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 459702 bytes; application/pdf
EN
Relevância na Pesquisa
35.79%
The Three Gorges Dam on the Yangtze River in China has created a large physical barrier that will likely prevent gene flow between the populations upstream and downstream from the dam. Since construction of the dam is recent, the objective of this study was to provide pre-divergence data on mtDNA polymorphism and genetic exchange in both the yellow catfish and the southern catfish species using the D-loop, ND5, and ND6 regions. All PCR reactions were optimized except for the D-loop in the southern catfish. D-loop analysis of the yellow catfish indicated a high haplotype: sample ratio (6/14), high haplotype diversity (0.714 ± 0.079), and relatively low nucleotide diversity (0.01495 ± 0.172). ND5 and ND6 Haplotype diversity for the yellow catfish were also high, 0.800 ± 0.172 and 0.600 ± 0.175, respectively. Maximum Parsimony Networks and Minimum Spanning Networks provided haplotype relatedness, measured by number of mutations, for both closely related haplotypes and more distant haplotypes respectively. The D-loop haplotype “Y09, Y15, Y16, Y20, B46” was found both upstream of the Three Gorges Dam and ~ 2000 km downstream of the upstream population at 1000 Island Lake. This provides support that before the Three Gorges Dam was constructed...

Head- and flow-based formulations for frequency domain analysis of fluid transients in arbitrary pipe networks

Vitkovsky, J.; Lee, P.; Zecchin, A.; Simpson, A.; Lambert, M.
Fonte: ASCE-Amer Soc Civil Engineers Publicador: ASCE-Amer Soc Civil Engineers
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
35.8%
Applications of frequency-domain analysis in pipelines and pipe networks include resonance analysis, time-domain simulation, and fault detection. Current frequency-domain analysis methods are restricted to series pipelines, single-branching pipelines, and single-loop networks and are not suited to complex networks. This paper presents a number of formulations for the frequency-domain solution in pipe networks of arbitrary topology and size. The formulations focus on the topology of arbitrary networks and do not consider any complex network devices or boundary conditions other than head and flow boundaries. The frequency-domain equations are presented for node elements and pipe elements, which correspond to the continuity of flow at a node and the unsteady flow in a pipe, respectively. Additionally, a pipe-node-pipe and reservoir-pipe pair set of equations are derived. A matrix-based approach is used to display the solution to entire networks in a systematic and powerful way. Three different formulations are derived based on the unknown variables of interest that are to be solved: head-formulation, flow-formulation, and head-flow-formulation. These hold significant analogies to different steady-state network solutions. The frequency-domain models are tested against the method of characteristics (a commonly used time-domain model) with good result. The computational efficiency of each formulation is discussed with the most efficient formulation being the headformulation.; John P. Vítkovský; Pedro J. Lee; Aaron C. Zecchin; Angus R. Simpson; and Martin F. Lambert.

Simulação computacional de eventos termo-hidraulicos transitorios em multicircuitos com multibombas

Marcelo Antonio Veloso
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/02/2003 PT
Relevância na Pesquisa
45.88%
O programa computacional P ANTERA-2 (Programa para Análise Termo-hidráulica de Reatores a Água, Versão 2), cujos fundamentos são descritos neste trabalho, efetua a análise por subcanais de feixes de varetas em conjunção com a simulação de múltiplos circuitos. O programa resolve simultaneamente as equações de conservação da massa, dos momentos axial e lateral e da energia para a geometria de subcanais acopladas com as equações de balanço que descrevem o escoamento de um fluido em um número arbitrário de circuitos de remgeração conectados a um vaso de pressão que contém o feixe. Atendo-se à formulação de subcanais, a estratégia computacional básica de P ANTERA-2 provém dos códigos COBRA, mas um método implícito alternativo de solução orientado para o campo de pressões é usado para resolver as aproximações de diferenças finitas das leis de balanço. Os resultados previstos pelo modelo de subcanais compreendem as distribuições de densidades, entalpias, vazões de massa e pressões nos subcanais. O modelo de circuitos prevê as vazões nos circuitos individuais, a vazão total através do vaso de pressão e as velocidades de rotação das bombas em função do tempo subseqüente à falha de qualquer número das bombas de circulação. Os transitórios de vazão nos circuitos podem ser ocasionados pelas perdas de potência elétrica...

A Robust Docking Strategy for a Mobile Robot Using Flow Field Divergence

McCarthy , Christopher; Barnes, Nick; Mahony, Robert
Fonte: Institute of Electrical and Electronics Engineers (IEEE Inc) Publicador: Institute of Electrical and Electronics Engineers (IEEE Inc)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.82%
We present a robust strategy for docking a mobile robot in close proximity with an upright surface using optical flow field divergence and proportional feedback control. Unlike previous approaches, we achieve this without the need for explicit segmentatio

Real-time renormalization group in frequency space: A 2-loop analysis of the nonequilibrium anisotropic Kondo model at finite magnetic field

Schoeller, Herbert; Reininghaus, Frank
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.66%
We apply a recently developed nonequilibrium real-time renormalization group method in frequency space to describe nonlinear quantum transport through a small fermionic quantum system coupled weakly to several reservoirs via spin and/or orbital fluctuations. We provide an analytic and well-controlled procedure to solve the RG equations in the weak-coupling regime. Within a 2-loop analysis, we derive analytic formulas for the nonlinear conductance and the kernel determining the time evolution of the reduced density matrix. Most importantly, we present a consistent formalism how the RG flow is cut off by relaxation and dephasing rates, which is necessary to calculate the precise line shape at resonances. We apply the general formalism to the nonequilibrium anisotropic Kondo model at finite magnetic field. We consider the weak-coupling regime, where the maximum of voltage and bare magnetic field is larger than the Kondo-temperature. In this regime, we calculate the nonlinear conductance, the magnetic susceptibility, the renormalized spin relaxation and dephasing rates, and the renormalized g-factor. All quantities are considered up to the first logarithmic contributions at resonance. Up to a redefinition of the Kondo temperature, we confirm previous results for the conductance and the magnetic susceptibility in the isotropic case. In addition...

Statistical Analysis of High-Flow Traffic States

Knorr, Florian; Zaksek, Thomas; Brügmann, Johannes; Schreckenberg, Michael
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/12/2013
Relevância na Pesquisa
35.87%
The relation between the fundamental observables of traffic flow (i.e., vehicle density, flow rate, and average velocity) is of great importance for the study of traffic phenomena. Probably the most common source of such data are inductive loop detectors, which count the number of passing vehicles and measure their speed. We will present an analysis of detector data collected by more than 3000 loop detectors during the past three years on the motorway network of the state of North Rhine-Westphalia. Besides presenting some general aspects of traffic flow, our analysis focuses on the characteristics of so-called high-flow states, i.e. traffic states where the flow rate exceeds 50 vehicles per minute and lane (3000 veh/h/lane). We investigate the duration, frequency and other statistics of such states, the viability of the data and we study the conditions under which they occur. The factors that influence the existence of high-flow states in traffic are, for instance, the fraction of slow vehicles (namely trucks), the motorway's general topology (e.g. number of lanes), the hour of the day and day of the week. This information is directly accessible from the detector data.; Comment: 6 pages, 4 figures, presented at "Traffic and Granular Flow 2013" conference

Feedback-Mediated Dynamics in the Kidney: Mathematical Modeling and Stochastic Analysis

Ryu, Hwayeon
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2014
Relevância na Pesquisa
35.83%

One of the key mechanisms that mediate renal autoregulation is the tubuloglomerular feedback (TGF) system, which is a negative feedback loop in the kidney that balances glomerular filtration with tubular reabsorptive capacity. In this dissertation, we develop several mathematical models of the TGF system to study TGF-mediated model dynamics.

First, we develop a mathematical model of compliant thick ascending limb (TAL) of a short loop of Henle in the rat kidney, called TAL model, to investigate the effects of spatial inhomogeneous properties in TAL on TGF-mediated dynamics. We derive a characteristic equation that corresponds to a linearized TAL model, and conduct a bifurcation analysis by finding roots of that equation. Results of the bifurcation analysis are also validated via numerical simulations of the full model equations.

We then extend the TAL model to explicitly represent an entire short-looped nephron including the descending segments and having compliant tubular walls, developing a short-looped nephron model. A bifurcation analysis for the TGF loop-model equations is similarly performed by computing parameter boundaries, as functions of TGF gain and delay, that separate differing model behaviors. We also use the loop model to better understand the effects of transient as well as sustained flow perturbations on the TGF system and on distal NaCl delivery.

To understand the impacts of internephron coupling on TGF dynamics...