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Fabbri, Luca. "Computing primal solutions with exact arithmetics in SCIP." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8541/.
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The research for exact solutions of mixed integer problems is an active topic
in the scientific community. State-of-the-art MIP solvers exploit a floating-
point numerical representation, therefore introducing small approximations.
Although such MIP solvers yield reliable results for the majority of problems,
there are cases in which a higher accuracy is required. Indeed, it is known
that for some applications floating-point solvers provide falsely feasible
solutions, i.e. solutions marked as feasible because of approximations that
would not pass a check with exact arithmetic and cannot be practically
implemented.
The framework of the current dissertation is SCIP, a mixed integer
programs solver mainly developed at Zuse Institute Berlin. In the same site
we considered a new approach for exactly solving MIPs. Specifically, we
developed a constraint handler to plug into SCIP, with the aim to analyze
the accuracy of provided floating-point solutions and compute exact primal solutions starting from floating-point ones.
We conducted a few computational experiments to test the exact primal
constraint handler through the adoption of two main settings. Analysis
mode allowed to collect statistics about current SCIP solutions' reliability.
Our results confirm that floating-point solutions are accurate enough with
respect to many instances. However, our analysis highlighted the presence of
numerical errors of variable entity. By using the enforce mode, our constraint
handler is able to suggest exact solutions starting from the integer part of
a floating-point solution. With the latter setting, results show a general
improvement of the quality of provided final solutions, without a significant loss of performances.
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Gooze, Aaron Isaac. "Real-time transit information accuracy: impacts and proposed solutions." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47638.
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When presented in a practical format, real-time transit information can improve sustainable travel methods by enhancing the transit experience. Larger shifts towards public transportation have cascading effects on the environment, health and urban form. The research will identify the positive shift realized by the continued development of a set of real-time transit information tools, specifically in the Seattle region. In addition, it will analyze real-time prediction errors and their effects on the rider experience. Three years after the development of location-aware mobile applications for OneBusAway - a suite of real-time information tools - a survey of current users was conducted by the author in 2012 in order to compare the results to a 2009 study. The results show significant positive shifts in satisfaction with transit, perceptions of safety and ridership frequency as a result of the increased use of real-time arrival information. However, the research will also provide a perspective of the margin of error riders come to expect and the negative effects resulting from inaccuracies with the real-time data. While riders on average will ride less when they have experienced errors, a robust issue-reporting system as well as the resolution of the error can mitigate the initial negative effects. In response, the research provides a framework for a crowd-sourced error reporting process in order to improve the level of accuracy by means of a Transit Ambassador Program. Finally, a pilot program developed by the author is assessed against this framework and insight is provided within the context of the real-time information system.
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Davda, Kinner. "Accuracy in hip surgery : assessment, consequence and solution." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/29761.
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Hip arthroplasty is the most common and successful surgical treatment for the management of hip osteoarthrosis. However, complications arising from technical error in analysing the native hip, aswell as the position of the hip prosthesis can result in a suboptimal outcome for the patient. This thesis principally examines acetabular component orientation, investigating the use of technology in this critical aspect of hip arthroplasty surgery. In the first study, navigation technology is used to assess the performance of a current cohort of training and senior orthopaedic surgeons in a simulated surgical setting. A wide range of error in orientating an acetabular cup orientation to a target position is demonstrated. The second study seeks to establish a novel method of delineating the femoral neck axis in 3D using a sample of normal hip CT scans. Using such a proximal femoral frame of reference allows a standardised approach to assessing normal and abnormal hip morphology. The articular margin of the femoral head is shown to have a wave like pattern that consists of an anterior and posterior facet. The third study compares 2D and 3D measurements of inclination and version of acetabular components, finding a critical difference between the two in version measurements and that 3D measurements are more reliable. The thesis continues by examining the current methodology of analysing the concentration of cobalt and chromium metal ions in the joint fluid from a cohort of symptomatic patients with a metal on metal hip arthroplasty. A more robust laboratory method of processing fluid samples using a digestive oxidative method is presented. The relationship between concentrations of metal ion levels in joint fluid and several clinical parameters is investigated with no clear association shown, suggesting joint fluid in itself cannot be used as a marker for a failing metal on metal hip. The thesis concludes by comparing navigation technology to conventional 'freehand' method in orientating an acetabular component in a group of patients undergoing metal on metal hip resurfacing. The results suggest that navigation technology may substantially improve surgeon error in this task. Technology and three dimensional imaging can play a vital role in improving the accuracy of orientating an acetabular component in hip surgery. It can be employed in the pre-operative stages to assess trainee performance, intra-operatively to reduce surgical error and post operatively to investigate surgeon accuracy on CT imaging.
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Kruk, Serge. "High accuracy algorithms for the solutions of semidefinite linear programs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60548.pdf.
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Bilodeau, Bernard. "Accuracy of a truncated barotropic spectral model : numerical versus analytical solutions." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66037.
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García-Blanco, Raquel. "Efficient solvers for power flow equations : parametric solutions with accuracy control assessment." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/458887.
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The Power Flow model is extensively used to predict the behavior of electric grids and results in solving a nonlinear algebraic system of equations. Modeling the grid is essential for design optimization and control. Both applications require a fast response for multiple queries to a parametric family of power flow problems. Different solvers have been introduced especially designed for the algebraic nonlinear power flow equations, providing efficient solutions for single problems, even when the number of degrees of freedom is considerably large. However, there is no existing methodology providing an explicit solution of the Parametric Power Flow problem (viz. a computational vademecum, explicit in terms of the parameters).
This work aims precisely at designing algorithms producing computational vademecums for the Parametric Power Flow problem. Once these solutions are available, solving for different values of the parameters is an extremely fast (real-time) post-process and therefore both the optimal design and the control problem can readily be addressed.
In a first phase, a new family of iteratives solvers for the non-parametric version of the problem is devised. The method is based on a hybrid formulation of the problem combined with an alternated search directions scheme. These methods are designed such that it can be generalized to deal with the parametric version of the problem following a Proper Generalized Decomposition (PGD) strategy.
The solver for the parametric problem is conceived by performing the operations involving the unknowns in a PGD fashion. The algorithm follows the basic steps of the algebraic solver, but some operations are carried out in a PGD framework, that is requiring a nested iterative algorithm. The PGD solver is accompanied with an error assessment technique that allows monitoring the convergence of the iterative procedures and deciding the number of terms required to meet the accuracy prescriptions. Different examples of realistic grids and standard benchmark tests are used to demonstrate the performance of the proposed methodologies.El modelo de flujo de potencias se usa para predecir el comportamiento de redes eléctricas y desemboca en la resolución de un sistema de ecuaciones algebraicas no lineales. Modelar una red es esencial para optimizar su diseño y control. Ambas aplicaciones requieren una respuesta rápida a las múltiples peticiones de una familia paramétrica de problemas de flujo de potencias. Diversos métodos de resolución se diseñaron especialmente para resolver la versión algebraica de las ecuaciones de flujo de potencias. Sin embargo, no existe ninguna metodología que proporcione una solución explícita al problema paramétrico de flujo de potencias (esto quiere decir, un vademecum computacional explícito en términos de los parámetros). Esta tesis tiene como objetivo diseñar algoritmos que produzcan vademecums para el problema paramétrico de flujo de potencias. Una vez que las soluciones están disponibles, resolver problemas para diferentes valores de los parámetros es un posproceso extremadamente rápido (en tiempo real) y por lo tanto los problemas de diseño óptimo y control se pueden resolver inmediatamente. En la primera fase, una nueva familia de métodos de resolución iterativos para la versión algebraica del problema se construye. El método se basa en una formulación híbrida del problema combinado con un esquema de direcciones alternadas. Estos métodos se han diseñado para generalizarlos de forma que puedan resolver la versión paramétrica del problema siguiendo una estrategia llamada Descomposición Propia Generalizada (PGD). El método de resolución para el problema paramétrico calcula las incógnitas paramétricas usando la técnica PGD. El algoritmo sigue los mismo pasos que el algoritmo algebraico, pero algunas operaciones se llevan a cabo en el ambiente PGD, esto requiere algoritmos iterativos anidados. El método de resolución PGD se acompaña con una evaluación del error cometido permitiendo monitorizar la convergencia de los procesos iterativos y decidir el número de términos que requiere la solución para alcanzar la precisión preescrita. Diferentes ejemplos de redes reales y tests estándar se usan para demostrar el funcionamiento de las metodologías propuestas.
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Capper, Steven David. "High Accuracy Methods for the Solution to Two Point Boundray Value." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498602.
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Liu, Yang. "Improving the Accuracy of Variable Selection Using the Whole Solution Path." Bowling Green State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1435858170.
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Veluri, Subrahmanya Pavan Kumar. "Code Verification and Numerical Accuracy Assessment for Finite Volume CFD Codes." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/28715.
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A detailed code verification study of an unstructured finite volume Computational Fluid
Dynamics (CFD) code is performed. The Method of Manufactured Solutions is used to generate
exact solutions for the Euler and Navier-Stokes equations to verify the correctness of the code
through order of accuracy testing. The verification testing is performed on different mesh types
which include triangular and quadrilateral elements in 2D and tetrahedral, prismatic, and
hexahedral elements in 3D. The requirements of systematic mesh refinement are discussed,
particularly in regards to unstructured meshes. Different code options verified include the
baseline steady state governing equations, transport models, turbulence models, boundary
conditions and unsteady flows. Coding mistakes, algorithm inconsistencies, and mesh quality
sensitivities uncovered during the code verification are presented.
In recent years, there has been significant work on the development of algorithms for the
compressible Navier-Stokes equations on unstructured grids. One of the challenging tasks during
the development of these algorithms is the formulation of consistent and accurate diffusion
operators. The robustness and accuracy of diffusion operators depends on mesh quality. A survey
of diffusion operators for compressible CFD solvers is conducted to understand different
formulation procedures for diffusion fluxes. A patch-wise version of the Method of
Manufactured Solutions is used to test the accuracy of selected diffusion operators. This testing
of diffusion operators is limited to cell-centered finite volume methods which are formally
second order accurate. These diffusion operators are tested and compared on different 2D mesh
topologies to study the effect of mesh quality (stretching, aspect ratio, skewness, and curvature)
on their numerical accuracy. Quantities examined include the numerical approximation errors
and order of accuracy associated with face gradient reconstruction. From the analysis, defects in
some of the numerical formulations are identified along with some robust and accurate diffusion
operators.Ph. D.
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Ryan, Keegan P. "Experimental Testing of the Accuracy of Attitude Determination Solutions for a Spin-Stabilized Spacecraft." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/1007.
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Spin-stabilized spacecraft generally rely on sun and three-axis magnetic field sensor measurements for attitude determination. This study experimentally determines the total accuracy of attitude determination solutions using modest quality sensors. This was ac- complished by having a test spacecraft collect data during spinning motions. The data was then post-processed to find the attitude estimates, which were then compared to the exper- imentally measured attitude. This same approach will be used to test the accuracy of the attitude determination system of the DICE spacecraft to be built by SDL/USU.
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Bani-Hashemian, Mohammad Hossein. "Accurate and Efficient Solution of the Smoluchowski Equation." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-156440.
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The probability density function (PDF) of the relative position of molecules diffusing independently in three dimensional space according to Brownian motion and reacting with a certain probability when any two of them collide is given by the Smoluchowski equation. The PDF is used to sample particle positions in simulations of reaction-diffusion processes by particle-based simulation methods, like Green's Function Reaction Dynamics (GFRD) proposed by van Zon and ten Wolde. The GFRD algorithm is an event-driven algorithm, allowing the use of longer time steps, which is particularly efficient for simulating chemical reactions at low concentration in molecular biology. This study is based on the improved version of the GFRD algorithm developed by S. Hellander and P. Lötstedt, where the applicability of the algorithm is increased and computing the PDFs is simplified by using an operator splitting approach. The main idea is to split the spatial differential operator of the Smoluchowski equation into a radial part and an angular part, resulting in two one-dimensional time-dependent partial differential equations (PDEs) to be solved independently and sequentially. These equations can be solved analytically but the solutions are complicated and computationally expensive to evaluate. This thesis intends to compare the accuracy and efficiency of sampling the radial distance between two molecules and the relative angular position of the two molecules from directly evaluated exact PDFs or their finite difference approximations and interpolating the positions from precomputed tabulated data.
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De, Florio Mario. "Accurate Solutions of the Radiative Transfer Problem via Theory of Connections." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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In questa tesi viene presentato un nuovo approccio per risolvere una classe di Radiative Transfer Problems, utilizzando la Theory of Connections. Il metodo prevede di risolvere in modo efficiente e accurato un problema lineare con una condizione al contorno (Linear One-Point Boundary Value Problem) derivante dall'equazione integro-differenziale di Boltzmann per il Radiative Transfer tramite un'espansione di polinomi di Chebyshev e metodo Least-Squares.
L'algoritmo proposto risiede nella categoria dei metodi numerici per la soluzione delle equazioni del trasporto, ed è dimostrato essere accurato ed adatto per applicazioni nell'Atmospheric Science e Remote Sensing.
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Margitus, Michael. "Optimal interpolation grids for accurate numerical solutions of singular ordinary differential equations /." Online version of thesis, 2009. http://hdl.handle.net/1850/10823.
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Köylüoglu, Tugay, and Lukas Hennicks. "Evaluating rain removal image processing solutions for fast and accurate object detection." Thesis, KTH, Mekatronik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254446.
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Autonomous vehicles are an important topic in modern day research, both for the private and public sector. One of the reasons why self-driving cars have not yet reached consumer market is because of levels of uncertainty. This is often tackled with multiple sensors of different kinds which helps gaining robust- ness in the vehicle’s system. Radars, lidars and cameras are often the sensors used and the expenses can rise up quickly, which is not always feasible for different markets. This could be addressed with using fewer, but more robust sensors for visualization. This thesis addresses the issue of one particular failure mode for camera sensors, which is reduced view range affected by rainy weather. Kalman filter and discrete wavelet transform with bilateral filtering are evaluated as rain removal algorithms and tested with the state-of-the-art object detection algorithm, You Only Look Once (YOLOv3). Filtered videos in daylight and evening light were tested with YOLOv3 and results show that the accuracy is not improved enough to be worth implementing in autonomous vehicles. With the graphics card available for this thesis YOLOv3 is not fast enough for a vehicle to stop in time when driving in 110km/h and an obstacle appears 80m ahead, however an Nvidia Titan X is assumed to be fast enough. There is potential within the research area and this thesis suggests that other object detection methods are evaluated as future work.Autonoma fordon är för privat samt offentlig sektor ett viktigt område i modern forskning. Osäkerheten med autonoma fordon är en viktig anledning till varför de idag inte nått konsumentmarknaden. Systemen för autonoma fordon blir mer robusta med inkludering av flera sensorer av olika typer, vilka oftast är kameror, radar och lidars. Fordon med dessa sensorer kan snabbt öka i pris vilket gör dem mindre tillgängliga för olika marknader. Detta skulle kunna lösas med färre sensorer som däremot är mer robusta. Denna avhandling diskuterar problemet med en specific felmodell för kameror, vilket är minskat synfält som påverkas av regnigt väder. Kalman filter och diskret vågkomponent-transformation med bilateral filtrering utvärderades som regnborttagningsalgoritmer och testades med You Only Look Once (YOLOv3), en modern objektigenkänningsmetod. Filtrerade videofilmer i dagstid och kvällstid testades med YOLOv3 och resultaten visade att noggrannheten inte ökade tillräckligt mycket för att vara användbara för autonoma fordon. Med grafikkorten tillgängliga för denna avhandling är inte YOLOv3 snabb nog för ett fordon att hinna stanna i tid före kollision om bilen kör i 110km/h och ett föremål dyker upp 80m framför. Däremot antas det att fordon utrustade med Nvidias Titan X borde hinna stanna i tid före kollision. Avhandlingen ser däremot potential inom detta forskningsområde och föreslår att liknande test fast med andra objektigenkänningsmetoder bör utföras.
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Bommakanti, Hemanth Ram Kartik. "Impact of Time Synchronization Accuracy in Integrated Navigation Systems." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-260239.
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Global Navigation Satellite System/Inertial Measurement Unit (GNSS/IMU) Integrated Navigation Systems (INS) integrate the positive features of GNSS and IMU for optimal navigation guidance in high accuracy outdoor navigation systems, for example using Extended Kalman Filter (EKF) techniques. Time synchronization of IMU data with precise GNSS based time is necessary to accurately synchronize the two systems. This must be done in real-time for time sensitive navigation applications such as autonomous vehicles. The research is done in two parts. The first part is the simulation of inaccurate time-stamping in a single axis of nonlinear input data in a gyroscope and an accelerometer, to obtain the timing error value that is tolerable by a high accuracy GNSS/INS system. The second part is the creation of a real-time algorithm using an STM32 embedded system enabled with FreeRTOS real-time kernel for a GNSS receiver and antenna, along with an IMU sensor. A comparative analysis of the time synchronized system and an unsynchronized system is done based on the errors produced using gyroscope and accelerometer readings along a single axis from the IMU sensor, by conducting static and rotational tests on a revolving chair.The simulation concludes that a high accuracy GNSS/INS system can tolerate a timing error of up to 1 millisecond. The real-time solution provides IMU data paired with updated GNSS based time-stamps every 5 milliseconds. The timing jitter is reduced to a range of ±1 millisecond. Analysis of final angular rotation error and final position error from gyroscope and accelerometer readings respectively, indicate that the real-time algorithm produces a reduction in errors when the system is static, but there is no statistical evidence showing the reduction of errors from the results of the rotational tests.GNSS / IMU integrerade navigationssystem kombinerar de positiva egenskaperna hos GNSS och IMU för optimal prestanda i noggranna navigationssystem. Detta görs med hjälp av sensorfusion, till exempel EKF. Tidssynkronisering av IMU-data med exakt GNSS-baserad tid är nödvändigt för att noggrant synkronisera de två systemen. Detta måste göras i realtid för tidskänsliga navigationsapplikationer såsom autonoma fordon. Forskningen görs i två delar. Den första delen är simulering av icke-linjär rörelse i en axel med felaktig tidsstämpling hos ett gyroskop och en accelerometer. Detta görs för att erhålla det högsta tidsfel som är acceptabelt hos ett GNSS / INS-system med hög noggrannhet. Den andra delen är skapandet av en realtidsalgoritm med ett inbyggt STM32-system med FreeRTOS som realtidskärna för en GNSSmottagare och antenn, tillsammans med en IMU-sensor. En jämförande analys av det tidssynkroniserade systemet mot ett osynkroniserat system görs baserat på de positionsfel längs en axel som produceras av gyroskopoch accelerometermätningar. Detta görs genom att utföra statiska och roterande tester med hjälp av en roterande stol.Simuleringen visar att ett noggrant GNSS / INS-system tolererar ett tidsfel på upp till 1 millisekund. Realtidslösningen ger IMU-data med tidsstämplar synkroniserade med GNSS-tid var femte millisekund. Tidsjittret reduceras till ett intervall mellan ± 1 millisekund. Analysen av det slutliga vinkelrotationsfelet och positionsfelet från gyroskopoch accelerometermätningar indikerar att realtidsalgoritmen ger ett lägre fel när systemet är statiskt. Det finns dock inga statistiska bevis för förbättringen från resultaten av rotationstesterna.
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Holdship, Simon John. "In search of accurate quantum mechanical solutions to small systems of chemical interest." Thesis, University of Southampton, 1989. https://eprints.soton.ac.uk/421959/.
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Ayyalasomayajula, Haritha. "High-order accurate solution for flow through a turbine linear cascade." Cincinnati, Ohio : University of Cincinnati, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=1054757181.
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AYYALASOMAYAJULA, HARITHA. "HIGHER-ORDER ACCURATE SOLUTION FOR FLOW THROUGH A TURBINE LINEAR CASCADE." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054757181.
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Crossley, Amanda Jane. "Accurate and efficient numerical solutions for the Saint Venant equations of open channel flow." Thesis, University of Nottingham, 1999. http://eprints.nottingham.ac.uk/10109/.
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Within the eld of hydraulics there is a growing trend towards the use of computer based models, which have proven to be an invaluable tool in engineering. A range of commercial packages is available which encompass different mathematical models and a variety of solution strategies. A number of problems can be identified with the software currently available, and as a result, research continues into developing better numerical techniques for computational hydraulics. The issues most often addressed by researchers consider the application of faster and more accurate numerical methods, many of which were originally developed for gas dynamics problems. There has been a growing trend in favour of Riemann based methods constructed within the finite volume framework. Such methods are noted for their good conservation and shock capturing capabilities. However, the computational cost of employing theses algorithms can lead to excessively long run times, particularly when higher order mathematical models are used. This often is as a result of stability constraints placed upon explicit schemes, which require the smallest possible time step permitted throughout the grid, to be applied globally. One possibility for improving this situation is to use local time stepping, whereby individual cells are advanced by their own maximum allowable time steps. To incorporate this concept into a transient model requires the development of a suitable integration strategy, to ensure that the solution remains accurate in time. Two such strategies developed for the Euler equations are considered within this thesis for application to the Saint Venant equations of open channel flow. Both techniques have been demonstrated to reduce run times and improve the quality of solutions in the regions of discontinuities. The investigation considers the the first order scheme of Roe, together with a second order extension constructed using a ux limiter approach. he eects of using an upwind based source term treatment, specifically developed for Roe's scheme, are also considered, and the source term calculations are incorporated into the LTS framework. Results are presented for a series of steady state and transient test cases, which illustrate how local time stepping can lead to reduced run times and improved solution accuracy. The results also highlight the benets of using an upwind source term treatment, particularly when variations in the channel geometry occur.
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Platte, Rodrigo B. "Accuracy and stability of global radial basis function methods for the numerical solution of partial differential equations." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 8.72Mb, 143 p, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3181853.
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Lynch, M. A. M. "Accurate and efficient algorithms for the approximate solution of large hyperbolic problems." Thesis, Heriot-Watt University, 1992. http://hdl.handle.net/10399/1473.
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Pearson, M. L. "Strategy and strategy change in the solution of three term series problems under instructions stressing accuracy over speed." Thesis, Open University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355000.
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Ashraf, El-kutb Mousa. "Characteristics of Wet Tropospheric Delay Deduced from Water Vapor Radiometer Data and Their Implications for GPS Baseline Solution Accuracy." 京都大学 (Kyoto University), 1997. http://hdl.handle.net/2433/202445.
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Choudhary, Aniruddha. "Verification of Compressible and Incompressible Computational Fluid Dynamics Codes and Residual-based Mesh Adaptation." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51169.
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Code verification is the process of ensuring, to the degree possible, that there are no algorithm deficiencies and coding mistakes (bugs) in a scientific computing simulation. In this work, techniques are presented for performing code verification of boundary conditions commonly used in compressible and incompressible Computational Fluid Dynamics (CFD) codes. Using a compressible CFD code, this study assesses the subsonic inflow (isentropic and fixed-mass), subsonic outflow, supersonic outflow, no-slip wall (adiabatic and isothermal), and inviscid slip-wall. The use of simplified curved surfaces is proposed for easier generation of manufactured solutions during the verification of certain boundary conditions involving many constraints. To perform rigorous code verification, general grids with mixed cell types at the verified boundary are used. A novel approach is introduced to determine manufactured solutions for boundary condition verification when the velocity-field is constrained to be divergence-free during the simulation in an incompressible CFD code. Order of accuracy testing using the Method of Manufactured Solutions (MMS) is employed here for code verification of the major components of an open-source, multiphase flow code - MFIX. The presence of two-phase governing equations and a modified SIMPLE-based algorithm requiring divergence-free flows makes the selection of manufactured solutions more involved than for single-phase, compressible flows. Code verification is performed here on 2D and 3D, uniform and stretched meshes for incompressible, steady and unsteady, single-phase and two-phase flows using the two-fluid model of MFIX.
In a CFD simulation, truncation error (TE) is the difference between the continuous governing equation and its discrete approximation. Since TE can be shown to be the local source term for the discretization error, TE is proposed as the criterion for determining which regions of the computational mesh should be refined/coarsened. For mesh modification, an error equidistribution strategy to perform r-refinement (i.e., mesh node relocation) is employed. This technique is applied to 1D and 2D inviscid flow problems where the exact (i.e.,
analytic) solution is available. For mesh adaptation based upon TE, about an order of magnitude improvement in discretization error levels is observed when compared with the uniform mesh.Ph. D.
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Stern, Louis G. "An explicitly conservative method for time-accurate solution of hyperbolic partial differential equations on embedded Chimera grids /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/6758.
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Raghuvanshi, Anurag. "Characterization of Airborne Antenna Group Delay as a Function of Arrival Angle and its Impact on Accuracy and Integrity of the Global Positioning System." Ohio University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1533314646617932.
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Previti, Alberto <1985>. "Fast and accurate numerical solutions in some problems of particle and radiation transport: synthetic acceleration for the method of short characteristics, Doppler-broadened scattering kernel, remote sensing of the cryosphere." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6599/.
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The aim of this work is to present various aspects of numerical simulation of particle and radiation transport for industrial and environmental protection applications, to enable the analysis of complex physical processes in a fast, reliable, and efficient way.
In the first part we deal with speed-up of numerical simulation of neutron transport for nuclear reactor core analysis.
The convergence properties of the source iteration scheme of the Method of Characteristics applied to be heterogeneous structured geometries has been enhanced by means of Boundary Projection Acceleration, enabling the study of 2D and 3D geometries with transport theory without spatial homogenization.
The computational performances have been verified with the C5G7 2D and 3D benchmarks, showing a sensible reduction of iterations and CPU time.
The second part is devoted to the study of temperature-dependent elastic scattering of neutrons for heavy isotopes near to the thermal zone.
A numerical computation of the Doppler convolution of the elastic scattering kernel based on the gas model is presented, for a general energy dependent cross section and scattering law in the center of mass system.
The range of integration has been optimized employing a numerical cutoff, allowing a faster numerical evaluation of the convolution integral.
Legendre moments of the transfer kernel are subsequently obtained by direct quadrature and a numerical analysis of the convergence is presented.
In the third part we focus our attention to remote sensing applications of radiative transfer employed to investigate the Earth's cryosphere.
The photon transport equation is applied to simulate reflectivity of glaciers varying the age of the layer of snow or ice, its thickness, the presence or not other underlying layers, the degree of dust included in the snow, creating a framework able to decipher spectral signals collected by orbiting detectors.Questo lavoro si propone di presentare diversi aspetti della simulazione numerica del trasporto di particelle e di radiazione per applicazioni industriali e di protezione ambientale, per consentire l'analisi di processi fisici complessi in modo veloce, affidabile ed efficiente. Nella prima parte è trattata la velocizzazione della simulazione numerica del trasporto di neutroni per l'analisi del nocciolo di un reattore nucleare. Le proprietà di convergenza della source iteration del Metodo delle Caratteristiche applicate a geometrie strutturate eterogenee sono state migliorate per mezzo della Boundary Projection Acceleration, consentendo lo studio di geometrie 2D e 3D con la teoria del trasporto senza omogeneizzazione spaziale. Le prestazioni computazionali sono state verificate tramite il benchmark C5G7 2D e 3D, mostrando una sensibile riduzione del numero di iterazioni e del tempo di calcolo. La seconda parte è dedicata allo studio dello scattering elastico dei neutroni con isotopi pesanti in funzione della temperatura vicino alla zona termica. È presentato il calcolo numerico della convoluzione Doppler del kernel di scattering elastico col modello gas per una generale sezione d'urto dipendente dall'energia e per una generica legge di scattering nel sistema del centro di massa. L'intervallo di integrazione è stata ottimizzato utilizzando un cutoff numerico, consentendo una valutazione numerica più veloce dell'integrale. I momenti di Legendre del kernel di trasferimento sono successivamente ottenuti per quadratura diretta e validati tramite un'analisi numerica della convergenza. La terza parte è focalizzata alle applicazioni di telerilevamento del trasferimento radiativo per indagini sulla criosfera terrestre. L'equazione del trasporto per fotoni è applicata per simulare la riflettività dei ghiacciai a diverse età dello strato di neve o ghiaccio, al suo spessore, alla presenza o meno di altri strati sottostanti, al grado di polvere inclusa nella neve, creando un sistema in grado di decifrare segnali spettrali raccolti dai rivelatori orbitanti.
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Hardy, Benjamin Arik. "A New Method for the Rapid Calculation of Finely-Gridded Reservoir Simulation Pressures." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd1123.pdf.
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Yeh, Wen-Kai, and 葉文凱. "Accuracy analysis of navigational solutions using double- differenced C/A code psuedoranges." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/85313266617091043874.
Full textAbstract:
碩士國立成功大學
測量工程學系
83
The fast development of the Global Positioning System has made the GPS-based Automatic Vehicle Location and Navigation (AVLN) systems in creaasingly popular.By far, most of the ground vehicle navigation systems have employed the differential GPS method for positioning. The accuracy of navigational receivers using C/A code pseudorange position has been on the order of 5 - 10 meters. This study focus on a C/A code psuedorange double difference technique that combines the C/A code psuedorange measurments at a reference station and at a moving platform to generate an optimal navigation solution. For the purpose of continuous positioning, a supplementary positioning system is also incorported to overcome the problem of signal blocking. fully describe the characteristics of a moving platform and achieve system integration the Extended Kalman Filter is adopted to obtain smooth trajectory solutions. Experiments were conducted to evaluate the performance of the navigation solution from using C/A code psuedurange double difference measurement and fromusing a DGPS method. The results from the tests using a static and a kinematic method show that the accuracy and stability of C/A code measurements with double difference is better than the DGPS. Also,in a short time of singal-shelled condition for supplementary positioning system has functioned properly to achieve the goal of continuos positioning.
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"Improved accuracy of numerical solutions of coupled Stokes and Darcy flows based on boundary integrals." Tulane University, 2007.
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This thesis is focused on developing a numerical method for solving a problem where fluid flow governed by Stokes equations is coupled with flow through a porous medium which is governed by Darcy's equations. For closed smooth boundaries, flow in each region is represented as boundary integrals with densities to be determined to satisfy the boundary conditions. With the solution in this form the dimension of the problem reduces but the integrands are singular. The proposed numerical method is based on regularizing the integrands and discretizing the integrals by a quadrature. The numerical error is discussed and some convergence results are shown for Stokes flow in 3D. A way of reducing the error is discussed. Next, the fluid quantities in two dimensions are reformulated as single and double layer potentials and a solution method with higher accuracy is proposed. It is based on regularizing the kernels and subtracting the highest regularization error term. The method is applied to several test cases of Stokes and Darcy flows, and an increase of the convergence rate from first to second is observed. In the coupled case, the two solutions are coupled through appropriate interface conditions, which in this case do not require the velocity to be continuous. An example of a coupled problem is presented A fast summation technique for impulse methods in three dimensions is presented. Impulse methods provide a representation of Euler flows in terms of impulse variables. The fundamental solution of Darcy flow is a potential dipole, thus this is a robust method for computing Darcy velocity for dense gridsacase@tulane.edu
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Schofield, Grady Lynn. "Computing accurate solutions to the Kohn-Sham problem quickly in real space." Thesis, 2014. http://hdl.handle.net/2152/25983.
Full textAbstract:
Matter on a length scale comparable to that of a chemical bond is governed by the theory of quantum mechanics, but quantum mechanics is a many body theory, hence for the sake of chemistry or solid state physics, finding solutions to the governing equation, Schrodinger's equation, is hopeless for all but the smallest of systems. As the number of electrons increases, the complexity of solving the equations grows rapidly without bound. One way to make progress is to treat the electrons in a system as independent particles and to attempt to capture the many-body effects in a functional of the electrons' density distribution. When this approximation is made, the resulting equation is called the Kohn-Sham equation, and instead of requiring solving for one function of many variables, it requires solving for many functions of the three spatial variables. This problem turns out to be easier than the many body problem, but it still scales cubically in the number of electrons. In this work we will explore ways of obtaining the solutions to the Kohn-Sham equation in the framework of real-space pseudopotential density functional theory. The Kohn-Sham equation itself is an eigenvalue problem, just as Schrodinger's equation. For each electron in the system, there is a corresponding eigenvector. So the task of solving the equation is to compute many eigenpairs of a large Hermitian matrix. In order to mitigate the problem of cubic scaling, we develop an algorithm to slice the spectrum into disjoint segments. This allows a smaller eigenproblem to be solved in each segment where a post-processing step combines the results from each segment and prevents double counting of the eigenpairs. The efficacy of this method depends on the use of high order polynomial filters that enhance only a segment of the spectrum. The order of the filter is the number of matrix-vector multiplication operations that must be done with the Hamiltonian. Therefore the performance of these operations is critical. We develop a scalable algorithm for computing these multiplications and introduce a new density functional theory code implementing the algorithm.text
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Chen, Lan Chung, and 陳嵐中. "Very High Accurate Solutions of Motz's Problem by The Conformal Transformation Method." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/55033446222464324381.
Full textAbstract:
碩士國立中山大學
應用數學系
87
For the benchmark of singularity problems, Motz's problem, two most accurate numerical methods are provided: (1) The conformal transformation method (CTM) for the leading coefficients in the solution expansions. (2) The boundary approximation methods (BAM) for the entire solutions. In this paper, new analysis on truncation and rounding errors is made to guarantee very high accuracy of singular coefficients of the Motz solutions. Most importantly, we provide the following most accurate leading coefficients of the Motz solutions ever published so far, which may be used to test new algorithms for singularity problems in the 21th century.
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(7485122), Miaomiao Ma. "Accuracy Explicitly Controlled H2-Matrix Arithmetic in Linear Complexity and Fast Direct Solutions for Large-Scale Electromagnetic Analysis." Thesis, 2019.
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The design of advanced engineering systems generally results in large-scale numerical problems, which require efficient computational electromagnetic (CEM) solutions. Among existing CEM methods, iterative methods have been a popular choice since conventional direct solutions are computationally expensive. The optimal complexity of an iterative solver is O(NNitNrhs) with N being matrix size, Nit the number of iterations and Nrhs the number of right hand sides. How to invert or factorize a dense matrix or a sparse matrix of size N in O(N) (optimal) complexity with explicitly controlled accuracy has been a challenging research problem. For solving a dense matrix of size N, the computational complexity of a conventional direct solution is O(N3); for solving a general sparse matrix arising from a 3-D EM analysis, the best computational complexity of a conventional direct solution is O(N2). Recently, an H2-matrix based mathematical framework has been developed to obtain fast dense matrix algebra. However, existing linear-complexity H2-based matrix-matrix multiplication and matrix inversion lack an explicit accuracy control. If the accuracy is to be controlled, the inverse as well as the matrix-matrix multiplication algorithm must be completely changed, as the original formatted framework does not offer a mechanism to control the accuracy without increasing complexity.
In this work, we develop a series of new accuracy controlled fast H2 arithmetic, including matrix-matrix multiplication (MMP) without formatted multiplications, minimal-rank MMP, new accuracy controlled H2 factorization and inversion, new accuracy controlled H2 factorization and inversion with concurrent change of cluster bases, H2-based direct sparse solver and new HSS recursive inverse with directly controlled accuracy. For constant-rank H2-matrices, the proposed accuracy directly controlled H2 arithmetic has a strict O(N) complexity in both time and memory. For rank that linearly grows with the electrical size, the complexity of the proposed H2 arithmetic is O(NlogN) in factorization and inversion time, and O(N) in solution time and memory for solving volume IEs. Applications to large-scale interconnect extraction as well as large-scale scattering analysis, and comparisons with state-of-the-art solvers have demonstrated the clear advantages of the proposed new H2 arithmetic and resulting fast direct solutions with explicitly controlled accuracy. In addition to electromagnetic analysis, the new H2 arithmetic developed in this work can also be applied to other disciplines, where fast and large-scale numerical solutions are being pursued.
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(10731936), Hao Li. "Accuracy and Monotonicity of Spectral Element Method on Structured Meshes." Thesis, 2021.
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On rectangular meshes, the simplest spectral element method for elliptic equations is the classical Lagrangian Qk finite element method with only (k+1)-point Gauss-Lobatto quadrature, which can also be regarded as a finite difference scheme on all Gauss-Lobatto points. We prove that this finite difference scheme is (k + 2)-th order accurate for k ≥ 2, whereas Qk spectral element method is usually considered as a (k + 1)-th order accurate scheme in L2-norm. This result can be extended to linear wave, parabolic and linear Schrödinger equations.
Additionally, the Qk finite element method for elliptic problems can also be viewed as a finite difference scheme on all Gauss-Lobatto points if the variable coefficients are replaced by their piecewise Qk Lagrange interpolants at the Gauss Lobatto points in each rectangular cell, which is also proven to be (k + 2)-th order accurate.
Moreover, the monotonicity and discrete maximum principle can be proven for the fourth order accurate Q2 scheme for solving a variable coefficient Poisson equation, which is the first monotone and high order accurate scheme for a variable coefficient elliptic operator.
Last but not the least, we proved that certain high order accurate compact finite difference methods for convection diffusion problems satisfy weak monotonicity. Then a simple limiter can be designed to enforce the bound-preserving property when solving convection diffusion equations without losing conservation and high order accuracy.
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Sleiman, Mohamad. "A time-accurate finite element solution of the Navier-Stokes equations." Thesis, 1995. http://spectrum.library.concordia.ca/4740/1/MM01358.pdf.
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Tsang, Winnie. "Helping hand : an anatomically accurate inverse dynamics solution for unconstrained hand motion." 2005. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=362353&T=F.
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Chang, Jyh-Ren, and 張志仁. "Precise Orbit Determination and High Accurate Baseline Solution Using Regional GPS Network." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/94656043366799106299.
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Ho, Kung-Chu, and 何恭竹. "Investigation of Low Frequency Electrolytic Solution Behavior with an Accurate Electrical Impedance Method." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/01360196187680115271.
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博士國立臺灣大學
電子工程學研究所
105
This dissertation reports the investigation of strong univalent electrolytic solutions with a low-frequency electrical impedance method realized through a specific microfluidic device and high resolution instruments. We have shown the better repeatability and accuracy of the proposed impedance method, especially in the lower end of the investigated frequency regime. Moreover, the experimental data shows higher accuracy in the cases of concentrated electrolytic solutions. As verified by the experimentally measured data, the electrolytic behavior reveals strong frequency dispersion relation at low frequencies because dissolved ions not only accumulate at the electrode-electrolyte interface but also align themselves in the microfluidic device along the electric field direction. At higher frequencies, the periodic reversal of the electric field represents so fast that the ions behave less diffuse in the direction of the electric field. Therefore, the improved mobility of ionic carriers is responsible for the conduction mechanism. For the same electrolytic sample, the relaxation frequency of concentrated electrolytes becomes higher owing to the stronger total polarization coming from the higher conductivity as well as the lower resistance in the electrolytes, which is obvious in the concentration above 10-4 M. With the same concentration, the acidic electrolytes represent the highest conductivity, which can be ascribed to the extra assistance of proton transfer mechanism between hydronium ions and water molecules. What’s more, all electrolytic solutions appear the so-called relaxation frequency at each peak value of dielectric loss due to relaxing total polarization inside the solution device. The relaxation frequency of acidic electrolytes also becomes higher because of the proton transfer, which results in the higher conductivity as well as the lower bulk resistance in the acidic electrolytic solutions. Finally, we derived an AC conductivity in the electrolytic solution base on a second-order Newton differential equation of motion, then solved an optimal numerical solution by applying the least square error method (LSEM). We found that the tendency of the frequency-dependent mobility in our experiment is highly correlated to the conventional literatures, especially in the lower end of the frequency, that is, approaching to DC condition, which is sufficient to prove the high potential of predicting ability of the theoretical model. The results of this dissertation is expected to apply on the liquid circuit device development. We hope to further realize the ion movement from the experiment to seek the possibility of developing novel liquid devices with frequency-tunable dielectric constant. Based on this idea, a novel light valve with tunable amount of light output can be designed. That is, the gray scale can be changed. Then the conventional liquid crystal technology can be entirely replaced if the related technology has been well-developed.
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Ching-te, Hwang, and 黃景德. "Accurate one-dimensional approximate solutions and critical heat transfer characteristics analysis of an insulated oval duct." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/85050551977920241246.
Full textAbstract:
碩士崑山科技大學
機械工程研究所
94
Conventional unreliable heat transfer results of an insulated oval duct are generated by an inaccurate approximation of an oval perimeter equation. The greater the long-short-axes ratio, the bigger the error becomes. On the other hand, the present results are based on very accurate oval perimeters obtained by an integral method. The one-dimensional results of PWTR and 91-CPWTR models are compared with those of numerical results. It is found that in practical situations, that is, long-short-axes ratio is less or equal to 3.5, satisfactory and reliable solutions can be obtained by the one-dimensional PWTR model. However, when the long-short-axes ratio is greater than 3.5, accurate and reliable solutions can only be achieved by the one-dimensional 9-1CPWTR model, which returns most errors within ±0.5 % for situations of practical duct sizes and insulated thickness (t/R2＜0.5). Even in situations of a extraordinary large insulated thickness (t/R2=2.0), most errors are within ±2 %. Apart from this, the heat transfer characteristics of critical and neutral thickness of a very small insulated oval duct are also investigated in this study. It is found that the critical heat transfer characteristics of a very small insulated oval duct are different from those of an equivalent insulated circular duct. The bigger the long-short-axes ratio is, the greater difference becomes. In here, results are presented along with the change of dimensionless duct size or/and long-short-axes ratio.
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Dunsmore, Marnie. "A versatile and accurate 2-D solution of finite and infinite extent coplanar waveguide." Thesis, 1995. http://hdl.handle.net/2429/3552.
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Two rapidly converging 2-D models are proposed for the CPW static field problem. Numerical solution of the
Finite-Extent CPW static field problem yields two singularities, one due to the edge singularity behavior of the
charge, and the other due to the Green's function singularity when the source point x and field point x' are coincident.
The infinite extent CPW static field problem has both these singularities as well as a Green's function singularity
in the limit as the field point x' —>o°. The rapid convergence of these problems is obtained by extracting the Green's
function singularities and then treating the charge edge singularities using Gauss-Chebychev quadrature. These models
are easily adapted to different dielectric substrate configurations, including, but not confined to conventional free
standing CPW and conductor-backed CPW. This is achieved using a complex image space domain Green's function
which is both accurate and rapidly converging. Using the complex image Green's function, the extraction of singularities
and Gauss-Chebychev quadrature, the Finite-Extent and infinite extent CPW static field problems are solved for
the charge distribution, characteristic impedance and effective dielectric constant. The characteristic impedance and
effective dielectric constant results are compared against conformal mapping results. The charge distribution results
are compared against results obtained from electrooptic sampling. It is demonstrated that the models in this thesis are
accurate and show an improvement in convergence time of between one and two orders of magnitude compared to
existing CPW models.
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Towne, Aaron S. "Advancements in Jet Turbulence and Noise Modeling: Accurate One-Way Solutions and Empirical Evaluation of the Nonlinear Forcing of Wavepackets." Thesis, 2016. https://thesis.library.caltech.edu/9361/7/AST_thesis_final.pdf.
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Jet noise reduction is an important goal within both commercial and military aviation. Although large-scale numerical simulations are now able to simultaneously compute turbulent jets and their radiated sound, lost-cost, physically-motivated models are needed to guide noise-reduction efforts. A particularly promising modeling approach centers around certain large-scale coherent structures, called wavepackets, that are observed in jets and their radiated sound. The typical approach to modeling wavepackets is to approximate them as linear modal solutions of the Euler or Navier-Stokes equations linearized about the long-time mean of the turbulent flow field. The near-field wavepackets obtained from these models show compelling agreement with those educed from experimental and simulation data for both subsonic and supersonic jets, but the acoustic radiation is severely under-predicted in the subsonic case. This thesis contributes to two aspects of these models. First, two new solution methods are developed that can be used to efficiently compute wavepackets and their acoustic radiation, reducing the computational cost of the model by more than an order of magnitude. The new techniques are spatial integration methods and constitute a well-posed, convergent alternative to the frequently used parabolized stability equations. Using concepts related to well-posed boundary conditions, the methods are formulated for general hyperbolic equations and thus have potential applications in many fields of physics and engineering. Second, the nonlinear and stochastic forcing of wavepackets is investigated with the goal of identifying and characterizing the missing dynamics responsible for the under-prediction of acoustic radiation by linear wavepacket models for subsonic jets. Specifically, we use ensembles of large-eddy-simulation flow and force data along with two data decomposition techniques to educe the actual nonlinear forcing experienced by wavepackets in a Mach 0.9 turbulent jet. Modes with high energy are extracted using proper orthogonal decomposition, while high gain modes are identified using a novel technique called empirical resolvent-mode decomposition. In contrast to the flow and acoustic fields, the forcing field is characterized by a lack of energetic coherent structures. Furthermore, the structures that do exist are largely uncorrelated with the acoustic field. Instead, the forces that most efficiently excite an acoustic response appear to take the form of random turbulent fluctuations, implying that direct feedback from nonlinear interactions amongst wavepackets is not an essential noise source mechanism. This suggests that the essential ingredients of sound generation in high Reynolds number jets are contained within the linearized Navier-Stokes operator rather than in the nonlinear forcing terms, a conclusion that has important implications for jet noise modeling.
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Alberto, José Miguel Mamede Albuquerque Vieira. "MATHEMATICAL APPROACH FOR AN ACCURATE SOLUTION OF THE CIRCUIT MODEL OF RESONATOR ARRAYS FOR INDUCTIVE POWER TRANSFER." Doctoral thesis, 2018. http://hdl.handle.net/10316/80431.
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Meunier, Quentin. "Étude de deux solutions pour le support matériel de la programmation parallèle dans les multiprocesseurs intégrés : vol de travail et mémoires transactionnelles." Phd thesis, 2010. http://tel.archives-ouvertes.fr/tel-00532794.
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L'avènement des puces multicoeurs repose certaines questions quant aux moyens d'écrire les programmes, qui doivent alors intégrer un degré élevé de parallélisme. Nous abordons cette question par l'intermédiaire de deux points de vue orthogonaux. Premièrement via le paradigme du vol de travail, pour lequel nous effectuons une étude visant d'une part à rechercher quelles sont les caractéristiques architecturales simples donnant les meilleures performances pour une implémentation de ce paradigme ; et d'autre part à montrer que le surcout par rapport à une parallélisation statique est faible tout en permettant des gains en performances grâce à l'équilibrage dynamique des charges. Cette question est néanmoins surtout abordée via le paradigme de programmation à base de transactions -- ensemble d'instructions s'exécutant de manière atomique du point de vue des autres coeurs. Supporter cette abstraction nécessite l'implantation d'un système dit TM, souvent complexe, pouvant être logiciel ou matériel. L'étude porte premièrement sur la comparaison de systèmes TM matériels basés sur des choix architecturaux différents (protocole de cohérence de cache), puis sur l'impact d'un point de vue performances de plusieurs politiques de résolution des conflits, autrement dit des actions à prendre quand deux transactions essaient d'accéder simultanément les mêmes données.
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Hsieh, Meng-Shu, and 謝孟書. "An accurate solution to the clinical unmet need for the diagnosis of treatment-experienced Helicobacter Pylori:Gastric juice-based PCR assay." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/34053500939572449559.
Full textAbstract:
碩士高雄醫學大學
臨床醫學研究所
105
Background The culture method has been strongly emphasized in the clinical setting of Helicobacter pylori (H. pylori) eradication failure because retreatment strategy can be tailored based on the culture antibiotics susceptibility test. However, the culture method yields low accuracy, especially in treatment-experienced H. pylori infection. The current clinical unmet need in the setting of treatment-experienced H. pylori infection is one diagnostic method with satisfying accuracy as well as the ability to perform the antibiotics susceptibility test. Theoretically, gastric juiced-based PCR is able to provide both strengths, but there is no clinical data. Our study intended to provide the data regarding the diagnostic accuracy of gastric juice-based PCR in the treatment-experienced H. pylori infection and compare the results of gastric juice-based PCR with that of the culture method. Methods We included 711 patients and categorized them into 4 groups based on their previous treatment history: treatment-naïve, post 1st line therapy, post 2nd line therapy and post 3rd line therapy. The status of H. pylori infection in each subject was confirmed according to the following clinical gold standards: concordant positive histology and rapid urease test or positive urease breath test. We performed gastric juice-based PCR and culture in each subject and then calculated the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of gastric juice-based PCR as well as culture method. Finally, we compared the results with Fisher’s exact test. Results Our findings demonstrated that the accuracy of gastric juice-based PCR was higher than that of the traditional culture method in treatment-naïve patients (96% vs 87%, p values = 0.0001), in patients post 1st line therapy (97% vs 79%, p values = 0.0002), in patients post 2nd line therapy (96% vs 77%, p values = 0.0012) and in patients post 3rd line therapy (100% vs 70%, p values = 0.0092). The sensitivity of gastric juice-based PCR was also better than that of the traditional culture method in treatment-naïve patients (92% vs 58%, p values < 0.0001), in patients post 1st line therapy (90% vs 35%, p values < 0.0001), in patients post 2nd line therapy (93% vs 60%, p values = 0.0006) and in patients post 3rd line therapy (100% vs 22%, p values = 0.0023). The specificity, positive predictive and negative predictive values were calculated as well. The results indicated that gastric juice-based PCR outperformed the traditional culture method in diagnosis of treatment-experienced H pylori. Conclusion The gastric juice-based PCR yields more accurate diagnosis in treatment-experienced H. pylori than the traditional culture method and also provides the anti-microbial susceptibility test to guide subsequent retreatment therapy. Our study demonstrated that gastric juice-based PCR suits the current unmet need for the management of treatment-experienced H pylori and has very promising potential for widespread application in the setting of treatment failure.