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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Stabilizer Codes over Frobenius Rings

Nadella, Sushma 2012 May 1900 (has links)
In quantum information processing, the information is stored in the state of quantum mechanical systems. Since the interaction with the environment is unavoidable, there is a need for quantum error correction to protect the stored information. Until now, the methods for quantum error correction were mainly based on quantum codes that rely on the arithmetic in finite fields. In contrast, this thesis aims to develop a basic framework for quantum error correcting codes over a class of rings known as the Frobenius rings. This thesis focuses on developing the theory of stabilizer codes over the Frobenius rings and provides a systematic construction of codes over these rings. A special class of Frobenius rings called finite chain rings will be the emphasis of this thesis. The theory needed for comparing the minimum distance of stabilizer codes over the finite chain rings to that over the fields is studied in detail. This thesis finally derives that the minimum distance of stabilizer codes over finite chain rings cannot exceed the minimum distance over the fields.
2

The stabilizer of the group determinant and bounds for Lehmer's conjecture on finite abelian groups

Vipismakul, Wasin 23 October 2013 (has links)
Given a finite group G of cardinality N, the group determinant [theta]G associated to G is a homogeneous polynomial in N variables of degree N. We study two properties of [theta]G. First we determine the stabilizer of [theta](G) under the action of permuting its variables. Then we also prove that the Lehmer's constant for any finite abelian group must satisfy a system of congruence equations. In particular when G is a p-group, we can strengthen the result to establish upper and lower bounds for the Lehmer's constant. / text
3

Design and Stress Analysis of Dynamic Spinal Stabilizers

Ishii, Kohki 01 December 2010 (has links)
A dynamic lumbar spinal stabilizer with a helical machined spring element was created in the first stage. The stabilizer was built with 30 N/mm of axial stiffness because if the human body is moved to flexion and extension, this amount of a compressive and tensile load would be applied to the intervertebral disc. The stabilizer supports the loads instead of the disc. The stiffness was influenced by the number of coils, the thickness of coils, and length of the coil element. The stiffness can be determined by analytical equations or by finite element analysis (FE), such as ANSYS Workbench. In the second stage, the lumbar spine FE model was successfully constructed by using Autodesk Inventor 2010. There were three different analyzed models; (1) intact model, (2) fused model, and (3) dynamically stabilized model. This intact model is a simplified and basic model used for fused model and dynamically stabilized model. The range of motion (ROM) was the key term in this study. In other words, examination of each model was based on how much ROM was shown when the flexion, extension, and bending moments have been applied on the spine. The ROM of each model with three moments produced appropriate values compared to the references. The stress analysis is also important to optimize the design of the dynamic stabilizer. The maximum stress was 472 MPa on the stabilizer that is less than yield strength of Titanium alloy.
4

Upper bounds on minimum distance of nonbinary quantum stabilizer codes

Kumar, Santosh 01 November 2005 (has links)
The most popular class of quantum error correcting codes is stabilizer codes. Binary quantum stabilizer codes have been well studied, and Calderbank, Rains, Shor and Sloane (July 1998) have constructed a table of upper bounds on the minimum distance of these codes using linear programming methods. However, not much is known in the case of nonbinary stabilizer codes. In this thesis, we establish a bridge between selforthogonal classical codes over the finite field containing q2 elements and quantum codes, extending and unifying previous work by Matsumoto and Uyematsu (2000), Ashikhmin and Knill (November 2001), Kim and Walker (2004). We construct a table of upper bounds on the minimum distance of the stabilizer codes using linear programming methods that are tighter than currently known bounds. Finally, we derive code construction techniques that will help us find new codes from existing ones. All these results help us to gain a better understanding of the theory of nonbinary stabilizer codes.
5

Upper bounds on minimum distance of nonbinary quantum stabilizer codes

Kumar, Santosh 01 November 2005 (has links)
The most popular class of quantum error correcting codes is stabilizer codes. Binary quantum stabilizer codes have been well studied, and Calderbank, Rains, Shor and Sloane (July 1998) have constructed a table of upper bounds on the minimum distance of these codes using linear programming methods. However, not much is known in the case of nonbinary stabilizer codes. In this thesis, we establish a bridge between selforthogonal classical codes over the finite field containing q2 elements and quantum codes, extending and unifying previous work by Matsumoto and Uyematsu (2000), Ashikhmin and Knill (November 2001), Kim and Walker (2004). We construct a table of upper bounds on the minimum distance of the stabilizer codes using linear programming methods that are tighter than currently known bounds. Finally, we derive code construction techniques that will help us find new codes from existing ones. All these results help us to gain a better understanding of the theory of nonbinary stabilizer codes.
6

Classical solutions for D-branes in AdS

Parra Milián, S [UNESP] 12 August 2014 (has links) (PDF)
Made available in DSpace on 2015-09-17T15:24:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-08-12. Added 1 bitstream(s) on 2015-09-17T15:47:47Z : No. of bitstreams: 1 000844745.pdf: 560125 bytes, checksum: 6adc853f60c4ad9ad7a288228990dea7 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No presente trabalho comprometemo-nos ao estudo de soluções clássicas para D-branas no espaço de Anti-de Sitter, as quais surgem da solução de órbita do subgrupo estabilizador de um ponto na fronteira no espaço AdS. Começamos por fazer uma breve revisão da teoria de supercordas e apresentamos algumas características da geometria do espaço AdS. Então fazemos uma discussão sobre a ação efetiva a baixas energias e, por último, escrevemos a ação de uma D3-brana no espaço AdS5. O estudo desta solução particular da D-brana não é completo e acaba por fugir ao escopo deste trabalho. Esperamos complementá-lo num futuro breve e, com isto em mente, concluímos a dissertação com um resumo de deformações marginais da teoria de campo N = 4 SYM e sua gravidade dual / The main result of this dissertation is the study of the classical solutions for D-brane in Anti-de Sitter(AdS) space. They arised from the study of the orbit solution of the stablizer subgroup of a point on the boundary of the AdS space. To reach this goal we started making a brief summary of superstring theories, then we presented some geometric facts of the AdS space. A discussion of the effective low-energy action of a bosonic D-brane was done, then we wrote the action of a single D3-brane in the AdS5 space. Unfortunately, the study of this particular D-brane solution is not complete and goes beyond the scope of this dissertation. We intend to complete this work in the future, with this in mind a summary of the marginal deformation of N = 4 SYM field theory and its gravity dual were given in the last chapter / CAPES: 33015015001P7
7

Classical solutions for D-branes in AdS /

Parra Milián, S., (Segundo) January 2014 (has links)
Orientador: Andrey Yuryevich Mikhaylov / Banca: Nathan Jacob Berkovits / Banca: Vladimir Perchine / Resumo: No presente trabalho comprometemo-nos ao estudo de soluções clássicas para D-branas no espaço de Anti-de Sitter, as quais surgem da solução de órbita do subgrupo estabilizador de um ponto na fronteira no espaço AdS. Começamos por fazer uma breve revisão da teoria de supercordas e apresentamos algumas características da geometria do espaço AdS. Então fazemos uma discussão sobre a ação efetiva a baixas energias e, por último, escrevemos a ação de uma D3-brana no espaço AdS5. O estudo desta solução particular da D-brana não é completo e acaba por fugir ao escopo deste trabalho. Esperamos complementá-lo num futuro breve e, com isto em mente, concluímos a dissertação com um resumo de deformações marginais da teoria de campo N = 4 SYM e sua gravidade dual / Abstract: The main result of this dissertation is the study of the classical solutions for D-brane in Anti-de Sitter(AdS) space. They arised from the study of the orbit solution of the stablizer subgroup of a point on the boundary of the AdS space. To reach this goal we started making a brief summary of superstring theories, then we presented some geometric facts of the AdS space. A discussion of the effective low-energy action of a bosonic D-brane was done, then we wrote the action of a single D3-brane in the AdS5 space. Unfortunately, the study of this particular D-brane solution is not complete and goes beyond the scope of this dissertation. We intend to complete this work in the future, with this in mind a summary of the marginal deformation of N = 4 SYM field theory and its gravity dual were given in the last chapter / Mestre
8

Kinetic stabilization of transthyretin and its role as an inhibitor of Aβ amyloid formation

Nilsson, Lina January 2017 (has links)
Amyloid formation occurs when normally soluble proteins and peptides misfold and aggregate into intractable threadlike structures called fibrils. There are currently more than 30 proteins associated with this aberrant structure, including the Aβ peptide in Alzheimer’s disease (AD) and transthyretin (TTR) in TTR amyloidosis. TTR is a homotetrameric transporter protein present in both cerebrospinal fluid and plasma. Dissociation of its tetrameric structure is required for the formation of amyloid fibrils. Small molecule ligands able to bind and stabilize the tetrameric structure of TTR thus represent a potential therapeutic intervention. Interestingly, apart from TTR’s role as a toxic agent in TTR amyloidosis, it also has a role as an inhibitor of the Aβ toxicity associated with AD. The work presented in this thesis focused on small molecules that have the potential ability to prevent TTR amyloidosis. We also sought to gain a greater understanding of the interaction between TTR and the Aβ peptide with respect to Aβ fibril formation. The ability of a drug to stabilize TTR is directly correlated to its binding affinity. However, since TTR is a plasma protein, it is of great importance that the drug binds selectively to TTR. In paper I, we used a newly developed urea denaturation assay, in combination with isothermal titration calorimetry, to show that, in a complex environment such as plasma, the enthalpy of binding correlates better with a drug’s ability to stabilize TTR than the binding affinity. In paper II, we modified the highly selective but rapidly degraded TTR ligand luteolin in order to increase its resistance against biotransformation. Using a liver-based microsome assay, in combination with HPLC, we show how the luteolin analogues have gained increased stability. However, using the urea assay, we also show that the analogues have lost much of luteolin’s selectivity. In paper III, we show that tetrabromobisphenol A is a highly selective binder of TTR in plasma and is able to rescue cells from TTR-induced toxicity. In paper IV, we studied the interaction of TTR with Aβ and its effect on Aβ fibril formation. We used a ThT fluorescence-based assay and dot blotting to show that TTR inhibits Aβ amyloid formation and promotes the formation of high molecular weight assemblies with an open N-terminus. Using surface plasmon resonance, we further show how TTR is unable to inhibit fibril elongation and instead targets the nucleation processes, both primary and fibril-catalyzed secondary nucleation. To conclude, we present new molecules with the ability to selectively stabilize TTR that can serve as scaffolds in drug design. We also elucidate TTR’s inhibiting effects on toxic Aβ amyloid formation.
9

Design of Gyro Based Roll-Stabilization Controller for a Concept Amphibious Commuter Vehicle

Karagiannis, Ioannis January 2015 (has links)
In this master thesis the gyroscopic stabilization of a two-wheeled amphibious concept vehicle is investigated. The key idea is to neutralize external torques applied on the vehicle by the counter torque produced from the two gyroscopes attached on the vehicle. Here the gyroscopes are used as actuators, not as sensors. When a torque is applied in order to rotate a gyroscope whose flywheel is spinning, then the gyroscope precesses and it generates a moment, orthogonal to both the torque and the spinning axis. This phenomenon is known as gyroscopic precession. As the vehicle leans from its upright position we expect to generate sufficient gyroscopic reaction moment to bring the vehicle back and get it stabilized.   We first derive the equations of motion based on Lagrangian mechanics. It is worth mentioning that we only consider the control dynamics of a static vehicle. This is the so called regulator problem where we try to counteract the effects of disturbances. The trajectory tracking (servo problem) and the water-travelling can be considered as an extension of the current project. We linearize the dynamics around an equilibrium and we study the stability of the linearized model. We then design an LQG controller, a Glover-McFarlane controller and a cascade PID controller. Regarding the implementation part, we only focus on the cascade PID controller. The results from both simulations and experiments with a small-scale prototype are presented and discussed. / <p>MARINTEKNIKDAGAR PÅ KTH 2015</p>
10

Quantum codes over Finite Frobenius Rings

Sarma, Anurupa 2012 August 1900 (has links)
It is believed that quantum computers would be able to solve complex problems more quickly than any other deterministic or probabilistic computer. Quantum computers basically exploit the rules of quantum mechanics for speeding up computations. However, building a quantum computer remains a daunting task. A quantum computer, as in any quantum mechanical system, is susceptible to decohorence of quantum bits resulting from interaction of the stored information with the environment. Error correction is then required to restore a quantum bit, which has changed due to interaction with external state, to a previous non-erroneous state in the coding subspace. Until now the methods for quantum error correction were mostly based on stabilizer codes over finite fields. The aim of this thesis is to construct quantum error correcting codes over finite Frobenius rings. We introduce stabilizer codes over quadratic algebra, which allows one to use the hamming distance rather than some less known notion of distance. We also develop propagation rules to build new codes from existing codes. Non binary codes have been realized as a gray image of linear Z4 code, hence the most natural class of ring that is suitable for coding theory is given by finite Frobenius rings as it allow to formulate the dual code similar to finite fields. At the end we show some examples of code construction along with various results of quantum codes over finite Frobenius rings, especially codes over Zm.

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