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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.
431

A new link lifetime estimation method for greedy and contention-based routing in mobile ad hoc networks

Noureddine, H., Ni, Q., Min, Geyong, Al-Raweshidy, H. January 2014 (has links)
No / Greedy and contention-based forwarding schemes were proposed for mobile ad hoc networks (MANETs) to perform data routing hop-by-hop, without prior discovery of the end-to-end route to the destination. Accordingly, the neighboring node that satisfies specific criteria is selected as the next forwarder of the packet. Both schemes require the nodes participating in the selection process to be within the area that confronts the location of the destination. Therefore, the lifetime of links for such schemes is not only dependent on the transmission range, but also on the location parameters (position, speed and direction) of the sending node and the neighboring node as well as the destination. In this paper, we propose a new link lifetime prediction method for greedy and contention-based routing which can also be utilized as a new stability metric. The evaluation of the proposed method is conducted by the use of stability-based greedy routing algorithm, which selects the next hop node having the highest link stability.
432

Biodynamic Analysis of Human Torso Stability using Finite Time Lyapunov Exponents

Tanaka, Martin L. 15 April 2008 (has links)
Low back pain is a common medical problem around the world afflicting 80% of the population some time in their life. Low back injury can result from a loss of torso stability causing excessive strain in soft tissue. This investigation seeks to apply existing methods to new applications and to develop new methods to assess torso stability. First, the time series averaged finite time Lyapunov exponent is calculated from data obtained during seated stability experiments. The Lyapunov exponent is found to increase with increasing task difficulty. Second, a new metric for evaluating torso stability is introduced, the threshold of stability. This parameter is defined as the maximum task difficulty in which dynamic stability can be maintained for the test duration. The threshold of stability effectively differentiates torso stability at two levels of visual feedback. Third, the state space distribution of the finite time Lyapunov exponent (FTLE) field is evaluated for deterministic and stochastic systems. Two new methods are developed to generate the FTLE field from time series data. Using these methods, Lagrangian coherent structures (LCS) are found for an inverted pendulum, the Acrobot, and planar wobble chair models. The LCS are ridges in the FTLE field that separate two inherently different types of motion when applied to rigid-body dynamic systems. As a result, LCS can be used to identify the boundaries of the basin of stability. Finally, these new methods are used to find the basin of stability from time series data collected from torso stability experiments. The LCS and basins of stability provide a richer understanding into the system dynamics when compared to existing methods. By gaining a better understanding of torso stability, it is hoped this knowledge can be used to prevent low back injury and pain in the future. These new methods may also be useful in evaluating other biodynamic systems such as standing postural sway, knee stability, or hip stability as well as time series applications outside the area of biomechanics. / Ph. D.
433

Stability Analysis of Three-Phase AC Power Systems Based on Measured D-Q Frame Impedances

Wen, Bo 20 January 2015 (has links)
Small-signal stability is of great concern for distributed power systems with a large number of regulated power converters. These converters are constant-power loads (CPLs) exhibit a negative incremental input resistance within the output voltage regulation bandwidth. In the case of dc systems, design requirements for impedances that guarantee stability have been previously developed and are used in the design and specification of these systems. In terms of three-phase ac systems, a mathematical framework based on the generalized Nyquist stability criterion (GNC), reference frame theory, and multivariable control is set forth for stability assessment. However, this approach relies on the actual measurement of these impedances, which up to now has severely hindered its applicability. Addressing this shortcoming, this research investigates the small-signal stability of three-phase ac systems using measured d-q frame impedances. Prior to this research, negative incremental resistance is only found in CPLs as a results of output voltage regulation. In this research, negative incremental resistance is discovered in grid-tied inverters as a consequence of grid synchronization and current injection, where the bandwidth of the phase-locked loop determines the frequency range of the negative incremental resistance behavior, and the power rating of inverter determines the magnitude of the resistance. Prior to this research, grid synchronization stability issue and sub-synchronous oscillations between grid-tied inverter and its nearby rectifier under weak grid condition are reported and analyzed using characteristic equation of the system. This research proposes a more design oriented analysis approach based on the negative incremental resistance concept of grid-tied inverters. Grid synchronization stability issues are well explained under the framework of GNC. Although stability and its margin of ac system can be addressed using source and load impedances in d-q frame, method to specify the shape of load impedances to assure system stability is not reported. This research finds out that under unity power factor condition, three-phase ac system is decoupled. It can be simplified to two dc systems. Load impedances can be then specified to guarantee system stability and less conservative design. / Ph. D.
434

Vliv kompenzace kabelových sítí na stabilitu blízkých zdrojů / Effect of compensation to cable networks on the stability of nearby sources

Popelář, Vojtěch January 2014 (has links)
This thesis deals with the infulence of compensation cabel network on the stability of nearby power source. This issue is topical with the increase in the ratio of cable networks 110 kV in large cities. The work examines the theoretical concept of stability and factors that affect it. Mainly discusses the stability angle rotor of a synchronous machina. The practical part is performed in MODES software, that performs dynamic simulation of the behavior of the model. In this case, it will be behavior of synchronous machine during short-circuit in network at different values of compensation of this network.
435

Solid-state Stability of Antibody-drug Conjugates

Eunbi Cho (11192397) 28 July 2021 (has links)
<p>Antibody-drug conjugates (ADCs) combine the cytotoxicity of traditional chemotherapy with the site-specificity of antibodies by conjugating payloads to antibodies with immunoaffinity. However, the conjugation alters the physicochemical properties of antibodies, increasing the risks of various types of degradation. The effects of common risk factors such as pH, temperature, and light on the stability of ADCs differ from their effects on monoclonal antibodies (mAb) due to these altered physicochemical properties. </p> <p>To date, ADC researchers have developed linkers with improved <i>in vivo</i> stability, and begun to understand the deconjugation mechanisms <i>in vivo</i>. In contrast, the <i>in vitro</i> stability of ADCs has not gained comparable attention. All nine of the U.S. FDA approved ADCs are lyophilized to minimize the potential for degradation. However, there are few studies on the solid-state stability of ADCs. To evaluate lyophilized solids, pharmaceutical development relies heavily on accelerated stability studies, which take months to determine the best formulation. Characterization methods that are often used orthogonally with accelerated studies include Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, near-infrared spectroscopy (NIR), differential scanning calorimetry (DSC), and x-ray powder diffraction (XRPD). Results from these methods are often poorly correlated with stability, however. Thus, stability evaluation of solid-state ADC products, and other recombinant protein drugs, is often a bottleneck in their development.</p> <p>To provide knowledge on how to improve the <i>in vitro</i> stability of lyophilized ADC formulations, the solid-state stability of ADC formulations with varying risk factors was studied in this dissertation project. The first study investigated interactions between an ADC and excipients in terms of solid-state stability enhancement. The second study investigated the process-driven instability of ADCs during lyophilization using various concentrations of ADCs. The first two studies incorporate a new method called solid-state hydrogen/deuterium exchange coupled with mass spectrometry (ssHDX-MS) as an analytical predictor of solid-state stability. The last study investigated the effects of pH on the stability of labile hydrazones, as a model for common linker chemistry used in ADCs. </p>
436

Analysis And Development Of Voltage Stability Assessment Methods

Mahesh, S 06 1900 (has links) (PDF)
Voltage stability is the ability of the power system to maintain steady acceptable voltages at all the buses in a system under normal operating conditions and after being subjected to a disturbance. The increased consumption of electricity without the augmentation of the necessary transmission infrastructure has resulted in the overloading of the transmission lines. As a result, the transmission lines operate near the steady state stability limit. The transmission of large amounts of power through the lines results in the large voltage drops in the lines. Sudden disturbances like line or generator outage and fault in the transmission lines may occur because of natural or man made causes. Under the above mentioned conditions, the transmission system may not be able to supply the load demand. This results in drops in the system bus voltages which may be sudden or progressive. If the necessary remedial measures are not taken, then this may lead to blackout or collapse of the whole system. As a result of a number of voltage stability incidents reported from various countries, there is a widespread interest in understanding, characterizing and preventing this phenomena. This thesis is essentially concerned with analyzing the existing methods and the development of new methods for the assessment of voltage stability of power systems. We examine four existing methods for assessing voltage stability with regard to the computational effort involved in their calculation, the useful information we get by using them, their relative effectiveness in assessing the voltage stability and their consistency in predicting the voltage stability of the system. We also study the impact of the system conditions on several of these indices. Further, we propose a set of new indices which provide information similar to the conventional indices but are slightly different. The generalized circle diagram approach proposed earlier to study the variation of the system variables with respect to the independent node parameters is shown to be adoptable for finding the voltage stability limit of a system. It has been shown that the well known continuation power flow method used for voltage stability analysis is identical to the generalized circle diagram approach. A computationally simple approach, based on the Thevenin equivalent of the power system is used to determine the loadability limit of a system. In the continuation power flow method, it is inherently assumed that only one generator responds to the real power load increase of the system. However, an alternate view is presented where all the generators respond to the real power increase in the system and an algorithm is proposed to realize this condition. Using this algorithm, the generation pattern of the system is modified so as to increase the loadability limit of the system considerably. The origin of the voltage instability in power systems can be traced to the load characteristics. Induction motors constitute a significant proportion of the total industrial and residential loads. Two algorithms that are useful to study the voltage stability of systems having induction machines have been presented and validated. These methods are based on the induction machine static equations. The first method is useful in assessing the impact of network disturbances on voltage stability and the second facilitates the computation of the loadability limit. A criterion has been proposed to find the stability limit, stable and unstable operating regions for a system considering various types of induction motor loads on the basis of which, a practical algorithm is proposed and validated to determine the stability of the induction motors driving different types of loads in a large power system. In addition, a method is developed to determine the stability aspects when the constant torque loads and the constant input power loads driven by induction motors operate in a power system, which contains other types of loads like the constant P - Q type of loads. Switching capacitors at the induction motor terminals is one of the ways by which voltage instability occurring due to the induction motor loads can be prevented. A new technique is proposed wherein knowing the capacitance and the slip at the instant of switching, the rotor dynamics following the switching and the existence of a steady state operating point following the switching can be predicted. This approach can be used to choose appropriate capacitances to be switched at the induction motor terminals to prevent its stalling following a sudden load disturbance.
437

Optimization of the hull shape of a specialized vessel used to deploy wave energy converters

Larsson, Simon January 2016 (has links)
In this study, the initial hydrostatic stability, the hydrostatic stability and the structure realibility of three different barge-shaped vessels is simulated and evaluated in order to see which of the vessels would be the most optimal to use for deployment of wave energy converters, WECs. The vessels differ in their hull type: Bulbous-bow hull vessel, Barge hull vessel and Modified-barge hull vessel. In order to do the evaluation, the hull of each vessel is designed in DELFTship and further design is proceeded in SolidWorks 2014. Structural strength analysis is performed in SolidWorks 2014 and hydrostatic properties are simualted in Ansys Aqwa 16.0. The collected results are pointing at that the Modified-barge hull vessel is slightly superior to the others in terms of hydrostatic stability, while the structure stability is equal. The results of this study will provide a foundation for further evaluation of vessels capable of deploying wave energy converters.
438

Zhodnocení územního systému ekologické stability ve vybrané lokalitě a návrh doplnění / Evaluation of the territorial system of ecological stability in the selected locality and the proposal for its completion

TOMANOVÁ, Michaela January 2016 (has links)
The thesis research deals with the characteristics of a given (land)register from the perspective of natural, geographical and historical situation. The individual parts of the local USES are described further. The characteristics of individual segments are accompanied by a present condition of the particular segment. The photo documentation can be found in the attachment. USES evaluation was done using the methodology of evaluation of ecological networks in the landscape. New elements that should give the current USES more power in its function were also suggested. The obtained results were compared with land adjustments abroad. The thesis is complemented with a search related to that topic.
439

Analýza změn územního systému ekologické stability komplexní pozemkovou úpravou

BÍCOVÁ, Markéta January 2018 (has links)
This thesis deals with the analysis of the TSES changes by the complex landed adjustment. First of all, the terms of the landscape and the landscape ecology are defined in the literary survey by available literature. The greatest focus of the landscape ecology is connected with its functions and and its structure. TSES is described as well. This thesis analyzes elements of TSES biocentres, biocorridors within the chapter. Furthermore, this thesis describes some functions of the greenery in the landscape. The last part of the survey describes TSES in the landed adjustment and the definition of the landed adjustment on its own. The description of the territory was formulated this way: the basic characteristics of the territory, the natural characteristics of the territory and so on. Another chapter comes with the detailed methodology of the thesis. The results and the discussion are the last and the most important part of the thesis. Every element of the TSES in interest territory is described in a state of the draft, as the part of the complex landed adjustment and nowadays. Maps in attachment are enclosed to the results.
440

Strojové učení v úloze predikce vlivu aminokyselinových mutací na stabilitu proteinu / Prediction of Protein Stability upon Mutations Using Machine Learning

Malinka, František January 2014 (has links)
This thesis describes a new approach to the detection of protein stability change upon amino acid mutations. The main goal is to create a new meta-tool, which combines the outputs of eight well-established prediction tools and due to suitable method of consensus making, it is able to improve the overall prediction accuracy. The optimal strategy of combination of outputs of these tools is found by using a various number of machine learning methods. From all tested machine learning methods, KStar showed the highest prediction accuracy on the training dataset compiled from experimentally validated mutations originating from ProTherm database. Due to this reason, it is chosen as an optimal prediction technique. The general prediction abilities is validated on the testing dataset composed of multi-point amino acid mutations extracted also from ProTherm database. Since the multi-point mutations were not used for training any of integrated tools, we suppose that such comparison is objective. As a result, the developed meta-tool based on KStar technique improves the correlation coefficient about 0.130 on the training dataset and 0.239 on the testing dataset, respectively (the comparison is being made against the most succesful integrated tool). Based on the obtained results, it is possible to claim that machine learning methods are suitable technique for the problems from area of protein predictions.

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