Probability characteristics and sensitivity of wideband noise-like signal detector with duration selectivity

Для широкополосного обнаружителя шумового сигнала с квадратором и селекторами сигнала по уровню и длительности разработана методика определения порогов селекции по уровню и длительности, если задана вероятность ложной тревоги на максимально возможном интервале ожидания сигнала. В основе методики – применение «выбросовой» вероятностной модели работы обнаружителя в режиме ожидания и использование многомерной функции распределения вероятностей нормализованного помехового индикаторного процесса. Получена вероятностная характеристика обнаружения и изложена методика оценки чувствительности двухселекторного обнаружителя. Показано, что применение селекции по длительности позволяет повысить чувствительность двухселекторного обнаружителя по сравнению с односелекторным при равной вероятности ложной тревоги. Показано, что существует оптимальное сочетание порогов селекции по уровню и длительности, когда критерием оптимальности является максимум чувствительности обнаружителя. Этот максимум достигается, когда порог селекции по длительности составляет 0.1 от периода средней квадратичной частоты флуктуаций помехового индикаторного процесса. This article proposes a method for determining the level and duration thresholds in a wideband noise-like signal detector if the probability of a false alarm is set at the maximum possible signal waiting interval. The method is based on the use of «emissional» probabilistic model of the detector in standby mode and the use of a multidimensional probability distribution function of the normalized noise indicator process. A probabilistic characteristic of detection is obtained and also described a technique for the estimation of sensitivity of a two-step selection detector. It is shown that the use of selection by duration makes possible to increase the sensitivity of a two-step selection detector in comparison with a single-step selection detector with an equal probability of a false alarm. It is shown that there is an optimal combination of selection thresholds in terms of level and duration, when the optimality criterion is the maximum sensitivity of the detector. This maximum is reached when the duration selection threshold is about 0.1 of the period of the root-mean-square fluctuations frequency of the noise indicator process.

Where did I park my car? Influence of landmark permanency on navigation

Visual landmarks provide crucial information for human navigation. But what defines a landmark? To be uniquely recognized, a landmark should be distinctive and salient, while providing precise and accurate positional information. It should also be permanent, e.g., to find back your car, a nearby church seems a better landmark compared with a truck, as you learned the truck might likely move. To this end, we here investigate the learning of landmark permanency while treating permanency as a probabilistic characteristic for human navigation. Particularly we study the learning behaviour when exposed to landmarks whose permanency feature is probabilistically defined. We hypothesize that humans will be able to learn this feature and assign higher weight to more permanent landmarks. To test the hypothesis, we used a homing task where participants had to return to a position that was surrounded by three landmarks. In the learning phase we manipulated the permanency of one landmark by secretly repositioning it prior to returning to the home position. The statistics of repositioning was drawn from a normal distribution. In the test phase we investigated the weight allocated to the non- permanent landmark by analysing its influence on the navigational performance. The first experiment revealed the probabilistic nature of learning the prior of landmark’s permanency, the second experiment confirmed the results in modifying the statistic of the prior. The third and the fourth experiments showed that priors of permanency can be updated by experiences highlighting the capacity of adaptation to the environment.

Extracting Product Quality Information Expressed by Customers from Web Forum and its Applications

Topic forum always contains abundant product information such as requirement, quality, and evaluation. It is very significant to use these information in product development and management. Aiming at the product quality issues during its use, a method of extracting product quality information expressed by customers from web forum was presented. The content and its hybrid structure of product forum were analyzed. And the parse form in XML was presented as well. On the basis of these, the technology architecture of extracting product quality feature words from forum was proposed. In addition, the chronological characteristic and probabilistic characteristic among feature words were researched with the consideration of the position, time, and its number of feature word in sentence or forum respectively, and the calculation models of them were constructed as well. Then the connectivity relations among feature words were established. As a result, the key factors that affect product quality can be inferred based on it.

Seismic Fragility Analysis of Hill Buildings Sited on Slopes

The hill buildings sited on slopes has been widely constructed in mountainous regions. In order to estimate the seismic vulnerability for this type of building under the effect of potential earthquakes, the exceedance probabilities of hill buildings and normal buildings in peak ground acceleration are calculated and compared by using the incremental dynamic analysis method. The fragility curves show the layout of hill buildings has considerable influence on the seismic performance. Specifically, due to the different layout for the hill buildings, the probabilistic characteristic at the collapse prevention level is significantly different from the characteristic of fragility curves at the initial performance level.

Comparative Seismic Risk Analysis of Existing Low-Rise RC Buildings Retrofitted by Metallic Energy Dissipating Devices

Existing non-seismically detailed low-rise RC buildings have higher seismic risks that are dependent on their seismic capacities and demand of building sites. Seismic risk analysis can be performed considering probabilistic characteristic of the structural damage. Structural damage is more accurately quantified by the damage indices than by a single engineering parameter. This study carries out comparative seismic risk analysis of a prototype building with and without metallic energy dissipating devices. Based on the probability distribution of damage index, it is demonstrated that the application of well-designed MEDDs to low-rise RC building can reduce its potential seismic risk.

A Unified Optimization Design Model Under Uncertainty

It is necessary to combine reliability-based design and robust design in the practical engineering. In this paper, a unified framework for integrated reliability-based design and robust design is proposed. In the proposed framework, traditional multi-objective optimization problem is converted to a single objective optimization problem to integrate reliability-based design and robust design without weight factors. The conversion from probabilistic objective function to deterministic objective function is achieved by inverse reliability strategy under the consideration of the probabilistic characteristic of the objective function. After that, an improved sequential optimization and reliability assessment (SORA) method is proposed to deal with the unified framework. Overall, two examples are implemented to illustrate the benefits of the proposed methods.

Resonance Reliability Assessment of Turbine Blade with Parametric Uncertainty

Stochastic finite element method and reliability technique are used to determine the safety degree of the turbine blade with parametric uncertainty. The material, geometric parameters and rotating speed of blade exhibit notable random fluctuations, so the conventional deterministic analysis of blade can’t provide complete information. The stochastic analysis can tackle the uncertainties in structural parameters and obtain the probabilistic characteristic of the vibration characteristic. In this paper, the study focuses on the reliability assessment of the blade with uncertainty parameters based on the stochastic finite element method (SFEM) and the mean-variance method. The perturbation stochastic finite element method (PSFEM) is used to calculate probabilistic characteristic of the natural vibration of the turbine blade. Based on the stochastic finite element method, the mean-variance method is used to calculate the resonance reliability of the blade. The example shows that the present method is valid.