Добірка наукової літератури з теми "Summary parametric filter sensitivity"

Summary Objectives: The objective of this study was to explore suitable spatial filters for inverse estimation of cortical potentials from the scalp electroencephalogram. The effect of incorporating noise covariance into inverse procedures was examined by computer simulations and tested in human experiment. Methods: The parametric projection filter, which allows inverse estimation with the presence of information on the noise, was applied to an inhomogeneous three-concentric-sphere model under various noise conditions in order to estimate the cortical potentials from the scalp potentials. The method for determining the optimum regularization parameter, which can be applied for parametric inverse techniques, is also discussed. Results: Human visual evoked potential experiment was carried out to examine the performance of the proposed restoration method. The parametric projection filter gave more localized inverse solution of cortical potential distribution than the truncated SVD and Tikhonov regularization. Conclusion: The present simulation results suggest that incorporation of information on the noise covariance allows better estimation of cortical potentials, than inverse solutions without knowledge about the noise covariance, when the correlation between the signal and noise is low.

Background The prevalence of Schistosoma mansoni infection is usually assessed by the Kato-Katz diagnostic technique. However, Kato-Katz thick smears have low sensitivity, especially for light infections. Egg count models fitted on individual level data can adjust for the infection intensity-dependent sensitivity and estimate the ‘true’ prevalence in a population. However, application of these models is complex and there is a need for adjustments that can be done without modeling expertise. This study provides estimates of the ‘true’ S. mansoni prevalence from population summary measures of observed prevalence and infection intensity using extensive simulations parametrized with data from different settings in sub-Saharan Africa. Methodology An individual-level egg count model was applied to Kato-Katz data to determine the S. mansoni infection intensity-dependent sensitivity for various sampling schemes. Observations in populations with varying forces of transmission were simulated, using standard assumptions about the distribution of worms and their mating behavior. Summary measures such as the geometric mean infection, arithmetic mean infection, and the observed prevalence of the simulations were calculated, and parametric statistical models fitted to the summary measures for each sampling scheme. For validation, the simulation-based estimates are compared with an observational dataset not used to inform the simulation. Principal findings Overall, the sensitivity of Kato-Katz in a population varies according to the mean infection intensity. Using a parametric model, which takes into account different sampling schemes varying from single Kato-Katz to triplicate slides over three days, both geometric and arithmetic mean infection intensities improve estimation of sensitivity. The relation between observed and ‘true’ prevalence is remarkably linear and triplicate slides per day on three consecutive days ensure close to perfect sensitivity. Conclusions/significance Estimation of ‘true’ S. mansoni prevalence is improved when taking into account geometric or arithmetic mean infection intensity in a population. We supply parametric functions and corresponding estimates of their parameters to calculate the ‘true’ prevalence for sampling schemes up to 3 days with triplicate Kato-Katz thick smears per day that allow estimation of the ‘true’ prevalence.

Abstract Surface enhanced Raman is a powerful analytical tool with high sensitivity and unique specificity and promising applications in various branches of analytical chemistry. Despite the fabrication of ingenious enhancement substrate used in laboratory research, the development of simple, flexible, and cost-effective substrate is also great important for promoting the application of SERS in practical analysis. Recently, paper and filter membrane as support to fabricate flexible SERS substrates received considerable attentions. Paper-based SERS substrate has been reviewed but no summary on filter-based SERS substrate is available. Compared with paper, filter membrane has unique advantage in robust mechanics, diverse component, and tunable pore size. These characteristics endow the filter-based substrates great advantages for practical SERS analysis including simple and low-cost substrate preparation, high efficiency in preconcentration, separation and detection procedure. Therefore, filter-based substrates have shown great promise in SERS analysis in environment monitoring, food safety with high sensitivity and efficiency. As more and more work has been emerged, it is necessary to summarize the state of such a research topic. Here, the research on filter involved SERS analysis in the past eight years is summarized. A short introduction was presented to understand the background, and then the brief history of filter-based substrate is introduced. After that, the preparation of filter-based substrate and the role of filter are summarized. Then, the application of filter involved SERS substrate in analysis is presented. Finally, the challenges and perspective on this topic is discussed.

Summary Aim: The comparison between iterative reconstruction and filtered backprojection in the reconstruction of bone SPECT in the diagnosis of skeletal metastases. Patients, methods: 47 consecutive patients (vertebral segments: n = 435), with suspected malignancy of the vertebral column, were examined by bone scintigraphy and MRI (maximal interval between the two procedures ± 5 weeks). The SPECT-data were reconstructed with an iterative algorithm (ISA) and with filtered backprojection. We defined semiquantitative criteria in order to assess the quality of the tomograms. Conventional reconstruction was performed both by a Wiener-filter and a low-pass-filter. Iterative reconstruction was performed by the ISA algorithm. The clinical evaluation of the different reconstruction algorithms was performed by MRI as the gold-standard. Results: Sensitivity (%): 87.3 (ISA), 86.4 (low-pass), 79.7 (Wiener); specificity (%): 95.3 (ISA), 95 (low-pass), 85.4 (Wiener). The sensitivity of iterative reconstructed SPECT and low-pass reconstructed SPECT was significantly higher (p <0.05) compared with the sensitivity of SPECT reconstructed by the Wiener-filter. The specificity of iterative reconstruction ISA and low-pass-filter reconstructed SPECT were significantly higher compared with the SPECT data reconstructed by the Wiener-filter. ISA was significantly superior to the Wiener- SPECT relating to all criteria of quality. Iterative reconstruction was significantly superior to the low-pass-SPECT relating to 2 of 3 criteria. In addition the Wiener-SPECT was significantly inferior to the low-pass-SPECT regarding to 2 of 3 criteria. Conclusion: In our series the iterative algorithm ISA was the method of choice in the reconstruction of bone SPECT data. In comparison with conventional algorithms ISA offers a significantly higher quality of the tomograms and yields a high diagnostic accuracy.

This is a comparative study between manual volumetry (MV) and voxel based morphometry (VBM) as methods of evaluating the volume of brain structures in magnetic resonance images. The volumes of the hippocampus and the amygdala of 16 panic disorder patients and 16 healthy controls measured through MV were correlated with the volumes of gray matter estimated by optimized modulated VBM. The chosen structures are composed almost exclusively of gray matter. Using a 4 mm Gaussian filter, statistically significant clusters were found bilaterally in the hippocampus and in the right amygdala in the statistical parametric map correlating with the respective manual volume. With the conventional 12 mm filter,a significant correlation was found only for the right hippocampus. Therefore,narrowfilters increase the sensitivity of the correlation procedure, especially when small brain structures are analyzed. The two techniques seem to consistently measure structural volume.

The cryogenic resonant-mass gravitational radiation antenna at the University of Western Australia (UWA) has obtained a noise temperature of <2 mK using a zero order predictor filter. This corresponds to aIms burst strain sensitivity of 7x 10-19 . The antenna has been in continuous operation since August 1993. The antenna operates at about 5 K and consists of a 1� 5 tonne niobium bar with a 710 Hz fundamental frequency, and a closely tuned secondary mass of 0�45 kg effective mass. The vibrational state of the secondary mass is continuously monitored by a 9�5 GHz superconducting parametric transducer. This paper presents the current design and operation of the detector. From a two-mode model we show how we calibrate, characterise and theoretically determine the sensitivity of our detector. Experimental results confirm the theory.

Summary Objectives: Electroencephalographic burst activity characteristic of burst-suppression pattern (BSP) in sedated patients and of burst-interburst pattern (BIP) in the quiet sleep of healthy neonates have similar linear and non-linear signal properties. Strong interrelations between a slow frequency component and rhythmic, spindle-like activities with higher frequencies have been identified in previous studies. Time-varying characteristics of BSP and BIP prevent a definite pattern-related analysis. A continuous estimation of the bispectrum is essential to analyze these patterns. Parametric bispectral approaches provide this opportunity. Methods: The adaptation of an AR model leads to a parametric bispectrum by using the transfer function of the estimated AR filter. Time-variant parametric bispectral approaches require an estimation of AR parameters which consider higher order moments to preserve phase information. Accordingly, a time-variant parametric estimation of the bispectrum was introduced. Data driven simulations were performed to provide optimal parameters. BSP (12 patients) and BIP (6 neonates) were analyzed using this novel approach. Results: Significant differences in the time course of burst pattern during BSP and burst-like pattern before the onset of BSP could be shown. A rhythmic quadratic phase coupling (period 10 sec) was identified during BIP in all neonates. Conclusion: Quadratic phase couplings during BSP increases in the time course depending on depth of sedation. The visually detected burst activity in BIP is only the temporarily observable EEG correlate of a hidden neural process. Time-variant bispectral approaches offer the possibility of a better characterization of underlying neural processes leading to improved diagnostic tools used in clinical routine.

Summary Objective : The objective of this study is to explore suitable spatial filters for inverse estimation of cortical equivalent dipole layer imaging from the scalp electroencephalogram. We utilize cortical dipole source imaging to locate the possible generators of scalpmeasured movement-related potentials (MRPs) in human. Methods : The effects of incorporating signal and noise covariance into inverse procedures were examined by computer simulations and experimental study. The parametric projection filter (PPF) and parametric Weiner filter (PWF) were applied to an inhomogeneous threesphere head model under various noise conditions. Results : The present simulation results suggest that the PWF incorporating signal information provides better cortical dipole layer imaging results than the PPF and Tikhonov regularization under the condition of moderate and high correlation between signal and noise distributions. On the other hand, the PPF has better performance than other inverse filters under the condition of low correlation between signal and noise distributions. The proposed methods were applied to self-paced MRPs in order to identify the anatomic substrate locations of neural generators. The dipole layer distributions estimated by means of PPF are well-localized as compared with blurred scalp potential maps and dipole layer distribution estimated by Tikhonov regularization. The proposed methods demonstrated that the contralateral premotor cortex was preponderantly activated in relation to movement performance. Conclusions : In cortical dipole source imaging, the PWF has better performance especiallywhen the correlation between the signal and noise is high. The proposed inverse method was applicable to human experiments of MRPs if the signal and noise covariances were obtained.

Дисертація присвячена математичному моделюванню задач криптографії та обробки сигналів з використанням неканонічних гіперкомплексних числових систем, застосування яких зменшує кількість обчислень при функціонуванні таких моделей та дозволяє оптимізувати їх за окремими характеристиками. Результати моделювання задачі розділення секрету показали, що застосування неканонічних гіперкомплексних числових систем, починаючи з вимірності 4, зменшує кількість потрібних обчислень у порівнянні із застосуванням канонічних гіперкомплексних числових систем. Розроблено методи побудови структур неканонічних гіперкомплексних числових систем, що задовольняють критеріям побудови цифрового фільтра. Побудовано цифровий фільтр з коефіцієнтами у неканонічних гіперкомплексних числових системах та проведена його оптимізація за параметричною чутливістю.
The thesis is devoted to mathematical modeling of cryptography and signal problems using non-canonical hypercomplex numerical systems, which reduces the calculations amount during these models functioning and allows their optimization by individual characteristics. The modelling results of secret sharing scheme have shown that the use of non-canonical hypercomplex numerical systems starting from dimension 4 reduces the computation amount required in comparison with the use of canonical hypercomplex numerical systems. The methods for synthesis the noncanonical hypercomplex numerical system structures that satisfy the criteria for building a digital filter are developed. The digital filter is developed with the coefficients in noncanonical hypercomplex numerical systems and optimized by the parametric sensitivity.
Диссертация посвящена математическому моделированию задач криптографии и обработки сигналов с использованием неканонических гиперкомплексных числовых систем (ГЧС). Разработаны методы и способы представления и обработки данных в неканонических ГЧС, применение которых упрощает вид математических моделей, уменьшает количество вычислений при их функционировании и позволяет производить их оптимизацию по отдельным признакам. Анализ результатов работ последнего десятилетия по применению гиперкомплексных числовых систем в решении задач криптографии и обработки сигналов показал следущее: 1) применение канонических ГЧС к задаче разделения секрета повышает криптографическую стойкость, но вместе с тем увеличивает количество операций, требуемых для реализации такой задачи. Применение неканонических ГЧС дает возможность минимизировать количество вычислений за счет меньшей размерности системы; 2) синтез цифрового фильтра с использованием канонических ГЧС дает результаты по оптимизации его параметрической чувствительности, но поскольку выбор таких систем ограничен, неканонические ГЧС дают большие возможности по оптимизации чувствительности. В работе совершенствуются методы построения структур ГЧС заданной размерности, в том числе получения множества структур неканонических ГЧС, заданных в общем виде и неканонических гиперкомплексных числовых систем, изоморфных диагональной системе. Эти методы учитывают заданные ограничения представления данных в неканонических ГЧС для моделирования практических задач. Предлагается метод построения некоторых классов изоморфизма для неканонических ГЧС размерности 2. Изоморфные системы используются для минимизации вычислений при таком представления данных. В работе совершенствуются методы определения единичного элемента, нормы, сопряжения и делителей нуля для неканонических гиперкомплексных числовых систем; методы выполнения операций в таких системах. Впервые предлагается метод вычисления вычетов в неканонических ГЧС, который применяется в моделировании задачи разделения секрета и учитывает структурные особенности неканонических гиперкомплексных числовых систем. Предлагается модификация модулярной схемы разделения секрета, которая отличается от существующей представлением информации остатками в неканонических ГЧС по совокупности неканонических гиперкомплексных модулей. Реализована компьютерная модель задачи разделения секрета для неканонических ГЧС третьей и четвертой размерности в системе символьных вычислений MAPLE. Приведены результаты работы такой модели и сравнительные характеристики количества операций в части преобразования данных, непосредственно разделения секрета и восстановления данных. Анализ полученных результатов показал, что в целом, применение неканонических ГЧС к данной модели позволяет использовать меньшую размерность в зависимости от выбора констант при структурных единицах в таблице умножения системы, для обеспечения такой же криптостойкости, как и с использованием канонических ГЧС. Использование неканонической ГЧС размерности 3 для обеспечения такой же криптостойкости, как и при использовании канонической ГЧС размерности 4, не дает нужного эффекта для уменьшения количества вычислений, так как среднее количество операций увеличивается на 92%. Но уже при использовании неканонической ГЧС размерности 4 с 9-ю составными ячейками в таблице умножения с целыми коэффициентами из диапазона {-4,4}, для обеспечения такой же криптостойкости, как и при использовании канонической ГЧС размерности 6, количество требуемых вычислений уменьшается в среднем на 44%. Для успешного восстановления секрета, необходимо использовать числовые системы без делителей нуля и обладающих свойством мультипликативности нормы. В диссертационной работе впервые предлагается метод синтеза неканонических ГЧС, которые могут быть использованы при построении цифрового фильтра. Создана математическая модель рекурсивного цифрового фильтра с гиперкомплексными коэффициентами в полученных неканонических ГЧС третьей размерности. Впервые предлагается метод оптимизации суммарной параметрической чувствительности фильтра, построенного с использованием неканонических ГЧС который позволяет существенно уменьшить параметрическую чувствительность эквивалентного фильтра с вещественными коэффициентами (до ~50%) и существующих фильтров с гиперкомплексными коэффициентами (до ~40%). В работе описано расширение аналитически-программного инструментария в системе символьных вычислений MAPLE, который реализует предложенные модели и методы с учетом структурных особенностей неканонических ГЧС, а именно: определение основных свойств и выполнение операций над неканоническими гиперкомплексными числами; выполнение модулярных операций над неканоническими гиперкомплексными числами; построение структур неканонических ГЧС согласно заданным критериям, в том числе, критерию построения цифрового фильтра; реализация модели задачи разделения секрета в неканонических ГЧС и метода оптимизации параметрической чувствительности цифрового фильтра. Листинги кода приведены в приложениях.

Sensitivity analyses are frequently used during the design process of engineering systems to qualify and quantify the effect of parametric variation on the performance of a system. Two primary types of sensitivity analyses are generally used: local and global. Local analyses, generally involving derivative-based measures, have a significantly lower computational burden than global analyses but only provide measures of sensitivity around a nominal point. Global analyses, generally performed with a Monte Carlo sampling approach and variation-based measures, provide a complete description of a concept’s sensitivity but incur a large computational burden and require significantly more information regarding the distributions of the design parameters in a concept. Local analyses are generally suited to the early stages of design when parametric information is limited and a large number of concepts must be considered (necessitating a light computational burden). Global analyses are more suited towards the later stages of design when more information regarding parametric distributions is available and fewer concepts are being considered. Current derivative-based local approaches provide a significantly different set of measures than a global variation-based analysis. This makes a direct comparison of local to global measures impossible. To reconcile local and global sensitivity analyses, a hybrid local variation based sensitivity (HyVar) approach is presented. This approach has a similar computational burden to a local approach but produces measures in the same format as a global variation-based approach (contribution percentages). This HyVar sensitivity analysis is developed in the context of a functionality-based design and behavioral modeling framework. An example application of the method is presented along with a summary of results produced from a more comprehensive example.

Parametric roll is a nonlinear phenomenon that can rapidly create large roll angles coupled with significant pitch motions. Such motions can cause large loads especially in fore and aft parts of the ship structure, severe stresses on containers and their securing systems, and can be a threat for the crew of the ship. The large roll angles may increase to such values that can even cause capsizing. Even though there are many studies focusing on the parametric roll phenomenon using theoretical, numerical and experimental approaches, topics such as uncertainty quantification and sensitivity analysis in parametric roll have not attracted enough attention. In this paper, results from a study on uncertainty quantification in numerical simulation of parametric roll are presented. Numerical simulations were carried out in irregular seas using the Korean Container Ship (KCS). Motion of the ship was simulated with a time-domain program. Several parameters were considered as sources of uncertainty such as the GM, the length of the simulation time window, the phase, and the number of components of the irregular wave. To propagate these uncertainties in the computational model, Latin hypercube sampling (LHS) and Polynomial chaos expansion (PCE) methods were used, and their performances were compared. The paper ends with a summary of conclusions and recommendations.

As the force output of an electromagnetic actuator is limited, achieving reliable operation of a direct-acting solenoid valve at high pressures and flow rates can be challenging. The major performance obstacle is the hydrodynamic flow force acting on the spool as it moves between energized and de-energized states. With trends in the fluid power industry requiring valves to operate at higher pressures and volumetric flow rates, while minimizing electrical power consumption, methods to reduce hydrodynamic flow forces become critical in developing functional products. This paper presents CFD simulation and correlating experimental results in using back angles to reduce the hydrodynamic flow forces in a direct-acting, solenoid operated, cartridge-style, directional control valve. Traditional methods of calculating flow forces are discussed and a brief summary of prior research is presented. A commercially available CFD package, Fluent, was used to numerically estimate the flow forces using a realizable k-ε turbulence closure model. A parametric analysis of flow, pressure, and spool stroke showed sensitivity to the metering edge geometry. A special fixture was created to isolate and directly measure the forces acting on the spool. The addition of a +60° back-angle showed the largest flow force reduction of 36% compared to a spool with no back angle.