Stability Of Filter Research Articles

Amplitude stability analysis and experimental investigation of an AC excitation signal for capacitive sensors

Low-noise capacitive sensor is widely used in electrostatic accelerometers and inertial sensors. An AC excitation signal is necessary to realize the amplitude modulation of the slow differential capacitance. But the amplitude stability of this AC excitation signal will directly influence low-frequency performance and dynamic range of capacitive sensors which results in the deviation of scientific requirements. In this paper, a stable AC excitation signal is realized based on the classical direct digital frequency synthesis technology. The mathematical model of amplitude stability is systematically set up, and there are four main influencing factors including transition time stability of the digital-to-analog converter (DAC), frequency stability of the crystal oscillator, voltage stability of the reference and gain stability of the band-pass filter (BPF). Each contribution of these four sources is theoretically analyzed. Finally, an evaluation prototype board is achieved to investigate the stability experimentally. Performance testing results show that the amplitude stability could reach approximately 16 ppm/Hz1/2 at 1 mHz under present optimal components selection, and transition stability of the DAC is the primary factor for further improvement.

Asymptotic properties of linear filter for deterministic processes

It is known that Kalman–Bucy filter is stable with respect to initial conditions under the assumptions of uniform complete controllability and uniform complete observability. In this paper, we prove the stability of Kalman-Bucy filter for the case of noise free dynamical system, i.e., for deterministic processes. The earlier stability results cannot be applied for this case, as the system is not controllable. We further show that the optimal linear filter for a general class of non-Gaussian initial conditions is asymptotically proximal to Kalman–Bucy filter. It is also shown that the filter corresponding to non-zero system noise in the limit of small system noise approaches the filter corresponding to zero system noise in the case of Gaussian initial conditions.

LMI-Based Filter Design Conditions for Discrete-Time LPV Systems With Bounded Parameter Variation

In this article, we introduce novel filter design conditions for discrete-time linear parameter-varying (LPV) systems. The two main features of the proposed conditions are: the ability of handling LPV systems subject to variation in all matrices of the system and the generalization for systems with bounded rates of parameter variation. Filter stability and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> filtering problems are addressed through poly-quadratic Lyapunov functions in terms of linear matrix inequalities. Numerical examples illustrate the proposed designs effectiveness.

Challenges and opportunities for nanomaterials in spectral splitting for high-performance hybrid solar photovoltaic-thermal applications: A review

Hybrid photovoltaic-thermal (PV-T) collectors, which are capable of cogenerating useful thermal energy and electricity from the same aperture area, have a significantly higher overall efficiency and ability to displace emissions compared to independent, separate photovoltaic panels, solar thermal collectors or combinations thereof. Spectral splitting has emerged as a promising route towards next-generation high-performance PV-T collectors, and nanotechnology plays an important role in meeting the optical and thermal requirements of advanced spectral splitting PV-T collector designs. This paper presents a comprehensive review of spectral splitting technologies based on nanomaterials for PV-T applications. Emerging nanomaterials (nanofluids, nanofilms and nanowires) suitable for achieving spectral splitting based on reflection, diffraction, refraction and/or absorption approaches in PV-T collectors are presented, along with the associated challenges and opportunities of these design approaches. The requirements from such materials in terms of optical properties, thermal properties, stability and cost are discussed with the aim of guiding future research and innovation, and developing this technology towards practical application. Nanofluids and nanofilms are currently the most common nanomaterials used for spectral splitting, with significant progress made in recent years in the development of these materials. Nevertheless, there still remains a considerable gap between the optical properties of currently-available filters and the desired properties of ideal filters. Aiming to instruct and guide the future development of filter materials, a simple generalized method is further proposed in this paper to identify optimal filters and efficiency limits of spectral splitting PV-T systems for different scenarios. It is found that the optimal filter of a spectral splitting PV-T system is highly sensitive to the value of thermal energy relative to that of electricity, which therefore depends strongly on the application and location. The efficiency limit of spectral splitting PV-T collectors is significantly higher than that of standalone PV panels. The stability of nanomaterial filters remains a critical challenge for their long-term employment and also for high-temperature operation in practical applications.

Tram LC Filter Stabilization by Energy Storage System

&lt;span lang="EN-GB"&gt;The paper is focused on the tram input LC traction filter stabilization by the Energy Storage System. The input LC filter is almost undamped resonant circuit which is mainly excited by the motor constant torque command. The tram during voltage drops increases the current flow from the LC filter to hold constant torque and thereby further decreases the LC filter voltage, and vice versa. This could lead to unstable traction drive behaviour. The Energy Storage System can be used to stabilize LC filter voltage.&lt;/span&gt;

Adaptive partitioned methods for the time-accurate approximation of the evolutionary Stokes–Darcy system

This paper develops, analyzes and tests a time-accurate partitioned method for the Stokes–Darcy equations. The method combines a time filter and Backward Euler scheme, is second order accurate and provides, at no extra complexity, an estimate of the temporal error. This approach post-processes the solutions of Backward Euler scheme by adding three lines to original codes to increase the time accuracy from first order to second order. We prove long time stability and error estimates of Backward Euler plus time filter with constant time stepsize. Moreover, we extend the approach to variable time stepsize and construct adaptive algorithms. Numerical tests show convergence of our method and support the theoretical analysis.

Stability of the optimal filter in continuous time: beyond the Beneš filter

We are interested in the optimal filter in a continuous time setting. We want to show that the optimal filter is stable with respect to its initial condition. We reduce the problem to a discrete time setting and apply truncation techniques. Due to the continuous time setting, we need a new technique to solve the problem. In the end, we show that the forgetting rate is at least a power of the time t. The results can be re-used to prove the stability in time of a numerical approximation of the optimal filter.

Comprehensive chemotaxonomic analysis of saffron crocus tepal and stamen samples, as raw materials with potential antidepressant activity

Saffron crocus (Crocus sativus L.) has been widely grown in Iran. Its stigma is considered as the most valuable spice for which several pharmacological activities have been reported in preclinical and clinical studies, the antidepressant effect being the most thoroughly studied and confirmed. This plant part contains several characteristic secondary metabolites, including the carotenoids crocetin and crocin, and the monoterpenoid glucoside picrocrocin, and safranal. Since only the stigma is utilized industrially, huge amount of saffron crocus by-product remains unused. Recently, the number of papers dealing with the chemical and pharmacological analysis of saffron is increasing; however, there are no systematic studies on the chemical variability of the major by-products.In the present study, we harvested saffron crocus flowers from 40 different locations of Iran. The tepals and stamens were separated and subjected to qualitative and quantitative analysis by HPLC-DAD. The presence and amount of seven marker compounds, including crocin, crocetin, picrocrocin, safranal, kaempferol-3-O-sophoroside, kaempferol-3-O-glucoside, and quercetin-3-O-sophoroside were determined.The analytical method was validated for filter compatibility, stability, suitability, accuracy, precision, intermediate precision, and repeatability. Tepal and stamen samples contained three flavonol glycosides. The main constituent of the tepals was kaempferol-3-O-sophoroside (62.19–99.48 mg/g). In the stamen, the amount of flavonoids was lower than in the tepal. The amount of kaempferol-3-O-glucoside, as the most abundant compound, ranged between 1.72–7.44 mg/g. Crocin, crocetin, picrocrocin, and safranal were not detected in any of the analysed samples.Our results point out that saffron crocus by-products, particularly tepals might be considered as rich sources of flavonol glucosides. The data presented here can be useful in setting quality standards for plant parts of C. sativus that are currently considered as by-products of saffron production.

Micropollutant adsorption from water with engineered porous ceramic architectures produced by additive manufacturing and coated with natural zeolite

Treatment of waste and drinking waters has gained importance in both emerging and industrialized countries. New pharmaceutical products, industrial processes, agricultural activities are reducing water quality. To solve these problems we propose an efficient and thus economical purification method which uses commercial available natural zeolites as coating material on engineered porous ceramic substrates produced by additive manufacturing. The filters were produced varying the coating thickness and processing parameters such as calcination time and temperature. A testing device was assembled to investigate the filters’ performance by exposing them in flowing water (240 Lh-1). The micropollutant adsorption was tested in three different water matrices (distilled water, surface water and wastewater treatment plant effluent). A range of 0.05 mg NH4–N g−1 up to 3.1 mg NH4– NH4–N g−1 zeolite of ammonium nitrogen was observed on the processed filters. Good filter stability expressed as weight loss (<5%) was observed. The adsorption of ten tested micropollutants showed an overall efficiency of 41.5% and 43% on the surface modified zeolite filters. Natural zeolite filters showed good specific adsorption capacity for metoprolol, citalopram, venlaflaxine and clarithromycin whereas the surface modified zeolite (SMZ) filters adsorb better hydrochlorothiazide, diclofenac, candesartan, mecoprop and irbesartan.

Contribution of bacterial biodiversity on the operational performance of a styrene biotrickling filter

Long-term operational stability of biotrickling filters (BTFs) degrading volatile organic compounds (VOCs) is dependent on both physicochemical as well as biological properties. Effects of increasingly stressful levels of air pollutants on the microbial structure of biofilms within BTFs are not well understood, especially for VOCs such as styrene. To investigate the relationship between biofilm biodiversity and operational stability, the temporal dynamics of a biofilm from a biotrickling filter subjected to stepwise increasing levels of air polluted with styrene was investigated using 16S rDNA pyrosequencing and PCR-denaturing gradient gel electrophoresis (PCR-DGGE). As styrene contaminant loads were increased, microbial community composition was distinctly altered and diversity was initially reduced in early stages but gradually stabilized and increased diversity in later stages, suggesting a recovery and acclimatization period within the microbial community during incremental exposure of the pollutant. Although temporary reductions in known styrene-degrading bacterial genera (Pseudomonas and Rhodococcus) occurred under increased styrene loads, stable BTF performance was maintained due to functional redundancy. New candidate genera for styrene degradation (Azoarcus, Dokdonella) were identified in conditions of high styrene loads, and may have supported the observed stable BTF performance throughout the experiment. Styrene inlet load was found to be important modulator of community composition and may have been partly responsible for the observed temporary reductions of Pseudomonas. Notable differences between dominant genera detected via pyrosequencing compared to species detected by PCR-DGGE suggests that simultaneous implementation of both techniques is valuable for fully characterizing dynamic microbial communities.

Exponential filter stability via Dobrushin’s coefficient

Filter stability is a classical problem in the study of partially observed Markov processes (POMP), also known as hidden Markov models (HMM). For a POMP, an incorrectly initialized non-linear filter is said to be (asymptotically) stable if the filter eventually corrects itself as more measurements are collected. Filter stability results in the literature that provide rates of convergence typically rely on very restrictive mixing conditions on the transition kernel and measurement kernel pair, and do not consider their effects independently. In this paper, we introduce an alternative approach using the Dobrushin coefficients associated with both the transition kernel as well as the measurement channel. Such a joint study, which seems to have been unexplored, leads to a concise analysis that can be applied to more general system models under relaxed conditions: in particular, we show that if $(1 - \delta (T))(2-\delta (Q)) < 1$, where $\delta (T)$ and $\delta (Q)$ are the Dobrushin coefficients for the transition and the measurement kernels, then the filter is exponentially stable. Our findings are also applicable for controlled models.

Optimizing Source and Sensor Placement for Sound Field Control: An Overview

In order to control an acoustic field inside a target region, it is important to choose suitable positions of secondary sources (loudspeakers) and sensors (control points/microphones). This article provides an overview of state-of-the-art source and sensor placement methods in sound field control. Although the placement of both sources and sensors greatly affects control accuracy and filter stability, their joint optimization has not been thoroughly investigated in the acoustics literature. In this context, we reformulate five general source and/or sensor placement methods that can be applied for sound field control. We compare the performance of these methods through extensive numerical simulations in both narrowband and broadband scenarios.

On the Stability of Kalman Filter with Random Coefficients

Abstract Inspired by the random packet dropout problem widely existing in the networked control systems, we investigate the stability of Kalman filter with random coefficients. We present an excitation condition about the regression vectors to establish the Lp-stability and Lp-exponential stability of random Riccati equation. Furthermore, we prove the stability of the error equations of Kalman filter under the excitation condition and some conditions on the system matrix and noises, without relying on any stationarity or independence assumptions about the regressors.

A New Adaptive Extended Kalman Filter for a Class of Nonlinear Systems

This paper proposes a new adaptive extended Kalman filter (AEKF) for a class of nonlinear systems perturbed by noise which is not necessarily additive. The proposed filter is adaptive against the uncertainty in the process and measurement noise covariances. This is accomplished by deriving two recursive updating rules for the noise covariances, these rules are easy to implement and reduce the number of noise parameters that need to be tuned in the extended Kalman filter (EKF). Furthermore, the AEKF updates the noise covariances to enhance filter stability. Most importantly, in the worst case, the AEKF converges to the conventional EKF. The AEKF performance is determined based on the mean square error (MSE) performance measure and the stability is proven. The results illustrate that the proposed AEKF has a dramatic improved performance over the conventional EKF, the estimates are more stable with less noise.

Stable Approximation Schemes for Optimal Filters

A stable filter has the property that it asymptotically “forgets" initial perturbations. As a result of this property, it is possible to construct approximations of such filters whose errors remain small in time, in other words approximations that are uniformly convergent in the time variable. As uniform approximations are ideal from a practical perspective, finding criteria for filter stability has been the subject of many papers. In this paper, we seek to construct approximate filters that stay close to a given (possibly) unstable filter. Such filters are obtained through a general truncation scheme and, under certain constraints, are stable. The construction enables us to give a characterization of the topological properties of the set of optimal filters. In particular, we introduce a natural topology on this set, under which the subset of stable filters is dense.

ПОВЫШЕНИЕ ЭНЕРГОЭФФЕКТИВНОСТИ ПРОИЗВОДСТВА ЗА СЧЕТ ПРИМЕНЕНИЯ СИЛОВЫХ ФИЛЬТРОВ ВЫСШИХ ГАРМОНИК

Актуальность. В настоящее время все большее количество технологических процессов и производств в нефтегазовой отрасли реализуется на базе высокопроизводительного оборудования с полупроводниковыми преобразователями электрической энергии, в число которых, например, входят частотно-регулируемые электроприводы переменного тока или бесперебойные источники питания, которые относятся к классу нелинейных нагрузок и могут вызывать большое количество негативных явлений в работе распределительных сетей, включающих в себя несимметрию фазных напряжений и токов, резонансные процессы, тепловые потери в нейтральном проводе, перегрев двигателей и трансформаторов и т. д. Для улучшения электромагнитной совместимости различного рода электроприемников в составе промышленных систем электроснабжения довольно часто используют пассивные конденсаторные батареи для коррекции коэффициента мощности, которые малоэффективны в случае нелинейных процессов. Кроме этого, данный тип компенсационных устройств продолжает потреблять реактивную энергию при отсутствии каких-либо нагрузок и не удовлетворяет современным требованиям в области энергосбережения. Описанные выше недостатки в работе трехфазных систем переменного тока требуют разработки новых схемотехнических решений, методов анализа энергетических процессов и синтеза алгоритмов силовой фильтрации, позволяющих обеспечить нормированные показатели качества электрической энергии в распределительных сетях низкого и среднего классов напряжения вне зависимости от конкретного вида электрических цепей нагрузки. Цель исследования заключается в комплексном анализе существующих технических решений, направленных на повышение электромагнитной совместимости распределительных сетей, а также в описании основных ограничений в работе силовых фильтрокомпенсирующих устройств применительно к промышленным объектам минерально-сырьевого комплекса; в разработке базовых структур активных силовых фильтров с пониженными требованиями по производительности, объему памяти и быстродействию программно-аппаратной части системы управления, практическое применение которых обеспечивает нормированное качество электрической энергии при изменении режимов работы технологического оборудования или конфигурации питающей линии. Объекты: автономные или децентрализованные электроэнергетические системы переменного тока с преобразовательными устройствами силовой электроники и частотно-регулируемыми электроприводами, а также элементами силовой цепи с нелинейными характеристиками, например, реакторами или трансформаторами с насыщенными сердечниками, в которых присутствуют значительные искажения в мгновенной форме трехфазных сигналов; пассивные и активные силовые фильтры высших гармоник. Методы: некоммутативная алгебра кватернионов; четырехмерное гиперкомплексное пространство; методы спектрального анализа и разложения в ряд Фурье. Результат: краткий обзор различных подходов и технических средств к повышению качества электрической энергии в системах электроснабжения промышленных объектов минерально-сырьевого сектора, а также системы управления,рамках которых достигается синусоидальный закон изменения во времени сетевых токов с нулевым или опережающим/отстающим угловым сдвигом при одновременном соблюдении условия симметрии по мгновенным значениям.

Time-distributed multi-step delayed input and state estimation

This paper presents a refined complete multi-step delayed input and state estimation (MSDISE) by using the newly proposed system reformation approach, where a time-distributed unknown input filtering technique is used to facilitate the design. It is shown that within this new filtering approach, the optimal MSDISE can be readily achieved through the filters developed by Hsieh (2000) or Gillijns and De Moor (2007b). Asymptotic stability of the reformed state filter is explored for the corresponding time-invariant systems. Moreover, the relationships between the proposed asymptotic stability condition with those in literatures are also highlighted. A simulation example is given to show the effectiveness of the proposed results.

An Improved Stability Criterion for Digital Filters With Generalized Overflow Arithmetic and Time-Varying Delay

This brief concerns the stability of fixed-point state-space digital filters with generalized overflow arithmetic and a time-varying delay. A relaxed lemma that includes a commonly used lemma as a special case is developed to show the relationship between the state and the overflow arithmetic, and a Lyapunov functional with positive-definite conditions that are more relaxed than usual is constructed. As a result, a less conservative stability criterion is established, and the efficiency and merit of the criterion are illustrated with a numerical example.

A bench scale study on the startup, performance and optimization of the biological degradation of obnoxious air containing trimethylamine

Trimethylamine [TMA] possess various toxic and contributes a hazardous impact on the living organism. The best treatment to eradicate TMA has to be explored and checked. The operation of a biotrickling filter seeded with Agromyces and Ochrobactrum sp. was optimized for degrading trimethylamine [TMA]. The filter bed was adjusted for continuous treating of TMA up to 20 days. The profile of TMA inlet concentration [IC] and air flow rate on the elimination capacity [EC] and removal efficiency [RE] was examined. A variation of RE [24.71–88.45%] in TMA degradation the filter bed was observed on different inlet loading rates [ILR]. The highest RE and microbial growth was recorded at a height of 45 cm. The output values were statistically deduced by carrying out an analysis of variance [ANOVA] to explicate the key and interacting properties. The biotrickling filter stability was also successfully determined with a temporary shutdown for a prolonged period of 15 days. The maximum EC attained for TMA was 29.28 g m-3 h-1 at inlet loading rate [ILR] of 57.6 g m-3 h-1.

Athermalization of a self-assembled rolled-up TiO2 microtube ring resonator through incorporation of a positive thermo-optic coefficient material in planar bilayers

For the first time, this paper theoretically and experimentally investigates the thermal stability of optical filters based on self-assembled TiO2 rolled-up microtube ring resonators (RUMRs) by incorporating positive thermo-optic coefficient (TOC) materials (e.g., SiO2 and/or Si3N4). The influence of the TOC, refractive index, and thickness of the positive TOC materials on the filtering performance of the TiO2 RUMR is theoretically studied. The results illustrate that an increase in temperature leads to a blueshift in the resonant wavelength of the RUMR-based optical filter, which changes at a rate of − 33.3 pm/K owing to the negative TOC of TiO2 (− 4.9 ± 0.5 × 10−5/K). By increasing the thickness of SiO2 or Si3N4 as a positive TOC material together with TiO2, the temperature-induced resonant shifts of TiO2/SiO2 and/or TiO2/Si3N4 RUMRs are theoretically obtained. The TIRS varies between − 40 pm/K (− 22 pm/K) and about 30 pm/K (22 pm/K) for TiO2/SiO2 (TiO2/Si3N4) RUMRs. It is shown that thermal stability occurs when the thickness of the SiO2 (Si3N4) layer is ~ 16 nm (12 nm). At the end of this study, as a proof of concept, an experiment is demonstrated by fabricating an RUMR based on TiO2/SiO2 on the flat silicon wafer. The experimental results show that the athermalization of the system is experimentally achieved by selecting the appricated thickness ratio of TiO2/SiO2. This novel approach for athermalization of the resonators opens up interesting perspectives on the implementation of vertical and multi-routing coupling between photonic and optoelectronic layers and more specifically in a three-integration fashion.