On Controlling the Transient Response of Linear Time Invariant Systems with Fixed Structure Controllers

The problem of controlling transient response is important in many industrial applications; for example, the speed and accuracy of motion control of robots directly relates to the productivity of the robot. The objective of transient control is to determine a feedback controller of a fixed structure that renders the closed loop response of a specified system to lie in a specified envelope. One may associate a set of errors which measures the deviation of the response from the envelope. The set of errors may be defined in such a way that all the errors are non‐negative if and only if the response does not deviate from the envelope at any time. The transient problem can be thus posed as the problem of determining a stabilizing controller that renders the set of all errors to be non‐negative at every time. One may associate a control parameter vector K with a controller of a specified structure. The main topic of investigation of this paper is to find a bound for the set of real control parameters, K, so that a rational, proper transfer function, has a decaying, non‐negative impulse response. It is assumed that the coefficients of the polynomials N(s, k) and D(s, K) are affine in K.     

A framework for preservation of cloud users’ data privacy using dynamic reconstruction of metadata

In the rising paradigm of cloud computing, attainment of sustainable levels of cloud users’ trust in using cloud services is directly dependent on effective mitigation of its associated impending risks and resultant security threats. Among the various indispensible security services required to ensure effective cloud functionality leading to enhancement of users’ confidence in using cloud offerings, those related to the preservation of cloud users’ data privacy are significantly important and must be matured enough to withstand the imminent security threats, as emphasized in this research paper. This paper highlights the possibility of exploiting the metadata stored in cloud's database in order to compromise the privacy of users’ data items stored using a cloud provider's simple storage service. It, then, proposes a framework based on database schema redesign and dynamic reconstruction of metadata for the preservation of cloud users’ data privacy. Using the sensitivity parameterization parent class membership of cloud database attributes, the database schema is modified using cryptographic as well as relational privacy preservation operations. At the same time, unaltered access to database files is ensured for the cloud provider using dynamic reconstruction of metadata for the restoration of original database schema, when required. The suitability of the proposed technique with respect to private cloud environments is ensured by keeping the formulation of its constituent steps well aligned with the recommendations proposed by various Standards Development Organizations working in this domain.     

Structural and high temperature conduction studies of (Na<Subscript>0.46</Subscript>Bi<Subscript>0.46</Subscript>Ba<Subscript>0.08</Subscript>) (Mn<Subscript>x</Subscript>Ti<Subscript>1−x</Subscript>O<Subscript>3</Subscript>)–CuO lead-free piezoelectric ceramics

Polycrystalline lead-free (Na_0.46Bi_0.46Ba_0.08)(Mn_xTi_1?xO₃)?+?0.2CuO ceramics (x?=?0.0, 0.5, 2.0, 3.0 wt%) were prepared via solid-state reaction method. X-ray diffraction (XRD) analysis confirmed the formation of single-phase perovskite structure and indicated the presence of morphotropic phase boundary, where the tetragonal and rhombohedral phases co-existed for all the synthesized compositions. Scanning electron microscopy (SEM) analysis revealed that the average grain size decreased with the increase in Mn content. Impedance spectroscopy (IS) indicated that Mn doping was found to decrease the grain boundary resistance. Two semi-circles were observed for higher Mn content which indicates the contribution of both bulk grains and grain boundaries. Non-Debye type and temperature dependent relaxation phenomenon was also revealed by IS studies. The activation energies at different frequencies were found to be 0.05–0.9 eV, indicating hopping charge conduction mechanism. These results have comprehensive implications for the expanded use of BNT based lead free piezoelectric ceramics for practical applications.     

Nanoscale heat transfer investigation of an array of impinging jet systems with different working fluids under crossflow with and without pin fins

In the current numerical study, the thermal and flow field performance of an array of confined multiple jets with air, water, and water‐Al₂O₃ nanofluid in the maximum crossflow configuration over the target plate with and without pin fins is investigated. The numerical results are validated with the experimental data; it is found that a reasonable prediction related to heat transfer can be made. For this study, steady‐state Reynolds‐averaged Navier‐Stokes simulations with the shear‐stress transport $k‐\omega$ turbulence model in ANSYS Fluent were performed. The simulations are performed with volumetric concentration $?=0.2\%$ to 3% and the jet's Reynolds number Re = 15 000 to 35 000. In all cases, the jet outlet‐to‐target plate distance $Z/D$ is 3. It is found that the increase in values of the volumetric concentration of nanoparticles results in a decrease of the Nusselt number and an increase of the convective heat transfer coefficient. This is because there is an increase in thermal conductivity of the working fluid with the increase in the volumetric concentration of nanoparticles for the same Reynolds number. About 81.5% and 89.1% enhancement in the average heat transfer flux values is observed for flat and pin fin‐roughened target plates, respectively, for $?=3\%$.     

亚麻籽麻纤维增强复合材料的制备及其力学性能

本文着重研究了亚麻籽麻纤维强度及其复合材料纵向拉伸和弯曲性能,旨在探求亚麻籽麻纤维在绿色复合材料领域的应用潜能。分别采用10 g/l NaOH和20 g/l NaOH对亚麻籽麻纤维进行脱胶处理。脱胶后纤维表面SEM照片显示,经20 g/l NaOH处理可脱除纤维表面大部分胶质,脱胶较为彻底和均匀。热处理对纤维的力学性能有较大影响,经150℃热处理后纤维强度下降了36.2%。选择低熔点PBS(聚丁二酸丁二醇酯)树脂与麻纤维采用热压成型制备了纤维体积分数为36%的复合材料。测试了复合材料的纵向拉伸和弯曲性能,并对破坏模式进行分析。结果显示:碱处理后,复合材料拉伸性能有所降低,弯曲强度分别提高了19.3%(10 g/l NaOH)和59.9%(20g/l NaOH),20 g/l NaOH处理后复合材料的纵向弯曲强度为42.69 MPa。研究表明,亚麻籽麻纤维可用于制备热塑性复合材料,并具有较好的力学性能和应用前景。     

Optimal homotopy asymptotic method for heat transfer in hollow sphere with robin boundary conditions

In this article, we have investigated heat transfer from a hollow sphere using a powerful and relatively new semi‐analytic technique known as the optimal homotopy asymptotic method (OHAM). Robin boundary conditions are applied on both the inner and outer surfaces. The effects of Biot numbers, uniform heat generation, temperature‐ dependent thermal conductivity, and temperature parameters on the dimensionless temperature and heat transfer are investigated. The results of OHAM are compared with a numerical method and are found to be in good agreement. It is shown that the dimensionless temperature increases with an increase in Biot number at the inner surface and temperature and heat generation parameters, whereas it decreases with an increase in the Biot number at the outer surface and the dimensionless thermal conductivity and radial distance parameters. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res 43(2): 124‐133, 2014; Published online 20 June 2013 in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21067     

Models for fiber stress utilization in air jet yarns

Abstract

The coefficient of fiber stress utilization of air jet viscose staple spun yarns was predicted from the experimental specific stress-strain curves of both fiber and yarns. The coefficient of fiber stress utilization was calculated from Gegauff’s model, single integral model (SIM) and double integral model (DIM). Results showed that the single integral model overestimated the coefficient of fiber stress utilization considering actual stress-strain relationship which was not considered by Gegauff’s model. When fiber orientation effect in the air jet yarn was considered in double integral equation, the predicted coefficient of fiber stress utilization was in good agreement with the experimental coefficient of fiber stress utilization before the process of break. Furthermore, the yarn specific stress was also evaluated from the predicted coefficient of fiber stress utilization from double integral model and experimental fiber specific stress-strain curve for all three air jet viscose yarns. The predicted yarn specific stress-strain curves were in good agreement with experimental yarn specific stress-strain curves for all air jet yarns.     

A generic low-noise CMOS readout interface for 64?×?64 imaging array with on-chip ADC

This paper presents a low-noise and high dynamic-range CMOS readout-IC (ROIC) for a 64?×?64 array of opto-electrical sensors. The readout chain comprises a pixel preamplifier array, correlated-double-sampling based switched-capacitor gain blocks, class-AB output buffer for driving off-chip loads and a 12-bit pipeline ADC for on-chip digitization. The pixel preamplifiers array, occupying an area of 30???m?×?30???m per pixel, can either be hybridized to a separate IR or UV sensor or can be used as monolithic visible-light active CMOS pixel-array after exposing (by etching the pad) the embedded photodiode under the bonding pads. The ROIC is designed and fabricated in 0.25???m 1P/5?M CMOS technology with 5?mm?×?5?mm of total dimensions. The integrated readout chain, in integrate-then-read mode, demonstrates a dynamic range of 72?dB for electrically emulated sensor currents from 25?pA to 100?nA. It can support a frame rate of 700?fps, with single fully-differential analog as well as 12-bit digital output, at 10?MHz while consuming 17?mW with on-chip biases.     

基于双变压器的复合式谐振三电平零电流开关变换器

针对分布式光伏发电接入中压直流配电网的应用场合,提出了一种基于双变压器的复合式谐振三电平变换器。新型变换器是在传统中性点钳位型三电平电路的基础上,通过添加一个辅助电路实现了基础三电平电路的固定占空比运行,变换器工作于电流断续模式。其中,基础三电平电路传输大部分功率,而辅助电路采用脉宽调制方式,可以实现基础三电平电路在全负载范围内的零电流开关,从而显著降低变换器的开关损耗。重点讨论了辅助变压器变比和谐振电容对开关管电流、谐振电压峰值、谐振电感值大小的影响,提出了相应的参数设计指导原则。最后,制作了一套300～1 500 V/2 kW原理样机对所提变换器的性能进行了验证。     

Designing Bayesian Two-Sided Group Chain Sampling Plan for Gamma Prior Distribution

Acceptance sampling is used to decide either the whole lot will be accepted or rejected, based on inspection of randomly sampled items from the same lot. As an alternative to traditional sampling plans, it is possible to use Bayesian approaches using previous knowledge on process variation. This study presents a Bayesian two-sided group chain sampling plan (BTSGChSP) by using various combinations of design parameters. In BTSGChSP, inspection is based on preceding as well as succeeding lots. Poisson function is used to derive the probability of lot acceptance based on defective and non-defective products. Gamma distribution is considered as a suitable prior for Poisson distribution. Four quality regions are found, namely: (i) quality decision region (QDR), (ii) probabilistic quality region (PQR), (iii) limiting quality region (LQR) and (iv) indifference quality region (IQR). Producer’s risk and consumer’s risk are considered to estimate the quality regions, where acceptable quality level (AQL) is associated with producer’s risk and limiting quality level (LQL) is associated with consumer’s risk. Moreover, AQL and LQL are used in the selection of design parameters for BTSGChSP. The values based on all possible combinations of design parameters for BTSGChSP are presented and inflection points’ values are found. The finding exposes that BTSGChSP is a better substitute for the existing plan for industrial practitioners.