Study of Porous Silicon Prepared Using Metal-Induced Etching (MIE): a Comparison with Laser-Induced Etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.     

Optimal Design of 2D FIR Filters with Quadrantally Symmetric Properties Using Fractional Derivative Constraints

In this article, an optimal design of two-dimensional finite impulse response (2D FIR) filter with quadrantally even symmetric impulse response using fractional derivative constraints (FDCs) is presented. Firstly, design problem of 2D FIR filter is formulated as an optimization problem. Then, FDCs are imposed over the integral absolute error for designing of the quadrantally even symmetric impulse response filter. The optimized FDCs are applied over the prescribed frequency points. Next, the optimized filter impulse response coefficients are computed using a hybrid optimization technique, called hybrid particle swarm optimization and gravitational search algorithm (HPSO-GSA). Further, FDC values are also optimized such that flat passband and stopband frequency response is achieved and the absolute \(L_1\)-error is minimized. Finally, four design examples of 2D low-pass, high-pass, band-pass and band-stop filters are demonstrated to justify the design accuracy in terms of passband error, stopband error, maximum passband ripple, minimum stopband attenuation and execution time. Simulation results have been compared with the other optimization algorithms, such as real-coded genetic algorithm, particle swarm optimization and gravitational search algorithm. It is observed that HPSO-GSA gives improved results for 2D FIR-FDC filter design problem. In comparison with other existing techniques of 2D FIR filter design, the proposed method shows improved design accuracy and flexibility with varying values of FDCs.     

Towards graphical models for text processing

The continuous development of the Linked Data Web depends on the advancement of the underlying extraction mechanisms. This is of particular interest for the scientific publishing domain, where currently most of the data sets are being created manually. In this article, we present a Machine Learning pipeline that enables the automatic extraction of heading metadata (i.e., title, authors, etc) from scientific publications. The experimental evaluation shows that our solution handles very well any type of publication format and improves the average extraction performance of the state of the art with around 4%, in addition to showing an increased versatility. Finally, we propose a flexible Linked Data-driven mechanism to be used both for refining and linking the automatically extracted metadata.     

Robust control approach to force estimation in a constant position optical tweezers

Feedback enhanced optical tweezers with position regulation capability enable detection and estimation of forces in the pico-Newton regime. In this article we delineate the fundamental limitations and challenges of existing approaches for regulating position and force estimation in an optical tweezer. A modern control systems approach is shown to improve the bandwidth of force estimation by three to four times which is corroborated experimentally.     

Fuzzy R&D portfolio selection of interdependent projects

Global competition of markets has forced firms to invest in targeted R&D projects so that resources can be focused on successful outcomes. A number of options are encountered to select the most appropriate projects in an R&D project portfolio selection problem. The selection is complicated by many factors, such as uncertainty, interdependences between projects, risk and long lead time, that are difficult to measure. Our main concern is how to deal with the uncertainty and interdependences in project portfolio selection when evaluating or estimating future cash flows. This paper presents a fuzzy multi-objective programming approach to facilitate decision making in the selection of R&D projects. Here, we present a fuzzy tri-objective R&D portfolio selection problem which maximizes the outcome and minimizes the cost and risk involved in the problem under the constraints on resources, budget, interdependences, outcome, projects occurring only once, and discuss how our methodology can be used to make decision support tools for optimal R&D project selection in a corporate environment. A case study is provided to illustrate the proposed method where the solution is done by genetic algorithm (GA) as well as by multiple objective genetic algorithm (MOGA).     

Designing flexible service systems: application to machine tools

Service system design process is complex in nature and involves many stakeholders. The process becomes more critical in the context of machine tools due to market competition, complexity of services, competency requirements and cost constraints. The objective of this paper is to propose a generic approach for the design of a service system for machine tools which can support a variety of business models along with meeting customers’ demand for flexibility. The proposed approach makes use of fundamental service design steps and offers flexibility to the customers to choose the services, service mechanisms, service levels and service frequencies as per their requirements considering the economic aspects, and thus underlines the involvement and participation of customers in the service design process. It also facilitates service designers to visualize the roles of stakeholders involved in the service process and highlights the importance of customer involvement for customer service assurance and better service experience. Application of the approach is discussed through a case study conducted in association with a leading Indian machine tool manufacturing group.     

Acoustic modeling problem for automatic speech recognition system: advances and refinements (Part II)

In automatic speech recognition (ASR) systems, hidden Markov models (HMMs) have been widely used for modeling the temporal speech signal. As discussed in Part I, the conventional acoustic models used for ASR have many drawbacks like weak duration modeling and poor discrimination. This paper (Part II) presents a review on the techniques which have been proposed in literature for the refinements of standard HMM methods to cope with their limitations. Current advancements related to this topic are also outlined. The approaches emphasized in this part of review are connectionist approach, explicit duration modeling, discriminative training and margin based estimation methods. Further, various challenges and performance issues such as environmental variability, tied mixture modeling, and handling of distant speech signals are analyzed along with the directions for future research.     

Bandwidth estimation in high mobility scenarios of IEEE 802.11 infrastructure‐less mobile ad hoc networks

Bandwidth estimation in mobile ad hoc networks (MANET), where each node can move randomly and is capable of frequently changing its link with other nodes, is a challenging task. Motivation of this work is in contrast with TCP new‐reno which decreases the congestion window both in the event of link failure and congestion, which in the case of packet loss due to link failure should be close to available channel bandwidth. The proposed novel approach capture the node's mobility behavior in broadcast and unicast scenarios of IEEE 802.11 standard to efficiently estimate the sender's window size. This proposal introduces a data structure and source‐to‐destination path stability metric to imitate the mobility behavior of network and presents the analytic characterization of steady‐state throughput as a function of packet loss, round trip time, and path stability over IEEE 802.11 infrastructure‐less MANET. The performance is evaluated over random‐walk, random‐waypoint, and Gauss‐Markov mobility models in 2D and 3D environments using QualNet 7.4 network simulator. The proposed analytical model is also evaluated through two‐tailed statistical test. Analytical, statistical, and simulation‐based comparisons demonstrate the effectiveness of proposed method in high‐mobility scenarios.     

Numerical evaluation of transient deflection and frequency responses of sandwich shell structure using higher order theory and different mechanical loadings

The static deflection, frequency and transient responses of the layered sandwich shell (flat/curved) structure computed under the different types of mechanical loading. The higher order polynomial kinematic type of mid-plane kinematics is derived for the mathematical modeling and subsequent numerical analysis. A suitable home-made code is prepared in MATLAB for the computation of deflection (static and dynamic) parameter using the proposed mathematical model. Furthermore, the numerical solution accuracy has been verified by comparing the numerical output with those available published data including the convergence test as a priori. In addition, the influences of the variable design parameters (span-to-thickness ratios, curvature ratios, aspect ratios, core-to-face thickness ratios, lamination configurations, shell configurations, and support conditions) on the deflection, frequency, and the transient values are computed extensively and the inferences provided in details.

     

A multi‐stub loaded compact UWB BPF with a broad notch band and extended stopband characteristics

A compact ultrawideband (UWB) bandpass filter (BPF) employing the principle of multiple mode resonance characteristics to create UWB passband with high selectivity and simultaneously having extensive stopband characteristic is presented. Utilizing five stubs attached along with the asymmetric trisection stepped impedance resonator (ATSSIR), the proposed resonator enables seven transmission poles inside the passband. As an additional attributes the projected filter triggers one transmission zero at 5.0 GHz which helps to mitigate WLAN signal interference. No additional circuitry is used to generate a notch band. The proposed prototype of UWB BPF is fabricated and estimated. Simulated and estimated results are in great understanding. The prospective filter displays a deliberate passband from 2.9 to 11.02 GHz. The filter unveils deceptive free wide upper stop band attributes till 25 GHz with least attenuation of 10 dB all through the stop band.