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Development of magnetoelectric nanocomposite for soft technology
No full textThe proliferation of flexible and stretchable electronics has led to substantial advancements in principles, material combinations and technologies. The integration of magnetoelectric systems in soft electronics is inevitable by virtue of their extensive applications. Recently, 2D layered materials have emerged as potential candidates due to their excellent flexibility and atomic-scale thickness scalability in addition to their interesting physics. This paper presents a new perspective on the development of magnetoelectric nanocomposites through materials engineering on a pliant mica with excellent mechanical, thermal and chemical stabilities. The unique features of 2D muscovite mica and the power of van der Waals epitaxy are expected to contribute significantly to the emerging transparent soft-technology research applications
Achieving Overlap of Multiple, Arbitrarily Shaped Footprints Using Rendezvous Cones
No full textThis paper addresses the problem of achieving the overlap of footprints of unmanned aerial vehicles used for search and surveillance or for establishing communication between remote areas. The need of the footprints to overlap is dictated by the requirement that no part of the sensed area is left uncovered in a search and surveillance operation or by the need to position a relay unmanned aerial vehicle in the overlap region of two distant unmanned aerial vehicles in order to enable them to communicate with each other. The problem is generalized by considering arbitrarily shaped footprints that can arise in various applications. The concept of a rendezvous cone, which invokes several notions from hyperbolic geometry and collision dynamics in the relative velocity framework, is used as the basis for the development of nonlinear analytical guidance laws that enable the overlap of footprints to the requisite depth. Simulations are presented that demonstrate the effectiveness of the developed guidance laws
Minkowski Tensors in Two Dimensions: Probing the Morphology and Isotropy of the Matter and Galaxy Density Fields
No full textWe apply the Minkowski tensor statistics to two-dimensional slices of the three-dimensional matter density field. The Minkowski tensors are a set of functions that are sensitive to directionally dependent signals in the data and, furthermore, can be used to quantify the mean shape of density fields. We begin by reviewing the definition of Minkowski tensors and introducing a method of calculating them from a discretely sampled field. Focusing on the statistic W-2(1,1)-a 2 x 2 matrix-we calculate its value for both the entire excursion set and individual connected regions and holes within the set. To study the morphology of structures within the excursion set, we calculate the eigenvalues lambda(1), lambda(2) for the matrix W-2(1,1) of each distinct connected region and hole and measure their mean shape using the ratio beta equivalent to <lambda(2)/lambda(1)>. We compare both W-2(1,1) and beta for a Gaussian field and a smoothed density field generated from the latest Horizon Run 4 cosmological simulation to study the effect of gravitational collapse on these functions. The global statistic W-2(1,1) is essentially independent of gravitational collapse, as the process maintains statistical isotropy. However, beta is modified significantly, with overdensities becoming relatively more circular compared to underdensities at low redshifts. When applying the statistics to a redshift-space distorted density field, the matrix W-2(1,1) is no longer proportional to the identity matrix, and measurements of its diagonal elements can be used to probe the large-scale velocity field
Performance Analysis of Media-Based Modulation With Imperfect Channel State Information
No full textMedia-based modulation (MBM) is an attractive modulation scheme where information bits are conveyed by digitally controlling the ON/OFF status of radio frequency mirrors (which are parasitic elements) placed near the transmit antenna. The MBM alphabet (which is the set of channel fade coefficients corresponding to all possible mirror ON/OFF status vectors) is estimated at the receiver through pilot transmissions. In this paper, we analyze the effect of imperfect channel estimation on the bit error performance of MBM. We present the analysis for generalized spatial modulation MBM (GSM-MBM). We analyze the performance for two types of detectors, namely the commonly studied mismatched detector, and the true maximum-likelihood (ML) detector that maximizes the likelihood by taking the statistics of the channel estimate into account. First, we derive an exact average pairwise error probability (PEP) expression for the mismatched detector using characteristic function approach, and obtain a union bound based upper bound on the average bit error probability (BEP). Next, given the estimate of the MBM alphabet, we derive the true ML detector for GSM-MBM, and derive an exact average PEP expression (by averaging the conditional PEP over the statistics of the channel estimate) and an upper bound on the average BEP. The exactness of the average PEP and the tightness of the average BEP upper bounds of the detectors are validated through simulations
Spectrally Resolved, Broadband Frequency Response Characterization of Photodetectors using Continuous-Wave Supercontinuum Sources
No full textA simple and powerful method using continuous wave supercontinuum lasers is demonstrated to perform spectrally resolved, broadband frequency response characterization of photodetectors in the NIR Band. In contrast to existing techniques, this method allows for a simple system to achieve the goal, requiring just a standard continuous wave(CW) high-power fiber laser source and an RF spectrum analyzer. From our recent work, we summarize methods to easily convert any high-power fiber laser into a CW supercontinuum. These sources in the time domain exhibit interesting properties all the way down to the femtosecond time scale. This enables measurement of broadband frequency response of photodetectors while the wide optical spectrum of the supercontinuum can be spectrally filtered to obtain this information in a spectrally resolved fashion. The method involves looking at the RF spectrum of the output of a photodetector under test when incident with the supercontinuum. By using prior knowledge of the RF spectrum of the source, the frequency response can be calculated. We utilize two techniques for calibration of the source spectrum, one using a prior measurement and the other relying on a fitted model. Here, we characterize multiple photodetectors from 150MHz bandwidth to >20GHz bandwidth at multiple bands in the NIR region. We utilize a supercontinuum source spanning over 700nm bandwidth from 1300nm to 2000nm. For spectrally resolved measurement, we utilize multiple wavelength bands such as around 1400nm and 1600nm. Interesting behavior was observed in the frequency response of the photodetectors when comparing broadband spectral excitation versus narrower band excitation
Effect of micropillar surface texturing on friction under elastic dry reciprocating contact
No full textSurface texturing is considered to be a promising method to improve the tribological properties. Depending upon the experimental conditions, the effect of texturing varies from favourable to unnoticeable to detrimental. In this work, surfaces with micropillars are studied under elastic dry reciprocating contact. An array of micropillars with different pillar heights are generated on stainless steel using wire-cut electrical discharge machining. The effect of stiffness of the micropillars on friction is investigated, keeping the number of micropillars in contact with a flat aluminium alloy (Al6061) slider and contact geometry constant. Reciprocating experiments are carried out against a flat surface such that about 81 micropillars are in contact. From the experimental results, it is found that the coefficient of friction is independent of the stiffness of the texture elements. However, work done per cycle significantly varied with the stiffness of texture element and applied normal load. A lumped system model with Coulomb friction shows that the work done per cycle varies quadratically with the normal load. The experimental results agree with this simplified model except in the incipient sliding regime. These results show how the work done per cycle varies, for different contact stiffness under elastic contact even though the coefficient of friction remains constant. The implication of this study for a macroscopic measured coefficient of friction as a function of microscopic asperity level friction is discussed
Optimal Sensor Collaboration for Parameter Tracking Using Energy Harvesting Sensors
No full textIn this paper, we design an optimal sensor collaboration strategy among neighboring nodes while tracking a time-varying parameter using wireless sensor networks in the presence of imperfect communication channels. The sensor network is assumed to be self-powered, where sensors are equipped with energy harvesters that replenish energy from the environment. In order to minimize the mean square estimation error of parameter tracking, we propose an online sensor collaboration policy subject to real-time energy harvesting constraints. The proposed energy allocation strategy is computationally light and only relies on the second-order statistics of the system parameters. For this, we first consider an offline nonconvex optimization problem, which is solved exactly when using semidefinite programming. Based on the offline solution, we design an online power allocation policy that requires minimal online computation and satisfies the dynamics of energy flow at each sensor. We prove that the proposed online policy is asymptotically equivalent to the optimal offline solution and show its convergence rate and robustness. We empirically show that the estimation performance of the proposed online scheme is better than that of the online scheme when channel state information about the dynamical system is available in the low SNR regime. Numerical results demonstrate the effectiveness of our approach
Reduced-complexity delay-efficient throughput-optimal distributed scheduling with heterogeneously delayed network-state information
No full textWe consider the problem of distributed scheduling in wireless communication networks where heterogeneously delayed queue lengths and channel states of all links are available at all the transmitters. In an earlier work (by Reddy et al. in Queueing Systems, 2012), a throughput-optimal scheduling policy (which we refer to henceforth as the R policy) for this setting was proposed. We study the R policy, and examine its two drawbacks - (i) its huge computational complexity, and (ii) its non-optimal average per-packet queueing delay. We show that the R policy unnecessarily constrains itself to work with information that is more delayed than that afforded by the system. We propose a new distributed scheduling policy that fully exploits the common state information available to all transmitters, thereby greatly improving upon the computational complexity and the delay performance relative to those of the R policy. We also establish the throughput optimality of our policy analytically. We evaluate the performance of the proposed policy and validate our analytical results through extensive numerical simulation. Thus, our work enlarges the ambit of networks for which throughput-optimal scheduling is practicable. (C) 2018 Elsevier B.V. All rights reserved
Formation of Anisotropic Nanostructures on Rutile TiO2(110) Surfaces and Their Photo-Absorption Properties
No full textEnhancement of absorption properties in nanostructures of rutile TiO2, fabricated through an ion beam sputtering process, are reported here. The nanostructures are anisotropic in nature, being elongated along the 001] direction. With increasing fluence, the anisotropy of the nanostructures increases. Their width along 10], however, is constrained and does not grow proportionally. The results indicate that the asymmetric diffusion of mobile species, created by preferential sputtering, on the rutile TiO2(110) surface plays a crucial role in defining the nanostructure morphology as well as the photo-absorption properties. An enhanced photo-absorption response from TiO2 nanostructures was also observed here. The results were obtained in the absence of any dopant material
Discovery of highly spin-polarized conducting surface states in the strong spin-orbit coupling semiconductor Sb2Se3
No full textMajority of the A(2)B(3)-type chalcogenide systems with strong spin-orbit coupling (SOC), such as Bi2Se3, Bi2Te3, and Sb2Te3, etc., are topological insulators. One important exception is Sb2Se3 where a topological nontrivial phase was argued to be possible under ambient conditions, but such a phase could be detected to exist only under pressure. In this paper, we show that Sb2Se3 like Bi2Se3 displays a generation of highly spin-polarized current under mesoscopic superconducting point contacts as measured by point-contact Andreev reflection spectroscopy. In addition, we observe a large negative and anisotropic magnetoresistance of the mesoscopic metallic point contacts formed on Sb2Se3. Our band-structure calculations confirm the trivial nature of Sb2Se3 crystals and reveal two trivial surface states one of which shows large spin splitting due to Rashba-type SOC. The observed high spin polarization and related phenomena in Sb2Se3 can be attributed to this spin splitting