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Robust stabilization of balanced and splay formations with heterogeneous controller gains
No full textThis paper analyses collective motion of multi-vehicle systems in balanced or splay formation when the vehicles are equipped with heterogeneous controller gains. Balancing refers to a situation in which the positional centroid of the vehicles is stationary. The splay formation is a special case of balancing in which the vehicles are spatially distributed with equal angular separation between them. The paper proposes strategies to achieve such balanced and splay formations about a desired centroid location while allowing the vehicles to move either along straight line paths or on individual circular orbits. Feedback control laws that can tolerate heterogeneity in the controller gains, which may be caused by imperfect implementation, are derived and analyzed. It is shown that drastic failures leading to controller gains becoming zero for almost half of the vehicles in the group can be tolerated and balanced formation can still be achieved. On the other hand, splay formation can still be achieved if the controller gain is zero for at most one vehicle. Simulation examples are given to illustrate the theoretical findings. (C) 2019 Published by Elsevier Ltd on behalf of The Franklin Institute
Equality of Lyapunov and Stability Exponents for Products of Isotropic Random Matrices
No full textIn the study of random matrices, Lyapunov exponents characterize the rate of exponential growth of the singular values of product of increasing number of random matrices of fixed order. These have been well studied objects in the literature. Only recently, absolute values of the eigenvalues of such products of random matrices have come under analytical study. The quantities that characterize the rate of exponential growth of the absolute values of eigenvalues have been named stability exponents, in order to distinguish them from that of the singular values. In the cases of Ginibre matrices and truncated Haar unitary matrices, the stability exponents have been observed to match with the Lyapunov exponents. In this article, we generalize this result to the case of all isotropic random matrices. We also derive the asymptotic joint probability distributions for the fluctuations of both the singular values and the absolute values of eigenvalues of product of increasing number of real or complex isotropic random matrices of fixed order. Moreover, Lyapunov exponents are distinct, unless the random matrices are random scalar multiples of Haar unitary matrices or orthogonal matrices. As a corollary of this, we show the probability that the product of real isotropic random matrices has all the eigenvalues real goes to one as n -> infinity
Glioblastoma vs temozolomide: can the red queen race be won?
No full textGlioblastoma is the most invasive form of brain tumor. Although temozolomide chemotherapy has been shown to significantly improve survival in patients with GBM, this increase is only trivial. The underlying cause is that many GBMs do not respond to temozolomide, and the rest produces resistance. In the past two decades, many attempts have been made to understand resistance mechanisms and to combine other treatments with temozolomide to maximize patient benefit. Unfortunately, it seems to be a red queen game, and the speed of disease development is as fast as the progress in the field. In order to win this game, a comprehensive approach is needed to decipher the details of the resistance mechanism and to transfer the basic research to the clinic. This article reviews the following: temozolomide discovery, chemistry, and mechanism of action, and mechanisms of resistance, as well as combination therapy with other strategies
Subcell Modeling of Partially Shaded Photovoltaic Modules
No full textIncreased photovoltaic installations in densely built-up areas give rise to non-uniform irradiation causing partial shading. Non-uniform irradiation further leads to non-uniform temperature, leading to a reduction in output and the formation of deteriorating hotspots. A detailed model involving subcell level behavior is pivotal in understanding the impact of partial shading. In this paper, such a model is developed that analyzes the output of photovoltaic (PV) modules under different translucent and opaque shades while incorporating the diffused light effects. This model further includes the temperature variation of the module and also captures the bypass diode characteristics. The proposed model is experimentally validated for horizontal, vertical, slant, and patch shading patterns with varying shading intensities. This subcell model is shown to perform better than four existing methods of partial shading output prediction. It improves the output open-circuit voltage and short-circuit current prediction accuracy by more than 10% when compared with the average irradiance-based modeling approach, which is the best among the existing methods. Overall, an output prediction accuracy of more than 93% is achieved for opaque shading and more than 95% for translucent shading. As this paper provides the output of PV modules under partial shading, it finds direct application in partial shading detection, prevention of hotspots, and global maximum power point tracking, thereby enhancing their life and efficiency
Evaluation of temperature dependent electrical transport parameters in Fe3O4/SiO2/n-Si metal-insulator-semiconductor (MIS) type Schottky barrier heterojunction in a wide temperature range
No full textIn this manuscript, we reported the electrical characteristics and structural analysis of In/Fe3O4/SiO2/n-Si/In MIS-type SBD heterostructure comprehensively in the temperature range 10-300K using I-V, XRD, TEM and AFM measurements. Pulsed laser deposition in association with DC magnetron sputtering techniques has been utilized to fabricate the proposed In/Fe3O4/SiO2/n-Si/In heterojunction. The fabricated heterojunction revealed that the I-V curves are non-linear and asymmetric in nature. Using these I-V curves in the forward-bias region, SBH is calculated as 0.02eV at 10K and 0.74eV at 300K. On the other hand, the ideality factor (n) value was calculated as 7.55 at 10K and 1.37 at 300K. The series resistance (R-S) values were also evaluated using Chenug's method and the values were 1121 at 10K and 334 at 300K. The dependence of important diode parameters such as SBH, n' and R-S' on measurement temperature was effectively explained firstly on account of triple Gaussian distribution of barrier heights with the help of barrier inhomogeneities of the prepared heterojunction. The value of the Richardson's constant calculated for the fabricated In/Fe3O4/SiO2/n-Si/In heterojunction in the 110-300K temperature regime was calculated to be 115.26A/cm(2)K(2) and is approximately equal to the theoretical value of 120A/cm(2)K(2) for n-type Si. In addition, the higher value (greater than one) of ideality factor at all operating temperatures from 10-300K demonstrated that the probable current transport across the Fe3O4/SiO2/n-Si junction is not only due to the thermionic emission (TE) mechanism. Hence, to reveal the origin of current transport mechanism i.e., other than TE, we noticed that the governing current transport process through the fabricated hetrojunction is mainly due to the tunneling assisted Poole-Frenkel class of emission across the Fe3O4/SiO2/n-Si junction which is found to be temperature-dependent
Shape Control for the Elastica Through Load Optimization
No full textFlexible elastic beams can function as dexterous manipulators at multiple length-scales and in various niche applications. As a step toward achieving controlled manipulation with flexible structures, we introduce the problem of approximating desired quasi-static deformations of a flexible beam, modeled as an elastica, by optimizing the loads applied. We presume the loads to be concentrated, with the number and nature of their application prescribed based on design considerations and operational constraints. For each desired deformation, we pose the problem of computing the requisite set of loads to mimic the target shape as one of optimal approximations. In the process, we introduce a novel generalization of the forward problem by considering the inclinations of the loads applied to be functionals of the solution. This turns out to be especially beneficial when analyzing tendon-driven manipulators. We demonstrate the shape control realizable through load optimization using a diverse set of experiments
Effect of stacking fault energy on the evolution of microstructure and texture during blast assisted deformation of FCC materials
No full textEffect of stacking fault energy (SFE) on microstructural and crystallographic aspect of high-velocity deformation of FCC metals (Ni, Cu, and austenitic stainless steel) via blast assisted deformation have been investigated in this work. Microstructural changes have been probed via XRD line profile analysis and electron back-scattered diffraction methods along with TEM analysis for selected samples. The texture of all deformed material tends towards a developed a-fiber, which is observed to be strain-dependent. The relative fraction of Brass to Goss texture components increases with a decrease in SFE. The annealing twin boundaries, present in the initial material, transform in segments or full to high angle random boundary in all the material due to the dislocation pile-up. However, the microstructure of the deformed material depends heavily on the SFE, with nickel showing dislocation cells, and, austenitic stainless steel (ASS) has a mix of features of homogeneous dislocation, deformation bands, and deformation twins. Relatively thick deformation twins form in grains having orientations other than {110} plane normal to the blast direction. The overall microstructure of ASS gives an impression of a superimposed microstructure. Such structure is expected to be a result of shock passage through the material followed by macroscopic straining. No such superimposed microstructure has been observed in nickel which is attributed to recovery behavior prevalent in high SFE materials
Simultaneous kernels of matrix Hadamard powers
No full textIn previous work Belton et al. (2016) 2], the structure of the simultaneous kernels of Hadamard powers of any positive semidefinite matrix was described. Key ingredients in the proof included a novel stratification of the cone of positive semidefinite matrices and a well-known theorem of Hershkowitz, Neumann, and Schneider, which classifies the Hermitian positive semidefinite matrices whose entries are 0 or 1 in modulus. In this paper, we show that each of these results extends to a larger class of matrices which we term 3-PMP (principal minor positive). (C) 2018 Elsevier Inc. All rights reserved
Toughening of high performance tetrafunctional epoxy with poly(allyl amine) grafted graphene oxide
No full textThe mechanical and thermal properties of epoxy composites were improved by using poly (allyl amine) (PAA) grafted graphene oxide (GO) as a toughening agent. The GO was first converted to GO-COOH where all the hydroxyl groups on the basal plane were converted to COOH containing groups. GO-COOH was reacted with PAA to yield GO-g-PAA. The effect of PAA grafted GO nanosheets as fillers on mechanical and thermal properties of aerospace grade epoxy was studied. Epoxy nanocomposites containing graphene oxide (GO) and GO-g-PAA nanosheets were fabricated by incorporating 0.35 to 1.4 wt% of filler. GO-g-PAA modified epoxy nanocomposites showed excellent improvement in flexural, compression and fracture properties compared to neat epoxy and GO modified epoxy. Fracture toughness increased from 0.94 MPa m to 1/2 for neat epoxy to 1.75 MPa m-1/2 (87%) for epoxy nanocomposites modified with 0.7 wt% of GO-g-PAA nanosheets. The temperature for 5% weight loss showed drastic improvement of 24 degrees C for epoxy nanocomposites modified with 0.7 wt% of GO-g-PAA nanosheets. The examination of fractured surfaces of modified epoxy nanocomposites showed better interaction of GO-g-PAA nanosheets with epoxy compared to GO nanosheets
A consensus guide to capturing the ability to inhibit actions and impulsive behaviors in the stop-signal task
No full textResponse inhibition is essential for navigating everyday life. Its derailment is considered integral to numerous neurological and psychiatric disorders, and more generally, to a wide range of behavioral and health problems. Response-inhibition efficiency furthermore correlates with treatment outcome in some of these conditions. The stop-signal task is an essential tool to determine how quickly response inhibition is implemented. Despite its apparent simplicity, there are many features (ranging from task design to data analysis) that vary across studies in ways that can easily compromise the validity of the obtained results. Our goal is to facilitate a more accurate use of the stop-signal task. To this end, we provide 12 easy-to-implement consensus recommendations and point out the problems that can arise when they are not followed. Furthermore, we provide user-friendly open-source resources intended to inform statistical-power considerations, facilitate the correct implementation of the task, and assist in proper data analysis