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FeRhCrSi: A new spin semimetal with room temperature spin-valve behavior

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arXiv 2022年

作者： Venkateswara, Y. Nag, Jadupati Samatham, S. Shanmukharao Patel, Akhilesh Kumar Babu, P.D. Varma, Manoj Raama Nayak, Jayita Suresh, K.G. Alam, Aftab Magnetic Materials Laboratory Department of Physics Indian Institute of Technology Bombay Mumbai400076 India Spectroscopic Investigations of Novel Systems Laboratory Department of Physics Indian Institute of Technology Kanpur Kanpur208016 India Graduate School of Advanced Science and Engineering Hiroshima University Hiroshima Higashihiroshima739-0046 Japan Department of Physics Chaitanya Bharathi Institute of Technology Gandipet Hyderabad500 075 India UGC-DAE Consortium for Scientific Research Mumbai Centre BARC Campus Mumbai400085 India Thiruvananthapuram695019 India Department of Physics Indian Institute of Technology Bombay Mumbai400076 India

Spin semimetals are a recently discovered new class of spintronic materials, which exhibit a band gap in one spin channel while a semimetallic feature in the other and thus allows for tunable spin transport. Here, we present experimental verification of spin semimetallic behavior in FeRhCrSi, a quaternary Heusler alloy with saturation moment 2 µB and Curie temperature > 400 K. It crystallises in the L21 structure with 50% antisite disorder between Fe and Rh. Below 300 K, it shows a weakly temperature dependent electrical resistivity with negative temperature coefficient, indicating the normal semimetal or spin semimetal behavior. Anomalous magnetoresistance data reveals dominant contribution from asymmetric part, a clear signature of spin-valve nature, which is retained even at room temperature. The asymmetric part of magneto-resistance shows an unusual increase with increasing temperature. Hall measurements confirm the anomalous nature of conductivity originating from the intrinsic Berry curvature, with holes being the majority carriers. Ab-initio simulation confirms a unique long-range ferrimagnetic ordering to be the ground state, explaining the origin behind the unexpected low saturation moment. The ferrimagnetic disordered structure confirms the spin semimetallic feature of FeRhCrSi, as observed experimentally. Copyright © 2022, The Authors. All rights reserved.

关键词： Ground state

Rigid Body Geometric Attitude Estimator using Multi-rate Sensors

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arXiv 2020年

作者： Bhatt, Maulik Sukumar, Srikant Sanyal, Amit K. Aerospace Engineering Indian Institute of Technology Bombay 400076 India Systems and Control Engineering Indian Institute of Technology Bombay 400076 India Mechanical and Aerospace Engineering Syracuse University SyracuseNY United States

— A geometric estimator is proposed for the rigid body attitude under multi-rate measurements using discrete-time Lyapunov stability analysis in this work. The angular velocity measurements are assumed to be sampled at a higher rate compared to the attitude. The attitude determination problem from two or more vector measurements in the body-fixed frame is formulated as Wahba’s problem. In the case when measurements are absent, a discrete-time model for attitude kinematics is assumed in order to propagate the measurements. A discrete-time Lyapunov function is constructed as the sum of a kinetic energy-like term that is quadratic in the angular velocity estimation error and an artificial potential energy-like term obtained from Wahba’s cost function. A filtering scheme is obtained by discrete-time stability analysis using a suitable Lyapunov function. The analysis shows that the filtering scheme is exponentially stable in the absence of measurement noise and the domain of convergence is almost global. For a realistic evaluation of the scheme, numerical experiments are conducted with inputs corrupted by bounded measurement noise. Simulation results exhibit convergence of the estimated states to a bounded neighborhood of the actual states. Copyright © 2020, The Authors. All rights reserved.

关键词： Lyapunov functions

Dynamic Analysis and Circuit Design of a New 3D Highly Chaotic System and its Application to Pseudo Random Number Generator (PRNG) and Image Encryption

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SN Computer Science 2024年第4期5卷 420页

作者： Sambas, Aceng Benkouider, Khaled Kaçar, Sezgin Ceylan, Nurdoğan Vaidyanathan, Sundarapandian Sulaiman, Ibrahim Mohammed Mohamed, Mohamad Afendee Ayob, Ahmad Faisal Mohamad Muni, Sishu Shankar Faculty of Informatics and Computing Universiti Sultan Zainal Abidin Campus Besut Terengganu Kuala 22200 Malaysia Department of Mechanical Engineering Universitas Muhamadiyah Tasikmalaya Tamansari Gobras Tasikmalaya 46196 Indonesia Department of Electronics Faculty of Technology Badji-Mokhtar University B.P. 12 Sidi Ammar Annaba 23000 Algeria Department of Electrical and Electronics Engineering Sakarya University of Applied Sciences Serdivan Sakarya 54050 Turkey Department of Mechanical Engineering Adıyaman University Merkez Adıyaman 02040 Turkey Centre for Control Systems Vel Tech University Tamil Nadu Chennai 600062 India School of Quantitative Science University Utara Malaysia Sintok Kedah Bukit Kayu Hitam 06010 Malaysia Faculty of Education and Arts Sohar University Sohar 311 Oman Faculty of Ocean Engineering Technology and Informatics Universiti Malaysia Terengganu Gong Badak Terengganu Kuala Terengganu 21300 Malaysia Department of Physical Sciences Department of Physical Sciences Indian Institute of Science Education and Research Mohanpur Kolkata 741246 India

In this paper, a new 3D dynamical system with four quadratic nonlinear terms is presented. It is shown that the proposed chaotic system has two saddle-foci, unstable, equilibrium points. Thus, the proposed chaotic system exhibits self-excited chaotic attractors. Dynamical analysis methods such as Lyapunov exponents spectrum, bifurcation diagrams, and phase portraits are used to explore the complex dynamical behaviors of the proposed chaotic system and analyze its basic qualitative properties. It is shown that the maximal Lyapunov exponent (MLE) of the new chaotic system is 7.196, which is a high value. The proposed highly chaotic system exhibits high complexity and it will be very useful for applications in cryptography, encryption and secure communications. The physical feasibility of the proposed system is verified by implementing its electronic circuit schematic using Multisim software. Additionally, a PRNG has been developed using the derived state variables and analyze with NIST-800–22 test. Lastly, we developed a PRNG-based image encryption and employ it for an encryption. The experimental outcomes obtained prove that the 3D chaotic system-based encryption application presented in this section has a very good performance. © The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd. 2024.

关键词： Chaos Image encryption Pseudo random number generator

Strategy-Proof Spectrum Allocation among Multiple Operators for Demand Varying Wireless Networks†

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arXiv 2020年

作者： Yadav, Indu Kulkarni, Ankur A. Karandikar, Abhay Department of Electrical Engineering Indian Institute of Technology Bombay Mumbai400076 India Systems and Control Department Indian Institute of Technology Bombay Mumbai400076 India Kanpur208016 India

To address the exponentially increasing data rate demands of end users, necessitates efficient spectrum allocation among co-existing operators in licensed and unlicensed spectrum bands to cater to the temporal and spatial variations of traffic in the wireless network. In this paper, we address the spectrum allocation problem among non-cooperative operators via auctions. The classical Vickrey-Clarke-Groves (VCG) approach provides the framework for a strategy-proof and social welfare maximizing auction at high computational complexity, which makes it infeasible for practical implementation. We propose sealed bid auction mechanisms for spectrum allocation which are computationally tractable and hence applicable for allocating spectrum by performing auctions in short durations as per the dynamic load variations of the network. We establish that the proposed algorithm is strategy-proof for uniform demand. Furthermore, for non-uniform demand we propose a algorithm that satisfies weak strategy-proofness. We also consider non-linear increase in the marginal valuations with demand. Simulation results are presented to exhibit the performance comparison of the proposed algorithms with VCG and other existing mechanisms. Copyright © 2020, The Authors. All rights reserved.

关键词： Wireless networks

A Heuristic Adaptive Traffic control Algorithm for Signalized Intersections

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A Heuristic Adaptive Traffic Control Algorithm for Signalize...

International Communication systems and Networks and Workshops, COMSNETS

作者： Bijul Raveendran Tom V. Mathew Nagendra R. Velaga Transportation Systems Engineering Indian Institute of Technology Bombay Mumbai India

ISBN: (数字)9781728131870

ISBN: (纸本)9781728131887

It is observed that most of the adaptive traffic control algorithms popular in countries with homogeneous traffic perform sub-optimally in heterogeneous non-lane-following traffic conditions owing to the inaccuracies in predicting demand, sub-optimal solutions, and time-consuming computation. The determination of demand based on discharge headway has also contributed to inaccuracies in demand estimation. Hence, this study proposes a heuristic adaptive traffic control algorithm using demand estimation based on queue length, which is expected to perform better in varying traffic composition, roadway geometry, and the presence of road-side friction. VISSIM 6.0 was used to evaluate the algorithm, with an existing vehicle-actuated algorithm used as a benchmark. In order to evaluate the developed algorithm, two test cases are presented with average stopped delay, average control delay, average queue length, and peak hour discharge. Results show significant improvements to the adaptive traffic control algorithm with respect to the parameters considered for evaluation.

关键词： Discharges (electric) Delays Heuristic algorithms Adaptive systems Estimation Communication systems Prediction algorithms

Integrated guidance and control design for time-constrained interception

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TechRxiv

TechRxiv 2020年

作者： Sinha, Abhinav Kumar, Shashi Ranjan Mukherjee, Dwaipayan The Intelligent Systems & Control Lab Department of Aerospace Engineering Indian Institute of Technology Bombay Powai Mumbai400076 India Department of Electrical Engineering Indian Institute of Technology Bombay Powai Mumbai400076 India

This paper proposes integrated guidance and control design to intercept a non-maneuvering target at a pre-specified time of interception. The problem is addressed considering nonlinear engagement kinematics and the interceptor is steered using the combined effects of canard as well as tail configurations (dual control interceptors). Different formulations of time-to-go, without the restrictive assumption of interceptor’s small heading angle, have been used in deriving the guidance commands, allowing the proposed strategies to remain effective over a wide range of impact time values. A weighted effort allocation scheme, in canard and tail deflections, has been proposed to generate the required lateral acceleration. The overall design uses sliding mode control owing to its simplicity of design. Finally, simulations are presented for various scenarios, including impaired actuator, vindicating the efficacy of the proposed technique. © 2020, CC BY-NC-SA.

关键词： Sliding mode control

Duopolistic platform competition for revenue and throughput

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arXiv 2020年

作者： Sood, Mansi Kulkarni, Ankur A. Moharir, Sharayu Carnegie Mellon University Pittsburgh United States Systems and Control Engineering Indian Institute of Technology Bombay Powai Mumbai400076 India Electrical Engineering Indian Institute of Technology Bombay PowaiMumbai400076 India

We consider two competing platforms operating in a two-sided market and offering identical services to their customers at potentially different prices. The objective of each platform is to maximize its throughput or revenue by suitably pricing its services. We assume that customers have a preference or loyalty to the platforms while the workers freelance for the two platforms. Assuming that the resulting interaction between the users is such that their aggregate utility is maximized, we show that for each value of the loyalty, there exists a pure strategy Nash equilibrium for both the throughput and revenue competition game and characterize it. Copyright © 2020, The Authors. All rights reserved.

关键词： Crowdsourcing

Development of Cfd Model for Cryogenic Liquid Rocket Injectors and Validation with Experiments

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SSRN

SSRN 2022年

作者： Sujithkumar, Raghavan Pillai Chenthil Kumar, K. Anil Kumar, K.R. Jayachnadran, T. Bodi, Kowsik Vikram Sarabhai Space Center Kerala Thiruvananthapuram695022 India Limited HSR Layout Bengaluru560102 India Indian Institute of Technology Madras IIT P.O. Chennai600036 India Indian Institute of Technology Bombay Mumbai400076 India Propulsion Systems Space Transportation Systems United States Nozzle and Combustor Study Project Aeronautics Entity Ventil Software Development Multiphysics Solver Development Department of Aerospace Engineering

In this work we present the computational and experimental study of combustors with GH2 and *** experimental setup is established to test the cryogenic liquid rocket combustors. It is used to study the subcritical injection, evaporation, mixing and burning of liquid oxygen and gaseous hydrogen, using a shear coaxial injector. A computational fluid dynamics (CFD) model for two phase flow with phase change and combustion is developed using both the Eulerian-Lagrangian and Eulerian-Eulerian frameworks to simulate these combustors. Multiple evaporation models were used to simulate LO2 evaporation while Modified Eddy Dissipation Concept is used to model combustion. The model is first validated against the earlier published measurements for validating both single phase and two phase flow combustion and then it is used to simulate the experiments conducted as a part of the present work. Comparison of the results shows that both the frameworks can produce similar results for the operating conditions considered. © 2022, The Authors. All rights reserved.

关键词： Combustion

Iterative Learning based feedforward control for Transition of a Biplane-Quadrotor Tailsitter UAS

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Iterative Learning based feedforward control for Transition ...

IEEE International Conference on Robotics and Automation (ICRA)

作者： Nidhish Raj Ashutosh Simha Mangal Kothari Abhishek Ravi N. Banavar Department of Aerospace Engineering Indian Institute of Technology Kanpur India Institute of Cybernetics Tallinn University of Technology Estonia Systems and Control Group Indian Institute of Technology Bombay Mumbai India

ISBN: (数字)9781728173955

ISBN: (纸本)9781728173962

This paper provides a real time on-board algorithm for a biplane-quadrotor to iteratively learn a forward transition maneuver via repeated flight trials. The maneuver is controlled by regulating the pitch angle and propeller thrust according to feedforward control laws that are parameterized by polynomials. Based on a nominal model with simplified aerodynamics, the optimal coefficients of the polynomials are chosen through simulation such that the maneuver is completed with specified terminal conditions on altitude and air speed. In order to compensate for modeling errors, repeated flight trials are performed by updating the feedforward control parameters according to an iterative learning algorithm until the maneuver is perfected. A geometric attitude controller, valid for all flight modes is employed in order to track the pitch angle according to the feedforward law. Further, a high-fidelity thrust model of the propeller for varying advance-ratio and orientation angle is obtained from wind tunnel data which is captured using a neural network model. This facilitates accurate application of feedforward thrust for varying flow conditions during transition. Experimental flight trials are performed to demonstrate the robustness and rapid convergence of the proposed learning algorithm.

关键词： Aerodynamics Propellers Wind tunnels Atmospheric modeling Feedforward systems Data models Trajectory