Amit Kumar - Indian Institute of Astrophysics, Bangalore

Amit Kumar
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Amit Kumar
Indian Institute of Astrophysics, Bangalore

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Computer Science - Data Structures and Algorithms (12)
Physics - Materials Science (9)
Computer Science - Computer Vision and Pattern Recognition (5)
Physics - Soft Condensed Matter (5)
Instrumentation and Methods for Astrophysics (4)
Physics - Strongly Correlated Electrons (3)
Computer Science - Architecture (2)
Physics - Mesoscopic Systems and Quantum Hall Effect (2)
Physics - Fluid Dynamics (2)
Computer Science - Computational Complexity (1)
Mathematics - Mathematical Physics (1)
Mathematical Physics (1)
Physics - Other (1)
Computer Science - Cryptography and Security (1)
Nuclear Theory (1)
High Energy Physics - Phenomenology (1)
Nuclear Experiment (1)
Mathematics - Probability (1)
Physics - Biological Physics (1)

Publications Authored By Amit Kumar

Keypoint detection is one of the most important pre-processing steps in tasks such as face modeling, recognition and verification. In this paper, we present an iterative method for Keypoint Estimation and Pose prediction of unconstrained faces by Learning Efficient H-CNN Regressors (KEPLER) for addressing the face alignment problem. Recent state of the art methods have shown improvements in face keypoint detection by employing Convolution Neural Networks (CNNs). Read More

We present the first attempt to extract the "$x$" dependence of the parton distribution function (PDF) of the quark gluon plasma (QGP). In the absence of knowledge regarding the mass of a QGP constituent, we define the new variable $x_N$, the nucleonic momentum fraction, which represents the ratio of the momentum of the parton to that of a self-contained section of the plasma that has the mass of a nucleon. Calculations are compared to data for single hadron suppression in terms of the nuclear modification factor $R_{AA}$ and the azimuthal anisotropy parameter $v_{2}$, as a function of transverse momentum $p_{T}$, centrality and energy of the collision. Read More

In this paper, some erroneous results for a dependent setup arising from independent sequence of Bernoulli trials are corrected. Next, a Stein operator for discrete Gibbs measure is derived using PGF approach. Also, an operator for dependent setup is derived and shown as perturbation of the Stein operator for discrete Gibbs measure. Read More

Ultraviolet Imaging Telescope (UVIT) is one of the payloads onboard AstroSat, India's first multi-wavelength Astronomy mission. UVIT is primarily designed to make high resolution images in wide field, in three wavelength channels simultaneously: FUV (130 - 180 nm), NUV (200 - 300 nm) and VIS (320 - 550 nm). The intensified imagers used in UVIT suffer from distortions, and a correction is necessary for these to achieve good astrometry. Read More

In this paper we initiate the study of the heterogeneous capacitated $k$-center problem: given a metric space $X = (F \cup C, d)$, and a collection of capacities. The goal is to open each capacity at a unique facility location in $F$, and also to assign clients to facilities so that the number of clients assigned to any facility is at most the capacity installed; the objective is then to minimize the maximum distance between a client and its assigned facility. If all the capacities $c_i$'s are identical, the problem becomes the well-studied uniform capacitated $k$-center problem for which constant-factor approximations are known. Read More

In this paper, we study the set cover problem in the fully dynamic model. In this model, the set of active elements, i.e. Read More

The crystal structure, magnetic ground state, and the temperature dependent microscopic spin-spin correlations of the frustrated honeycomb lattice antiferromagnet Na2Co2TeO6 have been investigated by powder neutron diffraction. A three dimensional (3D) long-range antiferromagnetic ordering has been found below TN ~ 24.8 K. Read More

We present the in-orbit performance and the first results from the ultra-violet Imaging telescope (UVIT) on ASTROSAT. UVIT consists of two identical 38cm coaligned telescopes, one for the FUV channel (130-180nm) and the other for the NUV (200-300nm) and VIS (320-550nm) channels, with a field of view of 28 $arcmin$. The FUV and the NUV detectors are operated in the high gain photon counting mode whereas the VIS detector is operated in the low gain integration mode. Read More

Spin-spin correlations and microscopic origin of net magnetization in the spin-1 trimer chain compound CaNi3P4O14 have been investigated by powder neutron diffraction. The present study reveals a 3D long-range magnetic ordering below 16 K where the magnetic structure consists of ferromagnetic trimers that are coupled ferromagnetically along the spin-chain. The moment components along the a and c axes arrange antiferromagnetically. Read More

Over the last four years, methods based on Deep Convolutional Neural Networks (DCNNs) have shown impressive performance improvements for object detection and recognition problems. This has been made possible due to the availability of large annotated datasets, a better understanding of the non-linear mapping between input images and class labels as well as the affordability of GPUs. In this paper, we present the design details of a deep learning system for end-to-end unconstrained face verification/recognition. Read More

The effect of electron doping on the structural, transport, and magnetic properties of Mn (IV) - rich Ca1-xYxMnO3 (x < 0.2) samples have been investigated using neutron diffraction, neutron depolarization, magnetization and resistivity techniques. The temperature dependence of resistivity follows the small polaron model and the activation energy exhibits a minimum for x=0. Read More

This paper presents regression methods for estimation of head pose from occluded 2-D face images. The process primarily involves reconstructing a face from its occluded image, followed by classification. Typical methods for reconstruction assume that the pixel errors of the occluded regions are independent. Read More

Over many decades, researchers working in object recognition have longed for an end-to-end automated system that will simply accept 2D or 3D image or videos as inputs and output the labels of objects in the input data. Computer vision methods that use representations derived based on geometric, radiometric and neural considerations and statistical and structural matchers and artificial neural network-based methods where a multi-layer network learns the mapping from inputs to class labels have provided competing approaches for image recognition problems. Over the last four years, methods based on Deep Convolutional Neural Networks (DCNNs) have shown impressive performance improvements on object detection/recognition challenge problems. Read More

We present an algorithm for extracting key-point descriptors using deep convolutional neural networks (CNN). Unlike many existing deep CNNs, our model computes local features around a given point in an image. We also present a face alignment algorithm based on regression using these local descriptors. Read More

In a brave new age of global connectivity and e-commerce, interconnections via networks have heightened, creating for both individuals and organizations, a state of complete dependence upon vulnerable systems for storage and transfer of information. Never before, have so many people had power in their own hands. The power to deface websites, access personal mail accounts, and worse more the potential to bring down entire governments, and financial corporations through openly documented software codes. Read More

Now a day reversible logic is an attractive research area due to its low power consumption in the area of VLSI circuit design. The reversible logic gate is utilized to optimize power consumption by a feature of retrieving input logic from an output logic because of bijective mapping between input and output. In this manuscript, we design 4 2 and 5 2 reversible compressor circuits using a new type of reversible gate. Read More

A large amount of research is currently going on in the field of reversible logic, which have low heat dissipation, low power consumption, which is the main factor to apply reversible in digital VLSI circuit design. This paper introduces reversible gate named as Inventive0 gate. The novel gate is synthesis the efficient adder modules with minimum garbage output and gate count. Read More

The classical center based clustering problems such as $k$-means/median/center assume that the optimal clusters satisfy the locality property that the points in the same cluster are close to each other. A number of clustering problems arise in machine learning where the optimal clusters do not follow such a locality property. Consider a variant of the $k$-means problem that may be regarded as a general version of such problems. Read More

The study of the ability of drug molecules to enter cells through the membrane is of vital importance in the field of drug delivery. In cases where the transport of the drug molecules through the membrane is not easily accomplishable, other carrier molecules are used. Spherical fullerene molecules have been postulated as potential carriers of highly hydrophilic drugs across the plasma membrane. Read More

In the Steiner Forest problem, we are given terminal pairs $\{s_i, t_i\}$, and need to find the cheapest subgraph which connects each of the terminal pairs together. In 1991, Agrawal, Klein, and Ravi, and Goemans and Williamson gave primal-dual constant-factor approximation algorithms for this problem; until now, the only constant-factor approximations we know are via linear programming relaxations. We consider the following greedy algorithm: Given terminal pairs in a metric space, call a terminal "active" if its distance to its partner is non-zero. Read More

Magnetic phases for the intermetallic compound NdMn1.4Co0.6Si2 have been investigated at various temperatures by dc magnetization, neutron diffraction and neutron depolarization. Read More

Fatigue failure in ferroelectrics has been intensively investigated in the past few decades. Most of the mechanisms discussed for ferroelectric fatigue have been built on the "hypothesis of variation in charged defects", which however are rarely evidenced by experimental observation. Here, using a combination of complex impedance spectra techniques, piezoresponse force microscopy and first-principles theory, we examine the microscopic evolution and redistribution of charged defects during the electrical cycling in BiFeO3 thin films. Read More

Online algorithms are usually analyzed using the notion of competitive ratio which compares the solution obtained by the algorithm to that obtained by an online adversary for the worst possible input sequence. Often this measure turns out to be too pessimistic, and one popular approach especially for scheduling problems has been that of "resource augmentation" which was first proposed by Kalyanasundaram and Pruhs. Although resource augmentation has been very successful in dealing with a variety of objective functions, there are problems for which even a (arbitrary) constant speedup cannot lead to a constant competitive algorithm. Read More

Space efficient algorithms play a central role in dealing with large amount of data. In such settings, one would like to analyse the large data using small amount of "working space". One of the key steps in many algorithms for analysing large data is to maintain a (or a small number) random sample from the data points. Read More

Isolated hydrogen and hydrogen pairs in bulk diamond matrix have been studied using density functional theory calculations. The electronic structure and stability of isolated and paired hydrogen defects are investigated at different possible lattice sites in pure diamond and boron doped diamond. Calculations revealed that isolated hydrogen defect is stable at bond center sites for pure diamond and bond center puckered site for boron doped diamond. Read More

We report on the electrical properties of current annealed graphene and few layer graphene devices. It is observed that current annealing for several hours results the n-type doping in the graphene layers. After current annealing Dirac point start to shift toward positive gate voltage and saturate at some fixed gate voltage. Read More

In the online Steiner tree problem, the input is a set of vertices that appear one-by-one, and we have to maintain a Steiner tree on the current set of vertices. The cost of the tree is the total length of edges in the tree, and we want this cost to be close to the cost of the optimal Steiner tree at all points in time. If we are allowed to only add edges, a tight bound of $\Theta(\log n)$ on the competitiveness is known. Read More

In the online Steiner tree problem, a sequence of points is revealed one-by-one: when a point arrives, we only have time to add a single edge connecting this point to the previous ones, and we want to minimize the total length of edges added. For two decades, we know that the greedy algorithm maintains a tree whose cost is O(log n) times the Steiner tree cost, and this is best possible. But suppose, in addition to the new edge we add, we can change a single edge from the previous set of edges: can we do much better? Can we maintain a tree that is constant-competitive? We answer this question in the affirmative. Read More

Affiliations: 1Indian Institute of Astrophysics, Bangalore, 2National Centre for Radio Astrophysics, TIFR, Pune, 3NRC Herzberg Institute of Astrophysics, Canada, 4Indian Institute of Astrophysics, Bangalore, 5Indian Institute of Astrophysics, Bangalore, 6Indian Institute of Astrophysics, Bangalore, 7Indian Institute of Astrophysics, Bangalore, 8Indian Institute of Astrophysics, Bangalore, 9Indian Institute of Astrophysics, Bangalore, 10Indian Institute of Astrophysics, Bangalore, 11Indian Institute of Astrophysics, Bangalore, 12Indian Institute of Astrophysics, Bangalore, 13Indian Institute of Astrophysics, Bangalore

Ultra Violet Imaging Telescope on ASTROSAT Satellite mission is a suite of Far Ultra Violet (FUV 130 to 180 nm), Near Ultra Violet (NUV 200 to 300 nm) and Visible band (VIS 320 to 550nm) imagers. ASTROSAT is the first multi wavelength mission of INDIA. UVIT will image the selected regions of the sky simultaneously in three channels and observe young stars, galaxies, bright UV Sources. Read More

Affiliations: 1Indian Institute of Astrophysics, Bangalore, 2National Centre for Radio Astrophysics, TIFR, Pune, 3Indian Institute of Astrophysics, Bangalore, 4Department of Physics and Astronomy, University of Calgary, Calgary, AB, Canada, 5Indian Institute of Astrophysics, Bangalore, 6Indian Institute of Astrophysics, Bangalore, 7Indian Institute of Astrophysics, Bangalore, 8ISRO Satellite Centre, Bangalore, 9Indian Institute of Astrophysics, Bangalore, 10Indian Institute of Astrophysics, Bangalore, 11ISRO Satellite Centre, Bangalore, 12Indian Institute of Astrophysics, Bangalore, 13Indian Institute of Astrophysics, Bangalore, 14Indian Institute of Astrophysics, Bangalore

Ultra Violet Imaging Telescope on ASTROSAT Satellite mission is a suite of Far Ultra Violet (FUV; 130 to 180 nm), Near Ultra Violet (NUV; 200 to 300 nm) and Visible band (VIS; 320 to 550nm) imagers. ASTROSAT is a first multi wavelength mission of INDIA. UVIT will image the selected regions of the sky simultaneously in three channels & observe young stars, galaxies, bright UV Sources. Read More

Flowing blood displays a phenomenon called margination, in which leukocytes and platelets are preferentially found near blood vessel walls, while erythrocytes are depleted from these regions. Here margination is investigated using direct hydrodynamic simulations of a binary suspension of stiff (s) and floppy (f) capsules, as well as a stochastic model that incorporates the key particle transport mechanisms in suspensions -- wall-induced hydrodynamic migration and shear-induced pair collisions. The stochastic model allows the relative importance of these two mechanisms to be directly evaluated and thereby indicates that margination, at least in the dilute case, is largely due to the differential dynamics of homogeneous (e. Read More

Orientation and microstructure are investigated in sheared Brownian suspensions of hard dicolloidal particles, with the dicolloids modeled as two fused spheres of varying radii and center to center separations. Two different particle shapes named homonuclear (aspect ratio 1.1) and fused-dumbbells (aspect ratio 1. Read More

The magnetic properties and transition from an antiferromagnetic (AFM) to a ferromagnetic (FM) state in semi Heusler alloys Cu1-xNixMnSb, with x < 0.3 have been investigated in details by dc magnetization, neutron diffraction, and neutron depolarization. We observe that for x < 0. Read More

We have studied the polarization fatigue of La and Mg co-substituted BiFeO3 thin film, where a polarization peak is observed during the fatigue process. The origin of such anomalous behavior is analyzed on the basis of the defect evolution using temperature-dependent impedance spectroscopy. It shows that the motion of oxygen vacancies (VO. Read More

Given a set of points $P \subset \mathbb{R}^d$, the $k$-means clustering problem is to find a set of $k$ {\em centers} $C = \{c_1,... Read More

Electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO2 and SrTiO3 are observed. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Ginsburg Landau Devonshire (GLD) theory. The possible origins of electromechanical coupling including ionic dynamics, surface-charge induced electrostriction, and ionically-induced ferroelectricity are identified. Read More

Affiliations: 1IBM Research - India New Delhi, 2Indian Institute of Technology Delhi, 3Indian Institute of Technology Delhi, 4IBM Research - India New Delhi

We consider a natural generalization of the Partial Vertex Cover problem. Here an instance consists of a graph G = (V,E), a positive cost function c: V-> Z^{+}, a partition $P_1,.. Read More

An accelerated boundary integral method for Stokes flow of a suspension of deformable particles is presented for an arbitrary domain and implemented for the important case of a planar slit geometry. The computational complexity of the algorithm scales as O(N) or $O(N\log N$), where $N$ is proportional to the product of number of particles and the number of elements employed to discretize the particle. This technique is enabled by the use of an alternative boundary integral formulation in which the velocity field is expressed in terms of a single layer integral alone, even in problems with non-matched viscosities. Read More

Spatial segregation in the wall normal direction is investigated in suspensions containing a binary mixture of Neo-Hookean capsules subjected to pressure driven flow in a planar slit. The two components of the binary mixture have unequal membrane rigidities. The problem is studied numerically using an accelerated implementation of the boundary integral method. Read More

We report on the investigation of magnetic field induced charge density wave and Hall coefficient sign reversal in a quasi-two dimensional electronic system of highly oriented pyrolytic graphite under very strong magnetic field. The change of Hall sign coefficient from negative to positive occurs at low temperature and high magnetic field just after the charge density wave transition, suggesting the role of hole-like quasi-particles in this effect. Angular dependent measurements show that the charge density wave transition and Hall sign reversal fields follow the magnetic field component along the c-axis of graphite. Read More

We have investigated the nanoscale switching properties of strain-engineered BiFeO3 thin films deposited on LaAlO3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. Read More

There has been much progress on efficient algorithms for clustering data points generated by a mixture of $k$ probability distributions under the assumption that the means of the distributions are well-separated, i.e., the distance between the means of any two distributions is at least $\Omega(k)$ standard deviations. Read More

In this paper we will be concerned with a class of packing and covering problems which includes Vertex Cover and Independent Set. Typically, one can write an LP relaxation and then round the solution. In this paper, we explain why the simple LP-based rounding algorithm for the \\VC problem is optimal assuming the UGC. Read More

In classical scheduling problems, we are given jobs and machines, and have to schedule all the jobs to minimize some objective function. What if each job has a specified profit, and we are no longer required to process all jobs -- we can schedule any subset of jobs whose total profit is at least a (hard) target profit requirement, while still approximately minimizing the objective function? We refer to this class of problems as scheduling with outliers. This model was initiated by Charikar and Khuller (SODA'06) on the minimum max-response time in broadcast scheduling. Read More

Using spectroscopic ellipsometry, the refractive index and absorption versus wavelength of the ferroelectric antiferromagnet Bismuth Ferrite, BiFeO_3 is reported. The material has a direct band-gap at 442 nm wavelength (2.81 eV). Read More