Ankit Kumar

Ag2Se is a potentially useful material with interesting magnetoresistive and thermoelectric properties. In several recent studies, the thermoelectric figure of merit (zT) of Ag2Se has been shown to approach 1 near 380 K (i.e., about 25 K below its superionic transition temperature). However, what plagues the use of Ag2Se in real life applications is its sample dependence and very poor reproducibility. In a recent work, it is clearly established that the root cause of this is Ag migration during high-temperature sintering or melting. Here, we show that high-density Ag2Se samples with high and reproducible zT (0.92 at 370 K) can be prepared by simple all-room-temperature techniques. The ease of sample preparation and high zT along with excellent reproducibility make Ag2Se a promising material for near-room-temperature applications.

ABSTRACT It is now clear that the stars in the Solar neighbourhood display large-scale coherent vertical breathing motions. At the same time, Milky Way-like galaxies experience tidal interactions with satellites/companions during their evolution. While these tidal interactions can excite vertical oscillations, it is still not clear whether vertical breathing motions are excited directly by the tidal encounters or are driven by the tidally-induced spirals. We test whether excitation of breathing motions are directly linked to tidal interactions by constructing a set of N-body models (with mass ratio 5:1) of unbound single fly-by interactions with varying orbital configurations. We first reproduce the well-known result that such fly-by interactions can excite strong transient spirals (lasting for ${\sim}2.9{-}4.2\,{\rm Gyr}$) in the outer disc of the host galaxy. The generation and strength of the spirals are shown to vary with the orbital parameters (the angle of interaction, and the orbital spin vector). Furthermore, we demonstrate that our fly-by models exhibit coherent breathing motions whose amplitude increases with height. The amplitudes of breathing motions show characteristic modulation along the azimuthal direction with compressing breathing motions coinciding with the peaks of the spirals and expanding breathing motions falling in the inter-arm regions – a signature of a spiral-driven breathing motion. These breathing motions in our models end when the strong tidally-induced spiral arms fade away. Thus, it is the tidally-induced spirals which drive the large-scale breathing motions in our fly-by models, and the dynamical role of the tidal interaction in this context is indirect.

Video anomaly detection is a critical task in various fields such as surveillance, security, and transportation, and has been gaining significant attention in recent years.Manually monitoring such anomalies can be time-consuming and monotonous in result. Detecting anomalies in videos is difficult because of erratic nature of the event. Motivated by these issues we purpose a promising approach for video anomaly detection by using Residual Variational Autoencoder(RVAE) model which is able to detect anomalies in an unsupervised manner.RVAE can capture more complex patterns in the data and improve the reconstruction error of the model, In this model, the encoder takes the input and provides a low-dimensional latent representation of it, and the decoder learns to reconstruct the original input with minimum loss. ConvLSTM layer is used to make better Spatio-temporal learning and residual connection to reduce the vanishing gradient problem. This model is implemented on three benchmark datasets ucds pedl, ped2, and Avenue datasets given the result shows good potential and it could be a step forward to improve the performance

Aerial imaging and surveillance play a crucial role in forestry and agriculture processes, utilizing Unmanned Aerial Vehicles (UAVs) for high-resolution remote sensing at close range. However, navigating through dense canopies or underneath them without colliding remains a challenging problem in aerial robotics. Quantifying the reachability of aerial space is a prerequisite for deciding upon the technical feasibility of such operations. Existing literature often suggests using reactive range-based methods that rely on expensive onboard sensors like depth cameras or LiDARs. This work presents a cost-effective geometrical analysis using a monocular camera and inertial sensors to generate reachability maps. An essential contribution is proposing an efficient sector division method that significantly reduces the search space required for analysis. The generated reachability map can serve as a valuable resource for planning optimal paths and operational settings, facilitating the collision-free traversal of UAVs through complex aerial environments with various obstructions and clutter.

Abstract We describe the survey design and science goals for One-hundred-deg 2 DECam Imaging in Narrowbands (ODIN), a NOIRLab survey using the Dark Energy Camera (DECam) to obtain deep (AB ∼ 25.7) narrowband images over an unprecedented area of sky. The three custom-built narrowband filters, N 419, N 501, and N 673, have central wavelengths of 419, 501, and 673 nm and respective FWHM of 7.5, 7.6, and 10.0 nm, corresponding to Ly α at z = 2.4, 3.1, and 4.5 and cosmic times of 2.8, 2.1, and 1.4 Gyr, respectively. When combined with even deeper, public broadband data from the Hyper Suprime-Cam, DECam, and in the future, the Legacy Survey of Space and Time, the ODIN narrowband images will enable the selection of over 100,000 Ly α -emitting (LAE) galaxies at these epochs. ODIN-selected LAEs will identify protoclusters as galaxy overdensities, and the deep narrowband images enable detection of highly extended Ly α blobs (LABs). Primary science goals include measuring the clustering strength and dark matter halo connection of LAEs, LABs, and protoclusters, and their respective relationship to filaments in the cosmic web. The three epochs allow for the redshift evolution of these properties to be determined during the period known as Cosmic Noon, where star formation was at its peak. The narrowband filter wavelengths are designed to enable interloper rejection and further scientific studies by revealing [O ii ] and [O iii ] at z = 0.34, Ly α and He ii 1640 at z = 3.1, and Lyman continuum plus Ly α at z = 4.5. Ancillary science includes similar studies of the lower-redshift emission-line galaxy samples and investigations of nearby star-forming galaxies resolved into numerous [O iii ] and [S ii ] emitting regions.

Major reason for mortality among systemic lupus erythematosus patients is renal failure due to the deposition of immune complexes in the glomeruli. Being a chronic disease with multiple relapses and remissions across the lifespan, it’s important to know the degree of nephritis for diagnosis as well as the long-term clinical management of the patients. Currently, renal biopsy is being used as the gold standard to diagnose and define the stages of the disease. However, renal biopsy being invasive only provides a localized picture of nephritis, and has the risk of bleeding. Additionally, it is also cost-intensive. Hence, a reliable, non-invasive biomarker is required for lupus nephritis. This study has evaluated extracellular mitochondrial components, including cell-free mitochondria, and cell-free mitochondrial DNA as probable biomarkers of the degree of nephritis. Both showed a significant correlation with proteinuria and protein-creatinine ratio. Our study substantiates their usage as clinical biomarkers of nephritis upon their validation in a larger cohort of lupus nephritis patients and other forms of nephritis. Although the current data suggest using cell-free mitochondria as a biomarker of lupus nephritis is better than the cell-free mitochondrial DNA.

It is well established that bars evolve significantly after they form in galaxy discs, often changing shape both in and out of the disc plane. In some cases they may bend or buckle out of the disc plane resulting in the formation of boxy/peanut/x-shape bulges. In this paper we show that the dark matter halo shape affects bar formation and buckling. We have performed N-body simulations of bar buckling in non-spherical dark matter halos and traced bar evolution for 8 Gyr. We find that bar formation is delayed in oblate halos, resulting in delayed buckling whereas bars form earlier in prolate halos leading to earlier buckling. However, the duration of first buckling remains almost comparable. All the models show two buckling events but the most extreme prolate halo exhibits three distinct buckling features. Bars in prolate halos also show buckling signatures for the longest duration compared to spherical and oblate halos. Since ongoing buckling events are rarely observed, our study suggests that most barred galaxies may have more oblate or spherical halos rather than prolate halos. Our measurement of BPX structures also shows that prolate halos promote bar thickening and disc heating more than oblate and spherical halos.

ABSTRACT Galaxy flybys are as common as mergers in low-redshift Universe and are important for galaxy evolution as they involve the exchange of significant amounts of mass and energy. In this study, we investigate the effect of minor flybys on the bulges, discs, and spiral arms of Milky Way mass galaxies for two types of bulges – classical bulges and boxy/peanut pseudo-bulges. Our N-body simulations comprise of two disc galaxies of mass ratios 10:1 and 5:1, where the discs of the galaxies lie in their orbital plane and the pericentre distance is varied. We performed photometric and kinematic bulge–disc decomposition at regular time-steps and traced the evolution of the disc size, spiral structure, bulge sersic index, bulge mass, and bulge angular momentum. Our results show that the main effect on the discs is disc thickening, which is seen as the increase in the ratio of disc scale height to scale radius. The strength of the spiral structure A2/A0 shows small oscillations about the mean time-varying amplitude in the pseudo-bulge host galaxies. The flyby has no significant effect on non-rotating classical bulge, which shows that these bulges are extremely stable in galaxy interactions. However, the pseudo-bulges become dynamically hotter in flybys indicating that flybys may play an important role in accelerating the rate of secular evolution in disc galaxies. This effect on pseudo-bulges is a result of their rotating nature as part of the bar. Also, flybys do not affect the time and strength of bar buckling.

We report on the dramatic improvement in the thermoelectric performance of TiCoSb by introducing three-dimensional (3D) modulation doping and synergistic band engineering in the composites of the form (1 – f)A + fB, where A and B refer to the phases Ti1–xNbxCoSb and Nb0.8+δCoSb, respectively, and f is the volume fraction of phase B. We show that the electrical conductivity and Seebeck coefficient of these composites increase simultaneously due to modulation doping, giving rise to colossal power factor (PF) enhancement from 0.3 μW cm–1 K–2 (TiCoSb) to 18 μW cm–1 K–2 (x = f ≈ 0.05) at 300 K and exceeding 25 μW cm–1 K–2 over a broad temperature range (T > 600 K). Due to the Ti–Nb point mass fluctuation in phase A, high concentration of defects in phase B, and interfacial phonon scattering between A and B, these composites also exhibit very low lattice thermal conductivity (κL), resulting in a high zT of 0.81 near 970 K. The simulation of κL using the Klemens model successfully describes the significant reduction of κL for these composites, observed experimentally. Our ab initio DFT calculations show that Ti1–xNbxCoSb exhibits band convergence as x increases, which contributes to improving the charge transport. Thus, benefiting from the synergistic effect of band convergence and 3D modulation doping, a high zT is obtained.

Motivated by recent advances in half-Heusler based thermoelectric materials, we investigated the phase stability and thermoelectric properties of compounds ZrNiSi, ZrNiGe, HfNiSi, NbCoSi, and ZrNiSb, some of which were recently reported in literature as promising half-Heuslers for thermoelectric applications using the first-principles density functional theory based calculations. Here, we show that all the named compounds actually crystallize with the orthorhombic TiNiSi structure type, which remains stable above room temperature up to at least 1100 K. In ZrNiSb, $5%$ excess Zr is required to obtain the pure orthorhombic phase. Our first-principles electronic band structure calculations reveal that they are semimetals. In ZrNiSi, ZrNiGe, and HfNiSi, the Fermi surface consists of small electron and hole pockets with electrons as the majority charge carriers. In NbCoSi and ZrNiSb, the majority carriers are holes. A pseudogaplike feature is observed in the electronic density of states with Fermi energy (${E}_{F}$) located either slightly below (ZrNiSi, ZrNiGe, and HfNiSi) or above the pseudogap (NbCoSi). In ZrNiSb no pseudogap is observed; however, the density of states at ${E}_{F}$ is still small. The electrical conductivity ($\ensuremath{\sigma}$) near room temperature is of the order of ${10}^{3}\phantom{\rule{4pt}{0ex}}\mathrm{S}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which is intermediate between that of the degenerate semiconductors and metallic alloys. Near room temperature the thermopower is negative for $\mathrm{ZrNi}X$ ($X$ = Si, Ge) and HfNiSi, and positive for NbCoSi and ZrNiSb as predicted theoretically. The average value of Seebeck coefficient is small, of the order of $10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{V}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. Despite reasonably high electrical conductivity, the thermal conductivity ($\ensuremath{\kappa}$) of these compounds is found to be generally low ($<15\phantom{\rule{4pt}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ near $300\phantom{\rule{4pt}{0ex}}\mathrm{K}$). In ${\mathrm{Zr}}_{1.05}\mathrm{Ni}\mathrm{Sb}$, which has the highest electrical conductivity ($\ensuremath{\approx}4000\phantom{\rule{4pt}{0ex}}\mathrm{S}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$), $\ensuremath{\kappa}$ is as low as $\ensuremath{\approx}4\phantom{\rule{4pt}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at $300\phantom{\rule{4pt}{0ex}}\mathrm{K}$, of which almost 70% is estimated to be due to the electronic contribution resulting in a lattice contribution which is $<1\phantom{\rule{4pt}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. This uncommon combination of high electrical conductivity and low thermal conductivity is interesting and invites further attention.

Unmanned Aerial Vehicles (UAVs) are becoming increasingly popular in rapid delivery of medical supplies, packages, food or other goods. In this paper, we present a solution to the delivery problem to a target vehicle which might be moving in a straight line with constant speed or may be maneuvering in a curved trajectory, using a delivery UAV. The proposed solution is based on a Circular Impact Time (CIT) Guidance law to solve the delivery problem. The problem is to match the motion of the delivery UAV with the target vehicle at the same speed and direction after approaching it from a distance. The original CIT guidance law was modified to meet this requirement by doing a guided speed adjustment of the delivery UAV. Numerical simulations are given to show the effectiveness of the proposed solution.

Galaxies usually reside in groups and clusters where they interact gravitationally. These interactions affect the internal dynamics of the galaxies. In this thesis, we have studied the effect of flyby interactions and dark matter distributions on the evolution of bulges and disks of spiral galaxies. To understand the effect of flyby interactions on the bulges, disks, and spiral arms of Milky Way mass galaxies, we simulated disk galaxies with classical bulges and boxy/peanut pseudo-bulges, then performed their flyby interactions with 1/10 and 1/5 mass galaxies. Using photometric and kinematic bulge-disk decompositions of the major galaxy, we showed that the disks get shorter and thicker during flyby interactions. Classical bulges remain intact. However, pseudo-bulges become dynamically hotter. Tidally induced spiral arms are transient density waves. They form soon after pericenter passage and decay in two phases; the initial rapid winding and the subsequent slow winding. We showed that the spirals are the main drivers of wave-like vertical breathing motion seen in the Milky Way. Tidal interactions do not directly induce breathing motion. In another work, we showed that the oblate dark matter halos delay bar formation, so bar buckling is also delayed, but probate halos promote multiple bucklings. Due to multiple bucklings, boxy/peanut bulges in prolate halos show the maximum thickness. Using SDSS galaxies, we found that pseudo-bulges are diffuse compared to classical bulges and are commonly found in low mass galaxies. In the local volume, pseudo-bulges overcome the classical bulges even in bulge dominated galaxies, so more than $75\%$ of local volume is rotation dominated. Finally, we showed that bulgeless galaxies in Illustris TNG50 are metal-poor, have high specific angular momentum as compared to the galaxies with bulges and fall at the lower end of baryonic to dark matter mass ratio.

The permeability of atomic hydrogen in monolayer hexagonal Boron Nitride(h-BN) and graphene has been studied using first-principles density functional theory based simulations. For the specific cases of physisorption and chemisoroption, barrier heights are calculated using the nudged elastic band approach. We find that the barrier potential for physisorption through the ring is lower for graphene than h-BN. In the case of chemisorption, where the H atom passes through by making bonds with the atoms in the ring, the barrier potential for the graphene was found to be higher than that of h-BN. We conclude that the penetration of H atom with notable kinetic energy (<3eV) through physiosorption is more probable for graphene as compared to h-BN. Whereas through chemisorption, lower kinetic energy (>3eV) H-atoms have a higher chance to penetrate through h-BN than graphene.

The use of internet-connected devices, especially small multi-rotor Unmanned Aerial Vehicles (UAVs), in scientific data gathering and applications is quite widespread. But due to limited intervention capability, the UAVs alone fail to automate agricultural tasks completely. Thereby, we propose a centralized framework capable of handling a heterogeneous mixture of UAVs and UGVs to cater to the needs of automating agriculture efficiently. The framework’s core is a novel heuristic decision module that creates new tasks by visually analyzing the farm and solves a vehicle routing problem to allocate it to agents optimally. It is also equipped with supporting modules to monitor their operation and, in case of failures, help them recover autonomously based on the task and agent assessment. The framework is used in three significant agricultural applications, namely yield prediction and drought stress detection in a simulated environment using ROS and Gazebo, and 3D mapping of a real farm. These applications demonstrate the use of the multi-agent collaborative framework in identifying agricultural tasks on a farm and executing them.

Cosmological simulations predict more classical bulges than their observational counterpart in the local Universe. Here, we quantify evolution of the bulges since $z=0.1$ using photometric parameters of nearly 39,000 unbarred disc galaxies from SDSS DR7 which are well represented by two components. We adopted a combination of the S\'ersic index and Kormendy relation to separate classical bulges and disc-like pseudo-bulges. We found that the fraction of pseudo-bulges (classical bulges) smoothly increases (decreases) as the Universe gets older. In the history of the Universe, there comes a point ($z \approx 0.016$) when classical bulges and pseudo-bulges become equal in number. The fraction of pseudo-bulges rises with increasing bulge to disc half-light radius ratio until R$_{\rm e}$/R$_{\rm hlr} \approx 0.6$ suggesting concentrated disc is the most favourable place for pseudo-bulge formation. The mean ellipticity of pseudo-bulges is always greater than that of classical bulges and it decreases with decreasing redshift indicating that the bulges tend to be more axisymmetric with evolution. Also, the massive bulges are progressing towards axisymmetry at steeper rate than the low-mass bulges. There is no tight correlation of bulge S\'ersic index evolution with other photometric properties of the galaxy. Using the sample of multi-component fitting of $S^4G$ data and $N-$body galaxy models, we have verified that our results are consistent or even more pronounced with multi-component fitting and high-resolution photometry.

Ankit, Kumar Tony, Lima Agnel Jana, Shuvrangshu Ghose, DebasishUnmanned aerial vehicle (UAV) applications with pick-and-place operation are plenty, and the same prevails in unmanned ground vehicle (UGV) domain. But low payload capacity for a UAV and the limited sensing capability of a UGV limit them to automate heavy-duty and large-scale construction. This complementary nature of these agents can be utilized together to cater to the needs of long-term autonomous construction. Thereby, we propose a software framework with its algorithmic details for multi-vehicle collaboration for autonomous pick-and-place operation. Three UAVs and a UGV coordinate among themselves to pick bricks of different sizes and place them at a specific location in a predetermined orientation. At the core of the decision-making process, distance-based optimization is done to generate the route plan for the agents. Generated route plan is then sent to agents via a scheduler which keeps their operations in check and, in case of failures, helps them recover autonomously. The framework provides end-to-end details on multi-vehicle pick-and-place operation, keeping collisions and failures in check. The software is developed in ROS and Gazebo environment and ready to implement on hardware. The modeling approach makes it easy to be modified and deployed to cater to any application such as warehouse stock management and package delivery, besides several other applications.

Abstract We investigate the minor interactions of two disk galaxies with mass ratio of 10:1 in fly-by encounters that do not lead to the merging of the galaxies. In our N-body simulations, we vary only the pericenter distances to see the effect of the fly-by on the bulge of the major galaxy over the course of the trajectory. At different time steps of the evolution, we did two-dimensional fittings of disk, bulge and bar to trace the variation in the sersic index of the bulge. Our results suggest that galaxy bulges can become boxy/disky through flyby interactions of galaxies.

This paper details the algorithms involved and task planner for vehicle collaboration in building a structure. This is the problem defined in challenge 2 of Mohammed Bin Zayed International Robotic Challenge 2020 (MBZIRC). The work addresses various aspects of the challenge for Unmanned Aerial Vehicles (UAVs) and Unmanned Ground Vehicle (UGV). The challenge involves repeated pick and place operations using UAVs and UGV to build two structures of different shape and sizes. The algorithms are implemented using the Robot Operating System (ROS) framework and visualised in Gazebo. The whole developed architecture could readily be implemented in suitable hardware.