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Rohit Kumar

Publications and source records attributed to Rohit Kumar.

At least 73 records · Page 4Linked to original sources
arXiv2023

Determination of the Equation of State from Nuclear Experiments and Neutron Star Observations

With recent advances in neutron star observations, major progress has been made in determining the pressure of neutron star matter at high density. This pressure is constrained by the neutron star deformability, determined from gravitational waves emitted in a neutron-star merger, and measurements of radii of two neutron stars, using a new X-ray observatory on the International Space Station. Previous studies have relied on nuclear theory calculations to provide the equation of state at low density. Here we use a combination of 15 constraints composed of three astronomical observations and twelve nuclear experimental constraints that extend over a wide range of densities. Bayesian Inference is then used to obtain a comprehensive nuclear equation of state. This data-centric result provides benchmarks for theoretical calculations and modeling of nuclear matter and neutron stars. Furthermore, it provides insights on the composition of neutron stars and their cooling via neutrino radiation.

nucl-th↗
arXiv2023

Whispering LLaMA: A Cross-Modal Generative Error Correction Framework for Speech Recognition

We introduce a new cross-modal fusion technique designed for generative error correction in automatic speech recognition (ASR). Our methodology leverages both acoustic information and external linguistic representations to generate accurate speech transcription contexts. This marks a step towards a fresh paradigm in generative error correction within the realm of n-best hypotheses. Unlike the existing ranking-based rescoring methods, our approach adeptly uses distinct initialization techniques and parameter-efficient algorithms to boost ASR performance derived from pre-trained speech and text models. Through evaluation across diverse ASR datasets, we evaluate the stability and reproducibility of our fusion technique, demonstrating its improved word error rate relative (WERR) performance in comparison to n-best hypotheses by relatively 37.66%. To encourage future research, we have made our code and pre-trained models open source at https://github.com/Srijith-rkr/Whispering-LLaMA.

cs.CL↗
arXiv2023

Influence of additional neutrons on the fusion cross-section beyond the N=8 shell

Fusion enhancement for neutron-rich isotopes of oxygen on carbon nuclei was probed. To measure the fusion cross-section a $^{20}$O beam accelerated to E$_{lab}$/A=2.7 MeV bombarded the active-target detector MuSIC@Indiana with a fill gas of CH$_4$. Examination of the average fusion cross-section over the interval 12 MeV $\leq$E$_{c.m.}$$\leq$ 17 MeV for $^{16-20}$O + $^{12}$C reveals that while even isotopes of oxygen exhibit essentially the same cross-section, the cross-section for odd isotopes can be either enhanced or suppressed relative to the even A members of the isotopic chain. Theoretical models fail to explain the observed experimental results.

nucl-ex↗
arXiv2023

Ultrahigh-performance superlattice mid-infrared nBn photodetectors at high operating temperatures

While advancing a physics-based comprehensive photodetector-simulation model, we propose a novel device design of the mid-wavelength infrared nBn photodetectors by exploiting the inherit flexibility of the $InAs_{1-x}Sb_{x}$ ternary alloy material system. To further explicate the physics of such photodetectors, we calculate several crucial transport and optoelectronic parameters, including the dark current density, absorption coefficient, responsivity, and the quantum efficiency of nBn photodetectors. A remarkable maximum efficiency of 57.39\% is achieved at room temperature at a bias of -0.25 V, coupled with a radiation power density of 50 mW/$cm^{2}$. The proposed structure features a maximum quantum efficiency of 44.18\% and 37.87\% at 60\% and 70\% of the $λ_c$, respectively. Furthermore, a maximum responsivity of 0.9257 A/W is shown within the mid-wavelength infrared spectrum. Through our comprehensive analysis, we also demonstrate that our proposed device design effectively reduces the dark current density by confining the electric field inside the barrier while preserving a superior level of quantum efficiency, and the current in such detectors is diffusion-limited. Insights uncovered here could be of broad interest to critically evaluate the potential of the nBn structures for mid-wavelength infrared photodetectors.

cond-mat.mes-hall↗
arXiv2023

Speech enhancement with frequency domain auto-regressive modeling

Speech applications in far-field real world settings often deal with signals that are corrupted by reverberation. The task of dereverberation constitutes an important step to improve the audible quality and to reduce the error rates in applications like automatic speech recognition (ASR). We propose a unified framework of speech dereverberation for improving the speech quality and the ASR performance using the approach of envelope-carrier decomposition provided by an autoregressive (AR) model. The AR model is applied in the frequency domain of the sub-band speech signals to separate the envelope and carrier parts. A novel neural architecture based on dual path long short term memory (DPLSTM) model is proposed, which jointly enhances the sub-band envelope and carrier components. The dereverberated envelope-carrier signals are modulated and the sub-band signals are synthesized to reconstruct the audio signal back. The DPLSTM model for dereverberation of envelope and carrier components also allows the joint learning of the network weights for the down stream ASR task. In the ASR tasks on the REVERB challenge dataset as well as on the VOiCES dataset, we illustrate that the joint learning of speech dereverberation network and the E2E ASR model yields significant performance improvements over the baseline ASR system trained on log-mel spectrogram as well as other benchmarks for dereverberation (average relative improvements of 10-24% over the baseline system). The speech quality improvements, evaluated using subjective listening tests, further highlight the improved quality of the reconstructed audio.

eess.AS↗
arXiv2023

On a fractional system of NLS-KDV equations with Hardy potentials

In this article, our main concern is to study the existence of bound and ground state solutions for the following fractional system of nonlinear Schrödinger-Korteweg-De Vries (NLS-KdV, in short) equations with Hardy potentials: \begin{equation*} \left\{ \begin{aligned} (-Δ)^{s_{1}} u - λ_{1} \frac{u}{|x|^{2s_{1}}} - u^{2_{s_{1}}^{*}-1} &= 2νh(x) u^{}v^{} & \quad \mbox{in} ~ \mathbb{R}^{N}, (-Δ)^{s_{2}} v - λ_{2} \frac{v}{|x|^{2s_{2}}} - v^{2_{s_{2}}^{*}-1} &= νh(x) u^{2} & \quad \mbox{in} ~ \mathbb{R}^{N}, u,v >0 \quad \mbox{in} ~ \mathbb{R}^{N} \setminus \{0\}, \end{aligned} \right. \end{equation*} where $s_{1},s_{2} \in (0,1)~\text{and}~λ_{i}\in (0, Λ_{N,s_{i}})$ with $Λ_{N,s_{i}} = 2 π^{N/2} \frac{Γ^{2}(\frac{N+2s_i}{4}) Γ(\frac{N+2s_i}{2})}{Γ^{2}(\frac{N-2s_i}{4}) ~|Γ(-s_{i})|}, (i=1,2)$. By imposing certain assumptions on the parameter $ν$ and on the function $h$, we obtain ground-state solutions using the concentration-compactness principle and the mountain-pass theorem.

math.AP↗
arXiv2023

Multilingual Tourist Assistance using ChatGPT: Comparing Capabilities in Hindi, Telugu, and Kannada

This research investigates the effectiveness of ChatGPT, an AI language model by OpenAI, in translating English into Hindi, Telugu, and Kannada languages, aimed at assisting tourists in India's linguistically diverse environment. To measure the translation quality, a test set of 50 questions from diverse fields such as general knowledge, food, and travel was used. These were assessed by five volunteers for accuracy and fluency, and the scores were subsequently converted into a BLEU score. The BLEU score evaluates the closeness of a machine-generated translation to a human translation, with a higher score indicating better translation quality. The Hindi translations outperformed others, showcasing superior accuracy and fluency, whereas Telugu translations lagged behind. Human evaluators rated both the accuracy and fluency of translations, offering a comprehensive perspective on the language model's performance.

cs.CL↗
arXiv2023

On critically coupled (s_1, s_2)-fractional system of Schrödinger equations with Hardy potential

In this article, our main concern is to study the existence of bound and ground state solutions for the following fractional system of Schrödinger equations with Hardy potentials: \begin{equation*} \left\{ \begin{aligned} (-Δ)^{s_{1}} u - λ_{1} \frac{u~~}{|x|^{2s_{1}}} - u^{2_{s_{1}}^{*}-1} = ναh(x) u^{α-1}v^β & \quad \mbox{in} ~ \mathbb{R}^{N}, (-Δ)^{s_{2}} v - λ_{2} \frac{v~~}{|x|^{2s_{2}}} - v^{2_{s_{2}}^{*}-1} = νβh(x) u^αv^{β-1} & \quad \mbox{in} ~ \mathbb{R}^{N}, u,v >0 \quad \mbox{in} ~ \mathbb{R}^{N} \setminus \{0\}, \end{aligned} \right. \end{equation*} where $s_{1},s_{2} \in (0,1)~\text{and}~λ_{i}\in (0, Λ_{N,s_{i}})$ with $Λ_{N,s_{i}} = 2 π^{N/2} \frac{Γ^{2}(\frac{N+2s_i}{4}) Γ(\frac{N+2s_i}{2})}{Γ^{2}(\frac{N-2s_i}{4}) ~|Γ(-s_{i})|}, (i=1,2)$. By imposing certain assumptions on the parameters and on the function h, we obtain ground-state solutions using the concentration-compactness principle and the mountain-pass theorem.

math.AP↗
arXiv2023

Obtaining high resolution excitation functions with an active thick-target approach and validating them with mirror nuclei

Measurement of fusion excitation functions for stable nuclei has largely been restricted to nuclei with significant natural abundance. Typically, to investigate neighboring nuclei with low natural abundance has required obtaining isotopically enriched material. This restriction often limits the ability to perform such measurements. We report the measurement of a high quality fusion excitation function for a $^{17}$O beam produced from unenriched material with 0.038\% natural abundance. The measurement is enabled by using an active thick-target approach and the accuracy of the result is validated using its mirror nucleus $^{17}$F and resonances. The result provides important information about the average fusion cross-section for the oxygen isotopic chain as a function of neutron excess.

nucl-ex↗
arXiv2023

Detection of $d_{1}\otimes d_{2}$ Dimensional Bipartite Entangled State: A Graph Theoretical Approach

Braunstein et. al. have started the study of entanglement properties of the quantum states through graph theoretical approach. Their idea was to start from a simple unweighted graph $G$ and then they have defined the quantum state from the Laplacian of the graph $G$. A lot of research had already been done using the similar idea. We ask here the opposite one i.e can we generate a graph from the density matrix? To investigate this question, we have constructed a unital map $ϕ$ such that $ϕ(ρ)=L_ρ+ρ$, where the quantum state is described by the density operator $ρ$. The entries of $L_ρ$ depends on the entries of the quantum state $ρ$ and the entries are taken in such a way that $L_ρ$ satisfies all the properties of the Laplacian. This make possible to design a simple connected weighted graph from the Laplacian $L_ρ$. We show that the constructed unital map $ϕ$ characterize the quantum state with respect to its purity by showing that if the determinant of the matrix $ϕ(ρ)-I$ is positive then the quantum state $ρ$ represent a mixed state. Moreover, we study the positive partial transpose (PPT) criterion in terms of the spectrum of the density matrix under investigation and the spectrum of the Laplacian associated with the given density matrix. Furthermore, we derive the inequality between the minimum eigenvalue of the density matrix and the weight of the edges of the connected subgraph of a simple weighted graph to detect the entanglement of $d_{1} \otimes d_{2}$ dimensional bipartite quantum states. Lastly, We have illustrated our results with few examples.

quant-ph↗
arXiv2023

High-frequency complex impedance analysis of the two-dimensional semiconducting MXene-$Ti_2CO_2$

The two-dimensional compound group of MXenes, which exhibit unique optical, electrical, chemical, and mechanical properties, are an exceptional class of transition metal carbides and nitrides. In addition to traditional applications in Li-S, Li-ion batteries, conductive electrodes, hydrogen storage, and fuel cells, the low lattice thermal conductivity coupled with high electron mobility in the semiconducting oxygen-functionalized MXene-$Ti_2CO_2$ has led to the recent interests in high-performance thermoelectric and nanoelectronic devices. Apart from the above dc-transport applications, it is crucial to also understand ac-transport across them, given the growing interest in applications surrounding wireless communications and transparent conductors. In this work, we investigate using our recently developed $ab~initio$ transport model, the real and imaginary components of electron mobility and conductivity to conclusively depict carrier transport beyond the room temperature for frequency ranges upto the terahertz range. We also contrast the carrier mobility and conductivity with respect to the Drude's model to depict its inaccuracies for a meaningful comparison with experiments. Our calculations show the effect of acoustic deformation potential scattering, piezoelectric scattering, and polar optical phonon scattering mechanisms. Without relying on experimental data, our model requires inputs calculated from first principles using density functional theory. Our results set the stage for providing ab-initio based ac-transport calculations given the current research on MXenes for high frequency applications.

cond-mat.mtrl-sci↗
arXiv2023

Advancing carrier transport models for InAs/GaSb type-II superlattice MWIR photodetectors

In order to provide the best possible performance, modern infrared photodetector designs necessitate extremely precise modeling of the superlattice absorber region. We advance the Rode's method for the Boltzmann transport equation in conjunction with the $\bf k.p$ band structure and the envelope function approximation for a detailed computation of the carrier mobility and conductivity of layered type-II superlattice structures, using which, we unravel two crucial insights. First, the significance of both elastic and inelastic scattering mechanisms, particularly the influence of the interface roughness and polar optical phonon scattering mechanisms in technologically relevant superlattice structures. Second, that the structure-specific Hall mobility and Hall scattering factor reveals that temperature and carrier concentrations significantly affect the Hall scattering factor, which deviates significantly from unity even for small magnetic fields. This reinforces the caution that should be exercised when employing the Hall scattering factor in experimental estimations of drift mobilities and carrier concentrations. Our research hence offers a comprehensive microscopic understanding of carrier dynamics in such technologically relevant superlattices. Our models also provide highly accurate and precise transport parameters beyond the relaxation time approximation and thereby paving the way to develop physics-based device modules for mid-wavelength infrared photodetectors.

cond-mat.mtrl-sci↗
arXiv2022

Landau-Bloch type theorem for elliptic and $K$-quasiregular harmonic mappings

In this paper, we establish an improved coefficient bounds for quasiregular and elliptic harmonic mappings and using these bounds we establish Landau-Bloch type theorem for $(K,K')$-elliptic and K-quasiregular harmonic mappings in plane. Furthermore, we prove the coefficient estimates for $K$-quasiconformal harmonic self maps defined on the unit disk $\mathbb{D}$.

math.CV↗
arXiv2022

Nodeless superconductivity in the topological nodal-line semimetal CaSb2

CaSb2 is a topological nodal-line semimetal that becomes superconducting below 1.6 K, providing an ideal platform to investigate the interplay between topologically nontrivial electronic bands and superconductivity. In this work, we investigated the superconducting order parameter of CaSb2 by measuring its magnetic penetration depth change Δλ(T) down to 0.07 K, using a tunneling diode oscillator (TDO) based technique. Well inside the superconducting state, Δλ(T) shows an exponential activated behavior, and provides direct evidence for a nodeless superconducting gap. By analyzing the temperature dependence of the superfluid density and the electronic specific heat, we find both can be consistently described by a two-gap s-wave model, in line with the presence of multiple Fermi surfaces associated with distinct Sb sites in this compound. These results demonstrate fully-gapped superconductivity in CaSb2 and constrain the allowed pairing symmetry.

cond-mat.supr-con↗
arXiv2022

Evaluation of the suitable analytical techniques for the investigation of the toxic elements and compounds in the Pyrotechnic materials (Green crackers)

The present manuscript reports the elemental as well as molecular study of the Green Crackers. Laser-induced breakdown spectroscopy has been used for elemental analysis, UV-Vis and Photoacoustic Spectroscopy (PAS) are used for molecular study of the green crackers. The spectral lines of several elements including heavy/toxic such as Al, Ba, Sr, Cr, Cu are observed in the LIBS spectra of green crackers like present in normal crackers. In addition to this, the electronic bands of diatomic molecules like AlO, SrO, and CaO are also observed in LIB spectra of the green crackers. PAS, which is non-destructive, useful for scattering & opaque substances, is more suitable than the UV-VIS method for the investigation of the various organic compounds/molecules present in the firecrackers. Molecular bands of these molecules (AlO, SrO and CaO) are also in the absorption spectra of the crackers recorded using PAS technique and UV-Vis spectroscopy technique. In addition to these, absorption bands of some additional compounds/molecules like AlO, SrO, CaCO3, KNO3, NH4NO3, NHClO4 are also observed in the PA spectra of the green crackers, which show that PAS is more appropriate technique than the UV-VIS method for the investigation of the organic compounds/molecules in firecrackers. To determine the exact concentration of the constituents (Al, Cr, Cu) in green crackers AAS has been used. The results of the present manuscript show that the green crackers are also toxic for the environment as well as for humans although with lesser intensity than traditional/normal crackers.

physics.plasm-ph↗
arXiv2022

Multiple solutions for a weighted $p$-Laplacian problem

We prove the existence of at least three solutions for a weighted $p$-Laplacian operator involving Dirichlet boundary condition in a weighted Sobolev space. The main tool we use here is a three solution theorem in reflexive Banach spaces due to G. Bonanno and B. Ricceri.

math.AP↗
arXiv2022

Local Relighting of Real Scenes

We introduce the task of local relighting, which changes a photograph of a scene by switching on and off the light sources that are visible within the image. This new task differs from the traditional image relighting problem, as it introduces the challenge of detecting light sources and inferring the pattern of light that emanates from them. We propose an approach for local relighting that trains a model without supervision of any novel image dataset by using synthetically generated image pairs from another model. Concretely, we collect paired training images from a stylespace-manipulated GAN; then we use these images to train a conditional image-to-image model. To benchmark local relighting, we introduce Lonoff, a collection of 306 precisely aligned images taken in indoor spaces with different combinations of lights switched on. We show that our method significantly outperforms baseline methods based on GAN inversion. Finally, we demonstrate extensions of our method that control different light sources separately. We invite the community to tackle this new task of local relighting.

cs.CV↗
arXiv2022

Nanomechanical Characterization of an Antiferromagnetic Topological Insulator

The antiferromagnetic topological insulator MnBi2Te4 (MBT) exhibits an ideal platform to study exotic topological phenomena and magnetic properties. The transport signatures of magnetic phase transitions in the MBT family materials have been well-studied. However, their mechanical properties and magneto-mechanical coupling have not been well-explored. We use nanoelectromechanical systems to study the intrinsic magnetism in MBT thin flakes via their magnetostrictive coupling. We investigate mechanical resonance signatures of magnetic phase transitions from antiferromagnetic (AFM) to canted antiferromagnetic (cAFM) to ferromagnetic (FM) phases versus magnetic field at different temperatures. The spin-flop transitions in MBT are revealed by frequency shifts of mechanical resonance. With temperatures going above TN, the transitions disappear in the resonance frequency map, consistent with transport measurements. We use a magnetostrictive model to correlate the frequency shifts with the spin-canting states. Our work demonstrates a technique to study magnetic phase transitions, magnetization and magnetoelastic properties of the magnetic topological insulator.

cond-mat.mes-hall↗