258 research outputs found
First person – Varun Jayeshkumar Shah
No full textABSTRACT
First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Varun Jayeshkumar Shah is the first author on ‘CRL7SMU1 E3 ligase complex-driven H2B ubiquitination functions in sister chromatid cohesion by regulating SMC1 expression’, published in Journal of Cell Science. Varun is a PhD student in the lab of Dr Subbareddy Maddika at the Centre for DNA Fingerprinting and Diagnostics (CDFD), Hyderabad, India, investigating the role of LisH-domain-containing proteins in the assembly of multi-subunit E3 ligase complexes.</jats:p
Neutron Stars and NuSTAR: A Systematic Survey of Neutron Star Masses in High Mass X-ray Binaries & Characterization of CdZnTe Detectors for NuSTAR
No full textMy thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy.
The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here — from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results.
Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses among all classes of neutron star binaries. Intrigued by this diversity — which points to diverse birth masses — we undertook a systematic survey to measure the masses of neutron stars in nine high-mass X-ray binaries. In this thesis, I present results from this ongoing project.
While neutron stars formed the primary focus of my work, I also explored other topics in compact objects. Appendix A describes the discovery and complete characterization of a 1RXS J173006.4+033813, a polar cataclysmic variable. Appendix B describes the discovery of a diamond planet orbiting a millisecond pulsar, and our search for its optical counterpart.</p
Social rights and economics : claims to health care and education in developing countries
No full textThe author analyzes contemporary rights-based and economic approaches to health care and education in developing countries. He assesses the foundations and uses of social rights in development, outlines an economic approach to improving health and education services, and then highlights the differences, similarities, and the hard questions that the economic critique poses for rights. The author argues that the policy consequences of rights overlap considerably with a modern economic approach. Both the rights-based and the economic approaches are skeptical that electoral politics and de facto market rules provide sufficient accountability for the effective and equitable provision of health and education services, and that further intrasectoral reforms in governance, particularly those that strengthen the hand of service recipients, are needed. There remain differences between the two approaches. Whether procedures for service delivery are ends in themselves, the degree of disaggregation at which outcomes should be assessed, the consequences of long-term deprivation, metrics used for making tradeoffs, and the behavioral distortions that result from subsidies are all areas where the approaches diverge. Even here, however, the differences are not irreconcilable, and advocates of the approaches need not regard each other as antagonists.Health Monitoring&Evaluation,Health Systems Development&Reform,Decentralization,Public Health Promotion,Early Child and Children's Health,Health Monitoring&Evaluation,Health Economics&Finance,Poverty Assessment,Agricultural Knowledge&Information Systems,Gender and Education
Coherency matrices for characterization of vector optical fields
No full textWe describe optical coherency matrices as a generalized method for characterizing the statistical properties of optical fields. We then use this formalism to classify optical fields, in terms of separability, and transfer of entropy between multiple degrees of freedom.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-12-01The student, Varun Ajit Kelkar, accepted the attached license on 2019-07-12 at 20:22.The student, Varun Ajit Kelkar, submitted this Thesis for approval on 2019-07-12 at 20:30.This Thesis was approved for publication on 2019-07-15 at 11:29.DSpace SAF Submission Ingestion Package generated from Vireo submission #14293 on 2020-02-28 at 17:34:54Made available in DSpace on 2020-03-02T22:28:39Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-07-15Embargo set by: Seth Robbins for item 113953
Lift date: 2022-03-02T22:28:46Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113953
Lift date: 2022-03-02T22:38:05Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113953
Lift date: 2022-03-02T22:39:04Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 113953 on 2022-03-03T10:15:30Z
Determination of structural changes and phase transformations in boron carbide by static and dynamic studies
No full textRecent transmission electron microscopy results demonstrate that the failure of B4C is commensurate with the segregation of boron icosahedra embedded in amorphous carbon in 2–3 nm wide amorphous bands along the (113) lattice direction, in good agreement with our recent theoretical results. Boron carbide is generally composed of multiple polytypes of B4C which have the same primitive lattice parameters but differ from each other by the location of the boron and carbon atoms in the unit cells. The unit cells are formed by a 12-atom B12-nCn icosahedron and a 3-atom (C3-nBn) chain. Our theoretical results indicate that one polytype, B12(C3), whose formation is responsible for
the failure of the entire material. This anomalous and poorly understood glass-like behavior in boron carbide has been the subject of research since its discovery over 70 years ago. The characterization of disorder in hot pressed and powder boron carbide samples
is therefore of primary interest. The research work has focused on characterization techniques which can be used at a micrometric sampling size so that individual powder grains of the material can be utilized. Specifically, micro-Raman and electrical
conductivity measurements can be used with micrometric gap cells to understand the disorder in B4C.The results also demonstrate that it is possible to induce transformations in boron carbide using electric fields that are comparable with those obtained under shock and nanoindentation. Our calculations present a hypothesis which can provide a solution to prevent the
premature failure of B4C. A route to achieve suppression of the B12(CCC) polytype without significantly affecting the elastic constants is via low concentration Silicon (Si) doping of B4C. Suppression of B12(CCC) by Si doping has implications towards
development of boron carbide armor with improved properties for protection against high velocity threats. In order to achieve this, nanostructures (nanowires, nanorods, etc.) of Sidoped boron carbide have been synthesized using a Solid-Liquid-Solid (SLS) growth
mechanism. The resulting structures have been characterized by SEM, TEM and Raman
spectroscopy and consolidated to evaluate their mechanical properties. In addition, the application of nanowires in a transparent and thermally conducting nanocomposite is demonstrated.Ph.D.Includes abstractVitaIncludes bibliographical referencesby Varun Gupt
Reducing LRIS longslit spectra in IRAF
No full textThe word IRAF scares me to date, though I am slowly getting used to using it. Here I am putting together my notes for reducing LRIS longslit spectra in IRAF. I will try to be general, but only to the extent that I expect my usage to vary. The document will often contain things which are pertinent to my current folders setup, gratings I use, etc.
The scripts referred to in this document are available on request. I might eventually upload a tarball containing all the codes
Sub-MeV spectroscopy with AstroSat-CZT imager for gamma ray bursts
No full textCadmium–Zinc–Telluride Imager (CZTI) onboard AstroSat has been a prolific Gamma-Ray Burst (GRB) monitor. While the 2-pixel Compton scattered events (100–300 keV) are used to extract sensitive spectroscopic information, the inclusion of the low-gain pixels (∼ 20% of the detector plane) after careful calibration extends the energy range of Compton energy spectra to 600 keV. The new feature also allows single-pixel spectroscopy of the GRBs to the sub-MeV range which is otherwise limited to 150 keV. We also introduced a new noise rejection algorithm in the analysis (‘Compton noise’). These new additions not only enhances the spectroscopic sensitivity of CZTI, but the sub-MeV spectroscopy will also allow proper characterization of the GRBs not detected by Fermi. This article describes the methodology of single, Compton event and veto spectroscopy in 100–900 keV combined for the GRBs detected in the first year of operation. CZTI in last five years has detected ∼ 20 bright GRBs. The new methodologies, when applied on the spectral analysis for this large sample of GRBs, has the potential to improve the results significantly and help in better understanding the prompt emission mechanism
Contextual Hate Speech Detection Leveraging RoBERTa: Overcoming Challenges in Online Communication
No full textThe growth in online communication has increased hate speech in an exponential way, presenting an urgent need and serious challenges for any company that deals with the safe and inclusive maintenance of digital environments. Traditional methods of detection, one that uses simple keyword-based techniques often fail to capture the original, context-dependent nature of hate speech that manifests through slang, code words, and euphemisms. This paper presents the application of RoBERTa, a strongly optimized variant of BERT, toward increasing the accuracy and resiliency of hate speech detection. Training on larger datasets and longer training periods, and dynamic masking make RoBERTa much more powerful in understanding and processing human languages in their diversified and subtle contexts. Especially, it investigates whether RoBERTa can overcome the inefficiencies of early models in detecting hate speech efficiently across languages and cultural contexts, including traditional machine learning approaches and early deep learning models like CNNs and RNNs. Comparative analysis has shown that it outperforms traditional approaches in finding contextually nuanced hate speech, especially with other techniques like ensembling models or emotion recognition. The research aims to come up with a very accurate and versatile hate speech detection system that could work in different languages and across changing linguistic patterns. Hence, the result concludes the potential of transformer-based models in raising online safety and inclusivity, as shown by RoBERTa
The Need for Continued Innovation in Solar, Wind, and Energy Storage
No full textVarun Sivaram is the Philip D. Reed fellow for science and technology at the Council on Foreign Relations. He is also an adjunct professor at Georgetown University, an adjunct senior research scholar at Columbia University, and a member of the energy and environment advisory boards at Stanford University. He is the author of the book, Taming the Sun: Innovations to Harness Solar Energy and Power the Planet (MIT University Press, 2018) and the editor of the book, Digital Decarbonization: Promoting Clean Energy Systems Through Digital Innovations (CFR Press, 2018). Forbes named him one of its 30 under 30 in law and policy, and Grist named him one of the top 50 leaders in sustainability
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