2,131 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
Tightly coupled GPS-gyro integration for spacecraft attitude determination
No full textThesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997.Includes bibliographical references (p. 197-199).by Varun Prui.M.S
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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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
Refuting FPT Algorithms for Some Parameterized Problems Under Gap-ETH
No full textIn this article we study a well-known problem, called Bipartite Token Jumping and not-so-well known problem(s), which we call, Half (Induced-) Subgraph, and show that under Gap-ETH, these problems do not admit FPT algorithms. The problem Bipartite Token Jumping takes as input a bipartite graph G and two independent sets S,T in G, where |S| = |T| = k, and the objective is to test if there is a sequence of exactly k-sized independent sets ⟨ I₀, I₁,⋯, I_ ⟩ in G, such that: i) I₀ = S and I_ = T, and ii) for every j ∈ [], I_{j} is obtained from I_{j-1} by replacing a vertex in I_{j-1} by a vertex in V(G) ⧵ I_{j-1}. We show that, assuming Gap-ETH, Bipartite Token Jumping does not admit an FPT algorithm. We note that this result resolves one of the (two) open problems posed by Bartier et al. (ISAAC 2020), under Gap-ETH. Most of the known reductions related to Token Jumping exploit the property given by triangles (i.e., C₃s), to obtain the correctness, and our results refutes FPT algorithm for Bipartite Token Jumping, where the input graph cannot have any triangles.
For an integer k ∈ ℕ, the half graph S_{k,k} is the graph with vertex set V(S_{k,k}) = A_k ∪ B_k, where A_k = {a₁,a₂,⋯, a_k} and B_k = {b₁,b₂,⋯, b_k}, and for i,j ∈ [k], {a_i,b_j} ∈ E(T_{k,k}) if and only if j ≥ i. We also study the Half (Induced-)Subgraph problem where we are given a graph G and an integer k, and the goal is to check if G contains S_{k,k} as an (induced-)subgraph. Again under Gap-ETH, we show that Half (Induced-)Subgraph does not admit an FPT algorithm, even when the input is a bipartite graph. We believe that the above problem (and its negative) result maybe of independent interest and could be useful obtaining new fixed parameter intractability results.
There are very few reductions known in the literature which refute FPT algorithms for a parameterized problem based on assumptions like Gap-ETH. Thus our technique (and simple reductions) exhibits the potential of such conjectures in obtaining new (and possibly easier) proofs for refuting FPT algorithms for parameterized problems
Novel Strategies for the Synthesis of Organo-Sulfur Compounds under Metal-Free Reaction Conditions
No full textThe thesis titled “Novel Strategies for the Synthesis of Organo-Sulfur Compounds Under Metal-free Reaction conditions” is presented into three main sections.
Section A– deals with the synthesis of thiourea and thioamide.
Section B– describes the sulfenylation of electron-rich arenes, ketones and β- diketones
Section C– deals with the sulfur/fluorine assisted deacylation of α-sulfenylated β- diketones.
Section A:
This section is divided in to two chapters, Chapter 1 and Chapter 2.
Chapter 1 of this section describes the non-isothiocyanate route to obtain trisubstituted thioureas of arylamines by using in situ generated dithiocarbamates of secondary amines. Trisubstituted thioureas of aryl amines are important precursors for the synthesis of heterocyles like 2-aminobenzothiazoles derivatives,1 amidines,2 and guanidines.3 Therefore, this strategy provides an excellent opportunity to access thioureas containing primary aryl amines without employing isothiocyanates. From the current method, the broad substrate scope was achieved with excellent yield of the corresponding products. Further, under the optimized reaction conditions a variety of functional groups like ketones, carboxylic acids, amides and sulfonamides were found to be well tolerated. A few representative examples are shown in Scheme 1.4
(a) Jordan, A. D.; Luo, C.; and Reitz, A. B. J. Org. Chem. 2003, 68, 8693. (b) Joyce, L. L.; Batey, R. A. Org. Lett. 2009, 11, 2792 and references therein. (c) Jamir, L.; Khatun, N.; Patel, B. K. RSC Adv., 2011, 1, 447.
1 Biswas, K.; Greaney, M. F. Org. Lett. 2011, 13, 4946.
2 (a) Wilson, L. J.; Klopfenstein, S. R.; Li, M. Tetrahedron Lett. 1999, 40, 3999. (b) Schneider, S. E.; Bishop, P. A.; Salazar, M. A.; Bishop, O. A.; Anslyn, E. V. Tetrahedron 1998, 54, 15063.
3 Varun, B. V.; Prabhu, K. R. RSC Adv.2013, 3, 3079.
Synopsis
Chapter 2 describes the rapid, high yielding and easily isolable method for the synthesis of thioamide by nucleophilic addition of electron-rich arenes to isothiocyanates. Thioamides are essential structural motifs which are found in a variety of biologically active molecules.5 They are also crucial building blocks for synthesizing sulfur conntaining heterocycles.6 The current method employs triflic acid (TfOH) to activate the nitrogen of isothiocyanate, where as, in the earlier methods AlCl3 was used.7 Also, the reaction was found to be highly regioselective and the broad substrate scope of the reaction was demonstrated (Scheme 2).85 (a) Cremlyn, R. J. An Introduction to Organosulfur Chemistry,John Wiley and Sons, Chichester, 1996. (b) Gottesman, M. M.; Fojo, T.; Bates, S. E. Nat. Rev. Cancer 2002, 2, 48; (c) Angehrn, P.; Goetschi, E.; Gmuender, H.; Hebeisen, P.; Hennig, M.; Kuhn, B.; Luebbers, T.; Reindl, P.; Ricklin, F.; Schmitt-Hoffmann, A. J. Med. Chem.2011, 54, 2207
6 (a)Shibuya, I.; Honda, K.; Gama, Y.; Shimizu, M. Heterocycles 2000, 53, 929. (b) Takido, T.; Itabashi, K.; Synthesis 1985, 430. (c) Shibuya, I.; Gama, Y.; Shimizu, M. Heterocycles 2001, 55, 381. (d) Wang, H.; Wang, L.; Shang, J.; Li, X.; Wang, H.; Gui, J.; Lei, A. Chem. Commun., 2012, 48, 76. (e) Alla, S. K.; Sadhu, P.; Punniyamurthy, T. J. Org. Chem., 2014, 79, 7502. (f) Chaudhari, P. S.; Pathare, S. P.; Akamanchi, K. G. J. Org. Chem., 2012, 77, 3716. (g) Mendoza-Espinosa, D.; Ung, G.; Donnadieu, B.; Bertrand, G. Chem. Commun.,2011, 47, 10614. (h) Potts, K. T.; Houghton, E.; Singh, U. P. J. Org. Chem., 1974, 39, 3627.
7 a) Jagodzinski, T.; Jagodzinska, E.; Jabłonski, Z. Tetrahedron 1986, (b) Jagodzinski, T. Synthesis 1988, 717.
8 Varun, B. V.; Sood, A.; Prabhu, K. R. RSC Adv.2014, 4, 60798.
Scheme 2: Synthesis of thioamide
Section B
This section is divided in to two chapters, Chapter 1 and Chapter 2.
Chapter 1 of this section describes a facile transition metal-free oxidative CDC (Cross Dehydrogenative Coupling) reaction leading to a regioselective thiolation of electron-rich arenes and hetero-arenes. This strategy provides a rare opportunity of using thione in a CDC reaction to form C–S bonds to obtain arylthiobenzoxazoles, hetero-arylthiobenzoxazoles and arylthiobenzthiazoles, which are pharmaceutically valuable compounds.9 This highly regioselective CDC reaction is unique as it requires the reversing the reactivity of sulfur to form the C–S bonds. Despite the propensity of thiols to undergo oxidation, this method provides an elegant and new avenue for synthesizing thioethers of benzazoles (Scheme 3).10 a) Greco, M. N.; Hageman, W. E.; Powell, E. T.; Tighe, J. J.; Persico, F. J. J. Med. Chem. 1992, 35, 3180. b) Zhang, J.-T.; Qi, J.; Feng, H.; Dong, Z. WO2010048603, 2010. c) Greco, M. N.; Hageman, W. E.; Powell, E. T.; Tighe, J. J.; Persico, F. J. J. Med. Chem. 1992, 35, 3180. d) Barchuk, W. T.; Dunford, P. J.; Edwards, J. P.; Fourie, A. M.; Karlsson, L.; Quan, J. M. US 2008194630. e) Koci, J.; Klimesova, V.; Waisser, K.; Kaustova, J.; Dahse, H.-M.; Moellmann, U.;Bioorg. Med. Chem. Lett. 2002, 12, 3275.
10 Varun, B. V.; Prabhu, K. R. J. Org. Chem.2014, 79, 9655.
xii
Synopsis
Scheme 3: C-H-Functionalization of electron-rich arenes
Chapter 2 is discussed in two parts, Part A and Part B.
Part A: deals with the C–H functionalization of β-diketones via CDC reactions. A variety β-diketones were sulfenylated at α-position with a variety of benzazole-2-thione derivatives. Sulfenylation of β-diketones is challenging as β-diketones undergo deacylation after sulfenylation in the reaction medium.11 The highlight of this work is that the resultant products do not undergo deacylation. Under the optimal reaction conditions a variety of functional group like ketones, acids and esters were well tolerated. Also, the resultant sulfenylated β-diketones were further manipulated to α,α-disubstituted β-diketones and pyrazoles (Scheme 4).12
11 (a) Ogura, K.; Sanada, K.; Takahashi, K.; Iida, H. Tetrahedron Lett.1982, 23, 4035. (b) Zou, L.-H.; Priebbenow, D. L.; Wang, L.; Mottweiler, J.; Bolm, C. Adv. Synth. & Catal. 2013, 355, 2558.
12 Varun, B. V.; Gadde, K.; Prabhu, K. R. Org. Lett. 2015, 17, 2944.
Scheme 4: C-H Functionalization of β-diketones via CDC reaction
Chapter 2, Part B: deals with the C–H functionalization of ketones via CDC, which is the continuation of the above discussed work (Chapter 2, Part B). The products obtained from this method can be further modified and can be used for the synthesis of α,β-unsaturated carbonyl compounds under Trost or Julia olefination reaction conditions.13 A variety of actophenone derivatives, propiophenone derivatives and simple alkyl ketones were sulfenylated at the α-position with various benzazole-2-thiones (Scheme 5).14
Scheme 5: C-H Functionalization of ketones via CDC reaction
(a) Trost, B. M.; Salzmann, T. N.; Hiroi, K. J. Am. Chem. Soc. 1975, 98, 4887. (b) Baudin, J. B.; Hareau, G.; Julia, S. A. Tetrahedron Lett. 1991, 32, 1175. (c) Blakemore, P. R.; Cole, W. J.; Kocienski, P. J.; Morley, A. Synlett 1998, 26.
14 Manuscript under preparation.
Section C
This section describes the ‘sulfur/fluorine assisted deacylation of β-diketones.’ Achieving a controlled mono fluorination at α- position of a ketone group is a difficult task. Therefore, an alternate approach is to have a sulfide group at α-position to a ketone (electron withdrawing moiety) and thereby providing additional stability to the generated reactive intermediate at α-position. Till date, this transformation has been achieved only by electrochemical methods.15 In continuation of our earlier work of α-sulfenyl β-diketones for exploring the synthetic utility of α-sulfenyl β-diketones (like benzylation and allylation), we performed the fluorination reaction. In this reaction, the fluorinated product (a diketone) underwent a de-acylation process to furnish the corresponding α-fluorinated ketone and we further optimized the reaction conditions and explored the substrate scope for this reaction. Under the optimized reaction conditions a variety of fluorinated products were isolated in excellent yield (Scheme 6)
Scheme 6: Sulfur/Fluorine assisted deacylation of β-diketones 15Fuchigami, T.; Shimojo, M.; Konno, A.; Nakagawa, K. J. Org. Chem. 1990, 55, 6074
16 Manuscript under preparation
sj-jpg-7-pie-10.1177_09544089211041192 - Supplemental material for Analysis of radiative nonlinear heat transfer in a convective flow of dusty fluid by capitalizing a non-Fourier heat flux model
No full textSupplemental material, sj-jpg-7-pie-10.1177_09544089211041192 for Analysis of radiative nonlinear heat transfer in a convective flow of dusty fluid by capitalizing a non-Fourier heat flux model by G. Sowmya, B. Saleh, R. J. Punith Gowda, R. Naveen Kumar, R. S. Varun Kumar and M. Radhika in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering</p
Reproducibility Dataset for CRYOWRF v1.0
No full textThis repository contains data required for reproducibility of the results to be published in the associated manuscript. Apart from reproducibility, the attached datasets also serve as templates for new users to adopt CRYOWRF in their research. The datasets consist of two folders organized in zip format: 1. REPRODUCIBILITY_SIMULATION: Consists of namelists for WPS, WRF and SNOWPACK to reproduce simulations published in the manuscript Additional files include datasets (from IMAU-FDM / RACMO, see "credits" below ) as well as helper python scripts to produce *.sno files which are used as initial conditions for SNOWPACK in CRYOWRF. 2. REPRODUCIBILITY_POSTPROCESSING: Includes outputs of CRYOWRF and python scripts used to prepare figures in the manuscript. Each of the folders have their own readme files for more details. Codecitation: Varun Sharma. (2021, July 2). vsharma-next/CRYOWRF: CRYOWRF v1.0 (Version v1.0). Zenodo. http://doi.org/10.5281/zenodo.5060165location: https://gitlabext.wsl.ch/atmospheric-models/CRYOWRF (stable releases / institutional repo) https://github.com/vsharma-next/CRYOWRF (dev branches / developer repo) Publication**Introducing CRYOWRF v1.0: Multiscale atmospheric flow simulations with advanced snow cover modelling.**Varun Sharma, Fraziska Gerber and Michael Lehning, Submitted to Geoscientific Model Development AcknowledgementsWe thank Peter Kuipers Munneke ([email protected]) for preparing and sharing outputs of IMAU-FDM and RACMO used for initial conditions for case Ia. The relevant citations for the methods through which these datasets were generated are:* Kuipers Munneke, P., S. R. M. Ligtenberg, B. P. Y. Noël, I. M. Howat, J. E. Box, E. Mosley-Thompson, J. R. McConnell, K. Steffen, J. T. Harper, S. B. Das and M. R. van den Broeke. 2015. Elevation change of the Greenland ice sheet due to surface mass balance and firn processes, 1960-2014. The Cryosphere, 9, 2009-2025. doi:10.5194/tc-9-2009-2015 * Ligtenberg, S. R. M., P. Kuipers Munneke, B. P. Y. Noël, and M. R. van den Broeke. 2018. Brief communication: Improved simulation of the present-day Greenland firn layer (1960-2016). The Cryosphere, 12, doi:10.5194/tc-12-1643-2018CRYO
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