Akhilesh Kumar Singh

Bio: Akhilesh Kumar Singh is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Rietveld refinement & Medicine. The author has an hindex of 37, co-authored 280 publications receiving 4628 citations. Previous affiliations of Akhilesh Kumar Singh include University of Strathclyde & Los Alamos National Laboratory.

Evidence for MB and MC phases in the morphotropic phase boundary region of (1-x)[Pb(Mg1/3Nb2/3)O3]-xPbTiO3: A Rietveld study

Abstract: We present here the results of the room-temperature dielectric measurements and Rietveld analysis of the powder x-ray diffraction data on $(1\ensuremath{-}x)[\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}]\ensuremath{-}x{\mathrm{PbTiO}}_{3}(\mathrm{PMN}\ensuremath{-}x\mathrm{PT})$ in the composition range $0.20l~xl~0.45$ to show that the morphotropic phase boundary region contains two monoclinic phases with space groups Cm (or ${M}_{B}$ type) and Pm (or ${M}_{C}$ type) stable in the composition ranges $0.27l~xl~0.30$ and $0.31l~xl~0.34,$ respectively. The structure of $\mathrm{PMN}\ensuremath{-}x\mathrm{PT}$ in the composition ranges $0l~xl~0.26$ and $0.35l~xl~1$ is found to be rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are compared with the predictions of Vanderbilt Cohen's theory.

Hybrid graphene metasurfaces for high-speed mid-infrared light modulation and single-pixel imaging

Abstract: During the past decades, major advances have been made in both the generation and detection of infrared light; however, its efficient wavefront manipulation and information processing still encounter great challenges. Efficient and fast optoelectronic modulators and spatial light modulators are required for mid-infrared imaging, sensing, security screening, communication and navigation, to name a few. However, their development remains elusive, and prevailing methods reported so far have suffered from drawbacks that significantly limit their practical applications. In this study, by leveraging graphene and metasurfaces, we demonstrate a high-performance free-space mid-infrared modulator operating at gigahertz speeds, low gate voltage and room temperature. We further pixelate the hybrid graphene metasurface to form a prototype spatial light modulator for high frame rate single-pixel imaging, suggesting orders of magnitude improvement over conventional liquid crystal or micromirror-based spatial light modulators. This work opens up the possibility of exploring wavefront engineering for infrared technologies for which fast temporal and spatial modulations are indispensable.

Trypanosoma cruzi trans-sialidase initiates a program independent of the transcription factors RORγt and Ahr that leads to IL-17 production by activated B cells.

Abstract: Here we identified B cells as a major source of rapid, innate-like production of interleukin 17 (IL-17) in vivo in response to infection with Trypanosoma cruzi. IL-17(+) B cells had a plasmablast phenotype, outnumbered cells of the TH17 subset of helper T cells and were required for an optimal response to this pathogen. With both mouse and human primary B cells, we found that exposure to parasite-derived trans-sialidase in vitro was sufficient to trigger modification of the cell-surface mucin CD45, which led to signaling dependent on the kinase Btk and production of IL-17A or IL-17F via a transcriptional program independent of the transcription factors RORγt and Ahr. Our combined data suggest that the generation of IL-17(+) B cells may be a previously unappreciated feature of innate immune responses required for pathogen control or IL-17-mediated autoimmunity.

Powder neutron diffraction study of phase transitions in and a phase diagram of (1-x)[Pb(Mg1/3Nb2/3)O3]-xPbTiO3

Abstract: Dielectric, piezoelectric resonance frequency, and powder neutron diffraction studies as a function of temperature have been performed on several compositions of $(1\ensuremath{-}x)[\mathrm{Pb}({\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}){\mathrm{O}}_{3}]\text{\ensuremath{-}}x\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ $(PM\mathrm{N}\text{\ensuremath{-}}x\mathrm{PT})$ ceramics in and outside the morphotropic phase boundary (MPB) region to investigate the phase transitions and phase stabilities in this mixed system. Anomalies in the temperature dependence of piezoelectric resonance frequency and dielectric constant are correlated with structural changes using Rietveld analysis of powder neutron diffraction data. The frequency dependent dielectric studies reveal relaxor ferroelectric behavior for $xl0.35$ and a normal ferroelectric behavior for $x\ensuremath{\geqslant}0.35$. The dielectric peak temperature and the Vogel-Fulcher freezing temperature are found to increase linearly with ``$x$'' while their difference, after decreasing linearly with $x$, vanishes at $x=0.35$ suggesting a crossover form relaxor ferroelectric to normal ferroelectric behavior at this composition. A phase diagram of the $\mathrm{PMN}\text{\ensuremath{-}}x\mathrm{PT}$ system showing the stability fields of ergodic relaxor, monoclinic ${M}_{B}$, monoclinic ${M}_{C}$, tetragonal and cubic phases is presented. Our results suggest the presence of a succession of three phase transitions, not reported earlier, corresponding to structural changes from the monoclinic ${M}_{B}$ to the monoclinic ${M}_{C}$ to the tetragonal to the cubic phases for $0.27\ensuremath{\leqslant}x\ensuremath{\leqslant}0.30$ on heating above room temperature. In addition, our studies confirm the earlier findings on transitions from the monoclinic ${M}_{C}$ to the tetragonal to the cubic phases for $0.31\ensuremath{\leqslant}x\ensuremath{\leqslant}0.34$ on heating above room temperature and tetragonal to monoclinic ${M}_{C}$ phase on cooling below room temperature for $x=0.36$. All these transitions are found to be accompanied with anomalies either in the temperature dependence of dielectric constant or the piezoelectric resonance frequency or both. Rietveld analyses of the powder neutron diffraction data at various temperatures on a pseudorhombohedral composition with $x=0.25$ suggest that the short range ${M}_{B}$ type monoclinic order present at room temperature grows to long range monoclinic order on lowering the temperature. The temperature variations of the unit cell parameters and atomic shifts are also presented to throw light on the nature of the various phase transitions in this mixed system.

Harrison's Principles of Internal Medicine

Abstract: The 11th edition of Harrison's Principles of Internal Medicine welcomes Anthony Fauci to its editorial staff, in addition to more than 85 new contributors. While the organization of the book is similar to previous editions, major emphasis has been placed on disorders that affect multiple organ systems. Important advances in genetics, immunology, and oncology are emphasized. Many chapters of the book have been rewritten and describe major advances in internal medicine. Subjects that received only a paragraph or two of attention in previous editions are now covered in entire chapters. Among the chapters that have been extensively revised are the chapters on infections in the compromised host, on skin rashes in infections, on many of the viral infections, including cytomegalovirus and Epstein-Barr virus, on sexually transmitted diseases, on diabetes mellitus, on disorders of bone and mineral metabolism, and on lymphadenopathy and splenomegaly. The major revisions in these chapters and many

Cytokines in inflammatory bowel disease

Abstract: Erroneous communication between the innate and adaptive immune systems through cytokines results in exaggerated or attenuated immune response. It is not known whether the pathologic immune response in inflammatory bowel disease has its origin in a dysbalance of pro- and anti-inflammatory cytokine release or whether it is secondary in subsequence of a defective intestinal barrier or the destructive power of aggressive microbiota in the gut lumen.

An Introduction to Genetic Statistics

Abstract: A reviewer for the Journal of the Royal Statistical Society of England comments \"This is the first book covering in one volume all important topics in genetical statistics.\" Written to provide basic probability ideas in terms of genetic situations, since the theory of genetics is a probability theory; to give a definitive treatment of applications of these ideas to genetic theory; and to describe statistical methods appropriate to the data models that are developed.