50175 research outputs found
Sort by
In vitro characterization of N-terminal truncated EpsC from Bacillus subtilis 168, a UDP-N-acetylglucosamine 4,6-dehydratase
No full textBacillus subtilis 168 EpsC is annotated as ``Probable polysaccharide biosynthesis protein'' in the SwissProt database. epsC is part of the eps operon, thought to be involved in the biosynthesis of exopolymeric substances (EPS). The present study was undertaken to determine the molecular function of EpsC. Sequence analysis of EpsC suggested the presence of a transmembrane domain. Two N-terminal deletion mutants in which residues 1-89 (EpsC(89)) and 1-115 (EPsC(115)) are deleted were cloned and overexpressed. Enzyme activity and substrate preferences were investigated by reverse phase HPLC, surface plasmon resonance (SPR) spectroscopy and absorption spectroscopy. These data show that EpsC has UDP-GlcNAc 4,6-dehydratase activity in vitro. Purified recombinant proteins were found to utilise UDP-Glc and TDP-Glc also as substrates. In addition, EpsC(115) could utilise UDP-Gal and UDP-GalNAc as substrates whereas EpsC(89) could only bind these two sugar nucleotides. These results show that deletion of a longer N-terminal region broadens substrate specificity. These broadened specificity is perhaps an outcome of the deletion of the putative transmembrane domain and may not be present in vivo. EpsC, together with the aminotransferase EpsN (Kaundinya CR et aL , Glycobiology, 2018) and acetyl-transferase EpsM (unpublished data), appears to be involved in the biosynthesis of N,N'-diacetylbacillosamine
A constitutive model for thermoplastics based on two temperatures
No full textPosed within a two-temperature thermodynamic framework, our aim is to propose a unified glass-rubber constitutive model for thermo-rheologically simple thermoplastic polymers. This modelling set-up usually applies to phenomena wherein sub-macroscopic processes involving different time scales occur and accordingly the thermodynamic system may be interpreted as comprising of two subsystems. The configurational subsystem contains the slower states, while the kinetic-vibrational subsystem comprises of the faster moving states. The two subsystems fail to equilibrate within experimental timescales in the glassy regime (low temperature or high strain rate) due to low structural relaxation rates. As transition to the rubbery regime commences at temperatures higher than glass transition or at sufficiently low loading rates, the two subsystems equilibrate within microscopic timescales. The model exploits physically inspired prescriptions for the free energies due to different underlying mechanisms-elastic stretching, localised shear transformations and infra-molecular straightening of chains. A simple temperature dependent formulation for structural relaxation in terms of heat transfer between the subsystems is used to capture transition between these mechanisms. The model is then validated against experimental results of uniaxial compression tests for various strain rates and temperatures establishing its ability to seamlessly transit between the glassy and rubbery regimes. Also demonstrated is the model's efficacy in capturing the key features of physical ageing and mechanical rejuvenation
Circuit complexity in interacting QFTs and RG flows
No full textWe consider circuit complexity in certain interacting scalar quantum field theories, mainly focusing on the phi(4) theory. We work out the circuit complexity for evolving from a nearly Gaussian unentangled reference state to the entangled ground state of the theory. Our approach uses Nielsen's geometric method, which translates into working out the geodesic equation arising from a certain cost functional. We present a general method, making use of integral transforms, to do the required lattice sums analytically and give explicit expressions for the d = 2, 3 cases. Our method enables a study of circuit complexity in the epsilon expansion for the Wilson-Fisher fixed point. We find that with increasing dimensionality the circuit depth increases in the presence of the phi(4) interaction eventually causing the perturbative calculation to breakdown. We discuss how circuit complexity relates with the renormalization group
OH absorption in the first quadrant of the Milky Way as seen by THOR
No full textContext. The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. Aims. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. Methods. This OH study is part of the HI/OH/Recombination line survey of the inner Milky Way (THOR). THOR is a Karl G. Jansky Very Large Array (VLA) large program of atomic, molecular and ionized gas in the range 15 degrees <= l <= 67 degrees and vertical bar b vertical bar <= 1 degrees. It is the highest-resolution unbiased OH absorption survey to date towards this region. We combine the optical depths derived from these observations with literature (CO)-C-13(1-0) and HI observations to determine the OH abundance. Results. We detect absorption in the 1665 and 1667 MHz transitions, that is, the ``main'' hyperfine structure lines, for continuum sources stronger than F-cont >= 0.1 Jy beam(-1). OH absorption is found against approximately 15% of these continuum sources with increasing fractions for stronger sources. Most of the absorption occurs in molecular clouds that are associated with Galactic H II regions. We find OH and (CO)-C-13 gas to have similar kinematic properties. The data indicate that the OH abundance decreases with increasing hydrogen column density. The derived OH abundance with respect to the total hydrogen nuclei column density (atomic and molecular phase) is in agreement with a constant abundance for AV < 10 - 20. Towards the lowest column densities, we find sources that exhibit OH absorption but no (CO)-C-13 emission, indicating that OH is a well suited tracer of the low column density molecular gas. We also present spatially resolved OH absorption towards the prominent extended H II-region W43. Conclusions. The unbiased nature of the THOR survey opens a new window onto the gas properties of the interstellar medium. The characterization of the OH abundance over a large range of hydrogen gas column densities contributes to the understanding of OH as a molecular gas tracer and provides a starting point for future investigations
Austenite stability and M2C carbide decomposition in experimental secondary hardening ultra-high strength steels during high temperature austenitizing treatments
No full textThe present study deals with the austenite stability and M2C carbide decomposition in three secondary hardening ultra-high strength (SHUHS) steels with varying levels of Cr and Mo (2Cr-1Mo, 2Cr-3Mo and 5Cr-5Mo) investigated using Vicker's hardness, optical and electron microscopy. These steels were subjected to high temperature austenitizing treatments at 1000, 1050, 1100 and 1150 degrees C. It has been established that increasing both Cr and Mo to 5 wt% as well as increasing the austenitizing temperature in this class of SHUHS steels is stabilizing the austenite such that almost 100% austenite is produced upon oil quenching. Further, higher Cr and Mo is also found to influence the stability of metastable M2C carbide formed during processing of the steels. While the M2C carbide in 2Cr-3Mo steel remained untransformed, it was found to transform partially to M6C during austenitization of 5Cr-5Mo steel. Hardness measurements on these steels revealed that hardness is relatively insensitive to austenitizing temperature in 2Cr-1Mo steel, decreased in 2Cr-3Mo and decreased more drastically in 5Cr-5Mo steel with austenitizing temperature. This dependence has been correlated to the influence of composition on M-s temperature and hence on retention of austenite as well as primary carbides. The experimental results were compared against theoretical calculations using ThermoCalc, which predict the presence of only M6C in both 2Cr-3Mo and 5Cr-5Mo steels. The apparent discrepancy between theoretical and experimental observations has been correlated to kinetic factors
High Temperature Superconductivity in the Cuprates: Materials, Phenomena and a Mechanism
No full textSuperconductivity in the cuprates, discovered in the late 1980s and occurring at unprecedentedly high temperatures (up to about 140K) in about thirty chemically distinct families, continues to be a major problem in physics. In this article, after a brief introduction of these square planar materials with weak interlayer coupling, we mention some of the salient electronic properties of hole doped cuprates such as the pseudogap phase and the Fermi arc. We then outline a phenomenological, Ginzburg Landau like theory developed by some of us for the emergent d-wave symmetry superconductivity in these materials, and confronted successfully with a large amount of experimental information. A more recent application of the approach to fluctuation diamagnetism and to the anomalously large Nernst effect is also discussed
Synthesis and characterization of Sm3+ activated La1-xGdxPO4 phosphors for white LEDs applications
No full textA series of orange-red light emitting Sm3+ activated La1-xGdxPO4 (0.00 x 1.00) phosphors were synthesized by the solid-state method. The structural parameters were confirmed by the Rietveld refinement method based on powder X-Ray diffraction (XRD) analysis. All the compounds crystallized in the monazite monoclinic structure with space group P 1 2(1)/n 1 (no. 14). The photoluminescence spectra of La0.95-xGdxPO4:Sm3+ phosphors were measured at the excitation wavelength of 400nm, exhibited characteristic emission peaks for Sm3+ at 560, 597, and 643nm. The purely magnetic dipole allowed transition ((4)G(5/2)(6)H(5/2)) at 560nm and partly magnetic dipole transition ((4)G(5/2) H-6(7/2)) at 597nm, responsible for orange-red light, dominated the emission spectra. In contrast to the magnetic dipole transitions, the electric dipole transition ((4)G(5/2)(6)H(9/2)) was found to be relatively less intense confirming high symmetrical crystal environment around Sm3+ in the host lattice. However, with subsequent substitution of Gd3+ at the lanthanide site in the host lattice, the crystal field suffered distortion and thus, influenced the photometric properties. From experimental results, it was evident that these phosphors have suitable Commission International de l'Eclairage (CIE), color correlated temperature (CCT) parameters, appreciable lifetime, and excellent color purity with respect to other reported rare earth ion doped orange-red phosphors. Further, these results could help in the improvisation of their use in optoelectronics especially white LEDs, photovoltaic cells and other strategic applications
Efficient enantiospecific synthesis of ent-conduramine F-1
No full textAn efficient enantiospecific total synthesis of ent-conduramine F-1 (aminocyclohexenetriol) was accomplished starting from the bis-Weinreb amide of tartaric acid. Key reactions in the synthesis include the desymmetrization of tartaric acid amide with vinylmagnesium bromide and installation of the required amine using Ellman sulfinimine. Ring closing metathesis was used to synthesize the required alkene in the cyclohexene. (C) 2018 Elsevier Ltd. All rights reserved
Coordinated Tuning of Graphene's Chemica Potential With NIR Wavelength and Temperature Under Kubo Framework for Enhanced Performance of SPR-Based Chemical Sensor
No full textThe performance of a Kretschmann configuration-based surface plasmon resonance sensor with fluoride glass prism, Ag layer, and graphene monolayer is simulated and analyzed under the coordinated tuning of temperature (293-373 K), near infrared (NIR) wavelength (1310-1700 nm), and graphene's chemical potential (0-1 eV). The simulation is carried out by considering the graphene's conductivity variations with wavelength, temperature, and chemical potential (As per Kubo formulation). For Ag layer, the phenomena of phononelectron scattering and electron-electron scattering are taken into account. Thermo-optic effect in dielectric media (ZBLAN prism and analyte samples, i.e., methanol and ethanol) is also considered. The simulation results indicate that a combination of shorter MR wavelength, higher temperature, and larger chemical potential can provide considerably enhanced performance. A deeper analysis predicts that 1310 nm wavelength, greater than 0.6 eV chemical potential, and 325-330 K temperature can he used as a pragmatic combination in order to achieve significantly enhanced sensing performance
How do animals find their way back home? A brief overview of homing behavior with special reference to social Hymenoptera
No full textPerforming efficient homing, i.e., returning to a previously known place, is crucial for the survival of any motile animal. Animals perform homing across different spatial scales and environments, employing various mechanisms with the aid of different sensorimotor systems molded by their varied evolutionary histories and ecological constraints. Despite these differences, most of the homing mechanisms across different taxa can be explained by some general basic mechanisms. Studies from social hymenopterans contribute substantially to the knowledge base of this study field and are, especially, interestingthey show excellent homing capabilities while possessing relatively simple neural architectures, and hence, their homing mechanisms are considered as economic solutions to a complex problem. Moreover, many of their homing mechanisms have also been observed in other taxa including vertebrates. With the advent of new technologies and increased research, our understanding of the hymenopteran homing is improving faster than everand therefore, a regular contemporary update might be of much help. In this review, I present a brief synthesis of previous and current understanding of homing mechanisms in social hymenopterans, with descriptions of the cues that they exploit for homing, and a comparative discussion on terminologies frequently used in social Hymenoptera with analogous terminologies used to describe similar phenomena in other taxa. I conclude with a note on the potential of applying the knowledge from homing studies in other fields of research like neurobiology and robotics, and possible future directions