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Rivalry in Bacillus subtilis colonies: enemy or family?
No full textTwo colonies of Bacillus subtilis of identical strains growing adjacent to each other on an agar plate exhibit two distinct types of interactions: they either merge as they grow or demarcation occurs leading to formation of a line of demarcation at the colony fronts. The nature of this interaction depends on the agar concentration in the growth medium and the initial separation between the colonies. When the agar concentration was 0.67% or lower, the two sibling colonies were found to always merge. At 1% or higher concentrations, the colonies formed a demarcation line only when their initial separation was 20 mm or higher. Interactions of a colony with solid structures and liquid drops have indicated that biochemical factors rather than the presence of physical obstacles are responsible for the demarcation line formation. A reaction diffusion model has been formulated to predict if two sibling colonies will form a demarcation line under given agar concentration and initial separation. The model prediction agrees well with experimental findings and generates a dimensionless phase diagram containing merging and demarcation regimes. The phase diagram is in terms of a dimensionless initial separation, (d) over bar, and a dimensionless diffusion coefficient, (D) over bar, of the colonies. The phase boundary between the two interaction regimes can be described by a power law relation between (d) over bar and (D) over bar
Direct In Situ Observation of Deformation Modes in Wedge Indentation of Metals
No full textWe study deformation patterns in wedge indentation of annealed metals (e.g., copper) using high-resolution, in situ imaging and image correlation. Based on attributes of the deformation such as velocity fields, grid distortion and strain distributions, we discriminate between two modes of deformation - a cutting mode with narrow-angle (sharp) wedges, e.g., apex angle of 30 degrees, and a radial-compression mode with wide-angle (blunt) wedges, e.g. apex angle of 120 degrees. The cutting mode is characterized by significant material flow parallel to the wedge face; and a thin region of very high strain (similar to 3), that is located immediately adjacent to the indenter face (wall-layer), and arises from friction-induced deformation. The radial-compression mode is distinguished by material flow normal to and away from the indenter face, with negligible velocity component parallel to the indenter face. The corresponding strain field is one of bulk deformation, with the highly-strained region (strain similar to 1) being of semicircular shape that extends from near the edge of indenter contact at the specimen surface, to well below the indenter tip. The observations show that indenter wall friction is likely to have a major influence on the deformation field only with narrow-angle indenters. Based on the observations of material flow, a suggestion is made (and validated) as to how the challenges faced in computational modeling of narrow-angle wedge indentation can be overcome. Implications for use of narrow-angle wedge indentation to study tribology of metalworking contacts, and ductile failure and damage in metals, are briefly discussed
Formation of hollow and solid carbon spheres in thermally stressed jet fuel in the low temperature autoxidation regime
No full textWe report the formation of hollow and solid carbon spheres and spherical nanostructures by self-assembly through thermal stressing of jet fuel (Jet A-1) in the autoxidation temperature range. The characterization of Jet A-1 deposits was conducted by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS). Additionally, high resolution mass spectrometry with electro spray ionization source (ESI-MS) have been used to identify large molecular weight compounds in the mass range 350 Da to 1000 Da in the thermally stressed fuel. Fourier transform infrared (FTIR) spectroscopy analysis revealed oxygenated functional groups in the jet fuel treated by flask tests. Compositional analysis of deposit by TEM EDS and scanning transmission electron microscopy (STEM) and a high-angle annular dark field (HAADF) detector identified multiple trace metallic elements such as Cu, Fe, Zn, Sn, Mg, Al and heteroatoms S, N, 0. Hollow carbon sphere formation was due to the catalytic activity of trace metals. Spherical particle growth in this method also appeared to follow Ostwald ripening mechanism. Simple flask static tests in the low temperature regime with jet fuel as hydrocarbon source without externally added catalysts thus is a novel method for hollow and solid carbon sphere synthesis and presented in this paper
A Broadband Rectangular Reentrant Cavity for Multiple-Beam Klystron
No full textBroadbanding of a rectangular reentrant cavity is proposed through reducing its unloaded quality factor by loading the cavity with periodic rectangular ridges placed on cavity transverse walls and orienting them perpendicular to the electric field. The effect of ridge loading on the cavity parameters, namely, resonant frequency, unloaded quality factor, and characteristics hunt impedance was investigated through 3-D electromagnetic simulations. Ridge loading of the cavity could facilitate around 70% reduction in the quality factor without any change in resonant frequency and negligible change in characteristic shunt impedance of that of a no-ridge-loaded cavity. The simulated resonant frequency and quality factor of typical S-band rectangular reentrant cavities were validated against measurements
Regional stochastic ground-motion model for low to moderate seismicity area with variable seismotectonic: application to Peninsular India
No full textA new stochastic ground motion prediction equation (GMPE) for low and diverse seismicity region, i.e., Peninsular India has been derived for a wide range of magnitude (Mw 4-8) and distance (10-500km). Source, path, and site terms have been determined by comparing the recorded and simulated response spectra using derived values from the literature. Uncertainty has been assessed through simulation by random sampling of the corresponding distribution of all the input parameters. To capture the non-uniform seismicity of Peninsular India, GMPE has been derived using constant stress and variable stress model. The synthetic data has been regressed using linear mixed-effect model algorithm by determining the functional form that is compatible for magnitude and distance scaling. Sensitivity analysis has been used in determining the impact of uncertainty of each input parameter on GMPE standard deviation. Further, new GMPEs have been validated using the recorded ground-motion data
Low-temperature saturation of phase coherence length in topological insulators
No full textImplementing topological insulators as elementary units in quantum technologies requires a comprehensive understanding of the dephasing mechanisms governing the surface carriers in these materials, which impose a practical limit to the applicability of these materials in such technologies requiring phase coherent transport. To investigate this, we have performed magnetoresistance (MR) and conductance fluctuations (CF) measurements in both exfoliated and molecular beam epitaxy grown samples. The phase breaking length (l(phi)) obtained from MR shows a saturation below sample dependent characteristic temperatures, consistent with that obtained from CF measurements. We have systematically eliminated several factors that may lead to such behavior of l(phi) in the context of TIs, such as finite size effect, thermalization, spin-orbit coupling length, spin-flip scattering, and surface-bulk coupling. Our work indicates the need to identify an alternative source of dephasing that dominates at low T in topological insulators, causing saturation in the phase breaking length and time
Glucosamine-6-phosphate synthase inhibiting C3-beta-cholesterol tethered spiro heterocyclic conjugates: Synthesis and their insight of DFT and docking study
No full textA series of novel covalent cholesterol-spiro pyrrolidine/pyrrolizidine heterocyclic hybrids possessing biologically active oxindole, indanedione, and acenaphthylene-1-one have been synthesized by the reaction of C3-beta-cholesteroalacrylate with heterocyclic di- and tri-ketones. All the sixteen compounds were obtained as a single isomer in good yield through a stereo- and regio- selective 1,3-dipolar cycloaddition methodology. Stereochemistry of the spiranic cycloadducts has been established by spectroscopic analysis and the regioselectivity outcome of the spiro adducts has been accomplished by DFT calculations at B3LYP/6-31G (d,p) level study. In vitro antibacterial activity of the newly synthesized cycloadducts were evaluated against highly pathogenic Gram-positive and Gram-negative bacteria and the most active compounds 5a, 13, and 14 underwent automated in silico molecular docking analysis in order to validate their effective orientation as a inhibitors bound in the active site of glucosamine-6-phosphate synthase (1XFF) enzyme by employing AutoDock Tools
Minimizing the Entropy Penalty for Ligand Binding: Lessons from the Molecular Recognition of the Histo Blood-Group Antigens by Human Galectin-3
No full textLigand conformational entropy plays an important role in carbohydrate recognition events. Glycans are characterized by intrinsic flexibility around the glycosidic linkages, thus in most cases, loss of conformational entropy of the sugar upon complex formation strongly affects the entropy of the binding process. By employing a multidisciplinary approach combining structural, conformational, binding energy, and kinetic information, we investigated the role of conformational entropy in the recognition of the histo blood-group antigens A and B by human galectin-3, a lectin of biomedical interest. We show that these rigid natural antigens are pre-organized ligands for hGal-3, and that restriction of the conformational flexibility by the branched fucose (Fuc) residue modulates the thermodynamics and kinetics of the binding process. These results highlight the importance of glycan flexibility and provide inspiration for the design of high-affinity ligands as antagonists for lectins
Inkjet-printed co-continuous mesoporous oxides for high-current power transistors
No full textLimited printing resolution has always been a major hindrance for printed electronics; irrespective of the high mobility demonstrated by solution-processed semiconductors, long-channel printed field-effect transistors (FETs) have demonstrated low On-state conductance and switching speeds. Although various concepts have been proposed to obtain narrow-channel printed FETs, the actual demonstration of high On-currents/channel conductance has been rare. In this context, herein, we report a general recipe to print co-continuous mesoporous structures with high surface-to-volume ratios for the first time for a large range of metallic and semiconducting oxides, both n- and p-type; next, by exploiting an innovative transistor architecture by printing an additional silver layer on top of the printed porous channel, we reduced the necessary length of electronic transport through the semiconductor material to a short vertical distance of the order of a few tens of nanometres. Basically, when a composite solid polymer electrolyte was used as a gate insulator, we essentially obtained channel length-independent transport with the unprecedented On-current of 67 mu A mu m(-1) and transconductance of 143 mu S mu m(-1) at the supply voltage of only 0.5 V. Among others, one may foresee the usage of these devices in high power switches and for drawing power from batteries in all-printed electronic circuits
