50175 research outputs found
Sort by
Non-Calcified Coronary Artery Plaque Characterization by Dual-Energy Computed Tomography
No full textBackground: Inversion of dual-energy computed tomography (DECT) data for obtaining the electron density and effective atomic number of substances has been a work in progress for the past forty years. It has been the practice to characterize the material in terms of Hounsfield Unit (HU) values obtained by two different energies. Objectives: Since HU values are equipment-dependent quantities, it is necessary to develop a method that characterizes the substance in terms of certain physical quantities that are equipment independent. Materials and Methods: The process that we adopt is to find a calibration method by which all equipment-dependent quantities are eliminated and we directly deal with quantities that are representative of the sample, namely its electron density and effective atomic number. We collect the DECT data from 21 samples of non-calcified coronary artery plaques in human cadavers. Results: With our standardized inversion method, we have obtained the electron density and effective atomic number of these samples. With physical models of lipids and proteins, it becomes possible to conclude that non-calcified plaque samples can have calcium dispersed in the lipid part of the plaque in trace amounts that cannot be observed by light based microscopy or by CT images alone. Conclusion: This characterization, may give a new insight in characterization of non-calcified coronary artery plaque and in medical diagnostics
Mechanistic study of the reduction of MoO2 to Mo2C under methane pulse conditions
No full textMolybdenum carbide (Mo2C), an interstitial transition metal carbide, has been used in a myriad of industrial applications due to its refractory nature, extreme hardness and strength, and high electrical and thermal conductivity. It also possesses catalytic activity for many chemical processes such as hydrodeoxygenation, reforming, water-gas shift, and the Fischer-Tropsch reaction. Among the current synthesis methods available to produce beta-Mo2C, temperature-programmed reduction yields materials with the highest specific surface areas. The objective of the present work is to perform a detailed investigation of the carburization process and to determine the key intermediate phases that are formed during reduction. To achieve this objective, we performed the carburization process under pulse conditions wherein a small amount of CH4 in each pulse was reacted with a packed bed of MoO2. Our XRD and TEM results demonstrate that the solid-phase transformation from MoO2 to beta-Mo2C follows a ``plum-pudding'' mechanism where Mo metal crystallites are constantly formed as the key intermediate phase throughout the matrix
Garnet pyroxenite from Nilgiri Block, southern India: Vestiges of a Neoarchean volcanic arc
No full textSouthern peninsular India preserves records of Late Neoarchean Early Paleoproterozoic continental building and cratonization. A transect from the Paleoarchean Dharwar Craton to the Neoarchean arc magmatic complex in the Nilgiri Block across the intervening Moyar Suture Zone reveals an arc-accretionary complex composed of banded iron formation (BIF), amphibolite, metatuff, garnet-kyanite schist, metagabbro, pyroxenite and charnockite. Here we investigate the petrology, geochronology and petrogenesis of the pyroxenite and garnet-clinopyroxenite. The pyroxenite is mainly composed of orthopyroxene and clinopyroxene with local domains/pockets enriched in a clinopyroxene-gamet assemblage. Thermobarometric calculations and phase equilibria modeling suggest that the orthopyroxene-and clinopyroxene-rich domains formed at 900-1000 degrees C, 1-1.2 GPa whereas the garnet-and clinopyroxene-rich domains record higher pressure of about 1.8-2 GPa at similar temperature conditions (900-1000 degrees C). Zircon U-Pb SHRIMP dating show weighted mean Pb-207-Pb-206 age of 2532 +/- 22 Ma, with metamorphic overgrowth at 2520 +/- 27 Ma and 2478 +/- 27 Ma. We propose a tectonic model involving decoupling and break-off of the oceanic plate along the southern flanks of the Dharwar Craton, which initiated oceanic plate subduction. Slab melting eventually built the Nilgiri volcanic arc on top of the overriding plate along the flanks of the Dharwar Craton. Our study supports an active plate tectonic regime at the end of the Archean Era, aiding in the growth of paleo-continents and their assembly into stable cratons. (C) 2018 Elsevier B.V. All rights reserved
Investigation of sulfur related defects in graphene quantum dots for tuning photoluminescence and high quantum yield
No full textThis paper presents a comprehensive study of the impact of defects on quantum yield in doped graphene quantum dots by having sulfur containing compounds (S-GQDs). The facile and high yielding hydrothermal method was used to process the S-GQDs by selecting two different compounds such as conc. H2SO4 and MgSO4 center dot 7H(2)O containing sulfur. Initially, the synthesized samples were characterized by using High Resolution Transmission Electron Microscope (HRTEM), Raman Spectroscopy, Fourier Transform Infra-Red Spectroscopy (FT-IR), Thermogravimetric and Differential Thermal Analysis (TGA/DTA), UV-vis spectroscopy, and Photoluminescence (PL). HRTEM images suggest that the majority of the both samples were in the narrow range of 5-20 nm in diameter. Optical properties of the GQDs are altered as a result of S-doping with purple tunable PL at shorter wavelengths. As expected, by using the different excitation energy in PL, appearance of peak introduces additional energy levels between pi and pi* that provide alternative electron transition pathways. The most remarkable finding is that the fluorescence quantum yield (FL QY) of S-doped GQDs is higher than that of the reported doped GQDs. This clearly suggests that the defects states related to S modify the electron density, tailor the PL characteristics and improvements in quantum yield of the GQDs. (c) 2018 Published by Elsevier B.V
Phase-field modeling of grain-boundary grooving and migration under electric current and thermal gradient
No full textGrain-boundary migration, void formation as well as associated hillock formation are important mechanisms which lead to the failure of interconnects in the microelectronic packages. An understanding of the underlying physics of each of the phenomena can allow better design of interconnects. In this paper, we formulate a new phase-field model based on a grand-potential formalism for studying the phenomena of grain-boundary grooving under the combined influence of pure diffusion controlled transport, electric current and thermal gradient. We separately investigate the contributions of each of the stimuli towards the process of grain-boundary migration and hillock formation, by performing phase-field simulations as well as comparing with analytical theories. Additionally, we qualitatively reproduce the phenomena observed in experiments on polycrystalline metals, wherein electromigration and thermomigration may act in unison or against each other towards their contributions in grooving, hillocking and void growth. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Wetting characteristics of vertically aligned graphene nanosheets
No full textVertically aligned graphene nanosheets (VAGNs) are a class of graphitic carbon in which few layers of graphene nanosheets are aligned perpendicular to the plane of the substrate. The change in water contact angle (from 103 degrees to 135 degrees) with VAGNs, as a function of change in the surface geometry, is analysed. Theoretical calculations and comparison with the experimental data shows that the apparent contact angle values of VAGNs are closer to that of the fully non-wetting mode or ideal Cassie mode of wetting. The ideal Cassie mode of wetting also explains the variation of the water contact angle of VAGNs with the surface morphology of the material and predicts how surface parameters can be modified to get the required wettability for a certain application of this material
Trifluoromethylthiolation of -Chloroaldehydes: Access to Quaternary SCF3-Containing Centers
No full textIn this study, a straightforward methodology was developed to access quaternary -trifluoromethylthiolated chloroaldehydes. Using the Munavalli reagent as the electrophilic SCF3 source, a base-catalyzed trifluoromethylthiolation reaction with a panel of -chloroaldehydes was successfully achieved under mild reaction conditions. The -trifluoromethylthiolated chloroaldehydes were obtained in moderate to high yields (up to 88%). This approach demonstrated a good functional-group tolerance and offered access to highly functionalized quaternary trifluoromethylthiolated aldehydes, inaccessible so far. The development of an enantioselective version was investigated by using a chiral phase-transfer catalyst, giving the enantioenriched product in moderate enantiomeric excess
Illuminating GPCR Signaling by Cryo-EM
No full textThe wave of resolution revolution in cryo-EM has touched, and made a significant impact on, the structural biology of GPCRs. High-resolution structures of several GPCR-G-protein complexes are now determined by cryo-EM and they illuminate fine structural details of this central macromolecular complex involved in cellular signaling
High-power continuous-wave supercontinuum generation in highly nonlinear fibers pumped with high-order cascaded Raman fiber amplifiers
No full textA novel method for efficient generation of a high-power, equalized continuous-wave supercontinuum source in an all-conventional silica fiber architecture is demonstrated. Highly nonlinear fiber is pumped in its anomalous dispersion region using a novel, high-power, L-band laser. The L-band laser encompasses a sixth-order cascaded Raman amplifier which is pumped with a high-power Ytterbium-doped fiber laser and amplifies a low-power, tunable L-band seed source. The supercontinuum generated 35 W of power with similar to 40% efficiency. The supercontinuum spectrum was measured to have a high degree of flatness of better than 5 dB over 400 nm of bandwidth (1.3-1.7 mu m, limited by spectrum analyzer range) and a power spectral density in this region of >50 mW/nm>50 mW/nm. The extent of the SC spectrum is estimated to be up to 2 mu m. (C) 2018 Optical Society of Americ
Leading logarithms of the two-point function in massless O(N) and SU(N) models to any order from analyticity and unitarity
No full textLeading (large) logarithms in non-renormalizable theories have been investigated in the recent past. Besides some general considerations, explicit results for the expansion coefficients (in terms of leading logarithms) of partial wave amplitudes and of scalar and vector form factors have been given. Analyticity and unitarity constraints have been used to obtain the expansion coefficients of partial waves in massless theories, yielding form factors and the scalar two-point function to five-loop order in the O(4)/O(3) model. Later, all order solutions for the partial waves in any O(N + 1)/O(N) model were found. Also, results up to four-loop order exist for massive theories. Here we extend the implications of analyticity and unitarity constraints on the leading logarithms to arbitrary loop order in massless theories. We explicitly obtain the scalar and vector form factors as well as the scalar two-point function in any O(N) and SU(N) type models. We present relations between the expansion coefficients of these quantities and those of the relevant partial waves. Our work offers a consistency check on the published results in the O(N) models for form factors, and new results for the scalar two-point function. For the SU(N) type models, we use the known expansion coefficients for partial waves to obtain those for scalar and vector form factors as well as for the scalar two-point function. Our results for the form factor offer a check for the known and future results for massive O(N) and SU(N) type models when the massless limit is taken. Mathematica notebooks which can be used to calculate the expansion coefficients are provided as supplementary material