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Thermodynamically Stable Mesoporous C3N7 and C3N6 with Ordered Structure and Their Excellent Performance for Oxygen Reduction Reaction
No full textCarbon nitrides with a high N/C atomic ratio (>2) are expected to offer superior basicity and unique electronic properties. However, the synthesis of these nanostructures is highly challenging since many parts of the C-N frameworks in the carbon nitride should be replaced with thermodynamically less stable N-N frameworks as the nitrogen content increases. Thermodynamically stable C3N7 and C3N6 with an ordered mesoporous structure are synthesized at 250 and 300 degrees C respectively via a pyrolysis process of 5-amino-1H-tetrazole (5-ATTZ). Polymerization of the precursor to the ordered mesoporous C3N7 and C3N6 is clearly proved by X-ray and electron diffraction analyses. A combined analysis including diverse spectroscopy and FDMNES and density functional theory (DFT) calculations demonstrates that the N-N bonds are stabilized in the form of tetrazine and/or triazole moieties in the C3N7 and C3N6. The ordered mesoporous C3N7 represents the better oxygen reduction reaction (ORR) performances (onset potential: 0.81 V vs reversible hydrogen electrode (RHE), electron transfer number: 3.9 at 0.5 V vs RHE) than graphitic carbon nitride (g-C3N4) and the ordered mesoporous C3N6. The study on the mechanism of ORR suggests that nitrogen atoms in the tetrazine moiety of the ordered mesoporous C3N7 act as active sites for its improved ORR activity
Time-resolved quantitative visualization of complex flow field emitted from an open ended shock tube using a wavefront measuring camera
No full textQuantitative visualization of shock-induced complex flow field emanating from the open end of a miniaturized hand-driven shock tube (Reddy tube) is presented. During operation, the planar shock wave of Mach number M-i=1.33 (+/- 0.6%) is discharged through the low-pressure driven-section, kept open to ambient room condition. From the moment of shock discharge, its after effects of evolving flow field are recorded for 300 mu s near the exit of the tube by using a high resolution (16 MP) wavefront measuring camera (WC) setup. The ability of the camera to identify the amplitude and phase of the incident light wave is utilized to measure the flow induced change in phase of the interrogating light beam quantitatively. Information about the evolving flow field with a spatial resolution of 40 mu m/pixel (for a field of view (FOV) 120 mm x 120 mm) and time resolution of 50 mu s is recorded in repeated runs. The measured phase information is used in the iterative refraction tomographic scheme to recover the three-dimensional (3D) density distribution of the flow field quantitatively, which reveals the internal features of the domain. Computational fluid dynamic (CFD) simulation is carried out for the same experimental conditions and it is found that recovered experimental density distribution shows good agreement with the results obtained through CFD simulation
Drain-Extended FinFET With Embedded SCR (DeFinFET-SCR) for High-Voltage ESD Protection and Self-Protected Designs
No full textThis article presents device design insights and design challenges for drain-extended FinFET devices with embedded silicon-controlled rectifier (SCR) (DeFinFET-SCR), which can be used as an electrostatic discharge (ESD) protection device and a self-protected high-voltage switch/driver for system-on-chip applications. The tradeoff between maximizing ESD robustness without hindering the transistor's operation is discussed in detail. An interplay between parasitic p-n-p turn-on and space charge modulation (SCM) is revealed, which strongly influences the strength of parasitic SCR and its turn-on efficiency during ESD and DC operations. Developed physical insights show that engineering p-n-p turn-on and onset of SCM are the key to maximize ESD robustness without causing early SCR turn-on during transistor operation. Based on new findings and developed physical insights, design guidelines have been derived for ESD robust DeFinFET-SCR
Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer
No full textReduction of surface temperatures of the planet by injecting sulfate aerosols in the stratosphere has been suggested as an option to reduce the amount of human-induced climate warming. Several previous studies have shown that for a specified amount of injection, aerosols injected at a higher altitude in the stratosphere would produce more cooling because aerosol sedimentation would take longer. In this study, we isolate and assess the sensitivity of stratospheric aerosol radiative forcing and the resulting climate change to the altitude of the aerosol layer. We study this by prescribing a specified amount of sulfate aerosols, of a size typical of what is produced by volcanoes, distributed uniformly at different levels in the stratosphere. We find that stratospheric sulfate aerosols are more effective in cooling climate when they reside higher in the stratosphere. We explain this sensitivity in terms of effective radiative forcing: volcanic aerosols heat the stratospheric layers where they reside, altering stratospheric water vapor content, tropospheric stability, and clouds, and consequently the effective radiative forcing. We show that the magnitude of the effective radiative forcing is larger when aerosols are prescribed at higher altitudes and the differences in radiative forcing due to fast adjustment processes can account for a substantial part of the dependence of the amount of cooling on aerosol altitude. These altitude effects would be additional to dependences on aerosol microphysics, transport, and sedimentation, which are outside the scope of this study. The cooling effectiveness of stratospheric sulfate aerosols likely increases with the altitude of the aerosol layer both because aerosols higher in the stratosphere have larger effective radiative forcing and because they have higher stratospheric residence time; these two effects are likely to be of comparable importance
Supramolecular Gelation of Europium and Calcium Cholates through the Nucleation-Elongation Growth Mechanism
No full textA detailed understanding of gelation mechanism can enable the properties of gels to be tuned for various applications, and may possibly help in understanding the aggregation of different biomolecules. We report a detailed study of the morphological and physio-chemical changes, dynamics (of a probe), and kinetics during the gelation of europium and calcium cholate hydrogels, leading to the development of a growth model. AFM images showed the transition of aggregated particles (100-150 nm) in the sol phase growing to a fibrous network in the gel through the entanglement of fibres, and not by dendritic growth (height analysis). The dynamic changes during this phase transformation were studied using a fluorescence probe (change in intensity and lifetime). We have been able to delineate the growth mechanism by using a combination of Eu(III) luminescence and a polarity sensitive fluorescence probe. The growth was found to follow the nucleation-elongation model, and these two phases responded in distinctly different fashions in rheological and luminescence measurements
Photocytotoxic Activity of Copper(II) and Zinc(II) Complexes of Curcumin and (Acridinyl)dipyridophenazine
No full textCopper(II) and zinc(II) beta-diketonates of N,N-donor ligands, viz. Cu(dppz)(cur)](NO3) (1), Cu(acdppz)(cur)](NO3) (2), Cu(acdppz) (acac)](NO3) (3), Zn(dppz)(cur)](NO3) (4) and Zn(acdppz)(cur)] (NO3) (5), where dppz is dipyrido3,2-a:2',3'-c]phenazine, acdppz is 11-(9-acridinyl)dipyrido3,2-a:2',3'-c]phenazine, cur and acac are mono-deprotonated curcumin (Hcur) and acetyl acetone (Hacac), were synthesized, characterized and their photocytotoxicity studied. An analogue of complex 3, viz. Cu(acdppz) (acac)(H2O)]Cl 1/2 (NO3) 1= 2 (3a), structurally characterized by X-ray crystallography, has a cationic complex in square-pyramidal geometry with CuN2O3 core with an axial aqua ligand. Complexes 1, 2, 4 and 5 displayed emission at similar to 520 nm (lambda(exc): 430 nm) in dimethyl sulfoxide (DMSO) giving a fluorescence quantum yield value within 0.01-0.06. The complexes, in contrast to free curcumin, were fairly stable in cellular media up to 36 h, with no apparent degradation of the bound curcumin. The complexes were photocytotoxic (IC50: 0.3 4.5 mu M) in human cervical cancer (HeLa), breast cancer (MCF-7) and liver cancer (HepG2) cells. The apoptotic cell death is due to reactive oxygen species formation. Complexes 2 and 5 showed significant uptake in HeLa cells, localizing predominantly in the cytoplasm. Mechanistic data from the pUC19 DNA photocleavage study suggest involvement of acridine and curcumin in photo-generation of singlet oxygen and hydroxyl radicals as the ROS in light of 400-700 nm
On the uniformity of rainfall distribution over India
No full textUnderstanding response of temporal distribution, timing, frequency and amount of high and low intensity rainfall to warming is important in water resources management. In this paper, Relative Entropy is used to investigate the spatial variability and change in uniformity of rainfall distribution over India. Temporal trends in atmospheric temperature can alter the frequency and amount of high and low intensity rainfall events, which influence the uniformity of rainfall distribution. The study is divided into two time periods, 1951-1980 and 1981-2010 based on time trend in annual mean temperature. The sensitivity of rainfall uniformity and high and low intensity rainfall events to annual mean temperature and the degree of coherence between them are investigated. The uniformity of rainfall distribution shows a significant spatial variability. Significant changes are observed in both the amount and timing of rainfall across India. A significant association between rainfall uniformity and low intensity of rainfall is observed in the recent past over a larger aerial extent compared to the distant past. It is concluded that rise in temperature modifies both high and low intensity rainfall events, thus altering the uniformity in rainfall distribution. A regionally varied strength of coherence between rainfall uniformity and high and low intensity rainfall is observed which may be due to regionally dependent soil moisture-precipitation feedbacks
Mn(I)-based photoCORMs for trackable, visible light-induced CO release and photocytotoxicity to cancer cells
No full textFour new Mn(l)-carbonyl complexes of general formula, Mn(L)(CO)(3)] (1 4) where L = 2-(benzod] thiazol-2-yl)phenol (L-1), 2-(benzod]thiazol-2-yl)-4,6-di-tert-butylphenol (L-2), 2-(2-hydroxyphenyl)-3H-anthra1,2-d]imidazole-6,11-dione (L-3) and 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-3H-anthra1,2-d] imidazole-6,11-dione (L-4) rapidly release CO cooperatively on activation with visible light accompanied by a visual change in luminescence properties of the complexes allowing us to track photo-activated CO release in HeLa cells. CO-induced photocytotoxicity by the complexes was also studied in HeLa cells. Photo-activated CO release and mechanism was spectroscopically and theoretically probed. Overall, Mn(I)-carbonyls with theranostics properties are potentially emerged as the next-generation phototheranostics
Bulk locality and asymptotic causal diamonds
No full textIn AdS/CFT, the non-uniqueness of the reconstructed bulk from boundary subregions has motivated the notion of code subspaces. We present some closely related structures that arise in flat space. A useful organizing idea is that of an asymptotic causal diamond (ACD): a causal diamond attached to the conformal boundary of Minkowski space. The space of ACDs is defined by pairs of points, one each on the future and past null boundaries, Z(+/-). We observe that for flat space with an IR cut-off, this space (a) encodes a preferred class of boundary subregions, (b) is a plausible way to capture holographic data for local bulk reconstruction, (c) has a natural interpretation as the kinematic space for holography, (d) leads to a holographic entanglement entropy in flat space that matches previous definitions and satisfies strong sub-additivity, and, (e) has a bulk union/intersection structure isomorphic to the one that motivated the introduction of quantum error correction in AdS/CFT. By sliding the cut-off, we also note one substantive way in which flat space holography differs from that in AdS. Even though our discussion is centered around flat space (and AdS), we note that there are notions of ACDs in other spacetimes as well. They could provide a covariant way to abstractly characterize tensor sub-factors of Hilbert spaces of holographic theories
Unraveling the Nature of Weak Hydrogen Bonds and Intermolecular Interactions Involving Elements of Group 14-17 via Experimental Charge Density Analysis
No full textMapping of charge densities in molecular crystals has been contemplated ever since it was recognized that X-rays are scattered by the electron density in the crystal. The methodology both from the experimental and theoretical perspective was standardized and applied extensively only during the last few decades, as technological advances were a prerequisite in both data collection and computation. Multipole formalism developed for accurate X-ray diffraction data is routinely utilized in conjunction with the concept of atoms in molecules to obtain quantitative estimates of the topological properties in molecular crystals which allow the evaluation of both bonded and non-bonded contacts. Recently, with the advent of quantum crystallography, combining Hirshfeld atom refinement along with libraries of extremely localized molecular orbitals, HAR-ELMOs, has emerged as an alternate approach. Apart from the weak hydrogen bonds, other highly directional non-bonded contacts like halogen, pnicogen, chalcogen and carbon bonds have been subjected to charge density analysis to experimentally observe and quantify sigma-holes using experimental high-resolution X-ray diffraction data. The recognition of lack of directional preferences in hydrophobic interactions is demonstrated experimentally which might have far reaching consequences in the areas of materials and biology