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Homogeneous Hermitian holomorphic vector bundles and the Cowen-Douglas class over bounded symmetric domains
No full textIt is known that all the vector bundles of the title can be obtained by holomorphic induction from representations of a certain parabolic Lie algebra on finite dimensional inner product spaces. The representations, and the induced bundles, have composition series with irreducible factors. Our first main result is the construction of an explicit differential operator intertwining the bundle with the direct sum of its factors. Next, we study Hilbert spaces of sections of these bundles. We use this to get, in particular, a full description and a similarity theorem for homogeneous n-tuples of operators in the Cowen-Douglas class of the Euclidean unit ball in C-n
Photodetection Properties of Nonpolar a-Plane GaN Grown by Three Approaches Using Plasma-Assisted Molecular Beam Epitaxy
No full textPresent work focuses on improving the quality of nonpolar a-plane GaN thin films by introducing unconventional new efficient growth conditions without compromising their UV photodetection properties. These epitaxial thin films are grown on r-plane sapphire using three different growth approaches by plasma-assisted molecular beam epitaxy (PAMBE). In situ reflection high-energy electron diffraction (RHEED) analysis is performed during and after the growth to monitor the growth mode, and it is found that the films assumed desired 2D mode during the growth. The crystalline quality and the phase purity of the films are assessed with the help of high-resolution X-ray diffraction and Raman spectroscopy. All the films are found to contain compressive stress, which indicate that all the films are strained and epitaxial. The temporal response is carried out in all the three batches, which is very stable. Sensitivity, responsivity, transit time, and gain values are estimated. Highest responsivity and the corresponding gain are found to be around 25 AW(-1), 86.47 at 1 V bias, respectively. These are the highest reported values so far for a-plane GaN at such low voltages
Molecular Hydration of Carbonic Acid: Ab Initio Quantum Chemical and Density Functional Theory Investigation
No full textMolecular hydration of carbonic acid (H2CO3) is investigated in terms of bonding patterns in H2CO3 center dot center dot center dot(H2O)(n) n = 1-4] hydrogen-bonded clusters within ab initio quantum chemical and density functional theory (DFT) frameworks. Successive addition of water molecules to H2CO3 center dot center dot center dot H2O entails elongation of O-H (hydroxyl) bond as well as contraction of specific intermolecular hydrogen bonds signifying hydration of carbonic acid; these structural features get markedly enhanced under the continuum solvation framework. A comparison between the structurally similar clusters H2CO3 center dot center dot center dot(H2O)(n) and HCOOH center dot center dot center dot(H2O)(n) n = 1-3] brings out the structural stability of the former. The present investigation in conjunction with the binding energy behavior of approaching water molecule(s) should serve as a precursor for pathways exploring aqueous dissociation of H2CO3 for larger clusters, as well as development of force-field potentials for acid dissociation process
Doped biphasic calcium phosphate: synthesis and structure
No full textHydroxyapatite, tricalcium phosphate, and a mixture of these, i.e biphasic calcium phosphate (BCP), are widely employed as ceramic materials in hard tissue engineering, despite their poor mechanical and functional properties. The method of ionic substitution inside their lattice structures has been examined extensively by researchers in their long efforts to develop materials, that closely resemble natural hard tissues. The presence of dopants has a deep impact on the phase assemblage, structural, and functional behaviors of BCP. In this context, the goal of the current article is to cover different aspects of ongoing research on doped biphasic calcium phosphate. Apart from providing brief descriptions of different synthesis routes for producing ion-modified BCPs, the limitations of each technique are also discussed. In addition, particular emphasis has been given to describing the key experimental results, which elucidate the structural changes occurring due to doping. In particular, the preferable substitution sites of different dopant ions and the resulting crystallographic changes are depicted quite elaborately. Finally, the effects of substitution on biological and mechanical properties of BCP are briefly mentioned. In summary, the present review focuses on the ionic substitutions in BCP systems and their collective effects on material behaviors
Acute vs. Chronic vs. Cyclic Hypoxia: Their Differential Dynamics, Molecular Mechanisms, and Effects on Tumor Progression
No full textHypoxia has been shown to increase the aggressiveness and severity of tumor progression. Along with chronic and acute hypoxic regions, solid tumors contain regions of cycling hypoxia (also called intermittent hypoxia or IH). Cyclic hypoxia is mimicked in vitro and in vivo by periodic exposure to cycles of hypoxia and reoxygenation (H-R cycles). Compared to chronic hypoxia, cyclic hypoxia has been shown to augment various hallmarks of cancer to a greater extent: angiogenesis, immune evasion, metastasis, survival etc. Cycling hypoxia has also been shown to be the major contributing factor in increasing the risk of cancer in obstructive sleep apnea (OSA) patients. Here, we first compare and contrast the effects of acute, chronic and intermittent hypoxia in terms of molecular pathways activated and the cellular processes affected. We highlight the underlying complexity of these differential effects and emphasize the need to investigate various combinations of factors impacting cellular adaptation to hypoxia: total duration of hypoxia, concentration of oxygen (O-2), and the presence of and frequency of H-R cycles. Finally, we summarize the effects of cycling hypoxia on various hallmarks of cancer highlighting their dependence on the abovementioned factors. We conclude with a call for an integrative and rigorous analysis of the effects of varying extents and durations of hypoxia on cells, including tools such as mechanism-based mathematical modelling and microfluidic setups
Crystallization properties of arsenic doped GST alloys
No full textWe present the enhanced properties observed in the phase change memory alloy Ge2Sb2Te5 (GST) when doped with arsenic. Although arsenic is known as a toxic element, our observations show that significant improvement can be obtained in GST systems on thermal stability, transition temperature between amorphous and crystalline phases and switching behaviors when doping with arsenic. Though both the GST and arsenic doped GST are amorphous in the as-deposited state, only GST alloy turns to crystalline NaCl-type structure after annealing at 150 degrees C for 1 h. Results from the resistance versus temperature study show a systematic increase in the transition temperature and resistivity in the amorphous and crystalline states when the arsenic percentage in the GST alloy increases. The crystallization temperature (T-c) of (GST)(0.)(85)AS(0)(.)(15) is higher than the T-c observed in GST. Optical band gap (E-opt) values of the as-deposited films show a clear increasing trend; 0.6 eV for GST to 0.76 eV for (GST)(0.)(85)AS(0)(.)(15). The decreases in E-opt for the samples annealed at higher temperatures shows significant optical contrast between the as-deposited and annealed samples. Though all (GST)(1-x)As-x alloys show memory switching behaviors, threshold switching voltages (V-T) of the studied alloys show an increasing trend with arsenic doping. For (GST)(0.)(85)AS(0)(.)(15), V-T is about 5.2V, which is higher than GST (4.0V). Higher transition temperature and higher threshold switching values show arsenic doping in GST can enhance the memory device properties by improving the thermal stability and data readability. Understanding the doping effect on the GST is important to understand its crystallization properties. Structure properties of amorphous GST, Ge2Sb2-0.3As0.3Te5 and (GST)(0.)As-85(0).(15) models were studied using first principles molecular dynamics simulations, compared their partial radial distribution functions, and q parameter order. Arsenic doping into GST features interesting structural and electronic effects revealed by the radial distribution functions, q order parameter and band gap value, in line with the experimental findings
Atomic structures of RNA nanotubes and their comparison with DNA nanotubes
No full textWe present a computational framework to model RNA based nanostructures and study their microscopic structures. We model hexagonal nanotubes made of 6 dsRNA (RNTs) connected by double crossover (DX) at different positions. Using several hundred nano-second (ns) long all-atom molecular dynamics simulations, we study the atomic structure, conformational change and elastic properties of RNTs in the presence of explicit water and ions. Based on several structural quantities such as root mean square deviation (RMSD) and root mean square fluctuation (RMSF), we find that the RNTs are almost as stable as DNA nanotubes (DNTs). Although the central portion of the RNTs maintain its cylindrical shape, both the terminal regions open up to give rise to a gating like behavior which can play a crucial role in drug delivery. From the bending angle distribution, we observe that the RNTs are more flexible than DNTs. The calculated persistence length of the RNTs is in the micron range which is an order of magnitude higher than that of a single dsRNA. The stretch modulus of the RNTs from the contour length distribution is in the range of 4-7 nN depending on the sequence. The calculated persistence length and stretch modulus are in the same range of values as in the case of DNTs. To understand the structural properties of RNTs at the individual base-pair level we have also calculated all the helicoidal parameters and analyzed the relative flexibility and rigidity of RNTs having a different sequence. These findings emphasized the fascinating properties of RNTs which will expedite further theoretical and experimental studies in this field
RGG-motif self-association regulates eIF4G-binding translation repressor protein Scd6
No full textRegulation of mRNA translation plays a key role in the control of gene expression. Scd6, a conserved RGG-motif containing protein represses translation by binding to translation initiation factor eIF4G1. Here we report that Scd6 binds itself in RGG-motif dependent manner and self-association regulates its repression activity. Scd6 self-interaction competes with eIF4G1 binding and methylation of Scd6 RGG-motif by Hmt1 negatively affects self-association. Results pertaining to Sbp1 indicate that self-association could be a general feature of RGG-motif containing translation repressor proteins. Taken together, our study reveals a mechanism of regulation of eIF4G-binding RGG-motif translation repressors
On the Diversity of Uncoded OTFS Modulation in Doubly-Dispersive Channels
No full textOrthogonal time-frequency space (OTFS) is a two-dimensional (2D) modulation technique designed in the delay-Doppler domain. A key premise behind OTFS is the transformation of a time-varying multipath channel into an almost non-fading 2D channel in the delay-Doppler domain such that all symbols in a transmission frame experience the same channel gain. It has been suggested in the recent literature that the OTFS can extract full diversity in the delay-Doppler domain, where full diversity refers to the number of multipath components separable in either the delay or Doppler dimension, but without formal analysis. In this paper, we present a formal analysis of the diversity achieved by the OTFS modulation along with supporting simulations. Specifically, we prove that the asymptotic diversity order of the OTFS (as SNR -> infinity) is one. However, in the finite SNR regime, the potential for a higher order diversity is witnessed before the diversity one regime takes over. Also, the diversity one regime is found to start at lower BER values for increased frame sizes. We also propose a phase rotation scheme for the OTFS using transcendental numbers and show that the OTFS, with this proposed scheme, extracts full diversity in the delay-Doppler domain
Joint modeling of lithosphere and mantle dynamics: Sensitivity to viscosities within the lithosphere, asthenosphere, transition zone, and D `' layers
No full textAlthough mantle rheology is one of the most important properties of the Earth, how a radial mantle viscosity structure affects lithosphere dynamics is still poorly known, particularly the role of the lithosphere, asthenosphere, transition zone, and D `' layer viscosities. Using constraints from the geoid, plate motions, and strain rates within plate boundary zones, we provide important new refinements to the radial viscosity profile within the key layers of the lithosphere, asthenosphere, transition zone, and D `' layer. We follow the approach of the joint modeling of lithosphere and mantle dynamics (Ghosh and Holt, 2012; Ghosh et al., 2013b, 2019; Wang et al., 2015) to show how the viscosities within these key layers influence lithosphere dynamics. We use the viscosity structure SH08 (Steinberger and Holme, 2008) as a starting model. The density variations within the mantle are derived from the tomography models which, based on prior modeling, had provided a best fit to the surface observables (Wang et al., 2015). Our results show that narrow viscosity ranges of moderately strong lithosphere (2.6-5.6 x 10(22) Pa-s) and moderately weak transition zone (5-9.3 x 10(20) Pa-s), as well as slightly large ranges of moderately weak asthenosphere (5-34 x 10(19) Pa-s) and D `' layer (4.8-18 x 10(20) Pa-s), are necessary to match all the surface observables. We also find that a very strong lithosphere (> 8.6 x 10(22) Pa-s) along with a weak asthenosphere (< 5.4 x 10(19) Pa-s) fits well with the surface observables. Our results show that the geoid is very sensitive to the viscosities of both the transition zone and D `' layer, while plate motions are slightly sensitive to them, but the orientations of stresses are insensitive to them