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699 result(s) for "Valluri, S"
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Band structure and transport studies of half Heusler compound DyPdBi: An efficient thermoelectric material
The discovery of Heusler alloys has revolutionized the research field of intermetallics due to the ease with which one can derive potential candidates for multifunctional applications. During recent years, many half Heusler alloys have been investigated for their thermoelectric properties. The f-electron-based rare-earth ternary half Heusler compound DyPdBi has its f energy levels located close to the Fermi energy level. Other research efforts have emphasized that such materials have good thermoelectric capabilities. We have explored using first principles the electronic band structure of DyPdBi by use of different exchange correlation potentials in the density functional theoretical framework. Transport coefficients that arise in the study of thermoelectric properties of DyPdBi have been calculated and have illustrated its potential as an efficient thermoelectric material. Both the theoretically estimated Seebeck coefficient and the power factor agree well with the available experimental results. Our calculations illustrate that it is essential to include spin-orbit coupling in these models of f-electron half Heusler materials.
Analytic Models of Brown Dwarfs and the Substellar Mass Limit
We present the analytic theory of brown dwarf evolution and the lower mass limit of the hydrogen burning main-sequence stars and introduce some modifications to the existing models. We give an exact expression for the pressure of an ideal nonrelativistic Fermi gas at a finite temperature, therefore allowing for nonzero values of the degeneracy parameter. We review the derivation of surface luminosity using an entropy matching condition and the first-order phase transition between the molecular hydrogen in the outer envelope and the partially ionized hydrogen in the inner region. We also discuss the results of modern simulations of the plasma phase transition, which illustrate the uncertainties in determining its critical temperature. Based on the existing models and with some simple modification, we find the maximum mass for a brown dwarf to be in the range 0.064 M ⊙ – 0.087 M ⊙ . An analytic formula for the luminosity evolution allows us to estimate the time period of the nonsteady state (i.e., non-main-sequence) nuclear burning for substellar objects. We also calculate the evolution of very low mass stars. We estimate that ≃11% of stars take longer than 1 0 7 yr to reach the main sequence, and ≃5% of stars take longer than 1 0 8 yr.
Efficient Parallel Processing of Second-Generation TDI Data for Galactic Binaries in Space-Based Gravitational Wave Missions
Space-based gravitational wave missions such as LISA, Taiji, and Tianqin rely on the time-delay interferometry (TDI) technique to observe low-frequency signals such as Galactic binaries (GBs), massive black-hole binaries, and extreme-mass-ratio inspirals. Among these sources, resolving the large population of GBs poses a central challenge for data analysis. In this work, we present GBSIEVER-C, a pipeline implemented in C and parallelized using OpenMP (Open Multi-Processing), along with a range of additional algorithmic optimizations, including a fast implementation of second-generation TDI response modeling. It builds upon the previous MATLAB-based pipeline that demonstrated competitive performance on LISA Data Challenge (LDC) data. To the best of our knowledge, GBSIEVER-C is the first pipeline to address the GB resolution problem using second-generation TDI data. We apply it to the GB dataset in Taiji Data Challenge (TDC) that contains 30 million GBs. Compared with our previous results on LDC data, it achieves improved source resolution, residual suppression, and parameter-estimation accuracy. These gains are consistent with the enhanced sensitivity expected from Taiji’s longer arm length. Although validated on Taiji data, the pipeline is fully compatible with LISA and similar mission configurations, and supports both single-detector and multi-detector network analyses.
An analytic study of the Wiedemann-Franz law and the thermoelectric figure of merit
Advances in optimizing thermoelectric material efficiency have seen parallel activities in theoretical and computational studies. In the current work, we calculate the exact Fermi-Dirac integrals to enable the generalization of the Wiedemann-Franz law (WF) in order to enhance the dimensionless thermoelectric figure of merit ZT = 2 κ . This is done by optimizing the Seebeck coefficient , the electrical conductivity , and the thermal conductivity κ in terms of the Lambert W, and the generalized Lambert W functions (offset log). In the calculation of the thermal conductivity κ, we include both electronic and phononic contributions. The solutions provide insight into the relevant parameter space including the physical significance of complex solutions and their dependance on the scattering parameter r and the reduced chemical potential *.
Fractional conductivity in 2D and 3D crystals
. In this work, we show that the phenomenon of fractional quantum Hall effect can be obtained for 2D and 3D crystal structures, using the noncommutative nature of spacetime and the Lambert W function. This fractional conductivity has been shown to be a consequence of the noncommutative geometry underlying the structure of graphene. Also, it has been shown, for graphene, that in the 3D case the conductivity is extremely small and depends on the self-energy that arises due to random fluctuations or zitterbewegung.
Differences in survival for patients with metastatic colorectal cancer by lines of treatment received and stage at original diagnosis
Summary Objective Few published studies have examined survival rates for patients with metastatic colorectal cancer (mCRC) by number of lines of treatment received or stage at diagnosis. This study aims to evaluate survival and numbers of lines of treatment in USA mCRC managed care patients. Methods To evaluate the impact of chemotherapy/biological on survival of patients with mCRC, adults with a diagnosis of CRC between 1 January 2005 and 31 May 2010 were identified from the Oncology Management registry. Registry data included stage and diagnosis date. Patients with stage IV CRC at original diagnosis or development of metastasis were included. Linked healthcare claims from a large USA database were used to identify lines of treatment after metastasis and patient characteristics. The patient population was enrolled in a commercial health insurance programme, with 10% of patients > 65 years of age. Patients were categorised by lines of treatment received (0, 1, 2, 3+) and stage at original diagnosis (0–3, 4, unknown). Survival following metastasis was evaluated using Cox proportional hazards models controlling for lines of treatment, disease stage, and other patient characteristics. Results Study population included commercially insured adult patients, ≥ 18 years of age (n = 598, mean age 54, 56% male), 16% of which did not receive chemotherapy/biological therapy after becoming metastatic, and 33% received only 1 line of treatment. Average follow‐up was 653 days, and 19% of patients died during the study period. Mean unadjusted length of follow‐up was 516, 511, 627 and 930 days for patients who received 0, 1, 2 and 3+ lines of treatment, respectively. In the Cox proportional hazards model, geographical region was the only variable significantly associated with survival (p < 0.05). Conclusion Lines of treatment received and stage at original diagnosis were not statistically significantly associated with survival after metastasis development.
Lambert W function methods in double square well and waveguide problems
Using methods related to the Lambert W function, we present solutions of two apparently different problems: (1) The one-dimensional double square well potential in quantum mechanics and (2) The transverse electric and magnetic modes for a step-index electromagnetic waveguide. The solution techniques provide insight into the bound energy states for the single and double square well problems and the allowed modes of propagation in a waveguide with varying refractive indices. The solutions can be viewed in either of two related complex plane representations. Comparison of the solution geometries suggests that interesting applications may be possible in nanostructures and devices which are designed to be sensitive to small changes in their environment.
Some applications of the Lambert W  function to physics
Two standard physics problems are solved in terms of the Lambert W function, to show the applicability of this recently defined function to physics. Other applications of the function are cited, but not described. The problems solved concern Wien's displacement law and the fringing fields of a capacitor, the latter problem being representative of some problems solved using conformal transformations. The physical content of the solutions remains unchanged, but they gain a new elegance and convenience.
Levels of bimatoprost acid in the aqueous humour after bimatoprost treatment of patients with cataract
Aim: To determine the aqueous humour concentration of the acid hydrolysis products of bimatoprost and latanoprost after a single topical dose of bimatoprost 0.03% or latanoprost 0.005% in humans. Methods: Randomised, controlled, double-masked, prospective study. 48 eyes of 48 patients scheduled for routine cataract surgery were randomised in an 8:2:2 ratio to treatment with a single 30 μl drop of bimatoprost 0.03%, latanoprost 0.005% or placebo at 1, 3, 6 or 12 h before the scheduled cataract surgery. Aqueous humour samples were withdrawn at the beginning of the surgical procedure and analysed using high-performance liquid chromatography–tandem mass spectrometry. Results: Bimatoprost acid (17-phenyl trinor prostaglandin F2α) was detected in aqueous samples at a mean concentration of 5.0 nM at hour 1, 6.7 nM at hour 3 and 1.9 nM at hour 6 after bimatoprost treatment. After latanoprost treatment, the mean concentration of latanoprost acid (13,14-dihydro-17-phenyl trinor prostaglandin F2α) in aqueous samples was 29.1 nM at hour 1, 41.3 nM at hour 3 and 2.5 nM at hour 6. Acid metabolites were below the limit of quantitation in all samples taken 12 h after dosing and in all samples from placebo-treated patients. None of the samples from latanoprost-treated patients contained quantifiable levels of non-metabolised latanoprost. Non-metabolised bimatoprost was detected in aqueous samples at a mean concentration of 6.6 nM at hour 1 and 2.4 nM at hour 3 after bimatoprost treatment. Conclusions: Low levels of bimatoprost acid were detected in aqueous humour samples from patients with cataract treated with a single dose of bimatoprost. Latanoprost acid concentrations in samples from patients treated with latanoprost were at least sixfold higher. These results suggest that bimatoprost acid in the aqueous humour does not sufficiently account for the ocular hypotensive efficacy of bimatoprost.
Ocular penetration of levofloxacin, ofloxacin and ciprofloxacin in eyes with functioning filtering blebs: investigator masked, randomised clinical trial
Background/aims: To compare the penetration of levofloxacin, ofloxacin and ciprofloxacin in the aqueous humour of eyes with functioning filtering blebs.Methods: In this investigator-masked study, 48 patients with functioning filtering blebs requiring cataract surgery were randomised into six groups of eight patients. Groups 1, 2 and 3 received topical ofloxacin 0.3% (Ocuflox®), ciprofloxacin 0.3% (Ciloxan®) and levofloxacin (Quixin®) respectively; Groups 4, 5 and 6 received the same treatment with the corresponding oral dose of ofloxacin 400 mg (Floxin), ciprofloxacin 400 mg (Cipro) and levofloxacin 250 mg (Levaquin). Aqueous antibiotic levels were determined by mass spectrometry of aqueous samples from each patient.Results: The mean aqueous level for topical levofloxacin was significantly higher than those achieved by topical ofloxacin or ciprofloxacin (p value = 0.02 and 0.01, respectively). The combination of topical and oral levofloxacin was significantly higher than topical levofloxacin alone (p = 0.05) and the ciprofloxacin combination (p = 0.003) but not significantly higher than the ofloxacin combination therapy.Conclusions: Topical levofloxacin penetrates better than ofloxacin or ciprofloxacin into the aqueous of eyes with functioning filtering blebs. The combination of topical and oral levofloxacin may be preferable in the treatment of bleb-associated infections (NCT 00392275; Clinical trials.gov).