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21.
James R. Podolske Max Loewenstein Prasad Varanasi 《Journal of Molecular Spectroscopy》1984,107(2):241-249
A diode laser spectrometer that was operated in sweep integration mode was used to measure individual line strengths for 17 R-branch transitions of the (ν4 + ν5)0 combination band of 12C2H2 at 7.4 μm. Analysis of these results gives a band strength Sv = 64.4 ± 2.0 cm?2 atm?1 at 296 K. Line-broadening parameters for several of these transitions were determined by using both N2 and He as broadening gases. 相似文献
22.
Lawrence P. Giver Prasad Varanasi Francisco P.J. Valero 《Journal of Quantitative Spectroscopy & Radiative Transfer》1984,31(3):203-213
Band intensities and profiles have been measured for the propane absorption bands from 680 to 1580cm-1 at 296 and 200 K. This work was stimulated by the discovery of several propane bands in the spectrum of Titan by the Voyager 1 spacecraft. The low temperature laboratory data show that the bands become narrower and the Q branches of the bands somewhat stronger than they are at room temperature. Random band model parameters were determined over the entire region from the 42 spectra obtained at room temperature. 相似文献
23.
The absolute intensities of all the J-multiplets between R(13) at 1375cm-1 and P(12) at 1225 cm-1, in the v4-fundamental of 12CH4, have been measured at 300°K. Our values are consistent with published band-intensity measurements and also with the theoretical line strength tabulation by Fox. Spectral transmittance computation using a Lorentz line shape with a hydrogen-broadened half-width of 0.075 cm-1 atm-1 at 300°K for all the lines in the band is in excellent agreement with our experimental data measured with a spectral resolution of 0.2 cm-1. Our best estimate for the absolute intensity of the band is 145±8 cm-2 atm-1 at STP. 相似文献
24.
P. Varanasi L.A. Pugh 《Journal of Quantitative Spectroscopy & Radiative Transfer》1973,13(11):1225-1228
Infrared absorption by ammonia has been measured between 2000 and 2200 cm-1 using samples of the gas diluted by hydrogen, helium and nitrogen. Data on absorption coeffiecients have been obtained employing path lengths up to ten meters and total pressures up to 8 atm. In the three cases of broadening studied, it is apparent that the measured absorption is neither due to the far wings of lines in the bands surrounding the region nor due to any dimer absorption. Thus, the observed absorption should be totally accountable by absorption due to local lines in the region. 相似文献
25.
Prasad Varanasi Sunil Sarangi 《Journal of Quantitative Spectroscopy & Radiative Transfer》1974,14(9):845-859
Collision-broadened line widths in CO-CO2 and CO-O2 collisions have been calculated by incorporating interactions due to octopoles and hexadecapoles and short range repulsive interactions into Anderson's theory. It is shown how these higher-order interactions can be manipulated to yield good agreement with experimental data. A critical evaluation of this totally empirical manipulation suggests that a thorough revision of the theory is required for all but simple dipole-dipole interactions. In the process of the evaluation, the values of the multipole moments are discussed. 相似文献
26.
Multiuser detection for asynchronous code division multiple access (CDMA) data transmission over the time-dispersive two-path Rician fading channel is considered. The multiuser maximum likelihood sequence detector (MLSD) is derived, and an equivalence of the fading channel to an asynchronous Gaussian intersymbol interference (AGISI) CDMA channel is established. However, the MLSD is found to be implementationally infeasible and this motivates the derivation of the optimum linear detector with near/far resistance as the performance criterion. The optimally near/far resistant linear time-invariant K-user detector is shown to consist of a cascade of a 2 K input/K output linear multiuser diversity combining filter followed by a K input/K output decorrelator that is designed for the equivalent AGISI/CDMA channel. This detector solves the near/far problem and also supports significantly higher bandwidth efficiencies for CDMA communication over the fading channel than does the conventional near/far limited single-user diversity combiner. The performance penalties incurred by multiuser detectors designed for the Gaussian channel when used over the Rician fading channel are also analytically characterized. It is shown that these penalties can be significant, making the case for the use of multiuser detectors optimized for this fading channel, particularly the optimum linear detector due to its relative implementational simplicity 相似文献
27.
van Eisden J. Yakimov M. Tokranov V. Varanasi M. Mohammed E.M. Young I.A. Oktyabrsky S.R. 《Photonics Technology Letters, IEEE》2008,20(1):42-44
We have proposed and demonstrated the principle of optical decoupling in a vertical-cavity surface-emitting laser (VCSEL)-electroabsorption modulator device by use of a duo-cavity device architecture. This technique promises ultrahigh-frequency modulation of the VCSEL output due to the elimination of the resonance influences on the intrinsic modulation transfer function. By adjusting spectral detuning between the resonances of the duo-cavity configuration, optical decoupling of output modulation by an electroabsorption modulator can be achieved. A flat ( 3 dB) response up to 20 GHz has been measured by proper detuning of the resonances. 相似文献
28.
Arun Kumar Varanasi Arghya Bhowmik Tanmay Sarkar Umesh V. Waghmare Mridula Dixit Bharadwaj 《Ionics》2014,20(3):315-321
With a goal to improve the performance of LiCoO2 as a cathode material in Li-ion batteries, we simulate substitution of various elements (X = Be, Mg, Al, Ga, Si and Ti) for Co using first-principles density functional theory and predict changes in its electrochemical potential. While the electrochemical potential of LiCoO2 is enhanced with substitution of Be, Mg, Al and Ga for Co, an opposite effect is predicted of Si and Ti substitution. We determine the electronic origin of these changes in electrochemical potential using (a) Bader method of topological analysis of charge density, (b) partial density of electronic states to estimate oxidation states of metal and oxygen, and charge re-distribution upon lithiation. We find that the distribution of electronic charge donated by Li is influenced by the nature of the X–O bond. A larger electron transfer to O (in XO6 octahedron) upon lithiation leads to stronger Li intercalation and thereby higher electrochemical voltage. Our findings provide a platform for a rational design of cathode materials in Li batteries with enhanced voltage. 相似文献
29.
Smith JD Meuler AJ Bralower HL Venkatesan R Subramanian S Cohen RE McKinley GH Varanasi KK 《Physical chemistry chemical physics : PCCP》2012,14(17):6013-6020
Clathrate hydrate formation and subsequent plugging of deep-sea oil and gas pipelines represent a significant bottleneck for deep-sea oil and gas operations. Current methods for hydrate mitigation are expensive and energy intensive, comprising chemical, thermal, or flow management techniques. In this paper, we present an alternate approach of using functionalized coatings to reduce hydrate adhesion to surfaces, ideally to a low enough level that hydrodynamic shear stresses can detach deposits and prevent plug formation. Systematic and quantitative studies of hydrate adhesion on smooth substrates with varying solid surface energies reveal a linear trend between hydrate adhesion strength and the practical work of adhesion (γ(total)[1 + cos?θ(rec)]) of a suitable probe liquid, that is, one with similar surface energy properties to those of the hydrate. A reduction in hydrate adhesion strength by more than a factor of four when compared to bare steel is achieved on surfaces characterized by low Lewis acid, Lewis base, and van der Waals contributions to surface free energy such that the practical work of adhesion is minimized. These fundamental studies provide a framework for the development of hydrate-phobic surfaces, and could lead to passive enhancement of flow assurance and prevention of blockages in deep-sea oil and gas operations. 相似文献
30.
Liyuan Zhang Warren Batchelor Swambabu Varanasi Takuya Tsuzuki Xungai Wang 《Cellulose (London, England)》2012,19(2):561-574
Four different cellulose nanofibers samples were prepared from northern bleached softwood kraft fibers. Fiber diameter distributions
were measured from SEM images. Fiber aspect ratios ranging from 84 to 146 were estimated from fiber suspension sedimentation
measurements. Three samples had heterogeneous distributions of fiber diameters, while one sample was more homogeneous. Sheet
forming experiments using filters with pores ranging from 150 to 5 μm showed that the samples with a heterogeneous distribution
of fiber dimensions could be easily formed into sheets at 0.2% initial solids concentration with all filter openings. On the
other hand, sheets could only be formed from the homogenous sample by using 0.5% or more initial solids content and a lower
applied vacuum and smaller filter openings. The forming data and estimated aspect ratios show reasonable agreement with the
predictions of the crowding number and percolation theories for the connectivity and rigidity thresholds for fiber suspensions. 相似文献