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91.
Abstract In this article, various issues involved in a ground-to-satellite optical communication link (i.e., acquisition time, uncertainty area, and channel noise) are discussed. Acquisition time of a free-space optical link is evaluated for coherent (sub-carrier BPSK and QPSK) and non-coherent (OOK and -PPM) modulation schemes over weak turbulent channel with transmit diversity. In the analysis, both uncorrelated and correlated beams are considered. It is seen that an increase in transmit diversity order helps to improve the acquisition time, irrespective of turbulence strength in the atmosphere. At high correlation, a marginal change in acquisition time is observed with the increase in diversity order. 相似文献
92.
J. Karátson 《Numerical Functional Analysis & Optimization》2013,34(5-6):590-611
The superlinear convergence of the preconditioned CGM is studied for nonsymmetric elliptic problems (convection-diffusion equations) with mixed boundary conditions. A mesh independent rate of superlinear convergence is given when symmetric part preconditioning is applied to the FEM discretizations of the BVP. This is the extension of a similar result of the author for Dirichlet problems. The discussion relies on suitably developed Hilbert space theory for linear operators. 相似文献
93.
S. Ravi Manoranjan Kar S. M. Borah P. S. R. Krishna 《Crystal Research and Technology》2008,43(12):1318-1322
Neutron powder diffraction patterns were recorded on CaMn1‐xCuxO3 (x = 0 and 0.20) compounds at different temperatures down to 11K. All the patterns were analyzed by employing Rietveld refinement technique and using the Fullprof program. The observed crystallographic peaks could be refined by using Pbnm space group and no structural transition has been observed down to 11K. An additional peak at 2θ = 16.7° has been observed with decrease in temperature below TN and its intensity was found to increase with decrease in temperature. It could be indexed to magnetic (101) plane. The magnetic ordering is found to be G‐type antiferromagnetic behaviour. The magnetic moment at 11K for the samples x = 0.0 and 0.20 are found to be 2.69 and 2.42μB. The doped Cu ions are found to be in Cu2+ state and take part antiferromagnetic interactions with Mn ions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
94.
T. Ghosh S. Bandyopadhyay K. K. Roy S. Kar A. K. Lahiri A. K. Maiti K. Goswami 《Crystal Research and Technology》2008,43(9):959-963
Thermally processed lead iodide (PbI2) thin films were prepared by the vacuum evaporation method in a constant ambient. Measured thickness of the film was verified analytically from the optical transmittance data in a wavelength range between 300 and 1600 nm. From the Tauc relation for the non‐direct inter band transition, the optical band gap of the film was found to be 2.58 eV for film thickness 300 nm. X‐ray diffraction analysis confirmed that PbI2 films are polycrystalline, having hexagonal structure. The low fluctuation in Urbach energy indicates that the grain size is quite small. The present findings are in agreement with the other results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
95.
Reactions between superdislocations involved in deformation in the basal, prismatic, and type-I and II pyramidal planes in single-crystal Ti3Al are considered. The types of dislocation interactions are established that result in the formation dislocation barriers (microcrack nuclei). The force and energy conditions for microcracks to arise are found. The interaction between a and 2c + a superdislocations results in microcracks with the plane of opening lying in basal and pyramidal planes; the interaction of 2c + a superdislocations in different pyramidal planes results in the formation of microcracks in prismatic and pyramidal planes; and the interaction of a superdislocations in basal and/or pyramidal planes does not cause the formation of dislocation barriers. The types of microcracks are classified in terms of the orientation of deformation axes of single crystals, and the regions of the stereographic triangle are determined characterized by a preferential type of crack opening. 相似文献
96.
S. Kar Y. K. Ho 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(2):157-165
We have investigated the bound states and resonance states of
plasma-embedded tdμ and ddμ molecular ions using accurate
correlated basis functions. The plasma effect has been taken care of by
considering the Debye shielding approach of plasma modeling which admits a
variety of plasma conditions. The density of resonance states are calculated
using the stabilization method. The ground and excited states energies, and
the S-wave resonance energies of tdμ and ddμ molecular ions
immersed in plasmas are reported for various shielding parameters, along
with the 1S and 2S threshold energies of the tμ and dμ atoms. 相似文献
97.
Melike Büşra Bayramoğlu Karşı Ercan Berberler 《International journal of environmental analytical chemistry》2019,99(5):428-443
The main aim of this study was to present the effects of barbecue smoke on a small-scale environment, a national park under the influence of intense barbecue smoke, and to scientifically support the sustainable usage of the park. Twelve-weekly bulk deposition samples were collected directly at the barbecuing area, and the samples were analysed for 16 US EPA’s priority PAH compounds and major ions. The mean concentrations of the individual PAHs in the bulk deposition samples ranged from 11.8 ng L?1 (Ane) to 1085 ± 581 ng L?1 (IcdP). The most frequently observed PAH compounds in the bulk deposition samples were Np, Anp, Flr, Phe, An, Flu, BkF, BaP and IcdP. The mean total PAH deposition fluxes were determined as 3.6 ± 5.6 µg m?2 day?1. The chloride, potassium and the sulphate fluxes were determined as 145.2 ± 267.8 µg m?2 day?1, 182.9 ± 291.9 µg m?2 day?1, and 111.9 ± 65.9 µg m?2 day?1, respectively. Dominant ions in the bulk deposition samples were potassium ion, chloride and sulphate which addressed as the fingerprint of barbecue grilling. 相似文献
98.
Karásek V Cizmár T Brzobohatý O Zemánek P Garcés-Chávez V Dholakia K 《Physical review letters》2008,101(14):143601
We create extended longitudinally optically bound chains of microparticles with the use of counterpropagating "nondiffracting" light fields, the so-called Bessel beams. The beam homogeneity and extended propagation range allow the creation of 200 microm long chains of organized microparticles. We observe short-range multistability within a single chain and long-range multistability between several distinct chains. Our observations are supported by theoretical results of the coupled dipole method. 相似文献
99.
Kar S Borghesi M Bulanov SV Key MH Liseykina TV Macchi A Mackinnon AJ Patel PK Romagnani L Schiavi A Willi O 《Physical review letters》2008,100(22):225004
Experimental evidence of plasma jets ejected from the rear side of thin solid targets irradiated by ultraintense (>10(19) W cm(-2)) laser pulses is presented. The jets, detected by transverse interferometric measurements with high spatial and temporal resolutions, show collimated expansion lasting for several hundreds of picoseconds and have substantially steep density gradients at their periphery. The role played by radiation pressure of the laser in the jet formation process is highlighted analytically and by extensive two-dimensional particle-in-cell simulations. 相似文献
100.
A. A. Serafetinides M. Makropoulou E. Fabrikesi E. Spyratou C. Bacharis R. R. Thomson A. K. Kar 《Applied Physics A: Materials Science & Processing》2008,93(1):111-116
The use of intraocular lenses (IOLs) is the most promising method to restore vision after cataract surgery. Several new materials,
techniques, and patterns have been studied for forming and etching IOLs to improve their optical properties and reduce diffractive
aberrations. This study is aimed at investigating the use of ultrashort laser pulses to ablate the surface of PMMA and intraocular
lenses, and thus provide an alternative to conventional techniques. Ablation experiments were conducted using various polymer
substrates (PMMA samples, hydrophobic acrylic IOL, yellow azo dye doped IOL, and hydrophilic acrylic IOL consist of 25% H2O). The irradiation was performed using 100 fs pulses of 800 nm radiation from a regeneratively amplified Ti:sapphire laser
system. We investigated the ablation efficiency and the phenomenology of the ablated patterns by probing the ablation depth
using a profilometer. The surface modification was examined using a high resolution optical microscope (IOLs) or atomic force
microscope—AFM (PMMA samples). It was found that different polymers exhibited different ablation characteristics, a result
that we attribute to the differing optical properties of the materials. In particular, it was observed that the topography
of the ablation tracks created on the hydrophilic intraocular lenses was smoother in comparison to those created on the PMMA
and hydrophobic lens. The yellow doped hydrophobic intraocular lenses show higher ablation efficiency than undoped hydrophobic
acrylic lenses. 相似文献