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101.
Mrinmay Pal Somnath Bandyopadhyay Palas Biswas Rimlee Debroy M. C. Paul Ranjan Sen Kamal Dasgupta S. K. Bhadra 《Optical and Quantum Electronics》2007,39(14):1231-1243
In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532–1,558 nm) in a single
stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of
the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed
gain flattening filter (GFF) is used in order to get the flat gain with gain variation ±0.5 dB for −20 dBm/ch input signal
power (total input signal power is −8.0 dBm) at a fixed average inversion level which is maintained by proper selection of
optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating
of length 20 mm. Gain variations are studied by changing the total input signal levels from −8.0 dBm to −20.0 dBm and maintained
within 20.0 ± 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed ±
0.5 dB gain-variation which is an important parameter in optical network system. 相似文献
102.
Ideal Bragg reflection waveguides (BRWs) are assumed to have an infinitely extended periodic cladding whereas in practice, the cladding of BRWs is of a finite extent. Bloch theorem is widely used to analyze the propagation characteristics of the BRWs. Since Bloch theorem is ideally valid only for an infinitely extended periodic medium, its application to study such BRWs is an approximation. We present a matrix method for a more accurate analysis of finite-clad BRWs and estimate the extent of errors involved in the values of the propagation constant obtained by the Bloch wave formalism. The proposed method can be used to obtain the mode effective indices as well as the radiation loss of a finite-clad BRW without resorting to solving any complex transcendental equation. In addition, since the method does not inherently assume a periodic cladding, it can also be used to analyze symmetric multi-channel BRWs, chirped structures and directional couplers. 相似文献
103.
An Ising model is studied here with isotropic nearest and next nearest neighbour competing interaction along the three axes of a simple cubic system. The phase diagram for this model is determined by Monte-Carlo simulation through a study of the correlation functions. 相似文献
104.
P.R.S. Gomes I. Padron E. Crema O.A. Capurro J.O. Fernández Niello G.V. Marti A. Arazi M. Trotta J. Lubian M.E. Ortega A.J. Pacheco M.D. Rodríguez J.E. Testoni R.M. Anjos L.C. Chamon M. Dasgupta D.J. Hinde K. Hagino 《Physics letters. [Part B]》2006
Complete and incomplete fusion cross sections for the 9Be + 144Sm reaction have been measured at near-barrier energies, using the delayed X-ray detection technique. At above-barrier energies these show a suppression of complete fusion for this weakly bound projectile on an intermediate mass target. The suppression factor, attributed to 9Be break-up, was deduced from a comparison of complete fusion yields with coupled-channels calculations, and appears consistent with measured incomplete fusion product yields. At ∼10%, it is considerably smaller than the value of ∼30% previously found for a 208Pb target. Simultaneous measurements of elastic and inelastic scattering permit a clearer picture of the reaction mechanisms. 相似文献
105.
K. Dasgupta P. Barat A. Sarkar P. Mukherjee D. Sathiyamoorthy 《Applied Physics A: Materials Science & Processing》2007,87(4):721-726
The use of graphite as a moderator in a low temperature thermal nuclear reactor is restricted due to accumulation of energy
caused by displacement of atoms by neutrons and high energetic particles. Thermal transients may lead to a release of stored
energy that may raise the temperature of the fuel clad above the design limit. Disordered carbon is thought to be an alternative
choice for this purpose. Two types of disordered carbon composites, namely, CB (made up of 15 wt. % carbon black dispersed
in carbonized phenolic resin) and PAN (made up of 20 vol. % chopped polyacrylonitrile carbon fibre dispersed in carbonized
phenolic resin matrix) have been irradiated with 145 MeV Ne6+ ions at three fluence levels of 1.0×1013, 5.0×1013 and 1.5×1014 Ne6+/cm2, respectively. The XRD patterns revealed that both the samples remained disordered even after irradiation. The maximum release
of stored energy for CB was 212 J/g and that of PAN was 906 J/g. For CB, the release of stored energy was a first order reaction
with activation energy of 2.79 eV and a frequency factor of 3.72×1028 per second. 13% of the defects got annealed by heating up to 700 °C. PAN showed a third-order release rate with activation
energy of 1.69 eV and a frequency factor of 1.77×1014 per second. 56% of the total defects got annealed by heating it up to 700 °C. CB seems to be the better choice than PAN as
it showed less energy release with a slower rate.
PACS 61.80.Jh; 61.80.-x; 61.43Er; 61.43.-j; 68.43.Vx 相似文献
106.
Mary Kurian Arnab Dasgupta Frederick L. Beyer Mary E. Galvin 《Journal of Polymer Science.Polymer Physics》2004,42(22):4075-4083
The morphological behavior of a series of polymer‐layered silicate nanocomposites (PLSNs) has been investigated. The goal was to probe the effect of “textured” silicate surfaces on PLSN morphology. The nanocomposites were fabricated by mixing montmorillonite clay that was carefully modified with tailor‐made polystyrene (PS) surfactants into a PS homopolymer matrix, where the chemical similarity of the matrix polymer and surfactants assures complete miscibility of surfactant and homopolymer. To examine the effect of silicate surface “texture,” clay was modified with combinations of long and short surfactants. The samples were then direct melt annealed to allow the equilibrium morphology to develop, and characterized by small‐angle X‐ray scattering. Based on the implications of the Balazs model and other work on the wetting behavior of polymer melts with longer surfactants and textured surfaces we expected that the intercalation of the homopolymer matrix material into the modified clay would be promoted. Extensive characterization of both the modified clays as well as the resultant nanocomposites clearly show that the modified clays exhibit a high degree of order, but also that only phase‐separated morphologies are formed in the corresponding nanocomposites. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4075–4083, 2004 相似文献
107.
It is shown that starting from a Fourier transform relation one can derive, in a surprisingly simple manner, all the well-known
results of lattice summation, that have been obtained so far by a complicated use of the Ewald theta transformation. We show
that the Ewald transformation follows directly from the Fourier transform relation. 相似文献
108.
109.
It is shown that for pulsed optical parametric oscillators there is an optimum pumppulse duration at which the threshold fluence is a minimum. The dependence of the threshold fluence on pump laser pulse duration is found to be substantial for lossy narrowband optical parametric oscillators. The pulse energy requirement for the pump laser may be substantially lowered by operating it at a pulse duration close to the optimum. 相似文献
110.
P. Sen S. Chakraborty Subinay Dasgupta B. K. Chakrabarti 《Zeitschrift für Physik B Condensed Matter》1992,88(3):333-338
We have estimated numerically the phase diagram of a one dimensional spin 1/2 quantum Ising model with competing nearest and next nearest neighbour interactions in presence of a transverse field. The method essentially is to diagonalise exactly the Hamiltonian for finite (10 spins) open chains and calculate the spin-spin correlations from the ground state eigenvector. The results obtained confirm the transition between ferromagnetic and paramagnetic phases for <0.5 and between antiphase and paramagnetic phase for >0.5. ( is the ratio of next nearest and nearest neighbour interactions.) The results perhaps indicate furthermore that (i) there is a disorder line passing through =0.5; (ii) the zero point quantum fluctuations destroy the order near =0.5 as the transverse field is switched on; and (iii) there is probably also a floating phase with slowly decayling correlation near the order-disorder phase boundary for >0.5. 相似文献