排序方式: 共有21条查询结果,搜索用时 15 毫秒
1.
Saswata Ghosh 《Optics Communications》2010,283(9):1832-387
An open four-level system of having two pairs of closely spaced levels (N-type configuration) is driven by a single electromagnetic field and tuned resonant with the average frequency of four dipole allowed transitions. Under the Doppler free condition and by using a semiclassical formulation of atom-field interaction for four dipole allowed transitions, we derive the optical Bloch equations for the said four-level system coupled to the driving field. In order to obtain the field induced polarization and hence the absorptive lineshapes, we use the usual perturbation method for getting the approximate analytical solution to the coupled optical Bloch equations for the density matrix elements. Through the off-diagonal complex density matrix elements, we introduce the field dependent phase angles arising out of the quantum interference between the levels participating in dipole allowed transitions. The difference between the field dependent and field independent phases are pointed out. In particular, we investigate the effects of Rabi frequencies and the field dependent phases on the absorptive lineshape. The analytical expressions for the effective linewidths, effective detunings and the induced polarization clearly indicate the role of quantum interference. 相似文献
2.
Madhumita Mukherjee Tanya Das Saswata Bose Chapal Kumar Das Alexander P. Kharitonov Kaushik Banik Tham Nguyen Chung Gunter Mennig 《Macromolecular Symposia》2009,277(1):24-35
Kevlar fiber was fluorinated and oxy-fluorinated directly in presence of undiluted fluorine and fluorine gas mixture and processed with Polycarbonate and LCP at 320 °C under 20 rpm in a twin-screw extruder. The composites were then injection molded into dumbbell shaped specimens under different conditions like various mold temperatures, injection temperatures, injection speeds and mold filling rates. Various physico-chemical characterizations have been performed under definite processing parameter. Orientation of fibers under different injection parameters was evaluated using mold flow simulation technique. Most injection molded or extruded structures however, exhibit non-uniform fiber orientation across the final parts, with a diverging variety of different local fiber orientation states. Distinct skin and core regions were observed in the injection molded parts and it has also been found out that fiber orientation is different in skin and core region for both unmodified and modified derivative, which affects the flow behavior. Processing parameters significantly affect the fiber orientation pattern in the skin and core region for all blended materials. It is worth mentioning that the maximum fiber orientation occurred during the extrusion process at the wall but different extent of fiber orientation is observed during the injection molding depending on the shape of the dumbbell specimen. This fibrillation has been corroborated by the SEM study in both the skin and core region. 相似文献
3.
Noga Alon Robert Berke Kevin Buchin Maike Buchin Péter Csorba Saswata Shannigrahi Bettina Speckmann Philipp Zumstein 《Discrete and Computational Geometry》2009,42(3):421-442
We show that the vertices of any plane graph in which every face is incident to at least g vertices can be colored by ⌊(3g−5)/4⌋ colors so that every color appears in every face. This is nearly tight, as there are plane graphs where all faces are incident
to at least g vertices and that admit no vertex coloring of this type with more than ⌊(3g+1)/4⌋ colors. We further show that the problem of determining whether a plane graph admits a vertex coloring by k colors in which all colors appear in every face is in ℘ for k=2 and is
-complete for k=3,4. We refine this result for polychromatic 3-colorings restricted to 2-connected graphs which have face sizes from a prescribed
(possibly infinite) set of integers. Thereby we find an almost complete characterization of these sets of integers (face sizes)
for which the corresponding decision problem is in ℘, and for the others it is
-complete.
Research of N. Alon was supported in part by the Israel Science Foundation, by a USA–Israeli BSF grant, and by the Hermann
Minkowski Minerva Center for Geometry at Tel Aviv University.
Research of R. Berke was supported in part by JSPS Global COE program “Computationism as a Foundation for the Sciences.”
Research of K. Buchin and M. Buchin was supported by the Netherlands’ Organisation for Scientific Research (NWO) under BRICKS/FOCUS
project no. 642.065.503.
Research of P. Csorba was supported by DIAMANT, an NWO mathematics cluster.
Research of B. Speckmann was supported by the Netherlands’ Organisation for Scientific Research (NWO) under project no. 639.022.707. 相似文献
4.
Provi Palit Saswata Rabi Benu Kumar Dey Debashis Palit Monir Uddin Tapashi Ghosh Roy 《Journal of the Iranian Chemical Society》2018,15(9):1947-1959
Biologically important tetraaza-macrocyclic ligand 3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene dihydroperchlorate, Me8[14]diene·2HClO4 (L1·2HClO4) was synthesized by the condensation of 1,2-diaminopropane with acetone in presence of quantitative amount of HClO4 and three isomeric ligands designated as LA, LB and LC were separated by the reduction of L1·2HClO4 with NaBH4 and fractional crystallization from xylene. The nitrato, nitro, bromido, and iodido complexes of palladium with diene ligand L1 were prepared by the interaction of L1·2HClO4 with K2[Pd(NO3)4], K2[Pd(NO2)4], K2[PdBr4], and K2[PdI4] (prepared by the reactions with PdCl2 with KNO3, KNO2, KBr, and KI, respectively), respectively. The bromide and iodido complexes of LA were prepared by the axial substitution reactions with [PdLACl2]Cl2. By contrast, similar complexes of other isomeric ligands LB and LC were prepared by axial addition reactions of [PdL?][PdCl4] (L′?=?LB or LC) with KBr and KI, respectively. The complexes were characterized on the basis of elemental analysis: IR, 1H-NMR, UV–Vis spectroscopic analysis, and magnetic and molar conductivity data. The antifungal and antibacterial activities of these compounds have been studied against some phyto-pathogenic fungi and bacteria. 相似文献
5.
A phase-field model for modeling the diffusional processes in an elastically anisotropic polycrystalline binary solid solution is described. The elastic interactions due to coherency elastic strain are incorporated by solving the mechanical equilibrium equation using an iterative-perturbation scheme taking into account elastic modulus inhomogeneity stemming from different grain orientations. We studied the precipitate interactions among precipitates across a grain boundary and grain boundary segregation–precipitate interactions. It was shown that the local pressure field from one coherent precipitate influences the shape of precipitates in other grains. The local pressure distribution due to primary coherent precipitates near the grain boundary leads to inhomogeneous solute distribution along the grain boundary, resulting in non-uniform distribution of secondary nuclei at the grain boundary. 相似文献
6.
7.
Park BJ Chang HJ Kim do H Kim WT Chattopadhyay K Abinandanan TA Bhattacharyya S 《Physical review letters》2006,96(24):245503
Phase separating systems present a unique opportunity for designing composites with hierarchical microstructure at different length scales. We report here our success in synthesizing phase separating metallic glasses exhibiting the entire spectrum of microstructural possibilities expected from a phase separating system. In particular, we report novel core shell and hierarchical structures of spherical glassy droplets, resulting from critical wetting behavior and limited diffusion. We also report synthesis of a bulk phase separating glass in a metallic glass system. The combination of unique core shell and hierarchical structures in metallic glass systems opens a new avenue for the microstructure design of metallic glasses. 相似文献
8.
Saswata Ghosh 《Optics Communications》2006,264(1):219-224
By using a semiclassical approach, we obtain 16 coupled optical Bloch equations involving density matrix elements for a V-type four level system with three closely spaced upper levels irradiated by a single mode of the electromagnetic field. The off-diagonal elements of the density matrix ρij are in general complex and arise due to the interference between the probability amplitudes of the levels i and j. Through the complex off-diagonal density matrix elements, we introduce the phase angles between the levels participating in dipole allowed/forbidden transitions. Therefore, the phase angles may be regarded as the outcome of the quantum coherence. Under rotating wave approximation, we use a perturbative approach to solve these Bloch equations analytically. These solutions for density matrix elements are used to obtain a closed form analytical expression for the imaginary part of the polarization and hence the absorptive lineshape. The proper choice of the decay constants induces the necessary coherence responsible for inversionless laser. 相似文献
9.
Saswata Ghosh 《Optik》2014
The group index and its lineshape of a relatively weak double-resonance probe pulse (signal) propagates through an open doubly driven N-type five-level atomic system are analytically formulated. It is shown that the signal can be controlled by manipulating the driving contribution of the two coupling fields, so that both superluminal and subluminal propagation can take place simultaneously at two different (probe field induced transition) frequency regimes with reduced absorption/gain. Hence the proposed double-control scheme may be exploited to observe the double-switching effect (i.e. from superluminal to subluminal and vice versa) with negligible distortion. In our realization this double-controlling mechanism may be regarded as simultaneous tuning of two knobs, to regulate the group index of the signal at double-frequency regimes. 相似文献
10.
Rabi Saswata Islam Md. Nazrul Islam Md. Din Sutradhar Ranajit K. 《Chemistry of Natural Compounds》2022,58(3):485-490
Chemistry of Natural Compounds - Bioactive terpenoids 1 and 2 along with a known compound, β-sitosterol, have been isolated from the DCM extract of the fruits of Lagerstroemia speciosa.... 相似文献