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101.
102.
Govind P Agrawal 《Pramana》1984,22(3-4):293-301
The role of level degeneracy in resonant nonlinear phenomena is examined by considering theJ=1 →J=0 atomic transition. The atomic medium is modelled as a homogeneously broadened three-level system and a closed-form expression
for the medium susceptibility is obtained. It is used to discuss several nonlinear phenomena such as saturated absorption,
optical bistability, and phase conjugation. The two-photon-induced coupling of the ground-state Zeeman sublevels leads to
interesting polarization effects. 相似文献
103.
Recently, angle-resolved photoemission spectroscopy measurements on Bi2Sr2CaCu2O8+δ, which possesses two CuO2 layers in the same unit cell, have yielded very interesting results. For the overdoped samples, these results show a splitting
of electronic states near k=(π, 0) point of Brillioun zone. On the other hand, no splitting is observed in the underdoped samples. In view of this, the
detailed studies including the doping and temperature dependence of the spectral properties become desirable. In this paper,
we consider cuprates possessing two CuO2 layers per unit cell. Each layer in the system is described by the t-t
1-J model and the two layers are coupled via an intrabilayer hopping term (t
⊥) and an intrabilayer exchange coupling (J
⊥). A self-consistent perturbation approach is used to calculate the electronic spectral function for different values of hole
density, hole momentum and temperature. We find that the imaginary part of the self energy is strongly momentum dependent
which contradicts the suggestion that the Fermi surface of cuprates may be described by marginal Fermi liquid theory. We have
calculated the spectral function for various values of intrabilayer parameters t
⊥ and J
⊥. For larger values of intrabilayer interactions we observe the splitting in the quasi-particle peak at k=(π, 0) which is in agreement with the recent observations. The splitting is also found to be sensitive to the hole concentration
as well as the temperature of the system. We have also discussed the reasons why the splitting is absent in underdoped bilayer
cuprates at low temperature. 相似文献
104.
Elisa Biasin Daniel R. Nascimento Benjamin I. Poulter Baxter Abraham Kristjan Kunnus Angel T. Garcia-Esparza Stanislaw H. Nowak Thomas Kroll Robert W. Schoenlein Roberto Alonso-Mori Munira Khalil Niranjan Govind Dimosthenis Sokaras 《Chemical science》2021,12(10):3713
Ru-complexes are widely studied because of their use in biological applications and photoconversion technologies. We reveal novel insights into the chemical bonding of a series of Ru(ii)- and Ru(iii)-complexes by leveraging recent advances in high-energy-resolution tender X-ray spectroscopy and theoretical calculations. We perform Ru 2p4d resonant inelastic X-ray scattering (RIXS) to probe the valence excitations in dilute solvated Ru-complexes. Combining these experiments with a newly developed theoretical approach based on time-dependent density functional theory, we assign the spectral features and quantify the metal–ligand bonding interactions. The valence-to-core RIXS features uniquely identify the metal-centered and charge transfer states and allow extracting the ligand-field splitting for all the complexes. The combined experimental and theoretical approach described here is shown to reliably characterize the ground and excited valence states of Ru complexes, and serve as a basis for future investigations of ruthenium, or other 4d metals active sites, in biological and chemical applications.Combined experimental and theoretical Ru 2p4d resonant inelastic X-ray scattering study probes the chemical bonding and the valence excited states of solvated Ru complexes. 相似文献
105.
Prashad M Har D Chen L Kim HY Repic O Blacklock TJ 《The Journal of organic chemistry》2002,67(19):6612-6617
An efficient and large-scale enantioselective synthesis of PNP405 (1), a purine nucleoside phosphorylase inhibitor, is described. This synthesis of 1 involved eight steps starting from o-fluorophenylacetic acid with a 21.6% overall yield and >99.5% enantiopurity. The key stereogenic center with (R)-configuration was created using Evans' asymmetric alkylation methodology. This synthesis also features the racemization-free reductive removal of the chiral auxiliary in 5 using sodium borohydride, protection of the gamma-cyano alcohol 6 as the trityl ether by a new water-assisted tritylation with trityl chloride and triethylamine or with trityl alcohol and catalytic trifluoroacetic acid, and an efficient one-pot cyclo-guanidinylation of 10 using cyanamide as the guanidinylating agent. 相似文献
106.
We develop a mathematical model for the energy landscape of polyhedral supramolecular cages recently synthesized by self-assembly (Sun et al. in Science 328:1144–1147, 2010). Our model includes two essential features of the experiment: (1) geometry of the organic ligands and metallic ions; and (2) combinatorics. The molecular geometry is used to introduce an energy that favors square-planar vertices (modeling \(\mathrm {Pd}^{2+}\) ions) and bent edges with one of two preferred opening angles (modeling boomerang-shaped ligands of two types). The combinatorics of the model involve two-colorings of edges of polyhedra with four-valent vertices. The set of such two-colorings, quotiented by the octahedral symmetry group, has a natural graph structure and is called the combinatorial configuration space. The energy landscape of our model is the energy of each state in the combinatorial configuration space. The challenge in the computation of the energy landscape is a combinatorial explosion in the number of two-colorings of edges. We describe sampling methods based on the symmetries of the configurations and connectivity of the configuration graph. When the two preferred opening angles encompass the geometrically ideal angle, the energy landscape exhibits a very low-energy minimum for the most symmetric configuration at equal mixing of the two angles, even when the average opening angle does not match the ideal angle. 相似文献
107.
Dr. Govind Goroba Pawar Dr. Ajit Prabhakar Kale Pooja Sah Prof. Manmohan Kapur 《European journal of organic chemistry》2023,26(3):e202201277
The total synthesis of the 14-membered resorcylic acid lactone neocosmosin A is described. The key step in the synthesis is the palladium-catalyzed α-arylation of TES-enol ethers of enones. The employment of the α-arylation approach to this class of resorcylic acid lactones is a new approach, which has the scope of being generalized into a unified approach for the synthesis of this class of natural products. 相似文献
108.
109.
Smith DS Kostov Y Rao G Gryczynski I Malicka J Gryczynski Z Lakowicz JR 《Journal of fluorescence》2005,15(6):895-900
Detection limitations for fluorescence methods are normally determined by the phenomenon itself rather than the sensitivity
of the instrumentation. These limitations make it necessary to have high sensitivity, high cost equipment causing fluorescence
methods to remain lab-oriented. Alleviation of the limitations can be achieved through the phenomenon of surface plasmon-coupled
emission (SPCE), which displays enhanced, directional, polarized fluorescence. Here we present the excitation of SPCE from
Rhodamine B with a light-emitting diode (LED). Incorporating the gains in sensitivity due to SPCE with LED excitation, it
could be possible to design low-cost, high-sensitivity sensors that would allow measurements to be performed in the field. 相似文献
110.
Pulses as short as 460 fs and a tuning range as wide as 200 nm around 1 microm have been achieved from a photonic-crystal-fiber-based parametric oscillator. The ring cavity with only 65 cm of photonic crystal fiber is synchronously pumped with a tunable passively mode-locked Yb-doped fiber laser. Widely extended tunability is achieved by using the modulation instability gain in normal dispersion as the result of high-order dispersion in the photonic crystal fiber. 相似文献