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61.
The use of α-lithiated dimethyl hydrazones as an efficient enolate equivalent for the alkylation of ketones has been reported1,2,3. Due to the ragioselectivity exhibited by acetone dimethyl hydrazone (1) towards the formation of bis alkylated products, we have used the easily avaiLable (1) as a convenient synthon for achieving a short and simple synthesis of pheromones, 1,7-dioxaspiro (5,5) undecane4 (2) and Z-6-Heneicosen-11-one (2). The key step in both the syntheses is the regioselective bis alkylation of (1) using butyl lithium as a base, as shown in Scheme I. 相似文献
62.
We observe the electromagnetically induced transparency (EIT) spectra inside a nitrogen filled Rb vapour cell (Rb-N2) in a five-level Λ-type system of D2 transition of Rb atom. The high contrast EIT resonance in buffer gas filled Rb cell is obtained under our experimental conditions.
The effect of velocity changing coherence preserving collisions to obtain the contrast resonance in buffer gas cell has been
discussed. We measured the dependence of EIT width and height on pump intensity and find that the EIT width (FWHM) and peak
height have a linear dependence on pump intensity. Our experimental results show that the presence of N2 buffer gas reduces
the power broadening of the observed resonances. 相似文献
63.
We consider a generalised two brane Randall–Sundrum model with non-zero cosmological constant on the visible TeV brane. Massive Kaluza–Klein modes for various bulk fields namely graviton, gauge field and antisymmetric second rank Kalb–Ramond field in a such generalized Randall–Sundrum scenario are determined. The masses for the Kaluza–Klein excitations of different bulk fields are found to depend on the brane cosmological constant indicating interesting consequences in warped brane particle phenomenology. 相似文献
64.
A study of self-quenching of lyoluminescence yield from gamma-irradiated saccharides and amino acids
Tissue equivalent (TE) lyoluminescence (LL) dosimetry requires practical amount of phosphor for dissolution, typically 5-30 mg. Pronounced mass quenching effect has been observed even in the region of 5 mg, in the cases of LL of lactose-monohydrate, d-glucose, d-mannose, raffinose, sucrose and 1-glutamine. Ordinary concentration-quenching is non-existent but yield per mg falls rapidly with increasing mass of the phosphor. The curves have been fitted with a self-absorption type formula. A well-recognised dose effect is present in quenching curves. The role of free radicals at high radiation doses has been discussed in the contribution of dose effect in quenching. 相似文献
65.
V.K. Sharma S. Mitra P. Maheshwari D. Dutta P.K. Pujari R. Mukhopadhyay 《The European physical journal. Special topics》2010,189(1):273-277
Dynamics of ethylene glycol (EG) adsorbed in H-ZSM5 zeolite as studied using quasielastic neutron scattering (QENS) technique
is reported here. Analysis of QENS data revealed that observed dynamics correspond to isotropic rotational motion of EG. Rotational
diffusion coefficient of EG adsorbed in H-ZSM5 zeolite is found to be slower compared to bulk and comparable to that of benzene
adsorbed in the same host. Positron Annihilation Spectroscopy (PAS) technique is used to understand the nature of guest-host
interaction and the results of both QENS and PAS are found to be consistent with each other. 相似文献
66.
We describe a method for analyzing short-pulse laser propagation through tissues for the detection of tumors and inhomogeneities in tissues with the goal of developing a time-resolved optical tomography system. Traditional methods for analyzing photon transport in tissues usually involve the parabolic or diffusion approximation, which implies infinite speed of propagation of the optical signal. To overcome such limitations we calculate the transmitted and reflected intensity distributions, using the damped-wave hyperbolic P(1) and the discrete-ordinates methods, for a wide range of laser, tissue, and tumor parameters. The results are compared with the parabolic diffusion P(1) approximation. 相似文献
67.
Rahul Pandit Samriddhi Sankar Ray Dhrubaditya Mitra 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(3-4):463-469
We give an overview of the progress that has been made in recent years in understanding dynamic multiscaling in homogeneous, isotropic turbulence and related problems. We emphasise the similarity of this problem with the dynamic scaling of time-dependent correlation functions in the vicinity of a critical point in, e.g., a spin system. The universality of dynamic-multiscaling exponents in fluid turbulence is explored by detailed simulations of the GOY shell model for fluid turbulence. 相似文献
68.
Summary We study the effective electron mass at the Fermi level in Kane-type semiconductors on the basis of fourth order in effective
mass theory and taking into account the interactions of the conduction electrons, heavy holes, light holes and split-off holes,
respectively. The results obtained are then compared to those derived on the basis of the well-known three-band Kane model.
It is found, takingn-Hg1−x
Cd
x
Te as an example, that the effective electron mass at the Fermi level in accordance with fourth-order model depends on the
Fermi energy, magnetic quantum number and the electron spin respectively due to the influence of band nonparabolicity only.
The dependence of effective mass on electron spin is due to spin-orbit splitting parameter of the valence band in three-band
Kane model and the Fermi energy due to band nonparabolicity in two-band Kane model. The same mass exhibits an oscillatory
magnetic-field dependence for all the band models as expected since the origin of oscillations in the effective mass in nonparabolic
compounds is the same as that of the Shubnikov-de Hass oscillations. In addition, the corresponding results for parabolic
energy bands have been obtained from the generalized expressions under certain limiting conditions. 相似文献
69.
Recently, linear programming problems with special structures have assumed growing importance in mathematical programming.
It is well known that exploiting network structures within linear programs can lead to considerable improvement of the computational
solution of large-scale linear programming problems. A linear program is said to contain an embedded network structure provided
that some subset of its constraints can be interpreted as specifying conservation of flow. If a column of the constraint matrix
has at most two non-zeros, then it leads to embedded generalized network structure and if these non-zeros are unit elements
and of opposite signs, then it leads to embedded pure network structure.
In this paper, we are concerned with algorithms for detecting embedded pure network structures within linear programs. The
network extraction methods are presented in two groups. The first group covers deletion and addition based algorithms and
the second group covers GUB based algorithms. We have extended the GUB based algorithm appearing in the second group by introducing
Markowitz merit count approach for exploiting matrix non zeros. A set of well known test problems has been used to carry out
computational experiments which show that our extensions to the GUB based algorithms give better results than the algorithms
reported earlier. 相似文献
70.
Amarendra Patra Apurba K. Mukhopadhyay Alok K. Mitra Aditi K. Acharyya 《Magnetic resonance in chemistry : MRC》1981,15(1):99-101
Some carbon-13 NMR signal assignments of diazepam, flurazepam, clonazepam and chlordiazepoxide have been revised and the assignments of nitrazepam are reported. The assignments of the various resonances were made by considering the changes in chemical shifts produced by the change of substituents and also by comparison with the chemical shifts of model compounds. 相似文献