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排序方式: 共有257条查询结果,搜索用时 15 毫秒
21.
In this study, in situ control growth of bismuth nanoparticles (Bi0 NPs) was demonstrated in bismuth-based glass dielectrics under an electron beam (EB) irradiation at room temperature. The
effects of EB irradiation were investigated in situ using transmission electron microscopy (TEM), selected-area electron diffraction
and high-resolution transmission electron microscopy. The EB irradiation for 2–8 min enhanced the construction of bismuth
nanoparticles with a rhombohedral structure and diameter of 4–9 nm. The average particle size was found to increase with the
irradiation time. Bismuth metal has a melting point of 271 °C and this low melting temperature makes easy the progress of
energy induced structural changes during in situ TEM observations. This is a very useful technique in nano-patterning for
integrated optics and other applications. 相似文献
22.
P. K. Karmakar R. Bera G. Tarafdar A. Maitra A. K. Sen 《International Journal of Infrared and Millimeter Waves》1991,12(11):1333-1348
Rain, perhaps, is the worst offender for utilising Millimeterwaves in practice. This paper describes the rain rate distribution from which millimeterwave attenuation distribution have been attempted. Results reveal that in our location (Calcutta: lat 23°N long 88.5°E) the rain rate distribution fits well with normal distribution. The cumulative distribution of rain rate also prompted the present authors to find out rain attenuation cumulative distribution for both terrestrial and earth-space paths in millimeterwave band. 相似文献
23.
Like liquid alkali metalsd-shell liquid metals show scaling behaviour in structure and interaction potentials. A realistic interaction potential model,
properly parametrized can reasonably describe the universality in the isothermal compressibility and vacancy formation energy
of 3d-liquid metals in electron ion plasma model. 相似文献
24.
The average effective pair potential energy function between two neighbouring molecules has been computed from the centre structure factor data of water and this shows an unusual feature at short range due to strong hydrogen bonding. The effective potential is highly temperature dependent and at elevated temperature it turns out to be approximately like that for simple liquids. The effective potential can be represented satisfactorily by the square well model. 相似文献
25.
A. K. Sen R. Bera P. K. Karmakar 《International Journal of Infrared and Millimeter Waves》1997,18(11):2233-2257
The use of Ka Band (20/30 GHz) for future satellite communications has been addressed. The exploitation of Ka band with a
bandwidth of 2500 MHz seems to represent the largest significant achievement in satellite communications potential, so far.
The problems associated with the use of this frequency band such as attenuation and receiver noise temperature (floor) variation
with rain has been addressed. The receiver noise floor variation with rain has so far been ignored. Therefore, in view of
propagation and noise study over this Ka Band, both signal attenuation and receiver noise floor variations with rain rate
are estimated using dual frequency radiometers operating at 22.235 and 31.4 GHz over a tropical station, Calcutta, India. 相似文献
26.
S. N. Karmakar R. K. Moitra P. Chaudhuri 《Zeitschrift für Physik B Condensed Matter》1985,58(2):133-140
In this paper we present a new theory for including both short range order and long range order simultaneously in the well known cluster Bethe lattice method for binary alloys. We have used this theory for obtaining the Friedel criterion for the appearance of magnetic moments in disordered states using the single band Hubbard model. This is followed by a study of this criterion in a two-bands-d hybridised Hubbard model, which is considered as a simulation of real transition metals. A new technique for solving this problem in the Bethe lattice network is presented, which yields an analytic solution for the critical correlation strength in the presence of hybridisation and short range order. It is found that in all cases hybridisation tends to diminish the tendency for magnetisation, which is in accord with physical expectations. 相似文献
27.
Dattatray J. Late Soumen Karmakar Mahendra A. More Sudha V. Bhoraskar Dilip S. Joag 《Journal of nanoparticle research》2010,12(7):2393-2403
Lanthanum hexaboride (LaB6) nanocrystallites/nanowires have been successfully synthesized using gas phase condensation in arc plasma. Our results show
that the LaB6 nanowires have ~20 nm diameter and length of several micrometers. The as-synthesized LaB6 nanocrystallites and nanowires are crystalline in nature. Field emission studies were carried out on as synthesized LaB6 nano-powder deposited on W and Re tips and foils, and also on Si foil substrates under ultra high vacuum. The Fowler–Nordheim
plots obtained from the current–voltage characteristics are found to be linear in accordance with the quantum mechanical tunneling
phenomenon. High value of field enhancement factor (8177) is observed for LaB6 on Re substrate, indicating that the electron emission is from the nanometric features of the LaB6. Our results show that the arc plasma synthesized LaB6 nanocrystalline film exhibits good emission stability as emitter without severe deviations from the initial set value and
also a strong ability to withstand the ion bombardment, which is useful for low operation voltage vacuum micro/nano electronic
devices. 相似文献
28.
J. Chowdhury S. Sil S. N. Karmakar B. Bhattacharyya 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(3):435-444
We have presented the role of the Coulomb interaction (U) and the magnetic
field [(B)\vec]\vec{B} on the ground state properties of the quasi-one dimensional
graphite ribbon structures at half-filling. Mean field Hartree-Fock
Approximation is used to study the systems. To understand the boundary effects
in graphite structures, we have compared the results of these systems
with those of the square lattice ribbon structures. Studying the density of
states, the Drude weight and the charge gap, we have drawn the U – B phase
diagrams for the zigzag and the armchair graphite ribbons. 相似文献
29.
An efficient, cost-effective and environmentally benign synthesis of novel tetracyclic bis-isoxazolopyrroloquinoline derivatives has been developed via one-pot four-component reaction of 4-amino-3-methyl-5-styrylisoxazoles, dimedone, aryl glyoxal monohydrates and 5-amino-3-methylisoxazole by employing water as a reaction medium and acetic acid (AcOH) as a green promoter. The advantages of this protocol are environmentally friendly, metal-free, less reaction time, operational simplicity, high yields, broad substrate scope and easy purification. Most significant of all, this method is green. 相似文献
30.
Sutapa Sen Manas K. Saha Tarakranjan Gupta Aswini K. Karmakar Parimal Kundu Samiran Mitra Michael B. Hursthouse K. M. Abdul Malik 《Journal of chemical crystallography》1998,28(10):771-777
The compound [Cu(phen)(O2CCF3)2]n (phen = 1,10-phenanthroline) has been synthesized and its crystal structure determined. It crystallizes in monoclinic space group C2/c, with a = 19.229(7), b = 11.281(5), c = 7.621(2) Å, = 104.305(12)°, and Z = 4. The crystal structure is polymeric, being built from infinite zigzag chains of trifluoroacetate bridged copper(II), with the phenanthroline ligands being stacked between the chains. The variable-temperature (13–300 K) magnetic susceptibility and ESR data are reported and a weak ferromagnetic exchange interaction is observed with the exchange parameter estimated as J = 2.9 cm–1. 相似文献