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161.
Acyclic digraphs, such as the covering digraphs of ordered sets, are usually drawn upward, i.e., with the edges monotonically increasing in the vertical direction. A digraph is upward planar if it admits an upward planar drawing. In this survey paper, we overview the literature on the problem of upward planarity testing. We present several characterizations of upward planarity and describe upward planarity testing algorithms for special classes of digraphs, such as embedded digraphs and single-source digraphs. We also sketch the proof of NP-completeness of upward planarity testing.Research supported in part by the National Science Foundation under grant CCR-9423847. 相似文献
162.
K. G. Chakraborty 《Zeitschrift für Physik A Hadrons and Nuclei》1974,268(2):179-182
In this paper the effect of biquadratic exchange on Curie temperature has been discussed on the basis of double-time temperature-dependent Green-function formalism with the utilization of Callen decoupling scheme. Calculation has been done for a spin-1 bcc Heisenberg ferromagnet by the method of Flax and Raich and it has been observed that the variation of Curie temperature with the biquadratic exchange parameter α obeys a law prescribed by the previous authors. 相似文献
163.
D K Chakraborty 《Pramana》1988,30(5):371-374
The energy of an electron in circular orbits around a proton in Schwarzschild geometry has been investigated and is found
to be red shifted. The electrical dipole moment of such a system is also estimated. 相似文献
164.
Peter P. Gaspar Bong Hyun Boo Sarangan Chari Ashim K. Ghosh Dewey Holten Christine Kirmaier Stanislaw Konieczny 《Chemical physics letters》1984,105(2):153-157
Two transient absorptions have been detected in the 266 nm laser photolysis of 2-phenylheptamethyltrisilane in cyclohexane solution at room temperature, and their time evolution was recorded in the presence and absence of air and added trapping agents. The shorter-lived 440 nm transient (t1/2 < 20μs) is tentatively assigned to the silylene :SiMePh and the more persistent 380 nm transient to the disilene MePhSiSiMePh. The reactivity of this silylene is much lower than had been expected. 相似文献
165.
K. G. Chakraborty 《Zeitschrift für Physik B Condensed Matter》1984,55(3):231-234
The statistical mechanics of a spin-one Bethe lattice is discussed. The exact expression for Curie temperature is derived using a Bethe-Peierls approximations. The effect of the inclusion of a single-spin anisotropy to each Ising model of the lattice is also studied. It is seen that under certain situations a first-order phase transition appears. 相似文献
166.
T. Chakraborty K. Niemel P. Pietilinen 《Physica E: Low-dimensional Systems and Nanostructures》1998,1(1-4)
We investigate the properties of a system of interacting electrons in a narrow channel in the quantum Hall effect regime. We find that an increase in the strength of the Coulomb interaction causes abrupt changes in the width of the charge-density profile of translationally invariant states. The resulting phase diagram includes many of the stable odd-denominator states and also a novel fractional quantum Hall state at lowest half-filled Landau level. The collective modes evaluated at
and at
reveal soft modes in between the translationally invariant states in the phase diagram.
1997 Elsevier Science B.V. All rights reserved. 相似文献
167.
Literature study of microwave-assisted digestion using electrothermal atomic absorption spectrometry
R. Chakraborty A. K. Das M. L. Cervera M. de la Guardia 《Fresenius' Journal of Analytical Chemistry》1996,355(2):99-111
The literature on the use of microwave-assisted digestion procedures for subsequent sample analysis by means of electrothermal atomic absorption spectrometry (ETAAS) is reviewed. The literature survey reveals that this digestion technique has been applied mainly for biological materials. The elements most extensively determined by this method are cadmium and lead followed by copper, chromium, nickel and iron. The microwave digestion conditions, ETAAS furnace programmes and analytical details of the developed methodologies have been carefully revised. 相似文献
168.
Frederick E. Ziegler Paul J. Gilligan Utpal R. Chakraborty 《Tetrahedron letters》1979,20(36):3371-3374
D-Glucose has been converted into its functionalized derivative a synthon (C1–C6) of the carbomycin macrolide antibiotics. 相似文献
169.
170.
Tapash Chakraborty 《Physics letters. [Part B]》1978,77(1):6-8
We calculate the model energy of nuclear matter within the FIY expansion scheme. Numerical results are presented for two semi-realistic central potentials and a state independent correlation function which is suitably constrained for good cluster convergence. 相似文献