Metallic layer in the Earth’s lower mantle

We predict the insulator-metal-insulator transitions for the temperature and pressure of the lower mantle with the metal layer thickness Δh ≈ 400 km at the depth of 1400–1800 km. The insulator-metal transition has the Mott-Hubbard origin, while the second transition from metal to insulator results from spin crossover of the Fe²⁺ ions from high spin S = 2 to low spin S = 0 state. The conductivity in the metal layer may attain 250 S/m. The depth profile of the conductivity is also suggested.     

Polynomial dual network simplex algorithms

We show how to use polynomial and strongly polynomial capacity scaling algorithms for the transshipment problem to design a polynomial dual network simplex pivot rule. Our best pivoting strategy leads to an O(m ² logn) bound on the number of pivots, wheren andm denotes the number of nodes and arcs in the input network. If the demands are integral and at mostB, we also give an O(m(m+n logn) min(lognB, m logn))-time implementation of a strategy that requires somewhat more pivots.Research supported by AFOSR-88-0088 through the Air Force Office of Scientific Research, by NSF grant DOM-8921835 and by grants from Prime Computer Corporation and UPS.Research supported by NSF Research Initiation Award CCR-900-8226, by U.S. Army Research Office Grant DAAL-03-91-G-0102, and by ONR Contract N00014-88-K-0166.Research supported in part by a Packard Fellowship, an NSF PYI award, a Sloan Fellowship, and by the National Science Foundation, the Air Force Office of Scientific Research, and the Office of Naval Research, through NSF grant DMS-8920550.     

Surjective stability for the K1-functor for some exceptional chevalley groups

Proofs are given for results on surjective stability for the K₁-functor for some exceptional Chevalley groups of normal types. Conditions are given (in terms of absolute stable rank) for stability for inclusions of Chevalley groups associated with maximal Standard inclusions of root Systems. The proofs are based on ideas of M. R. Stein. Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 198, pp. 65–88, 1991.     

Improved bounds on the max-flow min-cut ratio for multicommodity flows

In this paper we consider the worst case ratio between the capacity of min-cuts and the value of max-flow for multicommodity flow problems. We improve the best known bounds for the min-cut max-flow ratio for multicommodity flows in undirected graphs, by replacing theO(logD) in the bound byO(logk), whereD denotes the sum of all demands, andk demotes the number of commodities. In essence we prove that up to constant factors the worst min-cut max-flow ratios appear in problems where demands are integral and polynomial in the number of commodities.Klein, Rao, Agrawal, and Ravi have previously proved that if the demands and the capacities are integral, then the min-cut max-flow ratio in general undirected graphs is bounded byO(logClogD), whereC denotes the sum of all the capacities. Tragoudas has improved this bound toO(lognlogD), wheren is the number of nodes in the network. Garg, Vazirani and Yannakakis further improved this toO(logklogD). Klein, Plotkin and Rao have proved that for planar networks, the ratio isO(logD).Our result improves the bound for general networks toO(log² k) and the bound for planar networks toO(logk). In both cases our result implies the first non-trivial bound that is independent of the magnitude of the numbers involved. The method presented in this paper can be used to give polynomial time approximation algorithms to the minimum cuts in the network up to the above factors.Preliminary version appeared in Proceedings of the 25th Annual ACM Symposium on the Theory of Computing, 1993, 691-697.Research supported by U.S. Army Research Office Grant DAAL-03-91-G-0102, and by a grant from Mitsubishi Electric Laboratories.Research supported in part by a Packard Fellowship, an NSF PYI award, a Sloan Fellowship, and by the National Science Foundation, the Air Force Office of Scientific Research, and the Office of Naval Research, through NSF grant DMS-8920550.     

Incoherent scattering functions of 145 keV gamma rays by K-shell electrons in Y,Ag and Au

The values of incoherent scattering functions are determined experimentally for 145 keV gamma rays in elements Au, Ag and Y at scattering angles 40°, 70° and 100°, using a x-ray gamma coincidence technique. The corresponding theoretical values are obtained from the tabulations of Hubbellet al, and computed from the models of Jauch and Rohrlich and Shimizuet al. A comparison between the theoretical and experimental results showed that the non-relativistic approach adopted in the theory of Shimizuet al is inapplicable to the present cases. A gross agreement is noticed between the present experimental results and the other theoretical values.     

Xanthopterin in the Oriental Hornet (Vespa orientalis): Light Absorbance Is Increased with Maturation of Yellow Pigment Granules

The Oriental hornet bears both brown and yellow colors on its cuticle. The brown component is contributed by the pigment melanin, which is dispersed in the brown cuticle and provides protection against insolation, while the yellow‐colored part contains within pockets in the cuticle granules possessing a yellow pigment. These yellow granules (YG) are formed about 2 days prior to eclosion of the imago, and their production continues for about 3 days posteclosion. Xanthopterin is the main component of the granule and lends it its yellow color. Xanthopterin produces a characteristic excitation/emission maximum at 386/456 nm. Characterization by use of mass spectrometry showed the compound to have a molecular ion of 179, as expected from xanthopterin. Spectroscopic examination of the absorption of an entire stripe of yellow cuticle in the course of its metamorphosis revealed that the absorption steadily increases throughout the process to a maximal level of absorption about 3 days posteclosion. In the absence of the YG, the cuticle is permeable to the passage of all wavelengths within the visible range and to the UV range (290–750 nm) in all age groups of hornets. The newly ecloded hornets depart the nest to engage in activities requiring exposure to insolation only as the process of granule formation terminates, namely, when the layer of YG in the cuticle suffices to absorb all the harmful UV radiation.     

Parity of the band head at 3710 keV in 99Rh using clover detector as compton polarimeter

Clover detector has been used as a Compton polarimeter to measure the linear polarization of γ-rays produced in heavy ion fusion reaction. The polarization sensitivity of the clover detector has been measured over γ-ray energies ranging from 386 to 1368 ke V. The E1 multipolarity of the 1117 keV transition in ⁹⁹Rh has been established using this polarimeter. This has resulted in the assignment of negative parity to the band head at 3710 keV in ⁹⁹Rh.     

Growth of ultrathin YBa2Cu3O7−x films on the SrTiO3 substrate

The growth of ultrathin (1.7–7.3 nm) YBa₂Cu₃O_7?x films on the SrTiO₃(100) substrate is investigated by the mean-energy ion scattering technique. It is found that the growth of islands proceeds according to the two-dimensional and three-dimensional models and depends on the growth conditions.