Miniestaquia de corticeira-do-mato (Erythrina falcata Bentham de três procedências obtidas em sistema hidropônico.

Resumo

Electron effective mass and mobility in heavily doped n-GaAsN probed by Raman scattering

We investigate inelastic light scattering by longitudinal optic phonon-plasmon coupled modes LOPCMs in a series of heavily Se-doped, n-type GaAs1−xNx epilayers with x 0.4%. We perform a line shape analysis of the LOPCM spectra to estimate the optical effective mass, mopt , and the scattering time of the conduction electrons in GaAsN. We use these results to evaluate an effective carrier mobility for our samples. The values thus obtained, which we compare with measured electron Hall mobilities, indicate that the x-dependence of the mobility in GaAs1−xNx is dominated by the scattering time, rather than by the variation of the electron effective mass. The Raman analysis yields mopt values that are lower than those obtained from the band anticrossing model. © 2008 American Institute of Physics.This work is supported by the Spanish Government Projects MAT 2004-0664 and MAT2007-63617, and Ramon y Cajal Program and the EPSRC, United Kingdom. 1M. Henini, Dilute Nitride Semiconductors Elsevier Science, AmsterdamPeer reviewe

Quark mixings and flavor changing interactions with singlet quarks

Aspects of the quark mixings and flavor changing interactions are investigated in electroweak models with singlet quarks. The effects on the ordinary quark mixing are determined in terms of the quark masses and the parameters describing the mixing between the ordinary quarks q and the singlet quarks Q (q-Q mixing). Some salient features arise in the flavor changing interactions through the q-Q mixing. The unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix within the ordinary quark sector is violated, and the flavor changing neutral currents (FCNC's) appear both in the gauge and scalar couplings. The flavor changing interactions are calculated appropriately in terms of the q-Q mixing parameters and the quark masses, which really exhibit specific flavor structures. It is found that there are reasonable ranges of the model parameters to reproduce the ordinary quark mass hierarchy and the actual CKM structure even in the presence of q-Q mixing. Some phenomenological effects of the singlet quarks are also discussed. In particular, the scalar FCNC's may be more important in some cases, if the singlet quarks as well as the extra scalar particles from the singlet Higgs fields have masses $\sim$ 100 GeV -- 1 TeV.Comment: 32 pages, 7 figures, added reference

The Final Fate of the Rolling Tachyon

We propose an alternative interpretation of the boundary state for the rolling tachyon, which may depict the time evolution of unstable D-branes in string theory. Splitting the string variable in the temporal direction into the classical part, which we may call "time" and the quantum one, we observe the time dependent behaviour of the boundary. Using the fermion representation of the rolling tachyon boundary state, we show that the boundary state correctly describes the time-dependent decay process of the unstable D-brane into a S-brane at the classical level.Comment: 9 pages, revte

Recent Changes in the Japanese Wholesale System and the Importance of the Sogo Shosha

Interest in Japanese distribution as a field of academic study has waned in recent years, but there is a continuing concern with the activities of Japan’s general trading companies or Sogo Shosha. This research has concentrated largely on their function as international trade intermediaries but it has overlooked their role in the domestic economy. In recent years, the same Sogo Shosha have expanded their involvement in domestic distribution, in particular into food wholesaling, but more recently into retailing. The aim of this paper is to explore the extent of this involvement and to present an analysis of the reasons behind such a shift from both a managerial and a theoretical perspective. Further, we go on to look at the current and future consequences of such large, internationally powerful companies taking a significant share in domestic distribution in Japan

Closed String Tachyon Condensation: An Overview

These notes are an expanded version of a review lecture on closed string tachyon condensation at the RTN workshop in Copenhagen in September 2003. We begin with a lightning review of open string tachyon condensation, and then proceed to review recent results on localized closed string tachyon condensation, focusing on two simple systems, C/Z_n orbifolds and twisted circle compactifications.Comment: harvmac, 59 pages; references adde