Dirac and Klein-Gordon particles in one-dimensional periodic potentials

We evaluate the dispersion relation for massless fermions, described by the Dirac equation, and for zero-spin bosons, described by the Klein-Gordon equation, moving in two dimensions and in the presence of a one-dimensional periodic potential. For massless fermions the dispersion relation shows a zero gap for carriers with zero momentum in the direction parallel to the barriers in agreement with the well-known "Klein paradox". Numerical results for the energy spectrum and the density of states are presented. Those for fermions are appropriate to graphene in which carriers behave relativistically with the "light speed" replaced by the Fermi velocity. In addition, we evaluate the transmission through a finite number of barriers for fermions and zero-spin bosons and relate it with that through a superlattice.Comment: 9 pages, 12 figure

Labor productivity and natural resources: an assessment at the national level in Honduras

The study establishes the link between agricultural labor productivity and natural resources variables at the national level in Honduras. We show through spatial analysis of productivity and natural resources that the relationship between natural resource conditions and agricultural productivity is not as direct as one can imagine. Length of the rain)" season has a strong and quasi linear relation with income. Soil has little impact on productivity as well as slope and altitude since coffee production in the mountain has a strong relation on productivity. Access to the main cities and to the main seaports has little relation with productivity since some of the main cities are located in unproductive areas. Improving the small road network would have a more positive impact. The study suggests that good research and good policies can have a good impact on productivity

Water vapor radiometry research and development phase

This report describes the research and development phase for eight dual-channel water vapor radiometers constructed for the Crustal Dynamics Project at the Goddard Space Flight Center, Greenbelt, Maryland, and for the NASA Deep Space Network. These instruments were developed to demonstrate that the variable path delay imposed on microwave radio transmissions by atmospheric water vapor can be calibrated, particularly as this phenomenon affects very long baseline interferometry measurement systems. Water vapor radiometry technology can also be used in systems that involve moist air meteorology and propagation studies

The sax1 dwarf mutant of Arabidopsis thaliana shows altered sensitivity of growth responses to abscisic acid, auxin, giberellin and ethylene and is partially rescued by exogenous brassinosteroid

Genetic approaches using Arabidopsis thaliana aimed at the identification of mutations affecting events involved in auxin signalling have usually led to the isolation of auxin-resistant mutants. From a selection screen specifically developed to isolate auxin-hypersensitive mutants, one mutant line was selected for its increased sensitivity to auxin (x 2 to 3) for the root elongation response. The genetic analysis of sax1 (hypersensitive to abscisic acid and auxin) indicated that the mutant phenotype segregates as a single recessive Mendelian locus, mapping to the lower arm of chromosome 1. Sax1 seedlings grown in vitro showed a short curled primary root and small, round, dark-green cotyledons. In the greenhouse, adult sax1 plants were characterized by a dwarf phenotype, delayed development and reduced fertility. Further physiological characterization of sax1 seedlings revealed that the most striking trait was a large increase (x 40) in ABA-sensitivity of root elongation and, to a lesser extent, of ABA-induced stomatal closure; in other respects, hypocotyl elongation was resistant to gibberellins and ethylene. These alterations in hormone sensitivity in sax1 plants co-segregated with the dwarf phenotype suggesting that processes involved in cell elongation are modified. Treatment of mutant seedlings with an exogenous brassinosteroid partially rescued a wild-type size, suggesting that brassinosteroid biosynthesis might be affected in sax1 plants. Wild-type sensitivities to ABA, auxin and gibberellins were also restored in sax1 plants by exogenous application of brassinosteroid, illustrating the pivotal importance of the BR-related SAX1 gene

PULSED LASER AND ELECTRON BEAM INDUCED DIFFUSION OF ANTIMONY IN SILICON

The aim of this work is to compare the diffusion into silicon of a thin film (~ 100 Å) of deposited antimony induced either by a pulsed laser irradiation or electron beam and to interpret the different experimental behaviours as observed by Rutherford backscattering spectrometry, by using the calculated temperature distributions obtained by solving the heat flow equation for the two different annealing processes

D-term inflation and neutrino mass

We study a $D$-term inflation scenario in a model extended from the minimal supersymmetric standard model (MSSM) by two additional abelian factor groups focussing on its particle physics aspects. Condensates of the fields related to the inflation can naturally give a possible solution to both the $\mu$-problem in the MSSM and the neutrino mass through their nonrenormalizable couplings to the MSSM fields. Mixings between neutrinos and neutralinos are also induced by some of these condensates. Small neutrino masses are generated by a weak scale seesaw mechanism as a result of these mixings. Moreover, the decay of the condensates may be able to cause the leptogenesis. Usually known discrepancy between both values of a Fayet-Iliopoulos $D$-term which are predicted by the COBE normalization and also by an anomalous U(1) in the weakly-coupled superstring might be reconciled.Comment: 21 pages, LaTeX, small modifications, one reference adde

Two-loop neutrino masses with large R-parity violating interactions in supersymmetry

We attempt to reconcile large trilinear R-parity violating interactions in a supersymmetric (SUSY) theory with the observed pattern of neutrino masses and mixing. We show that, with a restricted number of such interaction terms with the $\lambda'$-type couplings in the range (0.1-1.0), it is possible to forbid one-loop contributions to the neutrino mass matrix. This is illustrated with the help of a `working example' where an econnomic choice of SUSY parameters is made, with three non-vanishing and `large' R-parity violating terms in the superpotential. The two-loop contributions in such a case can not only generate the masses in the requisite order but can also lead us to specific allowed regions of the parameter space.Comment: Revised version, 25 pages, 16 figure

PULSED ELECTRON BEAM ANNEALING OF As AND B IMPLANTED SILICON

p-type (100) silicon wafers have been implanted either by As or B ions at 20 and 200 keV energies and doses of 1016cm-2. Pulsed electron beam annealing has been performed with fluences of 1.1 and 1.4 J/cm2 using a mean electron energy of 15 keV. The pulse duration was 50 ns. The annealed layers have been investigated by Rutherford backscattering under random and channeling conditions and by S.I.M.S. profiling. Good crystal regrowth and high dopant activation occur in all cases except for the 200 keV Boron implant. Impurities redistribution is observed but no significant segregation effects appear. The experimental profiles are in good agreement with a diffusion model using a modified green function solution and taking into account dopant diffusion in liquid phase and the computed melt front location. The deduced diffusion coefficient are in the 5.10-5cm2/s range for boron and 2.10-4cm2/s range for arsenic