4,277 research outputs found
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 Ă…) 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 -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 -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 -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 -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
Dual-Seq Transcriptomics Reveals The Battle For Iron During Pseudomonas Aeruginosa Acute Murine Pneumonia
Determining bacterial gene expression during infection is fundamental to understand pathogenesis. In this study, we used dual RNA-seq to simultaneously measure P. aeruginosa and the murine host’s gene expression and response to respiratory infection. Bacterial genes encoding products involved in metabolism and virulence were differentially expressed during infection and the type III and VI secretion systems were highly expressed in vivo. Strikingly, heme acquisition, ferric-enterobactin transport, and pyoverdine biosynthesis genes were found to be significantly up-regulated during infection. In the mouse, we profiled the acute immune response to P. aeruginosa and identified the pro-inflammatory cytokines involved in acute response to the bacterium in the lung. Additionally, we also identified numerous host iron sequestration systems upregulated during infection. Overall, this work sheds light on how P. aeruginosa triggers a pro-inflammatory response and competes for iron with the host during infection, as iron is one of the central elements for which both pathogen and host fight during acute pneumonia
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