7,496 research outputs found
Occurrence of geminivirus in tomato-producing areas in Submedio Sao Francisco.
This is the first report of geminivirus in Submedio Sao Francisco and reveals a wide dispersal of this virus that was previously described in the Federal District (1994) and state of Sao Paulo (1997), Minas Gerais (1996) and Bahia (1996).Suplemento. Edição dos Resumos do 30 Congresso Brasileiro de Fitopatologia, Poços de Caldas, 1997
Determination of the (3x3)-Sn/Ge(111) structure by photoelectron diffraction
At a coverage of about 1/3 monolayer, Sn deposited on Ge(111) below 550 forms
a metastable (sqrt3 x sqrt3)R30 phase. This phase continuously and reversibly
transforms into a (3x3) one, upon cooling below 200 K. The photoemission
spectra of the Sn 4d electrons from the (3x3)-Sn/Ge(111) surface present two
components which are attributed to inequivalent Sn atoms in T4 bonding sites.
This structure has been explored by photoelectron diffraction experiments
performed at the ALOISA beamline of the Elettra storage ring in Trieste
(Italy). The modulation of the intensities of the two Sn components, caused by
the backscattering of the underneath Ge atoms, has been measured as a function
of the emission angle at fixed kinetic energies and viceversa. The bond angle
between Sn and its nearest neighbour atoms in the first Ge layer (Sn-Ge1) has
been measured by taking polar scans along the main symmetry directions and it
was found almost equivalent for the two components. The corresponding bond
lengths are also quite similar, as obtained by studying the dependence on the
photoelectron kinetic energy, while keeping the photon polarization and the
collection direction parallel to the Sn-Ge1 bond orientation (bond emission). A
clear difference between the two bonding sites is observed when studying the
energy dependence at normal emission, where the sensitivity to the Sn height
above the Ge atom in the second layer is enhanced. This vertical distance is
found to be 0.3 Angstroms larger for one Sn atom out of the three contained in
the lattice unit cell. The (3x3)-Sn/Ge(111) is thus characterized by a
structure where the Sn atom and its three nearest neighbour Ge atoms form a
rather rigid unit that presents a strong vertical distortion with respect to
the underneath atom of the second Ge layer.Comment: 10 pages with 9 figures, added reference
Probing the single-particle character of rotational states in F using a short-lived isomeric beam
A beam containing a substantial component of both the ,
ns isomeric state of F and its , 109.77-min ground
state has been utilized to study members of the ground-state rotational band in
F through the neutron transfer reaction , in inverse kinematics.
The resulting spectroscopic strengths confirm the single-particle nature of the
13/2 band-terminating state. The agreement between shell-model
calculations, using an interaction constructed within the shell, and our
experimental results reinforces the idea of a single-particle/collective
duality in the descriptions of the structure of atomic nuclei
Desenvolvimento de linhagens e cultivares de tomateiro para o Nordeste do Brasil com resistencia a Tospovirose e Geminiviroses.
A região Nordeste produz anualmente cerca de 240 mil toneladas de tomate para processamento industrial, sendo esta atividade responsável pela absorção de grande contingente de mão-de-obra envolvido direta e indiretamente no cultivo e no processamento de tomate. As tospoviroses, transmitidas por tripes, e as geminiviroses, transmitidas por mosca-branca, vêm causando grandes reduções na produtividade do tomateiro no Nordeste do Brasil. O controle químico dos insetos vetores muitas vezes não diminui a incidência destas viroses no tomateiro, sendo comum a ocorrência de campos com 100% de plantas mostrando sintomas destas doenças. O uso da resistência genética, como um dos componentes do manejo integrado de pragas (MIP), parece ser a medida mais eficaz para o controle destas duas viroses
Terahertz radiation driven chiral edge currents in graphene
We observe photocurrents induced in single layer graphene samples by
illumination of the graphene edges with circularly polarized terahertz
radiation at normal incidence. The photocurrent flows along the sample edges
and forms a vortex. Its winding direction reverses by switching the light
helicity from left- to right-handed. We demonstrate that the photocurrent stems
from the sample edges, which reduce the spatial symmetry and result in an
asymmetric scattering of carriers driven by the radiation electric field. The
developed theory is in a good agreement with the experiment. We show that the
edge photocurrents can be applied for determination of the conductivity type
and the momentum scattering time of the charge carriers in the graphene edge
vicinity.Comment: 4 pages, 4 figure, additional Supplemental Material (3 pages, 1
figure
Stellar ArAr reactions and their effect on light neutron-rich nuclide synthesis
The ArAr ( = 35 d) and
ArAr (269 y) reactions were studied for the first time
with a quasi-Maxwellian ( keV) neutron flux for Maxwellian Average
Cross Section (MACS) measurements at stellar energies. Gas samples were
irradiated at the high-intensity Soreq applied research accelerator
facility-liquid-lithium target neutron source and the Ar/Ar and
Ar/Ar ratios in the activated samples were determined by
accelerator mass spectrometry at the ATLAS facility (Argonne National
Laboratory). The Ar activity was also measured by low-level counting at
the University of Bern. Experimental MACS of Ar and Ar, corrected
to the standard 30 keV thermal energy, are 1.9(3) mb and 1.3(2) mb,
respectively, differing from the theoretical and evaluated values published to
date by up to an order of magnitude. The neutron capture cross sections of
Ar are relevant to the stellar nucleosynthesis of light neutron-rich
nuclides; the two experimental values are shown to affect the calculated mass
fraction of nuclides in the region A=36-48 during the weak -process. The new
production cross sections have implications also for the use of Ar and
Ar as environmental tracers in the atmosphere and hydrosphere.Comment: 18 pages + Supp. Mat. (13 pages) Accepted for publication in Phys.
Rev. Let
Spin Transfer from a Ferromagnet into a Semiconductor through an Oxide barrier
We present results on the magnetoresistance of the system Ni/Al203/n-doped
Si/Al2O3/Ni in fabricated nanostructures. The results at temperature of 14K
reveal a 75% magnetoresistance that decreases in value up to approximately 30K
where the effect disappears. We observe minimum resistance in the antiparallel
configurations of the source and drain of Ni. As a possibility, it seems to
indicate the existence of a magnetic state at the Si/oxide interface. The
average spin diffusion length obtained is of 650 nm approximately. Results are
compared to the window of resistances that seems to exist between the tunnel
barrier resistance and two threshold resistances but the spin transfer seems to
work in the range and outside the two thresholds
RELICS: The Reionization Lensing Cluster Survey and the Brightest High-z Galaxies
Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here the z ~ 6-8 candidate high-redshift galaxies from the Reionization Lensing Cluster Survey (RELICS), a Hubble and Spitzer Space Telescope survey of 41 massive galaxy clusters spanning an area of ≈200 arcmin². These clusters were selected to be excellent lenses, and we find similar high-redshift sample sizes and magnitude distributions as the Cluster Lensing And Supernova survey with Hubble (CLASH). We discover 257, 57, and eight candidate galaxies at z ~ 6, 7, and 8 respectively, (322 in total). The observed (lensed) magnitudes of the z ~ 6 candidates are as bright as AB mag ~23, making them among the brightest known at these redshifts, comparable with discoveries from much wider, blank-field surveys. RELICS demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. These brightly observed galaxies are excellent targets for follow-up study with current and future observatories, including the James Webb Space Telescope
Search for associated Higgs boson production using like charge dilepton events in p(p)over-bar collisions at root s=1.96 TeV
We present a search for associated Higgs boson production in the process p (p) over bar -> W/ZH -> l(+/-)l'(+/-) + X in ee, e mu, and mu mu final states. The search is based on data collected by the D0 experiment at the Fermilab Tevatron Collider at root s = 1.96 TeV corresponding to 5.3 fb(-1) of integrated luminosity. We require two isolated leptons (electrons or muons) with the same electric charge and additional kinematic requirements. No significant excess above background is observed, and we set 95% C. L. observed (expected) upper limits on ratio of the production cross section to the standard model prediction of 6.4 (7.3) for a Higgs boson mass of 165 GeV and 13.5 (19.8) for a mass of 115 GeV
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