2,621 research outputs found
The Karyotype of the parasitoid Chelonus insularis cresson (Hymenoptera, braconidae, cheloninae).
The Karyotype of chelonus insularis (Hymenoptera, Braconidae Cheloninae) is described. The males show an haploid number of seven chromosomes and the females a diploid number of fourteen chromosomes, confirming haplo-diploid sex determination. Comparisons of these results with karyotypes of other species of the same family were done and a possible mechanism involved in the karyotype evolution of this species is discussed
The seesaw mechanism at TeV scale in the 3-3-1 model with right-handed neutrinos
We implement the seesaw mechanism in the 3-3-1 model with right-handed
neutrinos. This is accomplished by the introduction of a scalar sextet into the
model and the spontaneous violation of the lepton number. We identify the
Majoron as a singlet under symmetry, which makes it
safe under the current bounds imposed by electroweak data. The main result of
this work is that the seesaw mechanism works already at TeV scale with the
outcome that the right-handed neutrino masses lie in the electroweak scale, in
the range from MeV to tens of GeV. This window provides a great opportunity to
test their appearance at current detectors, though when we contrast our results
with some previous analysis concerning detection sensitivity at LHC, we
conclude that further work is needed in order to validate this search.Comment: about 13 pages, no figure
Spin transport of electrons through quantum wires with spatially-modulated strength of the Rashba spin-orbit interaction
We study ballistic transport of spin-polarized electrons through quantum
wires in which the strength of the Rashba spin-orbit interaction (SOI) is
spatially modulated. Subband mixing, due to SOI, between the two lowest
subbands is taken into account. Simplified approximate expressions for the
transmission are obtained for electron energies close to the bottom of the
first subband and near the value for which anticrossing of the two lowest
subbands occurs. In structures with periodically varied SOI strength, {\it
square-wave} modulation on the spin transmission is found when only one subband
is occupied and its possible application to the spin transistor is discussed.
When two subbands are occupied the transmission is strongly affected by the
existence of SOI interfaces as well as by the subband mixing
Discrete symmetries, invisible axion and lepton number symmetry in an economic 3-3-1 model
We show that Peccei-Quinn and lepton number symmetries can be a natural
outcome in a 3-3-1 model with right-handed neutrinos after imposing a Z_11 x
Z_2 symmetry. This symmetry is suitably accommodated in this model when we
augmented its spectrum by including merely one singlet scalar field. We work
out the breaking of the Peccei-Quinn symmetry, yielding the axion, and study
the phenomenological consequences. The main result of this work is that the
solution to the strong CP problem can be implemented in a natural way, implying
an invisible axion phenomenologically unconstrained, free of domain wall
formation and constituting a good candidate for the cold dark matter.Comment: 17 pages, Revtex
Sub-terahertz, microwaves and high energy emissions during the December 6, 2006 flare, at 18:40 UT
The presence of a solar burst spectral component with flux density increasing
with frequency in the sub-terahertz range, spectrally separated from the
well-known microwave spectral component, bring new possibilities to explore the
flaring physical processes, both observational and theoretical. The solar event
of 6 December 2006, starting at about 18:30 UT, exhibited a particularly
well-defined double spectral structure, with the sub-THz spectral component
detected at 212 and 405 GHz by SST and microwaves (1-18 GHz) observed by the
Owens Valley Solar Array (OVSA). Emissions obtained by instruments in
satellites are discussed with emphasis to ultra-violet (UV) obtained by the
Transition Region And Coronal Explorer (TRACE), soft X-rays from the
Geostationary Operational Environmental Satellites (GOES) and X- and gamma-rays
from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz
impulsive component had its closer temporal counterpart only in the higher
energy X- and gamma-rays ranges. The spatial positions of the centers of
emission at 212 GHz for the first flux enhancement were clearly displaced by
more than one arc-minute from positions at the following phases. The observed
sub-THz fluxes and burst source plasma parameters were found difficult to be
reconciled to a purely thermal emission component. We discuss possible
mechanisms to explain the double spectral components at microwaves and in the
THz ranges.Comment: Accepted version for publication in Solar Physic
Optimization of Surface Display of DENV2 e Protein on a Nanoparticle to Induce Virus Specific Neutralizing Antibody Responses
The dengue virus (DENV) causes over 350 million infections, resulting in ∼25,000 deaths per year globally. An effective dengue vaccine requires generation of strong and balanced neutralizing antibodies against all four antigenically distinct serotypes of DENV. The leading live-attenuated tetravalent dengue virus vaccine platform has shown partial efficacy, with an unbalanced response across the four serotypes in clinical trials. DENV subunit vaccine platforms are being developed because they provide a strong safety profile and are expected to avoid the unbalanced immunization issues associated with live multivalent vaccines. Subunit vaccines often lack immunogenicity, requiring either a particulate or adjuvanted formulation. Particulate formulations adsorbing monomeric DENV-E antigen to the particle surface incite a strong immune response, but have no control of antigen presentation. Highly neutralizing epitopes are displayed by DENV-E quaternary structures. To control the display of DENV-E and produce quaternary structures, particulate formulations that covalently attach DENV-E to the particle surface are needed. Here we develop a surface attached DENV2-E particulate formulation, as well as analysis tools, using PEG hydrogel nanoparticles created with particle replication in nonwetting templates (PRINT) technology. We found that adding Tween-20 to the conjugation buffer controls DENV-E adsorption to the particle surface during conjugation, improving both protein stability and epitope display. Immunizations with the anionic but not the cationic DENV2-E conjugated particles were able to produce DENV-specific and virus neutralizing antibody in mice. This work optimized the display of DENV-E conjugated to the surface of a nanoparticle through EDC/NHS chemistry, establishing a platform that can be expanded upon in future work to fully control the display of DENV-E
Two-dimensional hole precession in an all-semiconductor spin field effect transistor
We present a theoretical study of a spin field-effect transistor realized in
a quantum well formed in a p--doped ferromagnetic-semiconductor-
nonmagnetic-semiconductor-ferromagnetic-semiconductor hybrid structure. Based
on an envelope-function approach for the hole bands in the various regions of
the transistor, we derive the complete theory of coherent transport through the
device, which includes both heavy- and light-hole subbands, proper modeling of
the mode matching at interfaces, integration over injection angles, Rashba spin
precession, interference effects due to multiple reflections, and gate-voltage
dependences. Numerical results for the device current as a function of
externally tunable parameters are in excellent agreement with approximate
analytical formulae.Comment: 9 pages, 11 figure
Explaining the Higgs Decays at the LHC with an Extended Electroweak Model
We show that the recent discovery of a new boson at the LHC, which we assume
to be a Higgs boson, and the observed enhancement in its diphoton decays
compared to the SM prediction, can be explained by a new doublet of charged
vector bosons from an extended electroweak gauge sector model with
SU(3)_C\otimesSU(3)_L\otimesU(1)_X symmetry. Our results show a good
agreement between our theoretical expected sensitivity to a 126--125 GeV Higgs
boson and the experimental significance observed in the diphoton channel at the
8 TeV LHC. Effects of an invisible decay channel for the Higgs boson are also
taken into account, in order to anticipate a possible confirmation of deficits
in the branching ratios into , , bottom quarks, and tau leptons.Comment: 16 pages, 5 figure
Produtividade e vigor do maracujazeiro-amarelo plantado em covas e plantio direto sob manejo orgânico.
O objetivo deste trabalho foi avaliar o vigor e a produtividade do maracujazeiro-amarelo plantado em diferentes tamanhos de cova e plantio direto sob manejo orgânico. O experimento foi conduzido de 2005 a 2007, no Setor de Agricultura Ecológica da Universidade Federal do Acre, em delineamento de blocos casualizados, constituídos de cinco tratamentos, quatro repetições e quatro plantas por parcela. Foram avaliados cinco tipos de preparo do solo: T1 cova do tamanho do torrão (0,19 x 0,063m) com adubação em cobertura; T2 cova de 0,30 x 0,30 x 0,30m com adubação de plantio na cova; T3 cova de 0,30 x 0,30 x 0,30m com adubação de plantio em cobertura; T4 cova de 0,50 x 0,50 x 0,50m com adubação de plantio na cova; e T5 cova de 0,50 x 0,50 x 0,50m com adubação de plantio em cobertura. O tamanho da cova e o plantio direto não influenciaram o vigor da planta e a biomassa de raízes. O número de frutos por planta e a produtividade, na segunda e na somatória das duas safras, foram maiores com plantio direto e com covas cúbicas de 0,30m. Após dois anos de cultivo, a densidade do solo foi maior na camada de 0-5cm de profundidade num raio de 20cm da planta para o plantio em covas de 0,50m com adubação na cova e menor para o plantio direto, não havendo diferença entre os demais tratamentos. O plantio direto ou o plantio em covas pequenas com dimensões de 0,30 x 0,30 x 0,30m proporcionou maior produtividade de maracujá que o plantio em covas maiores, mesmo não influenciando o vigor das plantas e a massa seca de raízes
Radiation-induced oscillatory magnetoresistance as a sensitive probe of the zero-field spin splitting in high mobility GaAs/AlGaAs devices
We suggest an approach for characterizing the zero-field spin splitting of
high mobility two-dimensional electron systems, when beats are not readily
observable in the Shubnikov-de Haas effect. The zero-field spin splitting and
the effective magnetic field seen in the reference frame of the electron is
evaluated from a quantitative study of beats observed in radiation-induced
magnetoresistance oscillations.Comment: 4 pages, 4 color figure
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