6,045 research outputs found
On thin-shell wormholes evolving in flat FRW spacetimes
We analize the stability of a class of thin-shell wormholes with spherical
symmetry evolving in flat FRW spacetimes. The wormholes considered here are
supported at the throat by a perfect fluid with equation of state
and have a physical radius equal to , where is a
time-dependent function describing the dynamics of the throat and is the
background scale factor. The study of wormhole stability is done by means of
the stability analysis of dynamic systems.Comment: 8 pages; to appear in MPL
Electronic spectroscopy of the alkaline-earth halide cluster Ca_2Cl_3
A visible spectrum of the cluster Ca_2Cl_3 was observed from 651 to 630 nm by 1 + 1[prime] resonant multiphoton ionization spectroscopy. Spectra were obtained for each of the four isotopomers: Ca2 35Cl3, Ca2 35Cl2 37Cl, Ca2 35Cl 37Cl2, and Ca2 37Cl3. The spectra were composed of a strong origin band at 15 350.8 cm^(–1) and several very weak vibronic bands. All of the bands were sharp with partially resolved rotational band contours. Density functional calculations predicted three minimum energy isomers. The spectrum was assigned to the 2B2<--X-tilde 2A1 transition of the lowest energy isomer, a planar C2v structure having a ring of two Cl and two Ca atoms and a terminal Cl atom. The ring isomer of Ca_2Cl_3 has the unpaired electron localized on one Ca^(2+) ion to form a Ca^+ chromophore. The two other predicted isomers, a D3h trigonal bipyramid and a C2v planar V-shaped structure, were not consistent with the observations
Efeito de espécies utilizadas no sistema plantio direto na Região Sul sobre o parasitismo e germinação de escleródios de Sclerotinia sclerotiorum.
Este trabalho teve como objetivo verificar a influência de diferentes espécies adaptadas para cultivo sob baixas temperaturas no parasitismo e germinação de escleródios de Sclerotinia sclerotiorum.Conpeex 2010
Sub-nanosecond, time-resolved, broadband infrared spectroscopy using synchrotron radiation
A facility for sub-nanosecond time-resolved (pump-probe) infrared
spectroscopy has been developed at the National Synchrotron Light Source of
Brookhaven National Laboratory. A mode-locked Ti:sapphire laser produces 2 ps
duration, tunable near-IR pump pulses synchronized to probe pulses from a
synchrotron storage ring. The facility is unique on account of the broadband
infrared from the synchrotron, which allows the entire spectral range from 2
cm-1 (0.25 meV) to 20,000 cm-1 (2.5 eV) to be probed. A temporal resolution of
200 ps, limited by the infrared synchrotron-pulse duration, is achieved. A
maximum time delay of 170 ns is available without gating the infrared detector.
To illustrate the performance of the facility, a measurement of electron-hole
recombination dynamics for an HgCdTe semiconductor film in the far- and mid
infrared range is presented.Comment: 11 pages with 9 figures include
Controle biológico de patógenos habitantes do solo com Trichoderma spp., na cultura do feijoeiro comum.
Integração dos tratamentos biológico e químico de sementes. Redução do inóculo inicial de Rhizoctonia solani e Fusarium solani. Redução do inóculo de Sclerotinia sclerotiorum.bitstream/CNPAF-2010/29841/1/circ-85.pd
On multi-scale asymptotic structure of eigenfunctions in a boundary value problem with concentrated masses near the boundary
We construct two-term asymptotics ?? k = ?m?2(M + ??k + O(?3/2)) of eigenvalues of a mixed boundary-value problem in ? R2 with many heavy (m > 2) concentrated masses near a straight part of the boundary ? . ? is a small positive parameter related to size and periodicity of the masses; k ? N. The main term M > 0
is common for all eigenvalues but the correction terms ?k , which are eigenvalues of a limit problem with the spectral Steklov boundary conditions on , exhibit the effect of asymptotic splitting in the eigenvalue sequence enabling the detection of asymptotic forms of eigenfunctions. The justification scheme implies isolating and purifying singularities of eigenfunctions and leads to a new spectral problem in weighed spaces with a "strongly" singular weight.This research work has been partially supported by Spanish MINECO, MTM2013-44883-P. Also, the research work of the first author has been partially supported by Russian Foundation of Basic research (project 15–01–02175)
Stable Gravastars of Anisotropic Dark Energy
Dynamical models of prototype gravastars made of phantom energy are
constructed, in which an infinitely thin spherical shell of a perfect fluid
with the equation of state divides the whole spacetime
into two regions, the internal region filled with a dark energy (or phantom)
fluid, and the external Schwarzschild region. It is found that in some cases
the models represent the "bounded excursion" stable gravastars, where the thin
shell is oscillating between two finite radii, while in other cases they
collapse until the formation of black holes or normal stars. In the phase
space, the region for the "bounded excursion" gravastars is very small in
comparison to that of black holes, but not empty, as found in our previous
papers. Therefore, although the existence of gravastars can not be completely
excluded from current analysis, the opposite is not possible either, that is,
even if gravastars exist, they do not exclude the existence of black holes.Comment: 35 pages, 43 figures, added some clarifying texts and corrected some
typos, accepted for publication in JCA
Optical conductivity of URuSi in the Kondo Liquid and Hidden-Order Phases
We measured the polarized optical conductivity of URuSi from room
temperature down to 5 K, covering the Kondo state, the coherent Kondo liquid
regime, and the hidden-order phase. The normal state is characterized by an
anisotropic behavior between the ab plane and c axis responses. The ab plane
optical conductivity is strongly influenced by the formation of the coherent
Kondo liquid: a sharp Drude peak develops and a hybridization gap at 12 meV
leads to a spectral weight transfer to mid-infrared energies. The c axis
conductivity has a different behavior: the Drude peak already exists at 300 K
and no particular anomaly or gap signature appears in the coherent Kondo liquid
regime. When entering the hidden-order state, both polarizations see a dramatic
decrease in the Drude spectral weight and scattering rate, compatible with a
loss of about 50 % of the carriers at the Fermi level. At the same time a
density-wave like gap appears along both polarizations at about 6.5 meV at 5 K.
This gap closes respecting a mean field thermal evolution in the ab plane.
Along the c axis it remains roughly constant and it "fills up" rather than
closing.Comment: 10 pages, 7 figure
Infrared properties of MgAlBC) single crystals in the normal and superconducting state
The reflectivity of -oriented MgAl(BC) single crystals has been measured by means of infrared
microspectroscopy for cm. An increase with doping of
the scattering rates in the and bands is observed, being more
pronounced in the C doped crystals. The -band plasma frequency also
changes with doping due to the electron doping, while the -band one is
almost unchanged. Moreover, a interband excitation, predicted
by theory, is observed at eV in the undoped sample,
and shifts to lower energies with doping. By performing theoretical calculation
of the doping dependence , the experimental observations can be
explained with the increase with electron doping of the Fermi energy of the
holes in the -band. On the other hand, the band density of
states seems not to change substantially. This points towards a reduction
driven mainly by disorder, at least for the doping level studied here. The
superconducting state has been also probed by infrared synchrotron radiation
for cm in one pure and one C-doped sample. In the
undoped sample ( = 38.5 K) a signature of the -gap only is observed.
At = 0.08 ( = 31.9 K), the presence of the contribution of the
-gap indicates dirty-limit superconductivity in both bands.Comment: 12 pages, 9 figure
Linearized stability analysis of gravastars in noncommutative geometry
In this work, we find exact gravastar solutions in the context of
noncommutative geometry, and explore their physical properties and
characteristics. The energy density of these geometries is a smeared and
particle-like gravitational source, where the mass is diffused throughout a
region of linear dimension due to the intrinsic uncertainty
encoded in the coordinate commutator. These solutions are then matched to an
exterior Schwarzschild spacetime. We further explore the dynamical stability of
the transition layer of these gravastars, for the specific case of
, where M is the black hole mass, to linearized
spherically symmetric radial perturbations about static equilibrium solutions.
It is found that large stability regions exist and, in particular, located
sufficiently close to where the event horizon is expected to form.Comment: 6 pages, 3 figure
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