473 research outputs found
Ab initio and nuclear inelastic scattering studies of FeSi/GaAs heterostructures
The structure and dynamical properties of the FeSi/GaAs(001) interface
are investigated by density functional theory and nuclear inelastic scattering
measurements. The stability of four different atomic configurations of the
FeSi/GaAs multilayers is analyzed by calculating the formation energies and
phonon dispersion curves. The differences in charge density, magnetization, and
electronic density of states between the configurations are examined. Our
calculations unveil that magnetic moments of the Fe atoms tend to align in a
plane parallel to the interface, along the [110] direction of the FeSi
crystallographic unit cell. In some configurations, the spin polarization of
interface layers is larger than that of bulk FeSi. The effect of the
interface on element-specific and layer-resolved phonon density of states is
discussed. The Fe-partial phonon density of states measured for the FeSi
layer thickness of three monolayers is compared with theoretical results
obtained for each interface atomic configuration. The best agreement is found
for one of the configurations with a mixed Fe-Si interface layer, which
reproduces the anomalous enhancement of the phonon density of states below 10
meVComment: 14 pages, 9 figures, 4 table
Spin-Phonon Coupling in Iron Pnictide Superconductors
The magnetic moment in the parent phase of the iron-pnictide superconductors
varies with composition even when the nominal charge of iron is unchanged. We
propose the spin-lattice coupling due to the magneto-volume effect as the
primary origin of this effect, and formulate a Landau theory to describe the
dependence of the moment to the Fe-As layer separation. We then compare the
superconductive critical temperature of doped iron pnictides to the local
moment predicted by the theory, and suggest that the spin-phonon coupling may
play a role in the superconductivity of this compound
A High Luminosity e+e- Collider to study the Higgs Boson
A strong candidate for the Standard Model Scalar boson, H(126), has been
discovered by the Large Hadron Collider (LHC) experiments. In order to study
this fundamental particle with unprecedented precision, and to perform
precision tests of the closure of the Standard Model, we investigate the
possibilities offered by An e+e- storage ring collider. We use a design
inspired by the B-factories, taking into account the performance achieved at
LEP2, and imposing a synchrotron radiation power limit of 100 MW. At the most
relevant centre-of-mass energy of 240 GeV, near-constant luminosities of 10^34
cm^{-2}s^{-1} are possible in up to four collision points for a ring of 27km
circumference. The achievable luminosity increases with the bending radius, and
for 80km circumference, a luminosity of 5 10^34 cm^{-2}s^{-1} in four collision
points appears feasible. Beamstrahlung becomes relevant at these high
luminosities, leading to a design requirement of large momentum acceptance both
in the accelerating system and in the optics. The larger machine could reach
the top quark threshold, would yield luminosities per interaction point of
10^36 cm^{-2}s^{-1} at the Z pole (91 GeV) and 2 10^35 cm^{-2}s^{-1} at the W
pair production threshold (80 GeV per beam). The energy spread is reduced in
the larger ring with respect to what is was at LEP, giving confidence that beam
polarization for energy calibration purposes should be available up to the W
pair threshold. The capabilities in term of physics performance are outlined.Comment: Submitted to the European Strategy Preparatory Group 01-04-2013 new
version as re-submitted to PRSTA
Topological (Sliced) Doping of a 3D Peierls System: Predicted Structure of Doped BaBiO3
At hole concentrations below x=0.4, Ba_(1-x)K_xBiO_3 is non-metallic. At x=0,
pure BaBiO3 is a Peierls insulator. Very dilute holes create bipolaronic point
defects in the Peierls order parameter. Here we find that the Rice-Sneddon
version of Peierls theory predicts that more concentrated holes should form
stacking faults (two-dimensional topological defects, called slices) in the
Peierls order parameter. However, the long-range Coulomb interaction, left out
of the Rice-Sneddon model, destabilizes slices in favor of point bipolarons at
low concentrations, leaving a window near 30% doping where the sliced state is
marginally stable.Comment: 6 pages with 5 embedded postscript figure
Phononic drumhead surface state in distorted kagome compound RhPb
RhPb was initially recognized as one of a CoSn-like compounds with
symmetry, containing an ideal kagome lattice of -block atoms. However,
theoretical calculations predict the realization of the phonon soft mode which
leads to the kagome lattice distortion and stabilization of the structure with
symmetry [A. Ptok et al., Phys. Rev. B 104, 054305 (2021)]. Here,
we present the single crystal x-ray diffraction results supporting this
prediction. Furthermore, we discuss the main dynamical properties of RhPb with
symmetry. The bulk phononic dispersion curves contain several
flattened bands, Dirac nodal lines, and triple degenerate Dirac points. As a
consequence, the phononic drumhead surface state is realized for the (100)
surface, terminated by the zigzag-like edge of Pb honeycomb sublattice.Comment: 10 pages, 7 figure
Phononic drumhead surface state in the distorted kagome compound RhPb
RhPb was initially recognized as one of CoSn-like compounds with P6/mmm symmetry, containing an ideal kagome lattice of d-block atoms. However, theoretical calculations predict the realization of the phonon soft mode, which leads to the kagome lattice distortion and stabilization of the structure with P2m symmetry [A. Ptok et al., Phys. Rev. B 104, 054305 (2021)]. Here, we present the single crystal x-ray diffraction results supporting this prediction. Furthermore, we discuss the main dynamical properties of RhPb with P2m symmetry, i.e. phonon dispersions and surface Green's functions using the modern theoretical methods based on density functional theory. The bulk phononic dispersion curves contain several flattened bands, Dirac nodal lines, and triple degenerate Dirac points. As a consequence, the phononic drumhead surface state is realized for the (100) surface, terminated by the zigzaglike edge of Pb honeycomb sublattice
Can Doubly Strange Dibaryon Resonances be Discovered at RHIC?
The baryon-baryon continuum invariant mass spectrum generated from
relativistic nucleus + nucleus collision data may reveal the existence of
doubly-strange dibaryons not stable against strong decay if they lie within a
few MeV of threshold. Furthermore, since the dominant component of these states
is a superposition of two color-octet clusters which can be produced
intermediately in a color-deconfined quark-gluon plasma (QGP), an enhanced
production of dibaryon resonances could be a signal of QGP formation. A total
of eight, doubly-strange dibaryon states are considered for experimental search
using the STAR detector (Solenoidal Tracker at RHIC) at the new Relativistic
Heavy Ion Collider (RHIC). These states may decay to Lambda-Lambda and/or
proton-Cascade-minus, depending on the resonance energy. STAR's large
acceptance, precision tracking and vertex reconstruction capabilities, and
large data volume capacity, make it an ideal instrument to use for such a
search. Detector performance and analysis sensitivity are studied as a function
of resonance production rate and width for one particular dibaryon which can
directly strong decay to proton-Cascade-minus but not Lambda-Lambda. Results
indicate that such resonances may be discovered using STAR if the resonance
production rates are comparable to coalescence model predictions for dibaryon
bound states.Comment: 28 pages, 5 figures, revised versio
Lattice dynamics of the heavy fermion compound URuSi
We report a comprehensive investigation of the lattice dynamics of
URuSi as a function of temperature using Raman scattering, optical
conductivity and inelastic neutron scattering measurements as well as
theoretical {\it ab initio} calculations. The main effects on the optical
phonon modes are related to Kondo physics. The B ( symmetry)
phonon mode slightly softens below 100~K, in connection with the
previously reported softening of the elastic constant, , of the
same symmetry, both observations suggesting a B symmetry-breaking
instability in the Kondo regime. Through optical conductivity, we detect clear
signatures of strong electron-phonon coupling, with temperature dependent
spectral weight and Fano line shape of some phonon modes. Surprisingly, the
line shapes of two phonon modes, E(1) and A(2), show opposite
temperature dependencies. The A(2) mode loses its Fano shape below 150
K, whereas the E(1) mode acquires it below 100~K, in the Kondo cross-over
regime. This may point out to momentum-dependent Kondo physics. By inelastic
neutron scattering measurements, we have drawn the full dispersion of the
phonon modes between 300~K and 2~K. No remarkable temperature dependence has
been obtained including through the hidden order transition. {\it Ab initio}
calculations with the spin-orbit coupling are in good agreement with the data
except for a few low energy branches with propagation in the (a,b) plane
EXPRESSÃO DAS CADERINAS NOS TUMORES MAMÁRIOS EM CADELAS
Mammary tumors are among the mostcommon neoplasia of canine females. The occurrenceof metastasis may be detected by proteic markers.Among them, exist the E-cadherin, a member ofcadherin family known for its important role in theregulation of intercellular adhesion in epithelial tissues.Studies suggest that E-cadherin may function as atumor and invasion suppressor molecule. Cadherinactivity is regulated by multiple mechanisms, includinginteraction with other proteins such as catenins. In thisreview, the authors approach the cadherin family andother related adhesion proteins including its function,physiopathology and potential use as marker fordiagnosis and prognosis of canine mammary tumors.Key words: cadherin, immunohistochemistry,As neoplasias mamárias são as que maisacometem as cadelas. O desenvolvimento do câncerpode levar à ocorrência de metástases que podemser detectadas por marcadores protéicos. Um destesmarcadores é a E-caderina, um membro da famíliadas caderinas conhecida por desempenhar um papelimportante na regulação da adesão intercelular emtecidos epiteliais. Estudos apontam que as E-caderinaspodem funcionar como moléculas supressorasde tumor e de invasão. A atividade das caderinas éregulada por múltiplos mecanismos, incluindo a interaçãocom outras proteínas como as cateninas. Nestarevisão os autores abordam a família das caderinas,incluindo sua função, fisiopatologia e potencial usocomo marcadores de diagnóstico e prognóstico nasneoplasias mamárias na cadela
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