385,582 research outputs found
Gluon-gluon contributions to the production of continuum diphoton pairs at hadron colliders
We compute the contributions to continuum photon pair production at hadron
colliders from processes initiated by gluon-gluon and gluon-quark scattering
into two photons through a four-leg virtual quark loop. Complete two-loop cross
sections in perturbative quantum chromodynamics are combined with contributions
from soft parton radiation resummed to all orders in the strong coupling
strength. The structure of the resummed cross section is examined in detail,
including a new type of unintegrated parton distribution function affecting
azimuthal angle distributions of photons in the pair's rest frame. As a result
of this analysis, we predict diphoton transverse momentum distributions in
gluon-gluon scattering in wide ranges of kinematic parameters at the Fermilab
Tevatron collider and the CERN Large Hadron Collider.Comment: 28 pages, 11 figures; published versio
DLC2 modulates angiogenic responses in vascular endothelial cells by regulating cell attachment and migration.
Deleted in liver cancer 1 (DLC1) is a RhoGTPase activation protein-containing tumor suppressor that associates with various types of cancer. Although DLC2 shares a similar domain structure with that of DLC1, the function of DLC2 is not well characterized. Here, we describe the expression and ablation of DLC2 in mice using a reporter-knockout approach. DLC2 is expressed in several tissues and in endothelial cells (ECs) of blood vessels. Although ECs and blood vessels show no histological abnormalities and mice appear overall healthy, DLC2-mutant mice display enhanced angiogenic responses induced by matrigel and by tumor cells. Silencing of DLC2 in human ECs has reduced cell attachment, increased migration, and tube formation. These changes are rescued by silencing of RhoA, suggesting that the process is RhoA pathway dependent. These results indicate that DLC2 is not required for mouse development and normal vessel formation, but may protect mouse from unwanted angiogenesis induced by, for example, tumor cells
Anomalous thermopower and Nernst effect in : entropy-current loss in precursor state
The heavy-electron superconductor CeCoIn exhibits a puzzling precursor
state above its superconducting critical temperature at = 2.3 K. The
thermopower and Nernst signal are anomalous. Below 15 K, the entropy current of
the electrons undergoes a steep decrease reaching 0 at .
Concurrently, the off-diagonal thermoelectric current is
enhanced. The delicate sensitivity of the zero-entropy state to field implies
phase coherence over large distances. The prominent anomalies in the
thermoelectric current contrast with the relatively weak effects in the
resistivity and magnetization.Comment: 5 figures, 4 page
Observation of Landau quantization and standing waves in HfSiS
Recently, HfSiS was found to be a new type of Dirac semimetal with a line of
Dirac nodes in the band structure. Meanwhile, Rashba-split surface states are
also pronounced in this compound. Here we report a systematic study of HfSiS by
scanning tunneling microscopy/spectroscopy at low temperature and high magnetic
field. The Rashba-split surface states are characterized by measuring Landau
quantization and standing waves, which reveal a quasi-linear dispersive band
structure. First-principles calculations based on density-functional theory are
conducted and compared with the experimental results. Based on these
investigations, the properties of the Rashba-split surface states and their
interplay with defects and collective modes are discussed.Comment: 6 pages, 5 figure
Magnetoelectricity and Magnetostriction due to the Rare Earth Moment in TmAl(BO)
The magnetic properties, the magnetostriction, and the magnetoelectric effect
in the d-electron free rare-earth aluminum borate TmAl(BO) are
investigated between room temperature and 2 K. The magnetic susceptibility
reveals a strong anisotropy with the hexagonal c-axis as the hard magnetic
axis. Magnetostriction measurements show a large effect of an in-plane field
reducing both, the a- and c-axis lattice parameters. The magnetoelectric
polarization change in a- and c-directions reaches up to 300 C/m at 70
kOe with the field applied along the a-axis. The magnetoelectric polarization
is proportional to the lattice contraction in magnetic field. The results of
this investigation prove the existence of a significant coupling between the
rare earth magnetic moment and the lattice in Al(BO) compounds
( = rare earth). They further show that the rare earth moment itself will
generate a large magnetoelectric effect which makes it easier to study and to
understand the origin of the magnetoelectric interaction in this class of
materials.Comment: 4 pages, 5 figure
Universality Class of Ferromagnetic Transition in Three-Dimensional Double-Exchange System - O(N) Monte Carlo Study -
Curie temperature and exponents are studied for the three-dimensional
double-exchange model. Applying the O(N) Monte Carlo algorithm, we perform
systematic finite-size scaling analyses on the data up to sites. The
obtained values of the critical exponents are consistent with those of the
Heisenberg universality class, and clearly distinct from the mean-field values.Comment: 3 pages including 2 figure
Kondo Insulator description of spin state transition in FeSb2
The thermal expansion and heat capacity of FeSb2 at ambient pressure agrees
with a picture of a temperature induced spin state transition within the Fe
t_{2g} multiplet. However, high pressure powder diffraction data show no sign
of a structural phase transition up to 7GPa. A bulk modulus B=84(3)GPa has been
extracted and the temperature dependence of the Gruneisen parameter has been
determined. We discuss here the relevance of a Kondo insulator description for
this material.Comment: Physical Review B in press (2005
Polarimetric variations of binary stars. II. Numerical simulations for circular and eccentric binaries in Mie scattering envelopes
We present numerical simulations of the periodic polarimetric variations
produced by a binary star placed at the center of an empty spherical cavity
inside a circumbinary ellipsoidal and optically thin envelope made of dust
grains. Mie single-scattering is considered along with pre- and post-scattering
extinction factors which produce a time-varying optical depth and affect the
morphology of the periodic variations. We are interested in the effects that
various parameters will have on the average polarization, the amplitude of the
polarimetric variations, and the morphology of the variability. We show that
the absolute amplitudes of the variations are smaller for Mie scattering than
for Thomson scattering. Among the four grain types that we have studied, the
highest polarizations are produced by grains with sizes in the range 0.1-0.2
micron. In general, the variations are seen twice per orbit. In some cases,
because spherical dust grains have an asymmetric scattering function, the
polarimetric curves produced also show variations seen once per orbit.
Circumstellar disks produce polarimetric variations of greater amplitude than
circumbinary envelopes.
Another goal of these simulations is to see if the 1978 BME (Brown, McLean, &
Emslie, ApJ, 68, 415) formalism, which uses a Fourier analysis of the
polarimetric variations to find the orbital inclination for Thomson-scattering
envelopes, can still be used for Mie scattering. We find that this is the case,
if the amplitude of the variations is sufficient and the true inclinations is
i_true > 45 deg. For eccentric orbits, the first-order coefficients of the
Fourier fit, instead of second-order ones, can be used to find almost all
inclinations.Comment: 23 pages, 5 figures, to be published in Astronomical Journa
Giant phonon anomalies in the pseudo-gap phase of TiOCl
We report infrared and Raman spectroscopy results of the spin-1/2 quantum
magnet TiOCl. Giant anomalies are found in the temperature dependence of the
phonon spectrum, which hint to unusual coupling of the electronic degrees of
freedom to the lattice. These anomalies develop over a broad temperature
interval, suggesting the presence of an extended fluctuation regime. This
defines a pseudo-gap phase, characterized by a local spin-gap. Below 100 K a
dimensionality cross-over leads to a dimerized ground state with a global
spin-gap of about 2~430 K.Comment: 4 pages, 3 figures, for further information see
http://www.peter-lemmens.d
- …