29,013 research outputs found
Mass Hierarchy Resolution in Reactor Anti-neutrino Experiments: Parameter Degeneracies and Detector Energy Response
Determination of the neutrino mass hierarchy using a reactor neutrino
experiment at 60 km is analyzed. Such a measurement is challenging due to
the finite detector resolution, the absolute energy scale calibration, as well
as the degeneracies caused by current experimental uncertainty of . The standard method is compared with a proposed Fourier
transformation method. In addition, we show that for such a measurement to
succeed, one must understand the non-linearity of the detector energy scale at
the level of a few tenths of percent.Comment: 7 pages, 6 figures, accepted by PR
Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems
All axisymmetric self-similar equilibria of self-gravitating, rotating,
isothermal systems are identified by solving the nonlinear Poisson equation
analytically. There are two families of equilibria: (1) Cylindrically symmetric
solutions in which the density varies with cylindrical radius as R^(-alpha),
with 0 <= alpha <= 2. (2) Axially symmetric solutions in which the density
varies as f(theta)/r^2, where `r' is the spherical radius and `theta' is the
co-latitude. The singular isothermal sphere is a special case of the latter
class with f(theta)=constant. The axially symmetric equilibrium configurations
form a two-parameter family of solutions and include equilibria which are
surprisingly asymmetric with respect to the equatorial plane. The asymmetric
equilibria are, however, not force-free at the singular points r=0, infinity,
and their relevance to real systems is unclear. For each hydrodynamic
equilibrium, we determine the phase-space distribution of the collisionless
analog.Comment: 13 pages, 7 figures, uses emulateapj.sty. Submitted to Ap
Semimetal to semimetal charge density wave transition in 1T-TiSe
We report an infrared study on 1-TiSe, the parent compound of the
newly discovered superconductor CuTiSe. Previous studies of this
compound have not conclusively resolved whether it is a semimetal or a
semiconductor: information that is important in determining the origin of its
unconventional CDW transition. Here we present optical spectroscopy results
that clearly reveal that the compound is metallic in both the high-temperature
normal phase and the low-temperature CDW phase. The carrier scattering rate is
dramatically different in the normal and CDW phases and the carrier density is
found to change with temperature. We conclude that the observed properties can
be explained within the scenario of an Overhauser-type CDW mechanism.Comment: 4 pages, 4 page
Prompt Iron Enrichment, Two r-Process Components, and Abundances in Very Metal-Poor Stars
We present a model to explain the wide range of abundances for heavy
r-process elements (mass number A > 130) at low [Fe/H]. This model requires
rapid star formation and/or an initial population of supermassive stars in the
earliest condensed clots of matter to provide a prompt or initial Fe inventory.
Subsequent Fe and r-process enrichment was provided by two types of supernovae:
one producing heavy r-elements with no Fe on a rather short timescale and the
other producing light r-elements (A < or = 130) with Fe on a much longer
timescale.Comment: 5 pages, 2 postscript figures, to appear in ApJ
SS Ari: a shallow-contact close binary system
Two CCD epochs of light minimum and a complete R light curve of SS Ari are
presented. The light curve obtained in 2007 was analyzed with the 2003 version
of the W-D code. It is shown that SS Ari is a shallow contact binary system
with a mass ratio and a degree of contact factor f=9.4(\pm0.8%). A
period investigation based on all available data shows that there may exist two
distinct solutions about the assumed third body. One, assuming eccentric orbit
of the third body and constant orbital period of the eclipsing pair results in
a massive third body with and P_3=87.00.278M_{\odot}$. Both of the cases
suggest the presence of an unseen third component in the system.Comment: 28 pages, 9 figures and 5 table
Anomalous metallic state of CuTiSe: an optical spectroscopy study
We report an optical spectroscopy study on the newly discovered
superconductor CuTiSe. Consistent with the development from a
semimetal or semiconductor with a very small indirect energy gap upon doping
TiSe, it is found that the compound has a low carrier density. Most
remarkably, the study reveals a substantial shift of the "screened" plasma edge
in reflectance towards high energy with decreasing temperature. This
phenomenon, rarely seen in metals, indicates either a sizeable increase of the
conducting carrier concentration or/and a decrease of the effective mass of
carriers with reducing temperature. We attribute the shift primarily to the
later effect.Comment: 4 figures, 4+ page
Non-local means based Rician noise filtering for diffusion tensor and kurtosis imaging in human brain and spinal cord
Background: To investigate the effect of using a Rician nonlocal means (NLM) filter on quantification of diffusion tensor (DT)- and diffusion kurtosis (DK)-derived metrics in various anatomical regions of the human brain and the spinal cord, when combined with a constrained linear least squares (CLLS) approach. /
Methods: Prospective brain data from 9 healthy subjects and retrospective spinal cord data from 5 healthy subjects from a 3 T MRI scanner were included in the study. Prior to tensor estimation, registered diffusion weighted images were denoised by an optimized blockwise NLM filter with CLLS. Mean kurtosis (MK), radial kurtosis (RK), axial kurtosis (AK), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD) and fractional anisotropy (FA), were determined in anatomical structures of the brain and the spinal cord. DTI and DKI metrics, signal-to-noise ratio (SNR) and Chi-square values were quantified in distinct anatomical regions for all subjects, with and without Rician denoising. /
Results: The averaged SNR significantly increased with Rician denoising by a factor of 2 while the averaged Chi-square values significantly decreased up to 61% in the brain and up to 43% in the spinal cord after Rician NLM filtering. In the brain, the mean MK varied from 0.70 (putamen) to 1.27 (internal capsule) while AK and RK varied from 0.58 (corpus callosum) to 0.92 (cingulum) and from 0.70 (putamen) to 1.98 (corpus callosum), respectively. In the spinal cord, FA varied from 0.78 in lateral column to 0.81 in dorsal column while MD varied from 0.91 × 10−3 mm2/s (lateral) to 0.93 × 10−3 mm2/s (dorsal). RD varied from 0.34 × 10−3 mm2/s (dorsal) to 0.38 × 10−3 mm2/s (lateral) and AD varied from 1.96 × 10−3 mm2/s (lateral) to 2.11 × 10−3 mm2/s (dorsal). /
Conclusions: Our results show a Rician denoising NLM filter incorporated with CLLS significantly increases SNR and reduces estimation errors of DT- and KT-derived metrics, providing the reliable metrics estimation with adequate SNR levels
Low-lying quasiparticle states and hidden collective charge instabilities in parent cobaltate superconductors (NaxCoO2)
We report a state-of-the-art photoemission (ARPES) study of high quality
single crystals of the NaxCoO2 series focusing on the fine details of the
low-energy states. The Fermi velocity is found to be small (< 0.5 eV.A) and
only weakly anisotropic over the Fermi surface at all dopings setting the size
of the pair wavefunction to be on the order of 10-20 nanometers. In the low
doping regime the exchange inter-layer splitting vanishes and two dimensional
collective instabilities such as 120-type fluctuations become kinematically
allowed. Our results suggest that the unusually small Fermi velocity and the
unique symmetry of kinematic instabilities distinguish cobaltates from other
unconventional oxide superconductors such as the cuprates or the ruthenates.Comment: Accepted for publication in Phys. Rev. Lett. (2006
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