33,940 research outputs found

### First-principles prediction of redox potentials in transition-metal compounds with LDA+U

First-principles calculations within the Local Density Approximation (LDA) or
Generalized Gradient Approximation (GGA), though very successful, are known to
underestimate redox potentials, such as those at which lithium intercalates in
transition metal compounds. We argue that this inaccuracy is related to the
lack of cancellation of electron self-interaction errors in LDA/GGA and can be
improved by using the DFT+$U$ method with a self-consistent evaluation of the
$U$ parameter. We show that, using this approach, the experimental lithium
intercalation voltages of a number of transition metal compounds, including the
olivine Li$_{x}$MPO$_{4}$ (M=Mn, Fe Co, Ni), layered Li$_{x}$MO$_{2}$ ($x=$Co,
Ni) and spinel-like Li$_{x}$M$_{2}$O$_{4}$ (M=Mn, Co), can be reproduced
accurately.Comment: 19 pages, 6 figures, Phys. Rev. B 70, 235121 (2004

### Theory of the cold collision frequency shift in 1S--2S spectroscopy of Bose-Einstein-condensed and non-condensed hydrogen

We show that a correct formulation of the cold collision frequency shift for
two photon spectroscopy of Bose-condensed and cold non-Bose-condensed hydrogen
is consistent with experimental data. Our treatment includes transport and
inhomogeneity into the theory of a non-condensed gas, which causes substantial
changes in the cold collision frequency shift for the ordinary thermal gas, as
a result of the very high frequency (3.9kHz) of transverse trap mode. For the
condensed gas, we find substantial corrections arise from the inclusion of
quasiparticles, whose number is very large because of the very low frequency
(10.2Hz) of the longitudinal trap mode. These two effects together account for
the apparent absence of a "factor of two" between the two possibilities.
Our treatment considers only the Doppler-free measurements, but could be
extended to Doppler-sensitive measurements. For Bose-condensed hydrogen, we
predict a characteristic "foot" extending into higher detunings than can arise
from the condensate alone, as a result of a correct treatment of the statistics
of thermal quasiparticles.Comment: 16 page J Phys B format plus 6 postscript figure

### Arcuate nucleus homeostatic systems reflect blood leptin concentration but not feeding behaviour during scheduled feeding on a high-fat diet in mice

Acknowledgements T.B. was funded by a CASE studentship from the BBSRC and AstraZeneca. J.B. was a summer student from Bordeaux Sciences Agro and funded by student laboratory experience grant from the British Society of Neuroendocrinology. The authors are also grateful for funding from the Scottish Government, and from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreements 266408 (Full4Health) and 245009 (NeuroFAST).Peer reviewedPublisher PD

### Exact relativistic treatment of stationary counter-rotating dust disks III. Physical Properties

This is the third in a series of papers on the construction of explicit
solutions to the stationary axisymmetric Einstein equations which can be
interpreted as counter-rotating disks of dust. We discuss the physical
properties of a class of solutions to the Einstein equations for disks with
constant angular velocity and constant relative density which was constructed
in the first part. The metric for these spacetimes is given in terms of theta
functions on a Riemann surface of genus 2. It is parameterized by two physical
parameters, the central redshift and the relative density of the two
counter-rotating streams in the disk. We discuss the dependence of the metric
on these parameters using a combination of analytical and numerical methods.
Interesting limiting cases are the Maclaurin disk in the Newtonian limit, the
static limit which gives a solution of the Morgan and Morgan class and the
limit of a disk without counter-rotation. We study the mass and the angular
momentum of the spacetime. At the disk we discuss the energy-momentum tensor,
i.e. the angular velocities of the dust streams and the energy density of the
disk. The solutions have ergospheres in strongly relativistic situations. The
ultrarelativistic limit of the solution in which the central redshift diverges
is discussed in detail: In the case of two counter-rotating dust components in
the disk, the solutions describe a disk with diverging central density but
finite mass. In the case of a disk made up of one component, the exterior of
the disks can be interpreted as the extreme Kerr solution.Comment: 30 pages, 20 figures; to appear in Phys. Rev.

### Antiproton-Hydrogen annihilation at sub-kelvin temperatures

The main properties of the interaction of ultra low-energy antiprotons ($%
E\le10^{-6}$ a.u.) with atomic hydrogen are established. They include the
elastic and inelastic cross sections and Protonium (Pn) formation spectrum. The
inverse Auger process ($Pn+e \to H+\bar{p}$) is taken into account in the
framework of an unitary coupled-channels model. The annihilation cross-section
is found to be several times smaller than the predictions made by the black
sphere absorption models. A family of $\bar{p}H$ nearthreshold metastable
states is predicited. The dependence of Protonium formation probability on the
position of such nearthreshold S-matrix singularities is analysed. An
estimation for the $H\bar{H}$ annihilation cross section is obtained.Comment: latex.tar.gz file, 22 pages, 9 figure

### On the structure of the scalar mesons $f_0(975)$ and $a_0(980)$

We investigate the structure of the scalar mesons $f_0(975)$ and $a_0(980)$
within realistic meson-exchange models of the $\pi\pi$ and $\pi\eta$
interactions. Starting from a modified version of the J\"ulich model for
$\pi\pi$ scattering we perform an analysis of the pole structure of the
resulting scattering amplitude and find, in contrast to existing models, a
somewhat large mass for the $f_0(975)$ ($m_{f_0}=1015$ MeV, $\Gamma_{f_0}=30$
MeV). It is shown that our model provides a description of
$J/\psi\rightarrow\phi\pi\pi/\phi KK$ data comparable in quality with those of
alternative models. Furthermore, the formalism developed for the $\pi\pi$
system is consistently extended to the $\pi\eta$ interaction leading to a
description of the $a_0(980)$ as a dynamically generated threshold effect
(which is therefore neither a conventional $q\overline{q}$ state nor a
$K\overline{K}$ bound state). Exploring the corresponding pole position the
$a_0(980)$ is found to be rather broad ($m_{a_0}=991$ MeV, $\Gamma_{a_0}=202$
MeV). The experimentally observed smaller width results from the influence of
the nearby $K\overline{K}$ threshold on this pole.Comment: 25 pages, 15 Postscript figure

### Invariance of the correlation energy at high density and large dimension in two-electron systems

We prove that, in the large-dimension limit, the high-density correlation
energy \Ec of two opposite-spin electrons confined in a $D$-dimensional space
and interacting {\em via} a Coulomb potential is given by \Ec \sim -1/(8D^2)
for any radial confining potential $V(r)$. This result explains the observed
similarity of \Ec in a variety of two-electron systems in three-dimensional
space.Comment: 4 pages, 1 figure, to appear in Phys. Rev. Let

### A simplified protocol for detecting two systemic bait markers (Rhodamine B and iophenoxic acid) in small mammals

We developed a method of quantifying levels of fluorescence in the whiskers of wild stoats (Mustela erminea) using fluorescence microscopy and Axiovision 3.0.6.1 software. The method allows for discrimination between natural fluorescence present in or on a whisker, and the fluorescence resulting from the ingestion of the systemic marker Rhodamine B (RB), although some visual judgement is still required. We also developed a new high performance liquid chromatography (HPLC) protocol for detecting the systemic marker iophenoxic acid (IPA) in the blood of laboratory rats (Rattus norvegicus) and wild stoats. With this method, the blood of an animal that has consumed IPA can be tested for the presence of the foreign IPA compound itself. This is a more reliable test than the previous method, which measured the raised level of natural blood protein-bound iodine correlated with IPA absorption. The quantity of blood required from animal subjects is very small (10 ÎŒl), so the testing is less intrusive and the method can be extended to smaller species. The extraction technique uses methanol, rather than acids and heavy metal salts, thereby simplifying the procedure. Recovery of IPA is quantitative, giving a highly reliable reading. In experiments on captive rats the IPA method proved successful. Of 12 positively marked carcasses, two that had not been frozen for the 24 h before blood samples were taken showed relatively lower IPA levels. The same IPA detection method, as well as the whisker analysis for RB, was applied successfully to a population of wild stoats to which both Rhodamine B and IPA were made available at bait stations. The presence of both bait markers was detectable in rats for at least 21 days and in stoats for at least 27 days

### Vibration isolation in a free-piston driven Expansion tube

The stress waves produced by rapid piston deceleration are a fundamental feature of free-piston driven expansion tubes, and wave propagation has to be considered in the design process. For lower enthalpy test conditions, these waves can traverse the tube ahead of critical flow processes, severely interfering with static pressure measurements of the passing flow. This paper details a new device which decouples the driven tube from the free-piston driver, and thus prevents transmission of stress waves. Following successful incorporation of the concept in the smaller X2 facility, it has now been applied to the larger X3 facility, and results for both facilities are presented

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