2,122 research outputs found
Polarized Neutron Matter: A Lowest Order Constrained Variational Approach
In this paper, we calculate some of the polarized neutron matter properties,
using the lowest order constrained variational method with the
potential and employing a microscopic point of view. A comparison is also made
between our results and those of other many-body techniques.Comment: 23 pages, 8 figure
Using Synthetic Spacecraft Data to Interpret Compressible Fluctuations in Solar Wind Turbulence
Kinetic plasma theory is used to generate synthetic spacecraft data to
analyze and interpret the compressible fluctuations in the inertial range of
solar wind turbulence. The kinetic counterparts of the three familiar linear
MHD wave modes---the fast, Alfven, and slow waves---are identified and the
properties of the density-parallel magnetic field correlation for these kinetic
wave modes is presented. The construction of synthetic spacecraft data, based
on the quasi-linear premise---that some characteristics of magnetized plasma
turbulence can be usefully modeled as a collection of randomly phased, linear
wave modes---is described in detail. Theoretical predictions of the
density-parallel magnetic field correlation based on MHD and Vlasov-Maxwell
linear eigenfunctions are presented and compared to the observational
determination of this correlation based on 10 years of Wind spacecraft data. It
is demonstrated that MHD theory is inadequate to describe the compressible
turbulent fluctuations and that the observed density-parallel magnetic field
correlation is consistent with a statistically negligible kinetic fast wave
energy contribution for the large sample used in this study. A model of the
solar wind inertial range fluctuations is proposed comprised of a mixture of a
critically balanced distribution of incompressible Alfvenic fluctuations and a
critically balanced or more anisotropic than critical balance distribution of
compressible slow wave fluctuations. These results imply that there is little
or no transfer of large scale turbulent energy through the inertial range down
to whistler waves at small scales.Comment: Accepted to Astrophysical Journal. 28 pages, 7 figure
Kinetic Scale Density Fluctuations in the Solar Wind
We motivate the importance of studying kinetic scale turbulence for
understanding the macroscopic properties of the heliosphere, such as the
heating of the solar wind. We then discuss the technique by which kinetic scale
density fluctuations can be measured using the spacecraft potential, including
a calculation of the timescale for the spacecraft potential to react to the
density changes. Finally, we compare the shape of the density spectrum at ion
scales to theoretical predictions based on a cascade model for kinetic
turbulence. We conclude that the shape of the spectrum, including the ion scale
flattening, can be captured by the sum of passive density fluctuations at large
scales and kinetic Alfven wave turbulence at small scales
Spin-glass state and long-range magnetic order in Pb(Fe1/2Nb1/2)O3
We have investigated the magnetic ground-state of the multiferroic relaxor
ferroelectric \pfn with SR spectroscopy and neutron scattering. We find
that a transition to a partially disordered phase occurs below T=20 K that
coexists with long-range antiferromagnetic ordering. The disordered phase
resembles a spin-glass. No clustering of magnetic ions could be evidenced by
SR so that the coexistence appears homogeneous in the sample
Divergence in Dialogue
Copyright: 2014 Healey et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.This work was supported by the Economic and Social Research Council (ESRC; http://www.esrc.ac.uk/) through the DynDial project (Dynamics of Conversational Dialogue, RES-062-23-0962) and the Engineering and Physical Sciences Research Council (EPSRC; http://www.epsrc.ac.uk/) through the RISER
project (Robust Incremental Semantic Resources for Dialogue, EP/J010383/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Phase I and pharmacological study of the farnesyltransferase inhibitor tipifarnib (Zarnestra®, R115777) in combination with gemcitabine and cisplatin in patients with advanced solid tumours
This phase I trial was designed to determine the safety and maximum tolerated dose (MTD) of tipifarnib in combination with gemcitabine and cisplatin in patients with advanced solid tumours. Furthermore, the pharmacokinetics of each of these agents was evaluated. Patients were treated with tipifarnib b.i.d. on days 1–7 of each 21-day cycle. In addition, gemcitabine was given as a 30-min i.v. infusion on days 1 and 8 and cisplatin as a 3-h i.v. infusion on day 1. An interpatient dose-escalation scheme was used. Pharmacokinetics was determined in plasma and white blood cells. In total, 31 patients were included at five dose levels. Dose-limiting toxicities (DLTs) consisted of thrombocytopenia grade 4, neutropenia grade 4, febrile neutropenia grade 4, electrolyte imbalance grade 3, fatigue grade 3 and decreased hearing grade 2. The MTD was tipifarnib 200 mg b.i.d., gemcitabine 1000 mg m−2 and cisplatin 75 mg m−2. Eight patients had a confirmed partial response and 12 patients stable disease. No clinically relevant pharmacokinetic interactions were observed. Tipifarnib can be administered safely at 200 mg b.i.d. in combination with gemcitabine 1000 mg m−2 and cisplatin 75 mg m−2. This combination showed evidence of antitumour activity and warrants further evaluation in a phase II setting
Astrophysical Gyrokinetics: Basic Equations and Linear Theory
Magnetohydrodynamic (MHD) turbulence is encountered in a wide variety of
astrophysical plasmas, including accretion disks, the solar wind, and the
interstellar and intracluster medium. On small scales, this turbulence is often
expected to consist of highly anisotropic fluctuations with frequencies small
compared to the ion cyclotron frequency. For a number of applications, the
small scales are also collisionless, so a kinetic treatment of the turbulence
is necessary. We show that this anisotropic turbulence is well described by a
low frequency expansion of the kinetic theory called gyrokinetics. This paper
is the first in a series to examine turbulent astrophysical plasmas in the
gyrokinetic limit. We derive and explain the nonlinear gyrokinetic equations
and explore the linear properties of gyrokinetics as a prelude to nonlinear
simulations. The linear dispersion relation for gyrokinetics is obtained and
its solutions are compared to those of hot-plasma kinetic theory. These results
are used to validate the performance of the gyrokinetic simulation code {\tt
GS2} in the parameter regimes relevant for astrophysical plasmas. New results
on global energy conservation in gyrokinetics are also derived. We briefly
outline several of the problems to be addressed by future nonlinear
simulations, including particle heating by turbulence in hot accretion flows
and in the solar wind, the magnetic and electric field power spectra in the
solar wind, and the origin of small-scale density fluctuations in the
interstellar medium.Comment: emulateapj, 24 pages, 10 figures, revised submission to ApJ:
references added, typos corrected, reorganized and streamline
Nonequilibrium Forces Between Neutral Atoms Mediated by a Quantum Field
We study all known and as yet unknown forces between two neutral atoms,
modeled as three dimensional harmonic oscillators, arising from mutual
influences mediated by an electromagnetic field but not from their direct
interactions. We allow as dynamical variables the center of mass motion of the
atom, its internal degrees of freedom and the quantum field treated
relativistically. We adopt the method of nonequilibrium quantum field theory
which can provide a first principle, systematic and unified description
including the intrinsic field fluctuations and induced dipole fluctuations. The
inclusion of self-consistent back-actions makes possible a fully dynamical
description of these forces valid for general atom motion. In thermal
equilibrium we recover the known forces -- London, van der Waals and
Casimir-Polder forces -- between neutral atoms in the long-time limit but also
discover the existence of two new types of interatomic forces. The first, a
`nonequilibrium force', arises when the field and atoms are not in thermal
equilibrium, and the second, which we call an `entanglement force', originates
from the correlations of the internal degrees of freedom of entangled atoms.Comment: 16 pages, 2 figure
Exploring Neutron-Rich Oxygen Isotopes with MoNA
The Modular Neutron Array (MoNA) was used in conjunction with a large-gap
dipole magnet (Sweeper) to measure neutron-unbound states in oxygen isotopes
close to the neutron dripline. While no excited states were observed in 24O, a
resonance at 45(2) keV above the neutron separation energy was observed in 23O.Comment: 6 pages, 4 Figures, submitted to Proc. Int. Conf. on Proton Emitting
Nuclei and Related Topics, PROCON0
- …