799 research outputs found
Direct kinetic energy extraction from neutron Compton profiles
Deep inelastic neutron scattering experiments provide access to atomic
momentum distributions and mean kinetic energies. These quantities are
intimately connected to nuclear quantum effects associated to the
equilibrium ground state of condensed systems. The method to derive the
single particle mean kinetic energy, directly employing the sum rules
associated to the scattering functions, from a set of deep inelastic
neutron scattering spectra is discussed. This method does not make use
of nonlinear fitting of the scattering spectr
Constant-q data representation in Neutron Compton scattering on the VESUVIO spectrometer
Standard data analysis on the VESUVIO spectrometer at ISIS is carried
out within the Impulse Approximation framework, making use of the West
scaling variable y. The experiments are performed using the
time-of-flight technique with the detectors positioned at constant
scattering angles. Line shape analysis is routinely performed in the
y-scaling framework, using two different (and equivalent) approaches:
(I) fitting the parameters of the recoil peaks directly to fixed-angle
time-of-flight spectral (2) transforming the time-of-flight spectra into
fixed-angle y spectra, referred to as the Neutron Compton Profiles, and
then fitting the line shape parameters. The present work shows that
scattering signals from different fixed-angle detectors can be collected
and rebinned to obtain Neutron Compton Profiles at constant wave vector
transfer, q, allowing for a suitable interpretation of data in terms of
the dynamical structure factor, S(q, w). The current limits of
applicability of such a procedure are discussed in terms of the
available q-range and relative uncertainties for the VESUVIO
experimental set up and of the main approximations involved. (C) 2008
Elsevier B.V. All rights reserved
Extensions and block decompositions for finite-dimensional representations of equivariant map algebras
Suppose a finite group acts on a scheme and a finite-dimensional Lie
algebra . The associated equivariant map algebra is the Lie
algebra of equivariant regular maps from to . The irreducible
finite-dimensional representations of these algebras were classified in
previous work with P. Senesi, where it was shown that they are all tensor
products of evaluation representations and one-dimensional representations. In
the current paper, we describe the extensions between irreducible
finite-dimensional representations of an equivariant map algebra in the case
that is an affine scheme of finite type and is reductive.
This allows us to also describe explicitly the blocks of the category of
finite-dimensional representations in terms of spectral characters, whose
definition we extend to this general setting. Applying our results to the case
of generalized current algebras (the case where the group acting is trivial),
we recover known results but with very different proofs. For (twisted) loop
algebras, we recover known results on block decompositions (again with very
different proofs) and new explicit formulas for extensions. Finally,
specializing our results to the case of (twisted) multiloop algebras and
generalized Onsager algebras yields previously unknown results on both
extensions and block decompositions.Comment: 41 pages; v2: minor corrections, formatting changed to match
published versio
Temperature dependence of the zero point kinetic energy in ice and water above room temperature
By means of Deep Inelastic Neutron Scattering we determined the temperature dependence of the proton kinetic energy in polycrystalline ice Ih between 5 K and 271 K. We compare our results with predictions form Path Integral quantum simulations and semiclassical quasi-harmonic models with phase-dependent frequencies. The latter show the best agreement with the experiment if the librational contribution is properly taken into account. The kinetic energy increase with temperature in ice is also found to be approximately a factor ∼ 5 smaller than in the case of liquid water above room temperature, highlighting the role played by anharmonic quantum fluctuations in the two phases
Formalism for obtaining nuclear momentum distributions by the Deep Inelastic Neutron Scattering technique
We present a new formalism to obtain momentum distributions in condensed
matter from Neutron Compton Profiles measured by the Deep Inelastic Neutron
Scattering technique. The formalism describes exactly the Neutron Compton
Profiles as an integral in the momentum variable . As a result we obtain a
Volterra equation of the first kind that relates the experimentally measured
magnitude with the momentum distributions of the nuclei in the sample. The
integration kernel is related with the incident neutron spectrum, the total
cross section of the filter analyzer and the detectors efficiency function. A
comparison of the present formalism with the customarily employed approximation
based on a convolution of the momentum distribution with a resolution function
is presented. We describe the inaccuracies that the use of this approximation
produces, and propose a new data treatment procedure based on the present
formalism.Comment: 11 pages, 8 figure
"Localization of inclusions in multiple prompt gamma ray analysis: a feasibility study"
We investigate the feasibility of using low energy gamma rays from neutron capture to localize slabs inside samples. A new system based on two gamma ray detectors with 2D collimators to be tested at the INES beamline at the pulsed neutron source ISIS (Oxford, UK) is described. The system provides a localization of slabs inside extended samples by using gamma ray self-absorption. Geant4 Monte Carlo simulations of the beamline were carried out to model gamma spectra from test samples
Pulsed neutron gamma-ray logging in archaeological site survey
An archaeological survey method based on neutron gamma-ray logging is described. The method relies on the measurement of capture gamma radiation induced by neutron irradiation from a pulsed generator. This technique provides elemental information on the irradiated zone by spectroscopic analysis of the gamma-ray data. This approach has been studied with Geant4 Monte Carlo simulations. In particular, irradiation volume for a deuterium–deuterium and deuterium–tritium (D-T) neutron generator and sampling volume for the D-T source were estimated. In addition, a neutron log response, which illustrates the capability of the neutron tool to localize artifacts lying beneath the surface, is shown
Proton momentum distribution in a protein hydration shell
The momentum distribution of protons in the hydration shell of a
globular protein has been measured through deep inelastic neutron
scattering at 180 and 290 K, below and above the crossover temperature
T-c=1.23T(g), where T-g=219 K is the glass transition temperature. It is
found that the mean kinetic energy of the water hydrogens shows no
temperature dependence, but the measurements are accurate enough to
indicate a sensible change of momentum distribution and effective
potential felt by protons, compatible with the transition from a single
to a double potential well. This could support the presence of tunneling
effects even at room temperature, playing an important role in
biological function
THE ROLE OF NUCLEOSIDE TRIPHOSPHATES IN CONTROL OF 3'-AMP AND 5'-AMP DEPHOSPHORYLATION IN CRUDE EXTRACTS OF B-SUBTILIS
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