757 research outputs found
Coherent Neutral Current Neutrino-Nucleus Scattering at a Spallation Source; a Valuable Experimental Probe
The coherent contribution of all neutrons in neutrino nucleus scattering due
to the neutral current is examined considering the Spallation Neutron Source
(SNS) as a source of neutrinos. SNS is a prolific pulsed source of electron and
muon neutrinos as well as muon antineutrinos.Comment: 15 LaTex pages, 14 figures, 3 Table
Suppression of Landau damping via electron band gap
The pondermotive potential in the X-ray Raman compression can generate an
electron band gap which suppresses the Landau damping. The regime is identified
where a Langmuir wave can be driven without damping in the stimulated Raman
compression. It is shown that the partial wave breaking and the frequency
detuning due to the trapped particles would be greatly reduced.Comment: 4 pages, 5 figure
MIMAC-He3 : A Micro-TPC Matrix of Chambers of He3 for direct detection of Wimps
The project of a micro-TPC matrix of chambers of \hetrois for direct
detection of non-baryonic dark matter is presented. The privileged properties
of He3 are highlighted. The double detection (ionization - projection of
tracks) is explained and its rejection evaluated. The potentialities of
MIMAC-He3 for supersymmetric dark matter search are discussed.Comment: to appear in Proc. of the 9th International Conference on Topics in
Astroparticle and Underground Physics (TAUP 2005), Zaragoza, Sept. 200
Measurement of the quenching factor of Na recoils in NaI(Tl)
Measurements of the quenching factor for sodium recoils in a 5 cm diameter
NaI(Tl) crystal at room temperature have been made at a dedicated neutron
facility at the University of Sheffield. The crystal has been exposed to 2.45
MeV mono-energetic neutrons generated by a Sodern GENIE 16 neutron generator,
yielding nuclear recoils of energies between 10 and 100 keVnr. A cylindrical
BC501A detector has been used to tag neutrons that scatter off sodium nuclei in
the crystal. Cuts on pulse shape and time of flight have been performed on
pulses recorded by an Acqiris DC265 digitiser with a 2 ns sampling time.
Measured quenching factors of Na nuclei range from 19% to 26% in good agreement
with other experiments, and a value of 25.2 \pm 6.4% has been determined for 10
keV sodium recoils. From pulse shape analysis, the mean times of pulses from
electron and nuclear recoils have been compared down to 2 keVee. The
experimental results are compared to those predicted by Lindhard theory,
simulated by the SRIM Monte Carlo code, and a preliminary curve calculated by
Prof. Akira Hitachi.Comment: 21 pages, 13 figure
Electron-Acoustic Phonon Energy Loss Rate in Multi-Component Electron Systems with Symmetric and Asymmetric Coupling Constants
We consider electron-phonon (\textit{e-ph}) energy loss rate in 3D and 2D
multi-component electron systems in semiconductors. We allow general asymmetry
in the \textit{e-ph} coupling constants (matrix elements), i.e., we allow that
the coupling depends on the electron sub-system index. We derive a
multi-component \textit{e-ph}power loss formula, which takes into account the
asymmetric coupling and links the total \textit{e-ph} energy loss rate to the
density response matrix of the total electron system. We write the density
response matrix within mean field approximation, which leads to coexistence of\
symmetric energy loss rate and asymmetric energy loss rate
with total energy loss rate at temperature
. The symmetric component F_{S}(T) F_{S}(T)\propto T^{n_{S}}n_{S}F_{A}(T). Screening strongly
reduces the symmetric coupling, but the asymmetric coupling is unscreened,
provided that the inter-sub-system Coulomb interactions are strong. The lack of
screening enhances and the total energy loss rate .
Especially, in the strong screening limit we find . A
canonical example of strongly asymmetric \textit{e-ph} matrix elements is the
deformation potential coupling in many-valley semiconductors.Comment: v2: Typos corrected. Some notations changed. Section III.C is
embedded in Section III.B. Paper accepted to PR
Donut and dynamic polarization effects in proton channeling through carbon nanotubes
We investigate the angular and spatial distributions of protons of the energy
of 0.223 MeV after channeling through an (11,~9) single-wall carbon nanotube of
the length of 0.2 m. The proton incident angle is varied between 0 and 10
mrad, being close to the critical angle for channeling. We show that, as the
proton incident angle increases and approaches the critical angle for
channeling, a ring-like structure is developed in the angular distribution -
donut effect. We demonstrate that it is the rainbow effect. When the proton
incident angle is between zero and a half of the critical angle for channeling,
the image force affects considerably the number and positions of the maxima of
the angular and spatial distributions. However, when the proton incident angle
is close to the critical angle for channeling, its influence on the angular and
spatial distributions is reduced strongly. We demonstrate that the increase of
the proton incident angle can lead to a significant rearrangement of the
propagating protons within the nanotube. This effect may be used to locate
atomic impurities in nanotubes as well as for creating nanosized proton beams
to be used in materials science, biology and medicine.Comment: 17 pages, 14 figure
Dispersion in a relativistic degenerate electron gas
Relativistic effects on dispersion in a degenerate electron gas are discussed
by comparing known response functions derived relativistically (by Jancovici)
and nonrelativistically (by Lindhard). The main distinguishing feature is
one-photon pair creation, which leads to logarithmic singularities in the
response functions. Dispersion curves for longitudinal waves have a similar
tongue-like appearance in the relativistic and nonrelativistic case, with the
main relativistic effects being on the Fermi speed and the cutoff frequency.
For transverse waves the nonrelativistic treatment has a nonphysical feature
near the cutoff frequency for large Fermi momenta, and this is attributed to an
incorrect treatment of the electron spin. We find (with two important provisos)
that one-photon pair creation is allowed in superdense plasmas, implying
relatively strong coupling between transverse waves and pair creation.Comment: 17 pages, 9 figures. Submitted to Physical Review
Orbital-Free Density Functional Theory: Kinetic Potentials and Ab-Initio Local Pseudopotentials
In the density functional (DF) theory of Kohn and Sham, the kinetic energy of
the ground state of a system of noninteracting electrons in a general external
field is calculated using a set of orbitals. Orbital free methods attempt to
calculate this directly from the electron density by approximating the
universal but unknown kinetic energy density functional. However simple local
approximations are inaccurate and it has proved very difficult to devise
generally accurate nonlocal approximations. We focus instead on the kinetic
potential, the functional derivative of the kinetic energy DF, which appears in
the Euler equation for the electron density. We argue that the kinetic
potential is more local and more amenable to simple physically motivated
approximations in many relevant cases, and describe two pathways by which the
value of the kinetic energy can be efficiently calculated. We propose two
nonlocal orbital free kinetic potentials that reduce to known exact forms for
both slowly varying and rapidly varying perturbations and also reproduce exact
results for the linear response of the density of the homogeneous system to
small perturbations. A simple and systematic approach for generating accurate
and weak ab-initio local pseudopotentials which produce a smooth slowly varying
valence component of the electron density is proposed for use in orbital free
DF calculations of molecules and solids. The use of these local
pseudopotentials further minimizes the possible errors from the kinetic
potentials. Our theory yields results for the total energies and ionization
energies of atoms, and for the shell structure in the atomic radial density
profiles that are in very good agreement with calculations using the full
Kohn-Sham theory.Comment: To be published in Phys. Rev.
Muon-Induced Background Study for an Argon-Based Long Baseline Neutrino Experiment
We evaluated rates of transversing muons, muon-induced fast neutrons, and
production of Cl and other cosmogenically produced nuclei that pose as
potential sources of background to the physics program proposed for an
argon-based long baseline neutrino experiment at the Sanford Underground
Research Facility (SURF). The Geant4 simulations were carried out with muons
and muon-induced neutrons for both 800 ft (0.712 km.w.e.) and 4850 ft levels
(4.3 km.w.e.). We developed analytic models to independently calculate the
Cl production using the measured muon fluxes at different levels of the
Homestake mine. The muon induced Cl production rates through stopped
muon capture and the muon-induced neutrons and protons via (n,p) and (p,n)
reactions were evaluated. We find that the Monte Carlo simulated production
rates of Cl agree well with the predictions from analytic models. A
depth-dependent parametrization was developed and benchmarked to the direct
analytic models. We conclude that the muon-induced processes will result in
large backgrounds to the physics proposed for an argon-based long baseline
neutrino experiment at a depth of less than 4.0 km.w.e.Comment: 12 pages, 15 figure
Classification of life by the mechanism of genome size evolution
The classification of life should be based upon the fundamental mechanism in
the evolution of life. We found that the global relationships among species
should be circular phylogeny, which is quite different from the common sense
based upon phylogenetic trees. The genealogical circles can be observed clearly
according to the analysis of protein length distributions of contemporary
species. Thus, we suggest that domains can be defined by distinguished
phylogenetic circles, which are global and stable characteristics of living
systems. The mechanism in genome size evolution has been clarified; hence main
component questions on C-value enigma can be explained. According to the
correlations and quasi-periodicity of protein length distributions, we can also
classify life into three domains.Comment: 53 pages, 9 figures, 2 table
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