1,631 research outputs found
Inclusive Quasi-Elastic Charged-Current Neutrino-Nucleus Reactions
The Quasi-Elastic (QE) contribution of the nuclear inclusive electron
scattering model developed in Nucl. Phys. A627 (1997) 543 is extended to the
study of electroweak Charged Current (CC) induced nuclear reactions, at
intermediate energies of interest for future neutrino oscillation experiments.
The model accounts for, among other nuclear effects, long range nuclear (RPA)
correlations, Final State Interaction (FSI) and Coulomb corrections.
Predictions for the inclusive muon capture in C and the reaction
C near threshold are also given. RPA correlations are
shown to play a crucial role and their inclusion leads to one of the best
existing simultaneous description of both processes, with accuracies of the
order of 10-15% per cent for the muon capture rate and even better for the LSND
measurement.Comment: 31 pages and 14 figures, accepted for publication as a regular
article in Physical Review
The thermodynamics of general anesthesia
It is known that the action of general anesthetics is proportional to their
partition coefficient in lipid membranes (Meyer-Overton rule). This solubility
is, however, directly related to the depression of the temperature of the
melting transition found close to body temperature in biomembranes. We propose
a thermodynamic extension of the Meyer-Overton rule which is based on free
energy changes in the system and thus automatically incorporates the effects of
melting point depression. This model provides a quantitative explanation of the
pressure reversal of anesthesia. Further, it explains why inflammation and the
addition of divalent cations reduce the effectiveness of anesthesia.Comment: 7 pages, 2 figure
The beta-decay of 22Al
In an experiment performed at the LISE3 facility of GANIL, we studied the
decay of 22Al produced by the fragmentation of a 36Ar primary beam. A
beta-decay half-life of 91.1 +- 0.5 ms was measured. The beta-delayed one- and
two-proton emission as well as beta-alpha and beta-delayed gamma decays were
measured and allowed us to establish a partial decay scheme for this nucleus.
New levels were determined in the daughter nucleus 22Mg. The comparison with
model calculations strongly favours a spin-parity of 4+ for the ground state of
22Al
Observation of beta decay of In-115 to the first excited level of Sn-115
In the context of the LENS R&D solar neutrino project, the gamma spectrum of
a sample of metallic indium was measured using a single experimental setup of 4
HP-Ge detectors located underground at the Gran Sasso National Laboratories
(LNGS), Italy. A gamma line at the energy (497.48 +/- 0.21) keV was found that
is not present in the background spectrum and that can be identified as a gamma
quantum following the beta decay of In-115 to the first excited state of Sn-115
(9/2+ --> 3/2+). This decay channel of In-115, which is reported here for the
first time, has an extremely low Q-value, Q = (2 +/- 4) keV, and has a much
lower probability than the well-known ground state-ground state transition,
being the branching ratio b = (1.18 +/- 0.31) 10^-6. This could be the beta
decay with the lowest known Q-value. The limit on charge non-conserving beta
decay of In-115 is set at 90% C.L. as tau > 4.1 10^20 y.Comment: 19 pages, 5 figures, 2 table
Quasi Free 238U (e,e'f)-Cross Section in Macroscopic-Microscopic Approach
We present the result of a theoretical study of inclusive quasi free
electrofission of U. The off-shell cross sections for the quasi free
reaction stage have been calculated within the Plane Wave Impulse Approximation
(PWIA), using a Macroscopic -Microscopic description of the proton and neutron
single particle momentum distributions. Electron wave function distortion
corrections were included using the effective momentum approximation, and the
Final State Interaction (FSI) effects were calculated using an optical
potential. The fissility for the proton single hole excited states of the
residual nucleus Pa was calculated both without and with contributions
of the pre-equilibrium emission of the particles. The fissility for
residual nuclei was calculated within the compound nucleus model.
The cross sections thus obtained were compared with available
experimental data.Comment: 26 pages, 7 figure
Phenomenological description of the states and in some even-even nuclei
A sixth-order quadrupole boson Hamiltonian is used to describe the states
and identified in several nuclei by various types of experiments.
Two alternative descriptions of energy levels are proposed. One corresponds to
a semi-classical approach of the model Hamiltonian while the other one provides
the exact eigenvalues. Both procedures yield close formulas for energies. The
first procedure involves four parameters, while the second involves a compact
formula with five parameters. In each case the parameters are fixed by a
least-square fit procedure. Applications are performed for eight even-even
nuclei.
Both methods yield results which are in a surprisingly good agreement with
the experimental data. We give also our predicted reduced transition
probabilities within the two approaches, although the corresponding
experimental data are not yet available.Comment: 27pages, 18 figure
Gravitationally induced electromagnetism at the Compton scale
It is shown that Einstein gravity tends to modify the electric and magnetic
fields appreciably at distances of the order of the Compton wavelength. At that
distance the gravitational field becomes spin dominated rather than mass
dominated. The gravitational field couples to the electromagnetic field via the
Einstein-Maxwell equations which in the simplest model causes the electrostatic
field of charged spinning particles to acquire an oblate structure relative to
the spin direction. For electrons and protons, a pure Coulomb field is
therefore likely to be incompatible with general relativity at the Compton
scale. In the simplest model, the magnetic dipole corresponds to the Dirac
g-factor, g=2. Also, it follows from the form of the electric field that the
electric dipole moment vanishes, in agreement with current experimental limits
for the electron. Quantitatively, the classical Einstein-Maxwell theory
predicts the magnetic and electric dipoles of the electron to an accuracy of
about one part in 10^{-3} or better. Going to the next multipole order, one
finds that the first non-vanishing higher multipole is the electric quadrupole
moment which is predicted to be -124 barn for the electron. Any non-zero value
of the electric quadrupole moment for the electron or the proton would be a
clear sign of curvature due to the implied violation of rotation invariance.
There is also a possible spherical modification of the Coulomb force
proportional to r^{-4}. However, the size of this effect is well below current
experimental limits. The corrections to the hydrogen spectrum are expected to
be small but possibly detectable.Comment: 11 pages, 3 figures: revised version published in Class. Quantum
Grav. 23 (2006) 3111-3122; Conclusions unchange
Contribution of nitrification and denitrification to N2O emissions from urine patches
Urine deposition by grazing livestock causes an immediate increase in nitrous oxide (N2O) emissions, but the responsible mechanisms are not well understood. A nitrogen-15 (15N) labelling study was conducted in an organic grass-clover sward to examine the initial effect of urine on the rates and N2O loss ratio of nitrification (i.e. moles of N2O-N produced per moles of nitrate produced) and denitrification (i.e. moles of N2O produced per moles of N2O + N2 produced). The effect of artificial urine (52.9 g N m-2) and ammonium solution (52.9 g N m-2) was examined in separate experiments at 45 and 35% water-filled pore space (WFPS), respectively, and in each experiment a water control was included. The N2O loss derived from nitrification or denitrification was determined in the field immediately after application of 15N-labelled solutions. During the next 24 h, gross nitrification rates were measured in the field, whereas the denitrification rates were measured in soil cores in the laboratory. Compared with the water control, urine application increased the N2O emission from 3.9 to 42.3 ÎŒg N2O-N m-2 h-1, whereas application of ammonium increased the emission from 0.9 to 6.1 ÎŒg N2O-N m-2 h-1. In the urine-affected soil, nitrification and denitrification contributed equally to the N2O emission, and the increased N2O loss resulted from a combination of higher rates and higher N2O loss ratios of the processes. In the present study, an enhanced nitrification rate seemed to be the most important factor explaining the high initial N2O emission from urine patches deposited on well-aerated soils
Micellar drug nanocarriers and biomembranes: how do they interact?
Pluronic based formulations are among the most successful nanomedicines and block-copolymer micelles including drugs that are undergoing phase I/II studies as anticancer agents. Using coarse-grained models, molecular dynamics simulations of large-scale systems, modeling Pluronic micelles interacting with DPPC lipid bilayers, on the ÎŒs timescale have been performed. Simulations show, in agreement with experiments, the release of Pluronic chains from the micelle to the bilayer. This release changes the size of the micelle. Moreover, the presence of drug molecules inside the core of the micelle has a strong influence on this process. The picture emerging from the simulations is that the micelle stability is a result of an interplay of drugâmicelle core and block-copolymerâbilayer interactions. The equilibrium size of the drug vector shows a strong dependency on the hydrophobicity of the drug molecules embedded in the core of the micelle. In particular, the radius of the micelle shows an abrupt increase in a very narrow range of drug molecule hydrophobicity
The Pt isotopes: comparing the Interacting Boson Model with Configuration Mixing and the Extended Consistent-Q formalism
The role of intruder configurations in the description of energy spectra and
B(E2) values in the Pt region is analyzed. In particular, we study the
differences between Interacting Boson Model calculations with or without the
inclusion of intruder states in the even Pt nuclei Pt. As a result,
it shows that for the description of a subset of the existing experimental
data, i.e., energy spectra and absolute B(E2) values up to an excitation energy
of about 1.5 MeV, both approaches seem to be equally valid. We explain these
similarities between both model spaces through an appropriate mapping. We point
out the need for a more extensive comparison, encompassing a data set as broad
(and complete) as possible to confront with both theoretical approaches in
order to test the detailed structure of the nuclear wave functions.Comment: To be published in NP
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