6,286 research outputs found
Reaction mechanisms involved in the production of neutron-rich isotopes
The reaction mechanisms best suited for the production of neutron-rich
nuclei, fragmentation and fission, are discussed. Measurements of the
production cross sections of reaction residues together with model calculations
allow to conclude about the expected production rates of neutron-rich isotopes
in future facilities.Comment: 9 pages, 8 figures Proceedings of the Third International Conference
on Fission and Properties of Neutron-Rich Nuclei November 3-9, 2002, Sanibel
Island, Florida, US
Dispersion of longitudinal momentum distributions induced in fragmentation reactions
On the basis of systematic measurements of fragmentation reactions, which
provide a detailed overview on the velocity distributions of residual nuclei,
an improved description of the kinematical properties of the fragmentation
residues is established. This work is dedicated to the fluctuations of their
momentum distributions. In contrast to previous investigations, limited to
close-to-projectile fragments, we extended our study to the entire production
range, down to the lightest observed fragments. In this context, beside the
contribution of abrasion and evaporation processes, we considered the effect of
the thermal break-up on the width of the momentum distributions. Using
approximated theoretical descriptions of the different reaction stages, a new
analytical formula for the variance of the momentum distribution is derived,
which is well adapted to technical applications.Comment: 14 pages, 3 figures, background info. at
http://www-wnt.gsi.de/charms
Threshold Resummed Spectra in B -> Xu l nu Decays in NLO (I)
We evaluate thresholds resummed spectra in B -> Xu l nu decays in
next-to-leading order. We present results for the distribution in E_X and in
m_X^2/E_X^2, for the distribution in E_X and E_l and for the distribution in
E_X, where E_X and m_X are the energy and the invariant mass of the final
hadronic state Xu respectively and E_l is the energy of the charged lepton. We
explicitly show that all these spectra (where there is no integration over the
hadronic energy) can be directly related to the photon spectrum in B -> Xs
gamma via short-distance coefficient functions.Comment: 33 pages, no figures. The section on the double distribution in the
hadron and electron energies has been largely rewritten with an improved
resummation scheme. Small stylistic changes in the remaining sections.
References adde
Experimental Indications for the Response of the Spectators to the Participant Blast
Precise momentum distributions of identified projectile fragments, formed in
the reactions 238U + Pb and 238U + Ti at 1 A GeV, are measured with a
high-resolution magnetic spectrometer. With increasing mass loss, the
velocities first decrease as expected from previously established systematics,
then level off, and finally increase again. Light fragments are on the average
even faster than the projectiles. This finding is interpreted as the response
of the spectators to the participant blast. The re-acceleration of projectile
spectators is sensitive to the nuclear mean field and provides a new tool for
investigating the equation of state of nuclear matter.Comment: 7 pages, 3 figures, background information on
http://www-wnt.gsi.de/kschmidt
Origin of the even-odd effect in the yields from high-energy reactions
The analysis of experimental production cross-sections of the light products of several nuclear reactions at high energy, measured at the FRS, GSI Darmstadt, revealed a very strong and complex even-odd staggering. The origin of this effect is related to the condensation process of heated nuclear matter while cooling down in the last evaporation step. The characteristics of the staggering correlate strongly with the lowest particle separation energy of the final experimentally observed nuclei. The study confirms the important role of the deexcitation process in fragmentation reactions, and indicates that sequential decay strongly influences the yields of light fragments, which are often used to extract information on the nature of nuclear reactions at high energies
Correlated Component Analysis for diffuse component separation with error estimation on simulated Planck polarization data
We present a data analysis pipeline for CMB polarization experiments, running
from multi-frequency maps to the power spectra. We focus mainly on component
separation and, for the first time, we work out the covariance matrix
accounting for errors associated to the separation itself. This allows us to
propagate such errors and evaluate their contributions to the uncertainties on
the final products.The pipeline is optimized for intermediate and small scales,
but could be easily extended to lower multipoles. We exploit realistic
simulations of the sky, tailored for the Planck mission. The component
separation is achieved by exploiting the Correlated Component Analysis in the
harmonic domain, that we demonstrate to be superior to the real-space
application (Bonaldi et al. 2006). We present two techniques to estimate the
uncertainties on the spectral parameters of the separated components. The
component separation errors are then propagated by means of Monte Carlo
simulations to obtain the corresponding contributions to uncertainties on the
component maps and on the CMB power spectra. For the Planck polarization case
they are found to be subdominant compared to noise.Comment: 17 pages, accepted in MNRA
Model calculations of a two-step reaction scheme for the production of neutron-rich secondary beams
A two-step reaction scheme for the production of extremely neutron-rich
radioactive beams, fission followed by cold fragmentation, is considered. The
cross sections of the second step, the cold fragmentation of neutron-rich
fission fragments, are estimated with different computer codes. Discrepancies
between an empirical systematics and nuclear-reaction codes are found.Comment: 31 pages, 13 figures, background information on
http://www-wnt.gsi.de/kschmidt
A field study on thermal comfort in naturally - ventilated buildings located in the equatorial climatic region of Cameroon
The purpose of this research is to create a thermal comfort data base in three climatic regions in Cameroon. This will help to define guidelines for constructing more comfortable buildings in Cameroon. There is not enough data regarding comfort in residential environment in the inter tropical sub Saharan Africa.
Thus experimental and subjective results of hygrometric thermal comfort conducted in 290 buildings located in three cities of the equatorial climatic zone of Cameroon is presented. An adaptive approach according to ASHRAE55/2004, ISO7730 and 10551 was adopted. A specific questionnaire has been elaborated for the investigation. 710 questionnaires in the dry season and 410 in the rainy season were distributed to inhabitants and filled while different experimental value of indoor parameters were measured. The comfortable temperature ranges for the three cities was found between 22. 1 C and 29.1 C. The 61.24 % of voters found acceptable their thermal habitat, the 13.72% considered it neutral
TEM Nanostructural Investigation of Ag-Conductive Filaments in Polycrystalline ZnO-Based Resistive Switching Devices
Memristive devices based on a resistive switching mechanism are considered very promising for nonvolatile memory and unconventional computing applications, even though many details of the switching mechanisms are not yet fully understood. Here, we report a nanostructural study by means of high-resolution transmission electron microscopy and spectroscopy techniques of a Ag/ZnO/Pt memristive device. To ease the localization of the filament position for its characterization, we propose to use the guiding effect of regular perturbation arrays obtained by FIB technology to assist the filament formation. HRTEM and EDX were used to identify the composition and crystalline structure of the so-obtained conductive filaments and surrounding regions. It was determined that the conducting paths are composed mainly of monocrystalline Ag, which remains polycrystalline in some circumstances, including the zone where the switching occurs and at secondary filaments created at the grain boundaries of the polycrystalline ZnO matrix. We also observed that the ZnO matrix shows a degraded quality in the switching zone, while it remains unaltered in the rest of the memristive device
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