3,254 research outputs found
Z-dependent Barriers in Multifragmentation from Poissonian Reducibility and Thermal Scaling
We explore the natural limit of binomial reducibility in nuclear
multifragmentation by constructing excitation functions for intermediate mass
fragments (IMF) of a given element Z. The resulting multiplicity distributions
for each window of transverse energy are Poissonian. Thermal scaling is
observed in the linear Arrhenius plots made from the average multiplicity of
each element. ``Emission barriers'' are extracted from the slopes of the
Arrhenius plots and their possible origin is discussed.Comment: 15 pages including 4 .ps figures. Submitted to Phys. Rev. Letters.
Also available at http://csa5.lbl.gov/moretto
Liquid-Drop Model and Quantum Resistance Against Noncompact Nuclear Geometries
The importance of quantum effects for exotic nuclear shapes is demonstrated.
Based on the example of a sheet of nuclear matter of infinite lateral
dimensions but finite thickness, it is shown that the quantization of states in
momentum space, resulting from the confinement of the nucleonic motion in the
conjugate geometrical space, generates a strong resistance against such a
confinement and generates restoring forces driving the system towards compact
geometries. In the liquid-drop model, these quantum effects are implicitly
included in the surface energy term, via a choice of interaction parameters, an
approximation that has been found valid for compact shapes, but has not yet
been scrutinized for exotic shapes.Comment: 9 pages with 3 figure
New approach of fragment charge correlations in 129Xe+(nat)Sn central collisions
A previous analysis of the charge (Z) correlations in the
plane for Xe+Sn central collisions at 32 MeV/u has shown an enhancement in the
production of equally sized fragments (low ) which was interpreted as
an evidence for spinodal decomposition. However the signal is weak and rises
the question of the estimation of the uncorrelated yield. After a critical
analysis of its robustness, we propose in this paper a new technique to build
the uncorrelated yield in the charge correlation function. The application of
this method to Xe+Sn central collision data at 32, 39, 45 and 50 MeV/u does not
show any particular enhancement of the correlation function in any
bin.Comment: 23 pages, 9 figures, revised version with an added figure and minor
changes. To appear in Nuclear Physics
The Geant4-DNA project
The Geant4-DNA project proposes to develop an open-source simulation software
based and fully included in the general-purpose Geant4 Monte Carlo simulation
toolkit. The main objective of this software is to simulate biological damages
induced by ionising radiation at the cellular and sub-cellular scale. This
project was originally initiated by the European Space Agency for the
prediction of deleterious effects of radiation that may affect astronauts
during future long duration space exploration missions. In this paper, the
Geant4-DNA collaboration presents an overview of the whole ongoing project,
including its most recent developments already available in the last Geant4
public release (9.3 BETA), as well as an illustration example simulating the
direct irradiation of a chromatin fibre. Expected extensions involving several
research domains, such as particle physics, chemistry and cellular and
molecular biology, within a fully interdiciplinary activity of the Geant4
collaboration are also discussed.Comment: presented by S. Incerti at the ASIA SIMULATION CONFERENCE 2009,
October 7-9, 2009, Ritsumeikan University, Shiga, Japa
Correlations in Nuclear Arrhenius-Type Plots
Arrhenius-type plots for multifragmentation process, defined as the
transverse energy dependence of the single-fragment emission-probability,
-ln(p_{b}) vs 1/sqrt(E_{t}), have been studied by examining the relationship of
the parameters p_{b} and E_{t} to the intermediate-mass fragment multiplicity
. The linearity of these plots reflects the correlation of the fragment
multiplicity with the transverse energy. These plots may not provide thermal
scaling information about fragment production as previously suggested.Comment: 12 pages, Latex, 3 Postscript figures include
Simulation of cellular irradiation with the CENBG microbeam line using GEANT4
Light-ion microbeams provide a unique opportunity to irradiate biological
samples at the cellular level and to investigate radiobiological effects at low
doses of high LET ionising radiation. Since 1998 a single-ion irradiation
facility has been developed on the focused horizontal microbeam line of the
CENBG 3.5 MV Van de Graaff accelerator. This setup delivers in air single
protons and alpha particles of a few MeV onto cultured cells, with a spatial
resolution of a few microns, allowing subcellular targeting. In this paper, we
present results from the use of the GEANT4 toolkit to simulate cellular
irradiation with the CENBG microbeam line, from the entrance to the microprobe
up to the cellular medium.Comment: 6 pages, 8 figures, presented at the 2003 IEEE-NSS conference,
Portland, OR, USA, October 20-24, 200
A statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy
Multifragment emission following Xe+Au collisions at 30, 40, 50 and 60 AMeV
has been studied with multidetector systems covering nearly 4-pi in solid
angle. The correlations of both the intermediate mass fragment and light
charged particle multiplicities with the transverse energy are explored. A
comparison is made with results from a similar system, Xe+Bi at 28 AMeV. The
experimental trends are compared to statistical model predictions.Comment: 7 pages, submitted to Phys. Rev.
Mass production of Bacillus subtilis and Trichoderma viride for the control of Phyllosticta citricarpa (Teleomorph: Guignardia citricarpa).
The work was aimed at studying the production of cells and metabolites of Bacilius subtilis (ACB-69) and of Trichoderma viride conidia (ACB-14) on different substrates, since they can potentially control Phyllosticta citricarpa. Our results showed that the medium consisting of cotton meal added of hydrolized protein provided the highest yield of B. subtiiis cells (2.44 x IO9 cells/mL), after the culture had been incubated for three days. This liquid substrate also provided conditions for the bacterium to produce thermostable metabolites, in sufficient amounts to inhibit the plant pathogen's micelial growth. The production of B. subtilis under the solid fermentation system performed better on the brewers rice substrate; the number of bactéria; cells decreased as the substrate concentration increased. In general, the liquid medium yielded a higher amount of B. subtilis than the solid medium. With regard to the large scale production of T. viride, it was verified that the substrates tested had a low spore production; the best substrate among those tested (com cob + hydrolized protein) only yielded 2.17 x IO6 conidia/mL. O objetivo foi estudar a produção de células e de metabólitos de Bacillus subtilis (ACB-69) e de conídios de Trichoderma viride (ACB-14) em diferentes substratos, pois apresentam potencial para o controle de Phyllosticta citricarpa. O meio constituído de farelo de algodão acrescido de proteína hidrolisada foi o que proporcionou maior produção de células de B. subtilis (2,4 x 109 células/mL), após três dias de incubação da cultura. Esse substrato líquido também propiciou condições para que a bactéria produzisse metabólitos termoestáveis e, em quantidades suficientes para inibir o crescimento micelial do fitopatógeno. A produção de B. subtilis pelo sistema de fermentação sólida foi melhor no substrato quirera de arroz sendo que o número de células da bactéria diminuiu à medida que aumentou a concentração do substrato. De um modo geral, o meio líquido foi superior ao sólido para a produção de B. subtilis. Com relação à produção de T. viride, verificou-se que os substratos testados apresentaram baixa produção de esporos, sendo que o melhor substrato testado (sabugo de milho + proteína hidrolisada) produziu apenas 2,2 x 106 conídios/mL
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