2,389 research outputs found
Light particle spectra from 35 MeV/nucleon 12C-induced reactions on 197Au
Energy spectra for p, d, t, 3He, 4He, and 6He from the reaction 12C+197Au at 35 MeV/nucleon are presented. A common intermediate rapidity source is identified using a moving source fit to the spectra that yields cross sections which are compared to analogous data at other bombarding energies and to several different models. The excitation function of the composite to proton ratios is compared with quantum statistical, hydrodynamic, and thermal models
Differential effects of the poly (ADP-ribose) polymerase (PARP) inhibitor NU1025 on topoisomerase I and II inhibitor cytotoxicity in L1210 cells in vitro
The potent novel poly(ADP-ribose) polymerase (PARP) inhibitor, NU1025, enhances the cytotoxicity of DNA-methylating agents and ionizing radiation by inhibiting DNA repair. We report here an investigation of the role of PARP in the cellular responses to inhibitors of topoisomerase I and II using NU1025. The cytotoxicity of the topoisomerase I inhibitor, camptothecin, was increased 2.6-fold in L1210 cells by co-incubation with NU1025. Camptothecin-induced DNA strand breaks were also increased 2.5-fold by NU1025 and exposure to camptothecin-activated PARP. In contrast, NU1025 did not increase the DNA strand breakage or cytotoxicity caused by the topoisomerase II inhibitor etoposide. Exposure to etoposide did not activate PARP even at concentrations that caused significant levels of apoptosis. Taken together, these data suggest that potentiation of camptothecin cytotoxicity by NU1025 is a direct result of increased DNA strand breakage, and that activation of PARP by camptothecin-induced DNA damage contributes to its repair and consequently cell survival. However, in L1210 cells at least, it would appear that PARP is not involved in the cellular response to etoposide-mediated DNA damage. On the basis of these data, PARP inhibitors may be potentially useful in combination with topoisomerase I inhibitor anticancer chemotherapy. © 2001 Cancer Research Campaign http://www.bjcancer.co
Bursts in a fiber bundle model with continuous damage
We study the constitutive behaviour, the damage process, and the properties
of bursts in the continuous damage fiber bundle model introduced recently.
Depending on its two parameters, the model provides various types of
constitutive behaviours including also macroscopic plasticity. Analytic results
are obtained to characterize the damage process along the plastic plateau under
strain controlled loading, furthermore, for stress controlled experiments we
develop a simulation technique and explore numerically the distribution of
bursts of fiber breaks assuming infinite range of interaction. Simulations
revealed that under certain conditions power law distribution of bursts arises
with an exponent significantly different from the mean field exponent 5/2. A
phase diagram of the model characterizing the possible burst distributions is
constructed.Comment: 9 pages, 11 figures, APS style, submitted for publicatio
A study of the phase transition in the usual statistical model for nuclear multifragmentation
We use a simplified model which is based on the same physics as inherent in
most statistical models for nuclear multifragmentation. The simplified model
allows exact calculations for thermodynamic properties of systems of large
number of particles. This enables us to study a phase transition in the model.
A first order phase transition can be tracked down. There are significant
differences between this phase transition and some other well-known cases
The phonon theory of liquid thermodynamics
Heat capacity of matter is considered to be its most important property
because it holds information about system's degrees of freedom as well as the
regime in which the system operates, classical or quantum. Heat capacity is
well understood in gases and solids but not in the third state of matter,
liquids, and is not discussed in physics textbooks as a result. The perceived
difficulty is that interactions in a liquid are both strong and
system-specific, implying that the energy strongly depends on the liquid type
and that, therefore, liquid energy can not be calculated in general form. Here,
we develop a phonon theory of liquids where this problem is avoided. The theory
covers both classical and quantum regimes. We demonstrate good agreement of
calculated and experimental heat capacity of 21 liquids, including noble,
metallic, molecular and hydrogen-bonded network liquids in a wide range of
temperature and pressure.Comment: 7 pages, 4 figure
Direct calculation of the hard-sphere crystal/melt interfacial free energy
We present a direct calculation by molecular-dynamics computer simulation of
the crystal/melt interfacial free energy, , for a system of hard
spheres of diameter . The calculation is performed by thermodynamic
integration along a reversible path defined by cleaving, using specially
constructed movable hard-sphere walls, separate bulk crystal and fluid systems,
which are then merged to form an interface. We find the interfacial free energy
to be slightly anisotropic with = 0.62, 0.64 and
0.58 for the (100), (110) and (111) fcc crystal/fluid
interfaces, respectively. These values are consistent with earlier density
functional calculations and recent experiments measuring the crystal nucleation
rates from colloidal fluids of polystyrene spheres that have been interpreted
[Marr and Gast, Langmuir {\bf 10}, 1348 (1994)] to give an estimate of
for the hard-sphere system of , slightly lower
than the directly determined value reported here.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
Soap Froths and Crystal Structures
We propose a physical mechanism to explain the crystal symmetries found in
macromolecular and supramolecular micellar materials. We argue that the packing
entropy of the hard micellar cores is frustrated by the entropic interaction of
their brush-like coronas. The latter interaction is treated as a surface effect
between neighboring Voronoi cells. The observed crystal structures correspond
to the Kelvin and Weaire-Phelan minimal foams. We show that these structures
are stable for reasonable areal entropy densities.Comment: 4 pages, RevTeX, 2 included eps figure
Biomechanics of predator–prey arms race in lion, zebra, cheetah and impala
The fastest and most manoeuvrable terrestrial animals are found in savannah habitats, where predators chase and capture running prey. Hunt outcome and success rate are critical to survival, so both predator and prey should evolve to be faster and/or more manoeuvrable. Here we compare locomotor characteristics in two pursuit predator–prey pairs, lion–zebra and cheetah–impala, in their natural savannah habitat in Botswana. We show that although cheetahs and impalas were universally more athletic than lions and zebras in terms of speed, acceleration and turning, within each predator–prey pair, the predators had 20% higher muscle fibre power than prey, 37% greater acceleration and 72% greater deceleration capacity than their prey. We simulated hunt dynamics with these data and showed that hunts at lower speeds enable prey to use their maximum manoeuvring capacity and favour prey survival, and that the predator needs to be more athletic than its prey to sustain a viable success rate
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