369 research outputs found
Synergistic Cytotoxicity Of Clofarabine, Fludarabine And Busulfan: Relevance To Myeloablative Therapy
Energy Scaling of Minimum-Bias Tunes
We propose that the flexibility offered by modern event-generator tuning
tools allows for more than just obtaining "best fits" to a collection of data.
In particular, we argue that the universality of the underlying physics model
can be tested by performing several, mutually independent, optimizations of the
generator parameters in different physical regions. For regions in which these
optimizations return similar and self-consistent parameter values, the model
can be considered universal. Deviations from this behavior can be associated
with a breakdown of the modeling, with the nature of the deviations giving
clues as to the nature of the breakdown. We apply this procedure to study the
energy scaling of a class of minimum-bias models based on multiple parton
interactions (MPI) and pT-ordered showers, implemented in the Pythia 6.4
generator. We find that a parameter controlling the strength of color
reconnections in the final state is the most important source of
non-universality in this model.Comment: 17 pages, 3 figures, 4 table
Exotic bulk viscosity and its influence on neutron star r-modes
We investigate the effect of exotic matter in particular, hyperon matter on
neutron star properties such as equation of state (EoS), mass-radius
relationship and bulk viscosity. Here we construct equations of state within
the framework of a relativistic field theoretical model. As hyperons are
produced abundantly in dense matter, hyperon-hyperon interaction becomes
important and is included in this model. Hyperon-hyperon interaction gives rise
to a softer EoS which results in a smaller maximum mass neutron star compared
with the case without the interaction. Next we compute the coefficient of bulk
viscosity and the corresponding damping time scale due to the non-leptonic weak
process including hyperons. Further, we investigate the role of the
bulk viscosity on gravitational radiation driven r-mode instability in a
neutron star of given mass and temperature and find that the instability is
effectively suppressed.Comment: 5 pages, 3 figure, presented in the Conference on Isolated Neutron
Stars: From the Interior to The Surface, London, UK, 24-28 April, 2006;
revised and final version to appear in Astrophys. Space Sc
Comparison of Busulfan + Melphalan to Melphalan 200 mg/m2 as Preparative Regimen for Autologous Transplantation in Multiple Myeloma
The ecology of sex explains patterns of helping in arthropod societies
Authors thank the Natural Sciences and Engineering Research Council of Canada (NGD), the Clarendon Fund (NGD) and the Natural Environment Research Council (LR, NE/K009516/1; AG, NE/K009524/1) for funding.Across arthropod societies, sib-rearing (e.g. nursing or nest defence) may be provided by females, by males or by both sexes. According to Hamilton's ‘haplodiploidy hypothesis’, this diversity reflects the relatedness consequences of diploid vs. haplodiploid inheritance. However, an alternative ‘preadaptation hypothesis’ instead emphasises an interplay of ecology and the co-option of ancestral, sexually dimorphic traits for sib-rearing. The preadaptation hypothesis has recently received empirical support, but remains to be formalised. Here, we mathematically model the coevolution of sex-specific helping and sex allocation, contrasting these hypotheses. We find that ploidy per se has little effect. Rather, the ecology of sex shapes patterns of helping: sex-specific preadaptation strongly influences who helps; a freely adjustable sex ratio magnifies sex biases and promotes helping; and sib-mating, promiscuity, and reproductive autonomy also modulate the sex and abundance of helpers. An empirical survey reveals that patterns of sex-specific helping in arthropod taxa are consistent with the preadaptation hypothesis.Publisher PDFPeer reviewe
A study on wear evaluation of railway wheels based on multibody dynamics and wear computation
The wear evolution of railway wheels is a very important issue in railway engineering. In the past, the reprofiling intervals of railway vehicle steel wheels have been scheduled according to designers' experience. Today, more reliable and accurate tools in predicting wheel wear evolution and wheelset lifetime can be used in order to achieve economical and safety benefits. In this work, a computational tool that is able to predict the evolution of the wheel profiles for a given railway system, as a function of the distance run, is presented. The strategy adopted consists of using a commercial multibody software to study the railway dynamic problem and a purpose-built code for managing its pre- and post-processing data in order to compute the wear. The tool is applied here to realistic operation scenarios in order to assess the effect of some service conditions on the wheel wear progression
Uniform random generation of large acyclic digraphs
Directed acyclic graphs are the basic representation of the structure
underlying Bayesian networks, which represent multivariate probability
distributions. In many practical applications, such as the reverse engineering
of gene regulatory networks, not only the estimation of model parameters but
the reconstruction of the structure itself is of great interest. As well as for
the assessment of different structure learning algorithms in simulation
studies, a uniform sample from the space of directed acyclic graphs is required
to evaluate the prevalence of certain structural features. Here we analyse how
to sample acyclic digraphs uniformly at random through recursive enumeration,
an approach previously thought too computationally involved. Based on
complexity considerations, we discuss in particular how the enumeration
directly provides an exact method, which avoids the convergence issues of the
alternative Markov chain methods and is actually computationally much faster.
The limiting behaviour of the distribution of acyclic digraphs then allows us
to sample arbitrarily large graphs. Building on the ideas of recursive
enumeration based sampling we also introduce a novel hybrid Markov chain with
much faster convergence than current alternatives while still being easy to
adapt to various restrictions. Finally we discuss how to include such
restrictions in the combinatorial enumeration and the new hybrid Markov chain
method for efficient uniform sampling of the corresponding graphs.Comment: 15 pages, 2 figures. To appear in Statistics and Computin
Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study
The effect of stress-triaxiality on growth of a void in a three dimensional
single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular
dynamics (MD) simulations using an embedded-atom (EAM) potential for copper
have been performed at room temperature and using strain controlling with high
strain rates ranging from 10^7/sec to 10^10/sec. Strain-rates of these
magnitudes can be studied experimentally, e.g. using shock waves induced by
laser ablation. Void growth has been simulated in three different conditions,
namely uniaxial, biaxial, and triaxial expansion. The response of the system in
the three cases have been compared in terms of the void growth rate, the
detailed void shape evolution, and the stress-strain behavior including the
development of plastic strain. Also macroscopic observables as plastic work and
porosity have been computed from the atomistic level. The stress thresholds for
void growth are found to be comparable with spall strength values determined by
dynamic fracture experiments. The conventional macroscopic assumption that the
mean plastic strain results from the growth of the void is validated. The
evolution of the system in the uniaxial case is found to exhibit four different
regimes: elastic expansion; plastic yielding, when the mean stress is nearly
constant, but the stress-triaxiality increases rapidly together with
exponential growth of the void; saturation of the stress-triaxiality; and
finally the failure.Comment: 35 figures, which are small (and blurry) due to the space
limitations; submitted (with original figures) to Physical Review B. Final
versio
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