869 research outputs found
Over-representation of specific regions of chromosome 22 in cells from human glioma correlate with resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea
BACKGROUND: Glioblastoma multiforme is the most malignant form of brain tumor. Despite treatment including surgical resection, adjuvant chemotherapy, and radiation, these tumors typically recur. The recurrent tumor is often resistant to further therapy with the same agent, suggesting that the surviving cells that repopulate the tumor mass have an intrinsic genetic advantage. We previously demonstrated that cells selected for resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) are near-diploid, with over-representation of part or all of chromosomes 7 and 22. While cells from untreated gliomas often have over-representation of chromosome 7, chromosome 22 is typically under-represented. METHODS: We have analyzed cells from primary and recurrent tumors from the same patient before and after in vitro selection for resistance to clinically relevant doses of BCNU. Karyotypic analyses were done to demonstrate the genetic makeup of these cells, and fluorescent in situ hybridization analyses have defined the region(s) of chromosome 22 retained in these BCNU-resistant cells. RESULTS: Karyotypic analyses demonstrated that cells selected for BCNU resistance were near-diploid with over-representation of chromosomes 7 and 22. In cells where whole copies of chromosome 22 were not identified, numerous fragments of this chromosome were retained and inserted into several marker and derivative chromosomes. Fluorescent in situ hybridization analyses using whole chromosome paints confirmed this finding. Additional FISH analysis using bacterial artificial chromosome probes spanning the length of chromosome 22 have allowed us to map the over-represented region to 22q12.3–13.32. CONCLUSION: Cells selected for BCNU resistance either in vivo or in vitro retain sequences mapped to chromosome 22. The specific over-representation of sequences mapped to 22q12.3–13.32 suggest the presence of a DNA sequence important to BCNU survival and/or resistance located in this region of chromosome 22
Confinement limit of Dirac particles in scalar 1D potentials
We present a general proof that Dirac particles cannot be localized below
their Compton length by symmetric but otherwise arbitrary scalar potentials.
This proof does not invoke the Heisenberg uncertainty relation and thus does
not rely on the nonrelativistic linear momentum relation. Further it is argued
that the result is also applicable for more general potentials, as e.g.
generated by nonlinear interactions. Finally a possible realisation of such a
system is proposed.Comment: 2 page
Relativistic calculations of pionic and kaonic atoms hyperfine structure
We present the relativistic calculation of the hyperfine structure in pionic
and kaonic atoms. A perturbation method has been applied to the Klein-Gordon
equation to take into account the relativistic corrections. The perturbation
operator has been obtained \textit{via} a multipole expansion of the nuclear
electromagnetic potential. The hyperfine structure of pionic and kaonic atoms
provide an additional term in the quantum electrodynamics calculation of the
energy transition of these systems. Such a correction is required for a recent
measurement of the pion mass
3D simulations of wind-jet interaction in massive X-ray binaries
High-mass microquasars may produce jets that will strongly interact with
surrounding stellar winds on binary system spatial scales. We study the
dynamics of the collision between a mildly relativistic hydrodynamical jet of
supersonic nature and the wind of an OB star. We performed numerical 3D
simulations of jets that cross the stellar wind with the code Ratpenat. The jet
head generates a strong shock in the wind, and strong recollimation shocks
occur due to the initial overpressure of the jet with its environment. These
shocks can accelerate particles up to TeV energies and produce gamma-rays. The
recollimation shock also strengthens jet asymmetric Kelvin-Helmholtz
instabilities produced in the wind/jet contact discontinuity. This can lead to
jet disruption even for jet powers of several times erg s.
High-mass microquasar jets likely suffer a strong recollimation shock that can
be a site of particle acceleration up to very high energies, but also
eventually lead to the disruption of the jet.Comment: Accepted for publication in A&A Letter
The Interaction of Quantum Gravity with Matter
The interaction of (linearized) gravitation with matter is studied in the
causal approach up to the second order of perturbation theory. We consider the
generic case and prove that gravitation is universal in the sense that the
existence of the interaction with gravitation does not put new constraints on
the Lagrangian for lower spin fields. We use the formalism of quantum off-shell
fields which makes our computation more straightforward and simpler.Comment: 25 page
Feigned Consensus: Usurping the Law in Shaken Baby Syndrome/Abusive Head Trauma Prosecutions
Few medico-legal matters have generated as much controversy--both in the medical literature and in the courtroom--as Shaken Baby Syndrome (SBS), now known more broadly as Abusive Head Trauma (AHT). The controversies are of enormous significance in the law because child abuse pediatricians claim, on the basis of a few non-specific medical findings supported by a weak and methodologically flawed research base, to be able to “diagnose” child abuse, and thereby to provide all of the evidence necessary to satisfy all of the legal elements for criminal prosecution (or removal of children from their parents). It is a matter, therefore, in which medical opinion claims to fully occupy the legal field. As controversies flare up increasingly in the legal arena, child abuse pediatricians and prosecutors now respond by claiming both that there is actually no real controversy about SBS/AHT, and that it is a purely medical “diagnosis” and not a legal conclusion, so testimony in support of the SBS hypothesis should not be challenged in court. This article, coauthored by four law professors, two physicians, and a physicist, demonstrates that there is very much a live controversy about the SBS/AHT hypothesis and maintains that, under traditional principles of evidence law, physicians should not be permitted to “diagnose” abuse in court (as opposed to identifying specific symptoms or medical findings)
Relativistic Multiple Scattering Theory and the Relativistic Impulse Approximation
It is shown that a relativistic multiple scattering theory for hadron-nucleus
scattering can be consistently formulated in four-dimensions in the context of
meson exchange. We give a multiple scattering series for the optical potential
and discuss the differences between the relativistic and non-relativistic
versions. We develop the relativistic multiple scattering series by separating
out the one boson exchange term from the rest of the Feynman series. However
this particular separation is not absolutely necessary and we discuss how to
include other terms. We then show how to make a three-dimensional reduction for
hadron-nucleus scattering calculations and we find that the relative energy
prescription used in the elastic scattering equation should be consistent with
the one used in the free two-body t-matrix involved in the optical potential.
We also discuss what assumptions are involved in making a Dirac Relativistic
Impulse Approximation (RIA).Comment: 20 pages, 9 figures, Accepted for publication in Journal of Physics
Modeling core collapse supernovae in 2 and 3 dimensions with spectral neutrino transport
The overwhelming evidence that the core collapse supernova mechanism is
inherently multidimensional, the complexity of the physical processes involved,
and the increasing evidence from simulations that the explosion is marginal
presents great computational challenges for the realistic modeling of this
event, particularly in 3 spatial dimensions. We have developed a code which is
scalable to computations in 3 dimensions which couples PPM Lagrangian with
remap hydrodynamics [1], multigroup, flux-limited diffusion neutrino transport
[2], with many improvements), and a nuclear network [3]. The neutrino transport
is performed in a ray-by-ray plus approximation wherein all the lateral effects
of neutrinos are included (e.g., pressure, velocity corrections, advection)
except the transport. A moving radial grid option permits the evolution to be
carried out from initial core collapse with only modest demands on the number
of radial zones. The inner part of the core is evolved after collapse along
with the rest of the core and mantle by subcycling the lateral evolution near
the center as demanded by the small Courant times. We present results of 2-D
simulations of a symmetric and an asymmetric collapse of both a 15 and an 11 M
progenitor. In each of these simulations we have discovered that once the
oxygen rich material reaches the shock there is a synergistic interplay between
the reduced ram pressure, the energy released by the burning of the shock
heated oxygen rich material, and the neutrino energy deposition which leads to
a revival of the shock and an explosion.Comment: 10 pages, 3 figure
Isospin Character of the Pygmy Dipole Resonance in 124Sn
The pygmy dipole resonance has been studied in the proton-magic nucleus 124Sn
with the (a,a'g) coincidence method at E=136 MeV. The comparison with results
of photon-scattering experiments reveals a splitting into two components with
different structure: one group of states which is excited in (a,a'g) as well as
in (g,g') reactions and a group of states at higher energies which is only
excited in (g,g') reactions. Calculations with the self-consistent relativistic
quasiparticle time-blocking approximation and the quasiparticle phonon model
are in qualitative agreement with the experimental results and predict a
low-lying isoscalar component dominated by neutron-skin oscillations and a
higher-lying more isovector component on the tail of the giant dipole
resonance
Mesoscale cyclogenesis over the western North Pacific Ocean during TPARC
Three cases of mesoscale marine cyclogenesis over the subtropics of the Western Pacific Ocean are investigated. Each case occurred during the THORPEX Pacific Asia Regional Campaign and Tropical Cyclone Structure (TCS-08) field phases in 2008. Each cyclone developed from remnants of disturbances that earlier showed potential for tropical cyclogenesis within the tropics. Two of the cyclones produced gale-force surface winds, and one, designated as a tropical cyclone, resulted in a significant coastal storm over eastern Japan. Development was initiated by a burst of organized mesoscale convection that consolidated and intensified the surface cyclonic circulation over a period of 12-24 h. Upper-tropospheric potential vorticity anomalies modulated the vertical wind shear that, in turn, influenced the periods of cyclone intensification and weakening. Weak baroclinicity associated with vertical shear was also deemed important in organizing mesoscale ascent and the convection outbreaks. The remnant tropical disturbances contributed exceptional water vapour content to higher latitudes that led to strong diabatic heating, and the tropical remnants contributed vorticity that was the seed of the development in the subtropics. Predictability of these events more than three days in advance appears to be minimal
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