1,459 research outputs found
Mott Effect and J/Psi Dissociation at the Quark-Hadron Phase Transition
We investigate the in-medium modification of pseudoscalar and vector mesons
in a QCD motivated chiral quark model by solving the Dyson-Schwinger equations
for quarks and mesons at finite temperature for a wide mass range of meson
masses, from light (pi, rho) to open-charm (D, D*) states. At the chiral /
deconfinement phase transition, the quark-antiquark bound states enter the
continuum of unbound states and become broad resonances (the hadronic Mott
effect). We calculate the in-medium cross sections for charmonium dissociation
due to collisions with light hadrons in a chiral Lagrangian approach, and show
that the D and D* meson spectral broadening lowers the threshold for charmonium
dissociation by pi and rho meson impact. This leads to a step-like enhancement
in the reaction rate. We suggest that this mechanism for enhanced charmonium
dissociation may be the physical mechanism underlying the anomalous J/Psi
suppression observed by NA50.Comment: 3 pages, 3 figures, uses EPJ style (included), contribution to the
Proceedings of the International Conference on Quark Nuclear Physics, June 9
- 14, 2002, Juelich, Germany; 1 figure added, text adde
E-cadherin is crucial for embryonic stem cell pluripotency and can replace OCT4 during somatic cell reprogramming
We report new functions of the cell-adhesion molecule E-cadherin in murine pluripotent cells. E-cadherin is highly expressed in mouse embryonic stem cells, and interference with E-cadherin causes differentiation. During cellular reprogramming of mouse fibroblasts by OCT4, SOX2, KLF4 and c-MYC, fully reprogrammed cells were exclusively observed in the E-cadherin-positive cell population and could not be obtained in the absence of E-cadherin. Moreover, reprogrammed cells could be established by viral E-cadherin in the absence of exogenous OCT4. Thus, reprogramming requires spatial cues that cross-talk with essential transcription factors. The cell-adhesion molecule E-cadherin has important functions in pluripotency and reprogramming
Probing the interiors of the ice giants: Shock compression of water to 700 GPa and 3.8 g/ccm
Recently there has been tremendous increase in the number of identified
extra-solar planetary systems. Our understanding of their formation is tied to
exoplanet internal structure models, which rely upon equations of state of
light elements and compounds like water. Here we present shock compression data
for water with unprecedented accuracy that shows water equations of state
commonly used in planetary modeling significantly overestimate the
compressibility at conditions relevant to planetary interiors. Furthermore, we
show its behavior at these conditions, including reflectivity and isentropic
response, is well described by a recent first-principles based equation of
state. These findings advocate this water model be used as the standard for
modeling Neptune, Uranus, and "hot Neptune" exoplanets, and should improve our
understanding of these types of planets.Comment: Accepted to Phys. Rev. Lett.; supplementary material attached
including 2 figures and 2 tables; to view attachments, please download and
extract the gzipped tar source file listed under "Other formats
The role of the cancer stem cell marker CD271 in DNA damage response and drug resistance of melanoma cells
Several lines of evidence have suggested that stemness and acquired resistance
to targeted inhibitors or chemotherapeutics are mechanistically linked. Here
we observed high cell surface and total levels of nerve growth factor
receptor/CD271, a marker of melanoma-initiating cells, in sub-populations of
chemoresistant cell lines. CD271 expression was increased in drug-sensitive
cells but not resistant cells in response to DNA-damaging chemotherapeutics
etoposide, fotemustine and cisplatin. Comparative analysis of melanoma cells
engineered to stably express CD271 or a targeting short hairpin RNA by
expression profiling provided numerous genes regulated in a CD271-dependent
manner. In-depth analysis of CD271-responsive genes uncovered the association
of CD271 with regulation of DNA repair components. In addition, gene set
enrichment analysis revealed enrichment of CD271-responsive genes in drug-
resistant cells, among them DNA repair components. Moreover, our comparative
screen identified the fibroblast growth factor 13 (FGF13) as a target of
CD271, highly expressed in chemoresistant cells. Further we show that levels
of CD271 determine drug response. Knock-down of CD271 in fotemustine-resistant
cells decreased expression of FGF13 and at least partly restored sensitivity
to fotemustine. Together, we demonstrate that expression of CD271 is
responsible for genes associated with DNA repair and drug response. Further,
we identified 110 CD271-responsive genes predominantly expressed in melanoma
metastases, among them were NEK2, TOP2A and RAD51AP1 as potential drivers of
melanoma metastasis. In addition, we provide mechanistic insight in the
regulation of CD271 in response to drugs. We found that CD271 is potentially
regulated by p53 and in turn is needed for a proper p53-dependent response to
DNA-damaging drugs. In summary, we provide for the first time insight in a
CD271-associated signaling network connecting CD271 with DNA repair, drug
response and metastasis
Constraining the Hadronic Contributions to the Muon Anomalous Magnetic Moment
The mini-proceedings of the Workshop on "Constraining the hadronic
contributions to the muon anomalous magnetic moment" which included the "13th
meeting of the Radio MonteCarLow WG" and the "Satellite meeting R-Measurements
at BES-III" held in Trento from April 10th to 12th, 2013, are presented. This
collaboration meeting aims to bring together the experimental e+e- collider
communities from BaBar, Belle, BESIII, CMD2, KLOE, and SND, with theorists
working in the fields of meson transitions form factors, hadronic contributions
to (g-2)_\mu and effective fine structure constant, and development of Monte
Carlo generator and Radiative Corrections for precision e+e- and tau physics.Comment: 45 pages, 17 contributions. Editors: P. Masjuan and G. Venanzon
Introduction to Configuration Path Integral Monte Carlo
In low-temperature high-density plasmas quantum effects of the electrons are
becoming increasingly important. This requires the development of new
theoretical and computational tools. Quantum Monte Carlo methods are among the
most successful approaches to first-principle simulations of many-body quantum
systems. In this chapter we present a recently developed method---the
configuration path integral Monte Carlo (CPIMC) method for moderately coupled,
highly degenerate fermions at finite temperatures. It is based on the second
quantization representation of the -particle density operator in a basis of
(anti-)symmetrized -particle states (configurations of occupation numbers)
and allows to tread arbitrary pair interactions in a continuous space.
We give a detailed description of the method and discuss the application to
electrons or, more generally, Coulomb-interacting fermions. As a test case we
consider a few quantum particles in a one-dimensional harmonic trap. Depending
on the coupling parameter (ratio of the interaction energy to kinetic energy),
the method strongly reduces the sign problem as compared to direct path
integral Monte Carlo (DPIMC) simulations in the regime of strong degeneracy
which is of particular importance for dense matter in laser plasmas or compact
stars. In order to provide a self-contained introduction, the chapter includes
a short introduction to Metropolis Monte Carlo methods and the second
quantization of quantum mechanics.Comment: chapter in book "Introduction to Complex Plasmas: Scientific
Challenges and Technological Opportunities", Michael Bonitz, K. Becker, J.
Lopez and H. Thomsen (Eds.) Springer Series "Atomic, Optical and Plasma
Physics", vol. 82, Springer 2014, pp. 153-194 ISBN: 978-3-319-05436-0 (Print)
978-3-319-05437-7 (Online
Variational quantum Monte Carlo calculations for solid surfaces
Quantum Monte Carlo methods have proven to predict atomic and bulk properties
of light and non-light elements with high accuracy. Here we report on the first
variational quantum Monte Carlo (VMC) calculations for solid surfaces. Taking
the boundary condition for the simulation from a finite layer geometry, the
Hamiltonian, including a nonlocal pseudopotential, is cast in a layer resolved
form and evaluated with a two-dimensional Ewald summation technique. The exact
cancellation of all Jellium contributions to the Hamiltonian is ensured. The
many-body trial wave function consists of a Slater determinant with
parameterized localized orbitals and a Jastrow factor with a common two-body
term plus a new confinement term representing further variational freedom to
take into account the existence of the surface. We present results for the
ideal (110) surface of Galliumarsenide for different system sizes. With the
optimized trial wave function, we determine some properties related to a solid
surface to illustrate that VMC techniques provide standard results under full
inclusion of many-body effects at solid surfaces.Comment: 9 pages with 2 figures (eps) included, Latex 2.09, uses REVTEX style,
submitted to Phys. Rev.
Phase Transition in Strongly Degenerate Hydrogen Plasma
Direct fermionic path-integral Monte-Carlo simulations of strongly coupled
hydrogen are presented. Our results show evidence for the hypothetical plasma
phase transition. Its most remarkable manifestation is the appearance of
metallic droplets which are predicted to be crucial for the electrical
conductivity allowing to explain the rapid increase observed in recent shock
compression measurments.Comment: 1 LaTeX file using jetpl.cls (included), 5 ps figures. Manuscript
submitted to JETP Letter
Ab initio Equation of State data for hydrogen, helium, and water and the internal structure of Jupiter
The equation of state of hydrogen, helium, and water effects interior
structure models of giant planets significantly. We present a new equation of
state data table, LM-REOS, generated by large scale quantum molecular dynamics
simulations for hydrogen, helium, and water in the warm dense matter regime,
i.e.for megabar pressures and temperatures of several thousand Kelvin, and by
advanced chemical methods in the complementary regions. The influence of
LM-REOS on the structure of Jupiter is investigated and compared with
state-of-the-art results within a standard three-layer model consistent with
astrophysical observations of Jupiter. Our new Jupiter models predict an
important impact of mixing effects of helium in hydrogen with respect to an
altered compressibility and immiscibility.Comment: to appear in ApJ in August 2008, 11 figure
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