5,989 research outputs found
Higher-order symmetry energy and neutron star core-crust transition with Gogny forces
We study the symmetry energy and the core-crust transition in neutron stars
using the finite-range Gogny nuclear interaction and examine the deduced
crustal thickness and crustal moment of inertia. We start by analyzing the
second-, fourth- and sixth-order coefficients of the Taylor expansion of the
energy per particle in powers of the isospin asymmetry for Gogny forces. These
coefficients provide information about the departure of the symmetry energy
from the widely used parabolic law. The neutron star core-crust transition is
evaluated by looking at the onset of thermodynamical instability of the liquid
core. The calculation is performed with the exact (i.e., without Taylor
expansion) Gogny EoS for the core, and also with its Taylor expansion in order
to assess the influence of isospin expansions on locating the inner edge of
neutron star crusts. It is found that the properties of the core-crust
transition derived from the exact EoS differ from the predictions of the Taylor
expansion even when the expansion is carried through sixth order in the isospin
asymmetry. Gogny forces, using the exact EoS, predict the ranges for the transition
density and for the transition pressure. The transition densities show an
anticorrelation with the slope parameter of the symmetry energy. The
transition pressures are not found to correlate with . Neutron stars
obtained with Gogny forces have maximum masses below and
relatively small moments of inertia. The crustal mass and moment of inertia are
evaluated and comparisons are made with the constraints from observed glitches
in pulsars.Comment: 24 pages, 15 figures, discussions and bibliography updated, to appear
in Physical Review
Transferring orbital and spin angular momenta of light to atoms
Light beams carrying orbital angular momentum, such as Laguerre-Gaussian
beams, give rise to the violation of the standard dipolar selection rules
during the interaction with matter yielding, in general, an exchange of angular
momentum larger than hbar per absorbed photon. By means of ab initio 3D
numerical simulations, we investigate in detail the interaction of a hydrogen
atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the
dependence of the angular momentum exchange with the polarization, the orbital
angular momentum, and the carrier-envelope phase of light, as well as with the
relative position between the atom and the light vortex. In addition, a
quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum
mechanics is used to gain physical insight into the absorption of angular
momentum by the hydrogen atom
Model for the hydration of non-polar compounds and polymers
We introduce an exactly solvable statistical-mechanical model of the
hydration of non-polar compounds, based on grouping water molecules in clusters
where hydrogen bonds and isotropic interactions occur; interactions between
clusters are neglected. Analytical results show that an effective strengthening
of hydrogen bonds in the presence of the solute, together with a geometric
reorganization of water molecules, are enough to yield hydrophobic behavior. We
extend our model to describe a non-polar homopolymer in aqueous solution,
obtaining a clear evidence of both ``cold'' and ``warm'' swelling transitions.
This suggests that our model could be relevant to describe some features of
protein folding.Comment: REVTeX, 6 pages, 3 figure
Structural and Vibrational Properties of the TiOPc monolayer on Ag(111)
The evolution of titanyl-phthalocyanine (TiOPc) thin films on Ag(111) has
been investigated using IRAS, SPA-LEED and STM. In the (sub)monolayer regime
various phases are observed that can be assigned to a 2D gas, a commensurate
and a point-on-line phase. In all three phases the non-planar TiOPc molecule is
adsorbed on Ag(111) in an oxygen-up configuration with the molecular
pi-conjugated backbone oriented parallel to the surface. The commensurate phase
reveals a high packing density, containing two molecules at inequivalent
adsorption sites within the unit cell. Both molecules assume different
azimuthal orientations which is ascribed to preferred sites and azimuthal
orientations with respect to the Ag(111) substrate and, to a lesser extent, to
a minimization of repulsive Pauli interactions between adjacent molecules at
short distances. At full saturation of the monolayer the latter interaction
becomes dominant and the commensurate long range order is lost. DFT
calculations have been used to study different adsorption geometries of TiOPc
on Ag(111). The most stable configurations among those with pointing up oxygen
atoms (bridge+, bridgex, topx) seem to correspond to those identified
experimentally. The calculated dependence of the electronic structure and
molecular dipole on the adsorption site and configuration is found to be rather
small.Comment: 28 pages, 6 figures, 2 table
O mercado da tilĂĄpia em 2014.
Mercado nacional. Descrição da evolução de cada polo produtor. Mercado externo.bitstream/item/117068/1/cnpasa.pd
SQG-Differential Evolution for difficult optimization problems under a tight function evaluation budget
In the context of industrial engineering, it is important to integrate
efficient computational optimization methods in the product development
process. Some of the most challenging simulation-based engineering design
optimization problems are characterized by: a large number of design variables,
the absence of analytical gradients, highly non-linear objectives and a limited
function evaluation budget. Although a huge variety of different optimization
algorithms is available, the development and selection of efficient algorithms
for problems with these industrial relevant characteristics, remains a
challenge. In this communication, a hybrid variant of Differential Evolution
(DE) is introduced which combines aspects of Stochastic Quasi-Gradient (SQG)
methods within the framework of DE, in order to improve optimization efficiency
on problems with the previously mentioned characteristics. The performance of
the resulting derivative-free algorithm is compared with other state-of-the-art
DE variants on 25 commonly used benchmark functions, under tight function
evaluation budget constraints of 1000 evaluations. The experimental results
indicate that the new algorithm performs excellent on the 'difficult' (high
dimensional, multi-modal, inseparable) test functions. The operations used in
the proposed mutation scheme, are computationally inexpensive, and can be
easily implemented in existing differential evolution variants or other
population-based optimization algorithms by a few lines of program code as an
non-invasive optional setting. Besides the applicability of the presented
algorithm by itself, the described concepts can serve as a useful and
interesting addition to the algorithmic operators in the frameworks of
heuristics and evolutionary optimization and computing
Interethnic diversity of NAT2 polymorphisms in Brazilian admixed populations
<p>Abstract</p> <p>Background</p> <p>N-acetyltransferase type 2 (Nat2) is a phase II drug- metabolizing enzyme that plays a key role in the bioactivation of aromatic and heterocyclic amines. Its relevance in drug metabolism and disease susceptibility remains a central theme for pharmacogenetic research, mainly because of its genetic variability among human populations. In fact, the evolutionary and ethnic-specific SNPs on the <it>NAT2 </it>gene remain a focus for the potential discoveries in personalized drug therapy and genetic markers of diseases. Despite the wide characterization of <it>NAT2 </it>SNPs frequency in established ethnic groups, little data are available for highly admixed populations. In this context, five common <it>NAT2 </it>SNPs (<it>G191A</it>, <it>C481T</it>, <it>G590A</it>, <it>A803G </it>and G<it>857A</it>) were investigated in a highly admixed population comprised of Afro-Brazilians, Whites, and Amerindians in northeastern Brazil. Thus, we sought to determine whether the distribution of <it>NAT2 </it>polymorphism is different among these three ethnic groups.</p> <p>Results</p> <p>Overall, there were no statistically significant differences in the distribution of <it>NAT2 </it>polymorphism when Afro-Brazilian and White groups were compared. Even the allele frequency of <it>191A</it>, relatively common in African descendents, was not different between the Afro-Brazilian and White groups. However, allele and genotype frequencies of <it>G590A </it>were significantly higher in the Amerindian group than either in the Afro-Brazilian or White groups. Interestingly, a haplotype block between <it>G590A </it>and <it>A803G </it>was verified exclusively among Amerindians.</p> <p>Conclusions</p> <p>Our results indicate that ethnic admixture might contribute to a particular pattern of genetic diversity in the <it>NAT2 </it>gene and also offer new insights for the investigation of possible new <it>NAT2 </it>gene-environment effects in admixed populations.</p
DTA0100, dual topoisomerase II and microtubule inhibitor, evades paclitaxel resistance in P-glycoprotein overexpressing cancer cells
The efficacy of microtubule targeting agents in cancer treatment has been compromised by the development of drug resistance that may involve both, P-glycoprotein overexpression and the changes in beta-tubulin isoforms' expression. The anti-Topoisomerase II activity of methyl 4-((E)-2-(methoxycarbonyl)vinyloxy)oct-2-ynoate (DTA0100) was recently reported. Herein, we further evaluated this propargylic enol ether derivative and found that it exerts inhibitory effect on tubulin polymerization by binding to colchicine binding site. DTA0100 mitotic arrest properties were investigated in two multi-drug resistant cancer cell lines with P-glycoprotein overexpression (colorectal carcinoma and glioblastoma). The sensitivity of multi-drug resistant cancer cell lines to DTA0100 was not significantly changed in contrast to microtubule targeting agents such as paclitaxel, vinblastine and colchicine. DTA0100 clearly induced microtubule depolymerization, leading to disturbance of cell cycle kinetics and subsequent apoptosis. The fine-tuning in beta-tubulin isoforms expression observed in multi drug resistant cancer cells may influence the efficacy of DTA0100. Importantly, DTA0100 blocked the Pglycoprotein function in both multi-drug resistant cancer cell lines without inducing the increase in Pglycoprotein expression. Therefore, DTA0100 acting as dual inhibitor of Topoisomerase II and microtubule formation could be considered as multi-potent anticancer agent. Besides, it is able to overcome the problem of drug resistance that emerges in the therapeutic approaches with either Topoisomerase II or microtubule targeting agents.Related to published version: [https://imagine.imgge.bg.ac.rs/handle/123456789/1079]This is the peer reviewed version of the paper: Podolski-ReniÄ, A., BankoviÄ, J., DiniÄ, J., Rios-Luci, C., Fernandes, M. X., Ortega, N., KovaÄeviÄ GrujiÄiÄ, N., Martin, V. S., Padron, J. M., & PesiÄ, M. (2017). DTA0100, dual topoisomerase II and microtubule inhibitor, evades paclitaxel resistance in P-glycoprotein overexpressing cancer cells. European Journal of Pharmaceutical Sciences, 105, 159â168. [https://doi.org/10.1016/j.ejps.2017.05.011
First direct constraints on Fierz interference in free neutron decay
Precision measurements of free neutron -decay have been used to
precisely constrain our understanding of the weak interaction. However the
neutron Fierz interference term , which is particularly sensitive to
Beyond-Standard-Model tensor currents at the TeV scale, has thus far eluded
measurement. Here we report the first direct constraints on this term, finding
,
consistent with the Standard Model. The uncertainty is dominated by absolute
energy reconstruction and the linearity of the beta spectrometer energy
response
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