4,347 research outputs found
Neutron star properties in density-dependent relativistic Hartree-Fock theory
With the equations of state provided by the newly developed density dependent
relativistic Hartree-Fock (DDRHF) theory for hadronic matter, the properties of
the static and -equilibrium neutron stars without hyperons are studied
for the first time, and compared to the predictions of the relativistic mean
field (RMF) models and recent observational data. The influences of Fock terms
on properties of asymmetric nuclear matter at high densities are discussed in
details. Because of the significant contributions from the - and
-exchange terms to the symmetry energy, large proton fractions in
neutron stars are predicted by the DDRHF calculations, which strongly affect
the cooling process of the star. The critical mass about 1.45 , close
to the limit 1.5 determined by the modern soft X-ray data analysis,
is obtained by DDRHF with the effective interactions PKO2 and PKO3 for the
occurrence of direct Urca process in neutron stars. The maximum masses of
neutron stars given by the DDRHF calculations lie between 2.45 M and
2.49 M, which are in reasonable agreement with high pulsar mass from PSR B1516+02B. It is also found that the mass-radius
relations of neutron stars determined by DDRHF are consistent with the
observational data from thermal radiation measurement in the isolated neutron
star RX J1856, QPOs frequency limits in LMXBs 4U 0614+09 and 4U 1636-536, and
redshift determined in LMXBs EXO 0748-676.Comment: 28 pages, 11 figure
Life fingerprints of nuclear reactions in the body of animals
Nuclear reactions are a very important natural phenomenon in the universe. On the earth, cosmic rays constantly cause nuclear reactions. High energy beams created by medical devices also induce nuclear reactions in the human body. The biological role of these nuclear reactions is unknown. Here we show that the in vivo biological systems are exquisite and sophisticated by nature in influence on nuclear reactions and in resistance to radical damage in the body of live animals. In this study, photonuclear reactions in the body of live or dead animals were induced with 50-MeV irradiation. Tissue nuclear reactions were detected by positron emission tomography (PET) imaging of the induced beta+ activity. We found the unique tissue "fingerprints" of beta+ (the tremendous difference in beta+ activities and tissue distribution patterns among the individuals) are imprinted in all live animals. Within any individual, the tissue "fingerprints" of 15O and 11C are also very different. When the animal dies, the tissue "fingerprints" are lost. The biochemical, rather than physical, mechanisms could play a critical role in the phenomenon of tissue "fingerprints". Radiolytic radical attack caused millions-fold increases in 15O and 11C activities via different biochemical mechanisms, i.e. radical-mediated hydroxylation and peroxidation respectively, and more importantly the bio-molecular functions (such as the chemical reactivity and the solvent accessibility to radicals). In practice biologically for example, radical attack can therefore be imaged in vivo in live animals and humans using PET for life science research, disease prevention, and personalized radiation therapy based on an individual's bio-molecular response to ionizing radiation
Converting Hybrid Wire-frames to B-rep Models
International audienceSolid reconstruction from engineering drawings is one of the efficient technologies to product solid models. The B-rep oriented approach provides a practical way for reconstructing a wide range of objects. However, its major limitation is the computational complexity involved in the search for all valid faces from the intermediate wire-frame, especially for objects with complicated face topologies. In previous work, we presented a hint-based algorithm to recognize quadric surfaces from orthographic views and generate a hybrid wire-frame as the intermediate model of our B-rep oriented method. As a key stage in the process of solid reconstructing, we propose an algorithm to convert the hybrid wire-frame to the final B-rep model by extracting all the rest faces of planes based on graph theory. The entities lying on the same planar surface are first collected in a plane graph. After all the cycles are traced in a simplified edge-adjacency matrix of the graph, the face loops of the plane are formed by testing loop containment and assigning loop directions. Finally, the B-rep model is constructed by sewing all the plane faces based on the M¨obius rule. The method can efficiently construct 2- manifold objects with a variety of face topologies, which is illustrated by results of implementatio
Unitary Constraints on Semiclassical Schwarzschild Black Holes in the Presence of Island
We reconsider dimensional asymptotically flat eternal Schwarzschild
black hole, and focus on the situation where the inner boundary of the
radiation region is chosen to be near the horizon (i.e. ). The
tension between the near horizon condition and the short-distance approximation
emerges in large dimensions in previous papers. We remove this tension by
introducing a more proper near horizon condition, thus the resulting island
solution is well-behaved in any dimensional spacetime. Interestingly,
a novel constraint is obtained in this situation as required by the existence
of the island solution, which directly leads to the constraints on the size of
the Schwarzschild black hole, the position of the inner boundary for the
radiation region, or the value of in any
dimension. When considering the large limit, the constraint on the size of
the Schwarzschild black hole obtained in this situation is in agreement with
the result given in . We interpret these as
the unitary constraints implied by the presence of island in semiclassical
gravity.Comment: 21 pages, 4 figures; new contents added in Section 3.2 to derive the
constraint, also many related modification
The Entanglement in Anisotropic Heisenberg XYZ Chain with inhomogeneous magnetic field
The thermal entanglement of a two-qubit anisotropic Heisenberg chain
under an inhomogeneous magnetic field b is studied. It is shown that when
inhomogeneity is increased to certain value, the entanglement can exhibit a
larger revival than that of less values of b. The property is both true for
zero temperature and a finite temperature. The results also show that the
entanglement and critical temperature can be increased by increasing
inhomogeneous exteral magnetic field
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