Massive stars and globular cluster formation

We first present chemodynamical simulations to investigate how stellar winds of massive stars influence early dynamical and chemical evolution of forming globular clusters (GCs). In our numerical models, GCs form in turbulent,high-density giant molecular clouds (GMCs), which are embedded in a massive dark matter halo at high redshifts. We show how high-density, compact stellar systems are formed from GMCs influenced both by physical processes associated with star formation and by tidal fields of their host halos. We also show that chemical pollution of GC-forming GMCs by stellar winds from massive stars can result in star-to-star abundance inhomogeneities among light elements (e.g., C, N, and O) of stars in GCs. The present model with a canonical initial mass function (IMF) also shows a C-N anticorrelation that stars with smaller [C/Fe] have larger [N/Fe] in a GC. Although these results imply that ``self-pollution'' of GC-forming GMCs by stellar winds from massive stars can cause abundance inhomogeneities of GCs, the present models with different parameters and canonical IMFs can not show N-rich stars with [N/Fe] ~ 0.8 observed in some GCs (e.g., NGC 6752). We discuss this apparent failure in the context of massive star formation preceding low-mass one within GC-forming GMCs (``bimodal star formation scenario''). We also show that although almost all stars (~97%) show normal He abundances (Y) of ~0.24 some stars later formed in GMCs can have Y as high as ~0.3 in some models. The number fraction of He-rich stars with Y >0.26 is however found to be small (~10^-3) for most models.Comment: 10 pages, 8 figures, accepted by Ap

Universal relaxation function in nonextensive systems

We have derived the dipolar relaxation function for a cluster model whose volume distribution was obtained from the generalized maximum Tsallis nonextensive entropy principle. The power law exponents of the relaxation function are simply related to a global fractal parameter $\alpha$ and for large time to the entropy nonextensivity parameter $q$. For intermediate times the relaxation follows a stretched exponential behavior. The asymptotic power law behaviors both in the time and the frequency domains coincide with those of the Weron generalized dielectric function derived from an extension of the Levy central limit theorem. They are in full agreement with the Jonscher universality principle. Moreover our model gives a physical interpretation of the mathematical parameters of the Weron stochastic theory and opens new paths to understand the ubiquity of self-similarity and power laws in the relaxation of large classes of materials in terms of their fractal and nonextensive properties.Comment: Two figures. Submitted for publicatio

Catalisadores químicos utilizados na síntese de biodiesel.

bitstream/item/55583/1/doc-07.pd

Study od a Slice at +9 to +15 degrees of Declination: I. The Neutral Hydrogen Content of Galaxies in Loose Groups

We examine the H1 content of spiral galaxies in groups by using a catalog of loose groups of galaxies identified in a magnitude limited sample m < 15.7 spanning the range 8 h to 18 h in right ascension and +9 to +15 in declination. The redshift completeness of the galaxy sample is ~95%. No significant effect of H1 depletion is found, although there may be a hint that the earliest type spirals are slightly deficient.Comment: 10 pages, Latex, 3 tables, 5 figures, to appear in the Astronomical Journa

Kaons and pions in strange quark matter

The behavior of kaons and pions in strange quark matter in weak equilibrium, is investigated within the SU(3) Nambu-Jona-Lasinio [NJL] model. This work focuses a region of high densities where the behavior of mesons has not been explored in the framework of this model. It is found that above the density where strange valence quarks appear in the medium, $\rho = 3.8 \rho_0$, a change of behavior of different observables is observed indicating a tendency to the restoration of flavor symmetry. In particular, the splitting between charge multiplets, $K^+, K^-; K^0, {\bar K^0} {and} \pi^+, \pi^-$ decrease and the low energy modes with quantum numbers of $K^-, \bar K^0 {and} \pi^+$, which are excitations of the Fermi sea, are less relevant than for lower densities.Comment: 10 pages, 3 figures included; revised version, some changes in the discussio

Indefinite Causal Order in a Quantum Switch

In quantum mechanics events can happen in no definite causal order: in practice this can be verified by measuring a causal witness, in the same way that an entanglement witness verifies entanglement. Indefinite causal order can be observed in a quantum switch, where two operations act in a quantum superposition of the two possible orders. Here we realise a photonic quantum switch, where polarisation coherently controls the order of two operations, $\hat{A}$ and $\hat{B}$, on the transverse spatial mode of the photons. Our setup avoids the limitations of earlier implementations: the operations cannot be distinguished by spatial or temporal position. We show that our quantum switch has no definite causal order, by constructing a causal witness and measuring its value to be 18 standard deviations beyond the definite-order bound

Thermodynamic properties of QCD in external magnetic fields

We consider the effect of strong external electromagnetic fields on thermodynamic observables in QCD, through lattice simulations with 1+1+1 flavors of staggered quarks at physical quark masses. Continuum extrapolated results are presented for the light quark condensates and for their tensor polarizations, as functions of the temperature and the magnetic field. We find the light condensates to undergo inverse magnetic catalysis in the transition region, in a manner that the transition temperature decreases with growing magnetic field. We also compare the results to other approaches and lattice simulations. Furthermore, we relate the tensor polarization to the spin part of the magnetic susceptibility of the QCD vacuum, and show that this contribution is diamagnetic.Comment: 13 pages, 9 figures, talks presented by FB and GE at Xth Quark Confinement and the Hadron Spectrum, 8-12 October 2012, TUM Campus Garching, Munich, German

Laser induced THz emission from femtosecond photocurrents in Co/ZnO/Pt and Co/Cu/Pt multilayers

The ultrashort laser excitation of Co/Pt magnetic heterostructures can effectively generate spin and charge currents at the interfaces between magnetic and nonmagnetic layers. The direction of these photocurrents can be controlled by the helicity of the circularly polarized laser light and an external magnetic field. Here, we employ THz time-domain spectroscopy to investigate further the role of interfaces in these photo-galvanic phenomena. In particular, the effects of either Cu or ZnO interlayers on the photocurrents in Co/X/Pt (X = Cu, ZnO) have been studied by varying the thickness of the interlayers up to 5 nm. The results are discussed in terms of spin-diffusion phenomena and interfacial spin-orbit torque.Comment: 15 pages, 6 figures, 2 table

Effective restoration of chiral and axial symmetries at finite temperature and density

The effective restoration of chiral and axial symmetries is investigated within the framework of the SU(3) Nambu-Jona-Lasinio model. The topological susceptibility, modeled from lattice data at finite temperature, is used to extract the temperature dependence of the coupling strength of the anomaly. The study of the scalar and pseudoscalar mixing angles is performed in order to discuss the evolution of the flavor combinations of $q \bar q$ pairs and its consequences for the degeneracy of chiral partners. A similar study at zero temperature and finite density is also realized.Comment: 5 pages, 1 figure. Talk given at Strange Quark Matter 2004, Cape Town, South Africa, 15-20 September, 200