Remarks on transient photon production in heavy ion collisions

In this note, we discuss the derivation of a formula that has been used in the literature in order to compute the number of photons emitted by a hot or dense system during a finite time. Our derivation is based on a variation of the standard operator-based $S$-matrix approach. The shortcomings of this formula are then emphasized, which leads to a negative conclusion concerning the possibility of using it to predict transient effects for the photon rate.Comment: 13 page

Modelling of an IR scintillation counter

A systematic study of the excitation and de-excitation mechanisms in ternary gas mixtures Ar+CO2+N2 is presented regarding the possibility of developing a proportional scintillation counter based on the detection of the infrared molecular emissions associated with the lowest vibrational states of molecules. The use of visible or near-infrared photons ([lambda]<1 [mu]m) for applications like imaging and quality control of microstructure detectors has been reported. In view of these applications we analyse the processes leading to near-infrared emissions in pure argon and give an estimation of the number of photons emitted per electron, at several pressures, as a function of the charge gain.http://www.sciencedirect.com/science/article/B6TJM-3YXB101-2M/1/b5bfeb3739389bb6dbe4d84c8746dbf

Dilute Nuclear Matter in Chiral Perturbation Theory

We use chiral perturbation theory to compute the effective nucleon propagator in an expansion about low density in the chiral limit. We neglect four-nucleon interactions and focus on pion exchange. Evaluating the nucleon self-energy on its mass shell to leading order, we show that the effective nucleon mass increases by a small amount. We discuss the relevance of our results to the structure of compact stars.Comment: Manuscript rewritten, especially conclusions about mass shifts; contact terms cannot be neglected. Computation unchange

EXPERIMENTAL INVESTIGATION OF A PARAFFIN BASED HYBRID ROCKET

Hybrid rockets are known to be simpler, safer, environmentally friend, and, more importantly, cheaper than most of the technologies for propulsion devices used today. Hybrid rockets can be applied as the propulsion system in satellites launch vehicles, micro-satellites and tactical missiles. This paper deals with combustion of ultra-high molecular weight polyethylene (UHMWPE) and paraffin as the solid fuels burning with gaseous oxygen (GOX) as well as N O as the oxidizer in lab scale hybrid rocket motors. A test 2 stand was built to carry out the experiments. The main objectives were to investigate the ignition of the solid fuels, burning performance and regression rates for different operating conditions. With paraffin-based fuel the hybrid motor had the regression rate enhanced two to three folds compared to the UHMWPE, as reported in the literature. The overall performance of the motor, with paraffin as the fuel, is comparable to other technologies. Paraffin-based hybrid rockets can, then, be a safer and cheaper alternative to satellite launch vehicles for the Brazilian space program

Periodic variations in the O-C diagrams of five pulsation frequencies of the DB white dwarf EC 20058-5234

Variations in the pulsation arrival time of five independent pulsation frequencies of the DB white dwarf EC 20058−5234 individually imitate the effects of reflex motion induced by a planet or companion but are inconsistent when considered in unison. The pulsation frequencies vary periodically in a 12.9 year cycle and undergo secular changes that are inconsistent with simple neutrino plus photon-cooling models. The magnitude of the periodic and secular variations increases with the period of the pulsations, possibly hinting that the corresponding physical mechanism is located near the surface of the star. The phase of the periodic variations appears coupled to the sign of the secular variations. The standards for pulsation-timing-based detection of planetary companions around pulsating white dwarfs, and possibly other variables such as subdwarf B stars, should be re-evaluated. The physical mechanism responsible for this surprising result may involve a redistribution of angular momentum or a magnetic cycle. Additionally, variations in a supposed combination frequency are shown to match the sum of the variations of the parent frequencies to remarkable precision, an expected but unprecedented confirmation of theoretical predictions.Web of Scienc

Role of paracrine factors released by mesenchymal progenitors from the umbilical cord in neurons/glial cell viability, proliferation and differentiation

[Excerpt] Umbilical Cord Stem Cells are able to integrate within the CNS upon injury and to improve the condition of animals suffering from neurodegenerative diseases. However the mechanisms by which such phenomena are mediated are unknown. Therefore the main objective of the present work was to understand how a population of umbilical cord mesenchymal progenitor cells isolated from the Wharton Jelly (HUCPVCs), regulates viability, proliferation and different ion of post-natal hippocampal neurons and cortical glial cells. Hippocampal neurons and glial cells were exposed to HUCPVCs conditioned media (CM) (obtained 24, 48, 72 and 96 after 3 days of culture of HUCPVCs) for 1 week. Cell viability (MTS test) experiments revealed that HUCPVCs CM obtained for all time points did not cause any deleterious effects on both cell populations when compared to the control condition. [...]info:eu-repo/semantics/publishedVersio

Fermentação em estado sólido: uma alternativa para o aproveitamento e valorização de resíduos agroindustriais tropicais.

bitstream/CNPAT-2010/9607/1/Ct-102.pd

Zero-mode analysis of quantum statistical physics

We present a unified formulation for quantum statistical physics based on the representation of the density matrix as a functional integral. We identify the stochastic variable of the effective statistical theory that we derive as a boundary configuration and a zero mode relevant to the discussion of infrared physics. We illustrate our formulation by computing the partition function of an interacting one-dimensional quantum mechanical system at finite temperature from the path-integral representation for the density matrix. The method of calculation provides an alternative to the usual sum over periodic trajectories: it sums over paths with coincident endpoints, and includes non-vanishing boundary terms. An appropriately modified expansion into Matsubara modes provides a natural separation of the zero-mode physics. This feature may be useful in the treatment of infrared divergences that plague the perturbative approach in thermal field theory.Comment: 9 pages, 5 figure