Diagnóstico para identificação de demandas de pesquisa no setor produtivo de suínos e aves no Estado do Pará.

bitstream/item/63289/1/Oriental-Doc103.pd

Measurements of the Cerenkov light emitted by a TeO2 crystal

Bolometers have proven to be good instruments to search for rare processes because of their excellent energy resolution and their extremely low intrinsic background. In this kind of detectors, the capability of discriminating alpha particles from electrons represents an important aspect for the background reduction. One possibility for obtaining such a discrimination is provided by the detection of the Cerenkov light which, at the low energies of the natural radioactivity, is only emitted by electrons. In this paper, the results of the analysis of the light emitted by a TeO2 crystal at room temperature when transversed by a cosmic ray are reported. Light is promptly emitted after the particle crossing and a clear evidence of its directionality is also found. These results represent a strong indication that Cerenkov light is the main, if not even the only, component of the light signal in a TeO2 crystal. They open the possibility to make large improvements in the performance of experiments based on this kind of material

The X-ray emission from Nova V382 Velorum: II. The super-soft component observed with BeppoSAX

Nova Velorum 1999 (V382 Vel) was observed by BeppoSAX 6 months after optical maximum and was detected as a bright X-ray supersoft source, with a count rate 3.454+-0.002 cts/s in the LECS. It was the softest and most luminous supersoft source observed with this instrument. The flux in the 0.1-0.7 keV range was not constant during the observation. It dropped by a factor of 2 in less than 1.5 hour and then was faint for at least 15 minutes, without significant spectral changes. The observed spectrum is not well fit with atmospheric models of a hot, hydrogen burning white dwarf. This is due mainly to a supersoft excess in the range 0.1-0.2 keV, but the fit can be significantly improved at higher energy if at least one emission feature is superimposed. We suggest that a ``pseudocontinuum'' was detected, consisting of emission lines in the supersoft X-ray range superimposed on the thermal continuum of a white dwarf atmosphere. As a result, an accurate determination of the effective temperature and gravity of the white dwarf at this post-outburst stage is not possible.Comment: To appear in MNRA

Issues to be Addressed for Transforming a Digital Library Application for Experts into One for Final Users

This paper reports on the effort we made in adapting and opening a specialist tool, focused on illumination and designed purposely for scholars and researchers, in order to be suitable also for the general public. We describe the ongoing process we are conducting: the adaptation and the improvement of the IPSA digital archive using the results we collected after several sessions of user interviews, following suggestions of both scholars and simple users. We discuss user studies dynamics, that we consider as a loop-interaction, and the consequences that they entail upon the system design.Department of Information Engineering, University of Padua, Via Gradenigo 6/a, 35131 Padua, Italy, Department of Cultural Heritage, University of Padua, Piazza Capitaniato 7, 35139 Padua, Italy

XMM-Newton observations of Nova LMC 2000

We report on three X-ray observations of Nova LMC 2000 with XMM at 17, 51 and 294 days after the maximum, respectively. X-ray spectral fits show a concordant decrease of the absorbing column and the X-ray luminosity. No supersoft X-ray emission is detected. The mass of the ejected shell is determined to be (less than) 7.5*E-5 msun. Though data are sparse, one interesting correlation becomes visible: sources with a long-duration supersoft X-ray phase have shorter orbital periods than those with short or no supersoft X-ray phase. This can be understood considering that (i) enough matter has to be accreted in order to ignite the H burning, and (ii) that H burning ceases when the mass of the remaining material (after shell ejection and burning) drops below a certain limit under which the temperature at the bottom of the envelope is too low for the shell burning to compensate the energy loss from the surface.Comment: 8 pages AA style with 10 figures; accepted for publication in A

Measurements and optimization of the light yield of a TeO2_2 crystal

Bolometers have proven to be good instruments to search for rare processes because of their excellent energy resolution and their extremely low intrinsic background. In this kind of detectors, the capability of discriminating alpha particles from electrons represents an important aspect for the background reduction. One possibility for obtaining such a discrimination is provided by the detection of the Cherenkov light which, at the low energies of the natural radioactivity, is only emitted by electrons. This paper describes the method developed to evaluate the amount of light produced by a crystal of TeO$_2$ when hit by a 511 keV photon. The experimental measurements and the results of a detailed simulation of the crystal and the readout system are shown and compared. A light yield of about 52 Cherenkov photons per deposited MeV was measured. The effect of wrapping the crystal with a PTFE layer, with the aim of maximizing the light collection, is also presented

Optical observations of "hot" novae returning to quiescence

We have monitored the return to quiescence of novae previously observed in outburst as supersoft X-ray sources, with optical photometry of the intermediate polar (IP) V4743 Sgr and candidate IP V2491 Cyg, and optical spectroscopy of these two and seven other systems. Our sample includes classical and recurrent novae, short period (few hours), intermediate period (1-2 days) and long period (symbiotic) binaries. The light curves of V4743 Sgr and V2491 Cyg present clear periodic modulations. For V4743 Sgr, the modulation occurs with the beat of the rotational and orbital periods. If the period measured for V2491 Cyg is also the beat of these two periods, the orbital one should be almost 17 hours. The recurrent nova T Pyx already shows fragmentation of the nebular shell less than 3 years after the outburst. While this nova still had strong [OIII] at this post-outburst epoch, these lines had already faded after 3 to 7 years in all the others. We did not find any difference in the ratio of equivalent widths of high ionization/excitation lines to that of the Hbeta line in novae with short and long orbital period, indicating that irradiation does not trigger high mass transfer rate from secondaries with small orbital separation. An important difference between the spectra of RS Oph and V3890 Sgr and those of many symbiotic persistent supersoft sources is the absence of forbidden coronal lines. With the X-rays turn-off, we interpret this as an indication that mass transfer in symbiotics recurrent novae is intermittent.Comment: In press in Monthly Notices of the Royal Astronomical Societ

First optical identification of a suprsoft X-ray source in M31

We propose the first association of an optical counterpart with a luminous supersoft X-ray source in M31, RX J0044.0+4118, observed with ROSAT in July 1991. The PSPC position is at 1.6" angular distance from a candidate nova in outburst in September of 1990. This is interesting because the incidence of classical novae among supersoft X-ray sources is an open question. The proposed optical counterpart was measured at R~17.7 in September of 1990, and it had faded to R>19.2 when it was observed again after 70 days. The light curve was too sparsely monitored for definite conclusions on the speed class of the nova. No other variable objects with V<23.5 were found in the ROSAT spatial error box. We evaluate that the probability that a classical or recurrent nova was in outburst in the ROSAT error box in the few years preceding the observation is very small, so the proposed identification is meaningful. We also show evidence that the associated supersoft X-ray source turned off in the third year after the outburst.Comment: To appear in Astronomy and Astrophysic

Symbolic Melodic Similarity: State of the Art and Future Challenges

Fostered by the introduction of the Music Information Retrieval Evaluation eXchange (MIREX) competition, the number of systems which calculate Symbolic Melodic Similarity has recently increased considerably. In order to understand the state of the art, we provide a comparative analysis of existing algorithms. The analysis is based on eight criteria that help characterising the systems, and highlighting strengths and weaknesses. We also propose a taxonomy which classifies algorithms based on their approach. Both taxonomy and criteria are fruitfully exploited for providing input for new forthcoming research in the area