11,189 research outputs found
Photometry of the Stingray Nebula (V839 Ara) from 1889-2015 Across the Ionization of Its Planetary Nebula
Up until around 1980, the Stingray was an ordinary B1 post-AGB star, but then
it suddenly sprouted bright emission lines like in a planetary nebula (PN), and
soon after this the Hubble Space Telescope (HST) discovered a small PN around
the star, so apparently we have caught a star in the act of ionizing a PN. We
report here on a well-sampled light curve from 1889 to 2015, with unique
coverage of the prior century plus the entire duration of the PN formation plus
three decades of its aftermath. Surprisingly, the star anticipated the 1980's
ionization event by declining from B=10.30 in 1889 to B=10.76 in 1980. Starting
in 1980, the central star faded fast, at a rate of 0.20 mag/year, reaching
B=14.64 in 1996. This fast fading is apparently caused by the central star
shrinking in size. From 1994-2015, the V-band light curve is almost entirely
from the flux of two bright [OIII] emission lines from the unresolved nebula,
and it shows a consistent decline at a rate of 0.090 mag/year. This steady
fading (also seen in the radio and infrared) has a time scale equal to that
expected for ordinary recombination within the nebula, immediately after a
short-duration ionizing event in the 1980s. We are providing the first direct
measure of the rapidly changing luminosity of the central star on both sides of
a presumed thermal pulse in 1980, with this providing a strong and critical set
of constraints, and these are found to sharply disagree with theoretical models
of PN evolution.Comment: ApJ accepted, 54 pages, 4 figures, one long data tabl
Sex-role orientation and response to cognitive stressors
The present study was aimed at investigating the
relationship between sex-role orientation, as defined by the
BSRI, and heart-rate response to stress. After being
administered both the BSRI and JAS, 35 female undergraduate
volunteers were randomly assigned to one of two orders of
presentation, of moderately stressful verbal and spatial
tasks. Heart-rate was measured throughout the experimental
situation, and subjects rated each task for perceived
pleasantness. A significant (p=.032) interaction was found
between masculinity and femininity, with the androgynous and
undifferentiated groups showing lower heart-rate increases to
both tasks. Neither the BSRI nor the JAS Type A scales were
found to be significantly related with subjects' performance
on either task, although a trend did emerge with higher
masculinity scores being linked with somewhat better
performance. Furthermore, masculinity was significantly
associated with reports of greater perceived pleasantness for
both tasks. While the Type A variable was positively
correlated with masculinity, and negatively correlated with
femininity, it did not account for any of the above
relationships
Conformal Galilean Spin-3 Gravity in 3d
We consider Galilean limit of conformal algebra for spin-2 and spin-3 fields,
and study the gauge theory of these algebras. We analyze the equations of
motion and obtain the spectra of the theories.Comment: 20 page
Modeling the momentum distributions of annihilating electron-positron pairs in solids
Measuring the Doppler broadening of the positron annihilation radiation or
the angular correlation between the two annihilation gamma quanta reflects the
momentum distribution of electrons seen by positrons in the
material.Vacancy-type defects in solids localize positrons and the measured
spectra are sensitive to the detailed chemical and geometric environments of
the defects. However, the measured information is indirect and when using it in
defect identification comparisons with theoretically predicted spectra is
indispensable. In this article we present a computational scheme for
calculating momentum distributions of electron-positron pairs annihilating in
solids. Valence electron states and their interaction with ion cores are
described using the all-electron projector augmented-wave method, and atomic
orbitals are used to describe the core states. We apply our numerical scheme to
selected systems and compare three different enhancement (electron-positron
correlation) schemes previously used in the calculation of momentum
distributions of annihilating electron-positron pairs within the
density-functional theory. We show that the use of a state-dependent
enhancement scheme leads to better results than a position-dependent
enhancement factor in the case of ratios of Doppler spectra between different
systems. Further, we demonstrate the applicability of our scheme for studying
vacancy-type defects in metals and semiconductors. Especially we study the
effect of forces due to a positron localized at a vacancy-type defect on the
ionic relaxations.Comment: Submitted to Physical Review B on September 1 2005. Revised
manuscript submitted on November 14 200
Isolamento e caracterização molecular do vírus de Influenza suína.
Projeto/Plano de Ação: 03.03.23.200
Diagnosing fouling of hollow fibre MF membranes in wastewater reclamation
Fouling in membrane filtration processes is problematic but inevitable as it occurs with the retention of contaminants that accumulate on the membrane surface. The causes of fouling are often specific, depending upon feed water constituents, the membrane, and the operation regime. Therefore, it is desirable that a thorough investigation is performed on fouled membrane elements of the affected plant. This technique is known as membrane autopsy , which identities the cause of poor membrane performance, and hence, gives the opportunity to rectify or mitigate the problem and improve future plant design. In this study, the cause of membrane fouling at a small water recycling plant using a hollow fibre micro filtration (MF) system is investigated. A membrane autopsy protocol has been developed for water recycling applications that consists of four major steps: I) tensile testing to investigate the membrane mechanical integrity, (II) direct visual inspection, III) membrane surface analysis using field-emission environmental scanning electron microscopy (FESEM) (as well as atomic force microscopy (AFM) although it is not used in this case) techiques, and IV) foulant constituent analysis. Results obtained from this study indicate that the membrane has been fouled by a mixture of colloids and organic matters, enhanced by the presence of multivalent cations. Possible measures to mitigate fouling in this particular case have also been suggested
Physics issues in simulations with dynamical overlap fermions
We discuss the impact of various improvements on simulations of dynamical
overlap fermions using the Hybrid Monte Carlo algorithm. We focus on the usage
of fat links and multiple pseudo-fermion fields.Comment: 14 pages, 10 figure
Abstract delta modelling
Article / Letter to editorLeiden Inst Advanced Computer Science
Thermal Dileptons from a Nonperturbative Quark-Gluon Phase
Assuming that gluon condensates are important even above the deconfining
phase transition, we develop a model for the dilepton yield from a quark gluon
plasma. Using a simple fire ball description of a heavy ion collision, and
various estimates of the strengths of the gluon condensates, we compare our
predicted dilepton yields with those observed in the CERES and HELIOS
experiments at CERN. The simple model gives an adequate description of the
data, and in particular it explains the observed considerable enhancement of
the yield in the low mass region.Comment: 7 pages, 6 figures, reference adde
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