33 research outputs found
Sub-milliarcsecond precision spectro-astrometry of Be stars
The origin of the disks around Be stars is still not known. Further progress
requires a proper parametrization of their structure, both spatially and
kinematically. This is challenging as the disks are very small. Here we assess
whether a novel method is capable of providing these data. We obtained spectro
astrometry around the Pa beta line of two bright Be stars, alpha Col and zeta
Tau, to search for disk signatures. The data, with a pixel to pixel precision
of the centroid position of 0.3..0.4 milliarcsecond is the most accurate such
data to date. Artefacts at the 0.85 mas level are present in the data, but
these are readily identified as they were non-repeatable in our redundant
datasets. This does illustrate the need of taking multiple data to avoid
spurious detections. The data are compared with simple model simulations of the
spectro astrometric signatures due to rotating disks around Be stars. The upper
limits we find for the disk radii correspond to disk sizes of a few dozen
stellar radii if they rotate Keplerian. This is very close to observationally
measured and theoretically expected disk sizes, and this paper therefore
demonstrates that spectro-astrometry, of which we present the first such
attempt, has the potential to resolve the disks around Be stars.Comment: 6 pages, A&A accepte
The influence of rotation in radiation driven winds from hot stars II. CAK topological analysis
The topological analysis from Bjorkman (1995) for the standard model that
describes the winds from hot stars by Castor, Abbott & Klein (1975) has been
extended to include the effect of stellar rotation and changes in the
ionization of the wind. The differential equation for the momentum of the wind
is non--linear and transcendental for the velocity gradient. Due to this
non--linearity the number of solutions that this equation possess is not known.
After a change of variables and the introduction of a new physically
meaningless independent variable, we manage to replace the non--linear momentum
differential equation by a system of differential equations where all the
derivatives are {\it{explicitely}} given. We then use this system of equations
to study the topology of the rotating--CAK model. For the particular case when
the wind is frozen in ionization () only one physical solution is
found, the standard CAK solution, with a X--type singular point. For the more
general case (), besides the standard CAK singular point, we
find a second singular point which is focal--type (or attractor). We find also,
that the wind does not adopt the maximal mass--loss rate but almost the
minimal.Comment: 11 pages, Astronomy and Astrophysics Accepte
Matrix-assisted laser desorption ionization hydrogen/deuterium exchange studies to probe peptide conformational changes
AbstractHydrogen/deuterium (H/D) exchange chemistry monitored by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is used to study solution phase conformational changes of bradykinin, α-melanocyte stimulating hormone, and melittin as water is added to methanol-d4, acetonitrile, and isopropanol-d8 solutions. The results are interpreted in terms of a preference for the peptides to acquire more compact conformations in organic solvents as compared to the random conformations. Our interpretation is supported by circular dichroism spectra of the peptides in the same solvent systems and by previously published structural data for the peptides. These results demonstrate the utility of MALDI-TOF as a method to monitor the H/D exchange chemistry of peptides and investigations of solution-phase conformations of biomolecules
High resolution optical spectroscopy of an LBV-candidate inside the CygOB2 association
For the first time, we obtained the high-resolution (R=15000 and 60000)
optical spectra for the extremely luminous star No.12, associated with the
IR-source IRAS20308+4104, a member of the CygOB2 association. We have found
about 200 spectral features in range 4552-7939AA, including the interstellar
NaI, KI lines and numerous DIBs, which are the strongest absorption lines in
the spectrum, along with the HeI, CII, and SiII lines. A two-dimensional
spectral classification indicates that the spectral type is B5+/-0.5 Ia+. Our
analysis of the Vr data shows the presence of a Vr gradient in the stellar
atmosphere, caused by the infall of matter onto the star. The strong Halpha
emission displays broad Thompson wings and time-variable core absorption,
providing evidence that the stellar wind is inhomogeneous, and a slightly
blue-shifted PCyg type absorption profile. We concluded that the wind is
variable in time.Comment: 20 pages, 5 figures, 2 table
The supernatural characters and powers of sacred trees in the Holy Land
This article surveys the beliefs concerning the supernatural characteristics and powers of sacred trees in Israel; it is based on a field study as well as a survey of the literature and includes 118 interviews with Muslims and Druze. Both the Muslims and Druze in this study attribute supernatural dimensions to sacred trees which are directly related to ancient, deep-rooted pagan traditions. The Muslims attribute similar divine powers to sacred trees as they do to the graves of their saints; the graves and the trees are both considered to be the abode of the soul of a saint which is the source of their miraculous powers. Any violation of a sacred tree would be strictly punished while leaving the opportunity for atonement and forgiveness. The Druze, who believe in the transmigration of souls, have similar traditions concerning sacred trees but with a different religious background. In polytheistic religions the sacred grove/forest is a centre of the community's official worship; any violation of the trees is regarded as a threat to the well being of the community. Punishments may thus be collective. In the monotheistic world (including Christianity, Islam and Druze) the pagan worship of trees was converted into the worship/adoration of saints/prophets; it is not a part of the official religion but rather a personal act and the punishments are exerted only on the violating individual
Application of Tagging Systems for Personnel and Vehicle Access Control
Controlling the access of equipment, and people, has become more critical
over the last few years for improving productivity and to meet safety
responsibilities imposed by legislated obligations to have safety
management systems. Hence Mine Site Technologies (MST) has spent the
last three years completing the development of the tagging system to meet
the mining industry’s requirements, particularly streamlining access
control. The basic tagging system tracks active Tags carried by personnel,
or attached to vehicles and equipment, within underground zones.
These Tags are detected (read) by Beacons placed strategically
throughout the mine. As a Tag, or Tags, go past a Beacon they are read
and the information transmitted back to the main database PC. This
allows the current whereabouts of personnel and equipment to be known,
as well as the history of their movements.
The objectives of implementing the TRACKER Tagging System at
Oaky No 1 Coal Mine were to:
• maintain a count of personnel inbye a particular point, and can
alarm when a pre-set number is reached (eg the limit imposed by
availability of SCSR’s, etc);
• maintain a count of vehicles (and vehicle type) inbye a point, and can
alarm if when a pre-set number is reached (eg when rated diesel units
exceeds the limit for the ventilation present in that zone);
• manage the vehicle fleet, by keeping track of various vehicles
underground better control and dispatch management of the
equipment is achieved;
• keep track of equipment, knowing the location of equipment (such as
forks, baskets, pumps, fans, etc) where last used or stored will
minimise the risk of losing gear and assist in keeping inventory to a
minimum; and
• locate personnel in emergency situations, by placing read Beacons
throughout the mine the location of all personnel can be known in
real time so that in the event of an emergency, their withdrawal can
be monitored