9,208 research outputs found
Detection of Contact Binaries Using Sparse High Phase Angle Lightcurves
We show that candidate contact binary asteroids can be efficiently identified
from sparsely sampled photometry taken at phase angles >60deg. At high phase
angle, close/contact binary systems produce distinctive lightcurves that spend
most of the time at maximum or minimum (typically >1mag apart) brightness with
relatively fast transitions between the two. This means that a few (~5) sparse
observations will suffice to measure the large range of variation and identify
candidate contact binary systems. This finding can be used in the context of
all-sky surveys to constrain the fraction of contact binary near-Earth objects.
High phase angle lightcurve data can also reveal the absolute sense of the
spin.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in ApJ
Extreme Kuiper Belt Object 2001 QG298 and the Fraction of Contact Binaries
Extensive time-resolved observations of Kuiper Belt object 2001 QG298 show a
lightcurve with a peak-to-peak variation of 1.14 +-0.04 magnitudes and
single-peaked period of 6.8872 +- 0.0002 hr. The mean absolute magnitude is
6.85 magnitudes which corresponds to a mean effective radius of 122 (77) km if
an albedo of 0.04 (0.10) is assumed. This is the first known Kuiper Belt object
and only the third minor planet with a radius > 25 km to display a lightcurve
with a range in excess of 1 magnitude. We find the colors to be typical for a
Kuiper Belt object (B-V = 1.00 +- 0.04, V-R = 0.60 +- 0.02) with no variation
in color between minimum and maximum light. The large light variation,
relatively long double-peaked period and absence of rotational color change
argue against explanations due to albedo markings or elongation due to high
angular momentum. Instead, we suggest that 2001 QG298 may be a very close or
contact binary similar in structure to what has been independently proposed for
the Trojan asteroid 624 Hektor. If so, its rotational period would be twice the
lightcurve period or 13.7744 +- 0.0004 hr. By correcting for the effects of
projection, we estimate that the fraction of similar objects in the Kuiper Belt
is at least 10% to 20% with the true fraction probably much higher. A high
abundance of close and contact binaries is expected in some scenarios for the
evolution of binary Kuiper Belt objects.Comment: 15 text pages,6 figures(Color),5 Tables, Accepted to AJ for May 200
Global CNS gene transfer for a childhood neurogenetic enzyme deficiency: Canavan disease.
The neurogenetic prototypic disease on which we chose to test our gene therapy strategy is Canavan disease (CD). CD is an autosomal recessive leukodystrophy associated with spongiform degeneration of the brain. At present the disease is uniformly fatal in affected probands. CD is characterized by mutations in the aspartoacylase (ASPA) gene, resulting in loss of enzyme activity. In this review, recent evidence is summarized on the etiology and possible treatments for CD. In particular, we discuss two gene delivery systems representing recent advances in both viral and liposome technology: a novel cationic liposome-polymer-DNA (LPD) complex, DCChol/DOPE-protamine, as well as recombinant adeno-associated virus (AAV) vectors
The ultracool dwarf DENIS-P J104814.7-395606. Chromospheres and coronae at the low-mass end of the main-sequence
We have obtained an XMM-Newton observation and a broad-band spectrum from the
ultraviolet to the near infrared with X-Shooter for one of the nearest M9
dwarfs, DENIS-P J1048-3956 (4pc). We integrate these data by a compilation of
activity parameters for ultracool dwarfs from the literature with the aim to
advance our understanding of these objects by comparing them to early-M type
dwarf stars and the Sun.
Our deep XMM-Newton observation has led to the first X-ray detection of
DENIS-P J1048-3956 (log Lx = 25.1) as well as the first measurement of its V
band brightness (V = 17.35mag). Flux-flux relations between X-ray and
chromospheric activity indicators are here for the first time extended into the
regime of the ultracool dwarfs. The approximate agreement of DENIS-P J1048-3956
and other ultracool dwarfs with flux-flux relations for early-M dwarfs suggests
that the same heating mechanisms work in the atmospheres of ultracool dwarfs,
albeit weaker as judged from their lower fluxes. The observed Balmer decrements
of DENIS-P J1048-3956 are compatible with optically thick plasma in LTE at low,
nearly photospheric temperature or optically thin LTE plasma at 20000K.
Describing the decrements with CaseB recombination requires different emitting
regions for Halpha and the higher Balmer lines. The high observed Halpha/Hbeta
flux ratio is also poorly fitted by the optically thin models. We derive a
similarly high value for the Halpha/Hbeta ratio of vB10 and LHS2065 and
conclude that this may be a characteristic of ultracool dwarfs. We add DENIS-P
J1048-3956 to the list of ultracool dwarfs detected in both the radio and the
X-ray band. The Benz-Guedel relation between radio and X-ray luminosity of
late-type stars is well-known to be violated by ultracool dwarfs. We speculate
on the presence of two types of ultracool dwarfs with distinct radio and X-ray
behavior.Comment: accepted for publication in Astronomy & Astrophysic
Photoluminescence dispersion as a probe of structural inhomogeneity in silica
We report time-resolved photoluminescence spectra of point defects in
amorphous silicon dioxide (silica), in particular the decay kinetics of the
emission signals of extrinsic Oxygen Deficient Centres of the second type from
singlet and directly-excited triplet states are measured and used as a probe of
structural inhomogeneity. Luminescence activity in sapphire
(-AlO) is studied as well and used as a model system to compare
the optical properties of defects in silica with those of defects embedded in a
crystalline matrix. Only for defects in silica, we observe a variation of the
decay lifetimes with emission energy and a time dependence of the first moment
of the emission bands. These features are analyzed within a theoretical model
with explicit hypothesis about the effect introduced by the disorder of
vitreous systems. Separate estimations of the homogenous and inhomogeneous
contributions to the measured emission linewidth are obtained: it is found that
inhomogeneous effects strongly condition both the triplet and singlet
luminescence activities of oxygen deficient centres in silica, although the
degree of inhomogeneity of the triplet emission turns out to be lower than that
of the singlet emission. Inhomogeneous effects appear to be negligible in
sapphire
The Role Of Awareness And Communications In Information Security Management: A Health Care Information Systems Perspective
The purpose and intent of this research study is to understand and interpret the perception of stakeholders in healthcare organizations concerning security awareness and communications. The data is analyzed using the demographic characteristics of age, gender, education, and relevant work experience in order to determine if there are any significant differences between the groups regarding the state of awareness and the communication functions in a health care environment. The statistical results are presented in tabular form with descriptive analysis applied to each of the categories. Data-based conclusions are drawn and future research directions are indicated and discussed
Adjunctive clotiapine for the management of delusions in two adolescents with anorexia nervosa
Clotiapine is an atypical antipsychotic indicated for the management of a series of acute psychotic disorders. The current literature lacks evidence concerning the tolerability and clinical use of this drug in the management of individuals with anorexia nervosa (AN). In this study, we report two cases of adolescents with AN, treated with clotiapine. The reason for the administration of clotiapine was, for both patients, the manifestation of bizarre delusions concerning food and calories. Patient 1 presented a presyncope after the first dose of clotiapine, and treatment was rapidly discontinued. Patient 2 was treated with clotiapine for 9 months; doses were titrated from 20 mg/day to 70 mg/day, with an improvement in the reported delusions, which also enhanced compliance with psychological and nutritional interventions. EKG, QTc, white blood count, and red blood count were not relevantly influenced by the introduction of clotiapine in either patient. No extrapyramidal effect was documented. These reports stress the need for further studies assessing the tolerability and potential effect of clotiapine in treating adolescents with AN and delusional symptomatology
Modelling the incomplete Paschen-Back effect in the spectra of magnetic Ap stars
We present first results of a systematic investigation of the incomplete
Paschen-Back effect in magnetic Ap stars. A short overview of the theory is
followed by a demonstration of how level splittings and component strengths
change with magnetic field strength for some lines of special astrophysical
interest. Requirements are set out for a code which allows the calculation of
full Stokes spectra in the Paschen-Back regime and the behaviour of Stokes I
and V profiles of transitions in the multiplet 74 of FeII is discussed in some
detail. It is shown that the incomplete Paschen-Back effect can lead to
noticeable line shifts which strongly depend on total multiplet strength,
magnetic field strength and field direction. Ghost components (which violate
the normal selection rule on J) show up in strong magnetic fields but are
probably unobservable. Finally it is shown that measurements of the integrated
magnetic field modulus are not adversely affected by the Paschen-Back
effect, and that there is a potential problem in (magnetic) Doppler mapping if
lines in the Paschen-Back regime are treated in the Zeeman approximation.Comment: 8 pages, 10 figures, to appear in MNRA
Two-color ionization of hydrogen by short intense pulses
Photoelectron energy spectra resulting by the interaction of hydrogen with
two short pulses having carrier frequencies, respectively, in the range of the
infrared and XUV regions have been calculated. The effects of the pulse
duration and timing of the X-ray pulse on the photoelectron energy spectra are
discussed. Analysis of the spectra obtained for very long pulses show that
certain features may be explained in terms of quantum interferences in the time
domain. It is found that, depending on the duration of the X-ray pulse, ripples
in the energy spectra separated by the infrared photon energy may appear.
Moreover, the temporal shape of the low frequency radiation field may be
inferred by the breadth of the photoelectron energy spectra.Comment: 12 pages, 8 figure
- …