162 research outputs found
Compact High-Velocity Clouds at High Resolution
Six examples of the compact, isolated high-velocity clouds catalogued by
Braun & Burton (1999) and identified with a dynamically cold ensemble of
primitive objects falling towards the barycenter of the Local Group have been
imaged with the Westerbork Synthesis Radio Telescope; an additional ten have
been imaged with the Arecibo telescope. The imaging reveals a characteristic
core/halo morphology: one or several cores of cool, relatively
high-column-density material, are embedded in an extended halo of warmer,
lower-density material. Several of the cores show kinematic gradients
consistent with rotation; these CHVCs are evidently rotationally supported and
dark-matter dominated. The imaging data allows several independent estimates of
the distances to these objects, which lie in the range 0.3 to 1.0 Mpc. The CHVC
properties resemble what might be expected from very dark dwarf irregular
galaxies.Comment: 12 pages, 7 figures, to appear in "The Chemical Evolution of the
Milky Way: Stars versus Clusters", eds. F. Matteuchi and F. Giovannelli,
Kluwer Academic Publisher
A high-velocity black hole on a Galactic-halo orbit in the solar neighborhood
Only a few of the dozen or so stellar-mass black holes have been observed
away from the plane of the Galaxy. Those few could have been ejected from
the plane as a result of a ``kick'' received during a supernova explosion, or
they could be remnants of the population of massive stars formed in the early
stages of evolution of the Galaxy. Determining their orbital motion should help
to distinguish between these options. Here we report the transverse motion (in
the plane of the sky) for the black hole X-ray nova XTE J1118+480 (refs 2-5),
from which we derive a large space velocity. This X-ray binary has an eccentric
orbit around the Galactic Centre, like most objects in the halo of the Galaxy,
such as ancient stars and globular clusters. The properties of the system
suggest that its age is comparable to or greater than the age of the Galactic
disk. Only an extraordinary ``kick'' from a supernova could have launched the
black hole into an orbit like this from a birth place in the disk of the
Galaxy.Comment: 8 pages including 2 color figures. Additional figures and animation
in http://www.iafe.uba.ar/astronomia/FM/mirabel.htm
Item bias detection in the Hospital Anxiety and Depression Scale using structural equation modeling: comparison with other item bias detection methods
Stellar Multiplicity
Stellar multiplicity is an ubiquitous outcome of the star formation process.
Characterizing the frequency and main characteristics of multiple systems and
their dependencies on primary mass and environment is therefore a powerful tool
to probe this process. While early attempts were fraught with selection biases
and limited completeness, instrumentation breakthroughs in the last two decades
now enable robust analyses. In this review, we summarize our current empirical
knowledge of stellar multiplicity for Main Sequence stars and brown dwarfs, as
well as among populations of Pre-Main Sequence stars and embedded protostars.
Clear trends as a function of both primary mass and stellar evolutionary stage
are identified that will serve as a comparison basis for numerical and
analytical models of star formation.Comment: original version submitted to ARA&A, final version to appear in vol.
51, comments welcome, 38 pages, 5 figure
Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo
We report the discovery of molecular hydrogen absorption in a Galactic
high-velocity cloud (HVC) in the direction of the Large Magellanic Cloud. For
the same HVC we derive an iron abundance which is half of the solar value.
Thus, all evidence points to a Galactic origin for high-velocity cloud complex
in front of the LMC.Comment: Published in Nature, this week; 14 pages, 3 figure
Motor function in Parkinson's disease and supranuclear palsy: simultaneous factor analysis of a clinical scale in several populations
BACKGROUND: In order to better understand the similarities and differences in the motor behaviour of different groups of patients, their scores on the Motor Examination section of the Unified Parkinson's Disease Rating Scale (UPDRS) were analysed simultaneously. The three groups consisted, respectively, of patients with Parkinson's disease (PD) on medication, patients with Parkinson's disease withdrawn from anti-parkinsonian medication for at least 12 hours, and patients diagnosed with a specific Parkinsonism syndrome: Progressive Supranuclear Palsy (PSP). METHODS: A total of 669 consecutively sampled patients from three separate hospital-based clinics participated (294 PD on medication; 200 PD off medication: 175 PSP). The Motor Examination section of the UPDRS was administered by neurologists at the three participating clinics. The patient scores on each item were recorded. To assess similarities and differences among the components of the UPDRS in these samples, we performed simultaneous or multigroup factor analysis on the covariance matrices of the three groups. In addition, it was investigated whether a single model for the Motor Examination section of the UPDRS could be developed which would be valid for all three groups at the same time. RESULTS: A single six-dimensional factor solution was found that fitted all groups, although this was not straightforward due to differences between the tremor-at-rest variables. The factors were identified as Tremor-at-rest, Postural Tremor, Axial Dysfunctioning, Rigidity, Left Bradykinesia and Right Bradykinesia. The analysis also pointed to a somewhat lower lateralization in bradykinesia for PSP patients. The groups differed in intensity of motor impairment, especially with respect to Tremor-at-Rest, but the overall relationships between the variables were shared by the three groups. In addition, apart from the common factor structure evidence of differences in body part-specific and motor-specific variances was found. CONCLUSION: From a clinical point of view, the analyses showed that using the Motor Examination section of the UPDRS is also appropriate for patients with PSP, because the correlational structure of the items is directly comparable to that of Parkinson's patients. Methodologically, the analysis of all groups together showed that it is possible to evaluate similarities and differences between factor structures in great detail
Cross-national comparison of the link between socioeconomic status and emotional and behavioral problems in youths
Introduction: In previous longitudinal studies in the US, lower socioeconomic status (SES) was associated with more emotional and behavioral problems. It remains unclear whether these findings can be generalized outside the US, as different countries vary in their health care systems and prevention of psychopathology in youth. Therefore, we studied the same associations in a comparable sample in The Netherlands and directly tested for differences between the US and The Netherlands. Methods: The US (N = 833) and Dutch (N = 708) population samples were followed-up for 9 years. Age at baseline ranged from 8 to 16 years. Parents filled out behavior checklists. Results: Analyses revealed very few differences between the two countries. In both countries, SES predicted syndrome scores and cumulative prevalence rates for internalizing and externalizing problems (withdrawn and aggressive behavior) and for thought and attention Problems. The SES gradient in syndrome scores was stable over time. Only for withdrawn behavior, the gradient was larger in young adulthood. Conclusion: Although the health care systems differ between the US and The Netherl
Galactic Effects on Habitability
The galactic environment has been suspected to influence planetary
habitability in many ways. Very metal-poor regions of the Galaxy, or those
largely devoid of atoms more massive than H and He, are thought to be unable to
form habitable planets. Moreover, if such planets do form, the young system is
subjected to close stellar passages while it resides in its stellar birth
cluster. Various potential hazards remain after clusters disperse. For
instance, central galactic regions may present risks to habitability via nearby
supernovae, gamma ray bursts (GRBs), and frequent comet showers. In addition,
planets residing within very wide binary star systems are affected by the
Galaxy, as local gravitational perturbations from the Galaxy can increase the
binary's eccentricity until it destabilizes the planets it hosts. Here we
review the most recent work on the main galactic influences over planetary
habitability. Although there must be some metallicity limit below which rocky
planets cannot form, recent exoplanet surveys show that they form around stars
with a very large range of metallicities. Once formed, the probability of star
clusters destabilizing planetary systems only becomes high for rare, extremely
long-lived clusters. Regarding threats to habitability from supernovae, GRBs,
and comet showers, many recent studies suggest that their hazards are more
limited than originally thought. Finally, denser regions of the Galaxy enhance
the threat that very wide binary companions pose to planetary habitability, but
the probability that a very wide binary star disrupts habitability will always
be substantially below 100% for any environment. While some Milky Way regions
must be more hospitable to habitable planets than others, it is difficult to
state that habitable planets are confined to any well-defined region of the
Galaxy or that any other particular region of the Galaxy is uninhabitable.Comment: Invited review chapter, accepted for publication in the "Handbook of
Exoplanets"; 19 pages; 2 figure
National Origin and Behavioural Problems of Toddlers: The Role of Family Risk Factors and Maternal Immigration Characteristics
In many societies the prevalence of behavioural problems in school-aged children varies by national origin. We examined the association between national origin and behavioural problems in 1½-year-old children. Data on maternal national origin and the Child Behavior Checklist for toddlers (n = 4943) from a population-based cohort in the Netherlands were used. Children from various non-Dutch backgrounds all had a significantly higher mean behavioural problem score. After adjustment for family risk factors, like family income and maternal psychopathology, the differences attenuated, but remained statistically significant. Non-Dutch mothers with immigration risk factors, such as older age at immigration or no good Dutch language skills, reported significantly more behavioural problems in their offspring. In conclusion, the present study indicated more behavioural problems in immigrant toddlers from various backgrounds. Researchers and policymakers aiming to tackle disparities in behavioural problems should take into account that risks associated with national origin are intertwined with unfavourable family and immigration characteristics
Seasonal Changes in Mood and Behavior Are Linked to Metabolic Syndrome
BACKGROUND: Obesity is a major public health problem worldwide. Metabolic syndrome is a risk factor to the cardiovascular diseases. It has been reported that disruptions of the circadian clockwork are associated with and may predispose to metabolic syndrome. METHODOLOGY AND PRINCIPAL FINDINGS: 8028 individuals attended a nationwide health examination survey in Finland. Data were collected with a face-to-face interview at home and during an individual health status examination. The waist circumference, height, weight and blood pressure were measured and samples were taken for laboratory tests. Participants were assessed using the ATP-III criteria for metabolic syndrome and with the Seasonal Pattern Assessment Questionnaire for their seasonal changes in mood and behavior. Seasonal changes in weight in particular were a risk factor of metabolic syndrome, after controlling for a number of known risk and potential confounding factors. CONCLUSIONS AND SIGNIFICANCE: Metabolic syndrome is associated with high global scores on the seasonal changes in mood and behavior, and with those in weight in particular. Assessment of these changes may serve as a useful indicator of metabolic syndrome, because of easy assessment. Abnormalities in the circadian clockwork which links seasonal fluctuations to metabolic cycles may predispose to seasonal changes in weight and to metabolic syndrome
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