5,539 research outputs found
HST Paschen alpha and 1.9 micron imaging of Sgr A West
We present HST/NICMOS images at 0.2" resolution of the HI Paschen Alpha (PaA)
emission line in a 70" x 90" region of the Galactic center centered on the
non-thermal radio source Sgr A*. The majority of the emission arises from
ionized gas in the mini-spiral in the central parsec. PaA emission is also seen
from 26 stellar sources, presumably early-type stars with mass-loss winds. The
new data reveal significant small-scale structure (<1"~0.04pc) in the ionized
gas of the mini-spiral; low surface brightness emission features are also seen
for the first time. Extinction, estimated from the ratio of observed PaA
emission to 6-cm continuum emission, varies from 20 to 50 mag with a median
Av=31.1 mag, in excellent agreement with earlier estimates for the stellar
sources and indepedent measurements derived using H92alpha recombination line
data. Large increases in extinction are seen along the periphery of the ionized
gas, suggesting that the ionized gas is partially extincted by dust in the
molecular clouds at the outside of the ionized regions. The small-scale,
filamentary structures in the ionized gas have a free thermal expansion time of
only ~ 3000 yrs; either magnetic fields or mass-loss winds from the hot
emission line stars may contain the ionized filaments. For both the ionized gas
and the stellar continuum, the centroids of the emission remain within ~+/- 1"
from a radius of 2" out to 40", providing further evidence that Sgr A* is
indeed at or extremely close to the dynamical center of the Galactic nucleus
stellar distribution. The 1.9 micron surface brightness increases inwards to
0.9" and then decreases or levels off closer to Sgr A*, possibly indicating the
core radius of the central stellar distribution or depletion of the late-type
stars by stellar collisions near the central black hole.Comment: 43 pages, 15 figures, 2 tables; Accepted to ApJ (9/1/03 issue
XMM-Newton observations of the supernova remnant IC443: I. soft X-ray emission from shocked interstellar medium
The shocked interstellar medium around IC443 produces strong X-ray emission
in the soft energy band (E<1.5 keV). We present an analysis of such emission as
observed with the EPIC MOS cameras on board the XMM-Newotn observatory, with
the purpose to find clear signatures of the interactions with the interstellar
medium (ISM) in the X-ray band, which may complement results obtained in other
wavelenghts. We found that the giant molecular cloud mapped in CO emission is
located in the foreground and gives an evident signature in the absorption of
X-rays. This cloud may have a torus shape and the part of torus interacting
with the IC443 shock gives rise to 2MASS-K emission in the southeast. The
measured density of emitting X-ray shocked plasma increases toward the
northeastern limb, where the remnant is interacting with an atomic cloud. We
found an excellent correlation between emission in the 0.3-0.5 keV band and
bright optical/radio filament on large spatial scales. The partial shell
structure seen in this band therefore traces the encounter with the atomic
cloud.Comment: 10 pages, 10 figures, accepted for publication in ApJ (20 September
2006, v649). For hi-res figures, see
http://www.astropa.unipa.it/Library/OAPA_preprints/ic443ele1.ps.g
Isolated X-ray -- infrared sources in the region of interaction of the supernova remnant IC 443 with a molecular cloud
The nature of the extended hard X-ray source XMMU J061804.3+222732 and its
surroundings is investigated using XMM-Newton, Chandra, and Spitzer
observations. This source is located in an interaction region of the IC 443
supernova remnant with a neighboring molecular cloud. The X-ray emission
consists of a number of bright clumps embedded in an extended structured
non-thermal X-ray nebula larger than 30" in size. Some clumps show evidence for
line emission at ~1.9 keV and ~3.7 keV at the 99% confidence level. Large-scale
diffuse radio emission of IC 443 passes over the source region, with an
enhancement near the source. An IR source of about 14" x 7" size is prominent
in the 24 um, 70 um, and 2.2 um bands, adjacent to a putative Si K-shell X-ray
line emission region. The observed IR/X-ray morphology and spectra are
consistent with those expected for J/C-type shocks of different velocities
driven by fragmented supernova ejecta colliding with the dense medium of a
molecular cloud. The IR emission of the source detected by Spitzer can be
attributed to both continuum emission from an HII region created by the ejecta
fragment and line emission excited by shocks. This source region in IC 443 may
be an example of a rather numerous population of hard X-ray/IR sources created
by supernova explosions in the dense environment of star-forming regions.
Alternative Galactic and extragalactic interpretations of the observed source
are also discussed.Comment: The Astrophysical Journal, v. 677 (April 2008), in pres
Mathematical Modeling of Risk-Taking in Bipolar Disorder: Evidence of Reduced Behavioral Consistency, With Altered Loss Aversion Specific to Those With History of Substance Use Disorder
Bipolar disorder (BD) is associated with excessive pleasure-seeking risk-taking behaviors that often characterize its clinical presentation. However, the mechanisms of risk-taking behavior are not well-understood in BD. Recent data suggest prior substance use disorder (SUD) in BD may represent certain trait-level vulnerabilities for risky behavior. This study examined the mechanisms of risk-taking and the role of SUD in BD via mathematical modeling of behavior on the Balloon Analogue Risk Task (BART). Three groupsâ18 euthymic BD with prior SUD (BD+), 15 euthymic BD without prior SUD (BDâ), and 33 healthy comparisons (HC)âcompleted the BART. We modeled behavior using four competing hierarchical Bayesian models, and model comparison results favored the Exponential-Weight Mean-Variance (EWMV) model, which encompasses and delineates five cognitive components of risk-taking: prior belief, learning rate, risk preference, loss aversion, and behavioral consistency. Both BD groups, regardless of SUD history, showed lower behavioral consistency than HC. BD+ exhibited more pessimistic prior beliefs (relative to BDâ and HC) and reduced loss aversion (relative to HC) during risk-taking on the BART. Traditional measures of risk-taking on the BART (adjusted pumps, total points, total pops) detected no group differences. These findings suggest that reduced behavioral consistency is a crucial feature of risky decision-making in BD and that SUD history in BD may signal additional trait vulnerabilities for risky behavior even when mood symptoms and substance use are in remission. This study also underscores the value of using mathematical modeling to understand behavior in research on complex disorders like BD
Why Is Cardiac Morbidity and Mortality Greater Around Christmas, New Yearâs, Monday Mornings and in the Morning Hours: Potential Roles of Unrecognized Ionized Hypomagnesemia and Release of Ceramides?
The following is the introduction to this article: There is a growing incidence of lethal cardiac events around Christmas, New Yearâs and in the morning hours from 4:00 to 10:00 a.m. which is well-established in the USA and in The Southern Hemisphere [1-7]. In addition, many cardiac deaths often occur on Mondays with no satisfactory explanation [2,3]. Many of these deaths are, for the most part, unexplained and listed as âdeath from ânatural causesâ. Although in the USA, the deaths which occur around Christmas and New Years happen in the cold âwinter months, this does not account for many cardiac incidences which occur throughout the year in the early a.m. hours or on Mondays. A number of explanations have been offered to explain the higher morbidities and mortalities at these special times of the year, morning hours and on Mondays, such as emotional stresses, too much ingestion of alcoholic beverages, improper medical facilities, diet, and/or changes in the physical environments [1-7]
The Barley Genome Sequence Assembly Reveals Three Additional Members of the <i>CslF </i>(1,3;1,4)-b-Glucan Synthase Gene Family
An important component of barley cell walls, particularly in the endosperm, is (1,3;1,4)-ÎČ-glucan, a polymer that has proven health benefits in humans and that influences processability in the brewing industry. Genes of the cellulose synthase-like (Csl) F gene family have been shown to be involved in (1,3;1,4)-ÎČ-glucan synthesis but many aspects of the biosynthesis are still unclear. Examination of the sequence assembly of the barley genome has revealed the presence of an additional three HvCslF genes (HvCslF11, HvCslF12 and HvCslF13) which may be involved in (1,3;1,4)-ÎČ-glucan synthesis. Transcripts of HvCslF11 and HvCslF12 mRNA were found in roots and young leaves, respectively. Transient expression of these genes in Nicotiana benthamiana resulted in phenotypic changes in the infiltrated leaves, although no authentic (1,3;1,4)-ÎČ-glucan was detected. Comparisons of the CslF gene families in cereals revealed evidence of intergenic recombination, gene duplications and translocation events. This significant divergence within the gene family might be related to multiple functions of (1,3;1,4)-ÎČ-glucans in the Poaceae. Emerging genomic and global expression data for barley and other cereals is a powerful resource for characterising the evolution and dynamics of complete gene families. In the case of the CslF gene family, the results will contribute to a more thorough understanding of carbohydrate metabolism in grass cell walls
Strategies for organic VLC: Effects of clipping on the performance of multi-band CAP modulation with polymer-based light-emitting diodes
We investigate, for the first time, the effect of signal clipping on multi-band carrier-less amplitude and phase (m-CAP) modulation in visible light communications based on PLEDs. We experimentally demonstrate a Q-factor improvement up to ~2.25 dB can be obtained with a clipping level of 50%
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Bayesian hierarchical vector autoregressive models for patient-level predictive modeling
Predicting health outcomes from longitudinal health histories is of central importance to healthcare. Observational healthcare databases such as patient diary databases provide a rich resource for patient-level predictive modeling. In this paper, we propose a Bayesian hierarchical vector autoregressive (VAR) model to predict medical and psychological conditions using multivariate time series data. Compared to the existing patient-specific predictive VAR models, our model demonstrated higher accuracy in predicting future observations in terms of both point and interval estimates due to the pooling effect of the hierarchical model specification. In addition, by adopting an elastic-net prior, our model offers greater interpretability about the associations between variables of interest on both the population level and the patient level, as well as between-patient heterogeneity. We apply the model to two examples: 1) predicting substance use craving, negative affect and tobacco use among college students, and 2) predicting functional somatic symptoms and psychological discomforts
Expanded Multiband Super-Nyquist CAP Modulation for Highly Bandlimited Organic Visible Light Communications
In this article, we experimentally demonstrate a novel expanded nonorthogonal multiband super-Nyquist carrier-less amplitude and phase (m-ESCAP) modulation for bandlimited organic visible light communication (VLC) systems. The proposed scheme has the same bandwidth requirement as the conventional m-CAP while breaking the orthogonality between subcarriers by purposely overlapping them. We compare m-ESCAP with the conventional m-CAP and a compressed nonorthogonal version of m-CAP (m-SCAP) in terms of measured bit error rate (BER) performance, bit rates, and spectral efficiencies. We show that the m-ESCAP system offers improvement in the bit rate of 10% and 20% compared to the m-CAP and m-SCAP, respectively, and in the spectral efficiency of 20% compared to m-CAP. These gains are achieved at the cost of increased BER, which, however, remains below the 7% forward error correction limit
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