764 research outputs found
New sub-millimeter limits on dust in the 55 Cancri planetary system
We present new, high-sensitivity sub-millimeter observations towards 55
Cancri, a nearby G8 star with one, or possibly two, known planetary
companion(s). Our 850 m map, obtained with the SCUBA instrument on the
James Clerk Maxwell Telescope, shows three peaks of emission at the 2.5 mJy
level in the vicinity of the star's position. However, the observed peaks are
25\arcsec--40\arcsec away from the star and a deep -band optical image
reveals faint point sources that coincide with two of the sub-millimeter peaks.
Thus, we do not find evidence for dust emission spatially associated with 55
Cancri. The excess 60 m emission detected with ISO may originate from one
or more of the 850 m peaks that we attribute to background sources. Our
new results, together with the HST/NICMOS coronographic images in the
near-infrared, place stringent limits on the amount of dust in this planetary
system, and argue against the existence of a detectable circumstellar dust disk
around 55 Cnc.Comment: 11 pages, 2 PostScript figures, to appear in The Astrophysical
Journal Letter
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Modulation of frontal effective connectivity during speech
Noninvasive neurostimulation methods such as transcranial direct current stimulation (tDCS) can elicit long-lasting, polarity-dependent changes in neocortical excitability. In a previous concurrent tDCS-fMRI study of overt picture naming, we reported significant behavioural and regionally specific neural facilitation effects in left inferior frontal cortex (IFC) with anodal tDCS applied to left frontal cortex (Holland et al., 2011). Although distributed connectivity effects of anodal tDCS have been modelled at rest, the mechanism by which 'on-line' tDCS may modulate neuronal connectivity during a task-state remains unclear. Here, we used Dynamic Causal Modelling (DCM) to determine: (i) how neural connectivity within the frontal speech network is modulated during anodal tDCS; and, (ii) how individual variability in behavioural response to anodal tDCS relates to changes in effective connectivity strength. Results showed that compared to sham, anodal tDCS elicited stronger feedback from inferior frontal sulcus (IFS) to ventral premotor (VPM) accompanied by weaker self-connections within VPM, consistent with processes of neuronal adaptation. During anodal tDCS individual variability in the feedforward connection strength from IFS to VPM positively correlated with the degree of facilitation in naming behaviour. These results provide an essential step towards understanding the mechanism of 'online' tDCS paired with a cognitive task. They also identify left IFS as a 'top-down' hub and driver for speech change
Dust in the 55 Cancri planetary system
The presence of debris disks around 1-Gyr-old main sequence stars
suggests that an appreciable amount of dust may persist even in mature
planetary systems. Here we report the detection of dust emission from 55
Cancri, a star with one, or possibly two, planetary companions detected through
radial velocity measurements. Our observations at 850m and 450m imply
a dust mass of 0.0008-0.005 Earth masses, somewhat higher than that in the the
Kuiper Belt of our solar system. The estimated temperature of the dust grains
and a simple model fit both indicate a central disk hole of at least 10 AU in
radius. Thus, the region where the planets are detected is likely to be
significantly depleted of dust. Our results suggest that far-infrared and
sub-millimeter observations are powerful tools for probing the outer regions of
extrasolar planetary systems.Comment: 8 pages and 2 figures, to appear in the Astrophysical Journa
Probing the cosmic star formation using long Gamma-Ray Bursts: New constraints from the Spitzer Space Telescope
We report on IRAC-4.5mic, IRAC-8.0mic and MIPS-24mic deep observations of 16
Gamma-Ray Burst (GRBs) host galaxies performed with the Spitzer Space
Telescope, and we investigate in the thermal infrared the presence of evolved
stellar populations and dust-enshrouded star-forming activity associated with
these objects. Our sample is derived from GRBs that were identified with
sub-arcsec localization between 1997 and 2001, and only a very small fraction
(~20%) of the targeted sources is detected down to f_4.5mic ~3.5microJy and
f_24mic ~85microJy (3sigma). This likely argues against a population dominated
by massive and strongly-starbursting (i.e., SFR > ~100 Msol/yr) galaxies as it
has been recently suggested from submillimeter/radio and optical studies of
similarly-selected GRB hosts. Furthermore we find evidence that some GRBs do
not occur in the most infrared-luminous regions -- hence the most actively
star-forming environments -- of their host galaxies. Should the GRB hosts be
representative of all star-forming galaxies at high redshift, models of
infrared galaxy evolution indicate that > ~50% of GRB hosts should have f_24mic
> ~100microJy. Unless the identification of GRBs prior to 2001 was prone to
strong selection effects biasing our sample against dusty galaxies, we infer in
this context that the GRBs identified with the current techniques can not be
directly used as unbiased probes of the global and integrated star formation
history of the Universe.Comment: ApJ in press, 23 pages, 8 figures (scheduled for the ApJ 10 May 2006,
v642 2 issue). Full resolution available at
http://perceval.as.arizona.edu/~elefloch/Publis/ms_grb_spitzer.pd
Intra-Cavity Frequency-Doubled VECSEL System for Narrow Linewidth Rydberg EIT Spectroscopy
Vertical external-cavity surface-emitting lasers (VECSELs) augmented by
intra-cavity nonlinear optical frequency conversion have emerged as an
attractive light source of ultraviolet to visible light for demanding
scientific applications, relative to other laser technologies. They offer high
power, low phase noise, wide frequency tunability, and excellent beam quality
in a simple and inexpensive system architecture. Here, we characterize the
frequency stability of an intra-cavity frequency-doubled VECSEL with 690 mW of
output power at 475 nm using the delayed self-heterodyne technique and direct
comparison with a commercial external-cavity diode laser (ECDL). We measure the
fundamental's Lorentzian linewidth to be kHz, and the total
linewidth to be kHz. In addition, we perform Rydberg-state
spectroscopy via electromagnetically induced transparency (EIT), observing
narrow 3.5 MHz full-width half-maximum EIT. By doing so, we demonstrate that
intra-cavity frequency-doubled VECSELs can perform precision spectroscopy at
the MHz level, and are a promising tool for contemporary, and future, quantum
technologies.Comment: 13 pages, 5 figure
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Ablation of AMP-Activated Protein Kinase 2 Activity Exacerbates Insulin Resistance Induced by High-Fat Feeding of Mice
Objective: We determined whether muscle AMP-activated protein kinase (AMPK) has a role in the development of insulin resistance. Research Design and Methods: Muscle-specific transgenic mice expressing an inactive form of the AMPK 2 catalytic subunit (2i TG) and their wild-type littermates were fed either a high-fat (60% kcal fat) or a control (10% kcal fat) diet for 30 weeks. Results: Compared with wild-type mice, glucose tolerance in 2i TG mice was slightly impaired on the control diet and significantly impaired on the high-fat diet. To determine whether the whole-body glucose intolerance was associated with impaired insulin sensitivity in skeletal muscle, glucose transport in response to submaximal insulin (450 U/ml) was measured in isolated soleus muscles. On the control diet, insulin-stimulated glucose transport was reduced by 50% in 2i TG mice compared with wild-type mice. High-fat feeding partially decreased insulin-stimulated glucose transport in wild-type mice, while high-fat feeding resulted in a full blunting of insulin-stimulated glucose transport in the 2i TG mice. High-fat feeding in 2i TG mice was accompanied by decreased expression of insulin signaling proteins in gastrocnemius muscle. Conclusions: The lack of skeletal muscle AMPK 2 activity exacerbates the development of glucose intolerance and insulin resistance caused by high-fat feeding and supports the thesis that AMPK 2 is an important target for the prevention/amelioration of skeletal muscle insulin resistance through lifestyle (exercise) and pharmacologic (e.g., metformin) treatments
The GRAPPA-OMERACT Working Group:4 Prioritized Domains for Completing the Core Outcome Measurement Set for Psoriatic Arthritis 2019 Updates
The Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA)-Outcome Measures in Rheumatology (OMERACT) Psoriatic Arthritis (PsA) working group provided updates at the 2019 GRAPPA annual meeting on its work toward developing a core outcome set for PsA. The working group prioritized 4 domains, including musculoskeletal disease activity (enthesitis and dactylitis), fatigue, physical function, and structural damage. In this report, the working group summarizes its progress in standardizing the core outcome set for these 4 domains.</p
An Unbiased Survey of 500 Nearby Stars for Debris Disks: A JCMT Legacy Program
We present the scientific motivation and observing plan for an upcoming
detection survey for debris disks using the James Clerk Maxwell Telescope. The
SCUBA-2 Unbiased Nearby Stars (SUNS) Survey will observe 500 nearby main
sequence and sub-giant stars (100 of each of the A, F, G, K and M spectral
classes) to the 850 micron extragalactic confusion limit to search for evidence
of submillimeter excess, an indication of circumstellar material. The survey
distance boundaries are 8.6, 16.5, 22, 25 and 45 pc for M, K, G, F and A stars,
respectively, and all targets lie between the declinations of -40 deg to 80
deg. In this survey, no star will be rejected based on its inherent properties:
binarity, presence of planetary companions, spectral type or age. This will be
the first unbiased survey for debris disks since IRAS. We expect to detect ~125
debris disks, including ~50 cold disks not detectable in current shorter
wavelength surveys. A substantial amount of complementary data will be required
to constrain the temperatures and masses of discovered disks. High resolution
studies will likely be required to resolve many of the disks. Therefore, these
systems will be the focus of future observational studies using a variety of
observatories to characterize their physical properties. For non-detected
systems, this survey will set constraints (upper limits) on the amount of
circumstellar dust, of typically 200 times the Kuiper Belt mass, but as low as
10 times the Kuiper Belt mass for the nearest stars in the sample
(approximately 2 pc).Comment: 11 pages, 7 figures (3 color), accepted by the Publications of the
Astronomical Society of the Pacifi
Imaging Spectroscopy for Extrasolar Planet Detection
Coronagraphic imaging in combination with moderate to high spectral
resolution may prove more effective in both detecting extrasolar planets and
characterizing them than a standard coronagraphic imaging approach. We envisage
an integral-field spectrograph coupled to a coronagraph to produce a 3D
datacube. For the idealised case where the spectrum of the star is well-known
and unchanging across the field, we discuss the utility of cross-correlation to
seek the extrasolar planet signal, and describe a mathematical approach to
completely eliminate stray light from the host star (although not its Poisson
noise). For the case where the PSF is dominated by diffraction and scattering
effects, and comprises a multitude of speckles within an Airy pattern typical
of a space-based observation, we turn the wavelength dependence of the PSF to
advantage and present a general way to eliminate the contribution from the star
while preserving both the flux and spectrum of the extrasolar planet. We call
this method `spectral deconvolution'. We illustrate the dramatic gains by
showing an idealized simulation that results in a 20-sigma detection of a
Jovian planet at 2 pc with a 2-m coronagraphic space telescope, even though the
planet's peak flux is only 1% that of the PSF wings of the host star. This
scales to detection of a terrestrial extrasolar planet at 2 pc with an 8-m
coronagraphic Terrestrial Planet Finder (TPF) in ~7 hr (or less with
appropriate spatial filtering). Data on the spectral characteristics of the
extrasolar planet and hence on its atmospheric constituents and possible
biomarkers are obtained naturally as part of this process.Comment: 62 pages 27 figures accepted for publication in Ap
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