10,813 research outputs found
The development of structural adhesive systems suitable for use with liquid oxygen /LOX/ Summary report, 20 Jun. 1969 - 19 Apr. 1970
Development of structural adhesive systems suitable for use with liquid oxyge
Discovery of an extended debris disk around the F2V star HD 15745
Using the Advanced Camera for Surveys aboard the Hubble Space Telescope, we
have discovered dust-scattered light from the debris disk surrounding the F2V
star HD 15745. The circumstellar disk is detected between 2.0" and 7.5" radius,
corresponding to 128 - 480 AU radius. The circumstellar disk morphology is
asymmetric about the star, resembling a fan, and consistent with forward
scattering grains in an optically thin disk with an inclination of ~67 degrees
to our line of sight. The spectral energy distribution and scattered light
morphology can be approximated with a model disk composed of silicate grains
between 60 and 450 AU radius, with a total dust mass of 10E-7 M_sun (0.03
M_earth) representing a narrow grain size distribution (1 - 10 micron).
Galactic space motions are similar to the Castor Moving Group with an age of
~10E+8 yr, although future work is required to determine the age of HD 15745
using other indicators.Comment: 7 pages, 4 figures, ApJ Letters, in pres
A Ring of Warm Dust in the HD 32297 Debris Disk
We report the detection of a ring of warm dust in the edge-on disk
surrounding HD 32297 with the Gemini-N/MICHELLE mid-infrared imager. Our
N'-band image shows elongated structure consistent with the orientation of the
scattered-light disk. The Fnu(11.2 um) = 49.9+/-2.1 mJy flux is significantly
above the 28.2+/-0.6 mJy photosphere. Subtraction of the stellar point spread
function reveals a bilobed structure with peaks 0.5"-0.6" from the star. An
analysis of the stellar component of the SED suggests a spectral type later
than A0, in contrast to commonly cited literature values. We fit
three-dimensional, single-size grain models of an optically thin dust ring to
our image and the SED using a Markov chain Monte Carlo algorithm in a Bayesian
framework. The best-fit effective grain sizes are submicron, suggesting the
same dust population is responsible for the bulk of the scattered light. The
inner boundary of the warm dust is located 0.5"-0.7" (~65 AU) from the star,
which is approximately cospatial with the outer boundary of the scattered-light
asymmetry inward of 0.5". The addition of a separate component of larger,
cooler grains that provide a portion of the 60 um flux improves both the
fidelity of the model fit and consistency with the slopes of the
scattered-light brightness profiles. Previous indirect estimates of the stellar
age (~30 Myr) indicate the dust is composed of debris. The peak vertical
optical depths in our models (~0.3-1 x 1e-2) imply that grain-grain collisions
likely play a significant role in dust dynamics and evolution. Submicron grains
can survive radiation pressure blow-out if they are icy and porous. Similarly,
the inferred warm temperatures (130-200 K) suggest that ice sublimation may
play a role in truncating the inner disk.Comment: ApJ accepted, 8 pages, 4 figure
First scattered light images of debris disks around HD 53143 and HD 139664
We present the first scattered light images of debris disks around a K star
(HD 53143) and an F star (HD 139664) using the coronagraphic mode of the
Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST). With
ages 0.3 - 1 Gyr, these are among the oldest optically detected debris disks.
HD 53143, viewed ~45 degrees from edge-on, does not show radial variation in
disk structure and has width >55 AU. HD 139664 is seen close to edge-on and has
belt-like morphology with a dust peak 83 AU from the star and a distinct outer
boundary at 109 AU. We discuss evidence for significant diversity in the radial
architecture of debris disks that appears unconnected to stellar spectral type
or age. HD 139664 and possibly the solar system belong in a category of narrow
belts 20-30 AU wide. HD 53143 represents a class of wide disk architecture with
characteristic width >50 AU.Comment: 7 pages, 3 figure
A systematic review and meta-regression analysis of the vitamin D intake-serum 25-hydroxyvitamin D relationship to inform European recommendations
The present study used a systematic review approach to identify relevant randomised control trials (RCT) with vitamin D and then apply meta-regression to explore the most appropriate model of the vitamin D intake–serum 25-hydroxyvitamin D (25(OH)D) relationship to underpin setting reference intake values. Methods included an updated structured search on Ovid MEDLINE; rigorous inclusion/exclusion criteria; data extraction; and meta-regression (using different model constructs).
In particular, priority was given to data from winter-based RCT performed at latitudes >49•58°N (n 12). A combined weighted linear model meta-regression analyses of natural log (Ln) total vitamin D intake
(i.e. diet and supplemental vitamin D)
versus achieved serum 25(OH)D in winter (that used by the North American Dietary Reference
Intake Committee) produced a curvilinear relationship (mean (95% lower CI) serum 25(OH)D (nmol/l) = 9•2 (8•5) Ln
(total vitamin D)).
Use of non-transformed total vitamin D intake data (maximum 1400 IU/d; 35µg/d) provided for a more linear relationship
(mean serum 25(OH)D (nmol/l) = 0•044 × (total vitamin D) + 33•035).
Although inputting an intake of 600 IU/d (i.e. the RDA) into the 95% lower CI curvilinear and linear models
predicted a serum 25(OH)D of 54•4 and 55•2 nmol/l, respectively, the total vitamin D intake that would
achieve 50 (and 40) nmol/l serum 25(OH)D was 359 (111) and 480 (260) IU/d, respectively.
Inclusion of 95% range in the model to account for inter-individual variability increased the predicted intake of
vitamin D needed to maintain serum 25(OH)D ≥50 nmol/l to 930 IU/d.
The model used to describe the vitamin D intake–status relationship needs to be considered carefully when
setting new reference intake values in Europe
Doubly Special Relativity with a minimum speed and the Uncertainty Principle
The present work aims to search for an implementation of a new symmetry in
the space-time by introducing the idea of an invariant minimum speed scale
(). Such a lowest limit , being unattainable by the particles, represents
a fundamental and preferred reference frame connected to a universal background
field (a vacuum energy) that breaks Lorentz symmetry. So there emerges a new
principle of symmetry in the space-time at the subatomic level for very low
energies close to the background frame (), providing a fundamental
understanding for the uncertainty principle, i.e., the uncertainty relations
should emerge from the space-time with an invariant minimum speed.Comment: 10 pages, 8 figures, Correlated paper in:
http://www.worldscientific.com/worldscinet/ijmpd?journalTabs=read. arXiv
admin note: substantial text overlap with arXiv:physics/0702095,
arXiv:0705.4315, arXiv:0709.1727, arXiv:0805.120
Health Implications of High Dietary Omega-6 Polyunsaturated Fatty Acids
Omega-6 (n-6) polyunsaturated fatty acids (PUFA) (e.g., arachidonic acid (AA)) and omega-3 (n-3) PUFA (e.g., eicosapentaenoic acid (EPA)) are precursors to potent lipid mediator signalling molecules, termed “eicosanoids,” which have important roles in the regulation of inflammation. In general, eicosanoids derived from n-6 PUFA are proinflammatory while eicosanoids derived from n-3 PUFA are anti-inflammatory. Dietary changes over the past few decades in the intake of n-6 and n-3 PUFA show striking increases in the (n-6) to (n-3) ratio (~15 : 1), which are associated with greater metabolism of the n-6 PUFA compared with n-3 PUFA. Coinciding with this increase in the ratio of (n-6) : (n-3) PUFA are increases in chronic inflammatory diseases such as nonalcoholic fatty liver disease (NAFLD), cardiovascular disease, obesity, inflammatory bowel disease (IBD), rheumatoid arthritis, and Alzheimer's disease (AD). By increasing the ratio of (n-3) : (n-6) PUFA in the Western diet, reductions may be achieved in the incidence of these chronic inflammatory diseases
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