10,653 research outputs found
Working Group 5: Measurements technology and active experiments
Technology issues identified by working groups 5 are listed. (1) New instruments are needed to upgrade the ability to measure plasma properties in space. (2) Facilities should be developed for conducting a broad range of plasma experiments in space. (3) The ability to predict plasma weather within magnetospheres should be improved and a capability to modify plasma weather developed. (4) Methods of control of plasma spacecraft and spacecraft plasma interference should be upgraded. (5) The space station laboratory facilities should be designed with attention to problems of flexibility to allow for future growth. These issues are discussed
Axiomatic approach to radiation reaction of scalar point particles in curved spacetime
Several different methods have recently been proposed for calculating the
motion of a point particle coupled to a linearized gravitational field on a
curved background. These proposals are motivated by the hope that the point
particle system will accurately model certain astrophysical systems which are
promising candidates for observation by the new generation of gravitational
wave detectors. Because of its mathematical simplicity, the analogous system
consisting of a point particle coupled to a scalar field provides a useful
context in which to investigate these proposed methods. In this paper, we
generalize the axiomatic approach of Quinn and Wald in order to produce a
general expression for the self force on a point particle coupled to a scalar
field following an arbitrary trajectory on a curved background. Our equation
includes the leading order effects of the particle's own fields, commonly
referred to as ``self force'' or ``radiation reaction'' effects. We then
explore the equations of motion which follow from this expression in the
absence of non-scalar forces.Comment: 17 pages, 1 figur
Hat-P-25b: A Hot-Jupiter Transiting a Moderately Faint G Star
We report the discovery of HAT-P-25b, a transiting extrasolar planet orbiting the V = 13.19 G5 dwarf star GSC 1788-01237, with a period P = 3.652836 ± 0.000019 days, transit epoch T_c = 2455176.85173 ± 0.00047 (BJD—barycentric Julian dates throughout the paper are calculated from Coordinated Universal Time, UTC), and transit duration 0.1174 ± 0.0017 days. The host star has a mass of 1.01 ± 0.03 M_☉, radius of 0.96^(+0.05)_(– 0.04) R_☉, effective temperature 5500 ± 80 K, and metallicity [Fe/H] = +0.31 ± 0.08. The planetary companion has a mass of 0.567 ± 0.022 M_J and radius of 1.190^(+0.081)_(–0.056) R_J yielding a mean density of 0.42 ± 0.07 g cm^(–3)
Human epicardial adipose tissue expresses a pathogenic profile of adipocytokines in patients with cardiovascular disease
Introduction: Inflammation contributes to cardiovascular disease and is exacerbated with
increased adiposity, particularly omental adiposity; however, the role of epicardial fat is poorly
understood.
Methods: For these studies the expression of inflammatory markers was assessed in epicardial fat
biopsies from coronary artery bypass grafting (CABG) patients using quantitative RT-PCR. Further,
the effects of chronic medications, including statins, as well as peri-operative glucose, insulin and
potassium infusion, on gene expression were also assessed. Circulating resistin, CRP, adiponectin
and leptin levels were determined to assess inflammation.
Results: The expression of adiponectin, resistin and other adipocytokine mRNAs were
comparable to that in omental fat. Epicardial CD45 expression was significantly higher than control
depots (p < 0.01) indicating significant infiltration of macrophages. Statin treated patients showed
significantly lower epicardial expression of IL-6 mRNA, in comparison with the control abdominal
depots (p < 0.001). The serum profile of CABG patients showed significantly higher levels of both
CRP (control: 1.28 ± 1.57 μg/mL vs CABG: 9.11 ± 15.7 μg/mL; p < 0.001) and resistin (control:
10.53 ± 0.81 ng/mL vs CABG: 16.8 ± 1.69 ng/mL; p < 0.01) and significantly lower levels of
adiponectin (control: 29.1 ± 14.8 μg/mL vs CABG: 11.9 ± 6.0 μg/mL; p < 0.05) when compared to
BMI matched controls.
Conclusion: Epicardial and omental fat exhibit a broadly comparable pathogenic mRNA profile,
this may arise in part from macrophage infiltration into the epicardial fat. This study highlights that
chronic inflammation occurs locally as well as systemically potentially contributing further to the
pathogenesis of coronary artery disease
A comparison of CFD and full-scale measurement for analysis of natural ventilation
CFD modelling techniques have been used to simulate the coupled external and internal flow in a cubic building with two dominant openings. CFD predictions of the time-averaged cross ventilation flow rates have been validated against full-scale experimental data under various weather conditions in England. RANS model predictions proved reliable when wind directions were near normal to the vent openings. However, when the fluctuating ventilation rate exceeded the mean flow, RANS models were incapable of predicting the total ventilation rate. Improved results are expected by applying more sophisticated turbulence models, such as LES or weighted quasi-steady approximations
HAT-P-26b: A Low-Density Neptune-Mass Planet Transiting a K Star
We report the discovery of HAT-P-26b, a transiting extrasolar planet orbiting
the moderately bright V=11.744 K1 dwarf star GSC 0320-01027, with a period P =
4.234516 +- 0.000015 d, transit epoch Tc = 2455304.65122 +- 0.00035 (BJD), and
transit duration 0.1023 +- 0.0010 d. The host star has a mass of 0.82 +- 0.03
Msun, radius of 0.79 + 0.10 - 0.04 Rsun, effective temperature 5079 +- 88 K,
and metallicity [Fe/H] = -0.04 +- 0.08. The planetary companion has a mass of
0.059 +- 0.007 MJ, and radius of 0.565 + 0.072 - 0.032 RJ yielding a mean
density of 0.40 +- 0.10 g cm-3. HAT-P-26b is the fourth Neptune-mass transiting
planet discovered to date. It has a mass that is comparable to those of Neptune
and Uranus, and slightly smaller than those of the other transiting
Super-Neptunes, but a radius that is ~65% larger than those of Neptune and
Uranus, and also larger than those of the other transiting Super-Neptunes.
HAT-P-26b is consistent with theoretical models of an irradiated Neptune-mass
planet with a 10 Mearth heavy element core that comprises >~ 50% of its mass
with the remainder contained in a significant hydrogen-helium envelope, though
the exact composition is uncertain as there are significant differences between
various theoretical models at the Neptune-mass regime. The equatorial
declination of the star makes it easily accessible to both Northern and
Southern ground-based facilities for follow-up observations.Comment: 16 pages, 9 figures, 5 tables, submitted to Ap
HAT-P-47b AND HAT-P-48b: Two Low Density Sub-Saturn-Mass Transiting Planets on the Edge of the Period--Mass Desert
We report the discovery of two new transiting extrasolar planets orbiting
moderately bright (V = 10.7 and 12.2 mag) F stars (masses of 1.39 Msun and 1.10
Msun, respectively). The planets have periods of P = 4.7322 d and 4.4087 d, and
masses of 0.21 MJ and 0.17 MJ which are almost half-way between those of
Neptune and Saturn. With radii of 1.31 RJ and 1.13 RJ, these very low density
planets are the two lowest mass planets with radii in excess that of Jupiter.
Comparing with other recent planet discoveries, we find that sub-Saturns
(0.18MJ < Mp < 0.3MJ) and super-Neptunes (0.05MJ < Mp < 0.18MJ) exhibit a wide
range of radii, and their radii exhibit a weaker correlation with irradiation
than higher mass planets. The two planets are both suitable for measuring the
Rossiter-McLaughlin effect and for atmospheric characterization. Measuring the
former effect would allow an interesting test of the theory that star-planet
tidal interactions are responsible for the tendency of close-in giant planets
around convective envelope stars to be on low obliquity orbits. Both planets
fall on the edge of the short period Neptunian desert in the semi-major
axis-mass plane.Comment: Submitted to AAS Journal
Tidal stirring and the origin of dwarf spheroidals in the Local Group
N-Body/SPH simulations are used to study the evolution of dwarf irregular
galaxies (dIrrs) entering the dark matter halo of the Milky Way or M31 on
plunging orbits. We propose a new dynamical mechanism driving the evolution of
gas rich, rotationally supported dIrrs, mostly found at the outskirts of the
Local Group (LG), into gas free, pressure supported dwarf spheroidals (dSphs)
or dwarf ellipticals (dEs), observed to cluster around the two giant spirals.
The initial model galaxies are exponential disks embedded in massive dark
matter halos and reproduce nearby dIrrs. Repeated tidal shocks at the
pericenter of their orbit partially strip their halo and disk and trigger
dynamical instabilities that dramatically reshape their stellar component.
After only 2-3 orbits low surface brightness (LSB) dIrrs are transformed into
dSphs, while high surface brightness (HSB) dIrrs evolve into dEs. This
evolutionary mechanism naturally leads to the morphology-density relation
observed for LG dwarfs. Dwarfs surrounded by very dense dark matter halos, like
the archetypical dIrr GR8, are turned into Draco or Ursa Minor, the faintest
and most dark matter dominated among LG dSphs. If disks include a gaseous
component, this is both tidally stripped and consumed in periodic bursts of
star formation. The resulting star formation histories are in good qualitative
agreement with those derived using HST color-magnitude diagrams for local
dSphs.Comment: 5 pages, 5 figures, to appear on ApJL. Simulation images and movies
can be found at the Local Group web page at
http://pcblu.uni.mi.astro.it/~lucio/LG/LG.htm
Hat-P-28b and Hat-P-29b: Two Sub-Jupiter Mass Transiting Planets
We present the discovery of two transiting exoplanets. HAT-P-28b orbits a V = 13.03 G3 dwarf star with a period P = 3.2572 days and has a mass of 0.63 ± 0.04 M_J and a radius of 1.21^(+0.11)_(–0.08) R_J yielding a mean density of 0.44 ± 0.09 g cm^(–3). HAT-P-29b orbits a V = 11.90 F8 dwarf star with a period P = 5.7232 days and has a mass of 0.78^(+0.08)_(–0.04) M_J and a radius of 1.11^(+0.14)_(–0.08) R_J yielding a mean density of 0.71 ± 0.18 g cm^(–3). We discuss the properties of these planets in the context of other known transiting planets
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