9,492 research outputs found
The mass and dynamical state of Abell 2218
Abell 2218 is one of a handful of clusters in which X-ray and lensing
analyses of the cluster mass are in strong disagreement. It is also a system
for which X-ray data and radio measurements of the Sunyaev-Zel'dovich decrement
have been combined in an attempt to constrain the Hubble constant. However, in
the absence of reliable information on the temperature structure of the
intracluster gas, most analyses have been carried out under the assumption of
isothermality. We combine X-ray data from the ROSAT PSPC and the ASCA GIS
instruments, enabling us to fit non-isothermal models, and investigate the
impact that this has on the X-ray derived mass and the predicted
Sunyaev-Zel'dovich effect.
We find that a strongly non-isothermal model for the intracluster gas, which
implies a central cusp in the cluster mass distribution, is consistent with the
available X-ray data and compatible with the lensing results. At r<1 arcmin,
there is strong evidence to suggest that the cluster departs from a simple
relaxed model. We analyse the dynamics of the galaxies and find that the
central galaxy velocity dispersion is too high to allow a physical solution for
the galaxy orbits. The quality of the radio and X-ray data do not at present
allow very restrictive constraints to be placed on H_0. It is apparent that
earlier analyses have under-estimated the uncertainties involved. However,
values greater than 50 km/s/Mpc are preferred when lensing constraints are
taken into account.Comment: 16 pages, 9 postscript figures, accepted for publication in MNRA
Bicycle Handlebar Width Does Not Affect Spirometry, Ventilation, or Gas Exchange
Bicycle fit may affect comfort, aerodynamics, efficiency, ventilation, and power generation. Handlebars determine how the rider interacts with the bicycle. A wide range of handlebar widths are commercially available, but it is unclear if the resultant position affects lung function, ventilation, gas exchange, or efficiency. PURPOSE We aimed to measure the effects of handlebar widths on ventilation, gas exchange, spirometry, and comfort during moderate constant power exercise. METHODS Twenty-four recreationally active adults completed the study (32 ± 5 yrs., 175 ± 9 cm, 74 ± 12 kg, 8 women, 16 men). Participants completed three moderate constant power bouts of exercise on a cycle ergometer (Lode Excalibur PFM) while using handlebars set equivalent to, or ± 4cm in width to the participant shoulder width. We used a one-way RMANOVA to compare the three handlebar widths. RESULTS There was no difference in gas exchange and ventilation between the three handlebar widths: V̇O2 (F[2, 23] = 0.99, p = 0.38), V̇CO2 (F[1.47, 23] = 0.39, p = 0.62), V̇E (F[2, 23] = 0.53, p = 0.59], VT (F[2, 23] = 0.44, p = 0.65], fBr (F[2, 23] = 0.17, p = 0.84], PetO2(F[2, 23] = 0.45, p = 0.64), PetCO2 (F[2, 23] = 0.25, p=0.78]. Similarly, there were no differences in inspiratory capacity during the bout (F[1.49, 22] = 1.34, p = 0.27) or any spirometry variables immediately following exercise: FVC (F[1.43, 22] = 0.88, p = 0.39], FEV1 (F[2, 22] = 0.30, p = 0.74], FEV1/FVC (F[2, 22] = 0.18, p = 0.84], PEF (F[2, 22] = 0.14, p = 0.87]. There was no difference in the overall comfort (F[2, 23] = 0.90, p = 0.41] or shoulder discomfort (F [2, 23] = 0.90, p = 0.42). CONCLUSIONS Bicycle handlebar widths within 4 cm shoulder width do not result in changes to ventilation, gas exchange, efficiency, spirometry, or comfort during moderate power cycling exercise. Within the limits of rider preference, comfort, and safety, handlebar width can be adjusted substantially for aerodynamic purposes without affecting rider physiology
The Potential For UK Portfolio Investors To Finance Sustainable Tropical Forestry
Environmental Economics and Policy, Resource /Energy Economics and Policy,
Techniques for measuring atmospheric aerosols at the High Resolution Fly's Eye experiment
We describe several techniques developed by the High Resolution Fly's Eye
experiment for measuring aerosol vertical optical depth, aerosol horizontal
attenuation length, and aerosol phase function. The techniques are based on
measurements of side-scattered light generated by a steerable ultraviolet laser
and collected by an optical detector designed to measure fluorescence light
from cosmic-ray air showers. We also present a technique to cross-check the
aerosol optical depth measurement using air showers observed in stereo. These
methods can be used by future air fluorescence experiments.Comment: Accepted for publication in Astroparticle Physics Journal 16 pages, 9
figure
A Unified Near Infrared Spectral Classification Scheme for T Dwarfs
A revised near infrared classification scheme for T dwarfs is presented,
based on and superseding prior schemes developed by Burgasser et al. and
Geballe et al., and defined following the precepts of the MK Process. Drawing
from two large spectroscopic libraries of T dwarfs identified largely in the
Sloan Digital Sky Survey and the Two Micron All Sky Survey, nine primary
spectral standards and five alternate standards spanning spectral types T0 to
T8 are identified that match criteria of spectral character, brightness,
absence of a resolved companion and accessibility from both northern and
southern hemispheres. The classification of T dwarfs is formally made by the
direct comparison of near infrared spectral data of equivalent resolution to
the spectra of these standards. Alternately, we have redefined five key
spectral indices measuring the strengths of the major HO and CH bands
in the 1-2.5 micron region that may be used as a proxy to direct spectral
comparison. Two methods of determining T spectral type using these indices are
outlined and yield equivalent results. These classifications are also
equivalent to those from prior schemes, implying that no revision of existing
spectral type trends is required. The one-dimensional scheme presented here
provides a first step toward the observational characterization of the lowest
luminosity brown dwarfs currently known. Future extensions to incorporate
spectral variations arising from differences in photospheric dust content,
gravity and metallicity are briefly discussed. A compendium of all currently
known T dwarfs with updated classifications is presented.Comment: 52 pages, 11 figures; accepted for publication to Ap
Magnetic Fluctuations in a Charge Ordered State of the One-Dimensional Extended Hubbard Model with a Half-Filled Band
Magnetic properties in a charge ordered state are examined for the extended
Hubbard model at half-filling. Magnetic excitations, magnetic susceptibilities
and a nuclear spin relaxation rate are calculated with taking account of
fluctuations around the mean-field solution. The relevance of the present
results to the observation in the 1:1 organic conductors, (TTM-TTP)I, is
discussed.Comment: 4 pages, 3 figures, to be published in J. Phys. Soc. Jpn. Vol.71
(2002) No.
Localizing gravitational wave sources with optical telescopes and combining electromagnetic and gravitational wave data
Neutron star binaries, which are among the most promising sources for the
direct detection of gravitational waves (GW) by ground based detectors, are
also potential electromagnetic (EM) emitters. Gravitational waves will provide
a new window to observe these events and hopefully give us glimpses of new
astrophysics. In this paper, we discuss how EM information of these events can
considerably improve GW parameter estimation both in terms of accuracy and
computational power requirement. And then in return how GW sky localization can
help EM astronomers in follow-up studies of sources which did not yield any
prompt emission. We discuss how both EM source information and GW source
localization can be used in a framework of multi-messenger astronomy. We
illustrate how the large error regions in GW sky localizations can be handled
in conducting optical astronomy in the advance detector era. We show some
preliminary results in the context of an array of optical telescopes called
BlackGEM, dedicated for optical follow-up of GW triggers, that is being
constructed in La Silla, Chile and is expected to operate concurrent to the
advanced GW detectors.Comment: 8 pages, 8 figures, Proceeding for Sant Cugat Forum for Astrophysic
The S2 VLBI Correlator: A Correlator for Space VLBI and Geodetic Signal Processing
We describe the design of a correlator system for ground and space-based
VLBI. The correlator contains unique signal processing functions: flexible LO
frequency switching for bandwidth synthesis; 1 ms dump intervals, multi-rate
digital signal-processing techniques to allow correlation of signals at
different sample rates; and a digital filter for very high resolution
cross-power spectra. It also includes autocorrelation, tone extraction, pulsar
gating, signal-statistics accumulation.Comment: 44 pages, 13 figure
Plans for phase coherent long baseline interferometry for geophysical applications using the Anik-B communications satellite
A pilot project to establish an operational phase stable very long baseline interferometer (VLBI) for geophysical studies is described. Methods for implementation as well as practical applications are presented
AGC 226067: A possible interacting low-mass system
We present Arecibo, GBT, VLA and WIYN/pODI observations of the ALFALFA source
AGC 226067. Originally identified as an ultra-compact high velocity cloud and
candidate Local Group galaxy, AGC 226067 is spatially and kinematically
coincident with the Virgo cluster, and the identification by multiple groups of
an optical counterpart with no resolved stars supports the interpretation that
this systems lies at the Virgo distance (D=17 Mpc). The combined observations
reveal that the system consists of multiple components: a central HI source
associated with the optical counterpart (AGC 226067), a smaller HI-only
component (AGC 229490), a second optical component (AGC 229491), and extended
low surface brightness HI. Only ~1/4 of the single-dish HI emission is
associated with AGC 226067; as a result, we find M_HI/L_g ~ 6 Msun/Lsun, which
is lower than previous work. At D=17 Mpc, AGC 226067 has an HI mass of 1.5 x
10^7 Msun and L_g = 2.4 x 10^6 Lsun, AGC 229490 (the HI-only component) has
M_HI = 3.6 x 10^6 Msun, and AGC 229491 (the second optical component) has L_g =
3.6 x 10^5 Lsun. The nature of this system of three sources is uncertain: AGC
226067 and AGC 229490 may be connected by an HI bridge, and AGC 229490 and AGC
229491 are separated by only 0.5'. The current data do not resolve the HI in
AGC 229490 and its origin is unclear. We discuss possible scenarios for this
system of objects: an interacting system of dwarf galaxies, accretion of
material onto AGC 226067, or stripping of material from AGC 226067.Comment: Accepted for publication in A&A. 6 pages, 4 figure
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