4,222 research outputs found
Heart Rate Response to Sound and Light
Heart rate response to varying sound and light intensitie
Observational Constraints on General Relativistic Energy Conditions, Cosmic Matter Density and Dark Energy from X-Ray Clusters of Galaxies and Type-Ia Supernovae
New observational constraints on the cosmic matter density and an
effectively redshift-independent equation of state parameter of the dark
energy are obtained while simultaneously testing the strong and null energy
conditions of general relativity on macroscopic scales. The combination of
REFLEX X-ray cluster and type-Ia supernova data shows that for a flat Universe
the strong energy condition might presently be violated whereas the null energy
condition seems to be fulfilled. This provides another observational argument
for the present accelerated cosmic expansion and the absence of exotic physical
phenomena related to a broken null energy condition. The marginalization of the
likelihood distributions is performed in a manner to include a large fraction
of the recently discussed possible systematic errors involved in the
application of X-ray clusters as cosmological probes. This yields for a flat
Universe, and
( errors without cosmic variance). The scatter in the different
analyses indicates a quite robust result around , leaving little room
for the introduction of new energy components described by quintessence-like
models or phantom energy. The most natural interpretation of the data is a
positive cosmological constant with $w_x=-1 or something like it.Comment: 11 pages, 5 figures, Astron. Astrophys. (in press
Emission Line Galaxies in the STIS Parallel Survey II: Star Formation Density
We present the luminosity function of [OII]-emitting galaxies at a median
redshift of z=0.9, as measured in the deep spectroscopic data in the STIS
Parallel Survey (SPS). The luminosity function shows strong evolution from the
local value, as expected. By using random lines of sight, the SPS measurement
complements previous deep single field studies. We calculate the density of
inferred star formation at this redshift by converting from [OII] to H-alpha
line flux as a function of absolute magnitude and find rho_dot=0.043 +/- 0.014
Msun/yr/Mpc^3 at a median redshift z~0.9 within the range 0.46<z<1.415 (H_0 =
70 km/s/Mpc, Omega_M=0.3, Omega_Lambda=0.7. This density is consistent with a
(1+z)^4 evolution in global star formation since z~1. To reconcile the density
with similar measurements made by surveys targeting H-alpha may require
substantial extinction correction.Comment: 16 preprint pages including 5 figures; accepted for publication in
Ap
Measurements of the Diffuse Ultraviolet Background and the Terrestrial Airglow with the Space Telescope Imaging Spectrograph
Far-UV observations in and near the Hubble Deep Fields demonstrate that the
Space Telescope Imaging Spectrograph (STIS) can potentially obtain unique and
precise measurements of the diffuse far-ultraviolet background. Although STIS
is not the ideal instrument for such measurements, high-resolution images allow
Galactic and extragalactic objects to be masked to very faint magnitudes, thus
ensuring a measurement of the truly diffuse UV signal. The programs we have
analyzed were not designed for this scientific purpose, but would be sufficient
to obtain a very sensitive measurement if it were not for a weak but
larger-than-expected signal from airglow in the STIS 1450-1900 A bandpass. Our
analysis shows that STIS far-UV crystal quartz observations taken near the limb
during orbital day can detect a faint airglow signal, most likely from NI\1493,
that is comparable to the dark rate and inseparable from the far-UV background.
Discarding all but the night data from these datasets gives a diffuse
far-ultraviolet background measurement of 501 +/- 103 ph/cm2/sec/ster/A, along
a line of sight with very low Galactic neutral hydrogen column (N_HI = 1.5E20
cm-2) and extinction (E(B-V)=0.01 mag). This result is in good agreement with
earlier measurements of the far-UV background, and should not include any
significant contribution from airglow. We present our findings as a warning to
other groups who may use the STIS far-UV camera to observe faint extended
targets, and to demonstrate how this measurement may be properly obtained with
STIS.Comment: 7 pages, Latex. 4 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in A
Imaging Fabry-Perot Spectroscopy of NGC 5775: Kinematics of the Diffuse Ionized Gas Halo
We present imaging Fabry-Perot observations of Halpha emission in the nearly
edge-on spiral galaxy NGC 5775. We have derived a rotation curve and a radial
density profile along the major axis by examining position-velocity (PV)
diagrams from the Fabry-Perot data cube as well as a CO 2-1 data cube from the
literature. PV diagrams constructed parallel to the major axis are used to
examine changes in azimuthal velocity as a function of height above the
midplane. The results of this analysis reveal the presence of a vertical
gradient in azimuthal velocity. The magnitude of this gradient is approximately
1 km/s/arcsec, or about 8 km/s/kpc, though a higher value of the gradient may
be appropriate in localized regions of the halo. The evidence for an azimuthal
velocity gradient is much stronger for the approaching half of the galaxy,
although earlier slit spectra are consistent with a gradient on both sides.
There is evidence for an outward radial redistribution of gas in the halo. The
form of the rotation curve may also change with height, but this is not
certain. We compare these results with those of an entirely ballistic model of
a disk-halo flow. The model predicts a vertical gradient in azimuthal velocity
which is shallower than the observed gradient, indicating that an additional
mechanism is required to further slow the rotation speeds in the halo.Comment: 18 pages, 18 figures. Uses emulateapj.cls. Accepted for publication
in Ap
Event driven executive
Tasks may be planned for execution on a single processor or are split up by the designer for execution among a plurality of signal processors. The tasks are modeled using a design aid called a precedence graph, from which a dependency table and a prerequisite table are established for reference within each processor. During execution, at the completion of a given task, an end of task interrupt is provided from any processor which has completed a task to any and all other processors including itself in which completion of that task is a prerequisite for commencement of any dependent tasks. The relevant updated data may be transferred by the processor either before or after signalling task completion to the processors needing the updated data prior to commencing execution of the dependent tasks. Coherency may be ensured, however, by sending the data before the interrupt. When the end of task interrupt is received in a processor, its dependency table is consulted to determine those tasks dependent upon completion of the task which has just been signalled as completed, and task dependency signals indicative thereof are provided and stored in a current status list of a prerequisite table. The current status of all current prerequisites are compared to the complete prerequisites listed for all affected tasks and those tasks for which the comparison indicates that all prerequisites have been met are queued for execution in a selected order
The Butcher-Oemler Effect in High Redshift X-ray Selected Clusters
We are engaged in a wide-field, multi-colour imaging survey of X-ray selected
clusters at intermediate and high redshift. We present blue fractions for the
first 8 out of 29 clusters, covering almost a factor of 100 in X-ray
luminosity. We find no correlation of blue fraction with redshift or X-ray
luminosity. The lack of a correlation with L, places strong constraints
on the importance of ram-pressure stripping as a driver of the Butcher-Oemler
effect.Comment: 4 pages, 4 figures, to be puplished in the proceedings of the ''Sesto
2001-Tracing Cosmic Evolution with Galaxy Clusters'', Sesto 3-6 July 2001,
Italy, eds, Stefano Borgan
Equalization in redundant channels
A miscomparison between a channel's configuration data base and a voted system configuration data base in a redundant channel system having identically operating, frame synchronous channels triggers autoequalization of the channel's historical signal data bases in a hierarchical, chronological manner with that of a correctly operating channel. After equalization, symmetrization of the channel's configuration data base with that of the system permits upgrading of the previously degraded channel to full redundancy. An externally provided equalization command, e.g., manually actuated, can also trigger equalization
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