3,743 research outputs found
Evaluation and comparison of tropical analyses during DST-5 and DST-6
Data systems tests were conducted to assess the adequacy of the global data base for numerical analysis and forecasting and in the process to determine the impact of meteorological satellite data. The results of these tests indicate that the satellite data impact is model and season dependent but definitely dependent on the method of data assimilation and the numerical model used to produce the analyses or initial conditions
Controlling platinum, ruthenium, and osmium reactivity for anticancer drug design
The main task of the medicinal chemist is to design molecules that interact
specifically with derailed or degenerating processes in a diseased organism,
translating the available knowledge of pathobiochemical and physiological data into
chemically useful information and structures. Current knowledge of the biological
and chemical processes underlying diseases is vast and rapidly expanding. In
particular the unraveling of the genome in combination with, for instance, the rapid
development of structural biology has led to an explosion in available information and
identification of new targets for chemotherapy. The task of translating this wealth of
data into active and selective new drugs is an enormous, but realistic, challenge. It
requires knowledge from many different fields, including molecular biology,
chemistry, pharmacology, physiology, and medicine and as such requires a truly
interdisciplinary approach.
Ultimately, the goal is to design molecules that satisfy all the requirements for a
candidate drug to function therapeutically. Therapeutic activity can then be achieved
by an understanding of and control over structure and reactivity of the candidate drug
through molecular manipulation
A Sensor Failure Simulator for Control System Reliability Studies
A real-time Sensor Failure Simulator (SFS) was designed and assembled for the Advanced Detection, Isolation, and Accommodation (ADIA) program. Various designs were considered. The design chosen features an IBM-PC/XT. The PC is used to drive analog circuitry for simulating sensor failures in real-time. A user defined scenario describes the failure simulation for each of the five incoming sensor signals. Capabilities exist for editing, saving, and retrieving the failure scenarios. The SFS has been tested closed-loop with the Controls Interface and Monitoring (CIM) unit, the ADIA control, and a real-time F100 hybrid simulation. From a productivity viewpoint, the menu driven user interface has proven to be efficient and easy to use. From a real-time viewpoint, the software controlling the simulation loop executes at greater than 100 cycles/sec
A search for distant radio galaxies from SUMSS and NVSS: III. radio spectral energy distributions and the z-alpha correlation
This is the third in a series of papers that present observations and results
for a sample of 76 ultra-steep-spectrum radio sources designed to find galaxies
at high redshift. Here we present multi-frequency radio observations, from the
Australia Telescope Compact Array, for a subset of 37 galaxies from the sample.
Matched resolution observations at 2.3, 4.8 and 6.2GHz are presented for all
galaxies, with the z<2 galaxies additionally observed at 8.6 and 18GHz. New
angular size constraints are reported for 19 sources based on high resolution
4.8 and 6.2GHz observations. Functional forms for the rest-frame spectral
energy distributions are derived: 89% of the sample is well characterised by a
single power law, whilst the remaining 11% show some flattening toward higher
frequencies: not one source shows any evidence for high frequency steepening.
We discuss the implications of this result in light of the empirical
correlation between redshift and spectral index seen in flux limited samples of
radio galaxies. Finally, a new physical mechanism to explain the redshift --
spectral index correlation is posited: extremely steep spectrum radio galaxies
in the local universe usually reside at the centres of rich galaxy clusters. We
argue that if a higher fraction of radio galaxies, as a function of redshift,
are located in environments with densities similar to nearby rich clusters,
then this could be a natural interpretation for the correlation. We briefly
outline our plans to pursue this line of investigation.Comment: MNRAS in pres
The physical determinants of the thickness of lamellar polymer crystals
Based upon kinetic Monte Carlo simulations of crystallization in a simple
polymer model we present a new picture of the mechanism by which the thickness
of lamellar polymer crystals is constrained to a value close to the minimum
thermodynamically stable thickness. This description contrasts with those given
by the two dominant theoretical approaches.Comment: 4 pages, 4 figures, revte
Radio Sources in the 2dF Galaxy Redshift Survey. I. Radio Source Populations
We present the first results from a study of the radio continuum properties
of galaxies in the 2dF Galaxy Redshift Survey, based on thirty 2dF fields
covering a total area of about 100 square degrees. About 1.5% of galaxies with
b(J) < 19.4 mag are detected as radio continuum sources in the NRAO VLA Sky
Survey (NVSS). Of these, roughly 40% are star-forming galaxies and 60% are
active galaxies (mostly low-power radio galaxies and a few Seyferts). The
combination of 2dFGRS and NVSS will eventually yield a homogeneous set of
around 4000 radio-galaxy spectra, which will be a powerful tool for studying
the distriibution and evolution of both AGN and starburst galaxies out to
redshift z=0.3.Comment: 14 pages, 7 figures, accepted for publication in PAS
From gas to galaxies
The unsurpassed sensitivity and resolution of the Square Kilometer Array
(SKA) will make it possible for the first time to probe the continuum emission
of normal star forming galaxies out to the edges of the universe. This opens
the possibility for routinely using the radio continuum emission from galaxies
for cosmological research as it offers an independent probe of the evolution of
the star formation density in the universe. In addition it offers the
possibility to detect the first star forming objects and massive black holes.
In deep surveys SKA will be able to detect HI in emission out to redshifts of
and hence be able to trace the conversion of gas into stars
over an era where considerable evolution is taking place. Such surveys will be
able to uniquely determine the respective importance of merging and accreting
gas flows for galaxy formation over this redshift range (i.e. out to when the
universe was only one third its present age). It is obvious that only SKA will
able to see literally where and how gas is turned into stars.
These and other aspects of SKA imaging of galaxies will be discussed.Comment: To be published in New Astronomy Reviews, Elsevier, Amsterdam as part
of "Science with the Square Kilometre Array", eds. C. Carilli and S.
Rawlings. 18 pages + 13 figures; high resolution version and other chapters
of "Science with the Square Kilometre Array" available at
http://www.skatelescope.org/pages/science_gen.ht
HI emission and absorption in nearby, gas-rich galaxies II. -- sample completion and detection of intervening absorption in NGC 5156
We present the results of a survey for intervening 21cm HI absorption in a
sample of 10 nearby, gas-rich galaxies selected from the HI Parkes All-Sky
Survey (HIPASS). This follows the six HIPASS galaxies searched in previous work
and completes our full sample. In this paper we searched for absorption along
17 sightlines with impact parameters between 6 and 46 kpc, making one new
detection. We also obtained simultaneous HI emission-line data, allowing us to
directly relate the absorption-line detection rate to the HI distribution. From
this we find the majority of the non-detections in the current sample are
because sightline does not intersect the HI disc of the galaxy at sufficiently
high column density, but that source structure is also an important factor.
The detected absorption-line arises in the galaxy NGC 5156 () at an
impact parameter of 19 kpc. The line is deep and narrow with an integrated
optical depth of 0.82 km s. High resolution Australia Telescope Compact
Array (ATCA) images at 5 and 8 GHz reveal that the background source is
resolved into two components with a separation of 2.6 arcsec (500 pc at the
redshift of the galaxy), with the absorption likely occurring against a single
component. We estimate that the ratio of the spin temperature and covering
factor, , is approximately 950 K in the outer disc of NGC
5156, but further observations using VLBI would allow us to accurately measure
the covering factor and spin temperature of the gas.Comment: 31 pages, 11 figure
Further Observational Evidence for a Critical Ionising Luminosity in Active Galaxies
We report the results of a survey for HI 21-cm absorption at redshifts of z >
2.6 in a new sample of radio sources with the Green Bank and Giant Metrewave
Radio Telescopes. From a total of 25 targets, we report zero detections in the
16 for which optical depth limits could be obtained. Based upon the detection
rate for z > 0.1 associated absorption, we would expect approximately four
detections. Of the 11 which have previously not been searched, there is
sufficient source-frame optical/ultra-violet photometry to determine the
ionising photon rate for four. Adding these to the literature, the hypothesis
that there is a critical rate of logQ = 56 ionising photons per second is now
significant at ~7 sigma. This reaffirms our assertion that searching z > 3
active galaxies for which optical redshifts are available selects sources in
which the ultra-violet luminosity is sufficient to ionise all of the neutral
gas in the host galaxy.Comment: Accepted by MNRA
HI in four star-forming low-luminosity E/S0 and S0 galaxies
We present HI data cubes of four low-luminosity early-type galaxies which are
currently forming stars. These galaxies have absolute magnitudes in the range
M_B=-17.9 to -19.9 (H_o=50 km/s/Mpc). Their HI masses range between a few times
10^8 and a few times 10^9 M_sun and the corresponding values for M_HI/L_B are
between 0.07 and 0.42, so these systems are HI rich for their morphological
type. In all four galaxies, the HI is strongly centrally concentrated with high
central HI surface densities, in contrast to what is typically observed in more
luminous early-type galaxies. In two galaxies (NGC 802 and ESO 118-G34), the
kinematics of the HI suggests that the gas is in a strongly warped disk, which
we take as evidence for recent accretion of HI. In the other two galaxies (NGC
2328 and ESO 027-G21) the HI must have been part of the systems for a
considerable time. The HI properties of low-luminosity early-type galaxies
appear to be systematically different from those of many more luminous
early-type galaxies, and we suggest that these differences are due to a
different evolution of the two classes. The star formation history of these
galaxies remains unclear. Their UBV colours and Halpha emission-line strengths
are consistent with having formed stars at a slowly-declining rate for most of
the past 10^10 years. However, the current data do not rule out a small burst
of recent star formation overlaid on an older stellar population.Comment: To appear in AJ, LateX, figures in gif format, paper also available
at http://www.nfra.nl/~morganti/LowLu
- …