1,036 research outputs found
The role of integrated information acquisition and management in the analysis of coastal ecosystem change
This book chapter represents a synthesis of the work which started in my PhD and which has been the conceptual basis for all of my research since 1993. The chapter presents a method for scientists and managers to use for selecting the type of remotely sensed data to use to meet their information needs associated with a mapping, monitoring or modelling application. The work draws on results from several of my ARC projects, CRC Rainforest and Coastal projects and theses of P.Scarth , K.Joyce and C.Roelfsema
Periodic fever associated with intermittent rhytmic delta activity : a syndrome of hypothalamic origin?
Item does not contain fulltex
ISO spectroscopy of compact HII regions in the Galaxy. II Ionization and elemental abundances
Based on the ISO spectral catalogue of compact HII regions by Peeters et al.
(2001), we present a first analysis of the hydrogen recombination and atomic
fine-structure lines originated in the ionized gas. The sample consists of 34
HII regions located at galactocentric distances between Rgal = 0 and 15 kpc.
The SWS HI recombination lines between 2 and 8 mum are used to estimate the
extinction law at these wavelengths for 14 HII regions. An extinction in the K
band between 0 and 3 mag. has been derived. The fine-structure lines of
N, O, Ne, S and Ar are detected in most of the sources. Most of these elements
are observed in two different ionization stages probing a range in ionization
potential up to 41 eV. The ISO data, by itself or combined with radio data
taken from the literature, is used to derive the elemental abundances relative
to hydrogen. The present data thus allow us to describe for each source its
elemental abundance, its state of ionization and to constrain the properties of
the ionizing star(s).Comment: Accepted in Astronomy and Astrophysics, 22 pages, 20 figures, 9
table
Differential Effects of Estradiol and Progesterone on Cardiovascular Risk Factors in Postmenopausal Women
Diabetes mellitus: pathophysiological changes and therap
3-He in the Milky Way Interstellar Medium: Ionization Structure
The cosmic abundance of the 3-He isotope has important implications for many
fields of astrophysics. We are using the 8.665 GHz hyperfine transition of
3-He+ to determine the 3-He/H abundance in Milky Way HII regions and planetary
nebulae. This is one in a series of papers in which we discuss issues involved
in deriving accurate 3-He/H abundance ratios from the available measurements.
Here we describe the ionization correction we use to convert the 3-He+/H+
abundance, y3+, to the 3-He/H abundance, y3. In principle the nebular
ionization structure can significantly influence the y3 derived for individual
sources. We find that in general there is insufficient information available to
make a detailed ionization correction. Here we make a simple correction and
assess its validity. The correction is based on radio recombination line
measurements of H+ and 4-He+, together with simple core-halo source models. We
use these models to establish criteria that allow us to identify sources that
can be accurately corrected for ionization and those that cannot. We argue that
this effect cannot be very large for most of the sources in our observational
sample. For a wide range of models of nebular ionization structure we find that
the ionization correction factor varies from 1 to 1.8. Although large
corrections are possible, there would have to be a conspiracy between the
density and ionization structure for us to underestimate the ionization
correction by a substantial amount.Comment: 36 pages, 4 figures To appear Astrophysical Journal, 20 August 2007,
vol 665, no
Deriving Telescope Mueller Matrices Using Daytime Sky Polarization Observations
Telescopes often modify the input polarization of a source so that the
measured circular or linear output state of the optical signal can be
signficantly different from the input. This mixing, or polarization
"cross-talk", is defined by the optical system Mueller matrix. We describe here
an efficient method for recovering the input polarization state of the light
and the full 4 x 4 Mueller matrix of the telescope with an accuracy of a few
percent without external masks or telescope hardware modification. Observations
of the bright, highly polarized daytime sky using the Haleakala 3.7m AEOS
telescope and a coude spectropolarimeter demonstrate the technique.Comment: Accepted for publication in PAS
Synchronized dynamics of cortical neurons with time-delay feedback
The dynamics of three mutually coupled cortical neurons with time delays in
the coupling are explored numerically and analytically. The neurons are coupled
in a line, with the middle neuron sending a somewhat stronger projection to the
outer neurons than the feedback it receives, to model for instance the relay of
a signal from primary to higher cortical areas. For a given coupling
architecture, the delays introduce correlations in the time series at the
time-scale of the delay. It was found that the middle neuron leads the outer
ones by the delay time, while the outer neurons are synchronized with zero lag
times. Synchronization is found to be highly dependent on the synaptic time
constant, with faster synapses increasing both the degree of synchronization
and the firing rate. Analysis shows that presynaptic input during the
interspike interval stabilizes the synchronous state, even for arbitrarily weak
coupling, and independent of the initial phase. The finding may be of
significance to synchronization of large groups of cells in the cortex that are
spatially distanced from each other.Comment: 21 pages, 11 figure
Mid-Infrared Emission Features in the ISM: Feature-to-Feature Flux Ratios
Using a limited, but representative sample of sources in the ISM of our
Galaxy with published spectra from the Infrared Space Observatory, we analyze
flux ratios between the major mid-IR emission features (EFs) centered around
6.2, 7.7, 8.6 and 11.3 microns, respectively. In a flux ratio-to-flux ratio
plot of EF(6.2)/EF(7.7) as a function of EF(11.3)/EF(7.7), the sample sources
form roughly a -shaped locus which appear to trace, on an overall
basis, the hardness of a local heating radiation field. But some driving
parameters other than the radiation field may also be required for a full
interpretation of this trend. On the other hand, the flux ratio of
EF(8.6)/EF(7.7) shows little variation over the sample sources, except for two
HII regions which have much higher values for this ratio due to an ``EF(8.6\um)
anomaly,'' a phenomenon clearly associated with environments of an intense
far-UV radiation field. If further confirmed on a larger database, these trends
should provide crucial information on how the EF carriers collectively respond
to a changing environment.Comment: 16 pages, 1 figure, 1 table; accepted for publication in ApJ Letter
- …