3,395 research outputs found
Computer programs for reduction of microphotometer data
Five computer programs for analyzing magnetic tape recordings of digital data from microphotomete
Strategic Review of Tropical Fisheries Management
This project addresses the constraints to tropical fisheries development with sustainable exploitation through a strategic assessment of tropical fisheries management with the following purposes: (1) To evaluate relevant research methods for the development of assessment models appropriate to the circumstances of tropical coastal fisheries; and (2) To evaluate the utility of existing strategies for the implementation of management advice. The report consists of three substantive chapters. Chapter 2 contains a detailed socio-economic assessment of various instruments and implementation strategies applicable to tropical capture fisheries. In Chapter 3, a detailed assessment of the fisheries for tropical large marine ecosystems has been conducted using a technique developed by FAO (Granger & Garcia 1996). The data used were the FAO statistics published regularly by FAO. This analysis has been conducted for each of the tropical large marine ecosystems and indicates that there is the potential for increased fishing in a number of these ecosystems. One of the clear requirements identified in Chapter 2 and implicit in Chapter 3, is that there is a significant need for simple and robust fisheries assessment methods which can estimate the potential of a particular resource, its capacity in terms of the level of fishing effort and its current status ie whether it is currently exploited sustainably or not. In Chapter 4, these problems are addressed directly and, using two approaches, significant simplification of fishery methods is developed. In the first approach, simple empirical relationships between the life history parameters of a species are used to develop models of potential yield which can be determined by a simple assessment of fish growth. In the second approach, optimal life history theory is applied to the key demographic parameters of exploited fish populations and using estimates of the Beverton & Holt invariants a significant simplifying of the basic stock assessment equations is developed
Preliminary Spectral Analysis of SN 1994I
We present optical spectra of the Type Ic supernova 1994I in M51 and
preliminary non-LTE analysis of the spectra. Our models are not inconsistent
with the explosions of C+O cores of massive stars. While we find no direct
evidence for helium in the optical spectra, our models cannot rule out small
amounts of helium. More than 0.1~\msol\ of helium seems unlikely.Comment: LaTeX, MN style, psfig, and natbib substyles, 7 pages, 4 figures, to
appear in MNRAS. Postscript file available from
http://www.nhn.uoknor.edu/~baro
SN 2005hj: Evidence for Two Classes of Normal-Bright SNe Ia and Implications for Cosmology
HET Optical spectra covering the evolution from about 6 days before to about
5 weeks after maximum light and the ROTSE-IIIb unfiltered light curve of the
"Branch-normal" Type Ia Supernova SN 2005hj are presented. The host galaxy
shows HII region lines at redshift of z=0.0574, which puts the peak unfiltered
absolute magnitude at a somewhat over-luminous -19.6. The spectra show weak and
narrow SiII lines, and for a period of at least 10 days beginning around
maximum light these profiles do not change in width or depth and they indicate
a constant expansion velocity of ~10,600 km/s. We analyzed the observations
based on detailed radiation dynamical models in the literature. Whereas delayed
detonation and deflagration models have been used to explain the majority of
SNe Ia, they do not predict a long velocity plateau in the SiII minimum with an
unvarying line profile. Pulsating delayed detonations and merger scenarios form
shell-like density structures with properties mostly related to the mass of the
shell, M_shell, and we discuss how these models may explain the observed SiII
line evolution; however, these models are based on spherical calculations and
other possibilities may exist. SN 2005hj is consistent with respect to the
onset, duration, and velocity of the plateau, the peak luminosity and, within
the uncertainties, with the intrinsic colors for models with M_shell=0.2 M_sun.
Our analysis suggests a distinct class of events hidden within the
Branch-normal SNe Ia. If the predicted relations between observables are
confirmed, they may provide a way to separate these two groups. We discuss the
implications of two distinct progenitor classes on cosmological studies
employing SNe Ia, including possible differences in the peak luminosity to
light curve width relation.Comment: ApJ accepted, 31 page
Spectral Consequences of Deviation from Spherical Composition Symmetry in Type Ia Supernovae
We investigate the prospects for constraining the maximum scale of clumping
in composition that is consistent with observed Type Ia supernova flux spectra.
Synthetic spectra generated without purely spherical composition symmetry
indicate that gross asymmetries make prominent changes to absorption features.
Motivated by this, we consider the case of a single unblended line forming in
an atmosphere with perturbations of different scales and spatial distributions.
Perturbations of about 1% of the area of the photodisk simply weaken the
absorption feature by the same amount independent of the line of sight.
Conversely, perturbations of about 10% of the area of the photodisk introduce
variation in the absorption depth which does depend on the line of sight. Thus,
1% photodisk area perturbations may be consistent with observed profile
homogeneity but 10% photodisk area perturbations can not. Based on this, we
suggest that the absence of significant variation in the depths of Si II 6355
absorption features in normal Type Ia spectra near maximum light indicates that
any composition perturbations in these events are quite small. This also
constrains future three-dimensional explosion models to produce ejecta profiles
with only small scale inhomogeneities.Comment: 11 pages, 6 figure
The Probable Detection of SN 1923A: The Oldest Radio Supernova?
Based upon the results of VLA observations, we report the detection of two
unresolved radio sources that are coincident with the reported optical position
of SN 1923A in M83. For the source closest to the SN position, the flux density
was determined to be 0.30 +/- 0.05 mJy at 20 cm and 0.093 +/- 0.028 mJy at 6
cm. The flux density of the second nearby source was determined to be 0.29 +/-
0.05 at 20 cm and 0.13 +/- 0.028 at 6 cm. Both sources are non-thermal with
spectral indices of alpha = -1.0 +/- 0.30 and -0.69 +/- 0.24, respectively. SN
1923A has been designated as a Type II-P. No Type II-P (other than SN 1987A)
has been detected previously in the radio. The radio emission from both sources
appears to be fading with time. At an age of approximately 68 years when we
observed it, this would be the oldest radio supernova (of known age) yet
detected
Reading the Spectra of the Most Peculiar Type Ia Supernova 2002cx
In spite of the apparent lack of Si II and S II features in its spectra, SN
2002cx was classified as a peculiar Type Ia supernova (SN Ia) on the basis of
its overall photometric and spectroscopic behavior. Spectra obtained near
maximum light contained Fe III features, as in SN 1991T-like events, but the
blueshifts of the Fe III absorptions were exceptionally low. The luminosity
also was low. We use the supernova synthetic--spectrum code SYNOW to study line
identifications in SN 2002cx. We find that the maximum-light spectra appear to
contain weak features of Si II, S II, Si III, and Ca II, which strengthens the
connection with SN 1991T-like events. We show that later spectra, obtained 12,
25, and 56 days after maximum, consist of P-Cygni resonance-scattering features
due to permitted Fe II and Co II lines. SN 2002cx had been thought to have made
the transition from a permitted-line to a forbidden-line spectrum between 25
and 56 days. Owing to the low expansion velocities the postmaximum spectral
features are narrower and easier to identify than they are in other SNe Ia. SN
2002cx will lead to improved line identifications in other SNe Ia and clarify
when the transition from a permitted-line to a forbidden-line spectrum occurs.
In the context of current SN Ia explosion models, we suggest that the
properties of SN 2002cx may be consistent with 3D deflagration models, which
are not favored for normal SNe Ia.Comment: 21 pages including 7 figures and 4 tables; accepted by PAS
A new species of rock-dwelling \u3cem\u3ePhyllodactylus\u3c/em\u3e (Squamata: Gekkonidae) from the Richtersveld, South Africa
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