8,076 research outputs found
Reproductive biology of carpenter seabream (Argyrozona argyrozona) (Pisces: Sparidae) in a marine protected area
The carpenter seabream (Argyrozona argyrozona) is an
endemic South African sparid that comprises an important part of the handline fishery. A three-year study (1998−2000) into its reproductive biology within the Tsitsikamma National Park revealed that these fishes are
serial spawning late gonochorists. The size at 50% maturity (L50) was estimated at 292 and 297 mm FL for both females and males, respectively. A likelihood ratio test revealed that there was no significant difference between male and female L50 (P>0.5). Both monthly gonadosomatic indices
and macroscopically determined ovarian stages strongly indicate that A. argyrozona within the Tsitsikamma
National Park spawn in the astral summer between November and April. The presence of postovulatory follicles (POFs) confirmed a six-month spawning season, and monthly proportions of early (0−6 hour old) POFs showed that spawning frequency was highest (once every 1−2 days) from December to March. Although spawning season was more highly correlated to photoperiod (r = 0.859) than temperature
(r = −0.161), the daily proportion of spawning fish was strongly correlated (r= 0.93) to ambient temperature over
the range 9−22oC. These results indicate that short-term upwelling events, a strong feature in the Tsitsikamma
National Park during summer, may negatively affect carpenter fecundity. Both spawning frequency and duration
(i.e., length of spawning season) increased with fish length. As a result of the allometric relationship between
annual fecundity and fish mass a 3-kg fish was calculated to produce fivefold more eggs per kilogram of body weight
than a fish of 1 kg. In addition to producing more eggs per unit of weight each year, larger fish also produce
significantly larger eggs
Electrostatic confinement of electrons in an integrable graphene quantum dot
We compare the conductance of an undoped graphene sheet with a small region
subject to an electrostatic gate potential for the cases that the dynamics in
the gated region is regular (disc-shaped region) and classically chaotic
(stadium). For the disc, we find sharp resonances that narrow upon reducing the
area fraction of the gated region. We relate this observation to the existence
of confined electronic states. For the stadium, the conductance looses its
dependence on the gate voltage upon reducing the area fraction of the gated
region, which signals the lack of confinement of Dirac quasiparticles in a
gated region with chaotic classical electron dynamics.Comment: 4 pages, 4 figures; [v2] Added discussion of large aspect ratio
What Does Desert Cost?
Desert plays a relatively minor role in philosophical discussions on distributive justice, whereas it plays a central role in philosophical discussions on retributive justice. At the same time, theorists of justice argue that separating both spheres is to some extent artificial. Quite a few political philosophers have claimed that this asymmetry of desert needs to be defended, and some have offered defenses.
I critically evaluate the last defense of the asymmetry that has not been challenged so far: Moriarty’s argument that an asymmetry in the costs of requiting desert between both spheres of justice (partially) vindicates the asymmetry of desert. It is my contention that his defense ultimately fails. The reason is that he does not specify a fairness threshold that systems setting out to reward desert need to live up to
Discussing Why Some Things Should Not Be for Sale
In Why Some Things Should Not Be For Sale, Debra Satz (2010) argues that four considerations should guide moral reflection on markets: does a market involve weak agency, extreme vulnerability, extremely harmful outcomes to individuals, or extremely harmful outcomes to society? If the answer is yes to one or more of these questions, a market could very well be noxious. In this paper, I assess to what extent Satz’ framework can indeed be used to discuss the moral status of markets. I claim that (1) it would be desirable to have a criterion that tells us when weak agency and extreme vulnerability make a market noxious; (2) it is unproductive to discuss the moral status of a theoretical market without first thinking about a regulatory framework for this market; and (3) it is paramount to consider all empirical evidence available on markets because they might turn out very differently in reality from how they look on paper
Photon heat transport in low-dimensional nanostructures
At low temperatures when the phonon modes are effectively frozen, photon
transport is the dominating mechanism of thermal relaxation in metallic
systems. Starting from a microscopic many-body Hamiltonian, we develop a
nonequilibrium Green's function method to study energy transport by photons in
nanostructures. A formally exact expression for the energy current between a
metallic island and a one-dimensional electromagnetic field is obtained. From
this expression we derive the quantized thermal conductance as well as show how
the results can be generalized to nonequilibrium situations. Generally, the
frequency-dependent current noise of the island electrons determines the energy
transfer rate.Comment: 4 pages, 3 Fig
Signatures of Klein tunneling in disordered graphene p-n-p junctions
We present a method for obtaining quantum transport properties in graphene
that uniquely combines three crucial features: microscopic treatment of charge
disorder, fully quantum mechanical analysis of transport, and the ability to
model experimentally relevant system sizes. As a pertinent application we study
the disorder dependence of Klein tunneling dominated transport in p-n-p
junctions. Both the resistance and the Fano factor show broad resonance peaks
due to the presence of quasi bound states. This feature is washed out by the
disorder when the mean free path becomes of the order of the distance between
the two p-n interfaces.Comment: 4 pages, 4 figure
Notes on simplicial rook graphs
The simplicial rook graph is the graph of which the vertices
are the sequences of nonnegative integers of length summing to , where
two such sequences are adjacent when they differ in precisely two places. We
show that has integral eigenvalues, and smallest eigenvalue , and that this graph has a large part of its
spectrum in common with the Johnson graph . We determine the
automorphism group and several other properties
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