687 research outputs found
The fish community of the berg river estuary and an assessment of the likely effects of reduced freshwater inflows
Data concerning the species composition, abundance and distribution of fishes inhabiting the Berg River estuary are presented and used to assess the value of the estuary to fish, and the likely eflects of reduced freshwater inflows. A total of 31 species was recorded, eight of which were classified as estuarine residents, 11 as marine estuarine-opportunists, six as marine stragglers and six were freshwater species. Liza richardsonii, an opportunist, was the most abundant (54% N) and widely distributed species encountered during the winter and summer seine-net surveys. Three other species (all residents) contributed more than 10% of the total catch; Atherina breviceps and Caffrogobius nudiceps occurring most abundantly in the lower estuary, and Gilchristella aestuaria in the middle estuary. The low number of species compared with estuaries in other regions of the South African coast reflect a well-established marine biogeographical trend. The higher proportions ol resident species, entirely dependent species and partially dependent species suggest, however, that west coast estuaries may be more important to the fish that inhabit them than are estuaries in other regions. It is concluded that the fish community of the estuary is already suffering the effects of habitat degradation and that further reductions in freshwater inllows are not desirable
The diets of fish in three south-western Cape estuarine systems
The stomach contents of 2756 fish of 14 species taken by seine and gill netting in the Bot River, Kleinmond and Palmiet estuaries on the south-western Cape coast of South Africa were examined. The small juveniles of all species consumed primarily zooplankton before switching to their adult diets. Seven of the species, Atherina breviceps, Caffrogobius multifasciatus, Clinus spatulatus, Galeichthys feliceps, Gilchnstella aestuaria, Monodactylus falciformis, Psammogobius knysnaensis and Syngnathus acus were carnivores which fed primarily on invertebrates; two, Hyporhamphus capensis and Sarpa salpa, were herbivores; three, Lithganathus lithognathus, Rhabdosargus globiceps and R. holubi were omnivores and two, Lichia amia and Pomatomus saltatrix were piscivores. Within these trophic groupings variations in the diets of fish from the different estuaries were noted as were changes in diet with season. Differences between estuaries were ascribed primarily to food availability and differences in the size ranges of the fish species sampled in them. Differences in the diet between size classes were primarily due to an increasing ability to handle larger food items. The few seasonal differences in diet that occurred appeared not to conform to any observable pattern. Twelve food categories provided > 1 % of food consumed by at least one species and each of these categories was represented in the guts of between 9 and 14 of the fish species examined. Six of the prey categories, Isopoda, Amphipoda, Decapoda, Teleostei, Algae and Spermatophyta each provided> 10% of the food consumed by all 14 species combined
Factors affecting the distribution, abundance and diversity of rock-pool fishes on the Cape Peninsula, South Africa
No Abstract
Security of the Bennett 1992 quantum-key distribution against individual attack over a realistic channel
The security of two-state quantum key distribution against individual attack
is estimated when the channel has losses and noises. We assume that Alice and
Bob use two nonorthogonal single-photon polarization states. To make our
analysis simple, we propose a modified B92 protocol in which Alice and Bob make
use of inconclusive results and Bob performs a kind of symmetrization of
received states. Using this protocol, Alice and Bob can estimate Eve's
information gain as a function of a few parameters which reflect the
imperfections of devices or Eve's disturbance. In some parameter regions, Eve's
maximum information gain shows counter-intuitive behavior, namely, it decreases
as the amount of disturbances increases. For a small noise rate Eve can extract
perfect information in the case where the angle between Alice's two states is
small or large, while she cannot extract perfect information for intermediate
angles. We also estimate the secret key gain which is the net growth of the
secret key per one pulse. We show the region where the modified B92 protocol
over a realistic channel is secure against individual attack.Comment: 16 pages, 15 figure
Melittin-induced changes in lipid multilayers. A solid-state NMR study
Solid-state 1H, 13C, 14N, and 31P NMR spectroscopy was used to study the effects of the bee venom peptide, melittin, on aligned multilayers of dimyristoyl-, dilauryl- and ditetradecyl-phosphatidylcholines above the gel to liquid-crystalline transition temperature, Tc. Both 31P spectra from the lipid headgroups and 1H resonances from the lipid acyl chain methylene groups indicate that the peptide does not affect the mosaic spread of the lipid molecules at lipid:peptide molar ratios of 10:1, or higher. None of the samples prepared above Tc showed any evidence of the formation of hexagonal or isotropic phases. Melittin-induced changes in the chemical shift anisotropy of the headgroup phosphate and the lipid carbonyl groups, and in the choline 14N quadrupole splittings, show that the peptide has effects on the headgroup order and on the molecular organization in the sections of the acyl chains nearest to the bilayer surface. The spin-lattice relaxation time for the lipid acyl chain methylene protons was found to increase and the rotating-frame longitudinal relaxation time to markedly decrease with the addition of melittin, suggesting that motions on the nanosecond time scale are restricted, whereas the slower, collective motions are enhanced in the presence of the peptide
Coherent information analysis of quantum channels in simple quantum systems
The coherent information concept is used to analyze a variety of simple
quantum systems. Coherent information was calculated for the information decay
in a two-level atom in the presence of an external resonant field, for the
information exchange between two coupled two-level atoms, and for the
information transfer from a two-level atom to another atom and to a photon
field. The coherent information is shown to be equal to zero for all
full-measurement procedures, but it completely retains its original value for
quantum duplication. Transmission of information from one open subsystem to
another one in the entire closed system is analyzed to learn quantum
information about the forbidden atomic transition via a dipole active
transition of the same atom. It is argued that coherent information can be used
effectively to quantify the information channels in physical systems where
quantum coherence plays an important role.Comment: 24 pages, 7 figs; Final versiob after minor changes, title changed;
to be published in Phys. Rev. A, September 200
Flagging health risks of chemicals by combining in vitro bioactivity data with environmental and consumer product exposure modeling
Security of quantum cryptography using balanced homodyne detection
In this paper we investigate the security of a quantum cryptographic scheme
which utilizes balanced homodyne detection and weak coherent pulse (WCP). The
performance of the system is mainly characterized by the intensity of the WCP
and postselected threshold. Two of the simplest intercept/resend eavesdropping
attacks are analyzed. The secure key gain for a given loss is also discussed in
terms of the pulse intensity and threshold.Comment: RevTeX4, 8pages, 7 figure
Tier 2 High-Throughput Exposure Screening of Chemicals in Consumer Products: Chemicals encapsulated in articles and in cosmetics
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