57,177 research outputs found
Ecology of fishes in Upper Newport Bay, California: seasonal dynamics and community structure
A total of 366 bimonthly (January 1978-January 1979) samples taken with six types of gear (otter trawl, gill net, bag seine, small seine, drop net, square enclosure - all
with replication except the gill net) at four stations in
upper Newport Bay, California yielded 51,816 fishes belonging to 46 species and weighing over 353 kg. Atherinops affinis (topsmelt) was the most abundant species accounting for 76% of total individuals. Seven species, all of low trophic levels, made up over 97% of the total catch. Mugil cephalus (striped mullet) ranked first in biomass (= 36% of the total) with six species accounting for more than 80% of the total biomass. The largest number of individuals (71%) was collected with the bag seine, the greatest number of species (35) was captured with the otter trawl and the largest percentage of the biomass (56%)was obtained with the gill net. Species richness, number of individuals and biomass were lowest in January (1978 or 1979) or March and highest in July (numbers, biomass) or September (species). Bimonthly diversity (H') values ranged from 0.48 to 2.17 (overall value 1.05) and tended to be inversely related to abundance levels. Species richness was greatest at Station 4 (the lowermost station) and least at Station 1 (the uppermost station). Numbers of individuals and biomass peaked at Station 2 and reached lowest levels at Station 1.
Length-frequency analysis of six of the most abundant
species indicated utilization of the upper bay by two or
more stages in the life history of these species.
More than 92,000 eggs belonging to seven taxa and an
unknown category and 426 larvae from 20 taxa were collected
with a 0.5 m net mounted on an epibenthic sled during the
same bimonthly periods and at the same stations as the
juvenile/adult samples. Most of the eggs were collected at
Station 2 in May with the numbers overwhelmingly dominated
by those of Anchoa compressa (deepbody anchovy) (99.7% of
total numbers). The most abundant larva was that of
Clevelandia ios (arrow goby). Nearly 60% of the total
larval catch was made up of members of the family Gobiidae.
Larval taxa and individuals were fewest in January (1978).
The number of taxa was highest in March, September and
January (1979) whereas larval numbers peaked in May. The
number of taxa and of individual larvae varied only slightly
among the four stations.
Asymptotic species accumulation curves indicated adequate sampling of juvenile/adult fishes. Cluster analysis
produced eight species groups of resident and periodic
species that variously utilize the three main habitats
(channel, inshore, pannes) in the upper bay. Species
richness and abundance were positively correlated with both
temperature and salinity. Temperature, salinity and depth
of capture were frequently correlated with individual species abundances and were used in combination to partially explain the spatial utilization of species and species groups.
The upper bay fish community is important and worthy of
preservation for at least three reasons: 1) it contains
species assemblages not duplicated in any other coastal
environment; 2) it contains life history stages of a
variety of coastal fish species; and 3) it contains large
populations of small, low-trophic level species and juveniles of other species which serve as forage for larger, predatory species that are frequently of economic importance. Members of the fish community respond noticeably to altered environmental conditions such as the heavy rainfall (and accompanying low salinity and high turbidity) that occurred during the early months of 1978. The short and long term, as yet often unpredictable, fluctuations in the populations emphasize the need for periodic monitoring and for the development of a mathematical model of the fish community if it is to be thoroughly understood and properly managed. (102pp.
The hydrogen sulfide emissions abatement program at the Geysers Geothermal Power Plant
The scope of the hydrogen sulfide (H2S) abatement program at The Geysers Geothermal Power Plant and the measures currently under way to reduce these emissions are discussed. The Geysers steam averages 223 ppm H2S by weight and after passing through the turbines leaves the plant both through the gas ejector system and by air-stripping in the cooling towers. The sulfide dissolved in the cooling water is controlled by the use of an oxidation catalyst such as an iron salt. The H2S in the low Btu ejector off gases may be burned to sulfur dioxide and scrubbed directly into the circulating water and reinjected into the steam field with the excess condensate. Details are included concerning the disposal of the impure sulfur, design requirements for retrofitting existing plants and modified plant operating procedures. Discussion of future research aimed at improving the H2S abatement system is also included
Investigation of wheat coleoptile response to phototropic stimulations
This report provides a summary of the preparations for, and the conduct and post-flight data analysis of, the Spacelab flight investigation FOTRAN, which flew on the IML-1 mission (STS-42) in January, 1992. The investigation was designed to provide data on the responses of wheat seedlings to various blue-light stimuli given while the plants were exposed to orbital microgravity conditions. Before the flight, a number of hypotheses were established which were to be tested by the data from the flight and parallel ground studies. A description of the experiment protocol developed for the mission is provided, and an account of the activities supported during preparations for and support of the flight experiment is given. Details of the methods used to reduce and analyze the data from the flight are outlined
Fluoride solid lubricants for extreme temperatures and corrosive environments
Fluoride solid lubricants for extreme temperature and corrosive environment
Hidden one-dimensional electronic structure and non-Fermi liquid angle resolved photoemission line shapes of -MoO
We report angle resolved photoemission (ARPES) spectra of
-MoO, a layered metal that undergoes two charge density wave
(CDW) transitions at 109 K and 30 K. We have directly observed the ``hidden
one-dimensional (hidden-1d)'' Fermi surface and an anisotropic gap opening
associated with the 109 K transition, in agreement with the band theoretical
description of the CDW transition. In addition, as in other hidden-1d materials
such as NaMoO, the ARPES line shapes show certain anomalies, which
we discuss in terms of non-Fermi liquid physics and possible roles of disorder.Comment: 3 figures; Erratum added to include missed reference
Effect of surface roughness on rate-dependent slip in simple fluids
Molecular dynamics simulations are used to investigate the influence of
molecular-scale surface roughness on the slip behavior in thin liquid films.
The slip length increases almost linearly with the shear rate for atomically
smooth rigid walls and incommensurate structures of the liquid/solid interface.
The thermal fluctuations of the wall atoms lead to an effective surface
roughness, which makes the slip length weakly dependent on the shear rate. With
increasing the elastic stiffness of the wall, the surface roughness smoothes
out and the strong rate dependence is restored again. Both periodically and
randomly corrugated rigid surfaces reduce the slip length and its shear rate
dependence.Comment: 15 pages, 5 figures; submitted to J. Chem. Phy
The Bacterial Photosynthetic Reaction Center as a Model for Membrane Proteins
Membrane proteins participate in many fundamental cellular processes. Until recently, an understanding of the function and properties of membrane proteins was hampered by an absence of structural information at the atomic level. A landmark achievement toward understanding the structure of membrane proteins was the crystallization (1) and structure determination (2-5) the photosynthetic reaction center (RC) from the purple bacteria Rhodopseudomonas viridis, followed by that of the RC from Rhodobacter sphaeroides (6-17). The RC is an integral membrane protein-pigment complex, which carries out the initial steps of photosynthesis (reviewed in 18). RCs from the purple bacteria Rps. viridis and Rb. sphaeroides are composed of three membrane-associated protein subunits (designated L, M, and H), and the following cofactors: four bacteriochlorophylls (Bchl or B), two bacteriopheophytins (Bphe or [phi]), two quinones, and a nonheme iron. The cofactors are organized into two symmetrical branches that are approximately related by a twofold rotation axis (2, 8). A central feature of the structural organization of the RC is the presence of 11 hydrophobic [alpha]-helixes, approximately 20-30 residues long, which are believed to represent the membrane-spanning portion of the RC (3, 9). Five membrane-spanning helixes are present in both the L and M subunits, while a single helix is in the H subunit. The folding of the L and M subunits is similar, consistent with significant sequence similarity between the two chains (19-25). The L and M subunits are approximately related by the same twofold rotation axis that relates the two cofactor branches.
RCs are the first membrane proteins to be described at atomic resolution; consequently they provide an important model for discussing the folding of membrane proteins. The structure demonstrates that [alpha]-helical structures may be adopted by integral membrane proteins, and provides confirmation of the utility of hydropathy plots in identifying nonpolar membrane-spanning regions from sequence data. An important distinction between the folding environments of water-soluble proteins and membrane proteins is the large difference in water concentration surrounding the proteins. As a result, hydrophobic interactions (26) play very different roles in stabilizing the tertiary structures of these two classes of proteins; this has important structural consequences. There is a striking difference in surface polarity of membrane and water-soluble proteins. However, the characteristic atomic packing and surface area appear quite similar.
A computational method is described for defining the position of the RC in the membrane (10). After localization of the RC structure in the membrane, surface residues in contact with the lipid bilayer were identified. As has been found for soluble globular proteins, surface residues are less well conserved in homologous membrane proteins than the buried, interior residues. Methods based on the variability of residues between homologous proteins are described (13); they are useful (a) in defining surface helical regions of membrane and water-soluble proteins and (b) in assigning the side of these helixes that are exposed to the solvent. A unifying view of protein structure suggests that water-soluble proteins may be considered as modified membrane proteins with covalently attached polar groups that solubilize the proteins in aqueous solution
Luttinger liquid ARPES spectra from samples of LiMoO grown by the temperature gradient flux technique
Angle resolved photoemission spectroscopy line shapes measured for
quasi-one-dimensional LiMoO samples grown by a temperature
gradient flux technique are found to show Luttinger liquid behavior, consistent
with all previous data by us and other workers obtained from samples grown by
the electrolyte reduction technique. This result eliminates the sample growth
method as a possible origin of considerable differences in photoemission data
reported in previous studies of LiMoO.Comment: Some text adde
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