23,682 research outputs found
Distribution and abundance of ichthyoplankton in Florida Bay
Ichthyoplankton was sampled at 14 stations with 60 cm bongo nets fitted with 0.333 mm mesh in basins throughout Florida Bay in 1994-1995. In addition, I compared collections made
using an epibenthic sled to those made with standard ichthyoplankton bongo nets at four stations during July 1997-November,1999 to determine ifthe two types of gear are complementary. In 1994-1995, in descending order of abundance, Clupeiformes, Gobiidae, Callionymidae,
Sciaenidae, Labrisomidae, Soleidae and Blenniidae dominated the ichthyoplankton. Densities of clupeiforms were generally very high (> 100 larvae 100 m-3) or high (10.0 - 99.9 larvae 100 m-3). Gobiid larvae were ubiquitous with highest densities occurring in waters in close proximity to
the Gulf of Mexico (109.7 larvae 100 m-3), lowest in two ofthree eastern Florida Bay stations (<1.0 larva 100 m-3). Spotted seatrout, Cynoscion nebulosus, dominated larval sciaenid collections and the only other sciaenid identified to species was the sand seatrout, Cynoscion arenarius.
Taxa differed markedly between collections taken by epibenthic sled and standard ichthyoplankton bongo nets. Taxa collected with standard ichthyoplankton gear were those that spawn in Florida Bay and have pelagic larvae (i.e., engraulids and gobiids). Taxa collected with
the sled were small resident species that have benthic larvae (i.e., syngnathids and cyprinodonts) or taxa that spawn outside the bay, but use the bay as a nursery area (i.e., gerreids and haemulids). Recently-settled red drum, Sciaenops ocellatus, were collected with the epibenthic
sled in November 1999, although juveniles of this important gamefish are rare in the bay
Conservation laws, radiative decay rates, and excited state localization in organometallic complexes with strong spin-orbit coupling
There is longstanding fundamental interest in 6-fold coordinated
() transition metal complexes such as [Ru(bpy)] and
Ir(ppy), particularly their phosphorescence. This interest has increased
with the growing realisation that many of these complexes have potential uses
in applications including photovoltaics, imaging, sensing, and light-emitting
diodes. In order to design new complexes with properties tailored for specific
applications a detailed understanding of the low-energy excited states,
particularly the lowest energy triplet state, , is required. Here we
describe a model of pseudo-octahedral complexes based on a pseudo-angular
momentum representation and show that the predictions of this model are in
excellent agreement with experiment - even when the deviations from octahedral
symmetry are large. This model gives a natural explanation of zero-field
splitting of and of the relative radiative rates of the three sublevels
in terms of the conservation of time-reversal parity and total angular momentum
modulo two. We show that the broad parameter regime consistent with the
experimental data implies significant localization of the excited state.Comment: 8 pages, 6 figs + sup info (20 pages, 19 figures - to view pdf
download the source files
The origin of the difference in the superconducting critical temperatures of the beta_H and beta_L phases of (BEDT-TTF)_2I_3
Incommensurate lattice fluctuations are present in the beta_L phase (T_c =
1.5 K) of ET_2I_3 (where ET is BEDT-TTF -
bis(ethylenedithio)tetrathiafulvalene) but are absent in the beta_H phase (T_c
= 7 K). We propose that the disorder in the conformational degrees of freedom
of the terminal ethylene groups of the ET molecules, which is required to
stabilise the lattice fluctuations, increases the quasiparticle scattering rate
and that this leads to the observed difference in the superconducting critical
temperatures, T_c, of the two phases. We calculate the dependence of T_c on the
interlayer residual resistivity. Our theory has no free parameters. Our
predictions are shown to be consistent with experiment. We describe experiments
to conclusively test our hypothesis.Comment: 4 pages, 1 figur
Spin-state ice in geometrically frustrated spin-crossover materials
Spin crossover materials contain metal ions that can access two spin-states:
one low-spin (LS), the other high-spin (HS). We propose that frustrated elastic
interactions can give rise to spin-state ices -- phases of matter without
long-range order, characterized by a local constraint or `ice rule'. The
low-energy physics of spin-state ices is described by an emergent
divergence-less gauge field with a gap to topological excitations that are
deconfined quasi-particles with spin fractionalized midway between the spins of
the LS and HS states.Comment: Major edit, some new results; 8+2 page
Geometrical frustration in the spin liquid beta'-Me3EtSb[Pd(dmit)2]2 and the valence bond solid Me3EtP[Pd(dmit)2]2
We show that the electronic structures of the title compounds predicted by
density functional theory (DFT) are well described by tight binding models. We
determine the frustration ratio, J'/J, of the Heisenberg model on the
anisotropic triangular lattice, which describes the spin degrees of freedom in
the Mott insulating phase for a range of Pd(dmit)2 salts. All of the
antiferromagnetic materials studied have J'/J 0.9, consistent
with predictions for the Heisenberg model. All salts with 0.5 < J'/J < 0.9,
where many-body theories find a number of competing ground states, are known,
experimentally, to be charge ordered, valence bond solids or spin liquids.Comment: Accepted for publication in Phys. Rev. Lett. 4+11 pages, 3+15
figures, major rewrite, added calculations of Hubbard
Hydraulic characteristics of flow through miniature slits
Hydraulic characteristics of micro-orifices arrayed in close proximity across the face of a liquid fuel injector are studied. Effects of geometry and flow variables on discharge coefficients and flow regimes are determined, as well as visible characteristics of the emerging liquid streams
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