3,878 research outputs found
Habitat connectivity in reef fish communities and marine reserve design in Old Providence-Santa Catalina, Colombia
On the insular platform of Old Providence/Santa Catalina, Colombia, we compared nearshore lagoonal patch reefs to those on the northern bank distant from the islands to determine the importance of habitat connectivity to fish community structure. Nearshore patch reefs had greater proximity to mangrove, seagrass and rocky shore habitats, and they had significantly more individuals. Nearshore reefs also tended to have a greater total biomass, more species, a higher proportion of predators of mobile invertebrates and small fishes, and a lower proportion of herbivores. Biomass of snappers and grunts at nearshore sites was four times greater compared to bank sites, and was correlated with the amount of seagrass and sand/rubble habitat within 500 m of each patch reef. We also compared length-frequency distributions and abundances of grunts and snappers among all sites (deep and shallow forereefs, patch reefs and deep and shallow leeside slopes). The results were consistent with ontogenetic migrations from shallow sites, primarily seagrass and mangrove habitats, to deeper sites and to those further out on the bank. The evidence suggests that species differed in both distance and direction of dispersal, which may be affected by the abundance and distribution of preferred habitats. Marine reserves near the islands should target nearshore nursery areas and patch reefs harboring species of limited dispersal capability. Reserves on the northern bank would protect spawners of those species showing the greatest dispersal capability
Numerical simulations of a two-dimensional lattice grain boundary model
We present detailed Monte Carlo results for a two-dimensional grain boundary
model on a lattice. The effective Hamiltonian of the system results from the
microscopic interaction of grains with orientations described by spins of unit
length, and leads to a nearest-neighbour interaction proportional to the
absolute value of the angle between the grains. Our analysis of the correlation
length xi and susceptibility chi in the high-temperature phase favour a
Kosterlitz-Thouless-like (KT) singularity over a second-order phase transition.
Unconstrained KT fits of chi and xi confirm the predicted value for the
critical exponent nu, while the values of eta deviate from the theoretical
prediction. Additionally we apply finite-size scaling theory and investigate
the question of multiplicative logarithmic corrections to a KT transition. As
for the critical exponents our results are similar to data obtained from the XY
model, so that both models probably lie in the same universality class.Comment: 13 pages, Latex, 7 figures, to appear in Physica
Wavelets as a variational basis of the XY model
We use Daubechies' orthonormal compact wavelets as a variational basis for
the model in two and three dimensions. Assuming that the fluctuations of
the wavelet coefficients are Gaussian and uncorrelated, minimization of the
free energy yields the fluctuation strength of wavelet coefficients at
different scales, from which observables can be computed. This model is able to
describe the low-temperature phase and makes a prediction about the phase
transition temperature.Comment: 3 pages, postscript. Contribution to the Lattice 93 workshop (Dallas,
Texas, October 1993
A n-qubit controlled phase gate with superconducting quantum interference devices coupled to a resonator
We present a way to realize a -qubit controlled phase gate with
superconducting quantum interference devices (SQUIDs) by coupling them to a
superconducting resonator. In this proposal, the two logical states of a qubit
are represented by the two lowest levels of a SQUID. An intermediate level of
each SQUID is utilized to facilitate coherent control and manipulation of
quantum states of the qubits. It is interesting to note that a -qubit
controlled phase gate can be achieved with SQUIDs by successively applying
a Jaynes-Cummings pulse to each of the control SQUIDs before and
after a Jaynes-Cummings pulse on the target SQUID.Comment: 9 pages, 4 figures, 1 table, RevTeX, Resubmitted to Phys. Rev.
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