Skeletal Extension, Density and Calcification of the Reef Coral, Montastrea Annularis: St. Croix, U.S. Virgin Islands

Parameters of the annual and subannual skeletal growth of 61 Montastrea annularis corals, collected at a variety of shallow depth sites on reefs of St. Croix, U.S. Virgin Islands, are determined by X-radiography and scanning densitometry for each year in the 10-year period, 1970–1979. Extension (linear growth) of the coral skeleton is correlated negatively with bulk density (mass per unit volume) and positively with calcification (mass addition). Density and mass are slightly positively correlated. No one parameter, however, is a perfect predictor of another. At least two parameters, from which the third can be calculated, are required for complete description of coral growth. The variations of parameters of subannual density bands in this study do not convey information additional to those of annual bands.When compared to a pristine site in St. Croix, coral from Round Reef within Christiansted Harbor (a location of past dredging and sewage pollution) have equivalent (and high) extension but significantly lower density and calcification. On the south coast, corals from a location of major dredging activity in the past have relatively low extension and calcification. These growth anomalies are probably pollution related. Collections of corals from one south coast site may have been biased by hurricane effects to nonrepresentative samples

Bound states of magnons in the S=1/2 quantum spin ladder

We study the excitation spectrum of the two-leg antiferromagnetic S=1/2 Heisenberg ladder. Our approach is based on the description of the excitations as triplets above a strong-coupling singlet ground state. The quasiparticle spectrum is calculated by treating the excitations as a dilute Bose gas with infinite on-site repulsion. We find singlet (S=0) and triplet (S=1) two-particle bound states of the elementary triplets. We argue that bound states generally exist in any dimerized quantum spin model.Comment: 4 REVTeX pages, 4 Postscript figure

Walnut agroforestry (1996)

Agroforestry, or growing trees and other crops together on the same land, has been practiced for years in other countries to achieve more sustainable and productive use of limited land resources. In the U.S., forestry and agriculture historically have been considered mutually exclusive land use alternatives. But with clear management objectives, careful planning and skillful intensive management, combining crops and trees can provide advantages that outweigh any perceived disadvantages. Agroforestry is a potential alternative to conventional mechanical methods for soil erosion control. It also allows for gradual removal of highly erodible cropland from row-crop production.New 1/92, Reprinted 5/96/5

Kinematic Analysis of Obstacle Clearance During Locomotion

This study investigated the effect of obstacles of different heights on the locomotion of 15 healthy subjects. The following parameters were studied: (1) the distance of the toe and heel markers from the obstacle during toe-off and heel contact, respectively, (2) the minimum clearance distance of the toe and heel markers, and (3) the angular displacements and velocities of the hip, knee, and ankle. Results show significant differences in joint angular kinematics and clearance distances as obstacle height increased. The kinematic and distance differences exhibited both strong linear and non-linear trends. Toe-off distance and heel contact distance did not change significantly with changes in obstacle height

Boosting jet power in black hole spacetimes

The extraction of rotational energy from a spinning black hole via the Blandford-Znajek mechanism has long been understood as an important component in models to explain energetic jets from compact astrophysical sources. Here we show more generally that the kinetic energy of the black hole, both rotational and translational, can be tapped, thereby producing even more luminous jets powered by the interaction of the black hole with its surrounding plasma. We study the resulting Poynting jet that arises from single boosted black holes and binary black hole systems. In the latter case, we find that increasing the orbital angular momenta of the system and/or the spins of the individual black holes results in an enhanced Poynting flux.Comment: 7 pages, 5 figure

Selection of VSH-derived “Pol-line” honey bees and evaluation of their Varroa-resistance characteristics

International audienceAbstractHoney bees with Varroa sensitive hygiene (VSH) have good resistance to Varroa destructor. We bred “Pol-line” bees by outcrossing VSH queens to US commercial stocks from 2008 to 2014 and then selecting colonies with low mite infestations. Beginning in 2011, field performance of colonies with outcrossed Pol-line queens was compared to colonies with outcrossed VSH queens. Mite infestations after one season were comparable in colonies of the two bee types. Queens from the most functional colonies of both bee types were added to the Pol-line breeding population each year. Mite resistance was investigated further by exposing mite-infested brood to colonies for 1 week in lab tests. The two bee types did not differ in the percentage of infested brood they removed or in the percentage of non-reproduction among remaining mites. Introgressing the VSH trait into commercial honey bee stock shows promise in creating bees that have useful mite resistance and desirable beekeeping characteristics