The Educational Achievement of U.S. Puerto Ricans

With longitudinal data, this article extends to the 1990s research on minority educational achievement and emphasizes the experiences of Puerto Ricans. The authors\u27 results suggest that compared with whites, blacks, and Mexicans, Puerto Ricans exhibit the lowest high school graduation rates and that their educational disadvantage is unique. Even if Puerto Ricans assumed the attributes of whites, they would graduate at lower rates than the latter. This finding, which has serious implications, deserves priority in the agendas of scholars and policy specialists alike

Quantum Monte Carlo scheme for frustrated Heisenberg antiferromagnets

When one tries to simulate quantum spin systems by the Monte Carlo method, often the 'minus-sign problem' is encountered. In such a case, an application of probabilistic methods is not possible. In this paper the method has been proposed how to avoid the minus sign problem for certain class of frustrated Heisenberg models. The systems where this method is applicable are, for instance, the pyrochlore lattice and the $J_1-J_2$ Heisenberg model. The method works in singlet sector. It relies on expression of wave functions in dimer (pseudo)basis and writing down the Hamiltonian as a sum over plaquettes. In such a formulation, matrix elements of the exponent of Hamiltonian are positive.Comment: 19 LaTeX pages, 6 figures, 1 tabl

Influence of anisotropic next-nearest-neighbor hopping on diagonal charge-striped phases

We consider the model of strongly-correlated system of electrons described by an extended Falicov-Kimball Hamiltonian where the stability of some axial and diagonal striped phases was proved. Introducing a next-nearest-neighbor hopping, small enough not to destroy the striped structure, we examine rigorously how the presence of the next-nearest-neighbor hopping anisotropy reduces the $\pi/2$-rotation degeneracy of the diagonal-striped phase. The effect appears to be similar to that in the case of anisotropy of the nearest-neighbor hopping: the stripes are oriented in the direction of the weaker next-nearest-neighbor hopping.Comment: 9 pages, 3 figures, 1 tabl

Immunohistochemical characteristics of porcine intrahepatic nerves under physiological conditions and after bisphenol A administration

Background: The neurochemistry of hepatic nerve fibres was investigated in large animal models after dietary exposure to the endocrine disrupting compound known as bisphenol A (BPA).   Materials and methods: Antibodies against neuronal peptides were used to study changes in hepatic nerve fibres after exposure to BPA at varying concentrations using standard immunofluorescence techniques. The neuropeptides investigated were substance P (SP), galanin (GAL), pituitary adenylate cyclase activating polypeptide (PACAP), calcitonin gene regulated peptide (CGRP) and cocaine and amphetamine regulated transcript (CART). Immunoreactive nerve fibres were counted in multiple sections of the liver and among multiple animals at varying exposure levels. The data was pooled and presented as mean ± standard error of the mean.   Results: It was found that all of the nerve fibres investigated showed upregulation of these neural markers after BPA exposure, even at exposure levels currently considered to be safe. These results show very dramatic increases in nerve fibres containing the above-mentioned neuropeptides and the altered neurochemical levels may be causing a range of pathophysiological states if the trend of over-expression is extrapolated to developing humans.   Conclusions: This may have serious implications for children and young adults who are exposed to this very common plastic polymer, if the same trends are occurring in humans

Ultrastructural features of supraspinal muscles in rabbits after long-term transcutaneous lateral electrical surface stimulation (LESS)

Lateral electrical surface stimulation is one of methods used in the therapy of the progressive form of idiopathic scoliosis (IS) in children and youth. However, there are data suggesting that this method may lead to serious adverse side effects, when used for a too long period of time per day. To clarify this issue, the present study was aimed at disclosing possible changes in the ultrastructural appearance of rabbit supraspinal muscles undergoing long-term stimulation (9 h per day, 3 months), an animal model successfully used to mimic the situation in humans. In comparison to the control animals, muscles of "overstimulated" rabbits exhibited clear signs of microscopical lesions, including depletion and disintegration of myofilaments, proliferation, dilatation and, sometimes, swelling of sarcoplasmic reticulum and/or mitochondria, as well as signs of destruction of the Z line. The above-mentioned abnormalities, especially the signs of degenerative processes associated with the Z line and the observed microlesions strongly suggest that the failure of the long-term LESS therapy of the IS may be attributable to these ultrastructural lesions

Sources of porcine longissimus dorsi muscle (LDM) innervation as revealed by retrograde neuronal tract-tracing.

The aim of the present study was to establish the origin of the motor, autonomic and sensory innervation of the L1-L2 segment of the porcine longissimus dorsi muscle (LDM), in order to provide morphological basis for further studies focusing on this neural pathway under experimental conditions, e.g. phototerapy and/or lateral electrical surface stimulation. To reach the goal of the study, multiple injections of the fluorescent neuronal tracer Fast Blue (FB) were made into the LDM region between the spinal processes of the vertebrae L1 and L2. The spinal cord (Th13-S1 segments) as well as the sensory and autonomic ganglia of interest, i.e., dorsal root (DRG) and sympathetic chain ganglia from corresponding spinal cord levels were collected three weeks later. FB-positive (FB+) motoneurons were observed exclusively within the nucleus ventromedialis at L1 and L2 spinal cord level, forming the most ventro-medially arranged cell column within this nucleus. Primary sensory and sympathetic chain neurons were found in appropriate ipsilateral ganglia at Th15-L3 levels. The vast majority of retrogradely traced neurons (virtually all motoneurons, approximately 76% of sensory and 99.4% of sympathetic chain ganglia neurons) was found at the L1 and L2 levels. The morphometric evaluation of FB-labeled DRG neurons showed that the majority of them (approximately 66%) belonged to the class of small-diameter perikarya (10-30 microm in diameter), whereas those of medium size (30-80 microm in diameter) and of large diameter (more than 80 microm) constituted 22.6% and 11.5% of all DRG neurons, respectively. The results of the present study demonstrated that the nerve terminals supplying porcine LDM originated from different levels of the spinal cord, dorsal root and sympathetic chain ganglia. Thus, the study has revealed sources and morphological characteristic of somatic, autonomic and spinal afferent neurons supplying porcine LDM, simultaneously pointing out the characteristic features of their distribution pattern

High Speed Dynamics of Collapsing Cylindrical Dust Fluid

We construct approximate solutions that will describe the last stage of cylindrically symmetric gravitational collapse of dust fluid. Just before the spacetime singularity formation, the speed of the dust fluid might be almost equal to the speed of light by gravitational acceleration. Therefore the analytic solution describing the dynamics of cylindrical null dust might be the crudest approximate solution of the last stage of the gravitational collapse. In this paper, we regard this null dust solution as a background and perform `high-speed approximation' to know the gravitational collapse of ordinary timelike dust fluid; the `deviation of the timelike 4-velocity vector field from null' is treated as a perturbation. In contrast with the null dust approximation, our approximation scheme can describe the generation of gravitational waves in the course of the cylindrically symmetric dust collapse.Comment: 15 page

Cumulant ratios and their scaling functions for Ising systems in strip geometries

We calculate the fourth-order cumulant ratio (proposed by Binder) for the two-dimensional Ising model in a strip geometry L x oo. The Density Matrix Renormalization Group method enables us to consider typical open boundary conditions up to L=200. Universal scaling functions of the cumulant ratio are determined for strips with parallel as well as opposing surface fields.Comment: 4 pages, RevTex, one .eps figure; references added, format change

A Reformulation of the Hoop Conjecture

A reformulation of the Hoop Conjecture based on the concept of trapped circle is presented. The problems of severe compactness in every spatial direction, and of how to superpose the hoops with the surface of the black hole, are resolved. A new conjecture concerning "peeling" properties of dynamical/trapping horizons is propounded. A novel geometric Hoop inequality is put forward. The possibility of carrying over the results to arbitrary dimension is discussed.Comment: 6 pages, no figures. New references included, typos corrected, explanatory comments added. Much shorter version, in order to match EPL length restrictions. To be published in EP