A Computer Simulation Model of Waterhyacinth and Weevil Interactions

A personal computer simulation model termed INSECT has been developed to evaluate biological control of waterhyacinth (Eichhornia crassipes (Mart.) Solms.) by two species of weevil (Neochetina eichhorniae Warner, and N. bruchi Hustache). The model results were compared with the data from three different locations. For each data set, the simulated plant biomass, adult and larva populations were plotted aqainst the 95% confidence intervals of the actual field observations. In many cases, the simulation results were within the 95% confidence intervals, and especially during the growing season, they indicated trends similar to those seen in the field data. However, there were discrepancies in both the magnitude and the trend for early and the late periods of the year. These initial results suggest that development of a model to simulate the impact of a biocontrol agent on waterhyacinth populations is a feasible approach to better understand the interactions within this control system

March Madness: NCAA Tournament Participation and College Alcohol Use

While athletic success may improve the visibility of a university to prospective students and thereby benefit the school, it may also increase risky behavior in the current student body. Using the Harvard School of Public Health College Alcohol Study, we find that a school\u27s participation in the NCAA Basketball Tournament is associated with a 47% increase in binge drinking by male students at that school. Additionally, we find evidence that drunk driving increases by 5% among all students during the tournament. (JEL I12, I23, Z28

Binary continuous random networks

Many properties of disordered materials can be understood by looking at idealized structural models, in which the strain is as small as is possible in the absence of long-range order. For covalent amorphous semiconductors and glasses, such an idealized structural model, the continuous-random network, was introduced 70 years ago by Zachariasen. In this model, each atom is placed in a crystal-like local environment, with perfect coordination and chemical ordering, yet longer-range order is nonexistent. Defects, such as missing or added bonds, or chemical mismatches, however, are not accounted for. In this paper we explore under which conditions the idealized CRN model without defects captures the properties of the material, and under which conditions defects are an inherent part of the idealized model. We find that the density of defects in tetrahedral networks does not vary smoothly with variations in the interaction strengths, but jumps from close-to-zero to a finite density. Consequently, in certain materials, defects do not play a role except for being thermodynamical excitations, whereas in others they are a fundamental ingredient of the ideal structure.Comment: Article in honor of Mike Thorpe's 60th birthday (to appear in J. Phys: Cond Matt.

Signaling, Polyubiquitination, Trafficking, and Inclusions: Sequestosome 1/p62's Role in Neurodegenerative Disease

Aggregated misfolded proteins are hallmarks of most neurodegenerative diseases. In a chronic disease state, including pathologic situations of oxidative stress, these proteins are sequestered into inclusions. Accumulation of aggregated proteins can be prevented by chaperones, or by targeting their degradation to the UPS. If the accumulation of these proteins exceeds their degradation, they may impair the function of the proteasome. Alternatively, the function of the proteasome may be preserved by directing aggregated proteins to the autophagy-lysosome pathway for degradation. Sequestosome 1/p62 has recently been shown to interact with polyubiquitinated proteins through its UBA domain and may direct proteins to either the UPS or autophagosome. P62 is present in neuronal inclusions of individuals with Alzheimer's disease and other neurodegenerative diseases. Herein, we review p62's role in signaling, aggregation, and inclusion formation, and specifically as a possible contributor to Alzheimer's disease. The use of p62 as a potential target for the development of therapeutics and as a disease biomarker is also discussed

Constant effective mass across the phase diagram of high-Tc_{c} cuprates

We investigate the hole dynamics in two prototypical high temperature superconducting systems: La$_{2-x}$Sr$_{x}$CuO$_{4}$ and YBa$_{2}$Cu$_{3}$O$_{y}$ using a combination of DC transport and infrared spectroscopy. By exploring the effective spectral weight obtained with optics in conjunction with DC Hall results we find that the transition to the Mott insulating state in these systems is of the "vanishing carrier number" type since we observe no substantial enhancement of the mass as one proceeds to undoped phases. Further, the effective mass remains constant across the entire underdoped regime of the phase diagram. We discuss the implications of these results for the understanding of both transport phenomena and pairing mechanism in high-T$_{c}$ systems.Comment: 5 pages, 2 figure

Optical investigations on Y2−xBixRu2O7Y_{2-x} Bi_x Ru_2 O_7: Electronic structure evolutions related to the metal-insulator transition

Optical conductivity spectra of cubic pyrochlore $Y_{2-x} Bi_x Ru_2 O_7$ (0.0$\leq${\it x}$\leq$2.0) compounds are investigated. As a metal-insulator transition (MIT) occurs around {\it x}$=$0.8, large spectral changes are observed. With increase of {\it x}, the correlation-induced peak between the lower and the upper Hubbard bands seems to be suppressed, and a strong mid-infrared feature is observed. In addition, the $p-d$ charge transfer peak shifts to the lower energies. The spectral changes cannot be explained by electronic structural evolutions in the simple bandwidth-controlled MIT picture, but are consistent with those in the filling-controlled MIT picture. In addition, they are also similar to the spectral changes of Y$_{2-x}$Ca$_{x}$Ru$_{2}$O$_{7}$ compounds, which is a typical filling-controlled system. This work suggests that, near the MIT, the Ru bands could be doped with the easily polarizable Bi cations.Comment: 5 figure

The a-axis optical conductivity of detwinned ortho-II YBa_2Cu_3O_6.50

The a-axis optical properties of a detwinned single crystal of YBa_2Cu_3O_6.50 in the ortho II phase (Ortho II Y123, T_c= 59 K) were determined from reflectance data over a wide frequency range (70 - 42 000 cm^-1) for nine temperature values between 28 and 295 K. Above 200 K the spectra are dominated by a broad background of scattering that extends to 1 eV. Below 200 K a shoulder in the reflectance appears and signals the onset of scattering at 400 cm^-1. In this temperature range we also observe a peak in the optical conductivity at 177 cm^-1. Below 59 K, the superconducting transition temperature, the spectra change dramatically with the appearance of the superconducting condensate. Its spectral weight is consistent, to within experimental error, with the Ferrell-Glover-Tinkham (FGT) sum rule. We also compare our data with magnetic neutron scattering on samples from the same source that show a strong resonance at 31 meV. We find that the scattering rates can be modeled as the combined effect of the neutron resonance and a bosonic background in the presence of a density of states with a pseudogap. The model shows that the decreasing amplitude of the neutron resonance with temperature is compensated for by an increasing of the bosonic background yielding a net temperature independent scattering rate at high frequencies. This is in agreement with the experiments.Comment: 13 pages 16 figure

Properties of a continuous-random-network model for amorphous systems

We use a Monte Carlo bond-switching method to study systematically the thermodynamic properties of a "continuous random network" model, the canonical model for such amorphous systems as a-Si and a-SiO$_2$. Simulations show first-order "melting" into an amorphous state, and clear evidence for a glass transition in the supercooled liquid. The random-network model is also extended to study heterogeneous structures, such as the interface between amorphous and crystalline Si.Comment: Revtex file with 4 figure

Magneto-optical investigation of the field-induced spin-glass insulator to ferromagnetic metallic transition of the bilayer manganite (La0.4_{0.4}Pr0.6_{0.6})1.2_{1.2}Sr1.8_{1.8}Mn2_2O7_7

We measured the magneto-optical response of (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ in order to investigate the microscopic aspects of the magnetic field driven spin-glass insulator to ferromagnetic metal transition. Application of a magnetic field recovers the ferromagnetic state with an overall redshift of the electronic structure, growth of the bound carrier localization associated with ferromagnetic domains, development of a pseudogap, and softening of the Mn-O stretching and bending modes that indicate a structural change. We discuss field- and temperature-induced trends within the framework of the Tomioka-Tokura global electronic phase diagram picture and suggest that controlled disorder near a phase boundary can be used to tune the magnetodielectric response. Remnants of the spin-glass insulator to ferromagnetic metallic transition can also drive 300 K color changes in (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$.Comment: 9 pages, 8 figure