Implications of the r-mode instability of rotating relativistic stars

Several recent surprises appear dramatically to have improved the likelihood that the spin of rapidly rotating, newly formed neutron stars (and, possibly, of old stars spun up by accretion) is limited by a nonaxisymmetric instability driven by gravitational waves. Except for the earliest part of the spin-down, the axial l=m=2 mode (an r-mode) dominates the instability, and the emitted waves may be observable by detectors with the sensitivity of LIGO II. A review of these hopeful results is followed by a discussion of constraints on the instability set by dissipative mechanisms, including viscosity, nonlinear saturation, and energy loss to a magnetic field driven by differential rotation.Comment: 20 pages LaTeX2e (stylefile included), 6 eps figures. Review to appear in the proceedings of the 9th Marcel Grossman Meeting, World Scientific, ed. V. Gurzadyan, R. Jantzen, R. Ruffin

Gravitational-wave driven instability of rotating relativistic stars

A brief review of the stability of rotating relativistic stars is followed by a more detailed discussion of recent work on an instability of r-modes, modes of rotating stars that have axial parity in the slow-rotation limit. These modes may dominate the spin-down of neutron stars that are rapidly rotating at birth, and the gravitational waves they emit may be detectable.Comment: 14 pages PTPTeX v.1.0. Contribution to proceedings of the 1999 Yukawa International Semina

Effect of Phenolic Matrix Microcracking on the Structural Response of a 3-D Woven Thermal Protection System

The effect of microcracking in the phenolic matrix of a three-dimensional woven thermal protection system (TPS) and the resulting material stiffness reduction was studied via a comparison of finite element analysis results from a linear analysis and an iterative linear analysis. A TPS is necessary to protect space vehicles from the aerodynamic heating of planetary entry. The Heatshield for Extreme Entry Environment Technology (HEEET) project has developed a TPS for use in high heat-flux and pressure missions. The material is a dual-layer continuous dry weave, which is then infiltrated with a low-density phenolic resin matrix to form a rigid ablator. The phenolic resin matrix does not have structural load transfer requirements, and testing has shown that the phenolic resin can fully satisfy thermal requirements when the matrix contains microcracks. Due to high stresses in the through-the-thickness direction of the material, phenolic microcracks may form in the matrix material, which would result in a reduction of stiffness. An exploratory study was conducted to determine if reduction in material stiffness would change the load paths and/or decrease the structural margins. A comparison was performed between a linear finite element analysis that did not take into account phenolic microcracking and an iterative linear finite element analysis that accounted for propagation of phenolic microcracking. Four subcases using varying assumptions were analyzed and the results indicate that the assumed strength at which the phenolic microcracking propagates was the critical parameter for determining the extent of microcracking in the phenolic matrix. Phenolic microcracking does not have an adverse effect on the structural response of the test article and is not a critical failure

Absolute Timing of the Crab Pulsar with RXTE

We have monitored the phase of the main X-ray pulse of the Crab pulsar with the Rossi X-ray Timing Explorer (RXTE) for almost eight years, since the start of the mission in January 1996. The absolute time of RXTE's clock is sufficiently accurate to allow this phase to be compared directly with the radio profile. Our monitoring observations of the pulsar took place bi-weekly (during the periods when it was at least 30 degrees from the Sun) and we correlated the data with radio timing ephemerides derived from observations made at Jodrell Bank. We have determined the phase of the X-ray main pulse for each observation with a typical error in the individual data points of 50 us. The total ensemble is consistent with a phase that is constant over the monitoring period, with the X-ray pulse leading the radio pulse by 0.0102+/-0.0012 period in phase, or 344+/-40 us in time. The error estimate is dominated by a systematic error of 40 us in the radio data, arising from uncertainties in the variable amount of pulse delay due to interstellar scattering and instrumental calibration. The statistical error is 0.00015 period, or 5 us. The separation of the main pulse and interpulse appears to be unchanging at time scales of a year or less, with an average value of 0.4001+/-0.0002 period. There is no apparent variation in these values with energy over the 2-30 keV range. The lag between the radio and X-ray pulses may be constant in phase (rotational) or constant in time (linear pathlength). We are not (yet) able to distinguish between these two interpretations.Comment: 11 pages, 2 figure

Finite-element Analysis Of Pressure Vessels

The finite-element technique has been applied in the analysis of a variety of pressure vessel problems. The example problems described in this paper suggest that the finite element method is perhaps the most suitable means currently available for obtaining quick and accurate solutions for real-life pressure vessel problems. Finite-element programs can be used by the practicing engineer. Companion programs are available that can be used to check the input data and graphically display both the input and output data. © 1972 by ASME

Naltrexone Reduces Ethanol- and/or Water-Reinforced Responding in Rhesus Monkeys: Effect Depends Upon Ethanol Concentration

The opioid antagonist naltrexone reduces responding for ethanol. If naltrexone produces this effect by blocking ethanol-induced opioid activity, then naltrexone should reduce responding for ethanol regardless of level of the ethanol responding relative to an alternatively available reinforcer. In addition, if naltrexone competitively blocks ethanol-induced opioid activity, then the naltrexone effect may be surmountable by increasing ethanol concentration and, thus, ethanol intake (g/kg). This study was conducted to determine whether naltrexone will selectively reduce ethanol-reinforced responding when the ethanol concentration is varied such that ethanol fluid deliveries are less than, greater than, or equal to the fluid deliveries of concurrently available water. Methods : Four adult male rhesus monkeys were allowed to respond for ethanol or water concurrently for 2 hr per day. Ethanol concentration was either 2%, 8%, or 32%. On various days, either saline or naltrexone (0.1 mg/kg) was given intramuscularly 30 min before the drinking session. Results : When ethanol fluid deliveries were greater than those of water (at 2% ethanol), naltrexone reduced responding for ethanol. When the ethanol and water fluid deliveries were approximately equal (at 8% ethanol), naltrexone reduced both ethanol and water fluid deliveries. When water fluid deliveries were greater than those of ethanol (at 32% ethanol), naltrexone reduced responding for water. Conclusions : Thus, naltrexone reduced responding for the preferred fluid, either ethanol or water, depending on ethanol concentration. The effect was not surmountable by increasing ethanol concentration and, therefore, ethanol intake (g/kg). Naltrexone may reduce ethanol-reinforced responding by a mechanism other than that of blocking ethanol-induced opioid activity. Naltrexone may be inducing an aversive interoceptive state.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66374/1/j.1530-0277.1999.tb04668.x.pd

Managing Risk in Farming: Concepts, Research, and Analysis

The risks confronted by grain and cotton farmers are of particular interest, given the changing role of the Government after passage of the 1996 Farm Act. With the shift toward less government intervention in the post-1996 Farm Act environment, a more sophisticated understanding of risk and risk management is important to help producers make better decisions in risky situations and to assist policymakers in assessing the effectiveness of different types of risk protection tools. In response, this report provides a rigorous, yet accessible, description of risk and risk management tools and strategies at the farm level. It also provides never-before-published data on farmers' assessments of the risks they face, their use of alternative risk management strategies, and the changes they would make if faced with financial difficulty. It also compares price risk across crops and time periods, and provides detailed information on yield variability.crop insurance, diversification, futures contracts, leasing, leveraging, liquidity, livestock insurance, marketing contracts, options contracts, production contracts, revenue insurance, risk, vertical integration, Farm Management, Risk and Uncertainty,

Noncontingent and Response-Contingent Intravenous Ethanol Attenuates the Effect of Naltrexone on Hypothalamic-Pituitary-Adrenal Activity in Rhesus Monkeys

Background : The mechanism by which the opioid antagonist naltrexone suppresses overconsumption of ethanol is unclear. Oral ethanol consumption in humans increases hypothalamic-pituitary-adrenal (HPA) activity, and recent studies suggest that naltrexone may reduce ethanol consumption by modifying the HPA-stimulating effects of ethanol. The purpose of this study was to measure in rhesus monkeys the effects of ethanol and naltrexone, alone and in combination, on plasma levels of adrenocorticotropin hormone (ACTH). Methods : Nine adult male and female rhesus monkeys with chronic, indwelling intravenous catheters were maintained on tethers that allowed ethanol delivery and blood sampling. In one study, the monkeys received intramuscular injections of saline or 0.32 mg/kg naltrexone followed by noncontingent intravenous bolus infusions of saline or 0.3 to 1.8 g/kg ethanol. In a second study, other monkeys were given intramuscular injections of saline or 0.01 to 0.3 mg/kg naltrexone and subsequently responded on levers to receive intravenous saline or ethanol 0.03 g/kg per injection. Results : Ethanol, delivered either response contingently or noncontingently, did not produce systematic changes in ACTH plasma levels. Naltrexone alone produced increases in plasma ACTH that were attenuated by the subsequent administration of noncontingent or response-contingent ethanol. Naltrexone also produced dose-dependent reductions in intravenous ethanol self-administration. Linear regression analysis indicated that ethanol intake was negatively correlated with the plasma levels of ACTH over time. Conclusions : The route of administration may modulate ethanol's effects on HPA activity. Ethanol may attenuate naltrexone's effect on the HPA axis by impairing HPA axis sensitivity to other stimuli. The negative correlation between ethanol intake and ACTH levels supports the notion that naltrexone's effect of increasing HPA axis activity may be related to its ability to suppress ethanol consumption.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66078/1/01.ALC.0000121655.48922.C4.pd