Effects of Fine Water Mist on a Confined Blast

A computational, multi-phase, model has been developed to study the interactions between water droplets and radial expansion of a gas cloud in a spherical chamber. Initial conditions for the gas cloud are specified based on chemical equilibrium calculations for the detonation of a high explosive (RDX). Mono-dispersed water droplets are injected at uniform concentration into the chamber prior to the expansion. A Lagrangian model is used to track the breakup of the parent drops near the shock front to form child drops, which are extremely small. The Navier–Stokes solutions show that the child droplets accumulate near the shock front and evaporate at 100 times higher rate than the parent droplets. Latent heat absorption is the dominant mechanism followed by the sensible heat absorption by the water vapor (and droplets), and momentum absorption from the high velocity gases by the child droplets. The simulations also show that the water vapor formed by the evaporation increases the gas density at the shock front. The increased density and reduced gas temperature (cooling) have opposite effects on the pressure at the shock front. This leads to only a modest suppression in the pressure. At realistic droplet concentrations (0.08 kg droplets/m³ of air), the water mist is shown to evaporate completely in a short time (2.42 ms) prior to shock reflection at the chamber wall mainly due to the breakup at the shock front. High concentrations of mist may be desirable, but are difficult to achieve in practice at the total flooding conditions.     

A mechanistic perspective of atmospheric oxygen sensitivity on composite energetic material reactions

Solid energetic composites have been used and studied in standard air environments, yet the contribution of atmospheric oxygen to reactive material combustion has not been investigated. This study experimentally examines the effect of atmospheric oxygen concentration (4% or 93% oxygen) on energy propagation of nanometric aluminum with copper oxide (Al + CuO), iron oxide (Al + Fe₂O₃), calcium iodate (Al + Ca(IO₃)₂), and iodine pentoxide (I₂O₅). In all cases energy propagation was examined in terms of flame speed and higher in the high oxygen environments. However, the convectively dominant reactions showed a smaller percent increase in flame speed mainly attributed to the reaction mechanism.     

A Survey of BGP Security Issues and Solutions

As the Internet's de facto interdomain routing protocol, the Border Gateway Protocol (BGP) is the glue that holds the disparate parts of the Internet together. A major limitation of BGP is its failure to adequately address security. Recent high-profile outages and security analyses clearly indicate that the Internet routing infrastructure is highly vulnerable. Moreover, the design of BGP and the ubiquity of its deployment have frustrated past efforts at securing interdomain routing. This paper considers the current vulnerabilities of the interdomain routing system and surveys both research and standardization efforts relating to BGP security. We explore the limitations and advantages of proposed security extensions to BGP, and explain why no solution has yet struck an adequate balance between comprehensive security and deployment cost.     

Longitudinal prescribing patterns of psychotropic drugs in nursing home residents.

Changes in the use of psychotropic drugs in a large nursing home were examined both in terms of usage for the total facility and in longitudinal changes within individuals. Data for the nursing home showed a gradual increase in use of antidepressants; a decrease in use of antianxiety medications and of sedative-hypnotics. Changes in the number of residents prescribed antipsychotics were not marked. Data within residents showed a great variability in number of psychotropic drugs used, in number of changes in dosage, and in specific patterns of medication change. The first drug change after admission (excluding day of admission) was more likely to involve initiation rather than discontinuation of psychotropic drugs. The medications studied were used over 4–7 months on the average, covering 20–30% of the resident's nursing home stay. The findings suggest that there is continued monitoring of psychotropic medications in the nursing home. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Highly doped galnAs using diethylberyllium by MOCVD for InP-based heterostructure bipolar transistor applications

Diethylberyllium has been used to produce high hole concentrations in latticematched Galnas grown by metalorganic chemical vapor deposition (MOCVD). Doping concentrations from p = 1 × 10¹⁹ up to 7.7 × 10¹⁹ cm⁻³ have been achieved at 500°C. To our knowledge, this is the highest doping level achieved by MOCVD in this material system. Secondary ion mass spectroscopy analysis showed a significant inclusion of oxygen in the as-grown material. Using beryllium-doped Galnas as the base layer, we have demonstrated InP-based heterostructure bipolar transistors. This shows diethylberyllium to be a promising p-type dopant for MOCVD applications.     

Chemosensory conditioning of Hermissenda crassicornis..

Bite–strike responses of Hermissenda crassicornis, elicited by chemosensory stimulation of the lips, were found to be modified when food extracts were paired with rotation-produced stimulation of the statocysts. Animals that received repeated pairings of an extract of 1 food (conditioned stimulus, CS) with rotation exhibited suppressed bite–strike responses to that food for up to 48 hr after training. This suppression was usually specific to the trained food and was pairing-specific as well. Discriminative conditioning was also demonstrated. Animals trained with 1 CS paired with rotation and a second CS that was unpaired (CS–) showed suppressed bite–strike responses to the first CS. The results demonstrate that Hermissenda can learn to avoid foods that reliably signal an aversive event and may allow an analysis of higher order conditioning phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mosquitoes or malaria? Rockefeller campaigns in the American South and Sardinia

Most members of the International Health Division of the Rockefeller Foundation remained convinced that diseases were the fundamental cause of human poverty and underdevelopment and that destruction of the larval stages of vector mosquitoes was the cheapest and most effective way to eliminate one of the most important of such diseases, malaria. But the validity of both their assumptions remains in question despite campaigns in the American South and elsewhere during the 1920s and 1930s and an unsuccessful attempt at "species eradication" in Sardinia immediately after World War II.     

Job scheduling methods for reducing waiting time variance

Minimizing Waiting Time Variance (WTV) is a job scheduling problem where we schedule a batch of n$n$ jobs, for servicing on a single resource, in such a way that the variance of their waiting times is minimized. Minimizing WTV is a well known scheduling problem, important in providing Quality of Service (QoS) in many industries. Minimizing the variance of job waiting times on computer networks can lead to stable and predictable network performance. Since the WTV minimization problem is NP-hard, we develop two heuristic job scheduling methods, called Balanced Spiral and Verified Spiral, which incorporate certain proven properties of optimal job sequences for this problem. We test and compare our methods with four other job scheduling methods on both small and large size problem instances. Performance results show that Verified Spiral gives the best performance for the scheduling methods and problems tested in this study. Balanced Spiral produces comparable results, but at less computational cost. During our investigation we discovered a consistent pattern in the plot of WTV over mean of all possible sequences for a set of jobs, which can be used to evaluate the sacrifice of mean waiting time while pursuing WTV minimization.     

Directable Weathering of Concave Rock Using Curvature Estimation

We address the problem of directable weathering of exposed concave rock for use in computer-generated animation or games. Previous weathering models that admit concave surfaces are computationally inefficient and difficult to control. In nature, the spheroidal and cavernous weathering rates depend on the surface curvature. Spheroidal weathering is fastest in areas with large positive mean curvature and cavernous weathering is fastest in areas with large negative mean curvature. We simulate both processes using an approximation of mean curvature on a voxel grid. Both weathering rates are also influenced by rock durability. The user controls rock durability by editing a durability graph before and during weathering simulation. Simulations of rockfall and colluvium deposition further improve realism. The profile of the final weathered rock matches the shape of the durability graph up to the effects of weathering and colluvium deposition. We demonstrate the top-down directability and visual plausibility of the resulting model through a series of screenshots and rendered images. The results include the weathering of a cube into a sphere and of a sheltered inside corner into a cavern as predicted by the underlying geomorphological models.