Finding Principal Null Direction for Numerical Relativists

We present a new method for finding principal null directions (PNDs). Because our method assumes as input the intrinsic metric and extrinsic curvature of a spacelike hypersurface, it should be particularly useful to numerical relativists. We illustrate our method by finding the PNDs of the Kastor-Traschen spacetimes, which contain arbitrarily many $Q=M$ black holes in a de Sitter back-ground.Comment: 10 pages, LaTeX style, WU-AP/38/93. Figures are available (hard copies) upon requests [[email protected] (H.Shinkai)

A Concept for Robust, High Density Terminal Air Traffic Operations

This paper describes a concept for future high-density, terminal air traffic operations that has been developed by interpreting the Joint Planning and Development Office s vision for the Next Generation (NextGen) Air Transportation System and coupling it with emergent NASA and other technologies and procedures during the NextGen timeframe. The concept described in this paper includes five core capabilities: 1) Extended Terminal Area Routing, 2) Precision Scheduling Along Routes, 3) Merging and Spacing, 4) Tactical Separation, and 5) Off-Nominal Recovery. Gradual changes are introduced to the National Airspace System (NAS) by phased enhancements to the core capabilities in the form of increased levels of automation and decision support as well as targeted task delegation. NASA will be evaluating these conceptual technological enhancements in a series of human-in-the-loop simulations and will accelerate development of the most promising capabilities in cooperation with the FAA through the Efficient Flows Into Congested Airspace Research Transition Team

State transition of a non-Ohmic damping system in a corrugated plane

Anomalous transport of a particle subjected to non-Ohmic damping of the power $\delta$ in a tilted periodic potential is investigated via Monte Carlo simulation of generalized Langevin equation. It is found that the system exhibits two relative motion modes: the locking state and the running state. Under the surrounding of sub-Ohmic damping ($0<\delta<1$), the particle should transfer into a running state from a locking state only when local minima of the potential vanish; hence the particle occurs a synchronization oscillation in its mean displacement and mean square displacement (MSD). In particular, the two motion modes are allowed to coexist in the case of super-Ohmic damping ($1<\delta<2$) for moderate driving forces, namely, where exists double centers in the velocity distribution. This induces the particle having faster diffusion, i.e., its MSD reads $= 2D^{(\delta)}_{eff} t^{\delta_{eff}}$. Our result shows that the effective power index $\delta_{\textmd{eff}}$ can be enhanced and is a nonmonotonic function of the temperature and the driving force. The mixture effect of the two motion modes also leads to a breakdown of hysteresis loop of the mobility.Comment: 7 pages,7 figure

Risk factors for the detection of Salmonella in ileocolic lymph nodes in US slaughtered pigs.

Salmonella harborage at slaughter can be viewed as a nsk for human health through contammation of the pork food cham. Better understanding of herd level factors associated with this harborage would be useful to prioritize further study of epidemiology and control of Salmonella in pork production. Ileocolic lymph node samples collected at slaughter from 115 Midwest US sw1ne herds were assayed for Salmonella entenca. A subset of these herds was collected sequentially one or two additional times. Herd characteristics and management factors were assessed by a written survey. Risk factors were screened at the univariate level (p \u3c 0.3), then offered for Inclusion by stepw1se analysis including herd I sample as a random statistical effect. Pigs at increased risk of Salmonella harborage at slaughter included those placed in finisher barns at heaver weights (OR 1.2 per 10 kg Increased we1ght), those from larger herds (OR 2 0 comparing upper quintile to lower quintile of herd size), those from herds that allowed VISitors w1th recent (\u3c8 h) contact with other herds (OR 2.2), or those fed pelleted feeds (OR 2.1 ). Further invest1gat1on of these risk factors and potential biological mechanisms will requ1re further study

Gravitational Geons Revisited

A careful analysis of the gravitational geon solution found by Brill and Hartle is made. The gravitational wave expansion they used is shown to be consistent and to result in a gauge invariant wave equation. It also results in a gauge invariant effective stress-energy tensor for the gravitational waves provided that a generalized definition of a gauge transformation is used. To leading order this gauge transformation is the same as the usual one for gravitational waves. It is shown that the geon solution is a self-consistent solution to Einstein's equations and that, to leading order, the equations describing the geometry of the gravitational geon are identical to those derived by Wheeler for the electromagnetic geon. An appendix provides an existence proof for geon solutions to these equations.Comment: 18 pages, ReVTeX. To appear in Physical Review D. Significant changes include more details in the derivations of certain key equations and the addition of an appendix containing a proof of the existence of a geon solution to the equations derived by Wheeler. Also a reference has been added and various minor changes have been mad

Identification of a porcine-specific adhesin of Salmonella typhimurium and a possible mechanism mediating persistent infections of swine

Salmonella enterica serotype Typhimurium (S. typhimuriwn) is one of the leading causes of food poisoning in man (4) and consumption of pork products is a major risk factor for disease (3, 5). A major outbreak of salmonellosis in Denmark caused by S. enterica and associated with the consumption of pork has stimulated renewed interest in Salmonella and food safety by pork producers, consumers, and the government (II). A combination of many factors has prompted the United States Department of Agriculture to place S. enterica at the top of its priority list of food borne pathogens (7). In Denmark. S. typhimurium is the most common serotype isolated from pigs (78.2 %) and is the second most common cause of food borne salmonellosis in humans (27.8 %) (I, II). In the United States S. typhimurium is of similar significance

Pipeline corridors through wetlands

This paper presents preliminary findings from six vegetational surveys of gas pipeline rights-of-way (ROW) through wetlands and quantifies the impacts of a 20-year-old pipeline ROW through a boreal forest wetland. Six sites of various ages were surveyed in ecosystems ranging from coastal marsh to forested wetland. At all sites except one, both the number and the percentage of wetland species on the Row approximated or exceeded those in the adjacent natural area. The boreal forest study showed that (1) adjacent natural wetland areas were not altered in type; (2) water sheet flow restriction had been reversed by nature; (3) no nonnative plant species invaded the natural area; (4) three-quarters of the ROW area was a wetland, and (5) the ROW increased diversity

Cauchy-characteristic Evolution of Einstein-Klein-Gordon Systems

A Cauchy-characteristic initial value problem for the Einstein-Klein-Gordon system with spherical symmetry is presented. Initial data are specified on the union of a space-like and null hypersurface. The development of the data is obtained with the combination of a constrained Cauchy evolution in the interior domain and a characteristic evolution in the exterior, asymptotically flat region. The matching interface between the space-like and characteristic foliations is constructed by imposing continuity conditions on metric, extrinsic curvature and scalar field variables, ensuring smoothness across the matching surface. The accuracy of the method is established for all ranges of $M/R$, most notably, with a detailed comparison of invariant observables against reference solutions obtained with a calibrated, global, null algorithm.Comment: Submitted to Phys. Rev. D, 16 pages, revtex, 7 figures available at http://nr.astro.psu.edu:8080/preprints.htm