Just noticeable differences for low-beam headlamp intensities

A recent study by Huey, Dekker, and Lyons (1994) concluded that a difference between two signal lamp intensities of less than 25% cannot be detected reliably by most drivers. Consequently, Huey et al. recommended that an intensity difference of 25% be used as a criterion for inconsequential noncompliance with federal regulations for signal lamps. The present study was designed to evaluate just noticeable differences for glare intensities of oncoming low-beam headlamps. The results of this study indicate that, under controlled conditions, just noticeable differences in the low-beam headlighting context are between 11% and 19%. In real-world conditions, just noticeable differences would probably be somewhat larger. Therefore, the recommendation by Huey et al. of using 25% as a criterion for inconsequential noncompliance of signal lamps is also about right for low-beam headlamps, at least with respect to how headlamps themselves are perceived by other drivers (such as discomfort glare). The 25% value may also apply with respect to how headlamps affect the ability of drivers to see illuminated objects, but further research on that issue would be desirable.Michigan University, Ann Arbor, Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/49359/1/UMTRI-97-4.pd

The Evolution of Distorted Rotating Black Holes III: Initial Data

In this paper we study a new family of black hole initial data sets corresponding to distorted ``Kerr'' black holes with moderate rotation parameters, and distorted Schwarzschild black holes with even- and odd-parity radiation. These data sets build on the earlier rotating black holes of Bowen and York and the distorted Brill wave plus black hole data sets. We describe the construction of this large family of rotating black holes. We present a systematic study of important properties of these data sets, such as the size and shape of their apparent horizons, and the maximum amount of radiation that can leave the system during evolution. These data sets should be a very useful starting point for studying the evolution of highly dynamical black holes and can easily be extended to 3D.Comment: 16 page

Trapped Surfaces in Vacuum Spacetimes

An earlier construction by the authors of sequences of globally regular, asymptotically flat initial data for the Einstein vacuum equations containing trapped surfaces for large values of the parameter is extended, from the time symmetric case considered previously, to the case of maximal slices. The resulting theorem shows rigorously that there exists a large class of initial configurations for non-time symmetric pure gravitational waves satisfying the assumptions of the Penrose singularity theorem and so must have a singularity to the future.Comment: 14 page

Assessment of three Resistance-Nodulation-Cell Division drug efflux transporters of Burkholderia cenocepacia in intrinsic antibiotic resistance

<p>Abstract</p> <p>Background</p> <p><it>Burkholderia cenocepacia </it>are opportunistic Gram-negative bacteria that can cause chronic pulmonary infections in patients with cystic fibrosis. These bacteria demonstrate a high-level of intrinsic antibiotic resistance to most clinically useful antibiotics complicating treatment. We previously identified 14 genes encoding putative Resistance-Nodulation-Cell Division (RND) efflux pumps in the genome of <it>B. cenocepacia </it>J2315, but the contribution of these pumps to the intrinsic drug resistance of this bacterium remains unclear.</p> <p>Results</p> <p>To investigate the contribution of efflux pumps to intrinsic drug resistance of <it>B. cenocepacia </it>J2315, we deleted 3 operons encoding the putative RND transporters RND-1, RND-3, and RND-4 containing the genes <it>BCAS0591</it>-<it>BCAS0593</it>, <it>BCAL1674</it>-<it>BCAL1676</it>, and <it>BCAL2822</it>-<it>BCAL2820</it>. Each deletion included the genes encoding the RND transporter itself and those encoding predicted periplasmic proteins and outer membrane pores. In addition, the deletion of <it>rnd-3 </it>also included <it>BCAL1672</it>, encoding a putative TetR regulator. The <it>B. cenocepacia rnd-3 </it>and <it>rnd-4 </it>mutants demonstrated increased sensitivity to inhibitory compounds, suggesting an involvement of these proteins in drug resistance. Moreover, the <it>rnd-3 </it>and <it>rnd-4 </it>mutants demonstrated reduced accumulation of N-acyl homoserine lactones in the growth medium. In contrast, deletion of the <it>rnd-1 </it>operon had no detectable phenotypes under the conditions assayed.</p> <p>Conclusion</p> <p>Two of the three inactivated RND efflux pumps in <it>B. cenocepacia </it>J2315 contribute to the high level of intrinsic resistance of this strain to some antibiotics and other inhibitory compounds. Furthermore, these efflux systems also mediate accumulation in the growth medium of quorum sensing molecules that have been shown to contribute to infection. A systematic study of RND efflux systems in <it>B. cenocepacia </it>is required to provide a full picture of intrinsic antibiotic resistance in this opportunistic bacterium.</p

Cosmological expansion on a dilatonic brane-world

In this paper we study brane-world scenarios with a bulk scalar field, using a covariant formalism to obtain a 4D Einstein equation via projection onto the brane. We discuss, in detail, the effects of the bulk on the brane and how the scalar field contribute to the gravitational effects. We also discuss choice of conformal frame and show that the frame selected by the induced metric provides a natural choice. We demonstrate our formalism by applying it to cosmological scenarios of Randall-Sundrum and Horava-Witten type models. Finally we consider the cosmology of models where the scalar field couples non-minimally to the matter on the brane. This gives rise to a novel scenario where the universe expands from a finite scale factor with an initial period of accelerated expansion, thus avoiding the singularity and flatness problem of the standard big bang model.Comment: 20 pages - Version to appear in Classical and Quantum Gravity. New section added on conformal rescaling of the metric. Some other minor changes made and references adde

Assessment of the Mobilizable Vector Plasmids pSUP202 and pSUP404.2 as Genetic Tools for the Predatory Bacterium Bdellovibrio bacteriovorus

Bdellovibrio and like organisms (BALOs) form the group of predatory bacteria which require Gram-negative bacteria as prey. Genetic studies with Bdellovibrio bacteriovorus can be performed with vectors which are introduced into the predator via conjugation. The usefulness of the two vectors pSUP202 and pSUP404.2 as genetic tools were assessed. Both vectors were transferable into B. bacteriovorus by conjugative matings with an Escherichia coli K12 strain as donor. The transfer frequency was higher for vector pSUP404.2 (approx. 10−1–10−4) as for pSUP202 (approx. 10−5–10−6). Vector pSUP202 with a pMB1 origin is unstable in the predatory bacterium, whereas pSUP404.2 is stably maintained in the absence of selective antibiotics. pSUP404.2 harbors two plasmid replicons, the p15A ori and the RSF1010 replication region The copy number of pSUP404.2 was determined by quantitative PCR in B. bacteriovorus and averages seven copies per genome. pSUP404.2 harbors two resistance genes (chloramphenicol and kanamycin) which can be used for cloning either by selection for transconjugants or by insertional inactivation

Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO

Gamma-ray bursts are believed to originate in core-collapse of massive stars. This produces an active nucleus containing a rapidly rotating Kerr black hole surrounded by a uniformly magnetized torus represented by two counter-oriented current rings. We quantify black hole spin-interactions with the torus and charged particles along open magnetic flux-tubes subtended by the event horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii) aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al. 2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating LIGO/Virgo detectors enables searches for nearby events and their spectral closure density 6e-9 around 250Hz in the stochastic background radiation in gravitational waves. At current sensitivity, LIGO-Hanford may place an upper bound around 150MSolar in GRB030329. Detection of Egw thus provides a method for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49