ALBERT

Notizen: A simple superconducting loop with a Josephson junction subject to a time-sinusoidal magnetic flux embedded in a noise background is considered. Cooperative effects, arising from the interplay between the noise and modulation are described; they manifest themselves in the response, measured as an output signal-to-noise ratio. In particular, it is shown that the response displays the stochastic resonance effect, wherein the output signal-to-noise ratio passes through a maximum at a critical value of the noise strength. A simple theory, based on the characterization of the superconducting quantum interference device as a bistable switching element, is seen to yield good qualitative agreement with the experimental results. © 1995 American Institute of Physics.

Notizen: We analyze the degradation process of proton-implanted, top-emitting vertical cavity surface emitting lasers using cross-sectional cathodoluminescence. The spatially resolved luminescence characteristics of the active regions, and p- and n-distributed Bragg reflector (DBR) mirrors before and after degradation of the devices are presented. Degradation has been observed not only in the active regions, but also remarkably in the p-DBR mirror stacks. We show that a significant minority carrier population is present in the p mirror under normal operating conditions to drive the degradation observed in the p mirror. © 1995 American Institute of Physics.

Notizen: A novel AlGaAs/AlAs–TiO2/SiO2 hybrid distributed Bragg reflector is implemented in a planar vertical cavity (top)-surface emitting laser (VCSEL) to control emission (near 850 nm) to a single TEM00-like mode. This structure exhibits (approximately-greater-than)30 dB side-mode suppression ratio and constant divergence (or modal profile) throughout its operating range (i.e., the detrimental effects of thermal lensing inherent in implanted VCSELs are eliminated); moreover, a record low threshold voltage (approximately-equal-to)1.6 V, (0.16 V above photon energy) is obtained, without sacrificing the producibility of the standard all-epitaxial structure. © 1995 American Institute of Physics.

Notizen: Riparian areas of large streams provide important habitat to many species and control many instream processes — but is the same true for the margins of small streams? This review considers riparian areas alongside small streams in forested, mountainous areas of the Pacific Northwest and asks if there are fundamental ecological differences from larger streams and from other regions and if there are consequences for management from any differences. In the moist forests along many small streams of the Pacific Northwest, the contrast between the streamside and upslope forest is not as strong as that found in drier regions. Small streams typically lack floodplains, and the riparian area is often constrained by the hillslope. Nevertheless, riparian-associated organisms, some unique to headwater areas, are found along small streams. Disturbance of hillslopes and stream channels and microclimatic effects of streams on the riparian area provide great heterogeneity in processes and diversity of habitats. The tight coupling of the terrestrial riparian area with the aquatic system results from the closed canopy and high edge-to-area ratio for small streams. Riparian areas of the temperate, conifer dominated forests of the Pacific Northwest provide a unique environment. Forest management guidelines for small streams vary widely, and there has been little evaluation of the local or downstream consequences of forest practices along small streams.

Notizen: The spore forming Gram-positive bacterium Bacillus anthracis, the causative agent of anthrax, has achieved notoriety due to its use as a bioterror agent. In the environment, B. anthracis exists as a dormant endospore. Germination of endospores during their internalization within the myeloid phagocyte, and the ability of those endospores to survive exposure to antibacterial killing mechanisms such as superoxide 〈inlineGraphic alt="inline image" href="urn:x-wiley:03781097:FML33:FML_33_mu1" location="equation/FML_33_mu1.gif"/〉, is a key initial event in the infective process. We report herein that endospores exposed to fluxes of 〈inlineGraphic alt="inline image" href="urn:x-wiley:03781097:FML33:FML_33_mu2" location="equation/FML_33_mu2.gif"/〉 typically found in stimulated phagocytes had no effect on viability. Further endospores of the Sterne strain of B. anthracis were found to scavenge 〈inlineGraphic alt="inline image" href="urn:x-wiley:03781097:FML33:FML_33_mu3" location="equation/FML_33_mu3.gif"/〉, which may enhance the ability of the bacterium to survive within the hostile environment of the phagolysosome. Most intriguing was the observation that endospore germination was stimulated by a flux of 〈inlineGraphic alt="inline image" href="urn:x-wiley:03781097:FML33:FML_33_mu4" location="equation/FML_33_mu4.gif"/〉 as low as 1 μM/min. Data presented herein suggest that B. anthracis may co-opt 〈inlineGraphic alt="inline image" href="urn:x-wiley:03781097:FML33:FML_33_mu5" location="equation/FML_33_mu5.gif"/〉 which is produced by stimulated myeloid phagocytes and is an essential element of host immunity, as a necessary step in productive infection of the host.

Notizen: Intermontane basins in the Trans-Pecos region of westernmost Texas and northern Chihuahua, Mexico, are target areas for disposal of interstate municipal sludge and have been identified as possible disposal sites for low-level radioactive waste. Understanding ground water movement within and between these basins is needed to assess potential contaminant fate and movement. Four associated basin aquifers are evaluated and classified; the Red Light Draw Aquifer, the Northwest Eagle Flat Aquifer, the Southeast Eagle Flat Aquifer, and the El Cuervo Aquifer. Encompassed on all but one side by mountains and local divides, the Red Light Draw Aquifer has the Rio Grande as an outlet for both surface drainage and ground water discharge. The river juxtaposed against its southern edge, the basin is classified as a topographically open, through-flowing basin. The Northwest Eagle Flat Aquifer is classified as a topographically closed and drained basin because surface drainage is to the interior of the basin and ground water discharge occurs by interbasin ground water flow. Mountains and ground water divides encompass this basin aquifer on all sides; yet, depth to ground water in the interior of the basin is commonly 〉500 feet. Negligible ground water discharge within the basin indicates that ground water discharges from the basin by vertical flow and underflow to a surrounding basin or basins. The most likely mode of discharge is by vertical, cross-formational flow to underlying Permian rocks that are more porous and permeable and subsequent flow along regional flowpaths beneath local ground water divides. The Southeast Eagle Flat Aquifer is classified as a topographically open and drained basin because surface drainage and ground water discharge are to the adjacent Wildhorse Flat area. Opposite the Eagle Flat and Red Light Draw aquifers is the El Cuervo Aquifer of northern Chihuahua, Mexico. The El Cuervo Aquifer has interior drainage to Laguna El Cuervo, which is a phreatic playa that also serves as a focal point of ground water discharge. Our evidence suggests that El Cuervo Aquifer may lose a smaller portion of its discharge by interbasin ground water flow to Indian Hot Springs, near the Rio Grande. Thus, El Cuervo Aquifer is a topographically closed basin that is either partially drained if a component of its ground water discharge reaches Indian Hot Springs or undrained if all its natural ground water discharge is to Laguna El Cuervo.