Atomic hydrogen maser active oscillator cavity and bulb design optimization

The performance characteristics and reliability of the active oscillator atomic hydrogen maser depend upon oscillation parameters which characterize the interaction region of the maser, the resonant cavity and atom storage bulb assembly. With particular attention to use of the cavity frequency switching servo (1) to reduce cavity pulling, it is important to maintain high oscillation level, high atomic beam flux utilization efficiency, small spin exchange parameter and high cavity quality factor. It is also desirable to have a small and rigid cavity and bulb structure and to minimize the cavity temperature sensitivity. Curves for a novel hydrogen maser cavity configuration which is partially loaded with a quartz dielectric cylinder and show the relationships between cavity length, cavity diameter, bulb size, dielectric thickness, cavity quality factor, filling factor and cavity frequency temperature coefficient are presented. The results are discussed in terms of improvement in maser performance resulting from particular design choices

Pulsed electron beam induced recrystallization and damage in GaAs

Single-pulse electron-beam irradiations of 300-keV 10^(15)Kr+/cm^2 or 300-keV 3×10^(12)Se+/cm^2 implanted layers in unencapsulated GaAs are studied as a function of the electron beam fluence. The electron beam pulse had a mean electron energy of ~-20 keV and a time duration of ~-10^(–7) s. Analyses by means of MeV He + channeling and TEM show the existence of narrow fluence window (0.4–0.7 J/cm^2) within which amorphous layers can be sucessfully recrystallized, presumably in the liquid phase regime. Too high a fluence produces extensive deep damage and loss of As

Aerospace Section

The Aerospace Section of the Engineering Division encourages communication and cooperation among information professionals concerned with aerospace, aeronautical and related technologies. In addition, it fosters dialog with entities such as NASA, the AIAA and other important sources of technical data and bibliographical services

Exploring Dual-Targeting GroEL/ES & PtpB Inhibitors as a New Antibiotic Strategy for Tuberculosis

Indiana University-Purdue University Indianapolis (IUPUI)Current Mycobacterium tuberculosis (Mtb) treatments suffer from an increase in antibiotic resistance strains and the lack of efficacy against latent state tuberculosis, thus novel approaches targeting different mechanisms of action are needed. One strategy to target Mtb is to target protein homeostasis pathways by inhibiting molecular chaperones, in particular, GroEL/ES (HSP60/10) chaperonin systems. Mtb has two homologs of GroEL, of which GroEL1 is not essential, but is important for cytokine-dependent granuloma formation, and GroEL2 is essential for survival and the likely canonical housekeeping chaperonin. Another strategy to target Mtb is to target the protein tyrosine phosphatase B (PtpB) virulence factor that Mtb secretes into host cells to help evade immune responses. Thus, we envisioned that this analog series might also be capable of inhibiting Mtb PtpB along with GroEL. By developing compound 1 inhibitors that could act on all of GroEL1, GroEL2, and PtpB, we could have an antibiotic candidate that targets all stages of tuberculosis: actively replicating bacteria, bacteria evading host cell immune response, and granuloma formation in latent disease. In the Johnson lab, previous studies explored GroEL/ES inhibitors, with compound 1 being one of the most potent inhibitors, inhibiting both Trypanosoma brucei and Staphylococcus aureus proliferation. In the present study, we have screened previously developed compound 1 analogs, as well as a series of newly synthesized analogs that we term “half-molecules”. In this study, our results indicated two potential avenues to explore for future research. The first is a series of carboxyl-bearing compound 1 inhibitors, compounds 2m-o, 2m-m, and 2m-p, which act solely on Mtb PtpB phosphatase activity without inhibiting GroEL. The second is a series of compound 1 inhibitors (e.g. 20R and 20L) that are able to inhibit both the PtpB phosphatase and GroEL/ES chaperonin system. Thus, this exploratory study showed the possibility of pursuing such a polypharmacological antibiotic strategy against Mtb infections and with further optimization, such dual-targeting GroEL/ES and PtpB inhibitors could be effective against all stages of tuberculosis

Steady-state thermally annealed GaAs with room-temperature-implanted Si

Semi-insulating Cr-doped single-crystal GaAs samples were implanted at room temperature with 300-keV Si ions in the dose range of (0.17–2.0)×1015 cm–2 and were subsequently steady-state annealed at 900 and 950°C for 30 min in a H2 ambient with a Si3N4 coating. Differential Hall measurements showed that an upper threshold of about 2×1018/cm3 exists for the free-electron concentration. The as-implanted atomic-Si profile measured by SIMS follows the theoretical prediction, but is altered during annealing. The Cr distribution also changes, and a band of dislocation loops ~2–3 kÅ wide is revealed by cross-sectional TEM at a mean depth of Rp~3 kÅ. Incomplete electrical activation of the Si is shown to be the primary cause for the effect

A study of the application of singular perturbation theory

A hierarchical real time algorithm for optimal three dimensional control of aircraft is described. Systematic methods are developed for real time computation of nonlinear feedback controls by means of singular perturbation theory. The results are applied to a six state, three control variable, point mass model of an F-4 aircraft. Nonlinear feedback laws are presented for computing the optimal control of throttle, bank angle, and angle of attack. Real Time capability is assessed on a TI 9900 microcomputer. The breakdown of the singular perturbation approximation near the terminal point is examined Continuation methods are examined to obtain exact optimal trajectories starting from the singular perturbation solutions

Do oil and gas platforms off California reduce recruitment of bocaccio (Sebastes paucispinis) to natural habitat? An analysis based on trajectories derived from high-frequency radar

To investigate the possibility that oil and gas platforms may reduce recruitment of rockfishes (Sebastes spp.) to natural habitat, we simulated drift pathways termed “trajectories” in our model) from an existing oil platform to nearshore habitat using current measurements from high-frequency (HF) radars. The trajectories originated at Platform Irene, located west of Point Conception, California, during two recruiting seasons for bocaccio (Sebastes paucispinis): May through August, 1999 and 2002. Given that pelagic juvenile bocaccio dwell near the surface, the trajectories estimate transport to habitat. We assumed that appropriate shallow water juvenile habitat exists inshore of the 50-m isobath. Results from 1999 indicated that 10% of the trajectories represent transport to habitat, whereas 76% represent transport across the offshore boundary. For 2002, 24% represent transport to habitat, and 69% represent transport across the offshore boundary. Remaining trajectories (14% and 7% for 1999 and 2002, respectively) exited the coverage area either northward or southward along isobaths. Deployments of actual drifters (with 1-m drogues) from a previous multiyear study provided measurements originating near Platform Irene from May through August. All but a few of the drifters moved offshore, as was also shown with the HF radar-derived trajectories. These results indicate that most juvenile bocaccio settling on the platform would otherwise have been transported offshore and perished in the absence of a platform. However, these results do not account for the swimming behavior of juvenile bocaccio, about which little is known