An Experimental Investigation of Silicone-to-Metal Bond Strength in Composite Space Docking System Seals

The National Aeronautics and Space Administration (NASA) is currently developing a new universal docking mechanism for future space exploration missions called the Low Impact Docking System (LIDS). A candidate LIDS main interface seal design is a composite assembly of silicone elastomer seals vacuum molded into grooves in an electroless nickel plated aluminum retainer. The strength of the silicone-tometal bond is a critical consideration for the new system, especially due to the presence of small areas of disbond created during the molding process. In the work presented herein, seal-to-retainer bonds of subscale seal specimens with different sizes of intentional disbond were destructively tensile tested. Nominal specimens without intentional disbonds were also tested. Tension was applied either uniformly on the entire seal circumference or locally in one short circumferential length. Bond failure due to uniform tension produced a wide scatter of observable failure modes and measured load-displacement behaviors. Although the preferable failure mode for the seal-to-retainer bond is cohesive failure of the elastomer material, the dominant observed failure mode under the uniform loading condition was found to be the less desirable adhesive failure of the bond in question. The uniform tension case results did not show a correlation between disbond size and bond strength. Localized tension was found to produce failure either as immediate tearing of the elastomer material outside the bond region or as complete peel-out of the seal in one piece. The obtained results represent a valuable benchmark for comparison in the future between adhesion loads under various separation conditions and composite seal bond strength

Interplay of paramagnetic, orbital and impurity effects on the phase transition of a normal metal to superconducting state

We derive the generalized Ginzburg-Landau free energy functional for conventional and unconventional singlet superconductors in the presence of paramagnetic, orbital and impurity effects. Within the mean field theory, we determine the criterion for appearence of the non uniform (Fulde-Ferrell-Larkin-Ovchinnikov) superconducting state, with vortex lattice structure and additional modulation along the magnetic field. We also discuss the possible change of the order of transition from normal to superconducting state. We find that the superconducting phase diagram is very sensitive to geometrical effects such as the nature of the order parameter and the shape of the Fermi surface. In particular, we obtain the qualitative phase diagrams for three-dimensional isotropic s-wave superconductors and in quasi two-dimensional d-wave superconductors under magnetic field perpendicular to the conducting layers. In addition, we determine the criterion for instability toward non uniform superconducting state in s-wave superconductors in the dirty limit.Comment: 15 pages, 4 figure

Energy Relaxation at a Hot-Electron Vortex Instability

At high dissipation levels, vortex motion in a superconducting film has been observed to become unstable at a certain critical vortex velocity v*. At substrate temperatures substantially below Tc, the observed behavior can be accounted for by a model in which the electrons reach an elevated temperature relative to the phonons and the substrate. Here we examine the underlying assumptions concerning energy flow and relaxation times in this model. A calculation of the rate of energy transfer from the electron gas to the lattice finds that at the instability, the electronic temperature reaches a very high value close to the critical temperature. Our calculated energy relaxation times are consistent with those deduced from the experiments. We also estimate the phonon mean free path and assess its effect on the flow of energy in the film.Comment: 8 pages, 7 figure

Infrared Spectroscopy of a Massive Obscured Star Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC

We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039) with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the vicinity of the southern nucleus (NGC 4039) in 0.39" seeing in K-band using NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the highest surface brightness peak in the mid-IR (12-18 micron) ISO image presented by Mirabel et al. (1998). We obtained high signal-to-noise 2.03 - 2.45 micron spectra of the nucleus and the obscured star cluster at R ~ 1900. The cluster is very young (4 Myr old), massive (16e6 M_sun), and compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius), assuming a Salpeter IMF (0.1 - 100 M_sun). Its hot stars have a radiation field characterized by T_eff ~ 39,000 K, and they ionize a compact H II region with n_e ~ 1e4 cm^(-3). The stars are deeply embedded in gas and dust (A_V ~ 9-10 mag), and their strong FUV field powers a clumpy photodissociation region with densities n_H >= 1e5 cm^(-3) on scales of up to 200 pc, radiating L[H_2 1-0 S(1)] = 9600 L_sun.Comment: 4 pages, 5 embedded figures. To appear in proceedings of 33d ESLAB Symposium: Star Formation from the Small to the Large Scale, held in Noordwijk, The Netherlands, Nov. 1999. Also available at http://astro.berkeley.edu/~agilber

The Effect of Simulated Lunar Dust on the Absorptivity, Emissivity, and Operating Temperature on AZ-93 and Ag/FEP Thermal Control Surfaces

JSC-1AF lunar simulant has been applied to AZ-93 and AgFEP thermal control surfaces on aluminum or composite substrates in a simulated lunar environment. The temperature of these surfaces was monitored as they were heated with a solar simulator and cooled in a 30 K coldbox. Thermal modeling was used to determine the absorptivity ( ) and emissivity ( ) of the thermal control surfaces in both their clean and dusted states. Then, a known amount of power was applied to the samples while in the coldbox and the steady state temperatures measured. It was found that even a submonolayer of simulated lunar dust can significantly degrade the performance of both white paint and second-surface mirror type thermal control surfaces under these conditions. Contrary to earlier studies, dust was found to affect as well as . Dust lowered the emissivity by as much as 16 percent in the case of AZ-93, and raised it by as much as 11 percent in the case of AgFEP. The degradation of thermal control surface by dust as measured by / rose linearly regardless of the thermal control coating or substrate, and extrapolated to degradation by a factor 3 at full coverage by dust. Submonolayer coatings of dust were found to not significantly change the steady state temperature at which a shadowed thermal control surface will radiate

The External Shear Acting on Gravitational Lens B 1422+231

In a number of multiply imaged quasar systems, a significant contribution to the lensing potential is provided by groups and clusters of galaxies associated with the primary lens. As part of an ongoing effort to gather observational data on these systems, we present spectroscopy and near-infrared and optical photometry of galaxies in the field of the quadruple lens system B 1422+231. The spectra show that the primary lens and five nearby galaxies belong to a compact group at z = 0.338. The median projected radius of this group is 35 h^{-1} kpc and its velocity dispersion is 550 km/s. A straightforward application of the virial theorem yields a group mass of 1.4 x 10^{13} h^{-1} M(sun), which provides sufficient external shear to produce the observed image configuration. This data rules out a class of models and improves the system's prospects for a measurement of the Hubble constant.Comment: 16 pages including 3 tables, 2 eps figures and 2 jpeg images. Submitted to the Astronomical Journa

The Rest-Frame Optical Spectrum of MS 1512-cB58

Moderate resolution, near-IR spectroscopy of MS1512-cB58 is presented, obtained during commissioning of the the Near IR Spectrometer (NIRSPEC) on the Keck II telescope. The strong lensing of this z=2.72 galaxy by the foreground cluster MS1512+36 makes it the best candidate for detailed study of the rest-frame optical properties of Lyman Break Galaxies. A redshift of z=2.7290+/-0.0007 is inferred from the emission lines, in contrast to the z=2.7233 calculated from UV observations of interstellar absorption lines. Using the Balmer line ratios, we find an extinction of E(B-V)=0.27. Using the line strengths, we infer an SFR=620+/-18 Msun/yr (H_0=75, q_0=0.1, Lambda =0), a factor of 2 higher than that measured from narrow-band imaging observations of the galaxy, but a factor of almost 4 lower than the SFR inferred from the UV continuum luminosity. The width of the Balmer lines yields a mass of M_vir=1.2x10^10 Msun. We find that the oxygen abundance is 1/3 solar, in good agreement with other estimates of the metallicity. However, we infer a high nitrogen abundance, which may argue for the presence of an older stellar population.Comment: 14 pages, including 3 figures. Accepted for publication in ApJ Letter

The First Spatially Resolved Mid-IR Spectra of NGC 1068 Obtained at Diffraction-limited Resolution with LWS at Keck I Telescope

We present spatially resolved mid-IR spectra of NGC 1068 with a diffraction-limited resolution of 0.25\arcsec using the Long Wavelength Spectrometer (LWS) at the Keck I telescope. The mid-infrared image of NGC 1068 is extended along the N-S direction. Previous imaging studies have shown the extended regions are located inside the ionization cones indicating that the mid-infrared emission arises perhaps from the inner regions of the narrow-line clouds instead of the proposed dusty torus itself. The spatially resolved mid-IR spectra were obtained at two different slit position angles, +8.0 and -13.0 degrees across the elongated regions in the mid-IR. From these spectra, we found only weak silicate absorption toward the northern extended regions but strong in the nucleus and the southern extended regions. This is consistent with a model of a slightly inclined cold obscuring torus which covers much of the southern regions but is behind the northern extension. While a detailed analysis of the spectra requires a radiative transfer model, the lack of silicate emission from the northern extended regions prompts us to consider a dual dust population model as one of the possible explanations in which a different dust population exists in the ionization cones compared to that in the dusty torus. Dust inside the ionization cones may lack small silicate grains giving rise to only a featureless continuum in the northern extended regions while dust in the dusty torus has plenty of small silicate grains to produce the strong silicate absorption lines towards the nucleus and the southern extended regions.Comment: Accepted to Ap

Tests of the Accelerating Universe with Near-Infrared Observations of a High-Redshift Type Ia Supernova

We have measured the rest-frame B,V, and I-band light curves of a high-redshift type Ia supernova (SN Ia), SN 1999Q (z=0.46), using HST and ground-based near-infrared detectors. A goal of this study is the measurement of the color excess, E_{B-I}, which is a sensitive indicator of interstellar or intergalactic dust which could affect recent cosmological measurements from high-redshift SNe Ia. Our observations disfavor a 30% opacity of SN Ia visual light by dust as an alternative to an accelerating Universe. This statement applies to both Galactic-type dust (rejected at the 3.4 sigma confidence level) and greyer dust (grain size > 0.1 microns; rejected at the 2.3 to 2.6 sigma confidence level) as proposed by Aguirre (1999). The rest-frame $I$-band light cur ve shows the secondary maximum a month after B maximum typical of nearby SNe Ia of normal luminosi ty, providing no indication of evolution as a function of redshift out to z~0.5. A n expanded set of similar observations could improve the constraints on any contribution of extragalactic dust to the dimming of high-redshift SNe Ia.Comment: Accepted to the Astrophysical Journal, 12 pages, 2 figure

Gemini Planet Imager Observational Calibrations VI: Photometric and Spectroscopic Calibration for the Integral Field Spectrograph

The Gemini Planet Imager (GPI) is a new facility instrument for the Gemini Observatory designed to provide direct detection and characterization of planets and debris disks around stars in the solar neighborhood. In addition to its extreme adaptive optics and corona graphic systems which give access to high angular resolution and high-contrast imaging capabilities, GPI contains an integral field spectrograph providing low resolution spectroscopy across five bands between 0.95 and 2.5 $\mu$m. This paper describes the sequence of processing steps required for the spectro-photometric calibration of GPI science data, and the necessary calibration files. Based on calibration observations of the white dwarf HD 8049B we estimate that the systematic error in spectra extracted from GPI observations is less than 5%. The flux ratio of the occulted star and fiducial satellite spots within coronagraphic GPI observations, required to estimate the magnitude difference between a target and any resolved companions, was measured in the $H$-band to be $\Delta m = 9.23\pm0.06$ in laboratory measurements and $\Delta m = 9.39\pm 0.11$ using on-sky observations. Laboratory measurements for the $Y$, $J$, $K1$ and $K2$ filters are also presented. The total throughput of GPI, Gemini South and the atmosphere of the Earth was also measured in each photometric passband, with a typical throughput in $H$-band of 18% in the non-coronagraphic mode, with some variation observed over the six-month period for which observations were available. We also report ongoing development and improvement of the data cube extraction algorithm.Comment: 15 pages, 6 figures. Proceedings of the SPIE, 9147-30