Singularity in the boundary resistance between superfluid 4^4He and a solid surface

We report new measurements in four cells of the thermal boundary resistance $R$ between copper and $^4$He below but near the superfluid-transition temperature $T_\lambda$. For $10^{-7} \leq t \equiv 1 - T/T_\lambda \leq 10^{-4}$ fits of $R = R_0 t^{x_b} + B_0$ to the data yielded $x_b \simeq 0.18$, whereas a fit to theoretical values based on the renormalization-group theory yielded $x_b = 0.23$. Alternatively, a good fit of the theory to the data could be obtained if the {\it amplitude} of the prediction was reduced by a factor close to two. The results raise the question whether the boundary conditions used in the theory should be modified.Comment: 4 pages, 4 figures, revte

OpTIIX: An ISS-Based Testbed Paving the Roadmap Toward a Next Generation Large Aperture UV/Optical Space Telescope

The next generation large aperture UV/Optical space telescope will need a diameter substantially larger than even that of JWST in order to address some of the most compelling unanswered scientific quests. These quests include understanding the earliest phases of the Universe and detecting life on exo-planets by studying spectra of their atmospheres. Such 8-16 meter telescopes face severe challenges in terms of cost and complexity and are unlikely to be affordable unless a new paradigm is adopted for their design and construction. The conventional approach is to use monolithic or preassembled segmented mirrors requiring complicated and risky deployments and relying on future heavy-lift vehicles, large fairings and complex geometry. The new paradigm is to launch component modules on relatively small vehicles and then perform in-orbit robotic assembly of those modules. The Optical Testbed and Integration on ISS eXperiment (OpTIIX) is designed to demonstrate, at low cost by leveraging the infrastructure provided by ISS, telescope assembly technologies and end-to-end optical system technologies. The use of ISS as a testbed permits the concentration of resources on reducing the technical risks associated with robotically integrating the components. These include laser metrology and wavefront sensing and control (WFS&C) systems, an imaging instrument, lightweight, low-cost deformable primary mirror segments and the secondary mirror. These elements are then aligned to a diffraction-limited optical system in space. The capability to assemble the optical system and remove and replace components via the existing ISS robotic systems like the Special Purpose Dexterous Manipulator (SPDM), or by the ISS flight crew, allows for future experimentation, as well as repair

The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance

The all sky surveys done by the Palomar Observatory Schmidt, the European Southern Observatory Schmidt, and the United Kingdom Schmidt, the InfraRed Astronomical Satellite and the 2 Micron All Sky Survey have proven to be extremely useful tools for astronomy with value that lasts for decades. The Wide-field Infrared Survey Explorer is mapping the whole sky following its launch on 14 December 2009. WISE began surveying the sky on 14 Jan 2010 and completed its first full coverage of the sky on July 17. The survey will continue to cover the sky a second time until the cryogen is exhausted (anticipated in November 2010). WISE is achieving 5 sigma point source sensitivities better than 0.08, 0.11, 1 and 6 mJy in unconfused regions on the ecliptic in bands centered at wavelengths of 3.4, 4.6, 12 and 22 microns. Sensitivity improves toward the ecliptic poles due to denser coverage and lower zodiacal background. The angular resolution is 6.1, 6.4, 6.5 and 12.0 arc-seconds at 3.4, 4.6, 12 and 22 microns, and the astrometric precision for high SNR sources is better than 0.15 arc-seconds.Comment: 22 pages with 19 included figures. Updated to better match the accepted version in the A

The Wide-Field Infrared Survey Explorer (WISE): Mission Description and Initial On-Orbit Performance

The all sky surveys done by the Palomar Observatory Schmidt, the European Southern Observatory Schmidt, and the United Kingdom Schmidt, the InfraRed Astronomical Satellite and the 2 Micron All Sky Survey have proven to be extremely useful tools for astronomy with value that lasts for decades. The Wide-field Infrared Survey Explorer is mapping the whole sky following its launch on 14 December 2009. WISE began surveying the sky on 14 Jan 2010 and completed its first full coverage of the sky on July 17. The survey will continue to cover the sky a second time until the cryogen is exhausted (anticipated in November 2010). WISE is achieving 5 sigma point source sensitivities better than 0.08, 0.11, 1 and 6 mJy in unconfused regions on the ecliptic in bands centered at wavelengths of 3.4, 4.6, 12 and 22 micrometers. Sensitivity improves toward the ecliptic poles due to denser coverage and lower zodiacal background. The angular resolution is 6.1", 6.4", 6.5" and 12.0" at 3.4, 4.6, 12 and 22 micrometers, and the astrometric precision for high SNR sources is better than 0.15"

Scaling and universality of the thermal conductivity of liquid 4 He near the superfluid transition and in restricted geometries

Abstract We present measurements of the thermal conductivity k(t, P, L) = l/q(t, P, L) near the superfluid transition of 4 He at saturated vapor pressure and confined in cylindrical geometries with radii L = 0.5 and 1.0 lm (t " T/T k (P) À 1). For L = 1.0 lm measurements at six pressures P are presented. At and above T k the data are consistent with a universal scaling function 1/m t valid for all P (q 0 and x are the pressure-dependent amplitude and effective exponent of the bulk resistivity q(t, P, 1) = q 0 t x and n = n 0 t Àm is the correlation length). Indications of breakdown of scaling and universality are observed below T k

Optimization of grounding resistance in multitrain DC subway system based on MOEA/D‐DE

Abstract Currently, in multitrain DC subway system, abnormal increase of rail potential (RP) and stray current (SC) has seriously threatened the safe operation of the system. Over voltage protection device (OVPD) is generally chosen to control the RP, but its action process may increase the amplitude of SC seriously. Here, the grounding resistance of OVPD is optimized by a proposed multi‐objective decomposition algorithm based on differential evolution (MOEA/D‐DE) to suppress the rise of RP and SC synergistically. Firstly, the simulation model of the DC subway system with multitrain is built, the power flow calculation is conducted, and the dynamic RP and leakage current (LC) at the location of traction substation are obtained. Secondly, the double objective optimization model of maximum RP and LC is established and solved by MOEA/D‐DE. Finally, the effectiveness of the proposed method is verified based on the data of Guangzhou Metro Line 2. Results show that the SC of the system can be controlled effectively with OVPD grounding mode after optimization, and integrated control of RP and SC can be accomplished

Thirty Meter Telescope: A status update on the first light instruments and the path beyond into early light instruments

This paper presents an overview of the suite of science instruments envisioned for the Thirty Meter Telescope. Specifically, the we'll explore the evolution within our first light and first decade instruments