Low cost space power generation

The success of this study has given a method of fabricating durable copolymer films without size limitations. Previously, only compression molded samples were durable enough to generate electrical energy. The strengthened specimens are very long lived materials. The lifetime was enhanced at least a factor of 1,300 in full pyroelectric conversion cycle experiments compared with extruded, non-strengthened film. The new techniques proved so successful that the lifetime of the resultant copolymer samples was not fully characterized. The lifetime of these new materials is so long that accelerated tests were devised to probe their durability. After a total of more than 67 million high voltage electrical cycles at 100 C, the electrical properties of a copolymer sample remained stable. The test was terminated without any detectable degradation to allow for other experiments. One must be cautious in extrapolating to power cycle performance, but 67 million electrical cycles correspond to 2 years of pyroelectric cycling at 1 Hz. In another series of experiments at reduced temperature and electrical stress, a specimen survived over one-third of a billion electrical cycles during nearly three months of continuous testing. The radiation-limited lifetimes of the copolymer were shown to range from several years to millions of years for most earth orbits. Thus, the pyroelectric copolymer has become a strong candidate for serious consideration for future spacecraft power supplies

Millimeter-wave passive ultra-compact imaging technology for synthetic vision & mobile platforms

Substantial technical progress was made on all of the three high-risk subsystems of this program. The subsystems include dielectric antenna, G-band receiver, and electro-optic image processor. Progress is approximately on-schedule for both the receiver and the electro-optic processor development, while greater than anticipated challenges have been discovered in the dielectric antenna development. Much of the information in this report was covered in greater detail in the One-Year Review Meeting held at TTC on 22 February 1996. The performance goals of the dielectric antenna project are: Scan Angle -- 20 deg. desired; Loss -- 6 dB end to end (3 dB average); Frequency -- 206-218 GHz (6% bandwidth); Beam width -- 0.25 deg.; and Length -- 12 inches. The scan angle requirement was chosen to satisfy the needs of aircraft pilots. This requirement, coupled with the presently limited bandwidth processors (1 GHz state-of-the-art and 12 GHz in development in this program) forces the antenna to be dielectric (high scan angle air-filled waveguide-based antennas would be too lossy and their performance would vary too much as a function of frequency). A high dielectric constant (e.g., 10) was initially chosen for the dielectric material. This choice lead to the following fabrication challenges: total thickness variation (TTV) tolerance is 1 micrometer; coupler spacing tolerance is 1 micrometer; width tolerance is larger, but unknown, and the surfaces must have mirror finish. Also of importance is the difficulty in obtaining raw materials that satisfy the overall length requirement of 12 inches while simultaneously satisfying the above specifications

1D to 3D Crossover of a Spin-Imbalanced Fermi Gas

We have characterized the one-dimensional (1D) to three-dimensional (3D) crossover of a two-component spin-imbalanced Fermi gas of 6-lithium atoms in a 2D optical lattice by varying the lattice tunneling and the interactions. The gas phase separates, and we detect the phase boundaries using in situ imaging of the inhomogeneous density profiles. The locations of the phases are inverted in 1D as compared to 3D, thus providing a clear signature of the crossover. By scaling the tunneling rate with respect to the pair binding energy, we observe a collapse of the data to a universal crossover point at a scaled tunneling value of 0.025(7).Comment: 5 pages, 4 figure

Update on a long-term, prospective study of capsulotomy and retinal detachment rates after cataract surgery

Journal ArticlePURPOSE: To evaluate the retinal detachment risks and neodymium:YAG (Nd:YAG) capsulotomy rates associated with different cataract approaches and intraocular lens (IOL) styles in a long-term,prospective clinical study. SETTING: Clinical practice of 1 ophthalmologist, Fort Collins, Colorado, USA. METHODS: Prospectively studied were surgical approach, date, and complications; IOL type; axial length; patient age and sex; Nd:YAG capsulotomy and date; and retinal detachment and date. RESULTS: Phacoemulsification had a lower risk of retinal detachment than intracapsular cataract extraction (ICCE) (0.4% versus 5.4%; P <.001) and extracapsular cataract extraction (ECCE) (0.4% versus 1.6%; P =. 002). Although retinal detachment was significantly associated with Nd:YAG for ECCE (3.1% versus 1.0%; P =.01), no patient in the phacoemulsification group had a retinal detachment after an Nd:YAG treatment. Retinal detachment was strongly associated with axial length of 24.0 mm and greater (P <.001), age of 60 years or less if axial length was 24.0 mm or greater (for ECCE, P =.001; for phacoemulsification, P =.01) and sex; that is, male (for ECCE, P =. 04; for phacoemulsification, P =.02). Regarding IOL styles the Surgidev B20/20 (P <.001) and AcrySof MA60 (P <.001) had significantly lower Nd:YAG rates, while the Cilco UPB 320 GS had a significantly higher Nd:YAG rate (P <.001). CONCLUSIONS: Cataract surgical approach and IOL style significantly affect Nd:YAG and retinal detachment rates. Being a man, being 60 years or younger, and especially having an axial length of 24.0 mm or greater were associated with detachment. Some Nd:YAG approaches may not put the patient at increased risk for retinal detachment

Phase diagram of a strongly interacting spin-imbalanced Fermi gas

We obtain the phase diagram of spin-imbalanced interacting Fermi gases from measurements of density profiles of Li6 atoms in a harmonic trap. These results agree with, and extend, previous experimental measurements. Measurements of the critical polarization at which the balanced superfluid core vanishes generally agree with previous experimental results and with quantum Monte Carlo (QMC) calculations in the Bardeen-Cooper-Schrieffer and unitary regimes. We disagree with the QMC results in the Bose-Einstein condensate regime, however, where the measured critical polarizations are greater than theoretically predicted. We also measure the equation of state in the crossover regime for a gas with equal numbers of the two fermion spin states