Planar sandwich antennas for submillimeter applications

A planar receiving antenna with a predictable pattern at submillimeter wavelength is demonstrated experimentally for the first time. It is single lobed and efficient, with a gain of approximately 8 dB at a wavelength of 119 µm

Antarctic meteorite descriptions, 1980

Specimens found in the Alan Hills area include 361 ordinary chondrites, 4 carbonaceous chondrites, 6 achondrites, and 2 irons. Thirteen specimens measured over 11 cm in diameter and 69 between 5 to 10 cm in diameter are reported. The remainder of the finds were small, and many were paired. One of the irons was estimated to weigh about 20 kilograms

Planar multimode detector arrays for infrared and millimeter-wave applications

A new type of detector array is described. By means of a suitably designed metallic network, many detector elements (each individually small compared to wavelength) are assembled into an impedance-matched termination for radiation incident normally on the plane of the device. Residual reactance is tuned out by means of a movable backshort. An array of 400 bismuth-film microbolometers with a total area of 1 cm^2 has been tested at 215 GHz. A coupling efficiency of approximately 60 percent was observed. The detector has a D^* of 4 x 10^8 cm · Hz^(1/2)/W at room temperature with response time on the order of 2 x 10^-7 s. Similar arrays of Schottky and SIS diodes can probably be constructed

Dynamics of protein-protein encounter: a Langevin equation approach with reaction patches

We study the formation of protein-protein encounter complexes with a Langevin equation approach that considers direct, steric and thermal forces. As three model systems with distinctly different properties we consider the pairs barnase:barstar, cytochrome c:cytochrome c peroxidase and p53:MDM2. In each case, proteins are modeled either as spherical particles, as dipolar spheres or as collection of several small beads with one dipole. Spherical reaction patches are placed on the model proteins according to the known experimental structures of the protein complexes. In the computer simulations, concentration is varied by changing box size. Encounter is defined as overlap of the reaction patches and the corresponding first passage times are recorded together with the number of unsuccessful contacts before encounter. We find that encounter frequency scales linearly with protein concentration, thus proving that our microscopic model results in a well-defined macroscopic encounter rate. The number of unsuccessful contacts before encounter decreases with increasing encounter rate and ranges from 20-9000. For all three models, encounter rates are obtained within one order of magnitude of the experimentally measured association rates. Electrostatic steering enhances association up to 50-fold. If diffusional encounter is dominant (p53:MDM2) or similarly important as electrostatic steering (barnase:barstar), then encounter rate decreases with decreasing patch radius. More detailed modeling of protein shapes decreases encounter rates by 5-95 percent. Our study shows how generic principles of protein-protein association are modulated by molecular features of the systems under consideration. Moreover it allows us to assess different coarse-graining strategies for the future modelling of the dynamics of large protein complexes

Determination Of Oxygen Chemical Diffusion Coefficients In Single Crystal SrTiO By Capacitance Manometry

The oxidation kinetics of a single crystal of SrTiOs were measured with a tensivolumetric system over the temperature range 700 -975 at 0.03 atm oxygen pressure. The oxidation was found to be oxygen diffusion limited with an activation energy of 14.9 - 1.3 kcal/mole. Combining the kinetic data with relative defect concentration data yielded an activation energy for oxygen self-diffusion of 57 - 16 kcal/mole. The enthalpy of formation of doubly ionized oxygen vacancies was calculated to be 126 - 13 kcal/mol. © 1975, The Electrochemical Society, Inc. All rights reserved

Long beating wavelength in the Schwarz-Hora effect

Thirty years ago, H.Schwarz has attempted to modulate an electron beam with optical frequency. When a 50-keV electron beam crossed a thin crystalline dielectric film illuminated with laser light, electrons produced the electron-diffraction pattern not only at a fluorescent target but also at a nonfluorescent target. In the latter case the pattern was of the same color as the laser light (the Schwarz-Hora effect). This effect was discussed extensively in the early 1970s. However, since 1972 no reports on the results of further attempts to repeat those experiments in other groups have appeared, while the failures of the initial such attempts have been explained by Schwarz. The analysis of the literature shows there are several unresolved up to now contradictions between the theory and the Schwarz experiments. In this work we consider the interpretation of the long-wavelength spatial beating of the Schwarz-Hora radiation. A more accurate expression for the spatial period has been obtained, taking into account the mode structure of the laser field within the dielectric film. It is shown that the discrepancy of more than 10% between the experimental and theoretical results for the spatial period cannot be reduced by using the existing quantum models that consider a collimated electron beam.Comment: 3 pages, RevTe

Self-dual Yang-Mills fields in pseudoeuclidean spaces

The self-duality Yang-Mills equations in pseudoeuclidean spaces of dimensions $d\leq 8$ are investigated. New classes of solutions of the equations are found. Extended solutions to the D=10, N=1 supergravity and super Yang-Mills equations are constructed from these solutions.Comment: 9 pages, LaTeX, no figure

How strong is the evidence for accelerated expansion?

We test the present expansion of the universe using supernova type Ia data without making any assumptions about the matter and energy content of the universe or about the parameterization of the deceleration parameter. We assume the cosmological principle to apply in a strict sense. The result strongly depends on the data set, the light-curve fitting method and the calibration of the absolute magnitude used for the test, indicating strong systematic errors. Nevertheless, in a spatially flat universe there is at least a 5 sigma evidence for acceleration which drops to 1.8 sigma in an open universe.Comment: 16 pages, 3 figure

Antarctic meteorite newsletter. Volume 4: Number 1, February 1981: Antarctic meteorite descriptions, 1976, 1977, 1978, 1979

This issue of the Newsletter is essentially a catalog of all antarctic meteorites in the collections of the Johnson Space Center Curation Facility and the Smithsonian except for 288 pebbles now being classed. It includes listings of all previously distributed data sheets plus a number of new ones for 1979. Indexes of samples include meteorite name/number, classification, and weathering category. Separate indexes list type 3 and 4 chondrites, all irons, all achondrites, and all carbonaceous chondrites