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The expression of fast and slow myosin isoforms in individual cells is associated with differences in shortening velocities and power output in fully differentiated vertebrate striated muscle. This paradigm in which shortening velocity is determined by the myosin isoform (and load) is inappropriate for smooth muscle. Smooth muscle tissues express multiple myosin heavy and light chain isoforms, and it is not currently possible to separate and identify chemically distinct native myosin hexamers (i.e., isoforms). It is not known if different isoforms are localized in subpopulations of cells or in specific cellular domains nor whether they combine preferentially to form a small number of native myosin hexamer isoforms. Potentially, thick filaments are aggregates of many different combinations of heavy and light chain isoforms that may or may not exhibit different kinetics. Shortening velocities in smooth muscle are regulated by Ca++-dependent crossbridge phosphorylation of the myosin regulatory light chains. Much of the observed diversity in power output in smooth muscle may be attributed to regulatory mechanisms modulating crossbridge cycling rates rather than contractile protein isoform expression.

Mucormycosis is an opportunistic, angioinvasive fungal infection characteristically affecting individuals with diabetes mellitus, chronic renal failure, and hematologic malignancies. In most cases it is a rapidly progressive infection with an 80% overall mortality. Radiographic manifestations are usually nonspecific focal consolidation or masses. The air crescent sign is a rare manifestation of angioinvasive fungi and indicates either aspergillosis or mucormycosis.

Peripheral myelin protein, 22 kDa (PMP22), is a myelin molecule associated with Schwann cells in peripheral nerves (Snipes, G. J., Suter, U., Welcher, A. A., and Shooter, E. M. (1992) J. Cell Biol. 117, 225-238). Mutations affecting the PMP22 gene have been implicated in the trembler mutation in mice (Suter, U., Welcher, A. A., Ozcelik, T., Snipes, G. J., Kosaras, B., Francke, U., Billings-Gagliardi, S., Sidman, R. L., and Shooter, E. M. (1992) Nature 356, 241-244; Suter, U., Moskow, J. J., Welcher, A. A., Snipes, G. J., Kosaras, B., Sidman, R. L., Buchberg, A. M., and Shooter, E. M. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 4382-4386) and Charcot-Marie-Tooth Disease in humans (Patel, P. I., Roa, B. B., Welcher, A. A., Schoener-Scott, R., Trask, B. J., Pentao, L., Snipes, G. J., Garcia, C. A., Francke, U., Shooter, E. M., Lupski, J. R., and Suter, U. (1992) Nature genet. 1, 159-165). In this report, we have studied PMP22 production in cultured rat Schwann cells. Schwann cells contain a 1.8-kilobase mRNA transcript coding for PMP22, and its production is up-regulated in vitro by forskolin. Metabolic labeling combined with immunoprecipitation methods using antibodies raised against synthetic peptides of PMP22 reveal that Schwann cells generate the protein from an 18-kDa precursor form which is post-translationally modified by N-linked glycosylation. A second molecule (molecular mass, 48 kDa) that reacted with PMP22 antibodies was also detected in Schwann cells but is not related chemically to PMP22 as determined by pulse-chase labeling. Metabolic labeling of rat sciatic nerve and Western blot analyses of purified rat sciatic nerve myelin reveal that deglycosylation of PMP22 gives rise to an 18-kDa protein similar in size to that in Schwann cells. These results indicate that cultured Schwann cells may provide a good model in which to investigate the production and function of PMP22 and to establish the cellular basis for the protein's involvement in inherited peripheral neuropathies.

The scattering of electromagnetic radiation from a finite conducting cylinder with complex permittivity at an arbitrary orientation was analyzed using a first approximation to the iteration technique for the integro-differential equation first developed by Shifrin and later modified by Acquista. The classical Kerker solution for a simple infinite dielectric cylinder was extended to a more physically realistic solution accounting for a finite length cylinder with complex permittivity by a modified Drude conductivity approach. The diameter of the cylinder is on the order of one wavelength of the incident radiation. The lowest order approximation to the internal field solution for the iteration process is a function of the effective polarized electric field inside the cylinder and the polarization matrix of the scattering medium. The polarization matrix of the cylinder is determined from the electrostatic solution for a finite cylinder in a constant electric field, and is a function of the length to diameter ratio (aspect ratio) and the permittivity of the cylinder. The electrostatic solution for a finite cylinder does not permit a closed solution; therefore the cylinder is approximated by an inscribed ellipsoid which provides a converging analytic expression. Results are compared to published data. The complex frequency dependent permittivity of the cylinder material was modeled using a modified Drude conductivity approach. The effects of typical variations in the length, diameter, and bulk conductivity of the cylinder were analyzed for TE, TM and TEM polarizations.

Laser-direct-write deposition of tungsten and laser ablation techniques have been successfully used to modify monolithic capacitors and inductors fabricated on GaAs substrates. The properties of the tungsten inductors and capacitors have been characterised at microwave frequencies and are in good agreement with theory. The new techniques permit postfabrication tuning with precision and versatility that are not achievable by any other method

Planar surface-oriented Pt/GaAs Schottky-barrier diodes have been fabricated and used to detect signals at submillimeter wavelengths. Video detection has been observed up to frequencies as high as 890 GHz. Harmonic mixing between the ninth harmonic of a 74.21-GHz signal and the second harmonic of 333.95-GHz radiation has also been obtained.

Laser-direct-write deposition of tungsten has been investigated as a technique for postfabrication trimming of GaAs monolithic microwave integrated circuits. Tungsten microstrip lines of 30 μΩ cm resistivity are deposited via a vapour-phase reaction induced by a focused argon-ion laser beam Lines of 1.8 μm thickness and 50μm width written on a semi-insulating GaAs substrate have a loss of 2.6 dB/cm at 16GHz. This trimming technique is proposed as a practical and accurate method for the optimisation of high-frequency GaAs circuits.

The microwave performance of the first GaAs permeable base transistors (PBTs) fabricated with 240-nm-periodicity tungsten base gratings is described. These PBTs have demonstrated a maximum stable gain of 20.1 dB at 26.5 GHz, which is believed to be the largest small-signal power gain for any microwave transistor at this frequency. Extrapolation of this maximum stable gain using a 6 dB/octave rolloff yields a maximum frequency of oscillation (f/sub max/) of 265 GHz. The breakdown voltage is approximately 20 V, which should make these devices excellent microwave power sources. Extrapolation microwave measurements on these devices from 3 GHz using a 6 dB/octave rolloff yields a unity-current-gain frequency (f/sub T/) of 38 GHz, which matches the best prior result for a PBT. These 240-nm-periodicity PBTs that have given the best f/sub T/ have been depletion-mode devices, suggesting that 240-nm-periodicity depletion-mode PBTs should have f/sub T/ values above 38 GHz.<>