Abstract. We present the results of 5 GHz VLBI observations of a compact steep spectrum source 3C 138. The data are consistent with the western end being the location of the central activity. The observed offset between different frequencies in the central region of 3C 138 can be accounted for by a frequency dependent shift of the synchrotron self-absorbed core. Our new measurements confirm the existence of a superluminal motion, but its apparent velocity of 3.3c is three times slower than the reported one. This value is consistent with the absence of parsec-scale counter-jet emission in the inner region, but seems still too high to allow the overall counter-jet to be seen in terms of Doppler boosting of an intrinsically identical jet. Either an interaction of jet with central dense medium, or an intrinsically asymmetrical jet must be invoked to reconcile the detected superluminal speed with the observed large scale asymmetry in 3C 138.

To interpret the emission of knots in the 3C 273 jet from radio to X-rays, we propose a synchrotron model in which, owing to the shock compression effect, the injection spectra from a shock into the upstream and downstream emission regions are asymmetric. Our model could well explain the spectral energy distributions of knots in the 3C 273 jet, and predictions regarding the knots' spectra could be tested by future observations.

We report on Very Long Baseline Array polarimetric observations of NRAO 530 at 5, 8, 15, 22 and 43 GHz made during one week in 1997 February. We present the total intensity, the fractional polarization and the electric vector position angle (EVPA) distributions at all these frequencies. A model fitting has been performed to the full polarization visibility data. From this, the fitted southernmost component A is confirmed as the core of the radio structure with relatively high brightness temperature and hard spectrum between 15 and 43 GHz in comparison with the central component B of dominant flux. The relatively high degree of polarization for the component A may arise from its complex radio structure, which can be resolved at 86 GHz. In contrast, the component B shows a well-fitted power-law spectrum with a spectral index of about −0.5 (f ∝ ν α ), and a linear correlation between EVPAs and wavelength square with an observed rotation measure of about −1062 rad m −2 , indicating its structural singleness. Assuming that the component B has a comparable degree of polarization without depolarization at these frequencies, the decrease in fractional polarization with wavelength mainly results from opacity and Faraday rotation, in which the opacity plays quite a large role. A spine-sheath-like structure in fractional polarization (m) is detected, covering almost the whole emission region at 5 and 8 GHz, with a degree of polarization relatively low along the jet spine, becoming higher towards two sides of the jet. The linear polarization at 5 GHz shows three separate polarized emission regions with alternately aligned and orthogonal polarization vectors down the jet. The polarization goes to zero between the top two regions, with the highest polarization level occurring at the top and bottom. The 5-and 8-GHz images show EVPA changes across the width of the jet as well as along the jet. These complex polarimetric properties can be explained in terms of either the presence of a large helical magnetic field or tangled magnetic fields compressed and sheared down the jet. These can be further determined by multifrequency polarimetric very long baseline interferometry observations with sufficient high resolution and sensitivity spanning an appropriate frequency range.

Pyrolyzation of photolithographically patterned photoresist on semiconductor substrates such as silicon, gallium arsenide, and indium phosphide, results in a convex-shaped, chemically inert, temporary form that functions as a mold upon which to lift-off evaporated thin films such as metals. The pyrolyzation process is simply a bake on a standard laboratory hot-plate that is ramped from room temperature to 300 °C air. The pyrolytic-photoresist form is subsequently removed in an oxygen plasma stripper leaving behind the three-dimensional lifted off thin films of free-standing, convex-shaped, full-arch air-bridges or half-arch air-bridges that we call air-ramps. Some applications are interconnects for high-speed devices; inter-level interconnects; out-of-plane coils for out-of-plane inductors; microdomes for eletromagnetic shielding; electrodes for field-emitter tips; and microelectromechanical structures. Pyrolyzing photoresist does not alter the good planarization capabilities of photoresist. Because pyrolytic photoresist is a version of the earliest form of synthetic thermoset resin called Bakelite, it can also be used as a reasonably good encapsulation material.