Influence of the quality of the heterointerface on the cyclotron resonance spectra of InAs/(AlGa)Sb heterostructures

Cyclotron resonance is measured in solitary type-II InAs-AlGaSb quantum wells grown by molecular-beam epitaxy under various growth conditions. Quantum oscillations observed in the cyclotron resonance spectra in InAs-GaSb samples are attributed to scattering by a short-range potential due to roughness of the heterointerface. A new method based on measurement of the cyclotron resonance spectra is proposed for assessing the quality of the heterointerface. Fiz. Tekh. Poluprovodn. 31, 1246–1248 (October 1997)     

Error-resilience improvement for block-transform video coders

An algorithm is presented to enhance the resilience of block-based video-coding algorithms against channel errors. The error-resilience algorithm described suggests the use of fixed length coding to alleviate the effect of Huffman coding on the synchronisation of the decode under erroneous conditions. The proposed mechanism modifies the order of transmission of the fixed-length video parameters to increase the chance of their arrival. Synchronisation words are sent at fixed-length intervals within the bit stream to reduce the possibility of the decoder falling on similar bit patterns within the bit stream. To limit the effect of error accumulation, the motion prediction process is halted and the differential coding of motion vectors is not applied. FEC techniques are applied on some error-sensitive segments of the reordered video bitstream. The effectiveness of the proposed error-resilience algorithm is evidenced by both subjective and objective results     

Four-channel polarization-insensitive optically transparent wavelength converter

Multichannel wavelength converters may be important components in the cross-connects in future wavelength-division multiplexed (WDM) transport networks. We demonstrate a multichannel, polarization-insensitive, optically transparent wavelength converter, based on four-wave mixing in two semiconductor optical amplifiers in a polarization-diversity arrangement. Bit-error-rate (BER) measurements with four input 2.5-Gb/s WDM channels, spaced by 2 nm, show penalties for wavelength conversion less than 2.6 dB at 10/sup -9/ BER. Changes in the state of polarization of the input signals cause the output power to change by less than 1.2 dB, and the corresponding power penalties change by less than 0.9 dB.     

Wavelength selection for low-saturation pulse oximetry

Conventional pulse oximeters are accurate at high oxygen saturation under a variety of physiological conditions but show worsening accuracy at lower saturation (below 70%). Numerical modeling suggests that sensors fabricated with 735 and 890 nm emitters should read more accurately at low saturation under a variety of conditions than sensors made with conventionally used 660 and 900 nm band emitters. Recent animal testing confirms this expectation. It is postulated that the most repeatable and stable accuracy of the pulse oximeter occurs when the fractional change in photon path lengths due to perturbations in the tissue (relative to the conditions present during system calibration) is equivalent at the two wavelengths. Additionally, the penetration depth (and/or breadth) of the probing light needs to be well matched at the two wavelengths in order to minimize the effects of tissue heterogeneity. At high saturation these conditions are optimally met with 660 and 900 nm band emitters, while at low saturation 735 and 890 nm provide better performance     

Thick-layer glycerin-containing bichromated gelatin for recording volume holograms

A thick-layer light-sensitive material consisting of glycerin-containing bichromated gelatin has been prepared and used to record real-time volume holograms with 0.44 μm helium-cadmium laser radiation. The thickness of the layers is 400–600 μm. The holographic sensitivity of the material is 1 J/cm². The highest diffraction efficiency of holograms recorded using a symmetric system with parallel beams is 32%. Pis’ma Zh. Tekh. Fiz. 23, 62–65 (April 12, 1997)     

STRESS INTENSITY FACTORS AND WEIGHT FUNCTIONS FOR SEMI-ELLIPTICAL SURFACE CRACKS IN FINITE-THICKNESS PLATES UNDER TWO-DIMENSIONAL STRESS DISTRIBUTION

Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%.     

Consequences of the 1979 Three Mile Island accident continued: further comment

The development of multimedia image review stations offers the cardiologist the ability to review multiple image sets in a single setting rather than moving from one review station to another. To accomplish this goal there are three essential barriers: 1) memory requirements for digital images; 2) standardization of data format; and 3) practical user interfaces. Image compression algorithms can be used to overcome the digital barrier; however, these must be used cautiously so as to not adversely affect image quality. The lack of standardization is being addressed by the implementation of the Digital Communication in Medicine (DICOM) standard, and practical user interfaces are being developed every day with the widespread implementation of World Wide Web technology. These solutions will allow the clinician to review all of a patient's image data in one location, such as in the office, on the nursing unit, or at home.     

Electronic transport in a type-II GaInAsSb/p-InAs heterojunction with different doping levels of the solid solution

Galvanomagnetic phenomena and photoconductivity in broken-gap type-II GaInAsSb/p-InAs heterojunctions with different levels of doping of the solid solution with donor (Te) or acceptor (Zn) impurities have been investigated. It has been determined that in such structures an electronic channel, which determines the galvanomagnetic effects in a wide range of doping levels, is present at the heterojunction. A sharp decrease of the Hall mobility was observed in the experimental heterostructures with a high level of doping of the epitaxial layer with an acceptor impurity. The observed effect is due to exhaustion of the electronic channel as a result of carrier localization in potential wells at the heterojunction. Fiz. Tekh. Poluprovodn. 31, 897–901 (August 1997)