High-voltage spark carbon-fiber sticky-tape data analyzer

An efficient method for detecting carbon fibers collected on a stick tape monitor was developed. The fibers were released from a simulated crash fire situation containing carbon fiber composite material. The method utilized the ability of the fiber to initiate a spark across a set of alternately biased high voltage electrodes to electronically count the number of fiber fragments collected on the tape. It was found that the spark, which contains high energy and is of very short duration, is capable of partially damaging or consuming the fiber fragments. It also creates a mechanical disturbance which ejects the fiber from the grid. Both characteristics were helpful in establishing a single discharge pulse for each fiber segment

Iterative Equalization and Source Decoding for Vector Quantized Sources

In this contribution an iterative (turbo) channel equalization and source decoding scheme is considered. In our investigations the source is modelled as a Gaussian-Markov source, which is compressed with the aid of vector quantization. The communications channel is modelled as a time-invariant channel contaminated by intersymbol interference (ISI). Since the ISI channel can be viewed as a rate-1 encoder and since the redundancy of the source cannot be perfectly removed by source encoding, a joint channel equalization and source decoding scheme may be employed for enhancing the achievable performance. In our study the channel equalization and the source decoding are operated iteratively on a bit-by-bit basis under the maximum aposteriori (MAP) criterion. The channel equalizer accepts the a priori information provided by the source decoding and also extracts extrinsic information, which in turn acts as a priori information for improving the source decoding performance. Simulation results are presented for characterizing the achievable performance of the iterative channel equalization and source decoding scheme. Our results show that iterative channel equalization and source decoding is capable of achieving an improved performance by efficiently exploiting the residual redundancy of the vector quantization assisted source coding

Diffusion and electron emission properties of duplex refractory metal thermionic emitters

Diffusion and electron emission properties of duplex refractory metal thermionic emitter

Iterative Detection of Three-Stage Concatenated FFH-MFSK

Serially concatenated and iteratively decoded Irregular Variable Length Coding (IrVLC) combined with precoded Fast Frequency Hopping (FFH) M-ary Frequency Shift Keying (MFSK) is considered. We employ EXtrinsic Information Transfer (EXIT) charts to investigate the 3-stage concatenation of the FFH-MFSK demodulator, the rate-1 decoder and the outer IrVLC decoder. The proposed joint source and channel coding scheme is capable of operating at low Signal-to-Noise Ratio (SNR) in Rayleigh fading channels contaminated by Partial Band Noise Jamming (PBNJ). The IrVLC scheme is comprised of a number of component Variable Length Coding (VLC) codebooks employing different coding rates for encoding particular fractions of the input source symbol stream. These fractions may be chosen with the aid of EXIT charts in order to shape the inverted EXIT curve of the IrVLC codec so that it can be matched with the EXIT curve of the inner decoder. We demonstrate that using the proposed scheme an infinitesimally low bit error ratio may be achieved at low SNR values

Fuel and fission product transport through chemically vapor-deposited fluoride tungsten

Fuel and fission product transport through chemically vapor-deposited fluoride tungste

Development of chemically vapor deposited rhenium emitters of (0001) preferred crystal orientation

Rhenium thermionic emitters were prepared by the pyrolysis of rhenium chlorides formed by the chlorination of rhenium pellets. The impurity contents, microstructures, degrees of (0001) preferred crystal orientation, and vacuum electron work functions of these emitters were determined as a function of deposition parameters, such as substrate temperature, rhenium pellet temperature and chlorine flow rate. A correlation between vacuum electron work function and degree of (0001) preferred crystal orientation was established. Conditions for depositing porosity-free rhenium emitters of high vacuum electron work functions were defined. Finally, three cylindrical rhenium emitters were prepared under the optimum deposition conditions

Zeeman and Orbital Effects of an in-Plane Magnetic Field in Cuprate Superconductors

We discuss the effects of a magnetic field applied parallel to the Cu-O ($ab$) plane of the high $T_c$ cuprate superconductors. After briefly reviewing the Zeeman effect of the field, we study the orbital effects, using the Lawrence-Doniach model for layered superconductors as a guide to the physics. We argue that the orbital effect is qualitatively different for in-plane and inter-layer mechanisms for superconductivity. In the case of in-plane mechanisms, interlayer couplings may be modeled as a weak interlayer Josephson coupling, whose effects disappear as $H\to\infty$; in this case Zeeman dominates the effect of the field. In contrast, in the inter-layer mechanism the Josephson coupling {\em is} the driving force of superconductivity, and we argue that the in-plane field suppresses superconductivity and provides an upper bound for $H_{c2}$ which we estimate very crudely.Comment: 4 pages with 1 embedded ps figure. Manuscript submitted to the MMM'99 conferenc