Electrical and optical feedback in an InGaAs/InP light-amplifyingoptical switch (LAOS)

A circuit model for optical and electrical feedback has been developed to investigate the cause of negative differential resistance (NDR) switching in a series connected heterojunction phototransistor (HPT) light-emitting diode (LED) device. The model considers optical feedback from the light generated in the LED, electrical feedback from the holes thermally emitted over the LED cladding layer, nonlinear gain of the HPT, the Early effect, and leakage resistance. The analysis shows that either electrical or optical feedback can be the dominant cause for the NDR, depending upon their relative strengths. The NDR observed in the devices was caused primarily by electrical feedback since the optical feedback is weak. For low input power, avalanche breakdown appears to initiate the NDR in the devices although avalanching alone cannot cause NDR     

An integrated air-gap-capacitor pressure sensor and digital readoutwith sub-100 attofarad resolution

The fabrication and characterization of an integrated air-gap-capacitor pressure sensor are presented. The capacitor fabrication process uses standard IC processing to create NMOS circuits, and an added polysilicon layer to create poly-to-n⁺ capacitors with a 0.6-μm-thick dielectric using deposited oxide. Subsequent processing is used to produce deformable, parallel-plate, air-gap capacitors on the front side alongside MOS circuits. Sensor chips are fabricated using 100-μm×100-μm, 100-fF air-gap capacitors with on-chip circuitry. The sensor chip is a part of a capacitive measurement system that uses a charge-redistribution sense technique to achieve very high capacitance resolution. The behavior of the pressure sensor chips was studied as a function of applied pressure in the 0-240-kPa (0-35-psi) range. Measurements indicate a sensitivity of 0.93 mV/kPa (6.40 mV/psi) with a deflection of 10 nm/kPa (70 nm/psi) at 0-69 kPa (0-10 psi). Standard deviations indicate a static pressure resolution of 0.54 kPa (0.078 psi), which translates to 30 attofarads at a sampling frequency of 11 kHz     

Application of artificial neural networks to the analysis of two‐dimensional fluorescence spectra in recombinant E coli fermentation processes

A two‐dimensional (2D) spectrofluorometer was used to monitor various fermentation processes with recombinant E coli for the production of 5‐aminolevulinic acid (ALA). The whole fluorescence spectral data obtained during a process were analyzed using artificial neural networks, ie self‐organizing map (SOM) and feedforward backpropagation neural network (BPNN). The SOM‐based classification of the whole spectral data has made it possible to qualitatively associate some process parameters with the normalized weights and variances, and to select some useful combinations of excitation and emission wavelengths. Based on the classified fluorescence spectra a supervised BPNN algorithm was used to predict some of the process parameters. It was also shown that the BPNN models could elucidate some sections of the process's performance, eg forecasting the process's performance. Copyright © 2005 Society of Chemical Industry     

Friction and wear of Inconel 690 and Inconel 600 for steam generator tube in room temperature water

In the steam generators of nuclear power plants, the flow of cooling water can cause the tubes to vibrate, resulting in fretting wear damage due to contacts between these tubes and their supports. The tubes are made of Inconel 690 and Inconel 600 and the supports are made of STS 304. In this paper, fretting wear tests in water were performed using the materials Inconel 690 and Inconel 600 in contact with STS 304. Fretting tests using a cross-cylinder type set up were conducted under various vibrating amplitudes and applied normal loads in order to measure friction forces and wear volumes. Also, conventional sliding tests using a pin-on-disk type set up were carried out to compare these test results.In the fretting tests, friction force was found to be strongly dependent on normal load and vibrating amplitude. Coefficients of friction decreased with an increase in the normal load and a decrease in the vibrating amplitude applied. Also, the wear of Inconel 600 and Inconel 690 was predicted using a work rate model. Depending on the normal load and vibrating amplitude applied, distinctively different wear mechanisms and often drastically different wear rates occurred. It was found that the fretting wear coefficients for Inconel 600 and Inconel 690 were 9.3×10⁻¹⁵ and 16.2×10⁻¹⁵ Pa⁻¹, respectively. This study shows that Inconel 690 can result in lesser friction forces and exhibits less wear resistance than Inconel 600 in room temperature water.     

Differentially coherent code acquisition in the MIMO-aided multi-carrier DS-CDMA downlink

Both differentially coherent and non-coherent code acquisition schemes designed for the multiple-input multiple-output (MIMO)-aided multi-carrier (MC)-DS-CDMA downlink are analysed, when communicating over uncorrelated Rayleigh channels. The attainable mean acquisition time (MAT) performance is studied as a function of both the number of multiple transmit/multiple receive antennas and that of the number of subcarriers. It is demonstrated that in contrast to the expectations, when the number of multiple transmit antennas and/or that of the subcarriers is increased in both the differentially coherent and the non-coherent code acquisition scenarios, the achievable MAT deteriorates over the entire signal-to-interference plus noise ratio (SINR) per chip (E_c/I_o) range considered, except for the scenario of single-carrier (SC)-DS-CDMA using P = 2 transmit antennas and R = 1 receive antenna. As expected, the degree of performance degradation depends upon the specific scheme and the E_c/I_o ratio considered, although paradoxically, the correctly synchronised MIMO-aided system is capable of attaining its target bit error ratio performance at reduced SINR values.     

Survey of nitrate and nitrite contents of vegetables grown in Korea.

A scientific basis for the evaluation of the risk to public health arising from excessive dietary intake of nitrate in Korea is provided. The nitrate () and nitrite () contents of various vegetables (Chinese cabbage, radish, lettuce, spinach, soybean sprouts, onion, pumpkin, green onion, cucumber, potato, carrot, garlic, green pepper, cabbage and Allium tuberosum Roth known as Crown daisy) are reported. Six hundred samples of 15 vegetables cultivated during different seasons were analysed for nitrate and nitrite by ion chromatography and ultraviolet spectrophotometry, respectively. No significant variance in nitrate levels was found for most vegetables cultivated during the summer and winter harvests. The mean nitrates level was higher in A. tuberosum Roth (5150 mg kg(-1)) and spinach (4259 mg kg(-1)), intermediate in radish (1878 mg kg(-1)) and Chinese cabbage (1740 mg kg(-1)), and lower in onion (23 mg kg(-1)), soybean sprouts (56 mg kg(-1)) and green pepper (76 mg kg(-1)) compared with those in other vegetables. The average nitrite contents in various vegetables were about 0.6 mg kg(-1), and the values were not significantly different among most vegetables. It was observed that nitrate contents in vegetables varied depending on the type of vegetables and were similar to those in vegetables grown in other countries. From the results of our studies and other information from foreign sources, it can be concluded that it is not necessary to establish limits of nitrates contents of vegetables cultivated in Korea due to the co-presence of beneficial elements such as ascorbic acid and alpha-tocopherol which are known to inhibit the formation of nitrosamine.