Nonlinear FIR differentiator for quantised input signals

The proposed nonlinear finite impulse response (FIR) differentiator is optimised for the reduction of quantisation error when processing signals of constant or slowly varying rate. Judicious use of a number theoretic approach to rate estimation for some input sequences reduces mean-squared error, relative to that of the optimum linear differentiator, whilst facilitating simple implementation.     

4H-SiC RF power MOSFETs

A 4H silicon carbide lateral RF MOSFET has been fabricated and characterized for the first time. The improved performance of this device was facilitated by a two-metal-layer process, which optimizes the conflicting requirements of acceptable inversion-layer mobility and low contact resistance. The cut-off frequency of the device with 1-μm gate length was in excess of 7 GHz     

Tunable Cerenkov lasers

The concept of a tunable Cerenkov laser is introduced and expressions for the operating wavelength and stimulated emission rate are developed. Emphasis is on the development of criteria which must be met if tunable far-infrared device operation is to be achieved.     

Diet digestibility and growth of holstein calves fed acidified milk replacers containing soy protein concentrate

Three experiments were conducted to determine the effects of acidification of milk replacers containing soy protein concentrate on diet digestibility and growth of Holstein bull calves. In Experiment 1, six calves (6 wk old) were fed at 10% of BW/d either acidified milk replacer containing soy protein concentrate or untreated milk replacer containing soy protein concentrate. Replacers were reconstituted to 12.5% DM for 10-d adjustment and 4-d collection periods to determine digestibility and N balance. Digestibilities of DM, ether extract, and N were similar between treatments. Nitrogen retention and N retention as a percentage of that absorbed were higher for calves fed the acidified diet. In Experiment 2, 20 calves (1 wk old) were fed diets identical to those diets fed in Experiment 1 at 20% of BW/d for 4 wk. Calves were allowed to adjust to the diet for 5 d. Growth parameters were measured and amount of feed offered was adjusted weekly. Calves fed the untreated diet had higher daily weight gains, girth gains, height gains, and better feed utilization. In Experiment 3, 21 calves were fed either the aforementioned diets or a replacer based on milk proteins at 10% of BW/d (12.5% DM) for 4 wk. Growth parameters were measured and DM intakes were adjusted weekly. Growth and feed conversion were similar across diets. Replacers containing soy protein concentrate or large amounts of whey may need to be supplemented with additional methionine to maximize rate of gain.     

Amplifying four-wavelength combiner, based on erbium/ytterbium-doped waveguide amplifiers and integrated splitters

We report the successful system demonstration of a four-wavelength integrated-optics amplifying combiner. The arrangement consists of an all-connectorized 4/spl times/1 glass splitter followed by a 4.5-cm-long Er/Yb-doped waveguide amplifier. When injecting 120 mW of 975-nm laser diode pump, we record, in the amplifying section, 11.6 dB of net gain in the single pass configuration and 23 dB in the double pass as well as a noise figure of 4.5 dB. These results show the potentiality of ion-exchange technology for the fabrication of lossless telecommunication devices.     

A Simplified Expression for the Probability of Error for Binary Multichannel Communications

We present a simplified expression for the probability of error, P_e, for binary multichannel communications. The original expression was derived by Proakis in 1968. More recently, Simon and Alouini presented an expression involving the generalised Marcum Q-function. In this letter we present a simplified form of Simon and Alouini's expression. The application of this result to the calculation of performance metrics for communications over fading channels is also discussed.     

On the feasibility of using an atmospheric discharge plasma as an RF antenna

The plasma produced by a laser-guided, electric discharge in the atmosphere has been formed in the shape of a folded monopole antenna with a characteristic frequency of 112 MHz. This plasma antenna has been used to transmit and receive signals at 112 MHz. While the plasma remained conducting, the signal transmitted from, and received on, the plasma antenna was within -1pm1dB of that transmitted from and received on a "standard" copper folded monopole antenna of the same size. During this time the signal transmitted from, and received on, the plasma antenna also remained approximately constant in amplitude (fluctuationssim pm1dB). This useful lifetime of the plasma antenna was varied fromsim 200 mus togeq 2000 mus by changing the dration of the electric discharge sustaining the plasma columns. In these experiments, the noise from the plasma antenna was not distinguishable from that developed using a copper antenna, but in both cases the noise was much larger than the true thermal noise background.     

Integrated Q-switched multiple-cavity glass waveguidelaser

A novel Q-switching scheme, using rapid variation of the path difference between the cavities of a multiple-cavity resonator, is described. A thermooptic phase modulator was used to switch the cavity loss of a Y-junction glass waveguide laser between high and low states. Q-switched pulses with durations of 5 μs and peak powers of 70 mW were obtained     

Multiplexing of Fiber-Optic Long-Period Grating-Based Interferometric Sensors

Two long-period gratings (LPGs) fabricated in series in an optical fiber form a Mach-Zehnder interferometer, producing a sinusoidal channelled spectrum within the characteristic LPG attenuation bands, which has the appearance of an interference fringe pattern. The phase of the fringes is sensitive to changes in the surrounding environmental parameters, such as refractive index. Fabrication of a number of identical cascaded LPG pairs with different separations produces independent fringe patterns of different frequencies within the attenuation bands. The application of basic Fourier techniques to analyze the transmission spectrum allows the phase of each fringe pattern to be determined independently, facilitating the differentiation of external effects acting on each interferometer.