Optimizing subcarrier-multiplexed WDM transmission links

We present an analytic approach to optimizing the information capacity of a subcarrier-multiplexed wavelength-division-multiplexed optical communication link. Receiver and relative-intensity noise, clipping distortion, and crosstalk between wavelength channels due to optical nonlinearities in the fiber are the signal impairments considered.     

Integrated learning: explicit strategies and their role in problem-solving instruction for students with learning disabilities

This study investigated the effectiveness of an explicit strategy as a means of linking facts, concepts, and problem solving in an unfamiliar domain of learning. Participants were 37 secondary students with learning disabilities. All students were taught health facts and concepts, which they then applied to problem-solving exercises presented through computer-simulation games. Students in the experimental group were taught an explicit strategy for solving the problems; the comparison group was given supportive feedback and encouraged to induce their own strategies. The explicit strategy group performed significantly better on two transfer measures, including videotaped problem-solving exercises.     

Estimation of maprotiline in serum by gas-chromatography, with use of a nitrogen-specific detector

We describe a gas-chromatographic procedure for estimating therapeutic concentrations of maprotiline, a new tetracyclic antidepressant, in serum by use of a nitrogen-specific detector. Desmethyldoxepin, a secondary amine similar in structure to maprotiline, is added as a mass internal standard to the specimen before extraction, to obviate the need for accurate measurements of volumes during extraction and analysis. Both maprotiline and the internal standard are converted to acetyl derivatives, to avoid the adsorption of secondary amines on the column. A highly selective liquid phase is used, which allows a very good separation of desmethyldoxepin, maprotiline, desmethylmaprotiline, and the interferences from serum and reagents.     

A discussion of the calculation of forces in the one-dimensional finite difference model of Hashmi and Thompson[1]

An examination is made of the one-dimensional finite difference method developed by Hashmi and Thompson[1] for the problem of projectile mushrooming, in order to establish the best method of calculating the force in an element. Although the degree of error is dependent on geometry, a solution which is generally nearly optimal is identified and comparisons are made with published experimental data.     

The interrelation of failure modes observed in the penetration of metallic targets

Three of the main modes of failure observed in the penetration of metallic armour are classified as ductile failure, adiabatic shear plugging and discing. It is demonstrated that a change from ductile modes of failure to those which involve adiabatic shearing or discing can be understood in terms of the work done to penetrate a target. Adiabatic shearing is possible if the rate of thermal softening exceeds the rate of work hardening of the target material. In adiabatic shear failure, where several shear bands propagate independently towards the rear of the target, intersection of one band with the rear surface may lead to asymmetry in the deformation. Asymmetric conditions do not favour further propagation of adiabatic shear bands and failure can be completed by discing and/or ductile tearing giving a mixed mode of failure. Discing is accentuated if the target plate shows relatively low toughness particularly in the through thickness orientation. Other studies have shown that the fractures associated with discing may be produced by shearing in the plane of the plate, and it is demonstrated that discing is more likely when fracture occurs on a number of parallel planes.     

Temporal dynamics of repetitions during the early stage of childhood stuttering: an acoustic study

The purpose of this study was to compare duration characteristics of single-syllable whole-word repetitions (with one and two repeated units) and part-word repetitions (with one repeated unit) in the speech of preschool children who stutter (N = 20) recorded near the onset of their stuttering to those of control nonstuttering children (N = 20). Disfluent episodes were identified in audiotape recordings of the subjects' conversational speech. The digitized signals were analyzed by means of the CSpeech computer software (Milenkovic, 1987). Using visual displays of sound spectrograms, the durations of the spoken repetition unit(s), the silent interval(s) between the units, and the total disfluency were measured. The stutters exhibited shorter silent intervals between spoken repetition units. The duration of the spoken repetition units was very similar for the two groups of children. The total duration of the stutterers' disfluencies was significantly shorter because of their shorter silent intervals when compared to disfluencies of equal repetition units produced by the control subjects. Statistical analysis revealed that silent interval duration was capable of differentiating stuttering from normally fluent children with 72-87% accuracy, dependent upon the disfluency type. To the degree that the groups of subjects represented random samples of the two specified populations from which they were drawn, there appears to be an overall tendency for repetitions during the early stage of stuttering to be produced at a faster rate than repetitions produced by nonstuttering children.     

Short-wavelength color visual fields in glaucoma suspects at risk

Glaucoma suspect eyes were seen during a five-year study on color visual fields that used a 440-nm test on a bright-yellow background (96 normal eyes, 55 suspect eyes, and 110 eyes that developed glaucoma). The predictive ability of the test was assessed in 25 eyes followed up for more than one year, five of which developed glaucoma. These five eyes and those at high risk showed higher mean defect (P < .0001) and number of defective points (P < .0001) than the other suspect groups, which were not significantly different from normal eyes. The mean defects (+/- standard deviations) and average number of defective points were 1.4 +/- 2.3 dB with 8.9 points (low-risk eyes), 1.1 +/- 1.2 dB with 8.0 points (medium-risk eyes), 6.7 +/- 2.8 dB with 27.7 points (high-risk eyes), and 9.3 +/- 1.8 dB with 39.4 points (eyes that developed glaucoma). Normal eyes had an average of 3.4 defective points. These results were similar when all 55 suspect eyes were analyzed. Color visual fields identify early functional loss in eyes at greatest risk for primary open-angle glaucoma.