π-N scattering in the operator droplet model

π-N scattering is treated within the framework of the operator droplet model. We have incorporated spin dependent effects, and we calculate the differential cross section, polarization and spin rotation parameters, R and A, at infinite energy. Considerable structures in R and A have been found in contrast with the prediction of the present favourite idea of S-channel helicity conservation for high-energy scattering. The original parametrization of the fit of Byers and Yang for π⁻p → π^On is used to calculate energy dependent amplitudes in elastic πN scattering. Without any new parameters, we have obtained a good fit for total cross sections, polarization and a consistent fit for the R- and A-parameters. Further possible developments are indicated.     

Evaluation of processes used to fabricate light-emitting diodes

An evaluation of n-type and zinc-diffused GaAs wafers has been made using photoluminescence sampling techniques. These techniques, which measure both the spectral and spatial photoluminescence response of a wafer, are shown to provide a good qualification of a wafer’s luminescence properties. Surface damage and wafer inhomogeneities are clearly revealed by imaging the photoluminescence response. The relative magnitude of the photoluminescence response is found to be dependent on the various conditions used for the zinc diffusions.     

Lower bounds for the energy levels of the lithium atom

A recent modification of the intermediate hamiltonian method, intended to circumvent the problem associated with a low-lying continuum in the operator H⁰, has been applied to the lithium atom with a basis of discrete hydrogenic functions. The intended raising of the continuum occurs, but not to the extent that the beginning of the continuum is raised above the ground state of the atom; indications are that no basis of discrete hydrogenic eigenfunctions can accomplish this. Since these calculations were performed on the full lithium atom hamiltonian, they are not strictly comparable to those of Fox and Siglillito, in which a simplified hamiltonian was used.     

PLASTEX: the palermo-leeds air shower tracking experiment

Summary An experiment is described in which air shower measurement are carried out by means of a ?track detector? placed in a test location near the center of a conventional array telescope currently in use for gamma-ray astronomy. This array, consisting of scintillators (GREX, operated at Haverah Park (U.K.) by the Department of Physics of the University of Leeds), provides, in the usual way, for each shower it selects, its own estimates of shower direction and shower particle density at the test location. Estimates of the muon density at the test location are provided by a large muon detector in operation nearby. The scintillator array triggers this muon detector and it is able to provide flexibly tailored trigger signals for the track detector. This detector named PLASTEX (acronym for Palermo Leeds Air Shower Tracking Experiment), consisting of tracking chambers above and below a thin sheet of lead, designed to provide data on charged particles incident from the air, on the stopping, scattering and multiplication of these particles in the lead sheet and on charged particles created in the lead sheet by shower photons. From these data estimates are derived of the densities and directional properties of the electrons, photons and muons striking the track detector. These results are to be compared with those given by the conventional detectors and with theoretical predictions given by simulations that are being carried out. The objective is to develop and assess optimal procedures for employing clusters of PLASTEX-type detectors as telescopes for the observation of UHE cosmic rays, including cosmic gammarays, over a very wide energy range. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Micropower circuits for bidirectional wireless telemetry in neural recording applications

State-of-the art neural recording systems require electronics allowing for transcutaneous, bidirectional data transfer. As these circuits will be implanted near the brain, they must be small and low power. We have developed micropower integrated circuits for recovering clock and data signals over a transcutaneous power link. The data recovery circuit produces a digital data signal from an ac power waveform that has been amplitude modulated. We have also developed an FM transmitter with the lowest power dissipation reported for biosignal telemetry. The FM transmitter consists of a low-noise biopotential amplifier and a voltage controlled oscillator used to transmit amplified neural signals at a frequency near 433 MHz. All circuits were fabricated in a standard 0.5-microm CMOS VLSI process. The resulting chip is powered through a wireless inductive link. The power consumption of the clock and data recovery circuits is measured to be 129 microW; the power consumption of the transmitter is measured to be 465 microW when using an external surface mount inductor. Using a parasitic antenna less than 2 mm long, a received power level was measured to be -59.73 dBm at a distance of one meter.     

Adult learners' criteria for explanations

This article explores adult learners’ preferences for explanations of mathematical statements in terms of kinds of reasoning and formats of presentation. Based on data from questionnaires and interviews it is concluded thatfamiliarity andclarity influenced students’ preferences more than the format or reasoning used. A contrast between the factors influencing students’ choices and those of instructors is also reported. Implications for teaching and research are drawn from the study.     

Implementation of multichannel sensors for remote biomedical measurements in a microsystems format

A novel microelectronic "pill" has been developed for in situ studies of the gastro-intestinal tract, combining microsensors and integrated circuits with system-level integration technology. The measurement parameters include real-time remote recording of temperature, pH, conductivity, and dissolved oxygen. The unit comprises an outer biocompatible capsule encasing four microsensors, a control chip, a discrete component radio transmitter, and two silver oxide cells (the latter providing an operating time of 40 h at the rated power consumption of 12.1 mW). The sensors were fabricated on two separate silicon chips located at the front end of the capsule. The robust nature of the pill makes it adaptable for use in a variety of environments related to biomedical and industrial applications.