Line-of-sight observations at 86 GHz with a very large and a small antenna

Amplitude variations over a 12.9 km terrestrial line-of-sight path were measured simultaneously on a1400 lambdaand a29 lambdaantenna at 86.16 GHz. Clear atmosphere data from two occasions with considerably different meteorological conditions are presented. Both sets have statistical and spectral parameters in good agreement with turbulence theory. Some of the data taken after a thunderstorm front passage show a slow gain reduction of the large antenna of up to 2 dB and an increase in variance to a level above that of the small antenna. The power spectral density of these data reveals that the excess fluctuation power is in the region of the spectrum which turbulence theory predicts to be flat. It shows an approximate1/fdependence. It is attributed to refractive bending of up to0.025deg. Gain reductions due to turbulence or turbulence induced angle-of-arrival variations were estimated to be negligible.     

The association of education with coronary heart disease mortality in the USSR Lipid Research Clinics Study

There is a strong inverse association between educational attainment and coronary heart disease (CHD) mortality in men in the USSR Lipid Research Clinics (LRC) Study. Less educated men were characterized by higher mean blood pressure, high density lipoprotein cholesterol (HDL-C), cigarettes smoked and by lower mean low density lipoprotein cholesterol (LDL-C) and body mass index (BMI). With respect to nutritional variables, less educated men were characterized by higher mean energy per kg body weight and alcohol intake and by lower mean intake of fat, saturated, mono- and polyunsaturated fatty acids, cholesterol, sucrose, and other sugars. The Keys score closely predicted the differences in plasma cholesterol among the educational groups in the randomly selected sample. In men without CHD at entry, the age and clinic-adjusted relative risk for CHD mortality was 2.4 for the least educated compared with the most educated group; on adjusting for systolic blood pressure, HDL-C, LDL-C, BMI, alcohol intake and number of cigarettes, the relative risk was reduced to 1.9. These data indicate that only 22% of the twofold excess of CHD mortality associated with low education was statistically attributable to the major risk factors. The failure to explain more of the education-CHD mortality gradient in the USSR LRC cohort was similar to observations from cohort studies in Great Britain and the US. Other correlates of low education must be explored to explain the association.     

Highly reliable planar GaInAs/InP photodiodes with high yield madeby atmospheric pressure MOVPE

A process for making GaInAs/InP PIN photodiodes based on atmospheric pressure MOVPE is described. The technique gives devices with very low dark currents (≪1 nA) and capacitances (<0.2 pF). Yields on large area wafers greater than 80% can be achieved and extremely good reliability has been demonstrated (<0.4 FIT at 20°C)     

RADIOACTIVE DECAY MEASUREMENT OF SINGLE MICROPARTICLES IN THE ELECTRODYNAMIC BALANCE: EXPERIMENTAL ASPECTS

Beta particle emission associated with the radioactive decay of ¹⁴C-tagged microparticles and microdroplets has been measured by suspending a radioactive microparticle in the superposed a.c. and d.c. electrical fields of an electrodynamic balance (picobalance) and recording the rate of increase of the d.c. voltage required to balance the gravitational force. The d.c. voltage increases as the charge on the microparticle decreases due to ion transport to the collector, and the rate of change of d.c. voltage required to maintain particle suspension is a measure of the radioactive decay rate. The principles are examined and experimental results are presented to show that low levels of radioactive decay can be measured. This technique has been applied to submicrometer size and micrometer size particles of ¹⁴C-labeled dotriacon-tane and to nonradioactive microdroplets in a radioactively contaminated chamber. The parameters that govern the efficiency of the microparticle collector are elucidated. Light-scattering data obtained by suspending the microdroplet in a polarized laser beam were used to determine the size and, in conjunction with d.c. voltage data, the charge on the collector.     

Phase diversity techniques for coherent optical receivers

In the present state of the art, coherent optical receivers most often operate in the heterodyne mode. Here a photodiode-amplifier combination having bandwidth greater than twice the bit rate (B) is needed: indeed bandwidths considerably greater than2Bare preferably employed to ease design of the bandpass filter needed for noise limitation, and to avoid demodulator penalties in some modulation schemes. For the high bit rate systems now coming into service (560 Mbit/s-2.4 Gbit/s), the optical receiver design requirements become more stringent for coherent heterodyne operation. The various modes of "zero IF" operation, however, require only baseband receiver module bandwidth. The options available are either homodyne (phase locked) operation, or phase diversity (multiport) techniques. In this paper, we compare these options, and show that phase diversity techniques are capable of good performance for high bit rate coherent receivers. In phase diversity operation, not only is phase locking avoided, but also the necessary frequency locking does not have high stability requirements. Furthermore, there are advantages in operating with a small frequency offset from zero (of the order of 1 percent of the bit rate). An experimental receiver has been operated at 320 and 680 Mbit/s, demodulating both amplitude shift keying (ASK) and differential phase shift keying (DPSK). Operation with FSK is also possible. Sensitivities so far achieved of -47.5 dBm (320-Mbit/s ASK) and -42 dBm (680- Mbit/s ASK) with limited local oscillator power are capable of substantial improvement when higher power local oscillators and lower noise receive modules become available. Demodulation of DPSK at 320 Mbit/s has also been achieved and shows a measured receiver sensitivity improvement of over 4 dB over ASK at the same bit rate and local oscillator power. These practical results show clearly that phase diversity is a very realistic option for high bit rate systems.     

SpaceStation©—Computer Simulation Tool Demonstrating Biological Systems

A computer-based SpaceStation© simulation program written to introduce first-year college students to concepts in biological systems engineering was tested in two freshman engineering courses. The program modeled the interactions among a human crew, fish, microbes, and plants in a closed environment with fixed amounts of oxygen, carbon dioxide, and water. Students were asked to rebalance the system after a significant percentage of the crew left or entered the station. The experience gained through working with the simulation helped the students discuss interactions within the system. The simulation and related discussion about the project were well-received by students. Presentations made by the students demonstrated creative involvement, awareness of interactions in biological systems, and increased awareness of the profession. The simulation developed only introductory levels of design skill in the students.