Ultrafast transient responses of optical wireless communication detectors.

In this work, fundamental ultrafast transient responses are studied for optical wireless communication (OWC) detectors. It is shown that material impulse responses, associated with transient photoconductivity, and geometrical input responses, associated with transient optical power, must be considered in tandem when OWC photodetection is pursued with broad spectral and directional characteristics. An OWC detector, composed of GaAs photoconductive gaps in a corner-cube geometry, is fabricated and analyzed. The GaAs material response times are investigated experimentally and found to range from approximately 3 ps to 200 fs for 390 nm (violet) to 780 nm (red) photoexcitation. The geometrical response times are investigated theoretically and found to range from approximately 2 to 20 ps for device dimensions from 1 to 10 mm. The overall response times manifest themselves in two distinct dimensional regimes, with differing levels of wavelength and dimension dependence. The relevance of these findings is discussed for future ultrafast OWC detectors.

Outbreak of brucellosis at a South-Australian abattoir. 2. Epidemiological investigations.

The outbreak of human brucellosis among employees of a large South Australian abattoir described previously coincided with an increase in the number of cattle showing a positive serological reaction for Brucella abortus being slaughtered. Comparisons showed that two other abattoirs in the area were slaughtering larger numbers of such cattle, but no cases of human brucellosis were diagnosed there. This suggested an additional risk at the abattoir concerned. All infected men had been employed in a particular part of the works. There was a possibility of movement of aerosols, produced on opening the uteri of pregnant cattle, to other parts of the works, putting a larger number of workers at risk of infection. Modifications to the plant greatly reduced the spread of aerosols. No cases of human brucellosis were recorded at this abattoir during the summer of 1980-81.

Outbreak of brucellosis at a South-Australian abattoir. 1. Clinical and serological findings.

During the period October 1979 to May 1980, 22 cases of acute brucellosis occurred at a South Australian abattoir. We obtained blood samples for serological investigations and culture of Brucella abortus, and tested the sera using the standard agglutination test (SAT), dithiothreitol test (DTT), anti-human globulin test (AHG) and complement fixation test (CFT). Patients showed large variations in antibody levels in each of these tests, both on presentation and after treatment. Blood culture was successful in six of 15 patients in whom it was attempted. Using the experience gained during the outbreak, we defined a set of serological criteria for the diagnosis of acute brucellosis, particularly in those who are occupationally exposed.

Passive infrared sensors: limitations on performance.

The performance of passive sensors for surveillance, radiometry, spectroscopy, astronomy is analyzed using idealizations of engineering features. Sensors are characterized by a finite number of degrees of freedom in each of two angles, wavelength, and time. An optimum number of degrees of freedom is found to sense a target field in four dimensions. Degrees of freedom are quite freely interchangeable between dimensions of different kinds. An optimum number of output states is related to the sensing or measurement requirment. An optimum weighting is found for averaging degrees of freedom into output states. Simple equations relate performance to an index of cost. Examples apply the results to estimate limits to sensor performance for several applications.