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This article discusses the design and measurement of high temperature superconductor transimpedance amplifiers using bi-crystal junction SQUID arrays. The peak to peak modulation voltages of the arrays as a function of their SQUID inductance were measured. The measured transresistance, dV/sub o//dI/sub i/, of a 30-element array of 5-pH SQUIDs was 4 V/A. The voltage modulation depth of the 30-element array was 2 mV and the white noise of the array was 1.0 nV/Hz/sup 1/2/ at 100 kHz. The dynamic range of the array was 120 dB in a one hertz bandwidth. This device has the potential to be used as a broadband amplifier for low impedance sources.

Mahogany (Swietenia macrophylla King) regenerates in areas of erosion on high terraces and in forest killed by flooding and deposition of alluvial sediments in the Chimanes Forest, Bolivia. These hydrological disturbances are patchy, and only one of five stands of mahogany that we inventoried was regenerating. Mahogany survives these disturbances significantly better than the common tree species. The long time between disturbances appears to favour late maturation. Mahogany trees allocate little photosynthates to reproduction until they are very large emergents, at least 80 cm in diameter. The episodic nature of the regeneration sites means that mahogany stands are composed of one or a few cohorts, which are vulnerable to overharvesting, particularly with the current use of a minimum cutting diameter to regulate harvest. The delayed onset of fecundity means that the small trees that escape harvest are not very fecund, resulting in minimal seed input to logged forest. Only 7–9% of the gaps created by logging contain natural regeneration after 20 + yr. A successful management plan for mahogany would entail a monocyclic harvest, with a rotation age of 100 + years, the estimated time that it takes for trees to achieve commercial size in natural forest. Since the number of seed trees that will be left is small, they should be concentrated in sites that are likely to be conducive to natural regeneration, such as near rivers and flood damaged forest. Seed production will be maximized for a given basal area (opportunity cost to loggers) if trees c. 110 cm dbh are selected as seed trees. The mahogany stocks in the Chimanes Forest are nearly exhausted, but the findings of this study could be used to help rebuild the mahogany populations, or to design management plans for the commercial species that have similar ecologies to mahogany.

Mahogany (Swietenia macrophyllaKing) regenerates in areas of erosion on high terraces and in forest killed by flooding and deposition of alluvial sediments in the Chimanes Forest, Bolivia. These hydrological disturbances are patchy, and only one of five stands of mahogany that we inventoried was regenerating. Mahogany survives these disturbances significantly better than the common tree species. The long time between disturbances appears to favour late maturation. Mahogany trees allocate little photosynthates to reproduction until they are very large emergents, at least 80 cm in diameter. The episodic nature of the regeneration sites means that mahogany stands are composed of one or a few cohorts, which are vulnerable to overharvesting, particularly with the current use of a minimum cutting diameter to regulate harvest. The delayed onset of fecundity means that the small trees that escape harvest are not very fecund, resulting in minimal seed input to logged forest. Only 7–9% of the gaps created by logging contain natural regeneration after 20+ yr. A successful management plan for mahogany would entail a monocyclic harvest, with a rotation age of 100+ years, the estimated time that it takes for trees to achieve commercial size in natural forest. Since the number of seed trees that will be left is small, they should be concentrated in sites that are likely to be conducive to natural regeneration, such as near rivers and flood damaged forest. Seed production will be maximized for a given basal area (opportunity cost to loggers) if treesc. 110 cm dbh are selected as seed trees. The mahogany stocks in the Chimanes Forest are nearly exhausted, but the findings of this study could be used to help rebuild the mahogany populations, or to design management plans for the commercial species that have similar ecologies to mahogany.

We measured the V-/spl Phi/ of 100-element SQUID arrays and compared them to simulations. Two SQUID inductances, 13 pH and 5 pH were studied. The change of voltage modulation depth per /spl Phi//sub 0/ in a 5 pH SQUID array was faster than that in a 13 pH SQUID array due to larger effective area variations. The effect of magnetic field uniformity on the SQUID arrays output was also studied. We found that a non-uniform magnetic field had the effect of reducing the output voltage and periodicity in V-/spl Phi/ for a SQUID array with high flux bias. >

A 7104-element serially connected SQUID array magnetometer has been designed and tested. The array had a measured magnetic field to voltage transfer function dV/dB of 1.2/spl times/10/sup 5/ volt/Tesla and a peak to peak modulation voltage of 0.6 volt. The sensitivity of the array magnetometer is 105 fT/Hz/sup 1/2/ at 20 kHz, and is limited by the 1/f noise of SQUIDs. The effective signal collection area of the array is 0.018 cm/sup 2/. The measured dynamic range of the array is 126 dB.

This paper concerns the exploitative competition of two predators for two prey species. We analyze the model proposed by MacArthur with more general parameters. MacArthur used the model to address questions of species packing on resources, but he did not completely determine analytically under what conditions will neither, one, or both predator species and one or both prey species, survive. Our analysis is global for all cases except one, for which we performed a numerical analysis. We conclude that the behavior of this predator-prey system is more complicated than previously thought. In particular, we analyze cases in which the two-predator, two-prey system catastrophically collapses to a one-predator, two-prey system, or even to one-predator, one-prey system. We also show that there are cases in which the initial numbers of the two predators determine the pattern of this collapse. These conclusions suggest that caution should be exercised in interpreting any conclusions of species packing that are based solely upon a graphical analysis of the MacArthur model.