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Is there an overriding principle of nature, hitherto overlooked, that governs all population behavior? A single principle that drives all the regimes observed in nature - exponential-like growth, saturated growth, population decline, population extinction, oscillatory behavior? In current orthodox population theory, this diverse range of population behaviors is described by many different equations - each with its own specific justification. The signature of an overriding principle would be a differential equation which, in a single statement, embraces all the panoply of regimes. A candidate such governing equation is proposed. The principle from which the equation is derived is this: The effect on the environment of a population's success is to alter that environment in a way that opposes the success., Comment: Revised equation-numbering to correspond to published version

Wigner found unreasonable the "effectiveness of mathematics in the natural sciences". But if the mathematics we use to describe nature is simply a carefully coded expression of our experience then its effectiveness is quite reasonable. Its effectiveness is built into its design. We consider group theory, the logic of symmetry. We examine the premise that symmetry is identity; that group theory encodes our experience of identification. To decide whether group theory describes the world in such an elemental way we catalogue the detailed correspondence between elements of the physical world and elements of the formalism. Providing an unequivocal match between concept and mathematical statement completes the case. It makes effectiveness appear reasonable. The case that symmetry is identity is a strong one but it is not complete. The further validation required suggests that unexpected entities might be describable by the irreducible representations of group theory.

We report the utilization of a high T/sub c/ symmetric two-hole RF-SQUID (superconducting quantum interference device) operating at liquid nitrogen temperature as a gradiometer in nondestructive testing (NDT). This technology offers a possibility of solving simultaneously four requirements: sensitivity, penetration depth, resolution, and portability of the device. We used the simple dipole model, and showed that the signal attenuation in the near zone agreed with our experimental results and is less than that of a plane wave. In our experiment we used a low frequency current of 30 Hz and demonstrated that the amplitude of the signal was reduced only by 20% after the insertion of 1" (2.54 cm) of aluminum alloy plates between the mock crack and the SQUID in agreement with the theoretical calculations. >

There is a pressure drop associated with an increase in the flow rate of a moving fluid. The venturi meter and the aspirator are familiar devices which derive from this phenomenon. This paper concerns itself with the detection of an analogous effect in the electron gas in a metal.