Finite-amplitude interfacial waves in the presence of a current

Solutions for interfacial waves of permanent form in the presence of a current wcre obtained for small-to-moderate wave amplitudes. A weakly nonlinear approximation was used to give simple analytical solutions to second order in wave height. Numerical methods were usctl to obtain solutions for larger wave amplitudes, details are reported for a number of selected cases. A special class of finite-amplitude solutions, closely related to the well-known Stokes surface waves, were identified. Factors limiting the existence of steady solutions are examined

A note on numerical computations of large amplitude standing waves

Numerical solutions of the inviscid equations that describe standing waves of finite amplitude on deep water are reported. The calculations suggest that standing waves exist of steepness, height and energy greater than the limiting wave of Penney & Price (1952). The computed profiles are found to be consistent with Taylor's (1953) experimental observations

A new type of three-dimensional deep-water wave of permanent form

A new class of three-dimensional, deep-water gravity waves of permanent form has been found using an equation valid for weakly nonlinear waves due to Zakharov (1968). These solutions appear as bifurcations from the uniform two-dimensional wave train. The critical wave heights are given as functions of the modulation wave vector. The three-dimensional patterns may be skewed or symmetrical. An example of the skewed wave pattern is given and shown to be stable. The results become exact in the limit of very oblique modulations

The Orbital Period of the Ultraluminous X-ray Source in M82

The ultraluminous x-ray source (ULX) in the galaxy M82 has been identified as a possible intermediate-mass black hole. We have found that the x-ray flux from M82 is modulated with a peak-to-peak amplitude corresponding to an isotropic luminosity of 2.4x10^40 erg/s in M82 and a period of 62.0 +/- 2.5 days, which we interpret as the orbital period of the ULX binary. This orbital period implies that the mass-donor star must be a giant or supergiant. Large mass-transfer rates, sufficient to fuel the ULX, are expected for a giant-phase mass donor in an x-ray binary. The giant phase has a short lifetime, indicating that we see the ULX in M82 in a brief and unusual period of its evolution.Comment: 3 pages, appeared in Scienc

The payoffs to agricultural biotechnology: an assessment of the evidence

Transgenic crops are relatively new technologies being adopted rapidly in the United States and in a few other countries. The economic impacts of these technologies have, thus far, been estimated in a piecemeal fashion. The purpose of this study was to collect and characterize the economic evidence available to date, organize it, and determine if any general implications can be drawn from it. The general classes of economic impacts at the farm level are discussed. The types of studies that generate estimates of these benefits are also characterized and categorized in terms of the implications for measuring economic impacts when the set of things held constant in the type of study does not correspond to those that economic theory suggests. The evidence is presented, along with some general implications drawn from the analysis. These implications are: (1) growing transgenic cotton is likely to result in reduced pesticide use in most years and is likely to be profitable in most years in most U.S. states in the Cotton Belt, 2) Bt corn will provide a small but significant yield increase in most years across the U.S. Corn Belt, and in some years and some places the increase will be substantial, and (3) although there is some evidence of a small yield loss in the Roundup Ready soybean varieties, in most years and locations savings in pesticide costs and, possibly, tillage costs will more than offset the lost revenue from the yield discrepancy. There is not yet enough evidence to generalize even these few conclusions to other countries. More farm- level studies in more years and across more locations are required before any additional implications can be drawn. Studies that measure the non-pecuniary benefits and costs of these technologies should be undertaken, as well.Transgenic plants., Technological innovations., Agricultural research Economic aspects., Rate of return., Impact assessment,