A self‐similar spectral shape (the TMA spectrum) to describe wind waves in water of finite depth is presented. The parametric spectral form is depth dependent and an extension of the deep water JONSWAP spectrum. The behavior of the spectrum in frequency and wave number space is discussed. About 2800 spectra selected from three data sets (TEXEL storm, MARSEN, ARSLOE) are investigated to show the general validity of the proposal self‐similar spectral shape.

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Strong relationships among dimensionless properties of braided streams indicate that similarity is preserved in streams with the same average number of channels but of different sizes. The degree of braiding in streams, conveniently measured by the average number of channe!s bisected by lines crossing the channel. increases with the product of discharge and gradient, but decreases with higher variance in discharge. A random walk simulation model of braiding duplicates many of the numerical relationships observed in natural streams, suggesting that most of the downstream variation in the number of channels in braided streams is explainable by local fluctuations in discharge and sediment in transport, as opposed to largescale factors such as valley constriction.

Helix ␣4 of Bacillus thuringiensis Cry toxins is thought to line the lumen of the pores they form in the midgut epithelial cells of susceptible insect larvae. To define its functional role in pore formation, most of the ␣4 amino acid residues were replaced individually by a cysteine in the Cry1Aa toxin. The toxicities and pore-forming abilities of the mutated toxins were examined, respectively, by bioassays using neonate Manduca sexta larvae and by a light-scattering assay using midgut brush border membrane vesicles isolated from M. sexta. A majority of these mutants had considerably reduced toxicities and pore-forming abilities. Most mutations causing substantial or complete loss of activity map on the hydrophilic face of the helix, while most of those having little or only relatively minor effects map on its hydrophobic face. The properties of the pores formed by mutants that retain significant activity appear similar to those of the pores formed by the wild-type toxin, suggesting that mutations resulting in a loss of activity interfere mainly with pore formation.Bacillus thuringiensis is a gram-positive spore-forming bacterium that produces a variety of insecticidal toxins which accumulate as protoxins in the form of parasporal crystals. Once ingested by susceptible insect larvae, the crystals become soluble in the midgut, and the protoxins are converted to active toxins by intestinal proteases. The activated toxins act by forming pores in the midgut luminal membrane after binding to specific receptors located at the membrane surface of the intestinal epithelium columnar cells (25). These pores are large enough to disrupt the ionic gradients established across the membrane and to cause the osmotic lysis of the cells (27).The structures of several insecticidal Cry toxins have been elucidated by X-ray crystallography (4,5,13,16,19,20,24). With the exception of a recently described crystal protein of unknown toxicity (1), they all share a remarkably similar threedomain structure. Domain I is composed of a bundle of seven amphipathic ␣-helices, with helix ␣5 surrounded by the other helices. Domain II is composed of three ␤-sheets with a "Greek key" topology forming a ␤-prism, and domain III is composed of two antiparallel sheets forming a ␤-sandwich with a "jelly roll" topology. While domain I is thought to be responsible for membrane insertion and pore formation, domains II and III are thought to be involved in the binding of the toxin to its receptors (9,16,19,25,27).Receptor binding presumably triggers a conformational change in the toxin molecule that leads to its oligomerization and insertion into the membrane. According to the umbrella model of insertion, a hairpin composed of helices ␣4 and ␣5 inserts into the membrane, while the rest of the helices are deployed over the membrane surface (2,14,15,28). Results from chemical modification of preformed Cry1Aa pores in artificial membranes, using a mutant toxin possessing an aspartic acid-to-cysteine substitution at residue 136 in helix ␣4, indicated that at le...

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