Acoustic backscattering by Hawaiian lutjanid snappers. 1. Target strength and swimbladder characteristics

The target strengths and swimbladder morphology of six snapper species were investigated using broadband sonar, x rays, and swimbladder casts. Backscatter data were obtained using a frequency-modulated sweep (60-200 kHz) and a broadband, dolphinlike click (peak frequency 120 kHz) from live fish, mounted and rotated around each of their three axes. X rays revealed species-specific differences in the shape, size, and orientation of the swimbladders. The angle between the fish's dorsal aspect and the major axis of its swimbladder ranged from 3 degrees to 12 degrees and was consistent between individuals within a species. This angle had a one-to-one relationship with the angle at which the maximum dorsal aspect target strength was measured (r2 = 0.93), regardless of species. Maximum dorsal aspect target strength was correlated with length within species. However, the swimbladder modeled as an air-filled prolate spheroid with axes measured from the x rays of the swimbladder predicted maximum target strength significantly better than models based on fish length or swimbladder volume. For both the dorsal and lateral aspects, the prolate spheroid model's predictions were not significantly different from the measured target strengths (observed power >0.75) and were within 3 dB of the measured values. This model predicts the target strengths of all species equally well, unlike those based on length.     

The methanation activity of W(110)

The methanation activity of W(110) was measured over a range of reactant partial pressures and temperatures (P_H2 = 1–1000 Torr, P_CO = 0.1–10 Torr, T = 475–820 K). Plotting the results in an Arrhenius fashion yielded a lower apparent activation energy (E_a = 56 kJmol^?1) than previously determined for Ni(100) (E_a = 103 kJmol^?1) with an activity surpassing that of Ni at lower temperatures. The H₂ pressure dependence of the methanation activity was found to be much stronger for W(110) than for Ni(100), the surface becoming increasingly inactive at the lowest H₂ pressures investigated. Auger electron spectroscopy revealed the active catalytic surface to be carbidic in nature.     

Analysis of the transmission,reflection and noise properties of distributed feedback laser amplifiers

The transmission and reflection characteristics of distributed feedback (DFB) laser amplifiers are determined. Near the oscillation threshold of a DFB mode a relation is found between gain and bandwidth which can be used to obtain an expression for an intrinsic noise linewidth that is analogous to that found by Schawlow and Townes.     

Isotope separation involving photoinduced changes in the electric and magnetic properties of molecules and atoms

Methods of isotope separation by optically induced changes in the electro- and magneto-static properties of neutral atoms and molecules are examined. Estimates are given of the maximum beam radius and throughput.     

Rearrangement of some chlorosubstituted 3-amino-3,4-dihydro-1-hydroxycarbostyrils in hydrogen halide acids

The general conditions and results of rearrangement studies of the 5-, 6-, 7-, and 8-chloro-substituted 3-amino-3,4-dihydro-1-hydroxycarbostyrils in concentrated hydrochloric and hydro-bromic acids to the corresponding dihalosubstituted 3-amino-3,4-dihydrocarbostyrils have been described. The 5-, 7- and 8-chlorocarbostyrilhydroxamic acids undergo nucleophilic displacement by either chloride or bromide ion preferentially at the 6-position to form the respective 5,6-, 6,7- and 6,8-dihalolactams. However, with the 3-amino-6-chloro-3,4-dihydro-1-hydroxycarbo-styril where the 6-position is blocked, nucleophilic displacement by halide ions occurs at the 8-position to afford the 6,8-dihalolactams. The 6,8-dichloro- and 6,8-dibromolactams were also prepared by alternative halogenation procedures for purposes of comparison with the rearrangement products.     

Collisional relaxation of transient vibrational energy distributions in a thermal unimolecular system. The variable encounter method

A method has been developed, called the Variable Encounter Method, for the study of the relaxation of an initial vibrationally cold ensemble of molecules into a vibrationally hot distribution by a known and variable number of successive collisions with a hot wall. The theory of the experiment is presented. The system studied was the isomerization of 1,1-cyclopropane-d₂ with a fused quartz wall temperature of 800 K to 1175 K, and average number of collisions from 2.3 to 22.3. Various modified gaussian and exponential models of energy transfer were found to give agreement with the data. The average down-step size was found to decline from ≤ 3500 cm^?1 at the lowest temperature to ≈ 2500 cm^? at the highest on the basis of a gaussian model. A mathematical analysis of the relation between mean first passage times and incubation times is given. Incubation times increase from ≈ 7 to ≈ 12 collisions with increasing temperature. Transient population distributions and the sequential reaction probabilities as a function of collision number are calculated.     

An analytical expression for the H matrix relevant to Rayleigh scattering

The matrix Riemann-Hilbert problem relevant to the scattering of polarized light is solved up to the resolution of two existence questions. The solution obtained is used to establish an explicit expression for the related H matrix, and evidence that the mentioned existence questions can be answered in the affirmative is provided by a numerical evaluation of the final result.