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Notes: We investigated the diffraction pattern of an acoustic beam produced by the edge of a dihedral angle. The incident beam is perpendicular to the edge, and the angular variations of the scattered field are recorded in a plane which is perpendicular to the edge. The frequency of excitation is 2.5 MHz, and the dimensions of the samples are much larger than the incident wavelength. The experimental measurements of the angular diagrams are discussed in terms of surface waves and conversion modes.

Notes: Several authors have reported a preference for the use of high palladium alloys in the construction of implant-fixed partial denture (IFPD) substructures. Heat-polymerized polymethyl methacrylate resins (PMMR) are used to secure denture teeth to IFPD substructures. Metadent (Sun Medical Co, Kyoto, Japan), a heat-polymerized PMMR containing 5% 4-methacryloxyethyl trimellitate anhydride (4-META), could possibly improve the overall design of the prosthesis because this resin adheres to resin and ceramic denture teeth and noble metals. However, adhesive bonding between Metadent and elemental palladium has been shown to be poor. The purpose of this study was to evaluate the potential for adhesive bonding between Metadent, titanate primers, and a ceramic layer pyrolytically fused to a high palladium alloy.〈section xml:id="abs1-2"〉〈title type="main"〉Materials and MethodsFive groups of 10 specimens were prepared. A layer of opaque porcelain was baked on all of the specimens under vacuum at 1760°F. The specimens were grouped as follows: (1) Metadent resin processed on ceramic with no primer, (2) Metadent resin with 10% ethyl acetoacetate titanate (DC) processed on ceramic with no primer, (3) Metadent resin with 10% DC processed to ceramic with a 2% tetraisopropyl (TPT) surface primer, (4) 4-Metadent resin with 10% DC processed to ceramic with a 2% isopropyl dimethacryloyl isostearoyl titanate (KR-7) surface primer, and (5) Metadent resin with 10% DC processed to ceramic with a titanium dioxide layer on the opaque and a KR-7 surface primer. The primers were in a methyl methacrylate (MMA) solution. All of the specimens were heat-polymerized under pressure at 212°F for 1 hour. One-half (25) of the specimens (5 from each group) were hydro-thermocycled at 4°C to 55°C, 0.5 minute dwell per bath for 3,000 cycles. All specimens were tested in shear on an MTS Universal machine at cross head speed of 0.5/mm/min.〈section xml:id="abs1-3"〉〈title type="main"〉ResultsThe results showed adhesion between the resin-ceramic layer in virtually all groups regardless of thermocycling effects. The control (heat cure without 10% DC and no primer) and the 10% DC with KR-7 and TPT primer groups had an average MPa of 7.5, 7.7, and 7.0, respectively. The failure mode of the specimens was adhesive, with the site of failure being the porcelain-metal interface〈section xml:id="abs1-4"〉〈title type="main"〉ConclusionIt was concluded that adhesion between palladium alloy and Metadent was possible when a ceramic layer was used as an intermediary interface. The limitation seemed to be the adhesion of the ceramic to the metal.

Notes: The scattering of a bounded acoustic beam by elastic infinite cylinders is investigated for oblique incidence. The nonspecular effects and the frequency analysis confirm the existence of dispersive leaky guided waves propagating along the axis of the cylinder. In the present work the nongeometrical effects and the resonance phenomena are used to measure the phase velocity dispersion curves. The experimental measurements obtained with a stainless-steel cylinder immersed in water are in good agreement with the theoretical calculations. The experiments are limited to the values of ka〈16 (k is the wave vector and a designates the radius of the cylinder).

Notes: The attenuation of Rayleigh surface waves by one- and two-dimensional rough surfaces is investigated on duraluminum and titanium samples. The root-mean-square deviation of the surface from flatness h (8.5〈h〈90 μm) satisfies the condition of validity of the perturbation theory approach ε=h/λR(very-much-less-than)1. The excitation frequencies of the transmitter vary from 2.2. to 10 MHz. Experimental results for one- and two-dimensional rough surfaces are presented and discussed. A comparison with the theoretical calculations of Eguiluz and Maradudin [Phys. Rev. B 28, 728 (1983)] confirms the F5 dependence of the attenuation α as aq(parallel)→0.

Notes: Wedge (or line) acoustic waves, propagating along the tip of an elastic wedge waveguide, are generated by pulsed YAG laser impact and detected by a wideband optical interferometer. In an ideal infinitely sharp and tall wedge guide, the antisymmetrical flexural (ASF) modes are nondispersive and their energies are mostly confined near the wedge tip. The displacement measurements with the optical probe on metallic wedges show broadband pulsed wave forms of ASF modes. Dispersive behavior of these wave forms, which are not predicted by the theoretical models, are clearly demonstrated. The dispersion curves of the phase velocity are quantitatively deduced by a phase analysis method.

Notes: In the previous paper, Cooley and Houck [1] examined the simultaneous use of common and antithetic random number streams as a variance-reduction strategy for simulation studies employing response surface methodology (RSM). Our paper supplements their work and further explores pseudorandom number assignments in response surface designs. Specifically, an alternative strategy for assigning pseudorandom numbers is proposed; this strategy is more efficient than that given by Cooley and Houck, especially when more than two factors are involved.

Notes: The reflectivity of incident longitudinal and transversal waves at the interface between two solid half-spaces is studied for different degrees of bonding. Numerical calculations based on Murty's assumptions [G. S. Murty, Geophys. J. R. Astron. Soc. 44, 388 (1976)] are compared with experimental measurements. The agreement between theory and experiments is reasonably good for RHHTT and RLL coefficients. The plots obtained for RVVTT reveal the existence of an interface wave, the theoretical angular position of which coincides with the critical angle calculated by assuming that this interface wave is a type of Rayleigh wave or interface wave, depending on the acoustical parameters.

Notes: Two lakes having similar soil types were studied to determine the effects of age and water fluctuations on plankton, benthos and fish populations. Bluff Lake is an older man-made lake which is drawn down in the mid-summer. Oktibbeha County Lake is a young lake and the water levels are maintained. Chemistry data from the two lakes indicate that their chemical properties are very similar. Neither lake would be considered very fertile.Net plankton populations in Bluff Lake and Oktibbeha County Lake were comparable when analyzed on a number of organisms per liter basis. Fluctuations of water levels did not seem to have an effect on the net plankton populations.The benthic population in Bluff Lake is slightly higher than that found in Oktibbeha County Lake. This is true for both numbers and weight per square meter. The species composition of benthic organisms in the two lakes were similar.Based on one-acre samples from each lake, Bluff Lake has a more balanced fish population than does Oktibbeha County Lake. Neither, however, seems to support populations of game fish in which a high percentage of these are in the available or harvestable range. Both lakes contain high populations of gizzard shad.

Notes: The lattice parameters, bond lengths and bond angles of Si2N2O have been determined at pressures up to 23 kbar by time-of-flight neutron diffraction. The average compressibility coefficients of the orthorhombic structure are Ka = 21 (2), Kb = 34 (2), Kc = 25 (2) and Kν = 79 (4) x 10−5 kbar−1, though the anisotropy is more pronounced at lower pressures with Ka (at zero pressure) estimated to be 10 (8) × 10–5 kbar−1. The major contribution to the compression is a cooperative rotation of adjacent SiN3O tetrahedra brought about by a decrease in the Si–O–Si bond angle. The shortening of one Si–N bond within each tetrahedron further enhances the compression, especially along the b direction.