Saw-tooth Surface Research Articles

Structure of the stable and metastable ripple phase of dipalmitoylphosphatidylcholine

Dipalmitoylphosphatidylcholine (DPPC) dispersed in excess water forms a stable ripple phase upon heating from the gel phase and a metastable ripple phase Pβ′ (mst) upon cooling from the liquid crystalline phase. The X-ray diffraction pattern of Pβ′ (mst) displays several reflections in the range from 1/25 to 1/2.8 nm−1, which can all be indexed on a two-dimensional monoclinic lattice (space group p2) with a=26.2, b=8.63 nm and γ=107°. In contrast to the stable ripple phase, which shows a sawtooth like surface profile and an almost constant bilayer thickness, the electron density map of the metastable ripple phase shows an almost symmetric surface profile with a modulation length of 26.2 nm. The lipid bilayer thickness varies from 3.9 to 4.4 nm, which most likely arises from a continuous periodic change of the tilt of the chains to the surface normal of between 30 and 40 degrees. A further important feature of the structure is the staggered stacking of the bilayers with water pockets enclosed.

Lubrication of Strip Rolling in the Low-Speed Mixed Regime

An analytical model for strip rolling in the low-speed mixed lubrication regime is developed. An average Reynolds equation for longitudinal saw-tooth surfaces under conditions of high fractional contact area, is combined with an analysis for asperity flattening under conditions of bulk plastic flow, to treat lubrication in the mixed regime. Analyses for the inlet zone and work zone and the influence of pressure on viscosity are included in the model. The model indicates that hydrodynamic lubrication effects are important at much lower speeds than previously considered possible. The film thickness predicted by the model is somewhat smaller than that measured using the oil drop method in rolling aluminum alloy with a mineral oil. Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995

Low Speed Mixed Lubrication of Bulk Metal Forming Processes

Abstract A simple analysis for the lubrication of saw-tooth surfaces with longitudinal lay under conditions of high fractional contact area is developed. This is then coupled with Wilson and Sheu’s asperity flattening model to treat the mixed lubrication of a bulk metal forming process (rolling). It is shown that, even under low speed conditions where the inlet zone does not generate significant hydrodynamic pressures, relatively high hydrodynamic pressures can be generated in the work zone. This explains the persistence of hydrodynamic effects noted in low speed experiments.

A Preliminary Study of the Echo Characters and Sedimentary Processes along the Continental Margin, Northeast of Taiwan

The regional mapping of the 3.5kHz echo characters in the areas off northeastern Taiwan provided valuable information about sedimentary processes on the sea floor. Seven distinctive echo types were recognized. These echo types were grouped into four major classes: indistinct, distinct, hyperbolic and irregular echoes. Indistinct echoes had three sub-classes: prolonged, prolonged with irregular saw-toothed surface and prolonged of semiprolonged with inclined sub-bottom reflectors cropping out laterally. Besides, the hyperbolic class included the large irregular hyperbolae and the broad gently rolling hyperbolae. The irregular echoes were similar to the distinct type but with a jumbled morphology. The echo character map showed that each of the physiographic provinces was characterized by a distinctive echo type. The very prolonged echo occurring on the narrow Ilan continental shelf indicated that strong current activlties prevailed in this region. The upper part of the continental slope, characterized by large irregular hyperbola, was dominanted by slumping and/or sliding processes. Meanwhile, the turbidity currents and mass-wasting processes had apparently been the primary agents shaping the lower part of the slope as indicated by the distinct echoes.

Binocular depth from surfaces versus volumes.

Subjects were asked to compare the relative depths of two binocular targets embedded in different random dot stereogram backgrounds. The disparities of the background points were either randomized, corresponding to a scattering of points within a volume, or arranged according to a sawtooth (triangle-wave) disparity profile (i.e., a set of slanted planar surfaces separated by sharp depth discontinuities). When the targets were embedded in the random volume, their depths were perceived in accordance with their relative disparities. But when the target points were embedded in the sawtooth surfaces their depths were systematically misperceived in a manner predicted by the incorrect depth interpretation of the background points. Rather than seeing a sawtooth pattern, the background points resembled a staircase in depth, and the targets, which appeared embedded in different steps, were misjudged in depth accordingly. The effect suggests a distinction between the depth processing of isolated binocular features and those associated with continuous surfaces.

The effects of crack surface friction and roughness on crack tip stress fields

A model is presented which can be used to incorporate the effects of friction and tortuosity along crack surfaces through a constitutive law applied to the interface between opposing crack surfaces. The problem of a crack with a saw-tooth surface in an infinite medium subjected to a far-field shear stress is solved and the ratios of mode I stress intensity to mode II stress intensity are calculated for various coefficients of friction and material properties. The results show that tortuosity and friction lead to an increase in fracture loads and alter the direction of crack propagation.

Scattering from a periodic rough surface between a fluid and a solid

A rigorous theory based on the extended boundary condition method is proposed to solve the problem of diffraction from a fluid/solid interface which has periodic roughness. The extended boundary condition is derived by applying Green's theorem to the total fields and the Green's functions for the periodic surface in the fluid region and the solid region separately. A complete set of basis functions (Fourier series) is then chosen for the expansions of the unknown displacements and the tractions on the surface. The set of integral equations is reduced to simple matrix equations which are solved for the coefficients of the basis functions of the surface fields. The diffraction efficiencies of the incident plane wave from the fluid to the reflected compressional waves and the transmitted compressional and shear waves of different Floquet modes are calculated. Energy conservation is used to check the accuracy of the numerical results. The case of a lossy (viscoelastic) solid is included in the study. For experimental verification, an acrylic block was machined to have a symmetric sawtooth surface profile with a height 0.49 mm and a period 5.08 mm. The scattering from this block immersed in water is measured at 500 kHz. The diffraction efficiencies of different Floquet modes in the water are measured versus angle of incidence. Very good agreement is achieved between the theory and the experiment.

Fracture of Ni-Fe base metallic glasses

The fracture toughnesses of specimens of three transition metal base metallic glasses, Ni48Fe29P14B6Al3, Ni39Fe38P14B6Al3 and Ni49Fe29P14B6Si2 are reported. Each alloy was tested in a characteristic thickness, i.e., 25μm (Ni48), ∼ 43μm (Ni39) and ∼ 72 μm (Ni49) andK C values of ∼ 120, 62 and 30 kg mm−3/2, respectively, were observed. It is suggested that this variation is associated primarily with a transition from plane strain (K IC ≃ 30 kg mm−3/2) toward plane stress conditions as sample thickness is decreased. The fatigue crack propagation rate in the Ni39 alloy is also reported;da/dn (mm/cycle) ≃ 2×10−8 ΔK 2.25, whereΔK has units of kg mm−3/2. When the respective data are plotted in terms of (ΔK/E), whereE is Young's modulus, the crack growth behaviour for the Ni-Fe glasses approximates that for crystalline ferrous alloys. A classical chevron pattern, macroscopically at 90° to the tensile axis, is observed when amorphous metallic alloy strips fracture under plane strain conditions. On a finer scale, the chevrons exhibit a sawtooth structure, and the sawtooth surfaces show a fine scale, equi-axed vein pattern. This indicates that local failure occurs by shear rupture.

Theory of the photo-emf in semiconductors with a sawtooth surface

The photo-diffusion emf in thin semiconductor slabs with sawtoothshaped surface is calculated for arbitrary surface- and volume-recombination speeds.

On the mechanical testing of thermoelectric modules

Computer simulation predicts that horizontal size segregation can be obtained in a vertically vibrated layer of granular material. This behavior is a consequence of two distinct phenomena that are unique to excited granular media: vibration which causes the large grains to rise to the top of the layer, and a vibrating base with a sawtooth surface profile which can produce stratified flows in opposite directions at different heights within the layer. The result of combining these effects is that large and small grains are horizontally driven in opposite directions.