Smooth Flat Surface Research Articles

Geología de la margen activa del Perú entre los 3° y 12° de latitud Sur

The Geology of the Peru Active Margin between 3 and 12° South Latitude The structure of the Andean type Peruvian margin is defined along three transverse multichannel seismic records located between 5° ans 12° S offshore Paita (CDP3), Chimbóte (CDP2) and Huacho (CDP1) from north to south. Additional data along these transects include extensive SeaBEAM and SeaMARC II surveys, dredging, and core sampling. During ODP Leg 112 the Joides Resolution drilled at 10 sites localed mainly along CDP1 (679, 680, 681, 682 and 683) and CDP2 (683, 684 and 685) transects. Results of the "Nazca Plate Project" (1972-1980) indicated that continental metamorphic rocks extend at least to the edge of the shelf and that sediment had accreted along the lower continental slope. The subsequent reprocessing of the CDP1, CDP2 and CDP3 multichannel seismic records and the bathymetric SeaBEAM survey off Paita and Chimbóte placed the boundary between continental basement and the accretionary complex along the middle slope-lower slope boundary. This boundary also marks a change in the tectonic regime from tensional upslope to compressional downslope. Seismic records CDP1 and CDP2 show an unconformity on basement below the Eocene section similar to that drilled at the Delphin and Ballena industry wells. The unconformity is inferred to be the first Incaic unconformity (67 to 57 Ma) documented onshore. During Leg 112, the Eocene section was sampled at three sites on the middle and lower slopes of the margin. At site 688, the Eocene contains a shallow marine sequence with shelf and upper slope benthic-foraminifera. This Eocene sequence (57 to 40 Ma) is cut by an unconformity along which the uppermost Eocene and Lower Oligocène (40 to 25 Ma) is missing. The unconformity corresponds to the last Incaic unconformity which extends seaward from the shelf to within 15 km of the trench axis and reaches a depth of 6.2 km below sea level. During the past 25 Ma, the minimum rate of subsidence of the outer continental margin off Huacho was 250 m. Ma1. The sedimentation of the past 25 Ma is marked by several local angular unconformities similar to that know onshore as Quechua 1 to 3 unconformities (18-19 Ma to Recent). At sites 688 and 682 on the lower slope, the basal Pliocene sequence includes finely laminated coastal upwelling facies which are restricted to deposition in water 150 to 500 m deep. Their recovery indicates 3.5 to 4 km of subsidence during the past 5-6 Ma which corresponds to a susidence rate of 675 m Ma1. This is consistent with the subsidence rate of 350 to 650 m Ma1 calculated from samples dredged upslope in the Lima basin. Seismic records CDP1 and CDP2 image and accretionary wedge stacked against the transition zone. At site 685, a hiatus of at least 4.3 Ma separates the undeformed Pleistocene slope sediment from the underlying late Miocene (6.1 to 6.8 Ma) accreted sediment that exhibits a pervasive compressional fabric. The accretionary began with the subduction to the trailing edge of the Nazca Ridge 6 Ma ago. Along records CDP3 off Paita, SeaBEAM bathymetry and additional seismic reflection records reveal mass wasting in the form of an avalanche debris on the lower slope. Two curved scarps cut the middle slope and mark slip surfaces seaward of which a 20 km by 33 km block was displaced 800 to 1000 m and back rotated 5° as it moved downslope. If this slip was catastrophic as was the avalanche debris documented downslope, a local 50 m high tsunami was generated during the past 50,000 yr. Block faulting of the middle slope area destroyed a smooth flat surface that may represent a seaward extension of a flat structure known onshore as the Tablaw. The Tablazo is of Quaternary age. The middle slope area along the CDP3 line may have, subsided as much as 3 km during the past 2 Ma at a rate of 1,500 m.Ma1. Estimates of the volume of material eroded from the Peru margin can be derived from the amount of subsidence along CDP1 and CDP3. Along CDP1 the estimated erosion during the past 5-6 Ma is 450 km3 per km along trench. Along CDP3, a more speculative value of erosion during the past 2 Ma is 300 km3 per km along trench. This yields rates of erosion-bet ween 75 and 150 km3, km1 Ma1 consistent with the 345 to 535 km3 calculated along the CDP1 line by von Huene et al. (in preparation) using the Coulomb wedge model. The lowest flux value of material removed by subcrustal erosion equal more or less the greatest flux value of sediment coming from the Nazca Plate.

Optical observations of ?junction growth? in asperities of copper, aluminium, PTFE and nylon under combined normal and tangential stresses

An experimental investigation is described in which the phenomenon of “junction growth” in model conical and spherical asperities of copper, aluminium, PTFE and nylon has been examined optically. The test asperity was first normally pressed against a smooth flat surface of soda-lime glass and the contact observed through the glass surface. In the presence of the normal load the asperity deformed plastically. When a tangential force was applied, the size of the real area of contact between the two solids, as measured in situ, was found to increase for all the asperities used. Depending upon the geometry and material of the test asperity, the increase in the size of the contact area was up to 40%. The behaviour was compared with an analytical expression for junction growth in the case of a right circular cylindrical asperity. The closest agreement between the measurements and the theory was found for the 60° conical asperities of work-hardened copper and for nylon spheres. The sliding of the asperity on the glass plate caused transfer of the material of the former to the latter. This occurred for all the asperities used. Moreover, the sliding of the metallic asperities resulted in up to ∼5 μm deep grooves on them as well as on the glass plate. These observations have also been briefly discussed.

On the significance of normal cross-sectional extension in beam theory with application to contact problems

The main features of contact problems of elastic beams are explored by considering a specific equilibrium problem of a beam in contact with a smooth rigid flat surface. Solutions of four separate linear theories, namely a general theory (G) and three others which are constructed as constrained theories are considered. These constrained theories differ from the general theory only by the degree of exclusion of one or both types of deformation usually referred to as (a) transverse normal strain and (b) transverse shear deformation. Thus, with both (a) and (b) absent, the constrained theory, corresponds to the Bernoulli-Euler beam theory (BE); with only (b) absent, the constrained theory (N) accounts for normal extensional deformation; and with only (a) absent, the constrained theory corresponds to the Timoshenko beam theory (T). Comparison of the predictions of the solutions of the three constrained theories with that of theory G shows that theory N contains the main physics of the contact problem and correctly predicts the conditions under which the beam loses contact. Also the contact force is continuous at the end points of the contact region. In contrast, neither of the other two constrained theories (BE or T) correctly predicts these features.

Selectively embedded epitaxial growth of ZnSe by low-pressure MOCVD using dimethylzinc and dimethylselenium

Selective growth of ZnSe layers embedded flatly over a ridged GaAs substrate, whose ridge-stripes are covered with SiO2 films, has been achieved by low-pressure MOCVD using dimethylzinc (DMZn) and dimethylselenium (DMSe) as source materials. When the gas pressure is less than 50 Torr and the (DMSe)/(DMZn) mole ratio is less than 6, selective area growth is realized. On the other hand, to bring about a smooth-flat surface for embedded growth requires a minimum substrate temperature of 600°C. From these results, we discuss a selective growth mechanism of ZnSe. Furthermore, a transverse mode stabilized AlGaAs/GaAs laser diode with a low threshold current of 30 mA and a high external differential quantum efficiency of 80% has been obtained by a self-aligned fabrication process using a selectively-grown ZnSe layer for injection blocking and optical confinement.

The radio power reflected from rough and undulating ionospheric surfaces

It is shown for both rough and undulating surfaces that the mean radio power reflected by the ionosphere averaged over a sufficiently long time is exactly the same as for a smooth flat surface at the same height provided the sounder is equally sensitive for echoes from all directions. When making radio wave absorption measurements under spread conditions the total integrated power over the whole time the direct echoes are being received must be used but the distance attenuation factor must be calculated from the time of arrival of the first echo.

The effect of surface roughness on the adhesion of elastic solids

This paper describes a study of the adhesion between elastic solids and the effect of roughness in reducing the adhesion. The experiments were carried out between optically smooth rubber spheres and a hard smooth flat surface of Perspex which could be roughened to various degrees. The radius of the rubber spheres was varied by a factor of 8, their elastic modulus by a factor of 10, while the centre line average (c.l.a.)of the roughened Perspex surface was varied from 0.12 to 1.5 μm. The results show that c.l.a. roughnesses which are small compared with the overall deformation occurring at the region of the rubber-Perspex contact can produce an extremely large reduction in adhesion. The effect is more marked for rubbers of higher modulus. On the other hand the curvature of the sphere (over the range examined) has little influence. For this reason and because the analytical problem of a sphere on a rough flat is extremely complicated a theoretical analysis has been developed for the simpler case of a smooth flat in contact with a rough flat surface. As in Greenwood & Williamson (1966) the rough surface is modelled by asperities all of the same radius of curvature and with heights following a Gaussian distribution of standard deviation σ. The overall contact force is obtained by applying the contact theory of Johnson, Kendall & Roberts (1971) to each individual asperity. The theory predicts that the adhesion expressed as a fraction of the maximum value depends upon a single parameter, 1/Δ e ,which is the ratio between a and the elastic displacement δ C that the tip of an asperity can sustain before it pulls off from the other surface. The analysis shows that the adhesion parameter may also be regarded as representing the statistical average of a competition between the compressive forces exerted by the higher asperities trying to prize the surfaces apart and the adhesive forces between the lower asperities trying to hold the surfaces together. Although the theory is derived for two nominally plane surfaces it is found to fit the experimental results for a sphere on a flat reasonably well.

Nuclepore Filter for the Preparation of Cytologic Diagnosis.

Recently, the filtrating method has routinely been applied to the cytodiagnosis of fluids.In this paper the Nuclepore membrane filter has been applied for cytologic study on the body fluid, urine and blood.The Nuclepore membrane filter is composed of polycarbonate film and has uniform pore of 5 microns in diameter.Cells collected on the smooth flat surface of the filter were well stained with the Papanicolaou method, PAS, various cytochemical methods such as acid and alkaline phosphatases, and also with the Giemsa stain without staining the filter itself. On the other hand, Millipore filter made of cellulose esters was stained with the Giemsa stain, and, thus found not suitable for the hematologic study by use of this stain.The advantages of this Nuclepore technique were easier handling and mounting, chemical inertness optical clarity, and high yield of cancer cells with an excellent morphologic preservation.

Laboratory study of air flowing over a smooth surface onto small water waves

This paper presents an experimental and analytical study of a two-layer shearing motion near a boundary. The two-layered flow arises when air passes from over a smooth solid flat surface onto a water surface on which small waves are traveling with the wind, but at speeds much less than that of the wind. The turbulent air motion itself generates the waves, which in turn cause a change from an aerodynamically smooth surface to a rough surface. A theoretical model involving the superposition of two distinct shear layers in the air flow, which follow the law of the wall, is proposed that represents an extension of earlier theory to include the effect of a pressure gradient in the downstream direction and the effect of a nonuniform shear stress along the wavy boundary. By using an empirical relation for the aerodynamic roughness length as a function of the average wave height and the local friction velocity, the theory can be applied to the laboratory data to estimate independently the local friction velocity and the distance from the average water surface to the junction between the two developing shearing layers. Comparison between the theoretical calculations and experimental results shows satisfactory agreement for a substantial distance downstream from the sudden change in surface roughness.