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Surface roughness

About: Surface roughness is a(n) research topic. Over the lifetime, 70112 publication(s) have been published within this topic receiving 1084515 citation(s). The topic is also known as: roughness & texture.
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Journal ArticleDOI
Abstract: Experimental results in the published literature show that at low normal stress the shear stress required to slide one rock over another varies widely between experiments. This is because at low stress rock friction is strongly dependent on surface roughness. At high normal stress that effect is diminished and the friction is nearly independent of rock type. If the sliding surfaces are separated by gouge composed of Montmorillonite or vermiculite the friction can be very low.

3,237 citations

01 May 1994-
Abstract: 1. The atmospheric boundary layer 2. Basic equations for mean and fluctuating quantites 3. Scaling laws for mean and turbulent quantites 4. Surface roughness and local advection 5. Energy fluxes at the land surface 6. The thermally stratified ABL 7. The cloud topped boundary layer 8. ABL modelling and parameterisation schemes 9. The impact of the ABL on climate.

2,172 citations

Journal ArticleDOI
Abstract: A method is developed for interpreting the statistics of the sun’s glitter on the sea surface in terms of the statistics of the slope distribution. The method consists of two principal phases: (1) of identifying, from geometric considerations, any point on the surface with the particular slope required for the reflection of the” sun’s rays toward the observer; and (2) of interpreting the average brightness of the sea surface in the vicinity of this point in terms of the frequency with which this particular slope occurs. The computation of the probability of large (and infrequent) slopes is limited by the disappearance of the glitter into a background consisting of (1) the sunlight scattered from particles beneath the sea surface, and (2) the skylight reflected by the sea surface.The method has been applied to aerial photographs taken under carefully chosen conditions in the Hawaiian area. Winds were measured from a vessel at the time and place of the aerial photographs, and cover a range from 1 to 14 m sec−1. The effect of surface slicks, laid by the vessel, are included in the study. A two-dimensional Gram-Charlier series is fitted to the data. As a first approximation the distribution is Gaussian and isotropic with respect to direction. The mean square slope (regardless of direction) increases linearly with the wind speed, reaching a value of (tan16°)2 for a wind speed of 14 m sec−1. The ratio of the up/ downwind to the crosswind component of mean square slope varies from 1.0 to 1.9. There is some up/downwind skewness which increases with increasing wind speed. As a result the most probable slope at high winds is not zero but a few degrees, with the azimuth of ascent pointing downwind. The measured peakedness which is barely above the limit of observational error, is such as to make the probability of very large and very small slopes greater than Gaussian. The effect of oil slicks covering an area of one-quarter square mile is to reduce the mean square slopes by a factor of two or three, to eliminate skewness, but to leave peakedness unchanged.

2,094 citations

Journal ArticleDOI
TL;DR: A low-temperature vapor-assisted solution process is demonstrated to construct polycrystalline perovskite thin films with full surface coverage, small surface roughness, and grain size up to microscale, paving the way for high reproducibility of films and devices.
Abstract: Hybrid organic/inorganic perovskites (e.g., CH3NH3PbI3) as light absorbers are promising players in the field of third-generation photovoltaics. Here we demonstrate a low-temperature vapor-assisted solution process to construct polycrystalline perovskite thin films with full surface coverage, small surface roughness, and grain size up to microscale. Solar cells based on the as-prepared films achieve high power conversion efficiency of 12.1%, so far the highest efficiency based on CH3NH3PbI3 with the planar heterojunction configuration. This method provides a simple approach to perovskite film preparation and paves the way for high reproducibility of films and devices. The underlying kinetic and thermodynamic parameters regarding the perovskite film growth are discussed as well.

1,996 citations

Journal ArticleDOI
01 Sep 1991-Nature
Abstract: THE forces between colloidal particles dominate the behaviour of a great variety of materials, including paints, paper, soil, clays and (in some circumstances) cells. Here we describe the use of the atomic force microscope to measure directly the force between a planar surface and an individual colloid particle. The particle, a silica sphere of radius 3.5 µm, was attached to the force sensor in the microscope and the force between the particle and the surface was measured in solutions of sodium chloride. The measurements are consistent with the double-layer theory1,2 of colloidal forces, although at very short distances there are deviations that may be attributed to hydration forces3–6 or surface roughness, and with previous studies on macroscopic systems4–6. Similar measurements should be possible for a wide range of the particulate and fibrous materials that are often encountered in industrial contexts, provided that they can be attached to the microscope probe.

1,843 citations

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No. of papers in the topic in previous years

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Topic's top 5 most impactful authors

Bharat Bhushan

78 papers, 6.1K citations

Georgios Palasantzas

33 papers, 601 citations

Zhanqiang Liu

30 papers, 496 citations

Pradeep L. Menezes

29 papers, 754 citations

Bo N. J. Persson

28 papers, 2.1K citations