Modeling surface roughness scattering in metallic nanowires
Moors, Kristof; Sorée, Bart; Magnus, Wim
2015-09-28
Ando's model provides a rigorous quantum-mechanical framework for electron-surface roughness scattering, based on the detailed roughness structure. We apply this method to metallic nanowires and improve the model introducing surface roughness distribution functions on a finite domain with analytical expressions for the average surface roughness matrix elements. This approach is valid for any roughness size and extends beyond the commonly used Prange-Nee approximation. The resistivity scaling is obtained from the self-consistent relaxation time solution of the Boltzmann transport equation and is compared to Prange-Nee's approach and other known methods. The results show that a substantial drop in resistivity can be obtained for certain diameters by achieving a large momentum gap between Fermi level states with positive and negative momentum in the transport direction.
Surface roughness scattering in multisubband accumulation layers
NASA Astrophysics Data System (ADS)
Fu, Han; Reich, K. V.; Shklovskii, B. I.
2016-06-01
Accumulation layers with very large concentrations of electrons where many subbands are filled became recently available due to ionic liquid and other new methods of gating. The low-temperature mobility in such layers is limited by the surface roughness scattering. However, theories of roughness scattering so far dealt only with the small-density single subband two-dimensional electron gas (2DEG). Here we develop a theory of roughness-scattering limited mobility for the multisubband large concentration case. We show that with growing 2D electron concentration n the surface dimensionless conductivity σ /(2 e2/h ) first decreases as ∝n-6 /5 and then saturates as ˜(d aB/Δ2)≫1 , where d and Δ are the characteristic length and height of the surface roughness and aB is the effective Bohr radius. This means that in spite of the shrinkage of the 2DEG thickness and the related increase of the scattering rate the 2DEG remains a good metal.
Scattering of light by molecules over a rough surface.
Long, Maureen; Khine, Michelle; Kim, Arnold D
2010-05-01
We present a theory for the multiple scattering of light by obstacles situated over a rough surface. This problem is important for applications in biological and chemical sensors. To keep the formulation of this theory simple, we study scalar waves. This theory requires knowledge of the scattering operator (t-matrix) for each of the obstacles as well as the reflection operator for the rough surface. The scattering operator gives the field scattered by the obstacle due to an exciting field incident on the scatterer. The reflection operator gives the field reflected by the rough surface due to an exciting field incident on the rough surface. We apply this general theory for the special case of point scatterers and a slightly rough surface with homogeneous Dirichlet and Neumann boundary conditions. We show examples that demonstrate the utility of this theory. PMID:20448766
Electromagnetic scattering and depolarization across rough surfaces: Full wave analysis
NASA Astrophysics Data System (ADS)
Bahar, Ezekiel; Huang, Guorong; Lee, Bom Son
1995-05-01
Full wave solutions are derived for vertically and horizontally polarized waves diffusely scattered across an interface that is two-dimensionally rough separating two different propagating media. Since the normal to the rough surface is not restricted to the reference plane of incidence, the waves are depolarized upon scattering; and the single scattered radiation fields are expressed as integrals of a surface element transmission scattering matrix that also accounts for coupling between the vertically and horizontally polarized waves. The integrations are over the rough surface area as well as the complete two-dimensional wave spectra of the radiation fields. The full wave solutions satisfy the duality and reciprocity relationships in electromagnetic theory, and the surface element scattering matrix is invariant to coordinate transformations. It is shown that in the high-frequency limit the full wave solutions reduce to the physical optics solutions, while in the low-frequency limit (for small mean square heights and slopes) the full wave solutions reduce to Rice's (1951) small perturbation solutions. Thus, the full wave solution accounts for specular point scattering as well as diffuse, Bragg-type scattering in a unified, self-consistent manner. It is therefore not necessary to use hybrid, perturbation and physical optics approaches (based on two-scale models of composite surfaces with large and small roughness scales) to determine the like- and cross-polarized fields scattered across the rough surface.
Surface roughness scattering of electrons in bulk mosfets
Zuverink, Amanda Renee
2015-11-01
Surface-roughness scattering of electrons at the Si-SiO_{2} interface is a very important consideration when analyzing Si metal-oxide-semiconductor field-effect transistors (MOSFETs). Scattering reduces the mobility of the electrons and degrades the device performance. 250-nm and 50-nm bulk MOSFETs were simulated with varying device parameters and mesh sizes in order to compare the effects of surface-roughness scattering in multiple devices. The simulation framework includes the ensemble Monte Carlo method used to solve the Boltzmann transport equation coupled with a successive over-relaxation method used to solve the two-dimensional Poisson's equation. Four methods for simulating the surface-roughness scattering of electrons were implemented on both devices and compared: the constant specularity parameter, the momentum-dependent specularity parameter, and the real-space-roughness method with both uniform and varying electric fields. The specularity parameter is the probability of an electron scattering speculariy from a rough surface. It can be chosen as a constant, characterizing partially diffuse scattering of all electrons from the surface the same way, or it can be momentum dependent, where the size of rms roughness and the normal component of the electron wave number determine the probability of electron-momentum randomization. The real-space rough surface method uses the rms roughness height and correlation length of an actual MOSFET to simulate a rough interface. Due to their charge, electrons scatter from the electric field and not directly from the surface. If the electric field is kept uniform, the electrons do not perceive the roughness and scatter as if from a at surface. However, if the field is allowed to vary, the electrons scatter from the varying electric field as they would in a MOSFET. These methods were implemented for both the 50-nm and 250-nm MOSFETs, and using the rms roughness heights and correlation lengths for real devices. The
Full Wave Single and Double Scatter from Rough Surfaces
NASA Astrophysics Data System (ADS)
Bahar, E.; El-Shenawee, M.
1994-12-01
Using the full wave approach, the single and double scattered electromagnetic fields from deterministic one-dimensional rough surfaces are computed. Full wave expressions for the single and double scattered far fields are given in terms of multidimensional integrals. These integrals are evaluated using the Cornell National Supercomputer IBM/3090. Applying the steepest descent approximation to the double scattered field expressions, the dimensions of the integrals are reduced from four to two in the case of one-dimensional rough surfaces. It is shown that double scatter in the backward direction is significant for near normal incidence when the rough surface is highly conducting and its mean square slope is very large. Even for one-dimensional rough surfaces, depolarization occurs when the reference plane of incidence is not parallel to the local planes of incidence and scatter. A geometrical optics approximation is used to interpret the results of the double scattered fields for normal incidence near backscatter. The physical interpretation of the results could shed light on the observed fluctuations in the enhanced backscatter phenomenon as the angle of incidence increases from near normal to grazing angles. The results show that double scatter strongly depends upon the mean square slope, the conductivity of the rough surface and the angle of incidence.
Depolarization of Light Scattered from Rough Cylindrical Surfaces
NASA Astrophysics Data System (ADS)
Aparicio, R.; Quintián, F. Perez; Rebollo, M. A.
2008-04-01
In this work we study the state of polarization of light scattered from rough cylindrical surfaces. The experimental results show that the amount of cross-polarized light at a particular observation angle is correlated with the roughness of the cylinders. We compare these results with those obtained using the Kirchhoff's vector theory and analyze if the differences can be modeled on multiple-scattering effects.
Scattering from a rough surface in presence of atmospheric turbulence
NASA Astrophysics Data System (ADS)
Basu, Santasri; Hyde, Milo W.; McCrae, Jack E.; Fiorino, Steven T.
2013-05-01
A Gaussian Schell Model (GSM) might be a convenient way to model extended beacons created on diffuse targets. Earlier, we used a full wave computational technique called the Method of Moments (MoM) to evaluate the scattered field from a rough impedance surface in vacuum. The MoM model showed several deviations from GSM. The present work uses a simulation approach based on physical optics approximation to study the scattering behavior in presence of atmospheric turbulence. A fully coherent beam is propagated through weak turbulence and is incident on the rough surface. The light scattered from the rough surface is again propagated through turbulence back to the source plane and the properties of the scattered radiation are studied through numerical simulations. The simulation results are compared with a GSM.
Speckle size of light scattered from slightly rough cylindrical surfaces
NASA Astrophysics Data System (ADS)
Berlasso, Ricardo G.; Quintian, Fernando Perez; Rebollo, Maria A.; Gaggioli, Nestor G.; Brea, Luis Miguel Sanchez; Martinez, Eusebio Bernabeu
2002-04-01
This research is an extension of the optical method of quality control presented in a previous paper [Appl. Opt. 39, 5811 (2000)] to the case of slightly rough cylindrical surfaces. Applying the Kirchhoff scalar diffraction theory yields an analytical expression of the autocorrelation function of the intensity scattered from slightly rough cylindrical surfaces. This function, which is related to speckle size and shape, is shown to depend on the surface correlation length, unlike for plane surfaces for which the speckle depends on the illuminated area only. The theoretical expression is compared with that for the speckle produced by the light scattered from a cylindrical bearing and from various high-quality wires, showing that the method allows the correlation lengths of high-quality cylindrical surfaces to be determined.
Rough surface scattering from moving ocean surfaces as an indicator of scattering mechanisms
NASA Technical Reports Server (NTRS)
Rodriguez, Ernesto; Kim, Yunjin
1993-01-01
Ever since Crombie used the Doppler spectrum of RF signals scattered from the ocean surface to provide conclusive evidence for Bragg resonant scattering, scattering from the ocean surface has served as a testing ground for the identification of governing scattering mechanisms in rough surface scattering. The moving ocean surface has the advantage for rough surface scattering that, being a dispersive medium, features with different spatial scales the tendency to travel at different speeds. Thus, by looking at the temporal signature of the scattered field, one can try to isolate the scattering mechanism. This feature has been exploited by various authors. To give a recent example, we cite the work of Plant, who examined the Doppler spectrum of the return signal to infer the presence of two-scale scattering in scattering at medium incidence angles. The problem with restricting oneself to the examination of the Doppler spectrum, as has been done traditionally, is that one restricts the phenomena under investigation to temporally homogeneous phenomena: transient phenomena, which are localized in time, are not localized in frequency space. There is increasing evidence that this type of phenomena, due to specular scattering or breaking waves, may also play an important role in determining the scattering mechanism in ocean-like surfaces. To overcome this problem, we introduce the use of the Wavelet Transform to study the frequency-temporal signatures of the scattered field from moving ocean waves. We calculate this signature using various analytic scattering theories and show that the Wavelet Transform provides a useful tool for separating the different scattering mechanisms operating in scattering in ocean-like surfaces. Next we simulate realistic nonlinear moving ocean waves and calculate the temporal scattered field signature by using the method of moments and the stop-start approximation: the surface is assumed stationary during a scattering event, but moves between
NASA Technical Reports Server (NTRS)
Fung, A. K.; Eom, H. J.
1983-01-01
A combination of the standard Kirchhoff method for rough surface scattering with the Rayleigh phase function radiative transfer method for volume scattering is employed in the present study of the effect of surface roughness on the polarization of the scattered field. It is found that for pure surface scattering, the polarization ratio between zero and 20 deg incidence angles is sensitive to surface roughness change. When both surface and volume scattering are present, however, copolarization nulls by colatitude or degree of polarization at zero to 15 deg incidence angle, and copolarization or crosspolarization nulls by longitude at large incidence angles, are better indicators of surface roughness changes. It is noted that degree of polarization and copolarization nulls by colatitude vary monotonously with incidence angle, while in combined surface and volume scattering these have, respectively, a minimum and a maximum. This characteristic allows the separation of combined surface and volume scattering from pure surface or volume scattering.
The phenomenon of simplified scattering from rough surfaces to reflection in fractional space
NASA Astrophysics Data System (ADS)
Safdari, Hadiseh; Vahabi, Mahsa; Jafari, Gholamreza
2015-11-01
In this paper, the scattering of incident plane waves from rough surfaces has been modeled in a fractional space. It is shown how wave scattering from a rough surface could correspond to a simple reflection problem in a fractional space. In an integer dimensional space, fluctuations of the surface result in wave scattering, while in the fractional space, these fluctuations are compensated by the geometry of space. In the fractional space, reflection is equivalent to scattering from the integer dimensional space. Comparing scattered wave functions from different self-affine rough surfaces in the framework of the Kirchhoff theory with the results from the fractional space, we see good agreement between them.
NASA Astrophysics Data System (ADS)
Arbab, M. H.; Winebrenner, D. P.; Thorsos, E. I.; Chen, A.
2010-11-01
Scattering of terahertz waves by surface roughness can obscure spectral signatures of chemicals at these frequencies. We demonstrate this effect using controlled levels of surface scattering on α-lactose monohydrate pellets. Furthermore, we show an implementation of wavelet methods that can retrieve terahertz spectral information from rough surface targets. We use a multiresolution analysis of the rough-surface-scattered signal utilizing the maximal overlap discrete wavelet transform (MODWT) to extract the resonant signature of lactose. We present a periodic extension technique to circumvent the circular boundary conditions of MODWT, which can be robustly used in an automated terahertz stand-off detection device.
Surface enhanced Raman scattering in electrochemical systems: The complex roles of surface roughness
NASA Astrophysics Data System (ADS)
Pemberton, Jeanne E.; Guy, Anita L.; Sobocinski, Raymond L.; Tuschel, David D.; Cross, Nathan A.
1988-06-01
A series of experiments designed to elucidate the presence and properties of large-scale and atomic-scale roughness produced on Ag electrodes with electrochemical oxidation-reduction cycle (ORC) pretreatments are presented. This report reviews surface enhanced Raman scattering (SERS) and scanning electron microscopic (SEM) characterization of Ag electrodes roughened with controlled-rate ORCs, and presents new results for the laser-induced thermal decay of SERS as a probe of Ag surface active sites and differential reflectance spectroscopy of electrochemically roughened Ag electrodes. These results are interpreted in terms of the presence and properties of both large-scale and atomic-scale roughness on these surfaces.
An iterative analytic—numerical method for scattering from a target buried beneath a rough surface
NASA Astrophysics Data System (ADS)
Xu, Run-Wen; Guo, Li-Xin; Wang, Rui
2014-11-01
An efficiently iterative analytical—numerical method is proposed for two-dimensional (2D) electromagnetic scattering from a perfectly electric conducting (PEC) target buried under a dielectric rough surface. The basic idea is to employ the Kirchhoff approximation (KA) to accelerate the boundary integral method (BIM). Below the rough surface, an iterative system is designed between the rough surface and the target. The KA is used to simulate the initial field on the rough surface based on the Fresnel theory, while the target is analyzed by the boundary integral method to obtain a precise result. The fields between the rough surface and the target can be linked by the boundary integral equations below the rough surface. The technique presented here is highly efficient in terms of computational memory, time, and versatility. Numerical simulations of two typical models are carried out to validate the method.
On high-frequency radiation scattering sensitivity to surface roughness in particulate media
NASA Astrophysics Data System (ADS)
Zohdi, T. I.
2016-06-01
This paper analyzes the sensitivity of high-frequency radiation scattering in particulate media, to particle surface roughness. Ray-tracing theory and computation are employed. Since the magnitude of the Poynting vector ray, the irradiance, is the appropriate quantity to be tracked, the behavior of the reflectance, which controls the ratio of the reflected and incident Poynting vector magnitudes, is of primary concern. The reflectance is a highly nonlinear function of the refractive indices and angle of incidence. The present work first addresses the relationship between a single scatterer's sensitivity to its surface roughness and then the response of a large number of scatterers to the surface roughness. The analysis indicates that, for a single scatterer, the sensitivity of the response to roughness decreases, up to a point, and then increases again, i.e., it is nonmonotone. However, for a system of multiple scatterers, this effect vanishes, due to multiple internal reflections which dominate the overall response characteristics. While it was relatively straightforward to compute the overall sensitivity of a single scattering body, for example a sphere, when multiple reflecting bodies are considered, numerical simulations are necessary because the reflected rays from one "rough" body will, in turn, be reflected to another "rough" body, etc. Examples are given for a system of randomly distributed scatterers.
NASA Astrophysics Data System (ADS)
Yang, Chao; Guo, Li-Xin; Wu, Zhen-Sen
2010-05-01
This paper is devoted to the study of polarization properties, scattering properties and propagation properties of global positioning system (GPS) scattering signal over the rough sea surface. To investigate the polarization and the scattering properties, the scattering field and the bistatic scattering coefficient of modified Kirchhoff approximation using the tapered incident wave is derived in detail. In modeling the propagation properties of the GPS scattering signal in the evaporation duct, the initial field of parabolic equation traditionally computed by the antenna pattern using fast Fourier transform (FFT) is replaced by the GPS scattering field. And the propagation properties of the GPS scattering signal in the evaporation duct with different evaporation duct heights and elevation angles of GPS are discussed by the improved discrete mixed Fourier transform taking into account the sea surface roughness.
Grynko, Yevgen; Shkuratov, Yuriy; Förstner, Jens
2016-08-01
We simulate light scattering by random irregular particles that have dimensions much larger than the wavelength of incident light at the size parameter of X=200 using the discontinuous Galerkin time domain method. A comparison of the DGTD solution for smoothly faceted particles with that obtained with a geometric optics model shows good agreement for the scattering angle curves of intensity and polarization. If a wavelength-scale surface roughness is introduced, diffuse scattering at rough interface results in smooth and featureless curves for all scattering matrix elements which is consistent with the laboratory measurements of real samples. PMID:27472601
Interference between magnetism and surface roughness in coherent soft X-ray scattering
Rahmim, A.; Tixier, S.; Tiedje, T.; Eisebitt, S.; Lorgen, M.; Scherer, R.; Eberhardt, W.; Luning, J.; Scholl, A.
2002-06-15
In coherent soft x-ray scattering from magnetically ordered surfaces there are contributions to the scattering from the magnetic domains, from the surface roughness, and from the diffraction associated with the pinhole aperture used as a coherence filter. In the present work, we explore the interplay between these contributions by analyzing speckle patterns in diffusely scattered x rays from the surface of magnetic thin films. Magnetic contrast from the surface of anti ferro magnetically ordered LaFeO3 films is caused by magnetic linear dichroism in resonant x-ray scattering. The samples studied possess two types of domains with their magnetic orientations perpendicular to each other. By tuning the x-ray energy from one of the two Fe-L3 resonant absorption peaks to the other, the relative amplitudes of the x-ray scattering from the two domains is inverted which results in speckle pattern changes. A theoretical expression is derived for the intensity correlation between the speckle patterns with the magnetic contrast inverted and not inverted. The model is found to be in good agreement with the x-ray-scattering observations and independent measurements of the surface roughness. An analytical expression for the correlation function gives an explicit relation between the change in the speckle pattern and the roughness, and magnetic and aperture scattering. Changes in the speckle pattern are shown to arise from beating of magnetic scattering with the roughness scattering and diffraction from the aperture. The largest effect is found when the surface roughness scatter is comparable in intensity to the magnetic scatter.
Scattering of surface plasmon-polaritons and volume waves by a rough gold film.
Sterligov, V A; Grytsaienko, I A; Men, Y
2016-08-15
A discrepancy between the theories of volume and surface plasmon-polaritons (SPPs) wave scattering was found. Its tentative explanation is related to the resonance-like emission of SPPs energy due to SPPs diffraction by a surface relief Fourier decomposition component. It was also shown that the sum of surface wave scattered intensity along a plane of incidence is proportional to surface roughness value. PMID:27519069
Fluctuation correlation of the scattered intensity from two-dimensional rough surfaces.
Zhang, Geng; Wu, Zhensen
2012-01-16
The fourth-order moment of the scattered light, namely, the correlation function of the scattered intensity fluctuation from two-dimensional optically weak homogeneous and isotropic rough surfaces obeying Gaussian distribution are investigated based on Beckmann theory and Gaussian moment theorem. Analytical and numerical results are given for the correlation functions of the scattered intensity fluctuation. Also two important special cases, two-frequency correlation and angular correlation, are discussed, as well as the influence of the incident and observation conditions and the characteristic parameters of the rough surfaces on the correlation function which could lead to a more clear understanding of the scattering property of the rough surface and provide a theoretical basis for the 3D target recognition. PMID:22274493
NASA Astrophysics Data System (ADS)
Shi, F.; Lowe, M. J. S.; Xi, X.; Craster, R. V.
2016-07-01
We develop an elastodynamic theory to predict the diffuse scattered field of elastic waves by randomly rough surfaces, for the first time, with the aid of the Kirchhoff approximation (KA). Analytical expressions are derived incorporating surface statistics, to represent the expectation of the angular distribution of the diffuse intensity for different modes. The analytical solutions are successfully verified with numerical Monte Carlo simulations, and also validated by comparison with experiments. We then apply the theory to quantitatively investigate the effects of the roughness and the shear-to-compressional wave speed ratio on the mode conversion and the scattering intensity, from low to high roughness within the valid region of KA. Both the direct and the mode converted intensities are significantly affected by the roughness, which leads to distinct scattering patterns for different wave modes. The mode conversion effect is very strong around the specular angle and it is found to increase as the surface appears to be more rough. In addition, the 3D roughness induced coupling between the out-of-plane shear horizontal (SH) mode and the in-plane modes is studied. The intensity of the SH mode is shown to be very sensitive to the out-of-plane correlation length, being influenced more by this than by the RMS value of the roughness. However, it is found that the depolarization pattern for the diffuse field is independent of the actual value of the roughness.
Scattering of electromagnetic waves from a periodic surface with random roughness
NASA Technical Reports Server (NTRS)
Yueh, H. A.; Shin, R. T.; Kong, J. A.
1988-01-01
Equations for the scattering of electromagnetic waves from a randomly perturbed periodic surface have been formulated using the extended boundary condition method and solved using the small perturbation method. Surface currents and scattered fields are solved for up to the second order. The results indicate that as the correlation length of the random roughness increases, the bistatic scattering patterns of the scattered fields show several beams associated with each Bragg diffraction direction of the periodic surface. The beam shape becomes broader with smaller correlation length. Results obtained using the Kirchhoff approximation are found to agree well with the present results for the hh and vv polarized backscattering coefficients for small angles of incidence.
NASA Astrophysics Data System (ADS)
Doronin, Alexander; Tchvialeva, Lioudmila; Markhvida, Igor; Lee, Tim K.; Meglinski, Igor
2016-07-01
In the framework of further development of a unified computational tool for the needs of biomedical optics, we introduce an electric field Monte Carlo (MC) model for simulation of backscattering of coherent linearly polarized light from a turbid tissue-like scattering medium with a rough surface. We consider the laser speckle patterns formation and the role of surface roughness in the depolarization of linearly polarized light backscattered from the medium. The mutual phase shifts due to the photons' pathlength difference within the medium and due to reflection/refraction on the rough surface of the medium are taken into account. The validation of the model includes the creation of the phantoms of various roughness and optical properties, measurements of co- and cross-polarized components of the backscattered/reflected light, its analysis and extensive computer modeling accelerated by parallel computing on the NVIDIA graphics processing units using compute unified device architecture (CUDA). The analysis of the spatial intensity distribution is based on second-order statistics that shows a strong correlation with the surface roughness, both with the results of modeling and experiment. The results of modeling show a good agreement with the results of experimental measurements on phantoms mimicking human skin. The developed MC approach can be used for the direct simulation of light scattered by the turbid scattering medium with various roughness of the surface.
Development of a laser-scattering-based probe for on-line measurement of surface roughness.
Wang, Shihua; Tian, Yunhui; Tay, Cho Jui; Quan, Chenggen
2003-03-01
The design and properties of an optical probe for on-line measurement of surface roughness are discussed. Based on light scattering, a probe that consists of a laser diode, a measuring lens, and a linear photodiode array was designed to detect surface roughness, in which the light scattered from a test surface at a relatively large scattering angle phi (=28 degrees) can be collected to enhance measuring range and repeatability. A coaxial design that incorporates a dual-laser probe and compressed air makes the proposed system insensitive to the position of the test surface and to surface conditions such as the presence of debris, vibration, and lubricants that result from machining. The results from measurements of several sets of specimens have demonstrated the feasibility of measuring surface roughness by using light scattering. On-line measurement on a diamond-turning lathe has shown that the proposed technique is stable and compact enough to be applicable to on-line measurement of surface roughness of an engineering surface. PMID:12638888
West, J.C.
1997-03-01
A hybrid moment-method/geometrical-theory-of-diffraction technique (MM/GTD) has been implemented to numerically calculate the electromagnetic scattering from one-dimensionally rough surfaces at extreme illumination angles (down to 0{degree} grazing). The hybrid approach allows the extension of the modeled scattering surface to infinity, avoiding the artificial edge diffraction that prevents use of the standard moment method at the smallest grazing angles. Numerical calculation of the backscattering from slightly rough large-scale surfaces approximating ocean wave features shows that roughness in strongly shadowed regions can contribute significantly to the total backscatter at vertical polarization. This is observed when the shadowing obstacle is several wavelengths high, and the magnitude of the shadow-region contribution does not depend on the radius-of-curvature of the shadowing feature. Strongly shadowed roughness does not significantly contribute to the backscatter at horizontal polarization, although weakly shadowed roughness near the incidence shadow boundary does. The calculations indicate that a shadowing-corrected two-scale model may be able to predict the distributed-surface portion of the sea-surface scattering from the ocean surface at grazing angles down to about 15{degree}, but at lower grazing the shadowing and large-scale curvature of the surface prevent the establishment of a Bragg resonance and invalidate the model.
NASA Astrophysics Data System (ADS)
Zhang, Jianing; Bi, Lei; Liu, Jianping; Panetta, R. Lee; Yang, Ping; Kattawar, George W.
2016-07-01
Constructing an appropriate particle morphology model is essential for realistic simulation of optical properties of atmospheric particles. This paper presents a model for generating surface roughness based on a combination of methods from discrete differential geometry combined with a stochastic partial differential equation for surface evolution introduced by Edwards and Wilkinson. Scattering of light by roughened particles is simulated using the Invariant Imbedding T-Matrix (II-TM) method. The effects of surface roughness on the single-scattering properties, namely, the phase matrix, asymmetry factor, and extinction efficiency, are investigated for a single wavelength in the visible range and for a range of size parameters up to x=50. Three different smooth shapes are considered: spherical, spheroidal, and hexagonal, the latter two in just the "compact particle" case of unit aspect ratio. It is shown that roughness has negligible effects on the optical scattering properties for size parameters less than 20. For size parameters ranging from 20 to 50, the phase matrix elements are more sensitive to the surface roughness than are two important integral optical properties, the extinction efficiency and asymmetry factor. As has been seen in studies using other forms of roughening, the phase function is progressively smoothed as roughness increases. The effect on extinction efficiency is to increase it, and on asymmetry factor is to decrease it. Each of these effects is relatively modest in the size range considered, but the trend of results suggests that greater effects will be seen for size parameters larger than ones considered here.
A new method to model x-ray scattering from random rough surfaces
NASA Astrophysics Data System (ADS)
Zhao, Ping; Van Speybroeck, Leon P.
2003-03-01
This paper presents a method for modeling the X-ray scattering from random rough surfaces. An actual rough surface is (incompletely) described by its Power Spectral Density (PSD). For a given PSD, model surfaces with the same roughness as the actual surface are constructed by preserving the PSD amplitudes and assigning a random phase to each spectral component. Rays representing the incident wave are reflected from the model surface and projected onto a flat plane, which approximates the model surface, as outgoing rays and corrected for phase delays. The projected outgoing rays are then corrected for wave densities and redistributed onto an uniform grid where the model surface is constructed. The scattering is then calculated by taking the Fast Fourier Transform (FFT) of the resulting distribution. This method is generally applicable and is not limited to small scattering angles. It provides the correct asymmetrical scattering profile for grazing incident radiation. We apply this method to the mirrors of the Chandra X-ray Observatory and show the results. We also expect this method to be useful for other X-ray telescope missions.
Light scattering by a rough surface of human skin. 2. Diffuse reflectance
NASA Astrophysics Data System (ADS)
Barun, V. V.; Ivanov, A. P.
2013-10-01
Based on the previously calculated luminance factors, we have investigated the integral characteristics of light reflection from a rough surface of the skin with large-scale inhomogeneities under various conditions of the skin illumination. Shadowing of incident and scattered beams by relief elements is taken into account. Diffuse reflectances by the Gaussian and the quasi-periodic surfaces are compared and, in general, both these roughness models are shown to give similar results. We have studied the effect of the angular structure of radiation multiply scattered deep in the tissue and the refraction of rays as they propagate from the dermis to the surface of the stratum corneum on the reflection characteristics of the skin surface. The importance of these factors is demonstrated. The algorithms constructed can be included in the schemes of calculation of the light fields inside and outside the medium in solving various direct and inverse problems of optics of biological tissues.
Light scattering by a rough surface of human skin. 2. Diffuse reflectance
Barun, V V; Ivanov, A P
2013-10-31
Based on the previously calculated luminance factors, we have investigated the integral characteristics of light reflection from a rough surface of the skin with large-scale inhomogeneities under various conditions of the skin illumination. Shadowing of incident and scattered beams by relief elements is taken into account. Diffuse reflectances by the Gaussian and the quasi-periodic surfaces are compared and, in general, both these roughness models are shown to give similar results. We have studied the effect of the angular structure of radiation multiply scattered deep in the tissue and the refraction of rays as they propagate from the dermis to the surface of the stratum corneum on the reflection characteristics of the skin surface. The importance of these factors is demonstrated. The algorithms constructed can be included in the schemes of calculation of the light fields inside and outside the medium in solving various direct and inverse problems of optics of biological tissues. (biophotonics)
NASA Astrophysics Data System (ADS)
Kuo, Chih-Hao
Efficient and accurate modeling of electromagnetic scattering from layered rough surfaces with buried objects finds applications ranging from detection of landmines to remote sensing of subsurface soil moisture. The formulation of a hybrid numerical/analytical solution to electromagnetic scattering from layered rough surfaces is first presented in this dissertation. The solution to scattering from each rough interface is sought independently based on the extended boundary condition method (EBCM), where the scattered fields of each rough interface are expressed as a summation of plane waves and then cast into reflection/transmission matrices. To account for interactions between multiple rough boundaries, the scattering matrix method (SMM) is applied to recursively cascade reflection and transmission matrices of each rough interface and obtain the composite reflection matrix from the overall scattering medium. The validation of this method against the Method of Moments (MoM) and Small Perturbation Method (SPM) is addressed and the numerical results which investigate the potential of low frequency radar systems in estimating deep soil moisture are presented. Computational efficiency of the proposed method is also discussed. In order to demonstrate the capability of this method in modeling coherent multiple scattering phenomena, the proposed method has been employed to analyze backscattering enhancement and satellite peaks due to surface plasmon waves from layered rough surfaces. Numerical results which show the appearance of enhanced backscattered peaks and satellite peaks are presented. Following the development of the EBCM/SMM technique, a technique which incorporates a buried object in layered rough surfaces by employing the T-matrix method and the cylindrical-to-spatial harmonics transformation is proposed. Validation and numerical results are provided. Finally, a multi-frequency polarimetric inversion algorithm for the retrieval of subsurface soil properties
A valuable method for online wire quality control: light scattering from cylindrical rough surfaces
NASA Astrophysics Data System (ADS)
Perez Quintian, Fernando; Rebollo, Maria A.; Berlasso, Ricardo G.; Gaggioli, Nestor G.
2003-05-01
In several applications, it is necessary to measure the surface characteristics of a wire so, it is important to do it during the manufacturing process. This work presents two main results: First, an analytical expression for the angular distribution of the mean scattered intensity from cylindrical rough surfaces as a function of the characteristic statistical parameters of the heights. This expression allows to measure the ratio T/σ between the correlation length and the roughness. Second, a quantitative relationship between the size and shape of the speckle grains in the Fraunhofer zone and the statistical properties of the cylindrical rough surface. In the first case, it is shown that the scanning process inherent to usual detection systems can be replaced by single step detection using a screen and a CCD camera. Therefore, this method can be applied to on line wire surface testing where conventional procedures are inadequate. In the second one, the experimental autocorrelation functions at different angles gives another method for measuring the parameter T/σ. Then, the study of the light scattered from cylindrical rough surfaces seem to be of great interest because of its potential application in NDT of manufacturing and finishing processes of components like pipes, junctions, wires and bearings.
Bilgen, M.; Rose, J.H. )
1994-11-01
An approximate analytic series solution is obtained for the effects of randomly rough surfaces on the time-dependent ultrasonic backscatter that are due to beam-microstructure interactions. The transmission of sound through the rough surface is modeled by scalar waves by use of the phase-screen and Fresnel approximations, whereas the transducer is assumed to produce a focused normally oriented Gaussian beam. The beam-microstructure interaction is described by a simple, generic model that attributes backscattering to inhomogeneities in the elastic constants of the sample; density variations are ignored. Key predictions of the approximate series solution are that (a) acoustic backscatter is relatively insensitive to surface roughness for unfocused probes, (b) roughness can dramatically reduce the backscatter noise seen by focused probes, (c) backscatter is increased at early times because of weak localization, and (d) backscatter is reduced at late times because of increased diffraction. The predictions of the series solution are briefly compared with available experiment. 32 refs., 10 figs.
Ray model of light scattering by flake pigments or rough surfaces with smooth transparent coatings.
Germer, Thomas A; Marx, Egon
2004-02-20
We derive expressions for the intensity and polarization of light singly scattered by flake pigments or a rough surface beneath a smooth transparent coating using the ray or facet model. The distribution of local surface normals is used to calculate the bidirectional reflectance distribution function (BRDF). We discuss the different distribution functions that can be used to characterize the distribution of local surface normals. The light-scattering model is validated by measurements of the BRDF and polarization by a metallic flake pigmented coating. The results enable the extraction of a slope distribution function from the data, which is shown to be consistent over a variety of scattering geometries. These models are appropriate to estimate or predict the appearance of flake pigment automotive paints. PMID:15008529
Lunar single-scattering, porosity, and surface-roughness properties with SMART-1/AMIE
NASA Astrophysics Data System (ADS)
Parviainen, H.; Muinonen, K.; Näränen, J.; Josset, J.-L.; Beauvivre, S.; Pinet, P.; Chevrel, S.; Koschny, D.; Grieger, B.; Foing, B.
2009-04-01
We analyze the single-scattering albedo and phase function, local surface roughness and regolith porosity, and the coherent backscattering, single scattering, and shadowing contributions to the opposition effect for specific lunar mare regions imaged by the SMART-1/AMIE camera. We account for shadowing due to surface roughness and mutual shadowing among the regolith particles with ray-tracing computations for densely-packed particulate media with a fractional-Brownian-motion interface with free space. The shadowing modeling allows us to derive the hundred-micron-scale volume-element scattering phase function for the lunar mare regolith. We explain the volume-element phase function by a coherent-backscattering model, where the single scatterers are the submicron-to-micron-scale particle inhomogeneities and/or the smallest particles on the lunar surface. We express the single-scatterer phase function as a sum of three Henyey-Greenstein terms, accounting for increased backward scattering in both narrow and wide angular ranges. The Moon exhibits an opposition effect, that is, a nonlinear increase of disk-integrated brightness with decreasing solar phase angle, the angle between the Sun and the observer as seen from the object. Recently, the coherent-backscattering mechanism (CBM) has been introduced to explain the opposition effect. CBM is a multiple-scattering interference mechanism, where reciprocal waves propagating through the same scatterers in opposite directions always interfere constructively in the backward-scattering direction but with varying interference characteristics in other directions. In addition to CBM, mutual shadowing among regolith particles (SMp) and rough-surface shadowing (SMr) have their effect on the behavior of the observed lunar surface brightness. In order to accrue knowledge on the volume-element and, ultimately, single-scattering properties of the lunar regolith, both SMp and SMr need to be accurately accounted for. We included four
MOLA-derived Roughness Data Used to Predict Surface Scattering for Mars Subsurface Radar Sounding
NASA Technical Reports Server (NTRS)
Plaut, J. J.; Garneau, S.
1999-01-01
The Mars Express orbiter, to be launched by the European Space Agency in 2003, will carry a low-frequency radar sounding instrument, MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding). The primary goal of MARSIS is to map the distribution of water, both solid and (if present) liquid, in the upper several km of the martian crust. Detecting discontinuities in the crust, such as an ice-water transition, presents many challenges for a Mars orbital radar sounder. One challenge that must be overcome is the presence of radar scattering (echoes) from the surface of Mars, expected to be detected by the sounder antennas at the same time as any echoes aris-ing from subsurface interfaces. As the transmitted spherical wavefront spreads within the crust of Mars,. it also interacts with surface topography at off-nadir positions, creating a "clutter" signal that can mask the subsurface echoes. The MARSIS instrument will utilize Doppler filtering to limit the off-nadir clutter in the along-track direction, and a nadir-null secondary antenna to identify strong off-nadir clutter from the cross-track direction. To evaluate the effects of off-nadir surface clutter and the capability of these schemes to reduce the clutter, it is necessary to predict the range of scattering behavior that may be expected from martian surface topography. In this paper, we utilize Mars Orbital Laser Altimeter (MOLA) data from the current Mars Global Surveyor mission to characterize the topographic roughness of a variety of martian terrain types, at scales relevant to the MARSIS clutter problem. Segments of MOLA altimetry profiles are reduced to the topographic parameters rms slope and fractal dimension, which then are used as inputs to a near-nadir radar scattering model to predict the strength of the clutter signal. Additional information is contained in the original extended abstract.
Electromagnetic wave scattering at near-grazing incidence from a gently undulating, rough surface
NASA Technical Reports Server (NTRS)
Vesecky, J. F.; Sperley, E. J.; Zebker, H. A.
1988-01-01
Models to estimate the reflection coefficient of a statistically rough surface, for example the works of Beckmann, Smith, and Vesecky are discussed. Bistatic radar experiments carried out during the Apollo 16 mission provide a data set with which to compare theoretical models and experimental data. These bistatic S-band radar experiments provide experimental estimates of the Moon's bistatic, forward scatter, reflection coefficient for grazing angles of 2.5 to 78 deg. Theoretical expressions for the reflection coefficient are developed for comparison with these experimental data. At grazing angles below 10 deg the models of Smith and Vesecky compare favorably with the data. Beckmann's model falls significantly more rapidly with decreasing grazing angle than does the data.
Scattering of Rarefied Gas Atoms from Rough Surface Simulated with Fractals
NASA Astrophysics Data System (ADS)
Aksenova, Olga A.
2003-05-01
The fractal approach to the model of surface roughness in the problem of gas-surface interaction is developed on the base of the generalization of two-dimensional model of roughness proposed by Blackmore and Zhou. The relation between the parameters of the model and the values influencing the aerodynamic coefficients is investigated. Computed results are compared with the values obtained using statistical model of roughness — the isotropic Gaussian random field.
NASA Astrophysics Data System (ADS)
Frezza, Fabrizio; Mangini, Fabio; Stoja, Endri; Tedeschi, Nicola
2013-04-01
In this work we present a numerical study of the effects that can be observed in the electromagnetic scattering of a plane wave due to the surface roughness of a buried scatterer. The latter is supposed to be a metallic pipeline modeled as a perfect-electric conducting cylinder immersed in a half-space occupied by a lossy medium. Considering the pipeline's cross-section, the surface roughness is modeled as a sinusoidal variation of the radius of the cylinder's surface with respect to the revolution angle. A linearly-polarized plane wave impinging normally to the interface between air and the previously-mentioned medium excites the structure. As a result, we monitor the three components of the scattered electric field along a line just above the interface between the two media. To perform the study, a commercially available simulator which implements the Finite Element Method was adopted. In order to discriminate the effects due only to the surface roughness, we compare the results obtained by the rough surface scatterers with the reference case of a perfect cylinder in which the surface roughness is absent, for a fixed depth and a fixed mean radius of the cylinder. In our study, we vary the amplitude and the angular frequency of the sinusoidal disturbance to model different surface roughness scenarios. For all the scenarios taken in consideration, a frequency sweep of the impinging radiation is performed. This allows us to investigate the relation between the excitation frequency and the sinusoidal disturbance frequency of the rough surface. The study has several implications in the field of civil engineering. One example might be the one in which the geometrical characteristics of the buried pipeline are known in advance, and it is important to continuously monitor the structural variations of its external surface due to the deterioration in time under the action of various environmental factors.
NASA Astrophysics Data System (ADS)
Bolghasi, Alireza; Ghadimi, Parviz; Chekab, Mohammad A. Feizi
2016-08-01
The aim of the present study is to improve the capabilities and precision of a recently introduced Sea Surface Acoustic Simulator (SSAS) developed based on optimization of the Helmholtz-Kirchhoff-Fresnel (HKF) method. The improved acoustic simulator, hereby known as the Modified SSAS (MSSAS), is capable of determining sound scattering from the sea surface and includes an extended Hall-Novarini model and optimized HKF method. The extended Hall-Novarini model is used for considering the effects of sub-surface bubbles over a wider range of radii of sub-surface bubbles compared to the previous SSAS version. Furthermore, MSSAS has the capability of making a three-dimensional simulation of scattered sound from the rough bubbly sea surface with less error than that of the Critical Sea Tests (CST) experiments. Also, it presents scattered pressure levels from the rough bubbly sea surface based on various incident angles of sound. Wind speed, frequency, incident angle, and pressure level of the sound source are considered as input data, and scattered pressure levels and scattering coefficients are provided. Finally, different parametric studies were conducted on wind speeds, frequencies, and incident angles to indicate that MSSAS is quite capable of simulating sound scattering from the rough bubbly sea surface, according to the scattering mechanisms determined by Ogden and Erskine. Therefore, it is concluded that MSSAS is valid for both scattering mechanisms and the transition region between them that are defined by Ogden and Erskine.
Random rough surface photofabrication
NASA Astrophysics Data System (ADS)
Brissonneau, Vincent; Escoubas, Ludovic; Flory, François; Berginc, Gérard
2011-10-01
Random rough surfaces are of primary interest for their optical properties: reducing reflection at the interface or obtaining specific scattering diagram for example. Thus controlling surface statistics during the fabrication process paves the way to original and specific behaviors of reflected optical waves. We detail an experimental method allowing the fabrication of random rough surfaces showing tuned statistical properties. A two-step photoresist exposure process was developed. In order to initiate photoresist polymerization, an energy threshold needs to be reached by light exposure. This energy is brought by a uniform exposure equipment comprising UV-LEDs. This pre-exposure is studied by varying parameters such as optical power and exposure time. The second step consists in an exposure based on the Gray method.1 The speckle pattern of an enlarged scattered laser beam is used to insolate the photoresist. A specific photofabrication bench using an argon ion laser was implemented. Parameters such as exposure time and distances between optical components are discussed. Then, we describe how we modify the speckle-based exposure bench to include a spatial light modulator (SLM). The SLM used is a micromirror matrix known as Digital Micromirror Device (DMD) which allows spatial modulation by displaying binary images. Thus, the spatial beam shape can be tuned and so the speckle pattern on the photoresist is modified. As the photoresist photofabricated surface is correlated to the speckle pattern used to insolate, the roughness parameters can be adjusted.
NASA Technical Reports Server (NTRS)
Sun, Wenbo; Videnn, Gorden; Lin, Bing; Hu, Yongxiang
2007-01-01
Light scattering and transmission by rough surfaces are of considerable interest in a variety of applications including remote sensing and characterization of surfaces. In this work, the finite-difference time domain technique is applied to calculate the scattered and transmitted electromagnetic fields of an infinite periodic rough surface. The elements of Mueller matrix for scattered light are calculated by an integral of the near fields over a significant number of periods of the surface. The normalized Mueller matrix elements of the scattered light and the spatial distribution of the transmitted flux for a monolayer of micron-sized dielectric spheres on a silicon substrate are presented. The numerical results show that the nonzero Mueller matrix elements of the system of the monolayer of dielectric spheres on a silicon substrate have specific maxima at some scattering angles. These maxima may be used in characterization of the feature of the system. For light transmitted through the monolayer of spheres, our results show that the transmitted energy focuses around the ray passing through centers of the spheres. At other locations, the transmitted flux is very small. The technique also may be used to calculate the perturbance of the electromagnetic field due to the presence of an isolated structure on the substrate.
Nanowetting of rough superhydrophobic surfaces
NASA Astrophysics Data System (ADS)
Zhang, H.; Lamb, R. N.; Cookson, D. J.
2007-12-01
Small angle x-ray scattering has been used to investigate the in situ immersive wetting of ultrarough surfaces which exhibit superhydrophobicity with extreme water contact angle (θA=169°). Reduced scattering contrast observed from rough surfaces when partially or totally wetted reveals significant physical differences between superhydrophobic surfaces not otherwise apparent from conventional contact angle measurements.
NASA Astrophysics Data System (ADS)
Stone, V. W.; Jonas, A. M.; Nysten, B.; Legras, R.
1999-08-01
The morphology of free surfaces of polyetherimide (PEI) samples has been characterized using atomic force microscopy in noncontact mode (NC-AFM), x-ray reflectivity (XRR), and x-ray diffuse scattering (XDS). PEI slabs have been prepared by molding pellets onto float glass. In order to characterize the roughness and morphology mathematically, we considered the surfaces as being self-affine with a rms roughness σ and Hurst coefficient H up to a finite correlation length ξ. NC-AFM topographs with σ=61+/-6.3 Å showed the presence of blobs on the surface having a slight tendency to form clusters. These features are reflected in the height-height correlation function which shows the presence of ``strong'' short-range (ξ1=1064 Å, H1=0.46) and ``weak'' long-range (ξ2=14537 Å, H2=0.99) correlations. The detection of the specularly reflected contribution in XRR scans only gives access to σ, the lateral fluctuations being averaged out over the coherence area. Scans in XDS include the detection of the diffuse (off-specular) scattering arising from lateral correlations in the surface fluctuations profile and are hence sensitive to σ, ξ, and H. The XDS data have been analyzed by simultaneous fits using the distorted-wave Born approximation up to the first order. Calculations were performed using previously published approximations. Best fits to the experimental data provided strongly different correlations length values (7570 Å<=ξ<=1245 Å) indicating that the estimation of the latter by XDS is somewhat ambiguous. This is in agreement with the strong discrepancy between the correlation lengths determined with x rays and NC-AFM, which can be accounted for by the limits of the perturbation theory for interfaces with high rms roughnesses.
NASA Astrophysics Data System (ADS)
Wei, Yiwen; Guo, Lixin
2016-04-01
This paper is aimed at applying the multiregion model to the composite EM scattering from a dielectric target and a dielectric rough surface. In the multiregion model, the rough surface is divided into multiple regions, the method of moment (MoM) is only adopted in the dominant region. Hence, this model can markedly reduce the number of unknowns. Firstly, we derived the single integral equation (SIE) in which the number of unknowns is half of those in the conventional MoM and the equations will be easier to deal with. Then the multiregion model is extended by SIE. With the multiregion model, one can obtain the accurate equivalent currents on the dominant region and accurate bistatic scattering coefficient in small and moderate scattering angles with much less time and memory requirement.
Chukhovskii, F N; Polyakov, A M
2010-11-01
The Green function formalism is applied to the problem of grazing-incidence small-angle X-ray scattering from statistically rough surfaces. Kirchhoff's integral equation is used to describe the X-ray wavefield propagation through a single rough surface separating vacuum and medium. Taking into account multiple diffuse X-ray scattering effects, the reflection R(coh)(θ) and transmission T(coh)(θ) coefficients of the specular wave are obtained using the Gaussian statistical model of rough surfaces in terms of the two-point height-height correlation function. In the limiting cases when the correlation length xi is equal to zero or infinity, analytical formulae for the reflection R(coh)(θ) and transmission T(coh)(θ) coefficients of the specular wave are obtained. It is important that in the case xi --> infinity they coincide with the corresponding reflection R(DW)(θ) and transmission T(DW)(θ) coefficients related to the conventional Debye-Waller approximation for describing the grazing X-ray scattering from a rough surface. In the case of finite values of correlation length \\xi the reflection |R(coh)(θ)|(2) and transmission |T(coh)(θ)|(2) scans are numerically calculated. PMID:20962372
The relationship between radar scattering and surface roughness of lunar volcanic features
NASA Astrophysics Data System (ADS)
Jawin, Erica R.; Kiefer, Walter S.; Fassett, Caleb I.; Bussey, D. Benjamin J.; Cahill, Joshua T. S.; Dyar, M. Darby; Lawrence, Samuel J.; Spudis, Paul D.
2014-11-01
Lunar roughness measurements derived from the Lunar Orbiter Laser Altimeter are compared to 12.6 cm wavelength radar data collected by the Miniature Radio Frequency instrument and 70 cm wavelength radar data collected by the Arecibo Observatory. These data are compared to assess how surface and subsurface roughness are correlated and affected by parameters including age and composition at length scales between 0.1 and 100 m. A range of features are analyzed including volcanic domes (Marius Hills, Rümker Hills, Gruithuisen, and Mairan Domes); mare (Imbrium, Serenitatis, and Oceanus Procellarum); pyroclastic dark mantle deposits (Sinus Aestuum, Sulpicius Gallus, and Mare Vaporum); and two young craters (Copernicus and Tycho). Statistically significant positive correlations exist between topographic roughness and both P- and S-band circular polarization ratios. The strongest correlation is observed at the longest length scales. Correlations weaken as length scales become less similar, potentially due to distinct processes controlling surface modification. Roughness is not significantly correlated with local slope. Although the Marius Hills are compositionally distinct from the Gruithuisen and Mairan domes, they are indistinguishable in roughness characteristics. Conversely, the Rümker Hills, mare, and dark mantle deposits are smoother at the length scales examined, possibly due to fine-grained mantling of regolith or pyroclastic deposits. The floor and ejecta of Tycho are the roughest surfaces measured in this study, while the floor and ejecta of Copernicus overlap the roughness distribution of the volcanic features. This study shows that many factors control the evolution of roughness over time on various length scales.
NASA Astrophysics Data System (ADS)
Sultan Salem, A. K.; Tyler, G. L.
2002-09-01
Understanding of electromagnetic scattering from surfaces is essential to interpretation of planetary radar observation of solid bodies, radio wave surface sounding from orbit, and many planetary remote sensing problems. The validity of Kirchhoff theory (KT) for analysis of scattering from fractal surfaces has not been clearly established. KT is exact for surfaces that are infinite, planar, and smooth. For other types of surfaces, KT is an approximation that has limited validity. The first limitation pertains to the local radius of curvature of the rough surface. The second pertains to the surface correlation length. By comparing the results from KT with empirical results, many authors assert the prime importance of the ratio of the correlation length to the wavelength (e.g., J.A. Ogilvy, Theory of Wave Scattering from Random Rough Surfaces, 104-110, Adam Hilger 1991). The larger this ratio, the better KT agrees with experimental results. We reformulate the second limitation as follows: The maximum wavelength should not exceed the correlation length of the surface for a valid application of KT. Since fractal functions are nowhere differentiable, band-limited fractals are used as models for physical surfaces. As first steps, some ad hoc procedures are used to band-limit the fractal surfaces before calculating the correlation length and local radius of curvature. Afterwards, a check is made to make sure that scattering can be analyzed accurately using KT. This check is extended to previous works that employ KT with fractal models (G. Franceschetti et al. 1999, M.K. Shepard and B.A. Campell 1999). The obtained results refer to the rigorous determination of a hypothesized filtering function (previously alluded to by Hagfors) to band-limit the mathematical fractal, transforming it into a physical representation for scattering calculations. The filtering function, if found, is expected to be helpful in understanding scattering from many types of surface models.
NASA Technical Reports Server (NTRS)
Yueh, S. H.; Kwok, R.
1993-01-01
In this paper, theoretical and numerical results of the polarimetric scattering and emission from random rough surfaces with anisotropic directional spectrum are presented for the remote sensing of ocean and soil surfaces. The polarimetric scattered field for rough dielectric surfaces is derived to the second order by the small perturbation method (SPM). It is found that the second-order scattered field is coherent in nature, and its coefficients for different polarizations present the lowest-order corrections to the Fresnel reflection coefficients of the surfaces. In addition, the cross-polarized (HV and VH) components of the coherent fields are reciprocal and not zero for surfaces with anisotropic directional spectrum when the azimuth angle of the incident direction is not aligned with the symmetry directions of surfaces. In order to verify the energy conservation condition of the theoretical results, which is important if the theory is to be applied to the passive polarimetry of rough surfaces, a Monte Carlo simulation is performed to numerically calculate the polarimetric reflectivities of one-dimensional random rough surfaces which are generated with a prescribed power-law spectrum in the spectral domain and transformed to the spatial domain by the FFT. The surfaces simulated by this approach are periodic with the period corresponding to the low-wavenumber cutoff. To calculate the scattering from periodic dielectric surfaces, the authors present a new numerical technique which applies the Floquet theorem to reduce the problem to one period and does not require the evaluation of one-dimensional periodic Green's function used in the conventional method of moment formulation. Once the scattering coefficients are obtained, the polarimetric Stokes vectors for the emission from the random surfaces are then calculated according to the Kirchhoff's law and are illustrated as functions of relative azimuth observation and row directions. The second-order SPM is also
Light reflection from a rough liquid surface including wind wave effects in a scattering atmosphere
NASA Astrophysics Data System (ADS)
Salinas, Santo V.; Liew, S. C.
2007-07-01
Visible and near-IR images of the ocean surface, taken from remote satellites, often contain important information of near-surface or sub-surface processes, which occur on, or over the ocean. Remote measurements of near surface winds, sea surface temperature and salinity, ocean color and underwater bathymetry, all, one way or another, depend on how well we understand sea surface roughness. However, in order to extract useful information from our remote measurements, we need to construct accurate models of the transfer of solar radiation inside the atmosphere as well as, its reflection from the sea surface. To approach this problem, we numerically solve the radiative transfer equation (RTE) by implementing a model for the atmosphere ocean system. A one-dimensional atmospheric radiation model is solved via the widely known doubling and adding method and the ocean body is treated as a boundary condition to the problem. The ocean surface is modeled as a rough liquid surface which includes wind interaction and wave states, such as wave age. The model can have possible applications to the retrieval of wind and wave states, such as wave age, near a Sun glint region.
NASA Technical Reports Server (NTRS)
Sun, W.; Loeb, N. G.; Videen, G.; Fu, Q.
2004-01-01
Natural particles such as ice crystals in cirrus clouds generally are not pristine but have additional micro-roughness on their surfaces. A two-dimensional finite-difference time-domain (FDTD) program with a perfectly matched layer absorbing boundary condition is developed to calculate the effect of surface roughness on light scattering by long ice columns. When we use a spatial cell size of 1/120 incident wavelength for ice circular cylinders with size parameters of 6 and 24 at wavelengths of 0.55 and 10.8 mum, respectively, the errors in the FDTD results in the extinction, scattering, and absorption efficiencies are smaller than similar to 0.5%. The errors in the FDTD results in the asymmetry factor are smaller than similar to 0.05%. The errors in the FDTD results in the phase-matrix elements are smaller than similar to 5%. By adding a pseudorandom change as great as 10% of the radius of a cylinder, we calculate the scattering properties of randomly oriented rough-surfaced ice columns. We conclude that, although the effect of small surface roughness on light scattering is negligible, the scattering phase-matrix elements change significantly for particles with large surface roughness. The roughness on the particle surface can make the conventional phase function smooth. The most significant effect of the surface roughness is the decay of polarization of the scattered light.
Light scattering by a rough surface of human skin. 1. The luminance factor of reflected light
Barun, V V; Ivanov, A P
2013-08-31
Based on the analytical solution of Maxwell's equations, we have studied the angular structure of the luminance factor of light reflected by the rough skin surface with large-scale relief elements, illuminated by a directed radiation beam incident at an arbitrary angle inside or outside the medium. The parameters of the surface inhomogeneities are typical of human skin. The calculated angular dependences are interpreted from the point of view of the angular distribution function of micro areas. The results obtained can be used for solving direct and inverse problems in biomedical optics, in particular for determining the depth of light penetration into a biological tissue, for studying the light action spectra on tissue chromophores under the in vivo conditions, for developing diagnostic methods of structural and biophysical parameters of a medium, and for optimising the mechanisms of interaction of light with biological tissues under their noninvasive irradiation through skin. (biomedical optics)
Roughness reduction on aspheric surfaces
NASA Astrophysics Data System (ADS)
Kiontke, S.; Kokot, Sebastian
2015-02-01
For a lot of applications like spectrometer and high power laser roughness as an important parameter has been discussed over and over again. Especially for high power systems the surface quality is crucial for determining the damage threshold and therefore the field of application. Above that, it has often been difficult to compare roughness measurements because of different measurement methods and the usage of filters and surface fits. Measurement results differ significantly depending on filters and especially on the measured surface size. Insights will be given how values behave depending on the quality of surface and the size of measured area. Many applications require a high quality of roughness in order to reduce scattering. Some of them in order to prevent from damage like high power laser applications. Others like spectrometers seek to increase the signal-to-noise ratio. Most of them have already been built with spherical surfaces. With higher demands on efficiency and more sophisticated versions aspherical surfaces need to be employed. Therefore, the high requirement in roughness known from spherical surfaces is also needed on aspherical surfaces. For one thing, the constant change of curvature of an aspherical surface accounts for the superior performance, for another thing, it prevents from using classical polishing technics, which guarantied this low roughness. New methods need to be qualified. In addition, also results of a new manufacturing process will be shown allowing low roughness on aspheric even with remarkable departure from the best fit sphere.
Sun, Wenbo; Loeb, Norman G; Videen, Gorden; Fu, Qiang
2004-03-20
Natural particles such as ice crystals in cirrus clouds generally are not pristine but have additional microroughness on their surfaces. A two-dimensional finite-difference time-domain (FDTD) program with a perfectly matched layer absorbing boundary condition is developed to calculate the effect of surface roughness on light scattering by long ice columns. When we use a spatial cell size of 1/120 incident wavelength for ice circular cylinders with size parameters of 6 and 24 at wavelengths of 0.55 and 10.8 microm, respectively, the errors in the FDTD results in the extinction, scattering, and absorption efficiencies are smaller than approximately 0.5%. The errors in the FDTD results in the asymmetry factor are smaller than approximately 0.05%. The errors in the FDTD results in the phase-matrix elements are smaller than approximately 5%. By adding a pseudorandom change as great as 10% of the radius of a cylinder, we calculate the scattering properties of randomly oriented rough-surfaced ice columns. We conclude that, although the effect of small surface roughness on light scattering is negligible, the scattering phase-matrix elements change significantly for particles with large surface roughness. The roughness on the particle surface can make the conventional phase function smooth. The most significant effect of the surface roughness is the decay of polarization of the scattered light. PMID:15065727
NASA Astrophysics Data System (ADS)
Tanaka, Hajime; Suda, Jun; Kimoto, Tsunenobu
2016-04-01
The authors present a calculation model of surface roughness scattering (SRS) in nanowires (NWs) based on atomistic description of electronic states by an s p3d5s* tight-binding scheme, and then this model is applied to hole transport in rectangular cross-sectional germanium (Ge) NWs. In this SRS model, the change of electronic band structures due to width or height reduction is first computed, and then it is expressed using an equivalent potential near the surface. The perturbation corresponding to a surface roughness is calculated from this equivalent potential. Using the aforementioned SRS model, hole mobility in Ge NWs was computed taking into account phonon scattering and SRS. The impacts of SRS on hole mobility in Ge NWs were analyzed, focusing on the valence band structure and hole states of NWs. The main results are as follows. At low hole density, the impacts of SRS are strongly dependent on NW geometry, and Ge NWs with high phonon-limited hole mobility, such as rectangular cross-sectional [110]-oriented NWs with large height along the [001] direction and square cross-sectional [111]-oriented NWs, tend to be less affected by SRS. At high hole density, however, the geometry dependence of hole mobility becomes weaker. These are understood from the nature of hole states and the valence band structure.
NASA Astrophysics Data System (ADS)
Zhang, Lisha
We present fast and robust numerical algorithms for 3-D scattering from perfectly electrical conducting (PEC) and dielectric random rough surfaces in microwave remote sensing. The Coifman wavelets or Coiflets are employed to implement Galerkin's procedure in the method of moments (MoM). Due to the high-precision one-point quadrature, the Coiflets yield fast evaluations of the most off-diagonal entries, reducing the matrix fill effort from O(N2) to O( N). The orthogonality and Riesz basis of the Coiflets generate well conditioned impedance matrix, with rapid convergence for the conjugate gradient solver. The resulting impedance matrix is further sparsified by the matrix-formed standard fast wavelet transform (SFWT). By properly selecting multiresolution levels of the total transformation matrix, the solution precision can be enhanced while matrix sparsity and memory consumption have not been noticeably sacrificed. The unified fast scattering algorithm for dielectric random rough surfaces can asymptotically reduce to the PEC case when the loss tangent grows extremely large. Numerical results demonstrate that the reduced PEC model does not suffer from ill-posed problems. Compared with previous publications and laboratory measurements, good agreement is observed.
NASA Astrophysics Data System (ADS)
Simonsen, I.; Hetland, Ø. S.; Kryvi, J. B.; Maradudin, A. A.
2016-04-01
An expression is obtained on the basis of phase perturbation theory for the contribution to the mean differential reflection coefficient from the in-plane co-polarized component of the light scattered diffusely from a two-dimensional randomly rough dielectric surface when the latter is illuminated by s -polarized light. This result forms the basis for an approach to inverting experimental light-scattering data to obtain the normalized-surface-height autocorrelation function of the surface. Several parametrized forms of this correlation function, and the minimization of a cost function with respect to the parameters defining these representations, are used in the inversion scheme. This approach also yields the rms height of the surface roughness, and the dielectric constant of the dielectric substrate if it is not known in advance. The input data used in validating this inversion consist of computer simulation results for surfaces defined by exponential and Gaussian surface-height correlation functions, without and with the addition of multiplicative noise, for a single or multiple angles of incidence. The reconstructions obtained by this approach are quite accurate for weakly rough surfaces, and the proposed inversion scheme is computationally efficient.
Jarvis, Andrew J C; Cegla, Frederic B
2014-07-01
The challenge of accurately simulating how incident scalar waves interact with rough boundaries has made it an important area of research within many scientific disciplines. Conventional methods, which in the majority of cases focus only on scattering in two dimensions, often suffer from long simulation times or reduced accuracy, neglecting phenomena such as multiple scattering and surface self-shadowing. A simulation based on the scalar wave distributed point source method (DPSM) is presented as an alternative which is computationally more efficient than fully meshed numerical methods while obtaining greater accuracy than approximate analytical techniques. Comparison is made to simulated results obtained using the finite element method for a sinusoidally periodic surface where scattering only occurs in two dimensions, showing very good agreement (<0.2 dB). In addition to two-dimensional scattering, comparison to experimental results is also carried out for scattering in three dimensions when the surface has a Gaussian roughness distribution. Results indicate that for two-dimensional scattering and for rough surfaces with a correlation length equal to the incident wavelength (λ) and a root mean square height less than 0.2λ, the scalar wave approximation predicts reflected pulse shape change and envelope amplitudes generally to within 1 dB. Comparison between transducers within a three-element array also illustrate the sensitivity pulse amplitude can have to sensor position above a rough surface, differing by as much as 17 dB with a positional change of just 1.25λ. PMID:24960707
Optical methods for cylindrical rough surface testing
NASA Astrophysics Data System (ADS)
Perez Quintian, F.; Rebollo, Maria A.; Gaggioli, Nestor G.; Raffo, C. A.
1999-07-01
This work studies theoretically the scattering of light from cylindrical rough surfaces. It is shown, for the conical diffraction configuration, that the mean intensity on an observation plane perpendicular to the cylinder longitudinal axis, is related to the statistical parameters that characterize the surface: the roughness (sigma) and the correlation length T.
Water-scattered signal to compensate for the rough sea surface effect on bottom lidar imaging.
Dolin, Lev S; Luchinin, Alexander G
2008-12-20
We investigate the possibility of using the water-backscattered radiation from a bottom sounding airborne imaging light detection and ranging (lidar) system to determine the surface slope at the point where the laser beam intersects the surface. We show that the refraction angle of the beam can be determined using receivers whose sensitivities vary linearly over their field of view. Equations are derived to estimate the statistical mean and variance values of this refracted angle. We demonstrate that the proposed algorithm improves lidar imaging. Numerical examples with reference to typical marine conditions are given. PMID:19104538
Sekiguchi, Yoshifumi; Kaneko, Hiroki
2016-02-01
For simulating light guide lighting systems, we have developed a ray-tracing model for an ink layer extracting light from a light guide. The model consists of the volume and the rough surface scattering calculated on the basis of Mie theory and the facet model, respectively. The model of an ink layer was required to conserve energy for analyzing how much light loss occurs in each component in the lighting system. Though a single-scattering rough surface model with a shadowing/masking function successfully describes the scattering distribution, shadowing light violates the energy conservation law because of a lack of multiple scattering. We developed the rough surface ray-tracing model (RSRT model), which includes the multiple scattering instead of the shadowing/masking effect. We investigated the applicability of the RSRT model for an ink layer by comparing the RSRT model with recent physical and facet models. Finally, we compared the calculated and measured scattering distributions of an ink layer, applied the developed ink layer model to the lighting system, and confirmed the developed model to be valid. PMID:26836100
A rough earth scattering model for multipath prediction
NASA Technical Reports Server (NTRS)
Page, L. J.; Chestnut, P. C.
1970-01-01
The most important phenomena to be considered in a model of radio wave communication between earth satellites are scattering from the surface of the earth. A model is derived and implemented on a computer to predict the field received after reflection from a rough, spherical earth. The scattering integrals are computed numerically; the domain of integration is the appropriate region on the surface of the earth. Calculations have been performed at VHF frequencies and for terrain which could be described as marshy land. Rough surface scattering calculations must be performed over a spherical earth when satellites are involved. There is a definite dependence on the values of the roughness, and the correlation length.
NASA Astrophysics Data System (ADS)
Li, Xiangzhen; Qi, Xiao; Han, Xiang'e.
2015-10-01
The characteristics of laser scattering from sea surface have a great influence on application performance, from submarine communication, laser detection to laser diffusion communication. Foams will appear when the wind speed exceeds a certain value, so the foam can be seen everywhere in the upper layer of the ocean. Aiming at the volume-surface composite model of rough sea surface with foam layer driven by wind, and the similarities and differences of scattering characteristics between blue-green laser and microwave, an improved two-scale method for blue-green laser to calculate the scattering coefficient is presented in this paper. Based on the improved two-scale rough surface scattering theory, MIE theory and VRT( vector radiative transfer ) theory, the relations between the foam coverage of the sea surface and wind speed and air-sea temperature difference are analyzed. Aiming at the Gauss sea surface in blue-green laser, the dependence of back- and bistatie-scattering coefficient on the incident and azimuth angle, the coverage of foams, as well as the wind speed are discussed in detail. The results of numerical simulations are compared and analyzed in this paper. It can be concluded that the foam layer has a considerable effect on the laser scattering with the increase of wind speed, especially for a large incident angle. Theoretical analysis and numerical simulations show that the improved two-scale method is reasonable and efficient.
Polarimetric scattering behavior of rough dielectric materials at terahertz frequencies
NASA Astrophysics Data System (ADS)
Digiovanni, David Anthony
Technologies in the terahertz region of the spectrum are finding increased usage in areas such as communications, remote sensing, and imaging, For example, driven by the promise of greater data transfer rates, free-space communication that traditionally operate in the radio and microwave bands are being developed at terahertz frequencies. Successful transition of communication systems to higher frequencies, particularly for systems located in indoor or urban environments, will require a thorough understanding of the reflection, transmission, absorption, and scattering behavior of a wide variety of materials and surface types. Scattering properties of rough surfaces have been studied extensively at radio and microwave frequencies, however, such properties have only recently become of interest at higher frequencies. The goal of this thesis was to develop a better understanding of electromagnetic scattering from dielectric rough surfaces at millimeter wavelengths and terahertz frequencies. This goal was achieved by measuring the polarimetric scattering behavior of dielectric materials and comparing the measured data to predictions made by rough surface scattering theory. The dielectric properties and the roughness of the samples were tailored in order to provide a controlled parameter space to investigate. Fully polarimetric radar imagery of the rough surfaces were acquired at 160 GHz, 240 GHz, and 1.55 THz. The backscattering measurements were collected as a function of polarization, incident angle, and frequency. The applicability of various rough surface scattering theories was determined for the different roughness regimes studied.
Reconstruction of scattering properties of rough air-dielectric boundary
NASA Astrophysics Data System (ADS)
Sokolov, V. G.; Zhdanov, D. D.; Potemin, I. S.; Garbul, A. A.; Voloboy, A. G.; Galaktionov, V. A.; Kirilov, N.
2016-08-01
The article is devoted to elaboration of the method of reconstruction of rough surface scattering properties. The object with rough surface is made of transparent dielectric material. Typically these properties are described with bi-directional scattering distribution function (BSDF). Direct measurement of such function is either impossible or very expensive. The suggested solution provides physically reasonable method for the rough surface BSDF reconstruction. The method is based on Monte-Carlo ray tracing simulation for BSDF calculation. Optimization technique is further applied to correctly reconstruct the BSDF. The results of the BSDF reconstruction together with measurement results are presented in the article as well.
Solvation forces between rough surfaces
Frink, L.J.; van Swol, F.
1998-04-01
We investigate the role of surface roughness on solvation forces and solvation free energies. Roughness is introduced by dividing a surface into an array of square tiles that are then randomly displaced in the direction perpendicular to the wall. The integrated wall strength of these tiled surfaces is independent of the surface roughness and hence this class of rough walls is ideally suited for isolating roughness effects. We use grand canonical Monte Carlo simulations of a Lennard-Jones fluid confined in a slit pore with rough walls to generate the solvation interactions as a function of roughness, tile size, and surface area. The simulation data are compared to a simple superposition approximation of smooth wall solvation interactions (obtained from simulation or density functional theory), based on a distribution of wall separations. We find that this approximation provides a surprisingly accurate route to the solvation interaction of rough surfaces. In general, increased roughness leads to a reduction of oscillations in the solvation forces and surface free energies. However, nonmonotonic behavior of the oscillation amplitude with roughness can be observed for finite surfaces. The washing out of the oscillations found for large surface roughness produces a solvation force that exhibits a broad repulsive peak with separation. The broad repulsion is a consequence of the resistance to squeezing out fluid from the smallest gaps between two opposing rough surfaces. It is as much a reflection of packing effects as are the solvation oscillations for perfectly smooth pores. In addition, we present results for patterned and undulating surfaces produced by an analogous modification of the one-body external field for smooth walls. Finally, we discuss the implications of our results for a number of experimental systems including self-assembled monolayers, microporous materials, protein solutions, and DNA crystals. {copyright} {ital 1998 American Institute of Physics.}
Does surface roughness amplify wetting?
Malijevský, Alexandr
2014-11-14
Any solid surface is intrinsically rough on the microscopic scale. In this paper, we study the effect of this roughness on the wetting properties of hydrophilic substrates. Macroscopic arguments, such as those leading to the well-known Wenzel's law, predict that surface roughness should amplify the wetting properties of such adsorbents. We use a fundamental measure density functional theory to demonstrate the opposite effect from roughness for microscopically corrugated surfaces, i.e., wetting is hindered. Based on three independent analyses we show that microscopic surface corrugation increases the wetting temperature or even makes the surface hydrophobic. Since for macroscopically corrugated surfaces the solid texture does indeed amplify wetting there must exist a crossover between two length-scale regimes that are distinguished by opposite response on surface roughening. This demonstrates how deceptive can be efforts to extend the thermodynamical laws beyond their macroscopic territory.
Measuring Roughnesses Of Optical Surfaces
NASA Technical Reports Server (NTRS)
Coulter, Daniel R.; Al-Jumaily, Gahnim A.; Raouf, Nasrat A.; Anderson, Mark S.
1994-01-01
Report discusses use of scanning tunneling microscopy and atomic force microscopy to measure roughnesses of optical surfaces. These techniques offer greater spatial resolution than other techniques. Report notes scanning tunneling microscopes and atomic force microscopes resolve down to 1 nm.
NASA Technical Reports Server (NTRS)
Gordon, Howard R.; Wang, Menghua
1992-01-01
The first step in the Coastal Zone Color Scanner (CZCS) atmospheric-correction algorithm is the computation of the Rayleigh-scattering (RS) contribution, L sub r, to the radiance leaving the top of the atmosphere over the ocean. In the present algorithm, L sub r is computed by assuming that the ocean surface is flat. Calculations of the radiance leaving an RS atmosphere overlying a rough Fresnel-reflecting ocean are presented to evaluate the radiance error caused by the flat-ocean assumption. Simulations are carried out to evaluate the error incurred when the CZCS-type algorithm is applied to a realistic ocean in which the surface is roughened by the wind. In situations where there is no direct sun glitter, it is concluded that the error induced by ignoring the Rayleigh-aerosol interaction is usually larger than that caused by ignoring the surface roughness. This suggests that, in refining algorithms for future sensors, more effort should be focused on dealing with the Rayleigh-aerosol interaction than on the roughness of the sea surface.
Surface roughness of flat and curved optical surfaces
NASA Technical Reports Server (NTRS)
George, M. C.; Reddy, Bandi Jagannadha; Jagannath, H.; Perera, M.; Venkateswarlu, P.
1989-01-01
Surface roughness measurement has several applications. Even a few A roughness will cause scattered light in optical systems. Smooth surfaces are required in a wide variety of instruments. For example, the outputs of the high power lasers are limited by the surface roughness of mirrors and windows. Similarly, the information storage capacity of magnetic media is limited by the roughness of the surface. Roughness reduces the resolving power of optics and distorts images. The performance of certain thin film components in electronic industries is affected by the roughness on the film surface. X-ray astronomical telescopes require smooth curved surfaces. To improve the surface quality, super sensitive detection methods are required. Wide ranging measurement techniques are developed based on interferometry, electron microscopy, C-rays, ellipsometry, light scattering, and using mechanical stylus, etc. Though there are several techniques available for measurement and evaluation of the surfaces, no single technique is fully adequate. Also, the technique used should be nondestructive and highly sensitive. So, an optical heterodyne profilometer was fabricated. Its current sensitivity is much better than 10A rms. It is a noncontact and nondestructive technique. The instrument can be operated even by unskilled personnel for routine measurements.
Estimating surface roughness using stereophotogrammetry
NASA Astrophysics Data System (ADS)
David, V.; Krasa, J.
2009-04-01
At the Department of Drainage, Irrigation and Landscape Engineering (CTU Prague) we use several mathematical models for soil erosion, sediment transport and surface runoff assessment. Here we continuously struggle for successful models parameterizations. One of the typical coefficients usually taken from literature instead of measurements is surface roughness, eg. Manning roughness (Maidment, 1993). Roughness is a key to surface runoff velocity and surface runoff depth estimation but often it is very roughly estimated. Within the COST 22 Action research we focused on estimating actual surface roughness using stereophotogrammetry. Our aim was to set up a simple low cost system useful for roughness measurements in nature conditions - mainly on agricultural fields. Our system consists of Canon EOS 400 digital camera with angle viewfinder, two robust tripods and a horizontal bar with sliding 3D tripod head. We tested different camera heights and focal distances as well as various parallaxes to obtain reasonable results. Finally we shot the surfaces from 1600 millimeters with 24 and 35 mm lens and parallaxes close to 100 mm. For 3D scene development we use Geomatica 10 GIS and its OrthoEngine module. Testing the proper system and many variables of the 3D scene modelling was an important part of the first year of the project. For these purposes we first prepared a calibrated and known 3D surface consisting of 70 by 70 cm grid and several geometrical objects of different sizes and shapes. Preparing the correct lighting conditions, finding the resolving power of the system and solving the problems with low contrast areas of measured surfaces was a time consuming but interesting task. After the system calibration we started with the actual terrain measurements. Our setup, system testing and preliminary results of the roughness computations are presented on the poster. Acknowledgement This research was acomplished within national COST project OC189 „Flood risk and its
Polymer Transport Near Rough Surfaces
NASA Astrophysics Data System (ADS)
Bloom, Moses; Whitmer, Jonathan; Luijten, Erik
2011-03-01
The rheology of dilute polymer solutions under confinement is important in biology, medicine, microfluidic device design, synthetic polymer processing, and even geologic porous media. However, the solution's specific interactions with the confining surface are poorly understood. This situation is exacerbated for composite nanoparticles, such as polymer/metallic hybrids. Using multi-particle collision dynamics, we find a rich array of transport regimes depending on small-scale surface roughness and the specific surface/solute interactions. These factors couple to hydrodynamic conditions, including flow strength and confinement geometry in unexpected ways. Our findings may be relevant to transport phenomena in certain rough-walled capillaries, such as the distribution of various nanoconjugates in vivo.
Polarimetric thermal emission from rough surfaces
NASA Technical Reports Server (NTRS)
Johnson, J. T.; Kong, J. A.; Shin, R. T.; Staelin, D. H.; Yueh, S. H.; Nghiem, S. V.; Kwok, R.; Oneill, K.; Lohanick, A.
1993-01-01
Recent theoretical works have suggested the potential of passive polarimetry in the remote sensing of geophysical media. It was shown that the third Stokes parameter U of the thermal emission may become larger for azimuthally asymmetric fields of observation. In order to investigate the potential applicability of passive polarimetry to the remote sensing of ocean surface, measurements of the polarimetric thermal emission from a sinusoidal water surface and a numerical study of the polarimetric thermal emission from randomly rough ocean surfaces were performed. Measurements of sinusoidal water surface thermal emission were performed using a sinusoidal water surface which was created by placing a thin sheet of fiberglass with a sinusoidal profile in two dimensions extended infinitely in the third dimension onto a water surface. The theory of thermal emission from a 'two-layer' periodic surface is derived and the exact solution is performed using both the extended boundary condition method (EBC) and the method of moments (MOM). The theoretical predictions are found to be in good agreement with the experimental results once the effects of the radiometer antenna pattern are included and the contribution of background noise to the measurements is modeled. The experimental results show that the U parameter indicates the direction of periodicity of the water surface and can approach values of up to 30 K for the surface observed. Next, a numerical study of polarimetric thermal emission from randomly rough surfaces was performed. A Monte Carlo technique utilizing an exact method for calculating thermal emission was chosen for the study to avoid any of the limitations of the commonly used approximate methods in rough surface scattering. In this Monte Carlo technique, a set of finite rough surface profiles in two dimensions with desired statistics was generated and extended periodically. The polarimetric thermal emission from each surface of the set was then calculated using
Extreme ultraviolet mask substrate surface roughness effects on lithography patterning
George, Simi; Naulleau, Patrick; Salmassi, Farhad; Mochi, Iacopo; Gullikson, Eric; Goldberg, Kenneth; Anderson, Erik
2010-06-21
In extreme ultraviolet lithography exposure systems, mask substrate roughness induced scatter contributes to LER at the image plane. In this paper, the impact of mask substrate roughness on image plane speckle is explicitly evaluated. A programmed roughness mask was used to study the correlation between mask roughness metrics and wafer plane aerial image inspection. We find that the roughness measurements by top surface topography profile do not provide complete information on the scatter related speckle that leads to LER at the image plane. We suggest at wavelength characterization by imaging and/or scatter measurements into different frequencies as an alternative for a more comprehensive metrology of the mask substrate/multilayer roughness effects.
Surface roughness of anodized titanium coatings.
Dugger, Michael Thomas; Chinn, Douglas Alan
2010-10-01
Samples of grade five 6Al4V titanium alloy were coated with two commercial fluoropolymer anodizations (Tiodize and Canadize) and compared. Neither coating demonstrates significant outgassing. The coatings show very similar elemental analysis, except for the presence of lead in the Canadize coating, which may account for its lower surface friction in humid environments. Surface roughness has been compared by SEM, contact profilometry, optical profilometry, power spectral density and bidirectional scattering distribution function (BSDF). The Tiodize film is slightly smoother by all measurement methods, but the Canadize film shows slightly less scatter at all angles of incidence. Both films exhibited initial friction coefficients of 0.2 to 0.4, increasing to 0.4 to 0.8 after 1000 cycles of sliding due to wear of the coating and ball. The coatings are very similar and should behave identically in most applications.
Surface roughness and infrared emission from the lunar surface
NASA Astrophysics Data System (ADS)
Vogler, Karl Joseph
1994-01-01
In order to understand thermal infrared spectra of the moon and solid-surfaced planetary bodies in terms of surface roughness and composition, a two-part project involving thermophysical computer models and infrared photometry has been pursued. The computer models calculate the infrared radiation emitted by an atmosphereless body with a macroscopically rough surface using radiative heat transfer methods. Multiple scattering of incident solar radiation, and multiple scattering and remission of thermal infrared radiation onto surrounding surface elements are included in the model. Surface roughness is modeled as paraboloidal holes characterized by a fractional coverage of a spherical object and a single depth-to-diameter ratio. Thermal emission from the rough surface is anisotropic and deviates from a gray body emission assumed by standard thermal models. The model explains to first-order published, mid infrared, measurements of the moon and Galilean Satellites. Surface composition is included by using results from Hapke for reflectance and emittance properties of a particulate surface. It is concluded that negative surface relief is required to explain the continuum behavior of the lunar thermal spectrum. An infrared photometer was constructed from an existing design and was configured in order to perform whole disk photometry of the moon at various phase angles. Measurements at 5.03, 8.4 and 11.5 micron were made at seven phase angles, ranging from -151 deg 55 min to 53 deg 27 min. The thermophysical computer models were modified so that disk-integrated emission as a function of phase angle could be calculated. Effects due to thermal inertia of the surface are not included in this simplified version of the model. The model calculations compare favorably with measurements of the moon made by the author, Sarri and Shorthill and Murdock. It is concluded that surface roughness is necessary in explaining the shape of the lunar thermal emission with phase angle.
Calibration of surface roughness standards
NASA Astrophysics Data System (ADS)
Thalmann, R.; Nicolet, A.; Meli, F.; Picotto, G. B.; Matus, M.; Carcedo, L.; Hemming, B.; Ganioglu, O.; De Chiffre, L.; Saraiva, F.; Bergstrand, S.; Zelenika, S.; Tonmueanwai, A.; Tsai, C.-L.; Shihua, W.; Kruger, O.; de Souza, M. M.; Salgado, J. A.; Ramotowski, Z.
2016-01-01
The key comparison EURAMET.L-K8.2013 on roughness was carried out in the framework of a EURAMET project starting in 2013 and ending in 2015. It involved the participation of 17 National Metrology Institutes from Europe, Asia, South America and Africa representing four regional metrology organisations. Five surface texture standards of different type were circulated and on each of the standards several roughness parameters according to the standard ISO 4287 had to be determined. 32 out of 395 individual results were not consistent with the reference value. After some corrective actions the number of inconsistent results could be reduced to 20, which correspond to about 5% of the total and can statistically be expected. In addition to the material standards, two softgauges were circulated, which allow to test the software of the instruments used in the comparison. The comparison results help to support the calibraton and measurement capabilities (CMCs) of the laboratories involved in the CIPM MRA. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
El-Shenawee, M; Rappaport, C; Silevitch, M
2001-12-01
We present a statistical study of the electric field scattered from a three-dimensional penetrable object buried under a two-dimensional random rough surface. Monte Carlo simulations using the steepest-descent fast multipole method (SDFMM) are conducted to calculate the average and the standard deviation of the near-zone scattered fields. The SDFMM, originally developed at the University of Illinois at Urbana-Champaign, has been modified to calculate the unknown surface currents both on the rough ground and on the buried object that are due to excitation by a tapered Gaussian beam. The rough ground medium used is an experimentally measured typical dry Bosnian soil with 3.8% moisture, while the buried object represents a plastic land mine modeled as an oblate spheroid with dimensions and burial depth smaller than the free-space wavelength. Both vertical and horizontal polarizations for the incident waves are studied. The numerical results show that the TNT mine signature is almost 5% of the total field scattered from the ground. Moreover, relatively recognizable object signatures are observed even when the object is buried under the tail of the incident beam. Interestingly, even for the small surface roughness parameters considered, the standard deviation of the object signature is almost 30% of the signal itself, indicating significant clutter distortion that is due to the roughness of the ground. PMID:11760205
Modeling Radar Scatter from Icy and Young Rough Lunar Craters
NASA Technical Reports Server (NTRS)
Thompson, Thomas (Tommy); Ustinov, Eugene; Spudis, Paul; Fessler, Brian
2012-01-01
For lunar orbital synthetic aperture radars, such as the Chandrayaan Mini-RF operating at S- band (13-cm) wavelength and the Lunar Reconnaissance Orbiter Mini-RF operating at S- band and X-band (3-cm) wavelengths, it is important to understand the radar backscattering characteristics of the icy and young, rough craters. Assuming a mixing model consisting of diffuse and quasi-specular scattering components, we have modeled the opposite-sense circular (OC) and same-sense circular (SC) backscattering characteristics. The specular component, consisting of only OC echoes, represents the echoes from the surface and subsurface layers that are oriented perpendicular to the radar's line-of-sight. The diffuse component, consisting of both SC and OC echoes, represents the echoes associated with either rocks or ice. Also, diffuse echoes have backscatter that is proportional to the cosine of the incidence angle. We modeled how these two (specular and diffuse) radar scattering components could be modulated by factors such as surface roughness associated with young craters. We also modeled how ice radar scattering components could be modulated by a thin regolith covering, and/or by the situation where ice occupies small patches within a larger radar pixel. We tested this modeling by examining 4 nonpolar craters and 12 polar craters using LRO Mini-RF data. Results indicate that icy and young rough craters can be distinguished based upon their SC enhancements (Alpha) and OC enhancements (Gamma). In addition, we also examined the craters that have unusual circular polarization ratios (CPRs) that likely result from a double bounce mode of scattering. Blocky fresh craters, icy craters, and craters exhibiting double bounce scattering can be separated based on the values of Alpha, Gamma, the ratio of Alpha/Gamma and the weighted sum of Alpha and Gamma.
Wind tunnel model surface gauge for measuring roughness
NASA Technical Reports Server (NTRS)
Vorburger, T. V.; Gilsinn, D. E.; Teague, E. C.; Giauque, C. H. W.; Scire, F. E.; Cao, L. X.
1987-01-01
The optical inspection of surface roughness research has proceeded along two different lines. First, research into a quantitative understanding of light scattering from metal surfaces and into the appropriate models to describe the surfaces themselves. Second, the development of a practical instrument for the measurement of rms roughness of high performance wind tunnel models with smooth finishes. The research is summarized, with emphasis on the second avenue of research.
Martian surface roughness and stratigraphy
NASA Astrophysics Data System (ADS)
Beyer, Ross Alan
2004-12-01
Orbital datasets can be combined and manipulated to learn about the three- dimensional structure of planetary surfaces, and the processes that have acted on them. The Mars Orbital Camera (MOC) is providing high-resolution images. These images allow qualitative inspection of features, and contain quantitative information about the shape of the surface. Using a photoclinometry technique derived from a lunar-Lambert photometric function, I am able to obtain estimates of the down-sun slope of each pixel in an image. This technique was calibrated against synthetic topography, compared to an area photoclinometry technique, and applied to the Viking and Pathfinder landing sites. It is a robust technique for obtaining the roughness and slope characteristics of large areas. It was applied to the potential landing sites for the Mars Exploration Rovers to evaluate site safety. The slopes from this point photoclinometry technique can be used to obtain a rough estimate of topography, which I used in a number of studies where topographic information was crucial. MOC images have shown that layering is pervasive on the martian surface. Mars Orbital Laser Altimeter (MOLA) data can be registered to MOC images to provide elevation constraints on layer outcrops. Such layers are observed in eastern Coprates Chasma both in the chasma rim and in a flat-topped massif. Observations indicate that the chasma stratigraphy consists of thin sequences of resistant layers and intervening thicker sequences of relatively less resistant layers. More resistant units cap the massif against erosion and result in steeper slopes than the weaker units would otherwise allow. These resistant layers can be used as stratigraphic markers which have allowed me to measure the subsidence and tilting of the massif relative to the chasma walls, providing evidence for tectonic motion in this portion of the Valles Marineris. These outcrops indicate that some of these layers may be analogus to terristrial flood
NASA Astrophysics Data System (ADS)
Meissner, Thomas; Wentz, Frank J.; Ricciardulli, Lucrezia
2014-09-01
In order to achieve the required accuracy in sea surface salinity (SSS) measurements from L-band radiometers such as the Aquarius/SAC-D or SMOS (Soil Moisture and Ocean Salinity) mission, it is crucial to accurately correct the radiation that is emitted from the ocean surface for roughness effects. We derive a geophysical model function (GMF) for the emission and backscatter of L-band microwave radiation from rough ocean surfaces. The analysis is based on radiometer brightness temperature and scatterometer backscatter observations both taken on board Aquarius. The data are temporally and spatially collocated with wind speeds from WindSat and F17 SSMIS (Special Sensor Microwave Imager Sounder) and wind directions from NCEP (National Center for Environmental Prediction) GDAS (Global Data Assimilation System). This GMF is the basis for retrieval of ocean surface wind speed combining L-band H-pol radiometer and HH-pol scatterometer observations. The accuracy of theses combined passive/active L-band wind speeds matches those of many other satellite microwave sensors. The L-band GMF together with the combined passive/active L-band wind speeds is utilized in the Aquarius SSS retrieval algorithm for the surface roughness correction. We demonstrate that using these L-band wind speeds instead of NCEP wind speeds leads to a significant improvement in the SSS accuracy. Further improvements in the roughness correction algorithm can be obtained by adding VV-pol scatterometer measurements and wave height (WH) data into the GMF.
Wetting properties of molecularly rough surfaces.
Svoboda, Martin; Malijevský, Alexandr; Lísal, Martin
2015-09-14
We employ molecular dynamics simulations to study the wettability of nanoscale rough surfaces in systems governed by Lennard-Jones (LJ) interactions. We consider both smooth and molecularly rough planar surfaces. Solid substrates are modeled as a static collection of LJ particles arranged in a face-centered cubic lattice with the (100) surface exposed to the LJ fluid. Molecularly rough solid surfaces are prepared by removing several strips of LJ atoms from the external layers of the substrate, i.e., forming parallel nanogrooves on the surface. We vary the solid-fluid interactions to investigate strongly and weakly wettable surfaces. We determine the wetting properties by measuring the equilibrium droplet profiles that are in turn used to evaluate the contact angles. Macroscopic arguments, such as those leading to Wenzel's law, suggest that surface roughness always amplifies the wetting properties of a lyophilic surface. However, our results indicate the opposite effect from roughness for microscopically corrugated surfaces, i.e., surface roughness deteriorates the substrate wettability. Adding the roughness to a strongly wettable surface shrinks the surface area wet with the liquid, and it either increases or only marginally affects the contact angle, depending on the degree of liquid adsorption into the nanogrooves. For a weakly wettable surface, the roughness changes the surface character from lyophilic to lyophobic due to a weakening of the solid-fluid interactions by the presence of the nanogrooves and the weaker adsorption of the liquid into the nanogrooves. PMID:26374050
Wetting properties of molecularly rough surfaces
Svoboda, Martin; Lísal, Martin; Malijevský, Alexandr
2015-09-14
We employ molecular dynamics simulations to study the wettability of nanoscale rough surfaces in systems governed by Lennard-Jones (LJ) interactions. We consider both smooth and molecularly rough planar surfaces. Solid substrates are modeled as a static collection of LJ particles arranged in a face-centered cubic lattice with the (100) surface exposed to the LJ fluid. Molecularly rough solid surfaces are prepared by removing several strips of LJ atoms from the external layers of the substrate, i.e., forming parallel nanogrooves on the surface. We vary the solid-fluid interactions to investigate strongly and weakly wettable surfaces. We determine the wetting properties by measuring the equilibrium droplet profiles that are in turn used to evaluate the contact angles. Macroscopic arguments, such as those leading to Wenzel’s law, suggest that surface roughness always amplifies the wetting properties of a lyophilic surface. However, our results indicate the opposite effect from roughness for microscopically corrugated surfaces, i.e., surface roughness deteriorates the substrate wettability. Adding the roughness to a strongly wettable surface shrinks the surface area wet with the liquid, and it either increases or only marginally affects the contact angle, depending on the degree of liquid adsorption into the nanogrooves. For a weakly wettable surface, the roughness changes the surface character from lyophilic to lyophobic due to a weakening of the solid-fluid interactions by the presence of the nanogrooves and the weaker adsorption of the liquid into the nanogrooves.
Terahertz NDE for Metallic Surface Roughness Evaluation
NASA Technical Reports Server (NTRS)
Madaras, Eric I.; Anastasi, Robert F.
2006-01-01
Metallic surface roughness in a nominally smooth surface is a potential indication of material degradation or damage. When the surface is coated or covered with an opaque dielectric material, such as paint or insulation, then inspecting for surface changes becomes almost impossible. Terahertz NDE is a method capable of penetrating the coating and inspecting the metallic surface. The terahertz frequency regime is between 100 GHz and 10 THz and has a free space wavelength of 300 micrometers at 1 THz. Pulsed terahertz radiation, can be generated and detected using optical excitation of biased semiconductors with femtosecond laser pulses. The resulting time domain signal is 320 picoseconds in duration. In this application, samples are inspected with a commercial terahertz NDE system that scans the sample and generates a set of time-domain signals that are a function of the backscatter from the metallic surface. Post processing is then performed in the time and frequency domains to generate C-scan type images that show scattering effects due to surface non-uniformity.
NASA Astrophysics Data System (ADS)
Duan, Xueyang
The objective of this dissertation is to develop forward scattering models for active microwave remote sensing of natural features represented by layered media with rough interfaces. In particular, soil profiles are considered, for which a model of electromagnetic scattering from multilayer rough surfaces with or without buried random media is constructed. Starting from a single rough surface, radar scattering is modeled using the stabilized extended boundary condition method (SEBCM). This method solves the long-standing instability issue of the classical EBCM, and gives three-dimensional full wave solutions over large ranges of surface roughnesses with higher computational efficiency than pure numerical solutions, e.g., method of moments (MoM). Based on this single surface solution, multilayer rough surface scattering is modeled using the scattering matrix approach and the model is used for a comprehensive sensitivity analysis of the total ground scattering as a function of layer separation, subsurface statistics, and sublayer dielectric properties. The buried inhomogeneities such as rocks and vegetation roots are considered for the first time in the forward scattering model. Radar scattering from buried random media is modeled by the aggregate transition matrix using either the recursive transition matrix approach for spherical or short-length cylindrical scatterers, or the generalized iterative extended boundary condition method we developed for long cylinders or root-like cylindrical clusters. These approaches take the field interactions among scatterers into account with high computational efficiency. The aggregate transition matrix is transformed to a scattering matrix for the full solution to the layered-medium problem. This step is based on the near-to-far field transformation of the numerical plane wave expansion of the spherical harmonics and the multipole expansion of plane waves. This transformation consolidates volume scattering from the buried random
Physically-based Ice Thickness and Surface Roughness Retrievals over Rough Deformed Sea Ice
NASA Astrophysics Data System (ADS)
Li, Li; Gaiser, Peter; Allard, Richard; Posey, Pamela; Hebert, David; Richter-Menge, Jacqueline; Polashenski, Christopher; Claffey, Keran
2016-04-01
The observations of sea ice thickness and ice surface roughness are critical for our understanding of the state of the changing Arctic. Currently, the Radar and/or LiDAR data of sea ice freeboard are used to infer sea ice thickness via isostasy. The underlying assumption is that the LiDAR signal returns at the air/snow interface and radar signal at the snow/ice interface. The elevations of these interfaces are determined based on LiDAR/Radar return waveforms. However, the commonly used threshold-based surface detection techniques are empirical in nature and work well only over level/smooth sea ice. Rough sea ice surfaces can modify the return waveforms, resulting in significant Electromagnetic (EM) bias in the estimated surface elevations, and thus large errors in the ice thickness retrievals. To understand and quantify such sea ice surface roughness effects, a combined EM rough surface and volume scattering model was developed to simulate radar returns from the rough sea ice 'layer cake' structure. A waveform matching technique was also developed to fit observed waveforms to a physically-based waveform model and subsequently correct the roughness induced EM bias in the estimated freeboard. This new EM Bias Corrected (EMBC) algorithm was able to better retrieve surface elevations and estimate the surface roughness parameter simultaneously. Both the ice thickness and surface roughness retrievals are validated using in-situ data. For the surface roughness retrievals, we applied this EMBC algorithm to co-incident LiDAR/Radar measurements collected during a Cryosat-2 under-flight by the NASA IceBridge missions. Results show that not only does the waveform model fit very well to the measured radar waveform, but also the roughness parameters derived independently from the LiDAR and radar data agree very well for both level and deformed sea ice. For sea ice thickness retrievals, validation based on in-situ data from the coordinated CRREL/NRL field campaign demonstrates
Measurement and modeling of rough surface effects on terahertz spectroscopy
NASA Astrophysics Data System (ADS)
Henry, S. C.; Schecklman, S.; Kniffin, G. P.; Zurk, L. M.; Chen, A.
2010-02-01
Recent improvements in sensing technology have driven new research areas within the terahertz (THz) portion of the electromagnetic (EM) spectrum. While there are several promising THz applications, several outstanding technical challenges need to be addressed before robust systems can be deployed. A particularly compelling application is the potential use of THz reflection spectroscopy for stand-off detection of drugs and explosives. A primary challenge for this application is to have sufficient signal-to-noise ratio (SNR) to allow spectroscopic identification of the target material, and surface roughness can have an impact on identification. However, scattering from a rough surface may be observed at all angles, suggesting diffuse returns can be used in robust imaging of non-cooperative targets. Furthermore, the scattering physics can also distort the reflection spectra, complicating classification algorithms. In this work, rough surface scattering effects were first isolated by measuring diffuse scattering for gold-coated sandpaper of varying roughness. Secondly, we measured scattering returns from a rough sample with a spectral signature, namely α-lactose monohydrate mixed with Teflon and pressed with sandpaper to introduce controlled roughness. For both the specular and diffuse reflection measurements, the application of traditional spectroscopy techniques provided the ability to resolve the 0.54 THz absorption peak. These results are compared with results from a smooth surface. Implications of the results on the ability to detect explosives with THz reflection spectroscopy are presented and discussed. In addition, the Small Perturbation Method (SPM) is employed to predict backscatter from lactose with a small amount of roughness.
Surface roughness effects on bidirectional reflectance
NASA Technical Reports Server (NTRS)
Smith, T. F.; Hering, R. G.
1972-01-01
An experimental study of surface roughness effects on bidirectional reflectance of metallic surfaces is presented. A facility capable of irradiating a sample from normal to grazing incidence and recording plane of incidence bidirectional reflectance measurements was developed. Samples consisting of glass, aluminum alloy, and stainless steel materials were selected for examination. Samples were roughened using standard grinding techniques and coated with a radiatively opaque layer of pure aluminum. Mechanical surface roughness parameters, rms heights and rms slopes, evaluated from digitized surface profile measurements are less than 1.0 micrometers and 0.28, respectively. Rough surface specular, bidirectional, and directional reflectance measurements for selected values of polar angle of incidence and wavelength of incident energy within the spectral range of 1 to 14 micrometers are reported. The Beckmann bidirectional reflectance model is compared with reflectance measurements to establish its usefulness in describing the magnitude and spatial distribution of energy reflected from rough surfaces.
Effect of Surface Roughness on Hydrodynamic Bearings
NASA Technical Reports Server (NTRS)
Majumdar, B. C.; Hamrock, B. J.
1981-01-01
A theoretical analysis on the performance of hydrodynamic oil bearings is made considering surface roughness effect. The hydrodynamic as well as asperity contact load is found. The contact pressure was calculated with the assumption that the surface height distribution was Gaussian. The average Reynolds equation of partially lubricated surface was used to calculate hydrodynamic load. An analytical expression for average gap was found and was introduced to modify the average Reynolds equation. The resulting boundary value problem was then solved numerically by finite difference methods using the method of successive over relaxation. The pressure distribution and hydrodynamic load capacity of plane slider and journal bearings were calculated for various design data. The effects of attitude and roughness of surface on the bearing performance were shown. The results are compared with similar available solution of rough surface bearings. It is shown that: (1) the contribution of contact load is not significant; and (2) the hydrodynamic and contact load increase with surface roughness.
ANALYZING SURFACE ROUGHNESS DEPENDENCE OF LINEAR RF LOSSES
Reece, Charles E.; Kelley, Michael J.; Xu, Chen
2012-09-01
Topographic structure on Superconductivity Radio Frequency (SRF) surfaces can contribute additional cavity RF losses describable in terms of surface RF reflectivity and absorption indices of wave scattering theory. At isotropic homogeneous extent, Power Spectrum Density (PSD) of roughness is introduced and quantifies the random surface topographic structure. PSD obtained from different surface treatments of niobium, such Buffered Chemical Polishing (BCP), Electropolishing (EP), Nano-Mechanical Polishing (NMP) and Barrel Centrifugal Polishing (CBP) are compared. A perturbation model is utilized to calculate the additional rough surface RF losses based on PSD statistical analysis. This model will not consider that superconductor becomes normal conducting at fields higher than transition field. One can calculate the RF power dissipation ratio between rough surface and ideal smooth surface within this field range from linear loss mechanisms.
Roughness Perception of Haptically Displayed Fractal Surfaces
NASA Technical Reports Server (NTRS)
Costa, Michael A.; Cutkosky, Mark R.; Lau, Sonie (Technical Monitor)
2000-01-01
Surface profiles were generated by a fractal algorithm and haptically rendered on a force feedback joystick, Subjects were asked to use the joystick to explore pairs of surfaces and report to the experimenter which of the surfaces they felt was rougher. Surfaces were characterized by their root mean square (RMS) amplitude and their fractal dimension. The most important factor affecting the perceived roughness of the fractal surfaces was the RMS amplitude of the surface. When comparing surfaces of fractal dimension 1.2-1.35 it was found that the fractal dimension was negatively correlated with perceived roughness.
Rough surface reconstruction for ultrasonic NDE simulation
Choi, Wonjae; Shi, Fan; Lowe, Michael J. S.; Skelton, Elizabeth A.; Craster, Richard V.
2014-02-18
The reflection of ultrasound from rough surfaces is an important topic for the NDE of safety-critical components, such as pressure-containing components in power stations. The specular reflection from a rough surface of a defect is normally lower than it would be from a flat surface, so it is typical to apply a safety factor in order that justification cases for inspection planning are conservative. The study of the statistics of the rough surfaces that might be expected in candidate defects according to materials and loading, and the reflections from them, can be useful to develop arguments for realistic safety factors. This paper presents a study of real rough crack surfaces that are representative of the potential defects in pressure-containing power plant. Two-dimensional (area) values of the height of the roughness have been measured and their statistics analysed. Then a means to reconstruct model cases with similar statistics, so as to enable the creation of multiple realistic realizations of the surfaces, has been investigated, using random field theory. Rough surfaces are reconstructed, based on a real surface, and results for these two-dimensional descriptions of the original surface have been compared with those from the conventional model based on a one-dimensional correlation coefficient function. In addition, ultrasonic reflections from them are simulated using a finite element method.
Replicated mask surface roughness effects on EUV lithographic patterning and line edge roughness
NASA Astrophysics Data System (ADS)
George, Simi A.; Naulleau, Patrick P.; Gullikson, Eric M.; Mochi, Iacopo; Salmassi, Farhad; Goldberg, Kenneth A.; Anderson, Erik H.
2011-04-01
To quantify the roughness contributions to speckle, a programmed roughness substrate was fabricated with a number of areas having different roughness magnitudes. The substrate was then multilayer coated. Atomic force microscopy (AFM) surface maps were collected before and after multilayer deposition. At-wavelength reflectance and total integrated scattering measurements were also completed. Angle resolved scattering based power spectral densities are directly compared to the AFM based power spectra. We show that AFM overpredicts the roughness in the picometer measurements range. The mask was then imaged at-wavelength for the direct characterization of the aerial image speckle using the SEMATECH Berkeley Actinic Inspection Tool (AIT). Modeling was used to test the effectiveness of the different metrologies in predicting the measured aerial-image speckle. AIT measured contrast values are 25% or more than the calculated image contrast values obtained using the measured rms roughness input. The extent to which the various metrologies can be utilized for specifying tolerable roughness limits on EUV masks is still to be determined. Further modeling and measurements are being planned.
Replicated mask surface roughness effects on EUV lithographic pattering and line edge roughness
George, Simi A.; Naulleau, Patrick P.; Gullikson, Eric M.; Mochi, Iacopo; Salmassi, Farhad; Goldberg, Kenneth A.; Anderson, Erik H.
2011-03-11
To quantify the roughness contributions to speckle, a programmed roughness substrate was fabricated with a number of areas having different roughness magnitudes. The substrate was then multilayer coated. Atomic force microscopy (AFM) surface maps were collected before and after multilayer deposition. At-wavelength reflectance and total integrated scattering measurements were also completed. Angle resolved scattering based power spectral densities are directly compared to the AFM based power spectra. We show that AFM overpredicts the roughness in the picometer measurements range. The mask was then imaged at-wavelength for the direct characterization of the aerial image speckle using the SEMATECH Berkeley Actinic Inspection Tool (AIT). Modeling was used to test the effectiveness of the different metrologies in predicting the measured aerial-image speckle. AIT measured contrast values are 25% or more than the calculated image contrast values obtained using the measured rms roughness input. The extent to which the various metrologies can be utilized for specifying tolerable roughness limits on EUV masks is still to be determined. Further modeling and measurements are being planned.
Surface roughness characterization of dental fillings: a diffractive analysis
NASA Astrophysics Data System (ADS)
April, Gilbert V.; Bouchard, Michel; Doucet, Michel
1993-02-01
The large number of new materials such as amalgams and the variety of techniques for finishing and polishing in operative dentistry has stimulated interest in simple, nondestructive methods of surface roughness evaluation. We studied an optical method based on the scattering of reflected coherent light on prepared samples of composite resins submitted to different surface treatments. The method should be able to measure the degree of flatness of the samples, thus enabling a classification procedure according to a figure of merit to be defined. The diffraction properties of such moderately rough surfaces has been correlated with mechanical profilometer measurements of the residual granular structure after polishing. Different surface treatments of composite resins result in distinctive levels of surface flatness, and it is shown that a relation between the intensity of the normalized specular reflection of a beam of coherent light and the rms surface roughness can be established for characterization purposes.
Layering of ionic liquids on rough surfaces
NASA Astrophysics Data System (ADS)
Sheehan, Alexis; Jurado, L. Andres; Ramakrishna, Shivaprakash N.; Arcifa, Andrea; Rossi, Antonella; Spencer, Nicholas D.; Espinosa-Marzal, Rosa M.
2016-02-01
Understanding the behavior of ionic liquids (ILs) either confined between rough surfaces or in rough nanoscale pores is of great relevance to extend studies performed on ideally flat surfaces to real applications. In this work we have performed an extensive investigation of the structural forces between two surfaces with well-defined roughness (<9 nm RMS) in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide by atomic force microscopy. Statistical studies of the measured layer thicknesses, layering force, and layering frequency reveal the ordered structure of the rough IL-solid interface. Our work shows that the equilibrium structure of the interfacial IL strongly depends on the topography of the contact.Understanding the behavior of ionic liquids (ILs) either confined between rough surfaces or in rough nanoscale pores is of great relevance to extend studies performed on ideally flat surfaces to real applications. In this work we have performed an extensive investigation of the structural forces between two surfaces with well-defined roughness (<9 nm RMS) in 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide by atomic force microscopy. Statistical studies of the measured layer thicknesses, layering force, and layering frequency reveal the ordered structure of the rough IL-solid interface. Our work shows that the equilibrium structure of the interfacial IL strongly depends on the topography of the contact. Electronic supplementary information (ESI) available: Optimized geometries and sizes for [HMIM] Ntf2, SEM images of the smooth and rough colloids, frequency of occurrence of layering in the resolved force-distance curves for all investigated systems with [HMIM] Ntf2, layer size and layering force measured with a sharp tip on mica for the same IL, and results of the kinetics experiments. See DOI: 10.1039/c5nr07805a
Simplified Approach to Predicting Rough Surface Transition
NASA Technical Reports Server (NTRS)
Boyle, R. J.; Stripf, M.
2009-01-01
Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consistent with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparisons are presented with published experimental data. Some of the data are for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach taken in this analysis is to treat the roughness in a statistical sense, consistent with what would be obtained from blades measured after exposure to actual engine environments. An approach is given to determine the equivalent sand grain roughness from the statistics of the regular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test conditions. Additional comparisons are made with experimental heat transfer data, where the roughness geometries are both regular and statistical. Using the developed analysis, heat transfer calculations are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.
Simplified Approach to Predicting Rough Surface Transition
NASA Technical Reports Server (NTRS)
Boyle, Robert J.; Stripf, Matthias
2009-01-01
Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consiste nt with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparison s are presented with published experimental data. Some of the data ar e for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach ta ken in this analysis is to treat the roughness in a statistical sense , consistent with what would be obtained from blades measured after e xposure to actual engine environments. An approach is given to determ ine the equivalent sand grain roughness from the statistics of the re gular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test co nditions. Additional comparisons are made with experimental heat tran sfer data, where the roughness geometries are both regular as well a s statistical. Using the developed analysis, heat transfer calculatio ns are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.
Photochemistry on rough metal surfaces
Goncher, G.M.; Parsons, C.A.; Harris, C.B.
1984-09-13
The general question of laser-induced photochemistry on metal surfaces is addressed. Specifically, the authors have studied resonant photodecomposition of a variety of aromatic molecules on roughened silver surfaces in ultrahigh vacuum. A continuous ion laser source at a number of different wavelengths in the region 350-410 nm was used to produce graphitic carbon on the surface which was monitored by Raman spectroscopy at the 1580-cm/sup -1/ band of surface carbon. Laser power-dependence studies of fragmentation rate for several molecules at 406.7nm indicate that the initial absorption step is a two-photon process. Energetic considerations imply that photochemistry for other molecules studied is also due to multiphoton absorption, except for benzaldehyde fragmentation at 350.7-nm excitation, where the photodecomposition rate is linear. Distance-dependence studies of photofragmentation rates by use of an inert spacer layer to separatte the molecule undergoing photochemistry from the surface indicate that energy transfer to the metal surface is important in determining the reaction rate. Decomposition mechanism has not been fully evaluated.
Thermal smoothing of rough surfaces in vacuo
NASA Technical Reports Server (NTRS)
Wahl, G.
1986-01-01
The derivation of equations governing the smoothing of rough surfaces, based on Mullins' (1957, 1960, and 1963) theories of thermal grooving and of capillarity-governed solid surface morphology is presented. As an example, the smoothing of a one-dimensional sine-shaped surface is discussed.
Multiphonon scattering from surfaces
NASA Astrophysics Data System (ADS)
Manson, J. R.; Celli, V.; Himes, D.
1994-01-01
We consider the relationship between several different formalisms for treating the multiphonon inelastic scattering of atomic projectiles from surfaces. Starting from general principles of formal scattering theory, the trajectory approximation to the scattering intensity is obtained. From the trajectory approximation, the conditions leading to the fast-collision approximation for multiquantum inelastic scattering are systematically derived.
Surface roughness effects on equilibrium temperature.
NASA Technical Reports Server (NTRS)
Houchens, A. F.; Hering, R. G.
1972-01-01
An analysis is presented for evaluation of equilibrium temperature distribution on radiatively adiabatic, adjoint planes which are uniformly irradiated by a collimated solar flux. The analysis employs a semigrey spectral model. Radiation properties for surface emitted radiation are obtained from the expressions of electromagnetic theory for smooth surfaces. Rough surface properties for solar radiation are given by the Beckmann bidirectional reflectance model. Numerical solutions to the governing equations yield equilibrium temperature distributions for a range of the influencing parameters. Surface roughness has little influence on equilibrium temperature for materials with high values for solar absorptance. However, for low or intermediate values of solar absorptance, roughness effects on the spatial distribution of reflected solar radiation can significantly alter equilibrium temperature particularly at surface elements where radiant interaction is small.
Ghost imaging for a reflected object with a rough surface
Wang Chunfang; Zhang Dawei; Chen Bin; Bai Yanfeng
2010-12-15
Ghost imaging for the reflected object with rough surface is investigated. The surface height variance {sigma}{sub h}{sup 2} and the correlation length l{sub c} have been introduced to characterize the rough surface. Based on a simple scattering model, we derive the analytical expressions which are used to describe the effects of {sigma}{sub h}{sup 2} and l{sub c} on ghost imaging. The results show that both {sigma}{sub h}{sup 2} and l{sub c} have no influence on the image resolution, while the convergence of the correlation decreases as {sigma}{sub h}{sup 2} increases. Additionally, the bucket detector used in the test arm can dramatically improve the visibility of ghost images. The results are backed up by numerical simulations, in which a Monte Carlo approach to generate a rough surface has been used.
The effect of roughness model on scattering properties of ice crystals
NASA Astrophysics Data System (ADS)
Geogdzhayev, Igor; van Diedenhoven, Bastiaan
2016-07-01
We compare stochastic models of microscale surface roughness assuming uniform and Weibull distributions of crystal facet tilt angles to calculate scattering by roughened hexagonal ice crystals using the geometric optics (GO) approximation. Both distributions are determined by similar roughness parameters, while the Weibull model depends on the additional shape parameter. Calculations were performed for two visible wavelengths (864 nm and 410 nm) for roughness values between 0.2 and 0.7 and Weibull shape parameters between 0 and 1.0 for crystals with aspect ratios of 0.21, 1 and 4.8. For this range of parameters we find that, for a given roughness level, varying the Weibull shape parameter can change the asymmetry parameter by up to about 0.05. The largest effect of the shape parameter variation on the phase function is found in the backscattering region, while the degree of linear polarization is most affected at the side-scattering angles. For high roughness, scattering properties calculated using the uniform and Weibull models are in relatively close agreement for a given roughness parameter, especially when a Weibull shape parameter of 0.75 is used. For smaller roughness values, a shape parameter close to unity provides a better agreement. Notable differences are observed in the phase function over the scattering angle range from 5° to 20°, where the uniform roughness model produces a plateau while the Weibull model does not.
In situ surface roughness measurement during PECVD diamond film growth
Zuiker, C.D.; Gruen, D.M.; Krauss, A.R.
1995-06-01
To investigate the development of surface morphology and bulk optical attenuation in diamond films, we have followed diamond film growth on silicon by in-situ laser reflection interferometry in a microwave plasma chemical vapor deposition system. A model for the interpretation of the reflectivity data in terms of film thickness, rms surface roughness and bulk losses due to scattering and absorption is presented. Results are compared with ex situ measurements of these quantities and found to be in good agreement.
A rough-surface thermophysical model for airless planets
NASA Technical Reports Server (NTRS)
Spencer, John R.
1990-01-01
A model for determining diurnal temperatures in spherical-section depressions and which encompasses both subsurface heat-flow and direct and scattered sunlight effects is presently applied to the disk-integrated thermal emission of a rough planetary surface with nonzero thermal inertia. Attention is given to the variation with roughness and thermal inertia of the beaming parameter eta, which characterizes zero-phase thermal emission by comparison with a smooth, nonrotating body and is almost independent of albedo for a given surface roughness. The thermal phase curve of Ceres is noted to be well matched by the model features of (1) prograde rotation, (2) 44-deg rms surface slope, and (3) a thermal inertia that is 30 percent of the lunar value.
A rough-surface thermophysical model for airless planets
Spencer, J.R. )
1990-01-01
A model for determining diurnal temperatures in spherical-section depressions and which encompasses both subsurface heat-flow and direct and scattered sunlight effects is presently applied to the disk-integrated thermal emission of a rough planetary surface with nonzero thermal inertia. Attention is given to the variation with roughness and thermal inertia of the beaming parameter eta, which characterizes zero-phase thermal emission by comparison with a smooth, nonrotating body and is almost independent of albedo for a given surface roughness. The thermal phase curve of Ceres is noted to be well matched by the model features of (1) prograde rotation, (2) 44-deg rms surface slope, and (3) a thermal inertia that is 30 percent of the lunar value. 23 refs.
Forward and inverse models of electromagnetic scattering from layered media with rough interfaces
NASA Astrophysics Data System (ADS)
Tabatabaeenejad, Seyed Alireza
This work addresses the problem of electromagnetic scattering from layered dielectric structures with rough boundaries and the associated inverse problem of retrieving the subsurface parameters of the structure using the scattered field. To this end, a forward scattering model based on the Small Perturbation Method (SPM) is developed to calculate the first-order spectral-domain bistatic scattering coefficients of a two-layer rough surface structure. SPM requires the boundaries to be slightly rough compared to the wavelength, but to understand the range of applicability of this method in scattering from two-layer rough surfaces, its region of validity is investigated by comparing its output with that of a first principle solver that does not impose roughness restrictions. The Method of Moments (MoM) is used for this purpose. Finally, for retrieval of the model parameters of the layered structure using scattered field, an inversion scheme based on the Simulated Annealing method is investigated and a strategy is proposed to address convergence to local minimum.
Correlation of Windspeed and Antarctic Surface Roughness
NASA Astrophysics Data System (ADS)
Stockham, Mark; Anita Collaboration
2015-04-01
When electromagnetic waves interact with a media interface the transmitted and reflected portions of the incoming wave depend on the incident angle of the wave and wavelength (as well as the material properties of the media). The roughness of the surface of Antarctica affects the radio frequency signals received by airborne experiments, such as the balloon-borne experiment ANITA (ANtarctic Impulsive Transient Antenna) which observes the reflected radio waves from cosmic ray-induced extensive air showers (EAS). Roughness of a given scale can cause decoherence of the reflected signal and is an important effect to understand when estimating the amplitude of the incoming wave based on the reflected wave. It is challenging to get a survey of surface roughness over many of the areas that these experiments are likely to pass over. Correlating historical wind speed records with statistical roughness as observed by the backscatter of satellite [Rémy F, Parouty S. Remote Sensing. 2009] and airborne experiments operating at different frequencies can possibly be used to predict time-dependent surface roughness with surface wind speed as the input. These correlations will be presented for a variety of areas on the Antarctic ice shelf. NASA Grant NNX11AC47G.
Degree of ice particle surface roughness inferred from polarimetric observations
NASA Astrophysics Data System (ADS)
Hioki, Souichiro; Yang, Ping; Baum, Bryan A.; Platnick, Steven; Meyer, Kerry G.; King, Michael D.; Riedi, Jerome
2016-06-01
The degree of surface roughness of ice particles within thick, cold ice clouds is inferred from multi-directional, multi-spectral satellite polarimetric observations over oceans, assuming a column-aggregate particle habit. An improved roughness inference scheme is employed that provides a more noise-resilient roughness estimate than the conventional best-fit approach. The improvements include the introduction of a quantitative roughness parameter based on empirical orthogonal function analysis and proper treatment of polarization due to atmospheric scattering above clouds. A global 1-month data sample supports the use of a severely roughened ice habit to simulate the polarized reflectivity associated with ice clouds over ocean. The density distribution of the roughness parameter inferred from the global 1-month data sample and further analyses of a few case studies demonstrate the significant variability of ice cloud single-scattering properties. However, the present theoretical results do not agree with observations in the tropics. In the extratropics, the roughness parameter is inferred but 74 % of the sample is out of the expected parameter range. Potential improvements are discussed to enhance the depiction of the natural variability on a global scale.
Venus surface roughness and Magellan stereo data
NASA Technical Reports Server (NTRS)
Maurice, Kelly E.; Leberl, Franz W.; Norikane, L.; Hensley, Scott
1994-01-01
Presented are results of some studies to develop tools useful for the analysis of Venus surface shape and its roughness. Actual work was focused on Maxwell Montes. The analyses employ data acquired by means of NASA's Magellan satellite. The work is primarily concerned with deriving measurements of the Venusian surface using Magellan stereo SAR. Roughness was considered by means of a theoretical analyses based on digital elevation models (DEM's), on single Magellan radar images combined with radiometer data, and on the use of multiple overlapping Magellan radar images from cycles 1, 2, and 3, again combined with collateral radiometer data.
Surface roughness modulations by submesoscale currents
NASA Astrophysics Data System (ADS)
Rascle, Nicolas; Chapron, Bertrand; Nouguier, Frederic; Ponte, Aurelien; Mouche, Alexis; Molemaker, Jeroen
2016-04-01
At times, high resolution images of sea surface roughness can provide stunning details of submesoscale upper ocean dynamics. As interpreted, transformations of short scale wind waves by horizontal current gradients are responsible for those spectacular observations. Here we present two major advances towards the quantitative interpretation of those observations. First, we show that surface roughness variations mainly trace two particular characteristics of the current gradient tensor, the divergence and the strain in the wind direction. Local vorticity and shear in the wind direction should not affect short scale roughness distribution and would not be detectable. Second, we discuss the effect of the viewing direction using sets of quasi-simultaneous sun glitter images, taken from different satellites to provide different viewing configurations. We show that upwind and crosswind viewing observations can be markedly different. As further confirmed with idealized numerical simulations, this anisotropy well traces surface current strain area, while more isotropic contrasts likely trace areas dominated by surface divergence conditions. These findings suggest the potential to directly observe surface currents at submesoscale by using surface roughness observations at multiple azimuth viewing angles. They also pave the way towards a better understanding of the coupling between ocean, waves and atmosphere at high resolution.
Root mean square roughness of nano porous silicon by scattering spectra
NASA Astrophysics Data System (ADS)
Dariani, R. S.; Ebrahimnasab, S.
2014-10-01
We demonstrate that surface roughness can be obtained by scattering spectra and is more accurate than mechanical devices such as scanning probe microscopy (SPM) and profilometry techniques such as stylus (contact) profilometry. Due to the probe effect in these techniques, most of the information may be lost. Root mean square ( σ) is obtained experimentally by scattering spectra and theoretically by the Davies-Bennett/Porteus equation. Then, σ is compared with AFM results. Roughness behaviour is studied for four nano porous silicon surfaces, which have been fabricated using the electrochemical method at different etching times. Also, a band gap region can be determined directly from reflection spectrum.
The geological interpretation of photometric surface roughness
NASA Technical Reports Server (NTRS)
Helfenstein, Paul
1988-01-01
A computer-generated km-scale relief map, whose topographic facets on scales of less than a few m are assumed to have smooth particulate surfaces, is the basis of the present investigation of the relationship between photometrically-derived values of Hapke's (1984) roughness parameter theta and topographic scale. The addition of m-km scale-range relief to the otherwise smooth surface alters integral photometric behavior in a way that is consistent with Hapke's equation; the roughness characterized by theta is an integral property over all scales up to the resolution limit of the photometric data used in its determination. With sufficient phase angle coverage, theta can distinguish terrains with very different integral roughnesses.
Surface forces: Surface roughness in theory and experiment
Parsons, Drew F. Walsh, Rick B.; Craig, Vincent S. J.
2014-04-28
A method of incorporating surface roughness into theoretical calculations of surface forces is presented. The model contains two chief elements. First, surface roughness is represented as a probability distribution of surface heights around an average surface height. A roughness-averaged force is determined by taking an average of the classic flat-surface force, weighing all possible separation distances against the probability distributions of surface heights. Second the model adds a repulsive contact force due to the elastic contact of asperities. We derive a simple analytic expression for the contact force. The general impact of roughness is to amplify the long range behaviour of noncontact (DLVO) forces. The impact of the elastic contact force is to provide a repulsive wall which is felt at a separation between surfaces that scales with the root-mean-square (RMS) roughness of the surfaces. The model therefore provides a means of distinguishing between “true zero,” where the separation between the average centres of each surface is zero, and “apparent zero,” defined by the onset of the repulsive contact wall. A normal distribution may be assumed for the surface probability distribution, characterised by the RMS roughness measured by atomic force microscopy (AFM). Alternatively the probability distribution may be defined by the histogram of heights measured by AFM. Both methods of treating surface roughness are compared against the classic smooth surface calculation and experimental AFM measurement.
Surface Roughness and Snow Accumulation in East Antarctica
NASA Astrophysics Data System (ADS)
Scambos, T. A.; Vornberger, P. L.; Bohlander, J. A.; Das, I.; Klinger, M.; Pope, A.; Lenaerts, J.; Fahnestock, M. A.
2015-12-01
A complex relationship exists between snow accumulation (e.g., net surface mass balance) and meter-scale surface roughness as represented by sastrugi and erosional structures over the East Antarctic Ice Sheet (EAIS). The morphology of the ice sheet at this scale is a result of a complex interaction between katabatic winds, synoptic storms, and the slope of the surface, all driving local patterns of snow accretion and sublimation. In megadune regions, the accumulation, surface slope, and surface roughness are highly correlated with slope. Smooth glazed surfaces are present on the steeper leeward wind-faces, and much rougher snow-accreting megadunes are present on the windward (depositional) slope. However, the highest elevation areas near the ridge crest of the EAIS (above ~3200 m) have a converse relationship between roughness and accumulation. Here, very low wind ridge crest areas are smooth and have higher accumulation than adjacent, slightly steeper regions that exhibit a slight increase in roughness. Below the main regions of megadunes (<~2000 m) wind glaze areas gradually become rougher as wind scouring and erosion dominate locally steeper regions. In coastal areas (<~1000), roughness is highly variable, and is tied to frequent synoptic storm deposition. We compare roughness data derived from MISR (Multi-angle Imaging SpectroRadiometer) and Landsat 8 acquisitions with available wind and accumulation data from climate model results and field measurements. Roughness is determined by sunlight scattering relative to viewing geometry (MISR) or from the amplitude of textural characteristics tied to surface sastrugi (Landsat 8). Both are validated by comparison with meter-scale images (WorldView-1) and field observations. MISR roughness mapping shows persistent qualitative patterns of surface roughness across the EAIS, but an absolute roughness scale mapping is difficult to generate because of complex viewing, illumination, and bi-directional reflectance variations
Surface roughness limited contrast to clutter ratios THz medical imaging (Conference Presentation)
NASA Astrophysics Data System (ADS)
Sung, Shijun; Bajwa, Neha; Goell, Jacob; Taylor, Zachary
2016-03-01
The THz electromagnetic properties of rough surface are explored and their effect on the observed contrast in THz images is quantified. Rough surface scatter is a major source of clutter in THz imaging as the rough features of skin and other tissues result in non-trivial reflection signal modulation. Traditional approaches to data collection utilize dielectric windows to flatten surfaces for THz imaging. However, there is substantial interest surrounding window free imaging as contact measurements are not ideal for a range of candidate diseases and injuries. In this work we investigate the variation in reflected signal in the specular direction from rough surfaces targets with known roughness parameters. Signal to clutter ratios are computed and compared with that predicted by Rayleigh Rough surface scattering theory. It is shown that Rayleigh rough surface scattering theory, developed for rough features larger than the interacting wavelength, holds acceptable at THz frequencies with rough features much smaller than the wavelength. Additionally, we present some biological tissue imaging examples to illustrate the impact of rough surface scattering in image quality.
Industrial characterization of nano-scale roughness on polished surfaces
NASA Astrophysics Data System (ADS)
Feidenhans'l, Nikolaj A.; Hansen, Poul-Erik; Pilný, Lukáš; Madsen, Morten H.; Bissacco, Giuliano; Petersen, Jan C.; Taboryski, Rafael
2015-10-01
We report a correlation between the scattering value "Aq" and the ISO standardized roughness parameter Rq. The Aq value is a measure for surface smoothness, and can easily be determined from an optical scattering measurement. The correlation equation extrapolates the Aq value from a narrow measurement range of +/-16° from specular to a broader range of +/-80°, corresponding to spatial surface wavelengths of 0.8 μm to 25 μm, and converts the Aq value to the Rq value for the surface. Furthermore, we present an investigation of the changes in scattering intensities, when a surface is covered with a thin liquid film. It is shown that the changes in the angular scattering intensities can be compensated for the liquid film, using empirically determined relations. This allows a restoration of the "true" scattering intensities which would be measured from a corresponding clean surface. The compensated scattering intensities provide Aq values within 5.7 % +/- 6.1 % compared to the measurements on clean surfaces.
Three-tier rough superhydrophobic surfaces.
Cao, Yuanzhi; Yuan, Longyan; Hu, Bin; Zhou, Jun
2015-08-01
A three-tier rough superhydrophobic surface was fabricated by growing hydrophobic modified (fluorinated silane) zinc oxide (ZnO)/copper oxide (CuO) hetero-hierarchical structures on silicon (Si) micro-pillar arrays. Compared with the other three control samples with a less rough tier, the three-tier surface exhibits the best water repellency with the largest contact angle 161° and the lowest sliding angle 0.5°. It also shows a robust Cassie state which enables the water to flow with a speed over 2 m s(-1). In addition, it could prevent itself from being wetted by the droplet with low surface tension (mixed water and ethanol 1:1 in volume) which reveals a flow speed of 0.6 m s(-1) (dropped from the height of 2 cm). All these features prove that adding another rough tier on a two-tier rough surface could futher improve its water-repellent properties. PMID:26184512
Surface Roughness Reduction on Divinylbenzene Foam Shells
NASA Astrophysics Data System (ADS)
Streit, Jon; Karnes, John; Motta, Brian; Petta, Nicole
2009-11-01
Inertial fusion energy targets for the Naval Research Laboratory's High Average Power Laser Program require millimeter-scale, low density foam capsules with a gas permeation barrier and an outer surface roughness less than 50 nm RMS. Divinylbenzene (DVB) foam is a candidate for the capsule wall material, but its porous, open celled surface has been both too rough and difficult to seal. To overcome this difficulty we have repurposed a previously reported dual stage initiator emulsion microencapsulation method, adding an additional step that enhances the surface of the foam capsules. Using both low and high temperature initiators allows the DVB foam to gel in the low temperature stage and a water soluble monomer to be added and polymerized during the high temperature stage without breaking down the emulsion. This method forms a submicron skin that covers the open celled DVB foam surface, resulting in a superior substrate for gas permeation barrier deposition.
Boltzmann active walkers and rough surfaces
NASA Astrophysics Data System (ADS)
Pochy, R. D.; Kayser, D. R.; Aberle, L. K.; Lam, L.
1993-06-01
An active walker model (AWM) was recently proposed by Freimuth and Lam for the generation of various filamentary patterns. In an AWM, the walker changes the landscape as it walks, and its steps are in turn influenced by the changing landscape. The landscape so obtained is a rough surface. In this paper, the properties of such a rough surface (with average height conserved) generated by a Boltzmann active walker in 1 + 1 dimensions is investigated in detail. The scaling properties of the surface thickness σ T is found to belong to a new class quite different from other types of fractal surfaces. For example, σ T is independent of the system size L, but is a function of the “temperature” T. Soliton propagation is found when T = 0.
Rough Fresnel zone plates over metallic surfaces.
Salgado-Remacha, Francisco Javier; Sanchez-Brea, Luis Miguel; Alvarez-Rios, Francisco Javier; Bernabeu, Eusebio
2010-04-01
We analyze the focusing properties of Fresnel zone plates fabricated over steel tapes using laser ablation. Our intention is to implement the use of micro-optical elements when the use of conventional chrome-glass elements is not indicated. Because of the manufacture process, the surface presents a certain anisotropic roughness, which reduces the focusing properties. First, we develop numerical simulations by means of the Rayleigh-Sommerfeld approach, showing how roughness in both levels of the Fresnel zone plate affects the focalization of the lens. We also manufacture Fresnel zone plates over steel tape, and perform experimental verification that corroborates the numerical results. PMID:20357856
Surface roughness effects in elastohydrodynamic contacts
NASA Technical Reports Server (NTRS)
Tripp, J. H.; Hamrock, B. J.
1985-01-01
Surface roughness effects in full-film EHL contacts were studied. A flow factor modification to the Reynolds equation was applied to piezoviscous-elastic line contacts. Results for ensemble-averaged film shape, pressure distribution, and other mechanical quantities were obtained. Asperities elongated in the flow direction by a factor exceeding two decreased both film shape and pressure extrema at constant load; isotropic or transverse asperities increased these extrema. The largest effects are displayed by traction, which increased by over 5% for isotropic or transverse asperities and by slightly less for longitudinal roughness.
Rough and Steep Terrain Lunar Surface Mobility
NASA Technical Reports Server (NTRS)
Wilcox, Brian
2005-01-01
In the summer of 2004, the NASA Exploration Systems Mission Directorate conducted an open call for projects relevant to human and robotic exploration of the Earth-Moon and Mars systems. A project entitled 'Rough and Steep Terrain Lunar Surface Mobility' was submitted by JPL and accepted by NASA. The principal investigator of this project describes the robotic vehicle being developed for this effort, which includes six 'wheels-on-legs' so that it can roll efficiently on relatively smooth terrain but walk (using locked wheels as footpads) when "the going gets rough".
Degree of ice particle surface roughness inferred from polarimetric observations
NASA Astrophysics Data System (ADS)
Hioki, S.; Yang, P.; Baum, B. A.; Platnick, S.; Meyer, K. G.; King, M. D.; Riedi, J.
2015-12-01
The degree of surface roughness of ice particles within thick, cold ice clouds is inferred from multi-directional, multi-spectral satellite polarimetric observations over oceans, assuming a column-aggregate particle habit. An improved roughness inference scheme is employed in the analysis that provides a more noise-resilient roughness estimate than the conventional best-fit approach. The improvements include the introduction of a quantitative roughness parameter based on empirical orthogonal function analysis and proper treatment of polarization due to atmospheric scattering above clouds. A global one-month data sample supports the use of a severely roughened ice habit to simulate the polarized reflectivity associated with ice clouds over ocean. The density distribution of the roughness parameter inferred from the global one-month data sample and further analyses of a few case studies demonstrate the significant variability of ice cloud single-scattering properties. The present theoretical results are in close agreement with observations in the extratropics but not in the tropics. Potential improvements are discussed to enhance the depiction of the natural variability on a global scale.
Wenzel Wetting on Slippery Rough Surfaces
NASA Astrophysics Data System (ADS)
Stogin, Birgitt; Dai, Xianming; Wong, Tak-Sing
2015-11-01
Liquid repellency is an important surface property used in a wide range of applications including self-cleaning, anti-icing, anti-biofouling, and condensation heat transfer, and is characterized by apparent contact angle (θ*) and contact angle hysteresis (Δθ*). The Wenzel equation (1936) predicts θ* of liquids in the Wenzel state, and is one of the most fundamental equations in the wetting field. However, droplets in the Wenzel state on conventional rough surfaces exhibit large Δθ* , making it difficult to experimentally verify the model with precision. As a result, precise verification of the Wenzel wetting model has remained an open scientific question for the past 79 years. Here we introduce a new class of liquid-infused surfaces called slippery rough surfaces -- surfaces with significantly reduced Δθ* compared to conventional rough surfaces--and use them to experimentally assess the Wenzel equation with the highest precision to date. We acknowledge the funding support by National Science Foundation (NSF) CAREER Award #: 1351462 and Office of Navy Research MURI Award #: N00014-12-1-0875. Stogin acknowledges the support from the NSF Graduate Research Fellowship (Grant No. DGE1255832).
Wetting on rough self-affine surfaces
NASA Astrophysics Data System (ADS)
Palasantzas, George
1995-05-01
In this paper, we present a general investigation of the effective potential for complete wetting on self-affine rough surfaces. The roughness effect is investigated by means of the height-height correlation model in Fourier space ~(1+aξ2q2)-1-H. The parameters H and ξ are, respectively, the roughness exponent and the substrate in-plane correlation length. It is observed that the effect of H on the free interface profile is significant for ξ
Poly-Gaussian model of randomly rough surface in rarefied gas flow
Aksenova, Olga A.; Khalidov, Iskander A.
2014-12-09
Surface roughness is simulated by the model of non-Gaussian random process. Our results for the scattering of rarefied gas atoms from a rough surface using modified approach to the DSMC calculation of rarefied gas flow near a rough surface are developed and generalized applying the poly-Gaussian model representing probability density as the mixture of Gaussian densities. The transformation of the scattering function due to the roughness is characterized by the roughness operator. Simulating rough surface of the walls by the poly-Gaussian random field expressed as integrated Wiener process, we derive a representation of the roughness operator that can be applied in numerical DSMC methods as well as in analytical investigations.
Backscattering from a Gaussian distributed, perfectly conducting, rough surface
NASA Technical Reports Server (NTRS)
Brown, G. S.
1977-01-01
The problem of scattering by random surfaces possessing many scales of roughness is analyzed. The approach is applicable to bistatic scattering from dielectric surfaces, however, this specific analysis is restricted to backscattering from a perfectly conducting surface in order to more clearly illustrate the method. The surface is assumed to be Gaussian distributed so that the surface height can be split into large and small scale components, relative to the electromagnetic wavelength. A first order perturbation approach is employed wherein the scattering solution for the large scale structure is perturbed by the small scale diffraction effects. The scattering from the large scale structure is treated via geometrical optics techniques. The effect of the large scale surface structure is shown to be equivalent to a convolution in k-space of the height spectrum with the following: the shadowing function, a polarization and surface slope dependent function, and a Gaussian factor resulting from the unperturbed geometrical optics solution. This solution provides a continuous transition between the near normal incidence geometrical optics and wide angle Bragg scattering results.
Soil Surface Roughness through Image Analysis
NASA Astrophysics Data System (ADS)
Tarquis, A. M.; Saa-Requejo, A.; Valencia, J. L.; Moratiel, R.; Paz-Gonzalez, A.; Agro-Environmental Modeling
2011-12-01
Soil erosion is a complex phenomenon involving the detachment and transport of soil particles, storage and runoff of rainwater, and infiltration. The relative magnitude and importance of these processes depends on several factors being one of them surface micro-topography, usually quantified trough soil surface roughness (SSR). SSR greatly affects surface sealing and runoff generation, yet little information is available about the effect of roughness on the spatial distribution of runoff and on flow concentration. The methods commonly used to measure SSR involve measuring point elevation using a pin roughness meter or laser, both of which are labor intensive and expensive. Lately a simple and inexpensive technique based on percentage of shadow in soil surface image has been developed to determine SSR in the field in order to obtain measurement for wide spread application. One of the first steps in this technique is image de-noising and thresholding to estimate the percentage of black pixels in the studied area. In this work, a series of soil surface images have been analyzed applying several de-noising wavelet analysis and thresholding algorithms to study the variation in percentage of shadows and the shadows size distribution. Funding provided by Spanish Ministerio de Ciencia e Innovación (MICINN) through project no. AGL2010- 21501/AGR and by Xunta de Galicia through project no INCITE08PXIB1621 are greatly appreciated.
Modeling superhydrophobic surfaces comprised of random roughness
NASA Astrophysics Data System (ADS)
Samaha, M. A.; Vahedi Tafreshi, H.; Gad-El-Hak, M.
2011-11-01
We model the performance of superhydrophobic surfaces comprised of randomly distributed roughness that resembles natural surfaces, or those produced via random deposition of hydrophobic particles. Such a fabrication method is far less expensive than ordered-microstructured fabrication. The present numerical simulations are aimed at improving our understanding of the drag reduction effect and the stability of the air-water interface in terms of the microstructure parameters. For comparison and validation, we have also simulated the flow over superhydrophobic surfaces made up of aligned or staggered microposts for channel flows as well as streamwise or spanwise ridge configurations for pipe flows. The present results are compared with other theoretical and experimental studies. The numerical simulations indicate that the random distribution of surface roughness has a favorable effect on drag reduction, as long as the gas fraction is kept the same. The stability of the meniscus, however, is strongly influenced by the average spacing between the roughness peaks, which needs to be carefully examined before a surface can be recommended for fabrication. Financial support from DARPA, contract number W91CRB-10-1-0003, is acknowledged.
Wetting failure of hydrophilic surfaces promoted by surface roughness
Zhao, Meng-Hua; Chen, Xiao-Peng; Wang, Qing
2014-01-01
Wetting failure is of vital importance to many physical phenomena, such as industrial coating and drop emission. Here we show when and how the surface roughness promotes the destabilization of a moving contact line on a hydrophilic surface. Beyond the balance of the driving force and viscous resistance where a stable wetting interface is sustained, wetting failure occurs and is modified by the roughness of the surface. The promoting effect arises only when the wetting velocity is high enough to create a gas-liquid-solid composite interface in the vicinity of the moving contact line, and it is a function of the intrinsic contact angle and proportion of solid tops. We propose a model to explain splashes of rough solid spheres impacting into liquids. It reveals a novel concept that dynamic wetting on hydrophilic rough surfaces can be similar to that on hydrophobic surfaces, and brings a new way to design surfaces with specific wetting properties. PMID:24948390
Enhancing capillary rise on a rough surface
NASA Astrophysics Data System (ADS)
Chow, Melissa; Wexler, Jason; Jacobi, Ian; Stone, Howard
2014-11-01
Liquid-infused surfaces have been proposed as a robust alternative to traditional air-cushioned superhydrophobic surfaces. However, if these surfaces are held vertically the lubricating oil can drain from the surface, and cause the surface to lose its novel properties. To examine this failure mode, we measure the drainage from a surface with model roughness that is scaled-up to allow for detailed measurements. We confirm that the bulk fluid drains from the surface until it reaches the level of the capillary rise height, although the detailed dynamics vary even in simple surface geometries. We then test different substrate architectures to explore how the roughness can be designed to retain greater amounts of oil. Supported under MRSEC NSF DMR 0819860 (PI: Prof. N. Phuan Ong) REU Site Grant: NSF DMR-1156422 (PI: Prof. Mikko Haataja), PREM CSUN Prime # NSF 1205734 and ONR MURI Grants N00014-12-1-0875 and N00014-12-1-0962 (Program Manager Dr. Ki-Han Kim).
Estimation of planetary surface roughness by HF sounder observation
NASA Astrophysics Data System (ADS)
Kobayashi, T.; Ono, T.
Japanese Martian exploration project "Nozomi" was to carry out several science missions. Plasma Wave Sounder, one of those onboard missions, was an HF sounder to study Martian plasma environment, and Martian surface with the altimetry mode (Oya and Ono, 1998) as well. The altimetry mode observation was studied by means of computer simulations utilizing the KiSS code which had been originally designed to simulate the SELENE Lunar Radar Sounder, a spaceborne HF GPR, based on Kirchhoff approximation theory (Kobayashi, Oya and Ono, 2002). We found an empirical power law for the standard deviation of observed altitudes over Gaussian random rough surfaces: it varies in proportion to the square of the RMS gradient of the surface √{2} hRMS{λ_0, where hRMS and λ_0 are the RMS height of the surface and the correlation distance of the surface, respectively. We applied Geometrical optics to understand this empirical power law, and derived a square power law for the standard deviation of the observed altitude. Our Geometrical optics model assumed the followings: 1) the observed surface is a Gaussian random rough surface, 2) the mean surface is a flat horizontal plane, 3) the observed surface echo is the back scattering echoes, 4) the observed altitude is the mean value of the apparent range of those back scattering echoes. These results imply that HF sounder may be utilized to measure the surface roughness of planetary bodies in terms of the RMS gradient of the surface. Refrence: H. Oya and T. Ono, A new altimeter for Mars land shape observations utilizing the ionospheric sounder system onboard the Planet-B spacecraft, Earth Planets Space, Vol. 50, pp.229-234, 1998 T. Kobayashi, H. Oya, and T. Ono, A-scope analysis of subsurface radar sounding of lunar mare region, Earth Planets Space, Vol. 54, pp.973-982, 2002
Studies on argon collisions with smooth and rough tungsten surfaces.
Ozhgibesov, M S; Leu, T S; Cheng, C H; Utkin, A V
2013-09-01
The aim of this work is to investigate argon scattering behaviors on the smooth and rough tungsten surfaces. Current work deals with numerical simulation of nanoscale heat transfer process accompanying with rarefied gas-solid substrate interactions using molecular dynamics (MD) method. Taking into account that this method is very time consuming, MD simulation using CUDA capable Graphic Cards is implemented. The results found that imperfection of the surface significantly influences on gas atom's momentum change upon collision. However, the energy exchange rate remains unchanged regardless to the surface roughness. This finding is in contrast with the results in extant literatures. We believed the results found in this paper are important for both numerical and theoretical analyses of rarefied gas flow in micro- and nano-systems where the choice of boundary conditions significantly influences flow. PMID:24007943
Flow over a Biomimetic Surface Roughness Microgeometry
NASA Astrophysics Data System (ADS)
Warncke Lang, Amy; Hidalgo, Pablo; Westcott, Matthew
2006-11-01
Certain species of sharks (e.g. shortfin mako and common hammerhead) have a skin structure that could result in a bristling of their denticles (scales) during increased swimming speeds (Bechert, D. W., Bruse, M., Hage, W. and Meyer, R. 2000, Fluid mechanics of biological surfaces and their technological application. Naturwissenschaften 80:157-171). This unique surface geometry results in a three-dimensional array of cavities* (d-type roughness geometry) forming within the surface and has been given the acronym MAKO (Micro-roughness Array for Kinematic Optimization). Possible mechanisms leading to drag reduction over the shark's body by this unique roughness geometry include separation control thereby reducing pressure drag, skin friction reduction (via the `micro-air bearing' effect first proposed by Bushnell (AIAA 83-0227)), as well as possible transition delay in the boundary layer. Initial work is confined to scaling up the geometry from 0.2 mm on the shark skin to 2 cm, with a scaling down in characteristic velocity from 10 - 20 m/s to 10 - 20 cm/s for laminar flow boundary layer water tunnel studies. Support for this research by NSF SGER grant CTS-0630489 and a University of Alabama RAC grant is gratefully acknowledged. * Patent pending.
Quantifying surface roughness over debris covered ice
NASA Astrophysics Data System (ADS)
Quincey, Duncan; Rounce, David; Ross, Andrew
2016-04-01
Aerodynamic roughness length (z0) remains a major uncertainty when determining turbulent heat fluxes over glacier surfaces, and can vary by an order of magnitude even within a small area and through the melt season. Defining z0 over debris-covered ice is particularly complex, because the surface may comprise clasts of greatly varying size, and the broader-scale surface relief can be similarly heterogeneous. Several recent studies have used Structure from Motion to data model debris-covered surfaces at the centimetric scale and calculate z0 based on measurements of surface microtopography. However, few have validated these measurements with independent vertical wind profile measurements, or considered how the measurements vary over a range of different surface types or scales of analysis. Here, we present the results of a field investigation conducted on the debris covered Khumbu Glacier during the post-monsoon season of 2015. We focus on two sites. The first is characterised by gravels and cobbles supported by a fine sandy matrix. The second comprises cobbles and boulders separated by voids. Vertical profiles of wind speed measured over both sites enable us to derive measurements of aerodynamic roughness that are similar in magnitude, with z0 at the second site exceeding that at the first by < 1 cm. During our observation period, snow covered the second site for three days, but the impact on z0 is small, implying that roughness is predominantly determined by major rock size obstacles rather than the general form of the surface. To complement these aerodynamic measurements we also conducted a Structure from Motion survey across each patch and calculated z0 using microtopographic methods published in a range of recent studies. We compare the outputs of each of these algorithms with each other and with the aerodynamic measurements, assess how they perform over a range of scales, and evaluate the validity of using microtopographic methods where aerodynamic measurements
Investigations of Titan's topography and surface roughness
NASA Astrophysics Data System (ADS)
Sharma, Priyanka
Saturn's moon, Titan is a geomorphologically active planetary object, and its surface is influenced by multiple processes like impact cratering, fluvial and aeolian erosion, lacustrine processes, tectonics, cryovolcanism and mantling. Disentangling the processes that compete to shape Titan's landscape is difficult in the absence of global topography data. In this thesis, I utilize techniques in topographic statistics, fractal theory, study of terrestrial analogs and landscape evolution modeling to characterize Titan's topography and surface roughness and investigate the relative roles of surface processes in sculpting its landscape. I mapped the shorelines of 290 North Polar Titanian lakes using the Cassini Synthetic Aperture Radar dataset. The fractal dimensions of the shorelines were calculated via the divider/ruler method and box-counting method, at length scales of (1--10) km and found to average 1.27 and 1.32, respectively. The inferred power-spectral exponent of Titan's topography was found to be ≤ 2, which is lower than the values obtained from the global topography of the Earth or Venus. In order to interpret fractal dimensions of Titan's shorelines in terms of the surficial processes at work, I repeated a similar statistical analysis with 114 terrestrial analogous lakes formed by different processes, using C-band radar backscatter data from the Shuttle Radar Topography Mission (SRTM). I found different lake generation mechanisms on Earth produce 'statistically different' shorelines; however, no specific set of processes could be identified for forming Titanian lake basins. Using the Cassini RADAR altimetry data, I investigated Titan's global surface roughness and calculated median absolute slopes, average relief and Hurst exponent (H) for the surface of Titan. I detected a clear trend with latitude in these roughness parameters. Equatorial regions had the smallest slopes, lowest values of H and smallest intra-footprint relief, compared to the mid
Robust surface roughness indices and morphological interpretation
NASA Astrophysics Data System (ADS)
Trevisani, Sebastiano; Rocca, Michele
2016-04-01
Geostatistical-based image/surface texture indices based on variogram (Atkison and Lewis, 2000; Herzfeld and Higginson, 1996; Trevisani et al., 2012) and on its robust variant MAD (median absolute differences, Trevisani and Rocca, 2015) offer powerful tools for the analysis and interpretation of surface morphology (potentially not limited to solid earth). In particular, the proposed robust index (Trevisani and Rocca, 2015) with its implementation based on local kernels permits the derivation of a wide set of robust and customizable geomorphometric indices capable to outline specific aspects of surface texture. The stability of MAD in presence of signal noise and abrupt changes in spatial variability is well suited for the analysis of high-resolution digital terrain models. Moreover, the implementation of MAD by means of a pixel-centered perspective based on local kernels, with some analogies to the local binary pattern approach (Lucieer and Stein, 2005; Ojala et al., 2002), permits to create custom roughness indices capable to outline different aspects of surface roughness (Grohmann et al., 2011; Smith, 2015). In the proposed poster, some potentialities of the new indices in the context of geomorphometry and landscape analysis will be presented. At same time, challenges and future developments related to the proposed indices will be outlined. Atkinson, P.M., Lewis, P., 2000. Geostatistical classification for remote sensing: an introduction. Computers & Geosciences 26, 361-371. Grohmann, C.H., Smith, M.J., Riccomini, C., 2011. Multiscale Analysis of Topographic Surface Roughness in the Midland Valley, Scotland. IEEE Transactions on Geoscience and Remote Sensing 49, 1220-1213. Herzfeld, U.C., Higginson, C.A., 1996. Automated geostatistical seafloor classification - Principles, parameters, feature vectors, and discrimination criteria. Computers and Geosciences, 22 (1), pp. 35-52. Lucieer, A., Stein, A., 2005. Texture-based landform segmentation of LiDAR imagery
Multilayer X-ray mirrors - Interfacial roughness, scattering, and image quality
NASA Technical Reports Server (NTRS)
Spiller, Eberhard; Stearns, Daniel; Krumrey, Michael
1993-01-01
Scattering of the multilayer coatings used for our normal incidence soft X-ray telescope at a wavelength of 63.5 A has been measured at 1.54 A and grazing angles of incidence and at soft X-rays near normal incidence. Furthermore, the edge of the moon is used as a known test target to estimate the amount of scattering in the arcsec range from images obtained on the date of the solar eclipse on July 11, 1991. The internal surfaces of the coating are inspected by high-resolution electron microscopy. A theoretical model describing the evolution and replication of roughness from layer to layer throughout the structure, which is in agreement with all experimental data, is presented. We find that practically all roughness caused by the growth of the multilayer structure occurs at spatial frequencies which are too high to produce scattering. The substrate roughness is replicated at lower spatial frequencies which might produce scattering within the field of view of an instrument. However, roughness in this range is below the 0.5 A level, again resulting in insignificant amounts of scatter.
Quantifying the effects of roughness scattering on reflection loss measurements.
Isakson, Marcia J; Chotiros, Nicholas P; Yarbrough, R Abraham; Piper, James N
2012-12-01
Seafloor reflection loss and roughness measurements were taken at the Experimental Validation of Acoustic Modeling Techniques experiment in 2006. The magnitude and phase of the reflection loss was measured at frequencies from 5 to 80 kHz and grazing angles from 7° to 77°. Approximately 1500 samples were taken for each angle. The roughness was measured with a laser profiler. Geoacoustic parameters such as water and sediment sound speed and density were measured concurrently. The reflection loss data were compared with three models: A flat interface elastic model based on geoacoustic measurements; a flat interface poro-elastic model based on the Biot/Stoll model; and a rough interface model based on the measured interface roughness power spectrum. The data were most consistent with the poro-elastic model including scattering. The elastic model consistently predicted values for the reflection loss which were higher than measured. The data exhibited more variability than the model due to layering and fluctuations in the propagating medium. PMID:23231100
Understanding EUV mask blank surface roughness induced LWR and associated roughness requirement
Yan, Pei-Yang; Zhang, Guojing; Gullickson, Eric M.; Goldberg, Kenneth A.; Benk, Markus P.
2015-03-01
Extreme ultraviolet lithography (EUVL) mask multi-layer (ML) blank surface roughness specification historically comes from blank defect inspection tool requirement. Later, new concerns on ML surface roughness induced wafer pattern line width roughness (LWR) arise. In this paper, we have studied wafer level pattern LWR as a function of EUVL mask surface roughness via High-NA Actinic Reticle Review Tool. We found that the blank surface roughness induced LWR at current blank roughness level is in the order of 0.5nm 3σ for NA=0.42 at the best focus. At defocus of ±40nm, the corresponding LWR will be 0.2nm higher. Further reducing EUVL mask blank surface roughness will increase the blank cost with limited benefit in improving the pattern LWR, provided that the intrinsic resist LWR is in the order of 1nm and above.
Experimental Investigation of the Problem of Surface Roughness
NASA Technical Reports Server (NTRS)
Schlichting, H
1937-01-01
Based on the universal laws of turbulent velocity distribution at rough and smooth walls, there is in the present work presented a method that allows surface roughness tests and in particular, measurements on the roughness of ship surfaces to be carried out in a much simpler manner. The types of roughness investigated were in the form of flat, rough plates installed in a square-section rectangular channel, the other three walls always being smooth. Twenty-one plates of various roughness were investigated, the roughness elements being the following: spheres of diameter 0.41 and 0.21, respectively, spherical segments, cones, and "short" and "long" angles.
Meaningful surface roughness and quality tolerances
NASA Astrophysics Data System (ADS)
Aikens, David M.
2010-08-01
Most tolerances on optical elements can be derived or calculated from the application requirements using computeraided optical design programs. For surface quality and surface roughness, however, there are few guidelines or tools for calculating appropriate tolerances. Typically, we simply use a legacy specification (e.g. 60-40 and 3 A RMS) with little thought for either the cost of achieving the specification or the penalty for failing to achieve it. Often these legacy specifications are ambiguous, unnecessarily costly and in some cases completely meaningless. This paper provides some basic rules and equations for calculation of the real or perceived impact of these specifications, and some guidelines for the initiate (and for some of us veterans as well) as to how to compose a meaningful tolerance.
Surface-roughness contributions to the electrical resistivity of polycrystalline metal films
NASA Astrophysics Data System (ADS)
Jacob, U.; Vancea, J.; Hoffmann, H.
1990-06-01
The influence of surface roughness on the electrical conductivity of polycrystalline metal films has to be considered at two different length scales. The large-scale surface roughness due to the granular arrangement of these films gives rise to a fluctuating film cross section. One-dimensional models of these fluctuations lead to roughness values consistent with scanning-tunneling-microscopy images of film surfaces. The microscopic surface roughness, mainly given by atomic steps on the crystallite surfaces, represents centers for surface scattering of conduction electrons. With this concept we were able to describe not only the thickness-dependent conductivity of films with natural (as-deposited) surface roughness, but also the increase in the resistance during subsequent coating with adatoms at 80 K owing to an artificial microscopic roughening of their surfaces.
NASA Astrophysics Data System (ADS)
Haghighi, Erfan; Kirchner, James; Or, Dani
2016-04-01
Evaporative drying of porous surfaces interacting with turbulent airflows is common in various industrial and natural applications. The intrinsic relief and roughness of natural porous surfaces are likely to influence the structure of interacting turbulent airflow boundary layers, and thus affect rates and patterns of heat and vapor fluxes from the surface. These links have been formalized in new mechanistic models that consider intermittent and localized turbulence-induced boundary layers, resulting in rich surface evaporation and energy exchange dynamics. The models were evaluated experimentally by systematically varying surface roughness elements in drying experiments of wavy and bluff-body covered sand surfaces in a wind tunnel. Thermal infrared signatures of localized evaporative fluxes as well as mean evaporative mass losses were recorded. The resulting patterns were in good agreement with model predictions for local and surface averaged turbulent exchange rates. Experimental and theoretical results suggest that evaporative water losses from wavy sand surfaces can be either enhanced or suppressed (relative to a flat surface), due to the complex interplay between the local boundary layer thickness and internal limitations on water flow to the evaporating surface. For sand surfaces covered by isolated cylindrical elements (bluff bodies), model predictions and measurements show persistent enhancement of evaporative fluxes from bluff-rough surfaces compared to a flat surface under similar conditions. This enhancement is attributed to the formation of vortices that thin the boundary layer over part of the interacting surface footprint. The implications of this study for interpreting and upscaling evapotranspiration rates from terrestrial surfaces will be discussed.
Speckle pattern texture analysis method to measure surface roughness
NASA Astrophysics Data System (ADS)
Kuznetsov, I.; Sadovoy, A.; Doronin, A.; Meglinski, I.
2013-02-01
Speckle pattern texture analysis method is applied to measure surface roughness of human skin. The method is based on analyzing of a gray level co-occurrence matrix occurred from a speckle image of a rough surface. Paper with different surface roughness is used as a skin phantom. The roughness is controlled by profilometry measurements. The developed methodology could find wide application in dermatology and tissue diagnostics.
Thermodynamics of capillary adhesion between rough surfaces.
de Boer, M P; de Boer, P C T
2007-07-01
According to the Dupré equation, the work of adhesion is equal to the surface energy difference in the separated versus the joined materials minus an interfacial energy term. However, if a liquid is at the interface between two solid materials, evaporation or condensation takes place under equilibrium conditions. The resulting matter exchange is accompanied by heat flow, and can reduce or increase the work of adhesion. Accounting for the energies requires an open-system control volume analysis based on the first law of thermodynamics. Depending on whether evaporation or condensation occurs during separation, a work term that is negative or positive must be added to the surface energy term to calculate the work of adhesion. We develop and apply this energy balance to several different interface geometries and compare the work of adhesion to the surface energy created. The model geometries include a sphere on a flat with limiting approximations and also with an exact solution, a circular disc, and a combination of these representing a rough interface. For the sphere on a flat, the work of adhesion is one half the surface energy created if equilibrium is maintained during the pull-off process. PMID:17368659
Theory of adhesion: Role of surface roughness
NASA Astrophysics Data System (ADS)
Persson, B. N. J.; Scaraggi, M.
2014-09-01
We discuss how surface roughness influences the adhesion between elastic solids. We introduce a Tabor number which depends on the length scale or magnification, and which gives information about the nature of the adhesion at different length scales. We consider two limiting cases relevant for (a) elastically hard solids with weak (or long ranged) adhesive interaction (DMT-limit) and (b) elastically soft solids with strong (or short ranged) adhesive interaction (JKR-limit). For the former cases we study the nature of the adhesion using different adhesive force laws (F ˜ u-n, n = 1.5-4, where u is the wall-wall separation). In general, adhesion may switch from DMT-like at short length scales to JKR-like at large (macroscopic) length scale. We compare the theory predictions to results of exact numerical simulations and find good agreement between theory and simulation results.
Incorporating Skew into RMS Surface Roughness Probability Distribution
NASA Technical Reports Server (NTRS)
Stahl, Mark T.; Stahl, H. Philip.
2013-01-01
The standard treatment of RMS surface roughness data is the application of a Gaussian probability distribution. This handling of surface roughness ignores the skew present in the surface and overestimates the most probable RMS of the surface, the mode. Using experimental data we confirm the Gaussian distribution overestimates the mode and application of an asymmetric distribution provides a better fit. Implementing the proposed asymmetric distribution into the optical manufacturing process would reduce the polishing time required to meet surface roughness specifications.
The roughness of the Martian surface: A scale dependent model
NASA Technical Reports Server (NTRS)
Shepard, M. K.; Guinness, E. A.; Arvidson, R. E.
1993-01-01
In the coming decade, several lander missions to Mars are planned (e.g., MESUR Pathfinder, MESUR). One of the dangers facing planners of these missions is the rough topography observed at both Viking Lander sites. Both landing sites are ubiquitously covered with meter-scale boulders. Objects of this size pose obvious threats to soft landers, especially at Mars where the distance from Earth causes prohibitive time lags between the transmission of commands and feedback from the spacecraft. An obvious solution is to scout for a 'smooth' site prior to the landing. However, the best resolutions realizable on current and future missions (i.e., Mars Observer) are on the order of several meters. Even at this scale, boulders of 1-2 meters in size are unresolvable. Additionally, the amount of time and spacecraft resources required to search even a small area of the planet are unrealistic given other mission objectives. An alternative is to determine the 'roughness' of the surface at a subpixel scale using bidirectional reflectance observations. Much larger areas of the planet can be searched, and much of the search can easily be automated. The morphology of the martian plains observed by the Viking Landers is physically simple. The surface is covered with a layer (approximately flat lying) of aeolian sediment from which numerous outcrops of bedrock and boulders protrude. This morphology, while simple, will be difficult to characterize from orbit using traditional bidirectional reflectance models for two reasons. First, modeling the surface as facets with Gaussian or exponential slope distributions is not realistic given the morphology described above. Second, the roughness parameter is an 'average' of the roughness at scales ranging from the wavelength of light being scattered to the pixel size of the observation. Thus, there is no definite scale of roughness that can be extracted from the Hapke roughness parameter. Using the concepts of geometric and boolean models
Rough surface scattering based on facet model
NASA Technical Reports Server (NTRS)
Khamsi, H. R.; Fung, A. K.; Ulaby, F. T.
1974-01-01
A model for the radar return from bare ground was developed to calculate the radar cross section of bare ground and the effect of the frequency averaging on the reduction of the variance of the return. It is shown that, by assuming that the distribution of the slope to be Gaussian and that the distribution of the length of the facet to be in the form of the positive side of a Gaussian distribution, the results are in good agreement with experimental data collected by an 8- to 18-GHz radar spectrometer system. It is also shown that information on the exact correlation length of the small structure on the ground is not necessary; an effective correlation length may be calculated based on the facet model and the wavelength of the incident wave.
NASA Astrophysics Data System (ADS)
Erofeev, A. I.; Friedlander, O. G.; Nikiforov, A. P.; Nesterov, S. B.; Nezhmetdinova, R. A.
2012-11-01
The interaction of high velocity free-molecular gas flow with the solid surface is studied. The influence of the surface structure on the momentum and scattering indicatrix of reflected molecular flow are investigated. The results of theoretical and experimental investigation of the gas flow scattered by a rough surface are given. Data about the surface structure, received by atomic force microscope are also reported.
Influence of surface roughness on the efficiency of X-ray mirrors with whispering gallery modes
Kozhevnikov, I. V.
2009-03-15
The influence of roughness on the propagation of an X-ray beam along a concave surface in the whispering gallery mode has been investigated. The transfer equation of beam intensity is derived and the conditions of concave surface smoothness necessary for effective beam rotation are obtained. It is shown that the influence of roughness on the beam rotation efficiency is not very strong: the roughness height should not exceed several nanometers. The point is that the scattered radiation is not lost but rotated by a concave surface and makes a significant contribution to the intensity of the output beam.
Application of wavelet transforms in terahertz spectroscopy of rough surface targets
NASA Astrophysics Data System (ADS)
Arbab, M. Hassan; Winebrenner, Dale P.; Thorsos, Eric I.; Chen, Antao
2010-02-01
Previously, it has been shown that scattering of terahertz waves by surface roughness of a target can alter the terahertz absorption spectrum and thus obscure the detection of some chemicals in both transmission and reflection geometries. In this paper it is demonstrated that by employing Maximal Overlap Discrete Wavelet Transform (MODWT) coefficients, wavelet-based methods can be used to retrieve spectroscopic information from a broadband terahertz signal reflected from a rough surface target. It is concluded that while the commonly used direct frequency domain deconvolution method fails to accurately characterize and detect the resonance in the dielectric constant of rough surface lactose pellets, wavelet techniques were able to successfully identify such features.
Backscatter from a periodic rough surface at near grazing incidence
NASA Technical Reports Server (NTRS)
Dominek, A. K.; Shamansky, H. T.
1987-01-01
The effect of periodic surface roughness on the radar cross section (RCS) was studied. The surface roughness was formed by a small sinusoidal variation in a planar surface. RCS measurements were obtained for two different sinusoidal variations near grazing incidence for both principle polarizations. Significant grating lobes were observed in the measurements which directly correspond to the roughness characteristics. A physical optics solution was generated and compared to the measurements with reasonable agreement.
Soil surface roughness characterization for microwave remote sensing applications
NASA Astrophysics Data System (ADS)
Marzahn, P.; Rieke-Zapp, D.; Ludwig, R.
2012-04-01
With this poster we present a simple and efficient method to measure soil surface roughness in an agricultural environment. Micro scale soil surface roughness is a crucial parameter in many environmental applications. In recent studies it is strongly recognized that soil surface roughness significantly influences the backscatter of agricultural surface, especially on bare fields. Indeed, while different roughness indices depend on their measurement length, no satisfying roughness parametrization and measurement technique has been found yet, introducing large uncertainty in the interpretation of the radar backscattering. In this study, we introduce a photogrammetric system which consists of a customized consumer grade Canon EOS 5d camera and a reference frame providing ground control points. With the system one can generate digital surface models (DSM) with a minimum size of 1 x 2.5 m2, extendable to any desired size, with a ground x,y- resolution of 2 mm. Using this approach, we generated a set of DSM with sizes ranging from 2.5 m2 to 22 m2, acquired over different roughness conditions representing ploughed, harrowed as well as crusted fields on different test sites. For roughness characterization we calculated in microwave remote sensing common roughness indices such as the RMS- height s and the autocorrelation length l. In an extensive statistical investigation we show the behavior of the roughness indices for different acquisition sizes of the proposed method. Results indicate, compared to results from profiles generated out of the dataset, that using a three dimensional measuring device, the calculated roughness indices are more robust in their estimation. In addition, a strong directional dependency of the proposed roughness indices was observed which could be related to the orientation of the seedbed rows to the acqusition direction. In a geostatistical analysis, we decomposed the acquired roughness indices into different scales, yielding a roughness quantity
Quantification of soil surface roughness evolution under simulated rainfall
Technology Transfer Automated Retrieval System (TEKTRAN)
Soil surface roughness is commonly identified as one of the dominant factors governing runoff and interrill erosion. The objective of this study was to compare several existing soil surface roughness indices and to test the Revised Triangular Prism surface area Method (RTPM) as a new approach to cal...
NASA Technical Reports Server (NTRS)
Yon, S. A.; Pieters, C. M.
1988-01-01
The nature of the interactions of visible and NIR radiation with the surfaces of rock and mineral samples was investigated by measuring the reflectance and the polarization properties of scattered and reflected light for slab samples of obsidian and fine-grained basalt, prepared to controlled surface roughness. It is shown that the degree to which radiation can penetrate a surface and then scatter back out, an essential criterion for mineralogic determinations based on reflectance spectra, depends not only upon the composition of the material, but also on its physical condition such as sample grain size and surface roughness. Comparison of the experimentally measured reflectance and polarization from smooth and rough slab materials with the predicted models indicates that single Fresnel reflections are responsible for the largest part of the reflected intensity resulting from interactions with the surfaces of dielectric materials; multiple Fresnel reflections are much less important for such surfaces.
An eigenvalue correction due to scattering by a rough wall of an acoustic waveguide.
Krynkin, Anton; Horoshenkov, Kirill V; Tait, Simon J
2013-08-01
In this paper a derivation of the attenuation factor in a waveguide with stochastic walls is presented. The perturbation method and Fourier analysis are employed to derive asymptotically consistent boundary-value problems at each asymptotic order. The derived approximation predicts the attenuation of the propagating mode in a rough waveguide through a correction to the eigenvalue corresponding to smooth walls. The proposed approach can be used to derive results that are consistent with those obtained by Bass et al. [IEEE Trans. Antennas Propag. 22, 278-288 (1974)]. The novelty of the method is that it does not involve the integral Dyson-type equation and, as a result, the large number of statistical moments included in the equation in the form of the mass operator of the volume scattering theory. The derived eigenvalue correction is described by the correlation function of the randomly rough surface. The averaged solution in the plane wave regime is approximated by the exponential function dependent on the derived eigenvalue correction. The approximations are compared with numerical results obtained using the finite element method (FEM). An approach to retrieve the correct deviation in roughness height and correlation length from multiple numerical realizations of the stochastic surface is proposed to account for the oversampling of the rough surface occurring in the FEM meshing procedure. PMID:23927093
Effect of surface roughness pattern on transient mixed elastohydrodynamic lubrication
NASA Astrophysics Data System (ADS)
Torabi, Amir; Akbarzadeh, Saleh; Salimpour, Mohammad Reza; Taei, Morteza
2016-03-01
Besides the surface roughness of two contacting surfaces, the surface roughness pattern i.e. longitudinal, transverse and isotropic significantly influences the tribological performance of the mechanical element. Their impression is more pronounced under the mixed elasto-hydrodynamic lubrication condition. The cam and flat follower mechanism is a typical sample in which adverse tribological conditions, including direct boundary interactions occurs. In this paper, the effect of surface roughness pattern on the film thickness and friction coefficient in a cam follower mechanism is investigated. Asperity interaction and friction coefficient analysis is conducted based on a novel elasto-plastic model. The lubrication model is qualitatively compared with the experimental results obtained from the pin on disk experiments for various surface roughness orientations. The results of transient lubrication analysis for a cam and follower lubrication problem are presented. It is shown that the longitudinal surface roughness pattern has a more desirable tribological performance than transverse surface pattern.
Characteristics of surface roughness associated with leading edge ice accretion
NASA Technical Reports Server (NTRS)
Shin, Jaiwon
1994-01-01
Detailed size measurements of surface roughness associated with leading edge ice accretions are presented to provide information on characteristics of roughness and trends of roughness development with various icing parameters. Data was obtained from icing tests conducted in the Icing Research Tunnel (IRT) at NASA Lewis Research Center (LeRC) using a NACA 0012 airfoil. Measurements include diameters, heights, and spacing of roughness elements along with chordwise icing limits. Results confirm the existence of smooth and rough ice zones and that the boundary between the two zones (surface roughness transition region) moves upstream towards stagnation region with time. The height of roughness grows as the air temperature and the liquid water content increase, however, the airspeed has little effect on the roughness height. Results also show that the roughness in the surface roughness transition region grows during a very early stage of accretion but reaches a critical height and then remains fairly constant. Results also indicate that a uniformly distributed roughness model is only valid at a very initial stage of the ice accretion process.
Droplet morphologies on particles with macroscopic surface roughness.
Stepánek, Frantisek; Rajniak, Pavol
2006-01-31
The equilibrium configuration of liquid droplets on the surface of macroscopically rough solid particles was determined by numerical simulations using the volume-of-fluid (VOF) method. The fractional surface coverage of the particle as a function of the droplet size, equilibrium contact angle, and the particle surface roughness amplitude and correlation length has been systematically investigated. Droplet size and contact angle were found to generally have a stronger effect on surface coverage than particle surface roughness. Because of droplet coalescence, a relatively large variation in surface coverage was observed for any given total liquid volume, particularly for larger values of the equilibrium contact angle. PMID:16430249
Surface roughness evolution of nanocomposite thin films
Turkin, A. A.; Pei, Y. T.; Shaha, K. P.; Chen, C. Q.; Vainshtein, D. I.; Hosson, J. Th. M. de
2009-01-01
An analysis of dynamic roughening and smoothening mechanisms of thin films grown with pulsed-dc magnetron sputtering is presented. The roughness evolution has been described by a linear stochastic equation, which contains the second- and fourth-order gradient terms. Dynamic smoothening of the growing interface is explained by ballistic effects resulting from impingements of ions to the growing thin film. These ballistic effects are sensitive to the flux and energy of impinging ions. The predictions of the model are compared with experimental data, and it is concluded that the thin film roughness can be further controlled by adjusting waveform, frequency, and width of dc pulses.
Rough surface improves stability of air- sounding balloons
NASA Technical Reports Server (NTRS)
Scoggins, J. R.
1965-01-01
Aerodynamic stability of balloons used for measuring the intensity and direction of atmospheric winds at various elevations is improved by incorporating a rough surface on the balloons. The rough-surfaced balloon is useful for collecting wind profiles and other meteorological data.
Counterintuitive MCNPX Results for Scintillator Surface Roughness Effect
2012-08-12
We have reported on our recent MCNPX simulation results of energy deposition for a group of 8 scintillation detectors, coupled with various rough surface patterns. The MCNPX results generally favored the detectors with various rough surface patterns. The observed MCNPX results are not fully explained by this work.
Ratilal, Purnima; Andrews, Mark; Donabed, Ninos; Galinde, Ameya; Rappaport, Carey; Fenneman, Douglas
2007-02-01
An analytic model is developed for the time-dependent ultrasound field reflected off a randomly rough vibrating surface for a continuously scanning ultrasound vibrometer system in bistatic configuration. Kirchhoff's approximation to Green's theorem is applied to model the three-dimensional scattering interaction of the ultrasound wave field with the vibrating rough surface. The model incorporates the beam patterns of both the transmitting and receiving ultrasound transducers and the statistical properties of the rough surface. Two methods are applied to the ultrasound system for estimating displacement and velocity amplitudes of an oscillating surface: incoherent Doppler shift spectra and coherent interferometry. Motion of the vibrometer over the randomly rough surface leads to time-dependent scattering noise that causes a randomization of the received signal spectrum. Simulations with the model indicate that surface displacement and velocity estimation are highly dependent upon the scan velocity and projected wavelength of the ultrasound vibrometer relative to the roughness height standard deviation and correlation length scales of the rough surface. The model is applied to determine limiting scan speeds for ultrasound vibrometer measuring ground displacements arising from acoustic or seismic excitation to be used in acoustic landmine confirmation sensing. PMID:17348511
Fine tuning the roughness of powder blasted surfaces
NASA Astrophysics Data System (ADS)
Wensink, Henk; Schlautmann, Stefan; Goedbloed, Martijn H.; Elwenspoek, Miko C.
2002-09-01
Powder blasting (abrasive jet machining) has recently been introduced as a bulk-micromachining technique for brittle materials. The surface roughness that is created with this technique is much higher (with a value of Ra between 1-2.5 μm) compared to general micromachining techniques. In this paper we study the roughness of powder blasted glass surfaces, and show how it depends on the process parameters. The roughness can also be changed after blasting by HF etching or by using a high-temperature anneal step. Roughness measurements and scanning electron microscopy images show the quantitative and qualitative changes in roughness. These post-processes will allow us to investigate the influence of surface roughness on the microsystem performance in future research.
Prediction of Frictional Drag over Rough Walls using Surface Statistics
NASA Astrophysics Data System (ADS)
Flack, Karen; Schultz, Michael
2014-11-01
Although the frictional drag of rough-wall-bounded flows has been studied extensively, several practical questions remain largely unresolved. First, the relationship between the shape of the roughness function in transitionally-rough regime and the surface topography which gives rise to it are not well understood. Second, it is not completely clear which textural parameters best describe a rough surface in a hydraulic sense. Furthermore, the range of roughness wavelengths that influence the skin-friction is not well established. The focus of the present work is to attempt to address these questions with a systematic study of the skin-friction of fifteen rough surfaces that were generated by grit blasting. The hydrodynamic tests were carried out over a large Reynolds number range. Five surfaces were prepared by grit blasting with a single scale blast media. These underwent hydrodynamic testing and were subsequently blasted with secondary and tertiary scale media in order to investigate the role that the incorporation of additional roughness length scales plays in determining the shape of the roughness function and the resulting hydraulic length scale. The presentation will focus on the appropriate statistical scales for prediction of the roughness function. Spatial filtering prior to the calculation of surface statistics will also be discussed. Work supported by the Office of Naval Research.
Determining Surface Roughness in Urban Areas Using Lidar Data
NASA Technical Reports Server (NTRS)
Holland, Donald
2009-01-01
An automated procedure has been developed to derive relevant factors, which can increase the ability to produce objective, repeatable methods for determining aerodynamic surface roughness. Aerodynamic surface roughness is used for many applications, like atmospheric dispersive models and wind-damage models. For this technique, existing lidar data was used that was originally collected for terrain analysis, and demonstrated that surface roughness values can be automatically derived, and then subsequently utilized in disaster-management and homeland security models. The developed lidar-processing algorithm effectively distinguishes buildings from trees and characterizes their size, density, orientation, and spacing (see figure); all of these variables are parameters that are required to calculate the estimated surface roughness for a specified area. By using this algorithm, aerodynamic surface roughness values in urban areas can then be extracted automatically. The user can also adjust the algorithm for local conditions and lidar characteristics, like summer/winter vegetation and dense/sparse lidar point spacing. Additionally, the user can also survey variations in surface roughness that occurs due to wind direction; for example, during a hurricane, when wind direction can change dramatically, this variable can be extremely significant. In its current state, the algorithm calculates an estimated surface roughness for a square kilometer area; techniques using the lidar data to calculate the surface roughness for a point, whereby only roughness elements that are upstream from the point of interest are used and the wind direction is a vital concern, are being investigated. This technological advancement will improve the reliability and accuracy of models that use and incorporate surface roughness.
Effect of surface roughness on flexural strength of veneer ceramics.
Fischer, H; Schäfer, M; Marx, R
2003-12-01
The strength of ceramic restorations depends on the occlusal surface roughness of the veneering porcelain, which is influenced by the final preparation. The hypothesis of the study was that roughnesses below a critical microscopic defect size--based only on fracture mechanics considerations--also affect flexural strength. The bending failure stress was evaluated on standard specimens of 4 veneer ceramics with 4 different surfaces of defined roughnesses, respectively. A linear correlation was found between roughness and failure stress. A "roughness-free" failure stress value was predicted for each tested material. This theoretical value can represent the "true" strength of the respective ceramic material. We conclude from our results that the final preparation of a ceramic restoration is critical to the strength of the material, and that ceramic veneering materials can be compared more objectively with respect to their strength by means of roughness-free strength values. PMID:14630897
Effect of surface roughness on the microwave emission from soils
NASA Technical Reports Server (NTRS)
Choudhury, B. J.; Schmugge, T. J.; Newton, R. W.; Chang, A. T. C.
1978-01-01
The effect of surface roughness on the brightness temperature of a moist terrain was studied through the modification of Fresnel reflection coefficient and using the radiative transfer equation. The modification involves introduction of a single parameter to characterize the roughness. It is shown that this parameter depends on both the surface height variance and the horizontal scale of the roughness. Model calculations are in good quantitative agreement with the observed dependence of the brightness temperature on the moisture content in the surface layer. Data from truck mounted and airborne radiometers are presented for comparison. The results indicate that the roughness effects are greatest for wet soils where the difference between smooth and rough surfaces can be as great as 50K.
Effect of surface roughness on the microwave emission from soils
NASA Technical Reports Server (NTRS)
Choudhury, B. J.; Schmugge, T. J.; Chang, A.; Newton, R. W.
1979-01-01
The effect of surface roughness on the brightness temperature of a moist terrain has been studied through the modification of Fresnel reflection coefficient and using the radiative transfer equation. The modification involves introduction of a single parameter to characterize the roughness. It is shown that this parameter depends on both the surface height variance and the horizontal scale of the roughness. Model calculations are in good quantitative agreement with the observed dependence of the brightness temperature on the moisture content in the surface layer. Data from truck mounted and airborne radiometers are presented for comparison. The results indicate that the roughness effects are great for wet soils where the difference between smooth and rough surfaces can be as great as 50 K.
Topological Analysis of Rough Surfaces Using Persistent Homology
NASA Astrophysics Data System (ADS)
Yamamoto, Ken
2015-11-01
This letter investigates rough surfaces using a topological method. The horizontal cross section of a rough surface consists of "islands", and we focus on the topological changes in the island shapes (generation and annihilation of islands and lakes) with changes in elevation. We apply persistent homology to track these topological changes. We numerically confirm that the life spans of the islands and lakes follow power-law distributions, whose scaling exponents vary according to the roughness of the surface. We also provide a theoretical explanation for the relation between these scaling exponents and the roughness exponent with a simple scaling argument. The proposed method successfully connects a topological property with the roughness of a surface.
Shape reconstruction of the multi-scale rough surface from multi-frequency phaseless data
NASA Astrophysics Data System (ADS)
Bao, Gang; Zhang, Lei
2016-08-01
We consider the problem of reconstructing the shape of multi-scale sound-soft large rough surfaces from phases measurements of the scattered field generated by tapered waves with multiple frequencies impinging on a rough surface. To overcome both the ill-posedness and nonlinearity of this problem for a single frequency, the Landweber regularization method based on the adjoint of the nonlinear objective functional is used. When the multi-frequency data is available, an approximation method is introduced to estimate the large-scale structure of the rough surface using the data measurements at the lowest frequency. The obtained estimate serves as an initial guess for a recursive linearization algorithm in frequency, which is used to capture the small scale structure of the rough surface. Numerical experiments are presented to illustrate the effectiveness of the method.
NASA Astrophysics Data System (ADS)
Basu, Santasri; Hyde, Milo W.; McCrae, Jack E.; Spencer, Mark F.; Fiorino, Steven T.
2014-10-01
In military applications that use adaptive optics, an extended beacon instead of a point source beacon is created at the target due to atmospheric turbulence and other factors. These beacons, which have a finite spatial extent and exhibit varying degrees of coherence, are typically modeled in existing literature as a Gaussian Schell Model (GSM) due to its analytical tractability. Earlier, we used a full wave computational technique to evaluate the scattered field from a rough impedance surface in vacuum. The results showed some deviations from GSM behavior. The present work uses a simulation approach based on Physical Optics (PO) approximation to study the scattering behavior in presence of atmospheric turbulence. A fully coherent Gaussian beam is propagated through atmospheric phase screens to the rough surface target plane. The PO current is computed on the rough surface and the scattered field right above the surface is determined. The scattered light is propagated through a second set of atmospheric phase screens and thus the double passage through the atmosphere is realized. The rough surface is simulated using statistical parameters derived from profilometer measurements of standard targets. Through multiple realizations of the atmosphere and the rough surface, the statistics of the scattered field is determined. The simulations are done with different strengths of turbulence and different roughness scales of the target. The results are compared with a GSM. An effects model where the rough surface is modeled as a phase screen has also been implemented in order to verify the nature of the speckle returns.
Theoretical model for the wetting of a rough surface.
Hay, K M; Dragila, M I; Liburdy, J
2008-09-15
Many applications would benefit from an understanding of the physical mechanism behind fluid movement on rough surfaces, including the movement of water or contaminants within an unsaturated rock fracture. Presented is a theoretical investigation of the effect of surface roughness on fluid spreading. It is known that surface roughness enhances the effects of hydrophobic or hydrophilic behavior, as well as allowing for faster spreading of a hydrophilic fluid. A model is presented based on the classification of the regimes of spreading that occur when fluid encounters a rough surface: microscopic precursor film, mesoscopic invasion of roughness and macroscopic reaction to external forces. A theoretical relationship is developed for the physical mechanisms that drive mesoscopic invasion, which is used to guide a discussion of the implications of the theory on spreading conditions. Development of the analytical equation is based on a balance between capillary forces and frictional resistive forces. Chemical heterogeneity is ignored. The effect of various methods for estimating viscous dissipation is compared to available data from fluid rise on roughness experiments. Methods that account more accurately for roughness shape better explain the data as they account for more surface friction; the best fit was found for a hydraulic diameter approximation. The analytical solution implies the existence of a critical contact angle that is a function of roughness geometry, below which fluid will spread and above which fluid will resist spreading. The resulting equation predicts movement of a liquid invasion front with a square root of time dependence, mathematically resembling a diffusive process. PMID:18586259
Light scattering by a reentrant fractal surface.
Mendoza-Suárez, A; Méndez, E R
1997-05-20
Recently, rigorous numerical techniques for treating light scattering problems with one-dimensional rough surfaces have been developed. In their usual formulation, these techniques are based on the solution of two coupled integral equations and are applicable only to surfaces whose profiles can be described by single-valued functions of a coordinate in the mean plane of the surface. In this paper we extend the applicability of the integral equation method to surfaces with multivalued profiles. A procedure for finding a parametric description of a given profile is described, and the scattering equations are established within the framework of this formalism. We then present some results of light scattering from a sequence of one-dimensional flat surfaces with defects in the form of triadic Koch curves. Beyond a certain order of the prefractal, the scattering patterns become stationary (within the numerical accuracy of the method). It can then be argued that the results obtained correspond to a surface with a fractal structure. These constitute, to our knowledge, the first rigorous calculations of light scattering from a reentrant fractal surface. PMID:18253371
Modeling of surface roughness effects on glaze ice accretion
NASA Technical Reports Server (NTRS)
Hansman, R. John, Jr.; Yamaguchi, Keiko; Berkowitz, Brian; Potapczuk, M.
1989-01-01
The cause and effects of roughness on accreting glaze ice surfaces were studied with microvideo observations. Distinct zones of surface water behavior were observed, including a smooth wet zone in the stagnation region with a uniform water film, a rough zone where surface tension effects caused coalescence of surface water into stationary beads, and a zone where roughness elements grow into horn shapes. In addition, a zone where surface water ran back as rivulets and a dry zone where rime feathers formed were observed. The locations and behaviors of these zones are discussed. A simple multizone modification to the glaze ice accretion model is proposed to include spatial variability in surface roughness. Two test cases using the multizone model showed significant improvements for the prediction of glaze ice shapes.
Surface roughness reduction using spray-coated hydrogen silsesquioxane reflow
NASA Astrophysics Data System (ADS)
Cech, Jiri; Pranov, Henrik; Kofod, Guggi; Matschuk, Maria; Murthy, Swathi; Taboryski, Rafael
2013-09-01
Surface roughness or texture is the most visible property of any object, including injection molded plastic parts. Roughness of the injection molding (IM) tool cavity directly affects not only appearance and perception of quality, but often also the function of all manufactured plastic parts. So called “optically smooth” plastic surfaces is one example, where low roughness of a tool cavity is desirable. Such tool surfaces can be very expensive to fabricate using conventional means, such as abrasive diamond polishing or diamond turning. We present a novel process to coat machined metal parts with hydrogen silsesquioxane (HSQ) to reduce their surface roughness. Results from the testing of surfaces made from two starting roughnesses are presented; one polished with grit 2500 sandpaper, another with grit 11.000 diamond polishing paste. We characterize the two surfaces with AFM, SEM and optical profilometry before and after coating. We show that the HSQ coating is able to reduce peak-to-valley roughness more than 20 times on the sandpaper polished sample, from 2.44(±0.99) μm to 104(±22) nm and more than 10 times for the paste polished sample from 1.85(±0.63) μm to 162(±28) nm while roughness averages are reduced 10 and 3 times respectively. We completed more than 10,000 injection molding cycles without detectable degradation of the HSQ coating. This result opens new possibilities for molding of affordable plastic parts with perfect surface finish.
Surface roughness effect on finite oil journal bearings
NASA Technical Reports Server (NTRS)
Majumdar, B. C.; Hamrock, B. J.
1981-01-01
A theoretical study of the performance of finite oil journal bearings is made, considering the surface roughness effect. The total load supporting ability under such a condition derives from the hydrodynamic as well as asperity contact pressure. These two components of load are calculated separately. The average Reynolds equation for partially lubricated surfaces is used to evaluate hydrodynamic pressure. An analytical expression for average film thickness is obtained and introduced to modify the average Reynolds equation. The resulting differential equation is then solved numerically by finite difference methods for mean hydrodynamic pressure, which in turn gives the hydrodynamic load. Assuming the surface height distribution as Gaussian, the asperity contact pressure is found. The effect of surface roughness parameter, surface pattern, eccentricity ratio, and length to diameter ratio on hydrodynamic load and on side leakage is investigated. It is shown that hydrodynamic load increases with increasing surface roughness when both journal and bearing surfaces have identical roughness structures or when the journal only has a rough surface. The trend of hydrodynamic load is reversed if the journal surface is smooth and the bearing surface is rough.
Surface Roughness of the Moon Derived from Multi-frequency Radar Data
NASA Astrophysics Data System (ADS)
Fa, W.
2011-12-01
Surface roughness of the Moon provides important information concerning both significant questions about lunar surface processes and engineering constrains for human outposts and rover trafficabillity. Impact-related phenomena change the morphology and roughness of lunar surface, and therefore surface roughness provides clues to the formation and modification mechanisms of impact craters. Since the Apollo era, lunar surface roughness has been studied using different approaches, such as direct estimation from lunar surface digital topographic relief, and indirect analysis of Earth-based radar echo strengths. Submillimeter scale roughness at Apollo landing sites has been studied by computer stereophotogrammetry analysis of Apollo Lunar Surface Closeup Camera (ALSCC) pictures, whereas roughness at meter to kilometer scale has been studied using laser altimeter data from recent missions. Though these studies shown lunar surface roughness is scale dependent that can be described by fractal statistics, roughness at centimeter scale has not been studied yet. In this study, lunar surface roughnesses at centimeter scale are investigated using Earth-based 70 cm Arecibo radar data and miniature synthetic aperture radar (Mini-SAR) data at S- and X-band (with wavelengths 12.6 cm and 4.12 cm). Both observations and theoretical modeling show that radar echo strengths are mostly dominated by scattering from the surface and shallow buried rocks. Given the different penetration depths of radar waves at these frequencies (< 30 m for 70 cm wavelength, < 3 m at S-band, and < 1 m at X-band), radar echo strengths at S- and X-band will yield surface roughness directly, whereas radar echo at 70-cm will give an upper limit of lunar surface roughness. The integral equation method is used to model radar scattering from the rough lunar surface, and dielectric constant of regolith and surface roughness are two dominate factors. The complex dielectric constant of regolith is first estimated
Estimating aerodynamic resistance of rough surfaces from angular reflectance
Technology Transfer Automated Retrieval System (TEKTRAN)
Current wind erosion and dust emission models neglect the heterogeneous nature of surface roughness and its geometric anisotropic effect on aerodynamic resistance, and over-estimate the erodible area by assuming it is not covered by roughness elements. We address these shortfalls with a new model wh...
Characterization of super smooth surfaces by light scattering techniques
NASA Astrophysics Data System (ADS)
Mattsson, Lars H.
1989-03-01
A characteristic feature of a supersmooth surface is its low scatter. The scatter is proportional to the square of the rms surface roughness. Therefore, light scattering is a suitable and nondestructive method for characterization of smooth surfaces. It is possible to detect scattering created by height differences of a few atomic layers but the lateral sensitivity is limited to the order of the wavelength, ~0.5μm. The new F 1048-87 ASTM standard test method for measuring the effective surface roughness of optical components is based on total integrated scattering (TIS). The amount of scattering, caused by the surface roughness, is of primary interest for optical applications, while the roughness itself is of greater concern in the fields of microelectronics and magnetic memory storage. This paper will highlight the use of a low noise TIS instrument for characterization of sub-Å roughness on semiconductor wafers, for thin film characterization, and for detection of traces of contamination on silicon surfaces.
Roughness assessment and wetting behavior of fluorocarbon surfaces.
Terriza, Antonia; Álvarez, Rafael; Borrás, Ana; Cotrino, José; Yubero, Francisco; González-Elipe, Agustín R
2012-06-15
The wetting behavior of fluorocarbon materials has been studied with the aim of assessing the influence of the surface chemical composition and surface roughness on the water advancing and receding contact angles. Diamond like carbon and two fluorocarbon materials with different fluorine content have been prepared by plasma enhanced chemical vapor deposition and characterized by X-ray photoemission, Raman and FT-IR spectroscopies. Very rough surfaces have been obtained by deposition of thin films of these materials on polymer substrates previously subjected to plasma etching to increase their roughness. A direct correlation has been found between roughness and water contact angles while a superhydrophobic behavior (i.e., water contact angles higher than 150° and relatively low adhesion energy) was found for the films with the highest fluorine content deposited on very rough substrates. A critical evaluation of the methods currently used to assess the roughness of these surfaces by atomic force microscopy (AFM) has evidenced that calculated RMS roughness values and actual surface areas are quite dependent on both the scale of observation and image resolution. A critical discussion is carried out about the application of the Wenzel model to account for the wetting behavior of this type of surfaces. PMID:22483335
Drop impact upon superhydrophobic surfaces with regular and hierarchical roughness
NASA Astrophysics Data System (ADS)
Lv, Cunjing; Hao, Pengfei; Zhang, Xiwen; He, Feng
2016-04-01
Recent studies demonstrate that roughness and morphologies of the textures play essential roles on the dynamics of water drop impacting onto superhydrophobic substrates. Particularly, significant reduction of contact time has greatly attracted people's attention. We experimentally investigate drop impact dynamics onto three types of superhydrophobic surfaces, consisting of regular micropillars, two-tier textures with nano/micro-scale roughness, and hierarchical textures with random roughness. It shows that the contact time is controlled by the Weber number and the roughness of the surface. Compared with drop impact on regular micropillared surfaces, the contact time can be finely reduced by increasing the Weber number on surfaces with two-tier textures, but can be remarkably reduced on surfaces with hierarchical textures resulting from the prompt splash and fragmentation of liquid lamellae. Our study may shed lights on textured materials fabrication, allowing a rapid drop detachment to realize broad applications.
Contribution of surface roughness to simulations of historical deforestation
NASA Astrophysics Data System (ADS)
Wang, Ye; Wang, Zhaomin
Surface roughness which partitions surface net radiation into energy fluxes is a key parameter for estimation of biosphere-atmosphere interactions and climate variability. An earth system model of intermediate complexity (EMIC), MPM-2, is used to derive the impact of surface roughness on climate from simulations of historical land cover change effects. The direct change in surface roughness leads to a global surface warming of 0.08 °C through altering the turbulence in the boundary layer. The regional temperature response to surface roughness associated deforestation is very strong at northern mid-latitudes with a most prominent warming of 0.72 °C around 50°N in the Eurasia continent during summer. They can be explained mainly as direct and indirect consequences of decreases in surface albedo and increases in precipitation in response to deforestation, although there are a few significant changes in precipitation. There is also a prominent warming of 0.25 °C around 40°N in the North American continent. This study indicates that land surface roughness plays a significant role which is comparable with the whole land conversion effect in climate change. Therefore, further investigation of roughness-climate relationship is needed to incorporate these aspects.
Modeling of surface roughness effects on glaze ice accretion
NASA Technical Reports Server (NTRS)
Hansman, R. John, Jr.; Yamaguchi, Keiko; Berkowitz, Brian M.; Potapczuk, Mark
1990-01-01
A series of experimental investigations focused on studying the cause and effect of roughness on accreting glaze ice surfaces were conducted. Detailed microvideo observations were made of glaze ice accretions on 1 to 4 inch diameter cylinders in three icing wind tunnels (the Data Products of New England six inch test facility, the NASA Lewis Icing Research Tunnel, and the B. F. Goodrich Ice Protection Research Facility). Infrared thermal video recordings were made of accreting ice surfaces in the Goodrich facility. Distinct zones of surface water behavior were observed; a smooth wet zone in the stagnation region with a uniform water film; a rough zone where surface tension effects caused coalescence of surface water into stationary beads; a horn zone where roughness elements grow into horn shapes; a runback zone where surface water ran back as rivulets; and a dry zone where rime feathers formed. The location of the transition from the smooth to the rough zone was found to migrate with time towards the stagnation point. The behavior of the transition appeared to be controlled by boundary layer transition and bead formation mechanisms at the interface between the smooth and rough zones. Regions of wet ice growth and enhanced heat transfer were clearly visible in the infrared video recordings of glaze ice surfaces. A simple multi-zone modification to the current glaze ice accretion model was proposed to include spatial variability in surface roughness.
Computer simulation of RBS spectra from samples with surface roughness
NASA Astrophysics Data System (ADS)
Malinský, P.; Hnatowicz, V.; Macková, A.
2016-03-01
A fast code for the simulation of common RBS spectra including surface roughness effects has been written and tested on virtual samples comprising either a rough layer deposited on a smooth substrate or smooth layer deposited on a rough substrate and simulated at different geometries. The sample surface or interface relief has been described by a polyline and the simulated RBS spectrum has been obtained as the sum of many particular spectra from randomly chosen particle trajectories. The code includes several procedures generating virtual samples with random and regular (periodical) roughness. The shape of the RBS spectra has been found to change strongly with increasing sample roughness and an increasing angle of the incoming ion beam.
Influence of particle surface roughness on creeping granular motion.
Sheng, Li-Tsung; Chang, Wei-Ching; Hsiau, Shu-San
2016-07-01
A core is formed at the center of a quasi-two-dimensional rotating drum filled more than half with granular material. The core rotates slightly faster than the drum (precession) and decreases in radius over time (erosion) due to the granular creeping motion that occurs below the freely flowing layer. This paper focuses on the effect of the surface roughness of particles on core dynamics, core precession, and core erosion. Two different surface roughness of glass particles having the same diameter were used in the experiments. The surface structures of the particles were quantitatively compared by measuring the coefficients of friction and using a simple image contrast method. The experiments were performed with five different filling levels in a 50-cm-diameter rotating drum. According to the results, core precession and core erosion are both dependent on the particle surface roughness. Core precession becomes weaker and erosion becomes stronger when using particles having a rough surface in the experiments. To explain the physics of core dynamics, the particles' surface roughness effect on the freely flowing layer and the creeping motion region were also investigated. The granular bed velocity field, maximum flowing layer depth δ, shear rate in the flowing layer γ[over ̇], and the creeping region decay constant y_{0} were also calculated in this paper. The effect of the particles' surface roughness on these physical variables well illustrates the physics of core dynamics and creeping granular motion. PMID:27575202
Influence of particle surface roughness on creeping granular motion
NASA Astrophysics Data System (ADS)
Sheng, Li-Tsung; Chang, Wei-Ching; Hsiau, Shu-San
2016-07-01
A core is formed at the center of a quasi-two-dimensional rotating drum filled more than half with granular material. The core rotates slightly faster than the drum (precession) and decreases in radius over time (erosion) due to the granular creeping motion that occurs below the freely flowing layer. This paper focuses on the effect of the surface roughness of particles on core dynamics, core precession, and core erosion. Two different surface roughness of glass particles having the same diameter were used in the experiments. The surface structures of the particles were quantitatively compared by measuring the coefficients of friction and using a simple image contrast method. The experiments were performed with five different filling levels in a 50-cm-diameter rotating drum. According to the results, core precession and core erosion are both dependent on the particle surface roughness. Core precession becomes weaker and erosion becomes stronger when using particles having a rough surface in the experiments. To explain the physics of core dynamics, the particles' surface roughness effect on the freely flowing layer and the creeping motion region were also investigated. The granular bed velocity field, maximum flowing layer depth δ , shear rate in the flowing layer γ ˙, and the creeping region decay constant y0 were also calculated in this paper. The effect of the particles' surface roughness on these physical variables well illustrates the physics of core dynamics and creeping granular motion.
Counterintuitive MCNPX Results for Scintillator Surface Roughness Effect
Yuan, Ding; Guss, Paul
2012-10-01
We performed a number of comparative MCNPX simulations of gamma energy depositions of scintillation crystals with smooth and rough surfaces. In the study, nine surface patterns (8 micro-roughness + 1 smooth) were coupled with eight common scintillation crystals for a total of 72 possible combinations. Although this was a preliminary study, the outcome was counterintuitive; results generally favored surfaces with micro-roughness over a conventional smooth surface as measured in terms of average energy depositions. The advantage gained through surface roughness is less significant for CdSe and LaCl3, but is most significant for the common NaI and the glass-like SiO2 scintillators. Based on the results of the 64 rough-surface coupled MCNPX simulations, 57 of the 64 (~89%) simulations showed some improvement in energy deposition. The mean improvement in energy deposition was 2.52%. The maximum improvement was about 8.75%, which was achieved when roughening the surface of a SiO2 scintillator using a micro cutting pattern. Further, for a conventional NaI scintillator, MCNPX results suggest that any roughness pattern would improve the energy deposition, with an average improvement of 3.83%. Although the likely causes remain unclear, we intend to focus on presenting simulation results instead of offering a sound explanation of the underlying physics.
Ice friction: The effects of surface roughness, structure, and hydrophobicity
Kietzig, Anne-Marie; Hatzikiriakos, Savvas G.; Englezos, Peter
2009-07-15
The effect of surface roughness, structure, and hydrophobicity on ice friction is studied systematically over a wide range of temperature and sliding speeds using several metallic interfaces. Hydrophobicity in combination with controlled roughness at the nanoscale is achieved by femtosecond laser irradiation to mimic the lotus effect on the slider's surface. The controlled roughness significantly increases the coefficient of friction at low sliding speeds and temperatures well below the ice melting point. However, at temperatures close to the melting point and relatively higher speeds, roughness and hydrophobicity significantly decrease ice friction. This decrease in friction is mainly due to the suppression of capillary bridges in spite of the presence of surface asperities that facilitate their formation. Finally, grooves oriented in the sliding direction also significantly decrease friction in the low velocity range compared to scratches and grooves randomly distributed over a surface.
Analysis of Surface Roughness at Overlapping Laser Shock Peening
NASA Astrophysics Data System (ADS)
Dai, F. Z.; Zhang, Z. D.; Zhou, J. Z.; Lu, J. Z.; Zhang, Y. K.
2016-02-01
The overlapping effects on surface roughness are studied when samples are treated by laser shock peening (LSP). Surface roughness of overlapped circular laser spot is calculated by ISO 25178 height parameters. The usually used overlapping styles namely isosceles-right-triangle-style (AAP) and equilateral-triangle-style (AAA) are carefully investigated when the overlapping degree in x-axis (ηx) is below 50%. Surface roughness of isosceles-right-triangle-style attains its minimum value at ηx of 29.3%, and attains its maximum value at ηx of 43.6%. Surface roughness of equilateral-triangle-style attains its minimum value at ηx of 42.3%, and attains its maximum value at ηx of 32%. Experimental results are well consistent with theoretical analysis.
Surface Roughness Measurement on a Wing Aircraft by Speckle Correlation
Salazar, Félix; Barrientos, Alberto
2013-01-01
The study of the damage of aeronautical materials is important because it may change the microscopic surface structure profiles. The modification of geometrical surface properties can cause small instabilities and then a displacement of the boundary layer. One of the irregularities we can often find is surface roughness. Due to an increase of roughness and other effects, there may be extra momentum losses in the boundary layer and a modification in the parasite drag. In this paper we present a speckle method for measuring the surface roughness on an actual unmanned aircraft wing. The results show an inhomogeneous roughness distribution on the wing, as expected according to the anisotropic influence of the winds over the entire wing geometry. A calculation of the uncertainty of the technique is given. PMID:24013488
Surface roughness measurement on a wing aircraft by speckle correlation.
Salazar, Félix; Barrientos, Alberto
2013-01-01
The study of the damage of aeronautical materials is important because it may change the microscopic surface structure profiles. The modification of geometrical surface properties can cause small instabilities and then a displacement of the boundary layer. One of the irregularities we can often find is surface roughness. Due to an increase of roughness and other effects, there may be extra momentum losses in the boundary layer and a modification in the parasite drag. In this paper we present a speckle method for measuring the surface roughness on an actual unmanned aircraft wing. The results show an inhomogeneous roughness distribution on the wing, as expected according to the anisotropic influence of the winds over the entire wing geometry. A calculation of the uncertainty of the technique is given. PMID:24013488
Ice friction: The effects of surface roughness, structure, and hydrophobicity
NASA Astrophysics Data System (ADS)
Kietzig, Anne-Marie; Hatzikiriakos, Savvas G.; Englezos, Peter
2009-07-01
The effect of surface roughness, structure, and hydrophobicity on ice friction is studied systematically over a wide range of temperature and sliding speeds using several metallic interfaces. Hydrophobicity in combination with controlled roughness at the nanoscale is achieved by femtosecond laser irradiation to mimic the lotus effect on the slider's surface. The controlled roughness significantly increases the coefficient of friction at low sliding speeds and temperatures well below the ice melting point. However, at temperatures close to the melting point and relatively higher speeds, roughness and hydrophobicity significantly decrease ice friction. This decrease in friction is mainly due to the suppression of capillary bridges in spite of the presence of surface asperities that facilitate their formation. Finally, grooves oriented in the sliding direction also significantly decrease friction in the low velocity range compared to scratches and grooves randomly distributed over a surface.
Equilibrium of wetting layers on rough surfaces
NASA Astrophysics Data System (ADS)
Liu, Kuang-Yu
The objective of this dissertation is to study physical adsorption on solids with complex surface geometry--especially on self-similar and self-affine fractal surfaces--in the context of three phase equilibria. Such studies will facilitate the prediction of the adsorbed film from known surface properties, e.g., topography or interactions (direct problem), and the inference of unknown surface properties from experimental data (inverse problem). These results will then be compared against wetting phenomena on planar surfaces and with other methods of probing complex surface geometries of solids. Chapter One offers the basic context, including wetting phenomena on planar surfaces, the cornerstone prediction of wetting transition on planar surfaces by Cahn, the concepts of fractal geometry, and the formation of fractal objects, for later comparison. The rest of this dissertation will be devoted to the study of multilayer adsorption on fractal surfaces. When a liquid film completely wets the surface, the number of adsorbed molecules as a function of the vapor pressure will depend strongly on the underlying surface geometry. The fractal structure leads to the Frenkel-Halsey-Hill type isotherms with the exponents in the corresponding power laws depending on the fractal dimension and on whether the dominant influence is from the substrate potential (van der Waals wetting) or from the film-vapor surface tension (capillary wetting). The transition between the two is the analog of Cahn's transition: The thermal disorder is replaced by the quenched disorder. This analogy is studied in Chapter Two for self-similar surfaces, and in Chapter Four for self-affine surfaces. In Chapter Two the derivation framework also automatically identifies well-defined coexistence lines in the pressure-dimension diagram. The effect of the repulsive part is examined there too. A simple analysis of adsorption/desorption hysteresis on self-similar surfaces in Chapter Three concludes that the
Surface roughness and three-dimensional heat conduction in thermophysical models
NASA Astrophysics Data System (ADS)
Davidsson, Björn J. R.; Rickman, Hans
2014-11-01
A thermophysical model is presented that considers surface roughness, cast shadows, multiple or single scattering of radiation, visual and thermal infrared self heating, as well as heat conduction in one or three dimensions. The code is suitable for calculating infrared spectral energy distributions for spatially resolved or unresolved minor Solar System bodies without significant atmospheres or sublimation, such as the Moon, Mercury, asteroids, irregular satellites or inactive regions on comet nuclei. It is here used to explore the effects of surface roughness on spatial scales small enough for heat conduction to erase lateral temperature gradients. Analytically derived corrections to one-dimensional models that reproduce the results of three-dimensional modeling are presented. We find that the temperature of terrains with such small-scale roughness is identical to that of smooth surfaces for certain types of topographies and non-scattering material. However, systematic differences between smooth and rough terrains are found for scattering materials, or topographies with prominent positive relief. Contrary to common beliefs, the roughness on small spatial scales may therefore affect the thermal emission of Solar System bodies.
A possibility of avoiding surface roughness due to insects
NASA Technical Reports Server (NTRS)
Wortmann, F. X.
1984-01-01
Discussion of a method for eliminating turbulence caused by the formation of insect roughness upon the leading edges and fuselage, particularly in aircraft using BLC. The proposed technique foresees the use of elastic surfaces on which insect roughness cannot form. The operational characteristics of highly elastic rubber surface fastened to the wing leading edges and fuselage edges are examined. Some preliminary test results are presented. The technique is seen to be advantageous primarily for short-haul operations.
Surface Roughness Parameter Uncertainties on Radar Based Soil Moisture Retrievals
NASA Technical Reports Server (NTRS)
Joseph, A. T.; vanderVelde, R.; O'Neill, P. E.; Lang, R.; Su, Z.; Gish, T.
2012-01-01
Surface roughness variations are often assumed to be negligible for the retrieval of sol moisture. Although previous investigations have suggested that this assumption is reasonable for natural vegetation covers (i.e. Moran et al. 2002), in-situ measurements over plowed agricultural fields (i.e. Callens et al. 2006) have shown that the soil surface roughness can change considerably due to weathering induced by rain.
Noncontact surface roughness measurement using a vision system
NASA Astrophysics Data System (ADS)
Koçer, Erdinç; Horozoǧlu, Erhan; Asiltürk, Ilhan
2015-02-01
Surface roughness measurement is one of the basic measurement that determines the quality and performance of the final product. After machined operations, tracer end tools are commonly used in industry in order to measure the surface roughness that occurred on the surface. This measurement technique has disadvantages such as user errors because it requires calibration of the device occurring during measurement. In this study, measuring and evaluation techniques were conducted by using display devices over surface image which occurred on the processed surfaces. Surface measurement which performed by getting image makes easier measurement process because it is non-contact, and does not cause any damage. Measurement of surface roughness, and analysis was conducted more precise and accurate. Experimentally obtained results of the measurements on the parts in contact with the device is improved compared with the results of the non-contact image processing software, and satisfactory results were obtained.
Heat Transfer Variation on Protuberances and Surface Roughness Elements
NASA Technical Reports Server (NTRS)
Henry, Robert C.; Hansman, R. John, Jr.; Breuer, Kenneth S.
1995-01-01
In order to determine the effect of surface irregularities on local convective heat transfer, the variation in heat transfer coefficients on small (2-6 mm diam) hemispherical roughness elements on a flat plate has been studied in a wind funnel using IR techniques. Heat transfer enhancement was observed to vary over the roughness elements with the maximum heat transfer on the upstream face. This heat transfer enhancement increased strongly with roughness size and velocity when there was a laminar boundary layer on the plate. For a turbulent boundary layer, the heat transfer enhancement was relatively constant with velocity, but did increase with element size. When multiple roughness elements were studied, no influence of adjacent roughness elements on heat transfer was observed if the roughness separation was greater than approximately one roughness element radius. As roughness separation was reduced, less variation in heat transfer was observed on the downstream elements. Implications of the observed roughness enhanced heat transfer on ice accretion modeling are discussed.
Computer-aided surface roughness measurement system
Hughes, F.J.; Schankula, M.H.
1983-11-01
A diamond stylus profilometer with computer-based data acquisition/analysis system is being used to characterize surfaces of reactor components and materials, and to examine the effects of surface topography on thermal contact conductance. The current system is described; measurement problems and system development are discussed in general terms and possible future improvements are outlined.
Characteristics of density currents over regular and irregular rough surfaces
NASA Astrophysics Data System (ADS)
Bhaganagar, K.
2013-12-01
Direct numerical simulation is used as a tool to understand the effect of surface roughness on the propagation of density currents. Simulations have been performed for lock-exchange flow with gate separating the dense and the lighter fluid. As the lock is released the dense fluid collapses with the lighter fluid on the top, resulting in formation of horizontally evolving density current. The talk will focus on the fundamental differences between the propagation of the density current over regular and irregular rough surfaces. The flow statistics and the flow structures are discussed. The results have revealed the spacing between the roughness elements is an important factor in classifying the density currents. The empirical relations of the front velocity and location for the dense and sparse roughness have been evaluated in terms of the roughness height, spacing between the elements and the initial amount of lock fluid. DNS results for a dense current flowing over a (a) smooth and (b) rough bottom with egg-carton roughness elements in a regular configuration. In these simulations the lock-exchange box is located in the middle of the channel and has two gates which allow two dense currents to be generated, one moving to the right and one to the left side of the channel. Note how the dense current interface presents smaller structures when over a rough bottom (right).
Optical system design of surface roughness photoelectric inspection instrument
NASA Astrophysics Data System (ADS)
Xiao, Ze-xin; Li, Peng; Cao, Jie; Xiao, Ran
2010-11-01
The light-section method for roughness measurement is one of the most classical measuring methods. According to light-section method which combine visual observation with photomicrography for testing surface roughness, domestic type of 9J is a traditional device. The surface roughness photoelectric inspection instrument which designed by the authors are also based on the theory of light-section, which integrates subjects of optics, mechanical, electronics and calculation. Surface roughness of object image can be obtained on the CCD sensor through the optical system. Using the autonomous software in the computer, the average height of workpiece unevenness Ra value can be measured and read in the monitor. Therefor, surface roughness level can be obtained. In order to design the optical system of device, there are three main aspects which should be finished: 1.Start with requirements of detective object, according to the detective range from Ra12.5 to Ra0.04 ruled by CNS(China National Standards) GB3505-83 the Surface Roughness Term Surface and the Parameters ,parameters on β(magnify power), NA(numerical aperture), WD(work distance), filed of object etc are defined and optimized. Meanwhile, good complementation and compatibility are noticed among three kinds magnification objectives. 2. Special type infinity image distance double telecentricity optical system is constructed. The main point is to design a set of objectives of long WD and infinity image distance flat field semi-apochromat. 3. How to match and optimize the CCD image sensor and lens.
Nanopatterning on rough surfaces using optically trapped microspheres
NASA Astrophysics Data System (ADS)
Tsai, Y.-C.; Fardel, R.; Arnold, C. B.
2011-06-01
While nanofabricated structures find an increasingly large number of applications, few techniques are able to pattern rough or uneven surfaces, or surfaces with pre-existing structure. In this letter we show that optical trap assisted nanopatterning (OTAN), a near-field laser based technique, is able to produce nanoscale features on surfaces with large roughness but without the need for focus adjustment. Patterning on model surfaces of polyimide with vertical steps greater than 0.5 μm shows a high degree of uniformity, demonstrating that OTAN is a suitable technique to pattern nontraditional surfaces for emerging technologies.
Self-consistent approach to x-ray reflection from rough surfaces
Feranchuk, I. D.; Feranchuk, S. I.; Ulyanenkov, A. P.
2007-02-15
A self-consistent analytical approach for specular x-ray reflection from interfaces with transition layers [I. D. Feranchuk et al., Phys. Rev. B 67, 235417 (2003)] based on the distorted-wave Born approximation (DWBA) is used for the description of coherent and incoherent x-ray scattering from rough surfaces and interfaces. This approach takes into account the transformation of the modeling transition layer profile at the interface, which is caused by roughness correlations. The reflection coefficients for each DWBA order are directly calculated without phenomenological assumptions on their exponential decay at large scattering angles. Various regions of scattering angles are discussed, which show qualitatively different dependence of the reflection coefficient on the scattering angle. The experimental data are analyzed using the method developed.
Effect of surface morphology on drag and roughness sublayer in flows over regular roughness elements
NASA Astrophysics Data System (ADS)
Placidi, Marco; Ganapathisubramani, Bharathram
2014-11-01
The effects of systematically varied roughness morphology on bulk drag and on the spatial structure of turbulent boundary layers are examined by performing a series of wind tunnel experiments. In this study, rough surfaces consisting of regularly and uniformly distributed LEGO™ bricks are employed. Twelve different patterns are adopted in order to methodically examine the individual effects of frontal solidity (λF, frontal area of the roughness elements per unit wall-parallel area) and plan solidity (λP, plan area of roughness elements per unit wall-parallel area), on both the bulk drag and the turbulence structure. A floating element friction balance based on Krogstad & Efros (2010) was designed and manufactured to measure the drag generated by the different surfaces. In parallel, high resolution planar and stereoscopic Particle Image Velocimetry (PIV) was applied to investigate the flow features. This talk will focus on the effects of each solidity parameter on the bulk drag and attempt to relate the observed trends to the flow structures in the roughness sublayer. Currently at City University London.
Interfacial thermodynamics of confined water near molecularly rough surfaces
Mittal, Jeetain; Hummer, Gerhard
2012-01-01
We study the effects of nanoscopic roughness on the interfacial free energy of water confined between solid surfaces. SPC/E water is simulated in confinement between two infinite planar surfaces that differ in their physical topology: one is smooth and the other one is physically rough on a nanometer length scale. The two thermodynamic ensembles considered, with constant pressure either normal or parallel to the walls, correspond to different experimental conditions. We find that molecular-scale surface roughness significantly increases the solid-liquid interfacial free energy compared to the smooth surface. For our surfaces with a water-wall interaction energy minimum of −1.2 kcal/mol, we observe a transition from a hydrophilic surface to a hydrophobic surface at a roughness amplitude of about 3 Å and a wave length of 11.6 Å, with the interfacial free energy changing sign from negative to positive. In agreement with previous studies of water near hydrophobic surfaces, we find an increase in the isothermal compressibility of water with increasing surface roughness. Interestingly, average measures of the water density and hydrogen-bond number do not contain distinct signatures of increased hydrophobicity. In contrast, a local analysis indicates transient dewetting of water in the valleys of the rough surface, together with a significant loss of hydrogen bonds, and a change in the dipole orientation toward the surface. These microscopic changes in the density, hydrogen bonding, and water orientation contribute to the large increase in the interfacial free energy, and the change from a hydrophilic to a hydrophobic character of the surface. PMID:21043431
Effect of surface roughness on characteristics of spherical shock waves
NASA Technical Reports Server (NTRS)
Huber, Paul W; Mcfarland, Donald R
1955-01-01
An investigation has been conducted on a small-scale test layout in which direct observation of the shock wave movement with time could be made in order to determine the effects of surface roughness on the characteristics of spherical shock waves. Data were obtained with 15-gram pentolite charges at four heights of burst, both for a smooth surface and for a surface completely covered with pyramid-shaped roughness elements. The observations resulted in determinations of shock peak overpressure and Mach stem height as a function of distance for each test. Comparison of the smooth-surface data with those obtained for the extremely rough condition showed a small net effort of roughness on the shock peak overpressures at the surface for all burst heights, the effect being to lower the overpressures. The effect of surface roughness on the Mach stem formation and growth was to delay the formation at the greatest charge height and to lower the height of the Mach stem for all heights.Comparison of the free-air shock peak overpressures with larger scale data showed good similarity of the overpressure-distance relationships. The data did not fit a geometrical similarity parameter for the path of the triple point at different heights of burst suggested by other investigators. A simple similarity parameter (relating the horizontal distance to the theoretical point of Mach formation) was found which showed only a small influence of burst height on the path of the triple point. While the data presented provide knowledge of the effect of many surface-roughness elements on the overall shock characteristics, the data do not provide insight into the details of the air-flow characteristics along the surface, nor the relative contribution of individual roughness elements to the results obtained.
Roughness and waviness requirements for laminar flow surfaces
NASA Technical Reports Server (NTRS)
Obara, Clifford J.; Holmes, Bruce J.
1986-01-01
Many modern metal and composite airframe manufacturing techniques can provide surface smoothness which is compatible with natural laminar flow (NLF) requirements. An important consideration is manufacturing roughness of the surface in the form of steps and gaps perpendicular to the freestream. The principal challenge to the design and manufacture of laminar flow surfaces today appears to be in the installation of leading-edge panels on wing, nacelle, and empennage surfaces. A similar challenge is in the installation of access panels, doors, windows, fuselage noses, and engine nacelles. Past work on roughness and waviness manufacturing tolerances and comparisons with more recent experiments are reviewed.
Calculations of microwave brightness temperature of rough soil surfaces: Bare field
NASA Technical Reports Server (NTRS)
Mo, T.; Schmugge, T. J.; Wang, J. R.
1985-01-01
A model for simulating the brightness temperatures of soils with rough surfaces is developed. The surface emissivity of the soil media is obtained by the integration of the bistatic scattering coefficients for rough surfaces. The roughness of a soil surface is characterized by two parameters, the surface height standard deviation sigma and its horizontal correlation length l. The model calculations are compared to the measured angular variations of the polarized brightness temperatures at both 1.4 GHz and 5 GHz frequences. A nonlinear least-squares fitting method is used to obtain the values of delta and l that best characterize the surface roughness. The effect of shadowing is incorporated by introducing a function S(theta), which represents the probability that a point on a rough surface is not shadowed by other parts of the surface. The model results for the horizontal polarization are in excellent agreement with the data. However, for the vertical polarization, some discrepancies exist between the calculations and data, particularly at the 1.4 GHz frequency. Possible causes of the discrepancy are discussed.
Parametric optical surface roughness measurement by means of polychromatic speckle autocorrelation
NASA Astrophysics Data System (ADS)
Patzelt, Stefan; Ciossek, Andreas; Lehmann, Peter; Schoene, Armin
1998-10-01
A method for determining surface roughness of engineering surfaces that is applicable to in-process measurements under harsh circumstances of industrial production plants (e.g. vibrations, humidity) is introduced. The rough surface is illuminated with polychromatic laser light. The angular distribution of scattered light intensities, i.e. a polychromatic speckle pattern, is the result of an incoherent superposition of monochromatic speckle intensities. The angular dispersion leads to increasing speckle widths with an increasing distance to the optical axis an effect called speckle elongation. This gives rise to a radial structure of the speckle pattern. However, with increasing surface roughness the radial structure vanishes because of a decreasing similarity of the monochromatic speckle patterns of the different wavelengths. The markedness of this effect is analyzed by digital image processing algorithms, e.g. the procedure of polychromatic speckle autocorrelation. The latest approach to an in-process roughness measurement device was made by the use of singlemode fiber-pigtailed laser diodes in order to supply a trichromatic, temporally partially coherent laser beam. A brief introduction to the theoretical background is followed by the presentation of the experimental setup. The image processing algorithms for calculating an optical roughness measure from digitalized speckle patterns are explained, and first results of surface roughness determination are presented.
X-ray reflectivity and surface roughness
Ocko, B.M.
1988-01-01
Since the advent of high brightness synchrotron radiation sources there has been a phenomenal growth in the use of x-rays as a probe of surface structure. The technique of x-ray reflectivity is particularly relevant to electrochemists since it is capable of probing the structure normal to an electrode surface in situ. In this paper the theoretical framework for x-ray reflectivity is reviewed and the results from previous non-electrochemistry measurements are summarized. These measurements are from the liquid/air interface (CCl/sub 4/), the metal crystal vacuum interface (Au(100)), and from the liquid/solid interface(liquid crystal/silicon). 34 refs., 5 figs.
Investigation Into the Accuracy of 3D Surface Roughness Characteristics
NASA Astrophysics Data System (ADS)
Kumermanis, M.; Rudzitis, J.; Mozga, N.; Ancans, A.; Grislis, A.
2014-04-01
The existing standards for surface roughness cover only two dimensions, while in reality this is three-dimensional (3D). In particular, the 3D surface roughness parameters are important for solving the contact surface mechanics problems as related to the accuracy of 3D surface roughness characteristics. One of the most important factors for determination of 3D characteristics is the number of data points (NDP) on the x- and y-axes (i.e. in cut-off length). The NDP has a profound effect on the accuracy of measurement results, measuring time and volume of the output data (especially along the y-axis, where the NDP is identical to the number of parallel profiles). At a too small NDP the results will be incorrect and with too broad scatter, while a too large NDP - though not enlarging the range of basic information - considerably increases the measuring time. Therefore, the aim of the work was to find the optimal NDP for such surface processing methods as grinding, spark erosion and shot methods of surface treatment. Eksistējošie virsmas raupjuma standarti apskata virsmas raupjumu tikai divās dimensijās. Tomēr reālais virsmas raupjums pēc savas dabas ir trīsdimensiju (3D) objekts. Līdz ar to virsmas raupjums ir jāraksturo ar 3D parametriem. Un no šo parametru noteikšanas precizitātes ir atkarīgi tālākie virsmas aprēķini, piemēram, virsmu kontaktēšanās process. Viens no svarīgākajiem faktoriem, raksturojot virsmas raupjumu 3D, pielietojot kontakta tipa mēriekārtas, ir datu punktu skaits pa abām mērīšanas asīm x un y. Ar datu punktu skaitu mēs saprotam to skaitu mērīšanas bāzes garumā. Datu punktu skaits būtiski ietekmē sagaidāmo mērījumu rezultātu precizitāti, mērīšanai nepieciešamo laiku un izejas datu faila izmērus (sevišķi y-ass virzienā, kur katrs datu punkts ir paralēls profils). Datu punktu skaitam ir jābūt optimālam. Pārāk mazs punktu skaits noved pie neprecīziem rezultātiem un lielas to izkliedes, savuk
Correlation between frictional force and surface roughness of orthodontic archwires.
Choi, Samjin; Hwang, Eun-Young; Park, Hun-Kuk; Park, Young-Guk
2015-01-01
Lateral force microscopy measures the lateral bending of the cantilever depending on the frictional force acting between the tip and surface. The aim of this study was to investigate and compare the relationship between the surface roughness and frictional resistance of four archwire and bracket combinations consisting of the 0.016-inch NiTi and 0.019 × 0.025-inch stainless steel archwires interacting clinically with two representative self-ligating brackets, active-type Clippy-C(®) ceramic self-ligating brackets, and passive-type Damon(®) stainless steel self-ligating brackets, using the lateral force microscopy technique. A 0.016-inch NiTi archwire interacting with passive-type Damon(®) stainless steel self-ligating brackets showed the smoothest surface roughness and the lowest frictional resistance compared to other combinations. The archwires interacting with passive-type Damon(®) stainless steel self-ligating brackets showed significantly lower surface roughness and frictional resistance than those interacting with active-type Clippy-C(®) ceramic self-ligating brackets. The frictional force in the in vivo archwire and bracket system increased with increasing surface roughness of the archwire. This positive correlation suggests that surface roughness can be used as an evaluating marker for estimating the efficiency of orthodontic treatment, rather than the direct measurement of frictional force. PMID:26018223
Structural contribution to the roughness of supersmooth crystal surface
Butashin, A. V.; Muslimov, A. E. Kanevsky, V. M.; Deryabin, A. N.; Pavlov, V. A.; Asadchikov, V. E.
2013-05-15
Technological advances in processing crystals (Si, sapphire {alpha}-Al{sub 2}O{sub 3}, SiC, GaN, LiNbO{sub 3}, SrTiO{sub 3}, etc.) of substrate materials and X-ray optics elements make it possible to obtain supersmooth surfaces with a periodicity characteristic of the crystal structure. These periodic structures are formed by atomically smooth terraces and steps of nano- and subnanometer sizes, respectively. A model surface with such nanostructures is proposed, and the relations between its roughness parameters and the height of atomic steps are determined. The roughness parameters calculated from these relations almost coincide with the experimental atomic force microscopy (AFM) data obtained from 1 Multiplication-Sign 1 and 10 Multiplication-Sign 10 {mu}m areas on the surface of sapphire plates with steps. The minimum roughness parameters for vicinal crystal surfaces, which are due to the structural contribution, are calculated based on the approach proposed. A comparative analysis of the relief and roughness parameters of sapphire plate surfaces with different degrees of polishing is performed. A size effect is established: the relief height distribution changes from stochastic to regular with a decrease in the surface roughness.
Interaction of fast charges with a rough metal surface
NASA Astrophysics Data System (ADS)
Lyon, Keenan; Zhang, Ying-Ying; Mišković, Z. L.; Song, Yuan-Hong; Wang, You-Nian
2015-09-01
We use the Green function formulation of a dielectric response formalism to study the dynamic polarization of a rough metal surface by a single charged particle and by a pair of charged particles that move parallel to the surface. While the surface roughness is treated nonperturbatively, the plasmon excitation of the metal electron gas is described locally. We find that the magnitudes of both the image potential and the stopping power of a single particle are increased by the increasing roughness and decreasing correlation length of the surface. On the other hand, both the long-range wake potential of a single charged particle and the interaction potential between two particles are weakly affected by the surface roughness. However, the strongest effects of the surface roughness are seen in the correlated stopping power of two charged particles, giving rise to oscillations in the dependence of the stopping ratio on their distance, both when the interparticle axis is perpendicular to their direction of motion and when the wake-related oscillations are damped by adiabatic suppression of plasmon excitations at low particle speeds.
Experiments to test theoretical models of the polarization of light by rough surfaces
NASA Technical Reports Server (NTRS)
Geake, J. E.; Geake, M.; Zellner, B. H.
1984-01-01
A number of attempts have been made to provide theoretical models of the physical processes involved in the polarization of light scattered by a rough surface, such as the regolith of an atmosphereless planet. Some laboratory experiments designed to test different aspects of these models are described. It is concluded that double Fresnel reflection is usually the dominant process in producing negative polarization, but that diffraction effects may play a significant part in double events involving small-scale surface features.
Response Ant Colony Optimization of end milling surface roughness.
Kadirgama, K; Noor, M M; Abd Alla, Ahmed N
2010-01-01
Metal cutting processes are important due to increased consumer demands for quality metal cutting related products (more precise tolerances and better product surface roughness) that has driven the metal cutting industry to continuously improve quality control of metal cutting processes. This paper presents optimum surface roughness by using milling mould aluminium alloys (AA6061-T6) with Response Ant Colony Optimization (RACO). The approach is based on Response Surface Method (RSM) and Ant Colony Optimization (ACO). The main objectives to find the optimized parameters and the most dominant variables (cutting speed, feedrate, axial depth and radial depth). The first order model indicates that the feedrate is the most significant factor affecting surface roughness. PMID:22294914
Thermal slip for liquids at rough solid surfaces
NASA Astrophysics Data System (ADS)
Zhang, Chengbin; Chen, Yongping; Peterson, G. P.
2014-06-01
Molecular dynamics simulation is used to examine the thermal slip of liquids at rough solid surfaces as characterized by fractal Cantor structures. The temperature profiles, potential energy distributions, thermal slip, and interfacial thermal resistance are investigated and evaluated for a variety of surface topographies. In addition, the effects of liquid-solid interaction, surface stiffness, and boundary condition on thermal slip length are presented. Our results indicate that the presence of roughness expands the low potential energy regions in adjacent liquids, enhances the energy transfer at liquid-solid interface, and decreases the thermal slip. Interestingly, the thermal slip length and thermal resistance for liquids in contact with solid surfaces depends not only on the statistical roughness height, but also on the fractal dimension (i.e., topographical spectrum).
Response Ant Colony Optimization of End Milling Surface Roughness
Kadirgama, K.; Noor, M. M.; Abd Alla, Ahmed N.
2010-01-01
Metal cutting processes are important due to increased consumer demands for quality metal cutting related products (more precise tolerances and better product surface roughness) that has driven the metal cutting industry to continuously improve quality control of metal cutting processes. This paper presents optimum surface roughness by using milling mould aluminium alloys (AA6061-T6) with Response Ant Colony Optimization (RACO). The approach is based on Response Surface Method (RSM) and Ant Colony Optimization (ACO). The main objectives to find the optimized parameters and the most dominant variables (cutting speed, feedrate, axial depth and radial depth). The first order model indicates that the feedrate is the most significant factor affecting surface roughness. PMID:22294914
Analysis of surface roughness generation in aircraft ice accretion
NASA Technical Reports Server (NTRS)
Hansman, R. J., Jr.; Reehorst, Andrew; Sims, James
1992-01-01
Patterns of roughness evolution have been studied analysis of high magnification video observations of accreting ice surfaces provided by the NASA Lewis Research Center. Three distinct patterns of surface roughness generation have been identified within the parametric regions studied. They include: Rime, Multi-Zone Glaze, and Uniform Glaze. Under most icing conditions, a brief period of transient rime ice growth was observed caused by heat conduction into the body. The resulting thin rime layer explains previously observed insensitivity of some ice accretions to substrate insensitivity of some ice accretions to substrate surface chemistry and may provide justification for simplifying assumptions in ice accretion sailing and modeling effects.
Surface roughness effects with solid lubricants dispersed in mineral oils
NASA Technical Reports Server (NTRS)
Cusano, C.; Goglia, P. R.; Sliney, H. E.
1983-01-01
The lubricating effectiveness of solid-lubricant dispersions are investigated in both point and line contacts using surfaces with both random and directional roughness characteristics. Friction and wear data obtained at relatively low speeds and at room temperature, indicate that the existence of solid lubricants such as graphite, MoS2, and PTFE in a plain mineral oil generally will not improve the effectiveness of the oil as a lubricant for such surfaces. Under boundary lubrication conditions, the friction force, as a function of time, initially depends upon the directional roughness properties of the contacting surfaces irrespective of whether the base oil or dispersions are used as lubricants.
Reflection of polarized light by rough surfaces: Monte Carlo modeling compared to measurements
NASA Astrophysics Data System (ADS)
Guirado, Daniel; Marcos Sanz, Juan; María Saiz, José; Muñoz, Olga; Stam, Daphne M.
2013-04-01
A Monte Carlo model of light scattering in a dense medium was developed in order to simulate the reflection of polarized light by rough surfaces [1]. This model calculates all four Stokes parameters of light scattered in all directions by a surface made of any material. Although multiple scattering is allowed, there is a limitation in the packing density of the medium, as independent scattering is assumed. The model can be applied to the study of light scattering by fluffy icy/dusty surfaces, e.g., various types of planetary or lunar regolith-type surfaces, icy moons or comets. The main goal of this work is to test the model by comparing scattering matrix elements calculated with the Monte Carlo model to experimentally measured scattering matrix elements as functions of the phase angle. We use a Sahara sand surface for this. The experimental scattering matrix is measured at the new apparatus developed at the University of Cantabria (Spain) [2]. Sample surfaces are prepared by putting together dust grains with a water-diluted glue coating. A surface's top layer was made with pure sand, to preserve the air-sand refractive index ratio. Calibration measurements have already been carried out successfully by using Spectralon as a Lambertian surface. After calibration, measurements of a surface made of Sahara sand were performed. In such measurements, deviations from Lambertian behavior were found, as well as a very prominent forward peak in the (1,1)-element of the matrix for grazing illumination angles. The values of I and -Q/I calculated by the model for the vertical scattering plane and non-polarized incident light were compared to the measured F11 and -F21/F11 elements for several incident directions. A good agreement between measurements and calculations was achieved. The forward-scattering peak of the (1,1)-element can be interpreted as a result of single scattering of horizontally incident light by the small features of the non-flat surface. In this case, light
Studies of the 3D surface roughness height
NASA Astrophysics Data System (ADS)
Avisane, Anita; Rudzitis, Janis; Kumermanis, Maris
2013-12-01
Nowadays nano-coatings occupy more and more significant place in technology. Innovative, functional coatings acquire new aspects from the point of view of modern technologies, considering the aggregate of physical properties that can be achieved manipulating in the production process with the properties of coatings' surfaces on micro- and nano-level. Nano-coatings are applied on machine parts, friction surfaces, contacting parts, corrosion surfaces, transparent conducting films (TCF), etc. The equipment available at present for the production of transparent conducting oxide (TCO) coatings with highest quality is based on expensive indium tin oxide (ITO) material; therefore cheaper alternatives are being searched for. One such offered alternative is zink oxide (ZnO) nano-coatings. Evaluating the TCF physical and mechanical properties and in view of the new ISO standard (EN ISO 25178) on the introduction of surface texture (3D surface roughness) in the engineering calculations, it is necessary to examine the height of 3D surface roughness, which is one of the most significant roughness parameters. The given paper studies the average values of 3D surface roughness height and the most often applied distribution laws are as follows: the normal distribution and Rayleigh distribution. The 3D surface is simulated by a normal random field.
Studies of the 3D surface roughness height
Avisane, Anita; Rudzitis, Janis; Kumermanis, Maris
2013-12-16
Nowadays nano-coatings occupy more and more significant place in technology. Innovative, functional coatings acquire new aspects from the point of view of modern technologies, considering the aggregate of physical properties that can be achieved manipulating in the production process with the properties of coatings’ surfaces on micro- and nano-level. Nano-coatings are applied on machine parts, friction surfaces, contacting parts, corrosion surfaces, transparent conducting films (TCF), etc. The equipment available at present for the production of transparent conducting oxide (TCO) coatings with highest quality is based on expensive indium tin oxide (ITO) material; therefore cheaper alternatives are being searched for. One such offered alternative is zink oxide (ZnO) nano-coatings. Evaluating the TCF physical and mechanical properties and in view of the new ISO standard (EN ISO 25178) on the introduction of surface texture (3D surface roughness) in the engineering calculations, it is necessary to examine the height of 3D surface roughness, which is one of the most significant roughness parameters. The given paper studies the average values of 3D surface roughness height and the most often applied distribution laws are as follows: the normal distribution and Rayleigh distribution. The 3D surface is simulated by a normal random field.
Pettit, J. R.; Walker, A.; Lowe, M. J. S.
2014-02-18
Defects which posses rough surfaces greatly affect ultrasonic wave scattering behaviour, often reducing the magnitude of reflected signals. Ultrasonic inspections rely upon this response for detecting and sizing flaws. For safety critical components reliable characterisation is crucial. Therefore, providing an accurate means to predict reductions in signal amplitude is essential. An extension of Kirchhoff theory has formed the basis for the UK power industry inspection justifications. However, it is widely recognised that these predictions are pessimistic owing to analytical approximations. A numerical full field modelling approach does not fall victim to such limitations. Here, a Finite Element model is used to aid in setting a non-conservative reporting threshold during the inspection of a large pressure vessel forging that might contain embedded rough defects. The ultrasonic response from multiple rough surfaces defined by the same statistical class is calculated for normal incident compression waves. The approach is validated by comparing coherent scattering with predictions made by Kirchhoff theory. At lower levels of roughness excellent agreement is observed, whilst higher values confirm the pessimism of Kirchhoff theory. Furthermore, the mean amplitude in the specular direction is calculated. This represents the information obtained during an inspection, indicating that reductions due to increasing roughness are significantly less than the coherent component currently being used.
NASA Astrophysics Data System (ADS)
Mendeleev, Vladimir Y.; Skovorod'ko, Sergey N.
2004-02-01
A relation between the intensity reflectances of approximately one-dimensional and one-dimensional rough surfaces within the diffraction solid angle in the specular direction for normal incidence is derived for an rms roughness greater than a wavelength. The relation shows that the reflectance of an approximately one-dimensional rough surface is proportional to the reflectance of a one-dimension rough surface. The validity of the derived relation is studied for an approximately one-dimensional rough steel surface with an rms roughness of 1.3 μm and a correlation length of 15.2 μm. The wavelength was 0.6328 μm and the angle of incidence was 4°. The reflectance of the rough steel surface was measured and estimated from the derived relation. Satisfactory agreement was found between the estimated and measured reflectance values.
How surface roughness affects chemical transfer from soil to surface runoff?
Technology Transfer Automated Retrieval System (TEKTRAN)
Soil surface roughness affects transport processes, e.g., runoff generation, infiltration, sediment detachment, etc., occurring on the surface. Nevertheless, how soil roughness affects chemical transport is less known. In this study, we partitioned roughness elements into mounds which diverge water ...
Scattering and Chemical Investigations of Semiconductor Surfaces.
NASA Astrophysics Data System (ADS)
Wallace, Robert Milo
1988-12-01
This two-part thesis describes: (i) the design of an ion scattering system to examine the surface and near-surface region of semiconductors, and (ii) the chemical reaction channels of unsaturated hydrocarbons on the silicon (100) surface. Details on the design and construction of an ultrahigh vacuum, high-energy ion scattering system are presented. The use of MeV ion scattering to investigate surface and near -surface regions of materials is described and the combination of ion scattering with complimentary surface science techniques is stressed. The thermal activation of chemical bonds of the adsorbed unsaturated hydrocarbon molecules ethylene, propylene, and acetylene is investigated on the Si(100)-(2 times 11) surface with a goal of understanding the surface chemistry of Si-C formation. The use of precision dosing techniques, Low Energy Electron Diffraction, Auger Electron Spectroscopy, and Temperature Programmed Desorption in the investigation of the remaining carbonaceous species is described. Comparisons of the adsorption and desorption behavior of these molecules is made in terms of the carbon -carbon double and triple bonds (ethylene to acetylene) and the methyl functional group (ethylene to propylene). We find that the monolayer saturation coverage of these hydrocarbons is in very good agreement with the number of dimer sites on the surface estimated from scanning-tunneling microscopy, which suggests that the bonding of these hydrocarbons to the Si(100) surface is similar. It is also found that ethylene, in particular, does not provide an efficient Si-C reaction channel upon thermal activation, with nearly 100% of the ethylene molecules desorbing. In contrast, acetylene is found to be very efficient in SiC formation: >=q90% of the adsorbed acetylene thermally dissociates and eventually leads to SiC formation. Propylene has an efficiency of roughly 70% upon heating. Evidence for the diffusion of carbon into the bulk is seen at >=q850 K for propylene and
On the Effects of Surface Roughness on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan; Edwards, Jack
2009-01-01
Surface roughness can influence laminar-turbulent transition in many different ways. This paper outlines selected analyses performed at the NASA Langley Research Center, ranging in speed from subsonic to hypersonic Mach numbers and highlighting the beneficial as well as adverse roles of the surface roughness in technological applications. The first theme pertains to boundary-layer tripping on the forebody of a hypersonic airbreathing configuration via a spanwise periodic array of trip elements, with the goal of understanding the physical mechanisms underlying roughness-induced transition in a high-speed boundary layer. The effect of an isolated, finite amplitude roughness element on a supersonic boundary layer is considered next. The other set of flow configurations examined herein corresponds to roughness based laminar flow control in subsonic and supersonic swept wing boundary layers. A common theme to all of the above configurations is the need to apply higher fidelity, physics based techniques to develop reliable predictions of roughness effects on laminar-turbulent transition.
Scaling of surface roughness in perfectly plastic disordered media
Barai, Pallab; Nukala, Phani K; Sampath, Rahul S; Simunovic, Srdjan
2010-01-01
This paper investigates surface roughness characteristics of localized plastic yield surface in a perfectly plastic disordered material. We model the plastic disordered material using perfectly plastic random spring model. Our results indicate that plasticity in a disordered material evolves in a diffusive manner until macroscopic yielding, which is in contrast to the localized failure observed in brittle fracture of disordered materials. On the other hand, the height-height fluctuations of the plastic yield surfaces generated by the spring model exhibit roughness exponents similar to those obtained in the brittle fracture of disordered materials, albeit anomalous scaling of plastic surface roughness is not observed. The local and global roughness exponents ({zeta}{sub loc} and {zeta}, respectively) are equal to each other, and the two-dimensional crack roughness exponent is estimated to be {zeta}{sub loc} = {zeta} = 0.67 {+-} 0.03. The probability density distribution p[{Delta}h({ell})] of the height differences {Delta}h({ell}) = [h(x+{ell})-h(x)] of the crack profile follows a Gaussian distribution.
The Aerodynamic Characteristics of Airfoils as Affected by Surface Roughness
NASA Technical Reports Server (NTRS)
HOCKER RAY W
1933-01-01
The effect on airfoil characteristics of surface roughness of varying degrees and types at different locations on an airfoil was investigated at high values of the Reynolds number in a variable density wind tunnel. Tests were made on a number of National Advisory Committee for Aeronautics (NACA) 0012 airfoil models on which the nature of the surface was varied from a rough to a very smooth finish. The effect on the airfoil characteristics of varying the location of a rough area in the region of the leading edge was also investigated. Airfoils with surfaces simulating lap joints were also tested. Measurable adverse effects were found to be caused by small irregularities in airfoil surfaces which might ordinarily be overlooked. The flow is sensitive to small irregularities of approximately 0.0002c in depth near the leading edge. The tests made on the surfaces simulating lap joints indicated that such surfaces cause small adverse effects. Additional data from earlier tests of another symmetrical airfoil are also included to indicate the variation of the maximum lift coefficient with the Reynolds number for an airfoil with a polished surface and with a very rough one.
Simulation of synthetic gecko arrays shearing on rough surfaces
Gillies, Andrew G.; Fearing, Ronald S.
2014-01-01
To better understand the role of surface roughness and tip geometry in the adhesion of gecko synthetic adhesives, a model is developed that attempts to uncover the relationship between surface feature size and the adhesive terminal feature shape. This model is the first to predict the adhesive behaviour of a plurality of hairs acting in shear on simulated rough surfaces using analytically derived contact models. The models showed that the nanoscale geometry of the tip shape alters the macroscale adhesion of the array of fibres by nearly an order of magnitude, and that on sinusoidal surfaces with amplitudes much larger than the nanoscale features, spatula-shaped features can increase adhesive forces by 2.5 times on smooth surfaces and 10 times on rough surfaces. Interestingly, the summation of the fibres acting in concert shows behaviour much more complex that what could be predicted with the pull-off model of a single fibre. Both the Johnson–Kendall–Roberts and Kendall peel models can explain the experimentally observed frictional adhesion effect previously described in the literature. Similar to experimental results recently reported on the macroscale features of the gecko adhesive system, adhesion drops dramatically when surface roughness exceeds the size and spacing of the adhesive fibrillar features. PMID:24694893
Simulation of synthetic gecko arrays shearing on rough surfaces.
Gillies, Andrew G; Fearing, Ronald S
2014-06-01
To better understand the role of surface roughness and tip geometry in the adhesion of gecko synthetic adhesives, a model is developed that attempts to uncover the relationship between surface feature size and the adhesive terminal feature shape. This model is the first to predict the adhesive behaviour of a plurality of hairs acting in shear on simulated rough surfaces using analytically derived contact models. The models showed that the nanoscale geometry of the tip shape alters the macroscale adhesion of the array of fibres by nearly an order of magnitude, and that on sinusoidal surfaces with amplitudes much larger than the nanoscale features, spatula-shaped features can increase adhesive forces by 2.5 times on smooth surfaces and 10 times on rough surfaces. Interestingly, the summation of the fibres acting in concert shows behaviour much more complex that what could be predicted with the pull-off model of a single fibre. Both the Johnson-Kendall-Roberts and Kendall peel models can explain the experimentally observed frictional adhesion effect previously described in the literature. Similar to experimental results recently reported on the macroscale features of the gecko adhesive system, adhesion drops dramatically when surface roughness exceeds the size and spacing of the adhesive fibrillar features. PMID:24694893
NASA Astrophysics Data System (ADS)
Yang, Le; Liu, Qinhuo
2012-10-01
The aerodynamic surface roughness z0 is a key parameter for climate and land-surface models to study surfaceatmosphere exchanges of mass and energy. The roughness length is difficult to estimate without wind speed profile data, which is intractable at regional to global scale. Theoretical formulations of roughness have been developed in terms of canopy attributes such as frontal area, height, and drag coefficient. This paper discusses the potential of radar altimetry, which provides the backscatter coefficient of the land surface at nadir view, to characterise the surface roughness at km scale. The AIEM model and ProSARproSIM are employed to simulate the backscatter coefficient under different surface condition and different observation geometry at bare soil and at pine forest, respectively. The altimetry backscatter decreases with increase of geometric roughness. The microwave backscatter measured at the nadir view is more sensitive to the surface roughness than that at the oblique observation, especially for the smooth surface. The direct forest return is the dominated scattering mechanism for normal incidence at forest area. Since we failed to collect the z0 measurement at arid and semi-arid area with sparse vegetation, the backscatter measurements at Ku and C band of altimeter Jason1 were analyzed with the ground measured aerodynamic surface roughness at three vegetated sites (Da yekou, Yin ke, and Chang Baisan) of China. The relationships we found between Jason1 sigma0 and z0 is not significant, since Jason1 lost track seriously at the three sites. Further research using the altimeter data of Jason2 and Cryosat is possible to demonstrate the potential to map z0 from orbit using radar altimeters.
Process entanglement as a neuronal anchorage mechanism to rough surfaces
NASA Astrophysics Data System (ADS)
Sorkin, Raya; Greenbaum, Alon; David-Pur, Moshe; Anava, Sarit; Ayali, Amir; Ben-Jacob, Eshel; Hanein, Yael
2009-01-01
The organization of neurons and glia cells on substrates composed of pristine carbon nanotube islands was investigated using high resolution scanning electron microscopy, immunostaining and confocal microscopy. Neurons were found bound and preferentially anchored to the rough surfaces; moreover, the morphology of the neuronal processes on the small, isolated islands of high density carbon nanotubes was found to be conspicuously curled and entangled. We further demonstrate that the roughness of the surface must match the diameter of the neuronal processes in order to allow them to bind. The results presented here suggest that entanglement, a mechanical effect, may constitute an additional mechanism by which neurons (and possibly other cell types) anchor themselves to rough surfaces. Understanding the nature of the interface between neurons and carbon nanotubes is essential to effectively harness carbon nanotube technology in neurological applications such as neuro-prosthetic and retinal electrodes.
Liu, Linsheng; Li, Xuefeng; Nonaka, Kazuhiro
2015-02-01
Depolarization at a rough surface relates to its roughness and irregularity (e.g., sags and crests) besides the material property. However, there is still lack of general theory to clearly describe the relationship between depolarization ratios and surface conditions, and one important reason is that the mechanism of depolarization relates to geometric parameters such as microcosmic height/particle distributions of sub-micro to nm levels. To study the mechanism in more detail, a compact laser instrument is developed, and depolarization information of a linearly polarized incident light is used for analyzing the roughness, during which a He-Ne laser source (λ = 632.8 nm) is used. Three nickel specimens with RMS roughness (Rq) less than λ/4 are fabricated and tested. Six different areas in each specimen are characterized in detail using an AFM. Rq are in the range of 34.1-155.0 nm, and the heights are non-Gaussian distribution in the first specimen and near-Gaussian distribution in the others. Off-specular inspection is carried out exactly on these 18 characterized areas, and results show that the cross-polarization ratios match quite well with Rq values of the first sample that has Rq ≤ λ/10 (or Rt ≤ λ), while they match well with maximum height, Rt, values of the other two that have Rt > λ (the maximum derivation is 11%). In addition, since this instrument is simple, portable, stable, and low-cost, it has great potential for practical online roughness testing after a linear calibration. PMID:25725823
Surface roughness of orthodontic band cements with different compositions
van de SANDE, Françoise Hélène; da SILVA, Adriana Fernandes; MICHELON, Douver; PIVA, Evandro; CENCI, Maximiliano Sérgio; DEMARCO, Flávio Fernando
2011-01-01
Objectives The present study evaluated comparatively the surface roughness of four orthodontic band cements after storage in various solutions. Material and Methods eight standardized cylinders were made from 4 materials: zinc phosphate cement (ZP), compomer (C), resin-modified glass ionomer cement (RMGIC) and resin cement (RC). Specimens were stored for 24 h in deionized water and immersed in saline (pH 7.0) or 0.1 M lactic acid solution (pH 4.0) for 15 days. Surface roughness readings were taken with a profilometer (Surfcorder SE1200) before and after the storage period. Data were analyzed by two-way ANOVA and Tukey's test (comparison among cements and storage solutions) or paired t-test (comparison before and after the storage period) at 5% significance level. Results The values for average surface roughness were statistically different (p<0.001) among cements at both baseline and after storage. The roughness values of cements in a decreasing order were ZP>RMGIC>C>R (p<0.001). After 15 days, immersion in lactic acid solution resulted in the highest surface roughness for all cements (p<0.05), except for the RC group (p>0.05). Compared to the current threshold (0.2 µm) related to biofilm accumulation, both RC and C remained below the threshold, even after acidic challenge by immersion in lactic acid solution. Conclusions Storage time and immersion in lactic acid solution increased the surface roughness of the majority of the tested cements. RC presented the smoothest surface and it was not influenced by storage conditions. PMID:21625737
TLS - a tool for channel bed surface roughness determination?
NASA Astrophysics Data System (ADS)
Baewert, Henning; Morche, David
2013-04-01
Channel bed surface roughness has a significant influence on flow characteristics of a stream. Since decades roughness coefficient determination is an integral part of fluvial geomorphological research. The methods used to directly measure channel bed roughness often require an exact knowledge of grain size distributions of a given stream reach. In some cases this method is impractical, especially for large catchments and systems involving a large degree of form roughness. In this context, the determination of bed surface roughness using Terrestrial Laser Scanning (TLS) provides new possibilities. The application of laser scanning has been increasingly used recently for channel morphology research (Heritage & Hetherington 2007, Milan et al. 2007, Hodge et al. 2009). However, the use of TLS data to quantify bed surface roughness leads to new methodological problems. One of these problems is known as the 'Shading Effect'. Because of this, portions of the channel surface situated behind a large obstacle cannot be surveyed. Hence, the first goal of this study is to determine the minimum number of scanning positions to accurately characterize channel bed roughness. For roughness calculation, the investigation area is divided into an orthogonal grid. The question about this is: Which grid cell size should be chosen? In general, the cell size is defined by the largest particle in the test area. This requires sediment sampling and leads to additional field work. To avoid this, this study further assesses the importance of grid cell size on bed roughness calculation. The ultimate goal of this study is to improve the application of TLS for roughness calculation in gravel-bed rivers. For this purpose several channel reaches in two different study sites were surveyed with an ILRIS 36D. One investigation area is situated in the Reintal valley located in the northern limestone Alps (Wettersteingebirge) Bavaria/Germany. The other one is situated in the proglacial area of the
Effect of Surface Roughness on Characteristics of Spherical Shock Waves
NASA Technical Reports Server (NTRS)
Huber, Paul W.; McFarland, Donald R.
1959-01-01
Measurements of peak overpressure and Mach stem height were made at four burst heights. Data were obtained with instrumentation capable of directly observing the variation of shock wave movement with time. Good similarity of free air shock peak overpressure with larger scale data was found to exist. The net effect of surface roughness on shock peak overpressures slightly. Surface roughness delayed the Mach stem formation at the greatest charge height and lowered the growth at all burst heights. A similarity parameter was found which approximately correlates the triple point path at different burst heights.
Scanning tunneling microscopy on rough surfaces-quantitative image analysis
NASA Astrophysics Data System (ADS)
Reiss, G.; Brückl, H.; Vancea, J.; Lecheler, R.; Hastreiter, E.
1991-07-01
In this communication, the application of scanning tunneling microscopy (STM) for a quantitative evaluation of roughnesses and mean island sizes of polycrystalline thin films is discussed. Provided strong conditions concerning the resolution are satisfied, the results are in good agreement with standard techniques as, for example, transmission electron microscopy. Owing to its high resolution, STM can supply a better characterization of surfaces than established methods, especially concerning the roughness. Microscopic interpretations of surface dependent physical properties thus can be considerably improved by a quantitative analysis of STM images.
Adhesion: role of bulk viscoelasticity and surface roughness.
Lorenz, B; Krick, B A; Mulakaluri, N; Smolyakova, M; Dieluweit, S; Sawyer, W G; Persson, B N J
2013-06-01
We study the adhesion between smooth polydimethylsiloxane (PDMS) rubber balls and smooth and rough poly(methyl methacrylate) (PMMA) surfaces, and between smooth silicon nitride balls and smooth PDMS surfaces. From the measured viscoelastic modulus of the PDMS rubber we calculate the viscoelastic contribution to the crack-opening propagation energy γeff(v,T) for a wide range of crack tip velocities v and for several temperatures T. The Johnson-Kendall-Roberts (JKR) contact mechanics theory is used to analyze the ball pull-off force data, and γeff(v,T) is obtained for smooth and rough surfaces. We conclude that γeff(v,T) has contributions of similar magnitude from both the bulk viscoelastic energy dissipation close to the crack tip, and from the bond-breaking process at the crack tip. The pull-off force on the rough surfaces is strongly reduced compared to that of the flat surface, which we attribute mainly to the decrease in the area of contact on the rough surfaces. PMID:23649298
Adhesion: role of bulk viscoelasticity and surface roughness
NASA Astrophysics Data System (ADS)
Lorenz, B.; Krick, B. A.; Mulakaluri, N.; Smolyakova, M.; Dieluweit, S.; Sawyer, W. G.; Persson, B. N. J.
2013-06-01
We study the adhesion between smooth polydimethylsiloxane (PDMS) rubber balls and smooth and rough poly(methyl methacrylate) (PMMA) surfaces, and between smooth silicon nitride balls and smooth PDMS surfaces. From the measured viscoelastic modulus of the PDMS rubber we calculate the viscoelastic contribution to the crack-opening propagation energy γeff(v,T) for a wide range of crack tip velocities v and for several temperatures T. The Johnson-Kendall-Roberts (JKR) contact mechanics theory is used to analyze the ball pull-off force data, and γeff(v,T) is obtained for smooth and rough surfaces. We conclude that γeff(v,T) has contributions of similar magnitude from both the bulk viscoelastic energy dissipation close to the crack tip, and from the bond-breaking process at the crack tip. The pull-off force on the rough surfaces is strongly reduced compared to that of the flat surface, which we attribute mainly to the decrease in the area of contact on the rough surfaces.
The Effect of Surface Irregularities on Wing Drag. 3; Roughness
NASA Technical Reports Server (NTRS)
Hood, Manley J.
1938-01-01
Tests have been made in the N.A.C.A. 8-foot high-speed wind tunnel of the drag caused by roughness on the surface of an airfoil of N.A.C.A. 23012 section and 5-foot chord. The tests were made at speeds from 80 t o 500 miles per hour at lift coefficients from 0 to 0.30. For conditions corresponding to high-speed flight, the increase in the drag was 30 percent of the profile drag of the smooth airfoil for the roughness produced by spray painting and 63 percent for the roughness produced. by 0.0037-inch carborundum grains. About one-half the drag increase was caused by the roughness on the forward one-fourth of the airfoil. Sandpapering the painted surface with No. 400 sandpaper made it sufficiently smooth that the drag was no greater than when the surface was polished. In the lower part of the range investigated the drag due to roughness increased rapidly with Reynolds Number.
Scatter of X-rays on polished surfaces
NASA Technical Reports Server (NTRS)
Hasinger, G.
1981-01-01
In investigating the dispersion properties of telescope mirrors used in X-ray astronomy, the slight scattering characteristics of X-ray radiation by statistically rough surfaces were examined. The mathematics and geometry of scattering theory are described. The measurement test assembly is described and results of measurements on samples of plane mirrors are given. Measurement results are evaluated. The direct beam, the convolution of the direct beam and the scattering halo, curve fitting by the method of least squares, various autocorrelation functions, results of the fitting procedure for small scattering, and deviations in the kernel of the scattering distribution are presented. A procedure for quality testing of mirror systems through diagnosis of rough surfaces is described.
Modelling surface roughness and rocks in LRO Diviner observations
NASA Astrophysics Data System (ADS)
Williams, J.-P.; Hayne, P. O.; Paige, D. A.
2012-09-01
The Diviner Lunar Radiometer Experiment on NASA's Lunar Reconnaissance Orbiter (LRO) observes radiance in 7 infrared spectral channels from which brightness temperatures of the lunar surface are derived. In general, Diviner's surface footprint contains small scale variations in temperature. This anisothermality results in different observed brightness temperatures in Diviner's individual channels. A three-dimensional heat diffusion model is used to explore anisothermality in Diviner observations resulting from surface roughness and rocks at multiple length-scales and illumination conditions.