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.

Surface Roughness Measurement on a Wing Aircraft by Speckle Correlation

PubMed Central

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.

PubMed

Salazar, Félix; Barrientos, Alberto

2013-09-05

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.

Shuttle orbiter boundary layer transition at flight and wind tunnel conditions

NASA Technical Reports Server (NTRS)

Goodrich, W. D.; Derry, S. M.; Bertin, J. J.

1983-01-01

Hypersonic boundary layer transition data obtained on the windward centerline of the Shuttle orbiter during entry for the first five flights are presented and analyzed. Because the orbiter surface is composed of a large number of thermal protection tiles, the transition data include the effects of distributed roughness arising from tile misalignment and gaps. These data are used as a benchmark for assessing and improving the accuracy of boundary layer transition predictions based on correlations of wind tunnel data taken on both aerodynamically rough and smooth orbiter surfaces. By comparing these two data bases, the relative importance of tunnel free stream noise and surface roughness on orbiter boundary layer transition correlation parameters can be assessed. This assessment indicates that accurate predications of transition times can be made for the orbiter at hypersonic flight conditions by using roughness dominated wind tunnel data. Specifically, times of transition onset and completion is accurately predicted using a correlation based on critical and effective values of a roughness Reynolds number previously derived from wind tunnel data.

Quantitative characterization of material surface — Application to Ni + Mo electrolytic composite coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kubisztal, J., E-mail: julian.kubisztal@us.edu.pl

A new approach to numerical analysis of maps of material surface has been proposed and discussed in detail. It was concluded that the roughness factor RF and the root mean square roughness S{sub q} show a saturation effect with increasing size of the analysed maps what allows determining the optimal map dimension representative of the examined material. A quantitative method of determining predominant direction of the surface texture based on the power spectral density function is also proposed and discussed. The elaborated method was applied in surface analysis of Ni + Mo composite coatings. It was shown that co-deposition ofmore » molybdenum particles in nickel matrix leads to an increase in surface roughness. In addition, a decrease in size of the embedded Mo particles in Ni matrix causes an increase of both the surface roughness and the surface texture. It was also stated that the relation between the roughness factor and the double layer capacitance C{sub dl} of the studied coatings is linear and allows determining the double layer capacitance of the smooth nickel electrode. - Highlights: •Optimization of the procedure for the scanning of the material surface •Quantitative determination of the surface roughness and texture intensity •Proposition of the parameter describing privileged direction of the surface texture •Determination of the double layer capacitance of the smooth electrode.« less

Microscale X-ray tomographic investigation of the interfacial morphology between the catalyst and micro porous layers in proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Prass, Sebastian; Hasanpour, Sadegh; Sow, Pradeep Kumar; Phillion, André B.; Mérida, Walter

2016-07-01

The interfacial morphology between the catalyst layer (CL) and micro porous layer (MPL) influences the performance of proton exchange membrane fuel cells (PEMFCs). Here we report a direct method to investigate the CL-MPL interfacial morphology of stacked and compressed gas diffusion layer (GDL with MPL)-catalyst coated membrane (CCM) assemblies. The area, origin and dimensions of interfacial gaps are studied with high-resolution X-ray micro computed tomography (X-μCT). The projected gap area (fraction of the CL-MPL interface separated by gaps) is higher for GDL-CCM assemblies with large differences in the surface roughness between CL and MPL but reduces with increasing compression and similarity in roughness. Relatively large continuous gaps are found in proximity to cracks in the MPL. These are hypothesized to form due to the presence of large pores on the surface of the GDL. Smaller gaps are induced by the surface roughness features throughout the CL-MPL interface. By modification of the pore sizes on the GDL surface serving as substrate for the MPL, the number and dimension of MPL crack induced gaps can be manipulated. Moreover, adjusting the CL and MPL surface roughness parameters to achieve similar orders of roughness can improve the surface mating characteristics of these two components.

Surface roughness in XeF{sub 2} etching of a-Si/c-Si(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevens, A.A.E.; Beijerinck, H.C.W.

2005-01-01

Single wavelength ellipsometry and atomic force microscopy (AFM) have been applied in a well-calibrated beam-etching experiment to characterize the dynamics of surface roughening induced by chemical etching of a {approx}12 nm amorphous silicon (a-Si) top layer and the underlying crystalline silicon (c-Si) bulk. In both the initial and final phase of etching, where either only a-Si or only c-Si is exposed to the XeF{sub 2} flux, we observe a similar evolution of the surface roughness as a function of the XeF{sub 2} dose proportional to D(XeF{sub 2}){sup {beta}} with {beta}{approx_equal}0.2. In the transition region from the pure amorphous to themore » pure crystalline silicon layer, we observe a strong anomalous increase of the surface roughness proportional to D(XeF{sub 2}){sup {beta}} with {beta}{approx_equal}1.5. Not only the growth rate of the roughness increases sharply in this phase, also the surface morphology temporarily changes to a structure that suggests a cusplike shape. Both features suggest that the remaining a-Si patches on the surface act effectively as a capping layer which causes the growth of deep trenches in the c-Si. The ellipsometry data on the roughness are corroborated by the AFM results, by equating the thickness of the rough layer to 6 {sigma}, with {sigma} the root-mean-square variation of the AFM's distribution function of height differences. In the AFM data, the anomalous behavior is reflected in a too small value of {sigma} which again suggests narrow and deep surface features that cannot be tracked by the AFM tip. The final phase morphology is characterized by an effective increase in surface area by a factor of two, as derived from a simple bilayer model of the reaction layer, using the experimental etch rate as input. We obtain a local reaction layer thickness of 1.5 monolayer consistent with the 1.7 ML value of Lo et al. [Lo et al., Phys. Rev. B 47, 648 (1993)] that is also independent of surface roughness.« less

A Transport Equation Approach to Modeling the Influence of Surface Roughness on Boundary Layer Transition

NASA Astrophysics Data System (ADS)

Langel, Christopher Michael

A computational investigation has been performed to better understand the impact of surface roughness on the flow over a contaminated surface. This thesis highlights the implementation and development of the roughness amplification model in the flow solver OVERFLOW-2. The model, originally proposed by Dassler, Kozulovic, and Fiala, introduces an additional scalar field roughness amplification quantity. This value is explicitly set at rough wall boundaries using surface roughness parameters and local flow quantities. This additional transport equation allows non-local effects of surface roughness to be accounted for downstream of rough sections. This roughness amplification variable is coupled with the Langtry-Menter model and used to modify the criteria for transition. Results from flat plate test cases show good agreement with experimental transition behavior on the flow over varying sand grain roughness heights. Additional validation studies were performed on a NACA 0012 airfoil with leading edge roughness. The computationally predicted boundary layer development demonstrates good agreement with experimental results. New tests using varying roughness configurations are being carried out at the Texas A&M Oran W. Nicks Low Speed Wind Tunnel to provide further calibration of the roughness amplification method. An overview and preliminary results are provided of this concurrent experimental investigation.

The Canopy Horizontal Array Turbulence Study (CHATS)

Treesearch

Edward G. Patton; Thomas W. Horst; Donald H. Lenschow; Peter P. Sullivan; Steven Oncley; Sean Burns; Alex Guenther; Andreas Held; Thomas Karl; Shane Mayor; Luciana Rizzo; Scott Spuler; Jielun Sun; Andrew Turnipseed; Eugene Allwine; Steven Edburg; Brian Lamb; Roni Avissar; Heidi E. Holder; Ron Calhoun; Jan Kleissl; William Massman; Kyaw Tha Paw U; Jeffrey C. Weil

2008-01-01

Turbulence in the planetary boundary layer (PBL) well above the surface has been shown to be independent of the details of the surface roughness. In this region well-quantified similarity relationships work well when characterizing turbulent fluxes (e.g., Raupach, 1979). However, in the near-surface layer which is directly influenced by roughness elements, i.e., the...

On the stability of von Kármán rotating-disk boundary layers with radial anisotropic surface roughness

NASA Astrophysics Data System (ADS)

Garrett, S. J.; Cooper, A. J.; Harris, J. H.; Özkan, M.; Segalini, A.; Thomas, P. J.

2016-01-01

We summarise results of a theoretical study investigating the distinct convective instability properties of steady boundary-layer flow over rough rotating disks. A generic roughness pattern of concentric circles with sinusoidal surface undulations in the radial direction is considered. The goal is to compare predictions obtained by means of two alternative, and fundamentally different, modelling approaches for surface roughness for the first time. The motivating rationale is to identify commonalities and isolate results that might potentially represent artefacts associated with the particular methodologies underlying one of the two modelling approaches. The most significant result of practical relevance obtained is that both approaches predict overall stabilising effects on type I instability mode of rotating disk flow. This mode leads to transition of the rotating-disk boundary layer and, more generally, the transition of boundary-layers with a cross-flow profile. Stabilisation of the type 1 mode means that it may be possible to exploit surface roughness for laminar-flow control in boundary layers with a cross-flow component. However, we also find differences between the two sets of model predictions, some subtle and some substantial. These will represent criteria for establishing which of the two alternative approaches is more suitable to correctly describe experimental data when these become available.

Structural properties 3,16-bis triisopropylsilylethynyl (pentacene) (TIPS-pentacene) thin films onto organic dielectric layer using slide coating method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rusnan, Fara Naila; Mohamad, Khairul Anuar; Seria, Dzul Fahmi Mohd Husin

3,16-bis triisopropylsilylethynyl (Pentacene) (TIPS-Pentacene) compactable interface property is important in order to have a good arrangement of molecular structure. Comparison for TIPS-Pentacene deposited between two different surface layers conducted. 0.1wt% TIPS-Pentacene diluted in chloroform were deposited onto poly(methylmeaclyrate) (PMMA) layered transparent substrates using slide coating method. X-ray diffraction (XRD) used to determine crystallinity of thin films. Series of (00l) diffraction peaks obtained with sharp first peaks (001) for TIPS-Pentacene deposited onto PMMA layer at 5.35° and separation of 16.3 Å. Morphology and surface roughness were carried out using scanning electron microscope (SEM) and surface profilemeter LS500, respectively.TIPS-Pentacene deposited onto PMMAmore » layer formed needled-like-shape grains with 10.26 nm surface roughness. These properties were related as thin film formed and its surface roughness plays important role towards good mobility devices.« less

Investigation of the influence of a step change in surface roughness on turbulent heat transfer

NASA Technical Reports Server (NTRS)

Taylor, Robert P.; Coleman, Hugh W.; Taylor, J. Keith; Hosni, M. H.

1991-01-01

The use is studied of smooth heat flux gages on the otherwise very rough SSME fuel pump turbine blades. To gain insights into behavior of such installations, fluid mechanics and heat transfer data were collected and are reported for a turbulent boundary layer over a surface with a step change from a rough surface to a smooth surface. The first 0.9 m length of the flat plate test surface was roughened with 1.27 mm hemispheres in a staggered, uniform array spaced 2 base diameters apart. The remaining 1.5 m length was smooth. The effect of the alignment of the smooth surface with respect to the rough surface was also studied by conducting experiments with the smooth surface aligned with the bases or alternatively with the crests of the roughness elements. Stanton number distributions, skin friction distributions, and boundary layer profiles of temperature and velocity are reported and are compared to previous data for both all rough and all smooth wall cases. The experiments show that the step change from rough to smooth has a dramatic effect on the convective heat transfer. It is concluded that use of smooth heat flux gages on otherwise rough surfaces could cause large errors.

Nanoscale Roughness and Morphology Affect the IsoElectric Point of Titania Surfaces

PubMed Central

Borghi, Francesca; Vyas, Varun; Podestà, Alessandro; Milani, Paolo

2013-01-01

We report on the systematic investigation of the role of surface nanoscale roughness and morphology on the charging behaviour of nanostructured titania (TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces have been characterized by direct measurement of the electrostatic double layer interactions between titania surfaces and the micrometer-sized spherical silica probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a colloidal probe provides well-defined interaction geometry and allows effectively probing the overall effect of nanoscale morphology. By using supersonic cluster beam deposition to fabricate nanostructured titania films, we achieved a quantitative control over the surface morphological parameters. We performed a systematical exploration of the electrical double layer properties in different interaction regimes characterized by different ratios of characteristic nanometric lengths of the system: the surface rms roughness Rq, the correlation length ξ and the Debye length λD. We observed a remarkable reduction by several pH units of IEP on rough nanostructured surfaces, with respect to flat crystalline rutile TiO2. In order to explain the observed behavior of IEP, we consider the roughness-induced self-overlap of the electrical double layers as a potential source of deviation from the trend expected for flat surfaces. PMID:23874708

Dimensional accuracy and surface property of titanium casting using gypsum-bonded alumina investment.

PubMed

Yan, Min; Takahashi, Hidekazu; Nishimura, Fumio

2004-12-01

The aim of the present study was to evaluate the dimensional accuracy and surface property of titanium casting obtained using a gypsum-bonded alumina investment. The experimental gypsum-bonded alumina investment with 20 mass% gypsum content mixed with 2 mass% potassium sulfate was used for five cp titanium castings and three Cu-Zn alloy castings. The accuracy, surface roughness (Ra), and reaction layer thickness of these castings were investigated. The accuracy of the castings obtained from the experimental investment ranged from -0.04 to 0.23%, while surface roughness (Ra) ranged from 7.6 to 10.3microm. A reaction layer of about 150 microm thickness under the titanium casting surface was observed. These results suggested that the titanium casting obtained using the experimental investment was acceptable. Although the reaction layer was thin, surface roughness should be improved.

Enhancement of vortex induced forces and motion through surface roughness control

DOEpatents

Bernitsas, Michael M [Saline, MI; Raghavan, Kamaldev [Houston, TX

2011-11-01

Roughness is added to the surface of a bluff body in a relative motion with respect to a fluid. The amount, size, and distribution of roughness on the body surface is controlled passively or actively to modify the flow around the body and subsequently the Vortex Induced Forces and Motion (VIFM). The added roughness, when designed and implemented appropriately, affects in a predetermined way the boundary layer, the separation of the boundary layer, the level of turbulence, the wake, the drag and lift forces, and consequently the Vortex Induced Motion (VIM), and the fluid-structure interaction. The goal of surface roughness control is to increase Vortex Induced Forces and Motion. Enhancement is needed in such applications as harnessing of clean and renewable energy from ocean/river currents using the ocean energy converter VIVACE (Vortex Induced Vibration for Aquatic Clean Energy).

Full wave two-dimensional modeling of scattering and inverse scattering for layered rough surfaces with buried objects

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 using VHF/UHF band radar measurements is devised. The top soil dielectric constant is first determined using an L-band inversion algorithm. For the retrieval of subsurface properties, a time-domain inversion technique is employed together with a parameter optimization for the pulse shape of time delay echoes from VHF/UHF band radar observations. Numerical studies to investigate the accuracy of the proposed inversion technique in presence of errors are addressed.

Correlation of nosetip boundary-layer transition data measured in ballistics-range experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reda, D.C.

1979-11-01

Preablated nosetips of various carbonaceous materials were tested in a ballistics range. Surface-temperature contours, measured with image-converter cameras, were used to define boundary-layer transition-fron contours. Measurements of surface roughness, surface temperature, average transition-calculations of nosetip flowfields, and with calculations of laminar boundary-layer development in these flowfields, to transform all data into various dimensionless parameters. These parameters were defined by previous attempts to correlate existing wind-tunnel data for transition on rough/blunt bodies.

Feather roughness reduces flow separation during low Reynolds number glides of swifts.

PubMed

van Bokhorst, Evelien; de Kat, Roeland; Elsinga, Gerrit E; Lentink, David

2015-10-01

Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small (proto) birds with an evolutionary window to high glide performance. © 2015. Published by The Company of Biologists Ltd.

Transition Experiments on Blunt Bodies with Isolated Roughness Elements in Hypersonic Free Flight

NASA Technical Reports Server (NTRS)

Reda, Daniel C.; Wilder, Michael C.; Prabhu, Dinesh K.

2010-01-01

Smooth titanium hemispheres with isolated three-dimensional (3D) surface roughness elements were flown in the NASA Ames hypersonic ballistic range through quiescent CO2 and air environments. Global surface intensity (temperature) distributions were optically measured and thermal wakes behind individual roughness elements were analyzed to define tripping effectiveness. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted predict key dimensionless parameters used to correlate transition on blunt bodies in hypersonic flow. For isolated roughness elements totally immersed within the laminar boundary layer, critical roughness Reynolds numbers for flights in air were found to be higher than those measured for flights in CO2, i.e., it was easier to trip the CO2 boundary layer to turbulence. Tripping effectiveness was found to be dependent on trip location within the subsonic region of the blunt body flowfield, with effective tripping being most difficult to achieve for elements positioned closest to the stagnation point. Direct comparisons of critical roughness Reynolds numbers for 3D isolated versus 3D distributed roughness elements for flights in air showed that distributed roughness patterns were significantly more effective at tripping the blunt body laminar boundary layer to turbulence.

Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choudhary, B. S.; Rajasthan Technical University, Rawatbhata Road, Kota 324010; Singh, A.

We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surfacemore » with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.« less

Variability in radar returns from Martian debris-covered glaciers attributed to surface debris layer roughness and composition: implications for the regional distribution of massive subsurface ice and near-surface pore-filling ice.

NASA Astrophysics Data System (ADS)

Petersen, E.; Holt, J. W.; Levy, J. S.; Lalich, D.

2017-12-01

Lobate debris aprons, lineated valley fill, and concentric crater fill are a class of Martian landform thought to be glaciers blanketed by a lithic debris layer. They are found in the mid latitudes (roughly 30-50°N and S) where surface ice is presently unstable. Shallow Radar (SHARAD) sounder observations are in many cases able to resolve the basal contact between the glacier and underlying bedrock, showing that the bulk composition of these features is water ice with < 20% lithic debris; they are thus often referred to as debris-covered glaciers (DCG). The basal contact of candidate glaciers is not always present in SHARAD radargrams, and variable reflection power between glacier sites suggests that non-detections may be due to a reduction of echo power below the noise floor. A likely candidate for signal loss is the variable roughness of different glacial surface textures. We test this mechanism of signal reduction via analysis of SHARAD reflections augmented by surface roughness analyses generated from HiRISE stereo DEMs. This method provides a means of constraining the electrical properties of the surface debris. We show that measured surface roughness is sufficient to explain basal reflection signal loss for five glacier sites in the region of Deuteronilus/Protonilus Mensae (R2 = 0.90), with the dielectric constant for the surface debris layer constrained to 4.9 ± 0.3. Assuming debris formed of basalt rock, this value is consistent with a porous debris layer containing up to 64% ice, or an ice-free debris layer with porosity of 28-34%. From this work, we conclude that (1) weak or non-existent basal reflections at these sites are due to roughness-induced radar signal loss and not due to differing properties of the basal interface, (2) all DCG candidates in this study exhibit similar bulk compositions of relatively pure water ice, and (3) the surface debris layer is formed of porous lithic debris which may contain a significant fraction of pore ice.

Influence of Cooling Condition on the Performance of Grinding Hardened Layer in Grind-hardening

NASA Astrophysics Data System (ADS)

Wang, G. C.; Chen, J.; Xu, G. Y.; Li, X.

2018-02-01

45# steel was grinded and hardened on a surface grinding machine to study the effect of three different cooling media, including emulsion, dry air and liquid nitrogen, on the microstructure and properties of the hardened layer. The results show that the microstructure of material surface hardened with emulsion is pearlite and no hardened layer. The surface roughness is small and the residual stress is compressive stress. With cooling condition of liquid nitrogen and dry air, the specimen surface are hardened, the organization is martensite, the surface roughness is also not changed, but high hardness of hardened layer and surface compressive stress were obtained when grinding using liquid nitrogen. The deeper hardened layer grinded with dry air was obtained and surface residual stress is tensile stress. This study provides an experimental basis for choosing the appropriate cooling mode to effectively control the performance of grinding hardened layer.

Effects of enviromentally imposed roughness on airfoil performance

NASA Technical Reports Server (NTRS)

Cebeci, Tuncer

1987-01-01

The experimental evidence for the effects of rain, insects, and ice on airfoil performance are examined. The extent to which the available information can be incorporated in a calculation method in terms of change of shape and surface roughness is discussed. The methods described are based on the interactive boundary layer procedure of Cebeci or on the thin layer Navier Stokes procedure developed at NASA. Cases presented show that extensive flow separation occurs on the rough surfaces.

Excitation of Crossflow Instabilities in a Swept Wing Boundary Layer

NASA Technical Reports Server (NTRS)

Carpenter, Mark H.; Choudhari, Meelan; Li, Fei; Streett, Craig L.; Chang, Chau-Lyan

2010-01-01

The problem of crossflow receptivity is considered in the context of a canonical 3D boundary layer (viz., the swept Hiemenz boundary layer) and a swept airfoil used recently in the SWIFT flight experiment performed at Texas A&M University. First, Hiemenz flow is used to analyze localized receptivity due to a spanwise periodic array of small amplitude roughness elements, with the goal of quantifying the effects of array size and location. Excitation of crossflow modes via nonlocalized but deterministic distribution of surface nonuniformity is also considered and contrasted with roughness induced acoustic excitation of Tollmien-Schlichting waves. Finally, roughness measurements on the SWIFT model are used to model the effects of random, spatially distributed roughness of sufficiently small amplitude with the eventual goal of enabling predictions of initial crossflow disturbance amplitudes as functions of surface roughness parameters.

Reduction of vortex induced forces and motion through surface roughness control

DOEpatents

Bernitsas, Michael M; Raghavan, Kamaldev

2014-04-01

Roughness is added to the surface of a bluff body in a relative motion with respect to a fluid. The amount, size, and distribution of roughness on the body surface is controlled passively or actively to modify the flow around the body and subsequently the Vortex Induced Forces and Motion (VIFM). The added roughness, when designed and implemented appropriately, affects in a predetermined way the boundary layer, the separation of the boundary layer, the level of turbulence, the wake, the drag and lift forces, and consequently the Vortex Induced Motion (VIM), and the fluid-structure interaction. The goal of surface roughness control is to decrease/suppress Vortex Induced Forces and Motion. Suppression is required when fluid-structure interaction becomes destructive as in VIM of flexible cylinders or rigid cylinders on elastic support, such as underwater pipelines, marine risers, tubes in heat exchangers, nuclear fuel rods, cooling towers, SPAR offshore platforms.

Composite Pillars with a Tunable Interface for Adhesion to Rough Substrates

PubMed Central

2016-01-01

The benefits of synthetic fibrillar dry adhesives for temporary and reversible attachment to hard objects with smooth surfaces have been successfully demonstrated in previous studies. However, surface roughness induces a dramatic reduction in pull-off stresses and necessarily requires revised design concepts. Toward this aim, we introduce cylindrical two-phase single pillars, which are composed of a mechanically stiff stalk and a soft tip layer. Adhesion to smooth and rough substrates is shown to exceed that of conventional pillar structures. The adhesion characteristics can be tuned by varying the thickness of the soft tip layer, the ratio of the Young’s moduli and the curvature of the interface between the two phases. For rough substrates, adhesion values similar to those obtained on smooth substrates were achieved. Our concept of composite pillars overcomes current practical limitations caused by surface roughness and opens up fields of application where roughness is omnipresent. PMID:27997118

Influence of Surface Roughness on the Second Order Transport of Turbulence in Non-Equilibrium Boundary Layers

DTIC Science & Technology

2006-10-08

FINAL REPORT to Air Force Office of Scientific Research (AFOSR) Project Title Influence of Surface Roughness on the Second Order Transport of...large amount of research has been performed to quantify the effects of Mach number, roughness, and wall curvature on turbulent boundary layers. However...18 a) b) c) Figure 3: a) A. D. Smith high pressure storage tank. b) Morin B series actuator controlling Virgo Engineers Trunion Mounted Ball Valve. c

Supersonic turbulent boundary layers with periodic mechanical non-equilibrium

NASA Astrophysics Data System (ADS)

Ekoto, Isaac Wesley

Previous studies have shown that favorable pressure gradients reduce the turbulence levels and length scales in supersonic flow. Wall roughness has been shown to reduce the large-scales in wall bounded flow. Based on these previous observations new questions have been raised. The fundamental questions this dissertation addressed are: (1) What are the effects of wall topology with sharp versus blunt leading edges? and (2) Is it possible that a further reduction of turbulent scales can occur if surface roughness and favorable pressure gradients are combined? To answer these questions and to enhance the current experimental database, an experimental analysis was performed to provide high fidelity documentation of the mean and turbulent flow properties along with surface and flow visualizations of a high-speed (M = 2.86), high Reynolds number (Retheta ≈ 60,000) supersonic turbulent boundary layer distorted by curvature-induced favorable pressure gradients and large-scale ( k+s ≈ 300) uniform surface roughness. Nine models were tested at three separate locations. Three pressure gradient models strengths (a nominally zero, a weak, and a strong favorable pressure gradient) and three roughness topologies (aerodynamically smooth, square, and diamond shaped roughness elements) were used. Highly resolved planar measurements of mean and fluctuating velocity components were accomplished using particle image velocimetry. Stagnation pressure profiles were acquired with a traversing Pitot probe. Surface pressure distributions were characterized using pressure sensitive paint. Finally flow visualization was accomplished using schlieren photographs. Roughness topology had a significant effect on the boundary layer mean and turbulent properties due to shock boundary layer interactions. Favorable pressure gradients had the expected stabilizing effect on turbulent properties, but the improvements were less significant for models with surface roughness near the wall due to increased tendency towards flow separation. It was documented that proper roughness selection coupled with a sufficiently strong favorable pressure gradient produced regions of "negative" production in the transport of turbulent stress. This led to localized areas of significant turbulence stress reduction. With proper roughness selection and sufficient favorable pressure gradient strength, it is believed that localized relaminarization of the boundary layer is possible.

Numerical simulation of electroosmotic flow in rough microchannels using the lattice Poisson-Nernst-Planck methods

NASA Astrophysics Data System (ADS)

Kamali, Reza; Soloklou, Mohsen Nasiri; Hadidi, Hooman

2018-05-01

In this study, coupled Lattice Boltzmann method is applied to solve the dynamic model for an electroosmotic flow and investigate the effects of roughness in a 2-D flat microchannel. In the present model, the Poisson equation is solved for the electrical potential, the Nernst- Planck equation is solved for the ion concentration. In the analysis of electroosmotic flows, when the electric double layers fully overlap or the convective effects are not negligible, the Nernst-Planck equation must be used to find the ionic distribution throughout the microchannel. The effects of surface roughness height, roughness interval spacing and roughness surface potential on flow conditions are investigated for two different configurations of the roughness, when the EDL layers fully overlap through the microchannel. The results show that in both arrangements of roughness in homogeneously charged rough channels, the flow rate decreases by increasing the roughness height. A discrepancy in the mass flow rate is observed when the roughness height is about 0.15 of the channel width, which its average is higher for the asymmetric configuration and this difference grows by increasing the roughness height. In the symmetric roughness arrangement, the mass flow rate increases until the roughness interval space is almost 1.5 times the roughness width and it decreases for higher values of the roughness interval space. For the heterogeneously charged rough channel, when the roughness surface potential ψr is less than channel surface potential ψs , the net charge density increases by getting far from the roughness surface, while in the opposite situation, when ψs is more than ψr , the net charge density decreases from roughness surface to the microchannel middle center. Increasing the roughness surface potential induces stronger electric driving force on the fluid which results in larger velocities in the flow.

Three-Dimensional Electromagnetic Scattering from Layered Media with Rough Interfaces for Subsurface Radar Remote Sensing

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 medium with the scattering from layered structure in general. Combined with scattering from multilayer rough surfaces, scattering contributions from subsurfaces and vegetation roots can be then simulated. Solutions of both the rough surface scattering and random media scattering are validated numerically, experimentally, or both. The experimental validations have been carried out using a laboratory-based transmit-receive system for scattering from random media and a new bistatic tower-mounted radar system for field-based surface scattering measurements.

A facile approach for reducing the working voltage of Au/TiO2/Au nanostructured memristors by enhancing the local electric field

NASA Astrophysics Data System (ADS)

Arab Bafrani, Hamidreza; Ebrahimi, Mahdi; Bagheri Shouraki, Saeed; Moshfegh, Alireza Z.

2018-01-01

Memristor devices have attracted tremendous interest due to different applications ranging from nonvolatile data storage to neuromorphic computing units. Exploring the role of surface roughness of the bottom electrode (BE)/active layer interface provides useful guidelines for the optimization of the memristor switching performance. This study focuses on the effect of surface roughness of the BE electrode on the switching characteristics of Au/TiO2/Au three-layer memristor devices. An optimized wet-etching treatment condition was found to modify the surface roughness of the Au BE where the measurement results indicate that the roughness of the Au BE is affected by both duration time and solution concentrations of the wet-etching process. Then we fabricated arrays of TiO2-based nanostructured memristors sandwiched between two sets of cross-bar Au electrode lines (junction area 900 μm2). The results revealed a reduction in the working voltages in current-voltage characteristic of the device performance when increasing the surface roughness at the Au(BE)/TiO2 active layer interface. The set voltage of the device (Vset) significantly decreased from 2.26-1.93 V when we increased the interface roughness from 4.2-13.1 nm. The present work provides information for better understanding the switching mechanism of titanium-dioxide-based devices, and it can be inferred that enhancing the roughness of the Au BE/TiO2 active layer interface leads to a localized non-uniform electric field distribution that plays a vital role in reducing the energy consumption of the device.

Graphene thickness dependent adhesion force and its correlation to surface roughness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pourzand, Hoorad; Tabib-Azar, Massood, E-mail: azar.m@utah.edu; Biomedical Engineering, University of Utah, Salt Lake City, Utah 84112

2014-04-28

In this paper, adhesion force of graphene layers on 300 nm silicon oxide is studied. A simple model for measuring adhesion force for a flat surface with sub-nanometer roughness was developed and is shown that small surface roughness decreases adhesion force while large roughness results in an effectively larger adhesion forces. We also show that surface roughness over scales comparable to the tip radius increase by nearly a factor of two, the effective adhesion force measured by the atomic force microscopy. Thus, we demonstrate that surface roughness is an important parameter that should be taken into account in analyzing the adhesionmore » force measurement results.« less

Diffusion of Drag-Reducing Polymers within a High-Reynolds-Number, Rough-Wall Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Elbing, Brian; Perlin, Marc; Dowling, David; Solomon, Michael; Ceccio, Steven

2008-11-01

Two experiments were conducted to investigate polymer drag reduction (PDR) within high Reynolds number (to 200 million based on downstream distance), rough-wall turbulent boundary layers. The first experiment was conducted at the U.S. Navy's Large Cavitation Channel on a 12.9 m long flat-plate at speeds to 20 m/s with the surface hydraulically smooth and fully rough. Local skin-friction measurements on the smooth and rough surfaces had maximum PDR levels of 65 and 75 percent, respectively. However, PDR decreased with increasing downstream distance and flow speed more rapidly on the rough surface, and at the top speed no measureable level of PDR was observed. The roughness-induced increased diffusion was quantified with near-wall concentration measurements and the second experiment, which measured concentration profiles on a 0.94 m long flat-plate with three surface conditions: smooth, 240-grit, and 60-grit sandpaper. The increased diffusion does not fully explain the smooth-rough PDR differences observed in the first experiment. Rheological analysis of drawn samples from the first experiment indicates that polymer degradation (chain scission) could be responsible for the remaining loss of rough-wall PDR. These results have implications for the cost effectiveness of PDR for surface ships.

Influence law of structural characteristics on the surface roughness of a magnetorheological-finished KDP crystal.

PubMed

Chen, Shaoshan; Li, Shengyi; Hu, Hao; Li, Qi; Tie, Guipeng

2014-11-01

A new nonaqueous and abrasive-free magnetorheological finishing (MRF) method is adopted for processing potassium dihydrogen phosphate (KDP) crystal due to its low hardness, high brittleness, temperature sensitivity, and water solubility. This paper researches the influence of structural characteristics on the surface roughness of MRF-finished KDP crystal. The material removal by dissolution is uniform layer by layer when the polishing parameters are stable. The angle between the direction of the polishing wheel's linear velocity and the initial turning lines will affect the surface roughness. If the direction is perpendicular to the initial turning lines, the polishing can remove the lines. If the direction is parallel to the initial turning lines, the polishing can achieve better surface roughness. The structural characteristic of KDP crystal is related to its internal chemical bonds due to its anisotropy. During the MRF finishing process, surface roughness will be improved if the structural characteristics of the KDP crystal are the same on both sides of the wheel. The processing results of (001) plane crystal show we can get the best surface roughness (RMS of 0.809 nm) if the directions of cutting and MRF polishing are along the (110) direction.

Progress Towards an LES Wall Model Including Unresolved Roughness

NASA Astrophysics Data System (ADS)

Craft, Kyle; Redman, Andrew; Aikens, Kurt

2015-11-01

Wall models used in large eddy simulations (LES) are often based on theories for hydraulically smooth walls. While this is reasonable for many applications, there are also many where the impact of surface roughness is important. A previously developed wall model has been used primarily for jet engine aeroacoustics. However, jet simulations have not accurately captured thick initial shear layers found in some experimental data. This may partly be due to nozzle wall roughness used in the experiments to promote turbulent boundary layers. As a result, the wall model is extended to include the effects of unresolved wall roughness through appropriate alterations to the log-law. The methodology is tested for incompressible flat plate boundary layers with different surface roughness. Correct trends are noted for the impact of surface roughness on the velocity profile. However, velocity deficit profiles and the Reynolds stresses do not collapse as well as expected. Possible reasons for the discrepancies as well as future work will be presented. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. Computational resources on TACC Stampede were provided under XSEDE allocation ENG150001.

Understanding EUV mask blank surface roughness induced LWR and associated roughness requirement

NASA Astrophysics Data System (ADS)

Yan, Pei-Yang; Zhang, Guojing; Gullikson, Eric M.; Goldberg, Ken 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.

Rough-to-smooth transition of an equilibrium neutral constant stress layer. [atmospheric flow over rough terrain

NASA Technical Reports Server (NTRS)

Logan, E., Jr.; Fichtl, G. H.

1975-01-01

A model is proposed for low-level atmospheric flows over terrains of changing roughness length, such as those found at the windward end of landing strips adjoining rough terrain. The proposed model is used to develop a prediction technique for calculating transition wind and shear-stress profiles in the region following surface roughness discontinuity. The model for the transition region comprises two layers: a logarithmic layer and a buffer layer. The flow is assumed to be steady, two-dimensional, and incompressible, with neutral hydrostatic stability. A diagram is presented for a typical wind profile in the transition region, obtained from the logarithmic and velocity defect profiles using shear stress calculated by relevant equations.

Compositions of Mg and Se, surface morphology, roughness and Raman property of Zn1-xMgxSeyTe1-y layers grown at various substrate temperatures or dopant transport rates by MOVPE

NASA Astrophysics Data System (ADS)

Nishio, Mitsuhiro; Saito, Katsuhiko; Urata, Kensuke; Okamoto, Yasuhiro; Tanaka, Daichi; Araki, Yasuhiro; Abiru, Masakatsu; Mori, Eiichiro; Tanaka, Tooru; Guo, Qixin

2015-03-01

The growth of undoped and phosphorus (P)-doped Zn1-xMgxSeyTe1-y layers on (100) ZnTe substrates by metalorganic vapor phase epitaxy was carried out. The compositions of Mg and Se, surface morphology, roughness and Raman property were characterized as a function of substrate temperature. Not only the compositions of Mg and Se but also the crystal quality of undoped Zn1-xMgxSeyTe1-y layer strongly depended upon the substrate temperature. Furthermore, the growth of Zn1-xMgxSeyTe1-y layer nearly-lattice-matched to ZnTe substrate was achieved independent of the transport rate of trisdimethylaminophosphorus. Undoped Zn1-xMgxSeyTe1-y layer nearly-lattice-matched to ZnTe led to improvement of surface roughness. On the other hand, P doping brought about deterioration of crystalline quality.

Discrete surface roughness effects on a blunt hypersonic cone in a quiet tunnel

NASA Astrophysics Data System (ADS)

Sharp, Nicole; White, Edward

2013-11-01

The mechanisms by which surface roughness creates boundary-layer disturbances in hypersonic flow are little understood. Work by Reshotko (AIAA 2008-4294) and others suggests that transient growth, resulting from the superposition of decaying non-orthogonal modes, may be responsible. The present study examines transient growth experimentally using a smooth 5-degree half-angle conic frustum paired with blunted nosetips with and without an azimuthal array of discrete roughness elements. A combination of hotwire anemometry and Pitot measurements in the low-disturbance Mach 6 Quiet Tunnel are used for boundary layer profiles downstream of the ring of roughness elements as well as azimuthal measurements to examine the high- and low-speed streaks characteristic of transient growth of stationary roughness-induced disturbances.

Thermodynamics of rough colloidal surfaces

NASA Astrophysics Data System (ADS)

Goldstein, Raymond E.; Halsey, Thomas C.; Leibig, Michael

1991-03-01

In Debye-Hückel theory, the free energy of an electric double layer near a colloidal (or any other) surface can be related to the statistics of random walks near that surface. We present a numerical method based on this correspondence for the calculation of the double-layer free energy for an arbitrary charged or conducting surface. For self-similar surfaces, we propose a scaling law for the behavior of the free energy as a function of the screening length and the surface dimension. This scaling law is verified by numerical computation. Capacitance measurements on rough surfaces of, e.g., colloids can test these predictions.

Carbon decorative coatings by dip-, spin-, and spray-assisted layer-by-layer assembly deposition.

PubMed

Hong, Jinkee; Kang, Sang Wook

2011-09-01

We performed a comparative surface analysis of all-carbon nano-objects (multiwall carbon nanotubes (MWNT) or graphene oxide (GO) sheets) based multilayer coatings prepared using three widely used nanofilm fabrication methods: dip-, spin-, and spray-assisted layer-by-layer (LbL) deposition. The resultant films showed a marked difference in their growth mechanisms and surface morphologies. Various carbon decorative coatings were synthesized with different surface roughness values, despite identical preparation conditions. In particular, smooth to highly rough all-carbon surfaces, as determined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), were readily obtained by manipulating the LbL deposition methods. As was confirmed by the AFM and SEM analyses, this finding indicated the fundamental morphological evolution of one-dimensional nano-objects (MWNT) and two-dimensional nano-objects (GO) by control of the surface roughness through the deposition method. Therefore, an analysis of the three LbL-assembly methods presented herein may offer useful information about the industrial use of carbon decorative coatings and provide an insight into ways to control the structures of multilayer coatings by tuning the morphologies of carbon nano-objects.

A Low-Speed Experimental Investigation of the Effect of a Sandpaper Type of Roughness on Boundary-Layer Transition

NASA Technical Reports Server (NTRS)

Von Doenhoff, Albert E; Horton, Elmer A

1958-01-01

An investigation was made in the Langley low-turbulence pressure tunnel to determine the effect of size and location of a sandpaper type of roughness on the Reynolds number for transition. Transition was observed by means of a hot-wire anemometer located at various chordwise stations for each position of the roughness. These observations indicated that when the roughness is sufficiently submerged in the boundary layer to provide a substantially linear variation of boundary-layer velocity with distance from the surface up to the top of the roughness, turbulent "spots" begin to appear immediately behind the roughness when the Reynolds number based on the velocity at the top of the roughness height exceeds a value of approximately 600. At Reynolds numbers even slightly below the critical value (value for transition), the sandpaper type of roughness introduced no measurable disturbances into the laminar layer downstream of the roughness. The extent of the roughness area does not appear to have an important effect on the critical value of the roughness Reynolds number.

Secondary flows in turbulent boundary layers over longitudinal surface roughness

NASA Astrophysics Data System (ADS)

Hwang, Hyeon Gyu; Lee, Jae Hwa

2018-01-01

Direct numerical simulations of turbulent boundary layers over longitudinal surface roughness are performed to investigate the impact of the surface roughness on the mean flow characteristics related to counter-rotating large-scale secondary flows. By systematically changing the two parameters of the pitch (P) and width (S) for roughness elements in the ranges of 0.57 ≤P /δ ≤2.39 and 0.15 ≤S /δ ≤1.12 , where δ is the boundary layer thickness, we find that the size of the secondary flow in each case is mostly determined by the value of P - S, i.e., the valley width, over the ridge-type roughness. However, the strength of the secondary flows on the cross-stream plane relative to the flow is increased when the value of P increases or when the value of S decreases. In addition to the secondary flows, additional tertiary and quaternary flows are observed both above the roughness crest and in the valley as the values of P and S increase further. Based on an analysis using the turbulent kinetic energy transport equation, it is shown that the secondary flow over the ridge-type roughness is both driven and sustained by the anisotropy of turbulence, consistent with previous observations of a turbulent boundary layer over strip-type roughness [Anderson et al., J. Fluid Mech. 768, 316 (2015), 10.1017/jfm.2015.91]. Careful inspection of the turbulent kinetic energy budget reveals that the opposite rotational sense of the secondary flow between the ridge- and strip-type roughness elements is primarily attributed to the local imbalance of energy budget created by the strong turbulent transport term over the ridge-type roughness. The active transport of the kinetic energy over the ridge-type roughness is closely associated with the upward deflection of spanwise motions in the valley, mostly due to the roughness edge.

Resistivity scaling due to electron surface scattering in thin metal layers

NASA Astrophysics Data System (ADS)

Zhou, Tianji; Gall, Daniel

2018-04-01

The effect of electron surface scattering on the thickness-dependent electrical resistivity ρ of thin metal layers is investigated using nonequilibrium Green's function density functional transport simulations. Cu(001) thin films with thickness d =1 -2 nm are used as a model system, employing a random one-monolayer-high surface roughness and frozen phonons to cause surface and bulk scattering, respectively. The zero-temperature resistivity increases from 9.7 ±1.0 μ Ω cm at d =1.99 nm to 18.7 ±2.6 μ Ω cm at d =0.9 0 nm, contradicting the asymptotic T =0 prediction from the classical Fuchs-Sondheimer model. At T =9 00 K, ρ =5.8 ±0.1 μ Ω cm for bulk Cu and ρ =13.4 ±1.1 and 22.5 ±2.4 μ Ω cm for layers with d =1.99 and 0.90 nm, respectively, indicating an approximately additive phonon contribution which, however, is smaller than for bulk Cu or atomically smooth layers. The overall data indicate that the resistivity contribution from surface scattering is temperature-independent and proportional to 1 /d , suggesting that it can be described using a surface-scattering mean-free path λs for 2D transport which is channel-independent and proportional to d . Data fitting indicates λs=4 ×d for the particular simulated Cu(001) surfaces with a one-monolayer-high surface roughness. The 1 /d dependence deviates considerably from previous 1 /d2 predictions from quantum models, indicating that the small-roughness approximation in these models is not applicable to very thin (<2 nm) layers, where the surface roughness is a considerable fraction of d .

Analysis of turbulent heat and momentum transfer in a transitionally rough turbulent boundary layer

NASA Astrophysics Data System (ADS)

Doosttalab, Ali; Dharmarathne, Suranga; Tutkun, Murat; Adrian, Ronald; Castillo, Luciano

2016-11-01

A zero-pressure-gradient (ZPG) turbulent boundary layer over a transitionally rough surface is studied using direct numerical simulation (DNS). The rough surface is modeled as 24-grit sandpaper which corresponds to k+ 11 , where k+ is roughness height. Reynolds number based on momentum thickness is approximately 2400. The walls are isothermal and turbulent flow Prandtl number is 0.71. We simulate temperature as passive scalar. We compute the inner product of net turbulent force (d (u1ui) / dxi) and net turbulent heat flux (d (ui θ / dxi)) in order to investigate (i) the correlation between these vectorial quantities, (II) size of the projection of these fields on each other and (IIi) alignment of momentum and hear flux. The inner product in rough case results in larger projection and better alignment. In addition, our study on the vortices shows that surface roughness promotes production of vortical structures which affects the thermal transport near the wall.

Solvent effect on polystyrene surface roughness on top of QCM sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakti, Setyawan P., E-mail: sakti@ub.ac.id; Rahmawati, Eka; Robiandi, Fadli

2016-03-11

Quartz Crystal Microbalance (QCM) has been used as a basis for many chemical sensors and biosensor. Its sensitivity to mass change which can detect a mass change on its surface down to sub ng/cm2 is one of its interesting aspects. Another interesting feature is its ability to work in liquid environment. However, there are many aspects which influence QCM sensor properties in contact with liquid. One of the aspects is surface roughness of the matrix layer where on top of it a biological sensitive layer will be immobilized. One of matrix layers in the immobilizing biological sensitive layer was polystyrene.more » Polystyrene was coated on the QCM sensor by using the spin coating method. During the coating process, polystyrene was solved using non-polar solvent. It is known that the physical and chemical properties of the solvent affect a transition process from soluble polymer becoming rigid polymer layer. In this work, we show that polystyrene solved in chloroform has a higher surface roughness compare to one solved in toluene, xylene, or tetrahydrofuran. Surface roughness of the polystyrene coating were measured using a non-contact profilometer. However, we also found that there is no difference on the electrical impedance of the QCM sensor coated with polystyrene resulted from differing solvent when the sensor was in contact with air and water. Thus, all of the mentioned solvent can be used to solve the polystyrene as a coating material for QCM sensor without affecting the electrical performance of the sensor, but the choice of the solution can be used as a simple method to control the difference roughness of the polystyrene coating.« less

Solvent effect on polystyrene surface roughness on top of QCM sensor

NASA Astrophysics Data System (ADS)

Sakti, Setyawan P.; Rahmawati, Eka; Robiandi, Fadli

2016-03-01

Quartz Crystal Microbalance (QCM) has been used as a basis for many chemical sensors and biosensor. Its sensitivity to mass change which can detect a mass change on its surface down to sub ng/cm2 is one of its interesting aspects. Another interesting feature is its ability to work in liquid environment. However, there are many aspects which influence QCM sensor properties in contact with liquid. One of the aspects is surface roughness of the matrix layer where on top of it a biological sensitive layer will be immobilized. One of matrix layers in the immobilizing biological sensitive layer was polystyrene. Polystyrene was coated on the QCM sensor by using the spin coating method. During the coating process, polystyrene was solved using non-polar solvent. It is known that the physical and chemical properties of the solvent affect a transition process from soluble polymer becoming rigid polymer layer. In this work, we show that polystyrene solved in chloroform has a higher surface roughness compare to one solved in toluene, xylene, or tetrahydrofuran. Surface roughness of the polystyrene coating were measured using a non-contact profilometer. However, we also found that there is no difference on the electrical impedance of the QCM sensor coated with polystyrene resulted from differing solvent when the sensor was in contact with air and water. Thus, all of the mentioned solvent can be used to solve the polystyrene as a coating material for QCM sensor without affecting the electrical performance of the sensor, but the choice of the solution can be used as a simple method to control the difference roughness of the polystyrene coating.

Numerical analysis of the effect of surface roughness on mechanical fields in polycrystalline aggregates

NASA Astrophysics Data System (ADS)

Guilhem, Yoann; Basseville, Stéphanie; Curtit, François; Stéphan, Jean-Michel; Cailletaud, Georges

2018-06-01

This paper is dedicated to the study of the influence of surface roughness on local stress and strain fields in polycrystalline aggregates. Finite element computations are performed with a crystal plasticity model on a 316L stainless steel polycrystalline material element with different roughness states on its free surface. The subsequent analysis of the plastic strain localization patterns shows that surface roughness strongly affects the plastic strain localization induced by crystallography. Nevertheless, this effect mainly takes place at the surface and vanishes under the first layer of grains, which implies the existence of a critical perturbed depth. A statistical analysis based on the plastic strain distribution obtained for different roughness levels provides a simple rule to define the size of the affected zone depending on the rough surface parameters.

Hardness and surface roughness of enamel and base layers of resin denture teeth after long-term repeated chemical disinfection.

PubMed

Neppelenbroek, Karin Hermana; Kurokawa, Luciana Ayumi; Procópio, Andréa Lemos Falcão; Pegoraro, Thiago Amadei; Hotta, Juliana; Mello Lima, Jozely Francisca; Urban, Vanessa Migliorini

2015-01-01

To evaluate the effect of successive cycles of disinfection in different denture cleansers on the surface roughness and the Vickers hardness of two layers of acrylic resin (base-BL and enamel-EL) of two commercial cross-linked artificial teeth. The occlusal surfaces of 60 acrylic resin denture posterior teeth (Trilux-TLX and SR Orthosit PE-SRO) embedded in autopolymerizing acrylic resin were ground fat with 1200-grit silicon carbide paper. Specimens were stored in distilled water at 37°C and then submitted to the microhardness (VHN) and roughness (μm) tests. Specimens were stored in distilled water at 37°C for 90 days and submitted to 720 disinfection cycles in sodium hypochlorite at 0.5%, 30% vinegar solution or distilled water (control). Afterward, micro-hardness and roughness tests were again performed. Data were analyzed using two-way ANOVA and Tukey's test (α=0.05). Hypochlorite immersion decreased the hardness of BL and EL of SRO teeth, with an average reduction of 10.11% (p<0.008). TLX teeth demonstrated a hardness reduction of 28.96% of both layers for all solutions including water (p<0.0000). The roughness of both teeth was not affected by denture cleansers (p>0.37). Hypochlorite promoted deleterious effects on the hardness of both layers of the artificial teeth tested. Immersion in vinegar and water also resulted in reduction of hardness of TLX teeth. The surface hardness of the different layers of cross-linked artificial teeth can be altered by daily disinfection in denture cleansers commonly indicated for removable dentures.

Correlation of nosetip boundary-layer transition data measured in ballistics-range experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reda, D.C.

1980-01-01

Preablated nosetips of various carbonaceous materials were tested in a ballistics range. Surface-temperature contours, measured with image-converter cameras, were used to define boundary-layer transition-front contours. Measurements of surface roughness, surface temperature, average transition-front location, and freestream environment were combined with calculations of nosetip flowfields, and with calculations of laminar boundary-layer development in these flowfields, to transform all data into various dimensionless parameters. These parameters were defined by previous attempts to correlate existing wind-tunnel data for transition on rough/blunt bodies. Of the available correlating techniques, only one, based on the concept of a constant (critical) roughness Reynolds number for transition, wasmore » found to successfully describe both the wind-tunnel and ballistics-range data, thereby validating the extrapolation of this concept to actual reentry-vehicle materials and environments.« less

Modification of the large-scale features of high Reynolds number wall turbulence by passive surface obtrusions

NASA Astrophysics Data System (ADS)

Monty, J. P.; Allen, J. J.; Lien, K.; Chong, M. S.

2011-12-01

A high Reynolds number boundary-layer wind-tunnel facility at New Mexico State University was fitted with a regularly distributed braille surface. The surface was such that braille dots were closely packed in the streamwise direction and sparsely spaced in the spanwise direction. This novel surface had an unexpected influence on the flow: the energy of the very large-scale features of wall turbulence (approximately six-times the boundary-layer thickness in length) became significantly attenuated, even into the logarithmic region. To the author's knowledge, this is the first experimental study to report a modification of `superstructures' in a rough-wall turbulent boundary layer. The result gives rise to the possibility that flow control through very small, passive surface roughness may be possible at high Reynolds numbers, without the prohibitive drag penalty anticipated heretofore. Evidence was also found for the uninhibited existence of the near-wall cycle, well known to smooth-wall-turbulence researchers, in the spanwise space between roughness elements.

Optimum deposition conditions of ultrasmooth silver nanolayers

PubMed Central

2014-01-01

Reduction of surface plasmon-polariton losses due to their scattering on metal surface roughness still remains a challenge in the fabrication of plasmonic devices for nanooptics. To achieve smooth silver films, we study the dependence of surface roughness on the evaporation temperature in a physical vapor deposition process. At the deposition temperature range 90 to 500 K, the mismatch of thermal expansion coefficients of Ag, Ge wetting layer, and sapphire substrate does not deteriorate the metal surface. To avoid ice crystal formation on substrates, the working temperature of the whole physical vapor deposition process should exceed that of the sublimation at the evaporation pressure range. At optimum room temperature, the root-mean-square (RMS) surface roughness was successfully reduced to 0.2 nm for a 10-nm Ag layer on sapphire substrate with a 1-nm germanium wetting interlayer. Silver layers of 10- and 30-nm thickness were examined using an atomic force microscope (AFM), X-ray reflectometry (XRR), and two-dimensional X-ray diffraction (XRD2). PACS 63.22.Np Layered systems; 68. Surfaces and interfaces; thin films and nanosystems (structure and nonelectronic properties); 81.07.-b Nanoscale materials and structures: fabrication and characterization PMID:24685115

Surface roughness effects on turbulent Couette flow

NASA Astrophysics Data System (ADS)

Lee, Young Mo; Lee, Jae Hwa

2017-11-01

Direct numerical simulation of a turbulent Couette flow with two-dimensional (2-D) rod roughness is performed to examine the effects of the surface roughness. The Reynolds number based on the channel centerline laminar velocity (Uco) and channel half height (h) is Re =7200. The 2-D rods are periodically arranged with a streamwise pitch of λ = 8 k on the bottom wall, and the roughness height is k = 0.12 h. It is shown that the wall-normal extent for the logarithmic layer is significantly shortened in the rough-wall turbulent Couette flow, compared to a turbulent Couette flow with smooth wall. Although the Reynolds stresses are increased in a turbulent channel flow with surface roughness in the outer layer due to large-scale ejection motions produced by the 2-D rods, those of the rough-wall Couette flow are decreased. Isosurfaces of the u-structures averaged in time suggest that the decrease of the turbulent activity near the centerline is associated with weakened large-scale counter-rotating roll modes by the surface roughness. This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1A09000537) and the Ministry of Science, ICT & Future Planning (NRF-2017R1A5A1015311).

Carbon buffer layers for smoothing superpolished glass surfaces as substrates for molybdenum /silicon multilayer soft-x-ray mirrors.

PubMed

Stock, H J; Hamelmann, F; Kleineberg, U; Menke, D; Schmiedeskamp, B; Osterried, K; Heidemann, K F; Heinzmann, U

1997-03-01

Zerodur and BK7 glass substrates (developed by Fa. Glaswerke Schott, D-55014 Mainz, Germany) from Carl Zeiss Oberkochen polished to a standard surface roughness of varsigma = 0.8 nm rms were coated with a C layer by electron-beam evaporation in the UHV. The roughness of the C-layer surfaces is reduced to 0.6 nm rms. A normal-incidence reflectance of 50% at a wavelength of 13 nm was measured for a Mo/Si multilayer soft-x-ray mirror with 30 double layers (N = 30) deposited onto the BK7/C substrate, whereas a similar Mo/Si multilayer (N = 30) evaporated directly onto the bare BK7 surface turned out to show a reflectance of only 42%.

Burnishing rolling process of the surface prepared in the turning process

NASA Astrophysics Data System (ADS)

Kulakowska, Agnieszka; Kukielka, Leon; Kaldunski, Pawel; Bohdal, Lukasz; Patyk, Radoslaw; Chodor, Jaroslaw; Kukielka, Krzysztof

2018-05-01

The aim of this article is to demonstrate the possibility of using burnishing rolling process as the technology of product development. The experimental researches were carried out, showing the ability to form the surface layer of the product with the desired properties. First, during turning rolling the surfaces of the samples were prepared. Then, the surfaces were burnished. The influence of turning process on the state of the surface layer parameters of C45 steel shafts are shown. Among the examined aspects the surface roughness, nano-roughness, material bearing, surface microstructure, metallographic structure were considered. Numerical simulation were conducted. Conclusions from the experiments and simulation were given.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Pei-Yang; Zhang, Guojing; Gullickson, Eric M.

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 maskmore » 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.« less

Cleaning of optical surfaces by capacitively coupled RF discharge plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, P. K., E-mail: praveenyadav@rrcat.gov.in; Rai, S. K.; Nayak, M.

2014-04-24

In this paper, we report cleaning of carbon capped molybdenum (Mo) thin film by in-house developed radio frequency (RF) plasma reactor, at different powers and exposure time. Carbon capped Mo films were exposed to oxygen plasma for different durations at three different power settings, at a constant pressure. After each exposure, the thickness of the carbon layer and the roughness of the film were determined by hard x-ray reflectivity measurements. It was observed that most of the carbon film got removed in first 15 minutes exposure. A high density layer formed on top of the Mo film was also observedmore » and it was noted that this layer cannot be removed by successive exposures at different powers. A significant improvement in interface roughness with a slight improvement in top film roughness was observed. The surface roughness of the exposed and unexposed samples was also confirmed by atomic force microscopy measurements.« less

Staphylococcus epidermidis adhesion on surface-treated open-cell Ti6Al4V foams.

PubMed

Türkan, Uğur; Güden, Mustafa; Sudağıdan, Mert

2016-06-01

The effect of alkali and nitric acid surface treatments on the adhesion of Staphylococcus epidermidis to the surface of 60% porous open-cell Ti6Al4V foam was investigated. The resultant surface roughness of foam particles was determined from the ground flat surfaces of thin foam specimens. Alkali treatment formed a porous, rough Na2Ti5O11 surface layer on Ti6Al4V particles, while nitric acid treatment increased the number of undulations on foam flat and particle surfaces, leading to the development of finer surface topographical features. Both surface treatments increased the nanometric-scale surface roughness of particles and the number of bacteria adhering to the surface, while the adhesion was found to be significantly higher in alkali-treated foam sample. The significant increase in the number of bacterial attachment on the alkali-treated sample was attributed to the formation of a highly porous and nanorough Na2Ti5O11 surface layer.

Numerical investigation of roughness effects in aircraft icing calculations

NASA Astrophysics Data System (ADS)

Matheis, Brian Daniel

2008-10-01

Icing codes are playing a role of increasing significance in the design and certification of ice protected aircraft surfaces. However, in the interest of computational efficiency certain small scale physics of the icing problem are grossly approximated by the codes. One such small scale phenomena is the effect of ice roughness on the development of the surface water film and on the convective heat transfer. This study uses computational methods to study the potential effect of ice roughness on both of these small scale phenomena. First, a two-dimensional condensed layer code is used to examine the effect of roughness on surface water development. It is found that the Couette approximation within the film breaks down as the wall shear goes to zero, depending on the film thickness. Roughness elements with initial flow separation in the air induce flow separation in the water layer at steady state, causing a trapping of the film. The amount of trapping for different roughness configurations is examined. Second, a three-dimensional incompressible Navier-Stokes code is developed to examine large scale ice roughness on the leading edge. The effect on the convective heat transfer and potential effect on the surface water dynamics is examined for a number of distributed roughness parameters including Reynolds number, roughness height, streamwise extent, roughness spacing and roughness shape. In most cases the roughness field increases the net average convective heat transfer on the leading edge while narrowing surface shear lines, indicating a choking of the surface water flow. Both effects show significant variation on the scale of the ice roughness. Both the change in heat transfer as well as the potential change in surface water dynamics are presented in terms of the development of singularities in the surface shear pattern. Of particular interest is the effect of the smooth zone upstream of the roughness which shows both a relatively large increase in convective heat transfer as well as excessive choking of the surface shear lines at the upstream end of the roughness field. A summary of the heat transfer results is presented for both the averaged heat transfer as well as the maximum heat transfer over each roughness element, indicating that the roughness Reynolds number is the primary parameter which characterizes the behavior of the roughness for the problem of interest.

Cover-layer with High Refractive Index for Near-Field Recording Media

NASA Astrophysics Data System (ADS)

Kim, Jin-Hong; Lee, Jun-Seok

2007-06-01

TiO2 nanoparticles are added into UV-curable resin to increase the refractive index of the cover-layer laminated for cover-layer incident near-field recording media. A high refractive index is required for the cover-layer operating with an optical head with a high numerical aperture. The eye pattern from a cover-layer coated 20 GB read-only memory disc in which the refractive index of the cover-layer is 1.75 is achieved, but the gap servo is unstable owing to the rough surface of the cover-layer. Even though the light loss due to the nanoparticles is negligible, a rough microstructure is developed by adding the nanoparticles into an organic binder material. To achieve a smooth surface for a stable gap servo, the solubility of the nanoparticles should be enhanced by the optimization of the surface of the nanoparticles.

Cover-Layer with High Refractive Index for Near-Field Recording Media

NASA Astrophysics Data System (ADS)

Kim, Jin-Hong; Lee, Jun-Seok

2007-06-01

TiO2 nanoparticles are added into UV-curable resin to increase the refractive index of the cover-layer laminated for cover-layer incident near-field recording media. A high refractive index is required for the cover-layer operating with an optical head with a high numerical aperture. The eye pattern from a cover-layer coated 20 GB read-only memory disc in which the refractive index of the cover-layer is 1.75 is achieved, but the gap servo is unstable owing to the rough surface of the cover-layer. Even though the light loss due to the nanoparticles is negligible, a rough microstructure is developed by adding the nanoparticles into an organic binder material. To achieve a smooth surface for a stable gap servo, the solubility of the nanoparticles should be enhanced by the optimization of the surface of the nanoparticles.

Experiments on Hypersonic Roughness Induced Transition by Means of Infrared Thermography

NASA Astrophysics Data System (ADS)

Schrijer, F. F. J.; Scarano, F.; van Oudheusden, B. W.; Bannink, W. J.

2005-02-01

Roughness induced boundary layer transition is experimentally investigated in the hypersonic flow regime at M = 9. The primary interest is the possible effect of stepwise geometry imperfections (2D isolated roughness) on (boundary layer) transition which may be caused on the EXPERT vehicle by the difference in thermal expansion due to the different materials used in the vehicle-nose construction. Also 3D isolated and 3D distributed roughness configurations were studied. Quantitative Infra-Red Thermography (QIRT) is used as primary diagnostic technique to measure the surface convective heat transfer and to detect boundary layer laminar-to-turbulent transition. The investigation shows that for a given height of the roughness element, the boundary layer is least sensitive to a step-like disturbance, whereas distributed 3D roughness was found to be effective in triggering transition. The experimental results have been compared to existing hypersonic transition correlations (PANT and Shuttle). Finally a transition criterion is evaluated which is based on the critical roughness height Reynolds number. Usage of this criterion enables a straightforward extrapolation to flight. Key words: hypersonic flow, boundary layer transition.

Tin doped indium oxide anodes with artificially controlled nano-scale roughness using segregated Ag nanoparticles for organic solar cells

NASA Astrophysics Data System (ADS)

Kim, Hyo-Joong; Ko, Eun-Hye; Noh, Yong-Jin; Na, Seok-In; Kim, Han-Ki

2016-09-01

Nano-scale surface roughness in transparent ITO films was artificially formed by sputtering a mixed Ag and ITO layer and wet etching of segregated Ag nanoparticles from the surface of the ITO film. Effective removal of self-segregated Ag particles from the grain boundaries and surface of the crystalline ITO film led to a change in only the nano-scale surface morphology of ITO film without changes in the sheet resistance and optical transmittance. A nano-scale rough surface of the ITO film led to an increase in contact area between the hole transport layer and the ITO anode, and eventually increased the hole extraction efficiency in the organic solar cells (OSCs). The heterojunction OSCs fabricated on the ITO anode with a nano-scale surface roughness exhibited a higher power conversion efficiency of 3.320%, than that (2.938%) of OSCs made with the reference ITO/glass. The results here introduce a new method to improve the performance of OSCs by simply modifying the surface morphology of the ITO anodes.

Structural investigations of human hairs by spectrally resolved ellipsometry

NASA Astrophysics Data System (ADS)

Chan, Danny; Schulz, Benjamin; Rübhausen, Michael; Wessel, Sonya; Wepf, Roger

2006-01-01

Human hair is a biological layered system composed of two major layers, the cortex and the cuticle. We show spectrally resolved ellipsometry measurements of the ellipsometric parameters Ψ and Δ of single human hairs. The spectra reflect the layered nature of hair and the optical anisotropy of the hair's structure. In addition, measurements on strands of human hair show a high reproducibility of the ellipsometric parameters for different hair fiber bundles from the same person. Based on the measurements, we describe a dielectric model of hair that explains the spectra in terms of the dielectric properties of the major parts of hair and their associated layer thicknesses. In addition, surface roughness effects modeled by a roughness layer with a complex refractive index given by an effective medium approach can be seen to have a significant effect on the measurements. We derive values for the parameters of the cuticle surface roughness layer of the thickness dACu=273 to 360 nm and the air inclusion fA=0.6 to 5.7%.

Near-field flow structures about subcritical surface roughness

NASA Astrophysics Data System (ADS)

Doolittle, Charles J.; Drews, Scott D.; Goldstein, David B.

2014-12-01

Laminar flow over a periodic array of cylindrical surface roughness elements is simulated with an immersed boundary spectral method both to validate the method for subsequent studies and to examine how persistent streamwise vortices are introduced by a low Reynolds number roughness element. Direct comparisons are made with prior studies at a roughness-based Reynolds number Rek (=U(k) k/ν) of 205 and a diameter to spanwise spacing ratio d/λ of 1/3. Downstream velocity contours match present and past experiments very well. The shear layer developed over the top of the roughness element produces the downstream velocity deficit. Upstream of the roughness element, the vortex topology is found to be consistent with juncture flow experiments, creating three cores along the recirculation line. Streamtraces stemming from these upstream cores, however, have unexpectedly little effect on the downstream flowfield as lateral divergence of the boundary layer quickly dissipates their vorticity. Long physical relaxation time of the recirculating wake behind the roughness remains a prominent issue for simulating this type of flowfield.

Impact of humidity on functionality of on-paper printed electronics.

PubMed

Bollström, Roger; Pettersson, Fredrik; Dolietis, Peter; Preston, Janet; Osterbacka, Ronald; Toivakka, Martti

2014-03-07

A multilayer coated paper substrate, combining barrier and printability properties was manufactured utilizing a pilot-scale slide curtain coating technique. The coating structure consists of a thin mineral pigment layer coated on top of a barrier layer. The surface properties, i.e. smoothness and surface porosity, were adjusted by the choice of calendering parameters. The influence of surface properties on the fine line printability and conductivity of inkjet-printed silver lines was studied. Surface roughness played a significant role when printing narrow lines, increasing the risk of defects and discontinuities, whereas for wider lines the influence of surface roughness was less critical. A smooth, calendered surface resulted in finer line definition, i.e. less edge raggedness. Dimensional stability and its influence on substrate surface properties as well as on the functionality of conductive tracks and transistors were studied by exposure to high/low humidity cycles. The barrier layer of the multilayer coated paper reduced the dimensional changes and surface roughness increase caused by humidity and helped maintain the conductivity of the printed tracks. Functionality of a printed transistor during a short, one hour humidity cycle was maintained, but a longer exposure to humidity destroyed the non-encapsulated transistor.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, Ming-Hung; School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan; Haung, Chiung-Fang

In this study, neodymium-doped yttrium orthovanadate (Nd:YVO{sub 4}) as a laser source with different scanning speeds was used on biomedical Ti surface. The microstructural and biological properties of laser-modified samples were investigated by means of optical microscope, electron microscope, X-ray diffraction, surface roughness instrument, contact angle and cell cytotoxicity assay. After laser modification, the rough volcano-like recast layer with micro-/nanoporous structure and wave-like recast layer with nanoporous structure were generated on the surfaces of laser-modified samples, respectively. It was also found out that, an α → (α + rutile-TiO{sub 2}) phase transition occurred on the recast layers of laser-modified samples.more » The Ti surface becomes hydrophilic at a high speed laser scanning. Moreover, the cell cytotoxicity assay demonstrated that laser-modified samples did not influence the cell adhesion and proliferation behaviors of osteoblast (MG-63) cell. The laser with 50 mm/s scanning speed induced formation of rough volcano-like recast layer accompanied with micro-/nanoporous structure, which can promote cell adhesion and proliferation of MG-63 cell on Ti surface. The results indicated that the laser treatment was a potential technology to enhance the biocompatibility for titanium. - Highlights: • Laser induced the formation of recast layer with micro-/nanoporous structure on Ti. • An α → (α + rutile-TiO{sub 2}) phase transition was observed within the recast layer. • The Ti surface becomes hydrophilic at a high speed laser scanning. • Laser-modified samples exhibit good biocompatibility to osteoblast (MG-63) cell.« less

A dynamic subgrid-scale parameterization of the effective wall stress in atmospheric boundary layer flows over multiscale, fractal-like surfaces

NASA Astrophysics Data System (ADS)

Anderson, William; Meneveau, Charles

2010-05-01

A dynamic subgrid-scale (SGS) parameterization for hydrodynamic surface roughness is developed for large-eddy simulation (LES) of atmospheric boundary layer (ABL) flow over multiscale, fractal-like surfaces. The model consists of two parts. First, a baseline model represents surface roughness at horizontal length-scales that can be resolved in the LES. This model takes the form of a force using a prescribed drag coefficient. This approach is tested in LES of flow over cubes, wavy surfaces, and ellipsoidal roughness elements for which there are detailed experimental data available. Secondly, a dynamic roughness model is built, accounting for SGS surface details of finer resolution than the LES grid width. The SGS boundary condition is based on the logarithmic law of the wall, where the unresolved roughness of the surface is modeled as the product of local root-mean-square (RMS) of the unresolved surface height and an unknown dimensionless model coefficient. This coefficient is evaluated dynamically by comparing the plane-average hydrodynamic drag at two resolutions (grid- and test-filter scale, Germano et al., 1991). The new model is tested on surfaces generated through superposition of random-phase Fourier modes with prescribed, power-law surface-height spectra. The results show that the method yields convergent results and correct trends. Limitations and further challenges are highlighted. Supported by the US National Science Foundation (EAR-0609690).

On the performance of surface renewal analysis to estimate sensible heat flux over two growing rice fields under the influence of regional advection

NASA Astrophysics Data System (ADS)

Castellví, F.; Snyder, R. L.

2009-09-01

SummaryHigh-frequency temperature data were recorded at one height and they were used in Surface Renewal (SR) analysis to estimate sensible heat flux during the full growing season of two rice fields located north-northeast of Colusa, CA (in the Sacramento Valley). One of the fields was seeded into a flooded paddy and the other was drill seeded before flooding. To minimize fetch requirements, the measurement height was selected to be close to the maximum expected canopy height. The roughness sub-layer depth was estimated to discriminate if the temperature data came from the inertial or roughness sub-layer. The equation to estimate the roughness sub-layer depth was derived by combining simple mixing-length theory, mixing-layer analogy, equations to account for stable atmospheric surface layer conditions, and semi-empirical canopy-architecture relationships. The potential for SR analysis as a method that operates in the full surface boundary layer was tested using data collected over growing vegetation at a site influenced by regional advection of sensible heat flux. The inputs used to estimate the sensible heat fluxes included air temperature sampled at 10 Hz, the mean and variance of the horizontal wind speed, the canopy height, and the plant area index for a given intermediate height of the canopy. Regardless of the stability conditions and measurement height above the canopy, sensible heat flux estimates using SR analysis gave results that were similar to those measured with the eddy covariance method. Under unstable cases, it was shown that the performance was sensitive to estimation of the roughness sub-layer depth. However, an expression was provided to select the crucial scale required for its estimation.

Boundary layer simulator improvement

NASA Technical Reports Server (NTRS)

Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

1989-01-01

Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

Characterizing the Effects of Convection on the Afternoon to Evening Boundary Layer Transition During Pecan 2015

DTIC Science & Technology

2016-12-01

roughness that is an input variable. For the FP2 site in Kansas, we searched for the climatological surface roughness height used in the Navy’s...COAMPS model for the latitude and longitude of FP2 and in the month of June/July. The climatological roughness height was found to be 0.25m. This is the...mean surface roughness for an area of 1 km on the side near FP2 as the climatological data has a horizontal grid resolution of 1 km. This roughness

Spatial characteristics of secondary flow in a turbulent boundary layer over longitudinal surface roughness

NASA Astrophysics Data System (ADS)

Hwang, Hyeon Gyu; Lee, Jae Hwa

2017-11-01

Direct numerical simulations of turbulent boundary layers (TBLs) over spanwise heterogeneous surface roughness are performed to investigate the characteristics of secondary flow. The longitudinal surface roughness, which features lateral change in bed elevation, is described by immersed boundary method. The Reynolds number based on the momentum thickness is varied in the range of Reθ = 300-900. As the TBLs over the roughness elements spatially develop in the streamwise direction, a secondary flow emerges in a form of counter-rotating vortex pair. As the spanwise spacing between the roughness elements and roughness width vary, it is shown that the size of the secondary flow is determined by the valley width between the roughness elements. In addition, the strength of the secondary flow is mostly affected by the spanwise distance between the cores of the secondary flow. Analysis of the Reynolds-averaged turbulent kinetic energy transport equation reveals that the energy redistribution terms in the TBLs over-the ridge type roughness play an important role to derive low-momentum pathways with upward motion over the roughness crest, contrary to the previous observation with the strip-type roughness. This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1A09000537) and the Ministry of Science, ICT & Future Planning (NRF-2017R1A5A1015311).

Effect of strain on the electron effective mobility in biaxially strained silicon inversion layers: An experimental and theoretical analysis via atomic force microscopy measurements and Kubo-Greenwood mobility calculations

NASA Astrophysics Data System (ADS)

Bonno, Olivier; Barraud, Sylvain; Mariolle, Denis; Andrieu, François

2008-03-01

Recently, in order to explain the long-channel electron effective mobility at a high sheet carrier density in strained silicon channel transistors, it has been suggested by [M. V. Fischetti, F. Gamiz, and W. Hansch, J. Appl. Phys. 92, 7230 (2002)] that biaxial tensile strain should smooth the Si/SiO2 interface. To address this topic, the roughness properties of biaxial strained silicon-on-insulator (s-SOI) films are investigated by means of atomic force microscopy. Through in-depth statistical analysis of the digitalized surface profiles, the roughness parameters are extracted for unstrained and strained SOI films, with 0.8% biaxial tensile strain. Especially, it is found that strain significantly reduces the roughness amplitude. Then, mobility calculations in SOI and s-SOI inversion layers are performed in the framework of the Kubo-Greenwood formalism. The model accounts for the main scattering mechanisms that are dominant in the high electron density range, namely phonon and surface roughness. Special attention has been paid to the modeling of the latter by accounting for all the contributions of the potential which arise from the deformed rough interface, and by using a multisubband wavelength-dependent screening model. This model is then applied to study the influence of the surface morphology on the mobility in s-SOI inversion layers. In this context, the mobility gain between s-SOI and unstrained SOI layers is found to agree significantly better with experimental data if the strain-induced decrease of the roughness amplitude is taken into account.

Applying Geospatial Techniques to Investigate Boundary Layer Land-Atmosphere Interactions Involved in Tornadogensis

NASA Astrophysics Data System (ADS)

Weigel, A. M.; Griffin, R.; Knupp, K. R.; Molthan, A.; Coleman, T.

2017-12-01

Northern Alabama is among the most tornado-prone regions in the United States. This region has a higher degree of spatial variability in both terrain and land cover than the more frequently studied North American Great Plains region due to its proximity to the southern Appalachian Mountains and Cumberland Plateau. More research is needed to understand North Alabama's high tornado frequency and how land surface heterogeneity influences tornadogenesis in the boundary layer. Several modeling and simulation studies stretching back to the 1970's have found that variations in the land surface induce tornadic-like flow near the surface, illustrating a need for further investigation. This presentation introduces research investigating the hypothesis that horizontal gradients in land surface roughness, normal to the direction of flow in the boundary layer, induce vertically oriented vorticity at the surface that can potentially aid in tornadogenesis. A novel approach was implemented to test this hypothesis using a GIS-based quadrant pattern analysis method. This method was developed to quantify spatial relationships and patterns between horizontal variations in land surface roughness and locations of tornadogenesis. Land surface roughness was modeled using the Noah land surface model parameterization scheme which, was applied to MODIS 500 m and Landsat 30 m data in order to compare the relationship between tornadogenesis locations and roughness gradients at different spatial scales. This analysis found a statistical relationship between areas of higher roughness located normal to flow surrounding tornadogenesis locations that supports the tested hypothesis. In this presentation, the innovative use of satellite remote sensing data and GIS technologies to address interactions between the land and atmosphere will be highlighted.

Numerical simulation of adverse-pressure-gradient boundary layer with or without roughness

NASA Astrophysics Data System (ADS)

Mottaghian, Pouya; Yuan, Junlin; Piomelli, Ugo

2014-11-01

Large-eddy and direct numerical simulations are carried out on flat-plate boundary layer over smooth and rough surfaces, with adverse pressure gradient.The deceleration is achieved by imposing a wall-normal freestream velocity profile, and is strong enough to cause separation at the wall. The Reynolds number based on momentum thickness and freestream velocity at inlet is 600. Numerical sandgrain roughness is applied based on an immersed boundary method, yielding a flow that is transitionally rough. The turbulence intensity increases before separation, and reaches a higher value for the rough case, indicating stronger mixing. Roughness also causes higher momentum deficit near the wall, leading to earlier separation. This is consistent with previous observation made on rough-wall flow separation over a ramp. In both cases, the turbulent kinetic energy peaks inside the shear layer above the detachment region, with higher values in the rough case; it then decreases approaching the reattachment region. Near the wall inside the separation bubble, the near-zero turbulent intensity indicates that the turbulent structures are lifted up in the separation region. Compared with the smooth case, the shear layer is farther from the wall and the reattachment length is longer on the rough wall.

Surface nanoporosity has a greater influence on osteogenic and bacterial cell adhesion than crystallinity and wettability

NASA Astrophysics Data System (ADS)

Rodriguez-Contreras, Alejandra; Guadarrama Bello, Dainelys; Nanci, Antonio

2018-07-01

There has been much emphasis on the influence of crystallinity and wettability for modulating cell activity, particularly for bone biomaterials. In this context, we have generated titanium oxide layers with similar mesoporous topography and surface roughness but with amorphous or crystalline oxide layers and differential wettability. We then investigated their influence on the behavior of MC3T3 osteoblastic and bacterial cells. There was no difference in cell adhesion, spreading and growth on amorphous and crystalline surfaces. The number of focal adhesions was similar, however, cells on the amorphous surface exhibited a higher frequency of mature adhesions. The crystallinity of the surface layers also had no bearing on bacterial adhesion. While it cannot be excluded that surface crystallinity, roughness and wettability contribute to some degree to determining cell behavior, our data suggest that physical characteristics of surfaces represent the major determinant.

Effect of Multi-Pass Ultrasonic Surface Rolling on the Mechanical and Fatigue Properties of HIP Ti-6Al-4V Alloy

PubMed Central

Li, Gang; Qu, Shengguan; Xie, Mingxin; Ren, Zhaojun; Li, Xiaoqiang

2017-01-01

The main purpose of this paper was to investigate the effect of a surface plastic deformation layer introduced by multi-pass ultrasonic surface rolling (MUSR) on the mechanical and fatigue properties of HIP Ti-6Al-4V alloys. Some microscopic analysis methods (SEM, TEM and XRD) were used to characterize the modified microstructure in the material surface layer. The results indicated that the material surface layer experienced a certain extent plastic deformation, accompanied by some dense dislocations and twin generation. Moreover, surface microhardness, residual stress and roughness values of samples treated by MUSR were also greatly improved compared with that of untreated samples. Surface microhardness and compressive residual stress were increased to 435 HV and −1173 MPa, respectively. The minimum surface roughness was reduced to 0.13 μm. The maximum depth of the surface hardening layer was about 55 μm. However, the practical influence depth was about 450 μm judging from the tensile and fatigue fracture surfaces. The ultimate tensile strength of the MUSR-treated sample increased to 990 MPa from the initial 963 MPa. The fatigue strength of the MUSR-treated sample was increased by about 25% on the base of 107 cycles, and the lifetime was prolonged from two times to two orders of magnitude at the applied stress amplitudes of 650–560 MPa. The improved mechanical and fatigue properties of MUSR-treated samples should be attributed to the combined effects of the increased microhardness and compressive residual stress, low surface roughness, grain refinement and micro-pore healing in the material surface-modified layer. PMID:28772494

New horizons in selective laser sintering surface roughness characterization

NASA Astrophysics Data System (ADS)

Vetterli, M.; Schmid, M.; Knapp, W.; Wegener, K.

2017-12-01

Powder-based additive manufacturing of polymers and metals has evolved from a prototyping technology to an industrial process for the fabrication of small to medium series of complex geometry parts. Unfortunately due to the processing of powder as a basis material and the successive addition of layers to produce components, a significant surface roughness inherent to the process has been observed since the first use of such technologies. A novel characterization method based on an elastomeric pad coated with a reflective layer, the Gelsight, was found to be reliable and fast to characterize surfaces processed by selective laser sintering (SLS) of polymers. With help of this method, a qualitative and quantitative investigation of SLS surfaces is feasible. Repeatability and reproducibility investigations are performed for both 2D and 3D areal roughness parameters. Based on the good results, the Gelsight is used for the optimization of vertical SLS surfaces. A model built on laser scanning parameters is proposed and after confirmation could achieve a roughness reduction of 10% based on the S q parameter. The Gelsight could be successfully identified as a fast, reliable and versatile surface topography characterization method as it applies to all kind of surfaces.

Rough-to-smooth transition of an equilibrium neutral constant stress layer

NASA Technical Reports Server (NTRS)

Logan, E., Jr.; Fichtl, G. H.

1975-01-01

Purpose of research on rough-to-smooth transition of an equilibrium neutral constant stress layer is to develop a model for low-level atmospheric flow over terrains of abruptly changing roughness, such as those occurring near the windward end of a landing strip, and to use the model to derive functions which define the extent of the region affected by the roughness change and allow adequate prediction of wind and shear stress profiles at all points within the region. A model consisting of two bounding logarithmic layers and an intermediate velocity defect layer is assumed, and dimensionless velocity and stress distribution functions which meet all boundary and matching conditions are hypothesized. The functions are used in an asymptotic form of the equation of motion to derive a relation which governs the growth of the internal boundary layer. The growth relation is used to predict variation of surface shear stress.

Grinding and its influence to ground surface durability

NASA Astrophysics Data System (ADS)

Holesovsky, F.; Novak, M.

2011-01-01

A number of parameters of running process effect on the formed surface at grinding. Above all, the following influences can be mentioned: grinding wheel speed, workpiece speed, tool properties, rigidity of machine tool, etc. The plastic deformation and thermal load of surface layer are evoked at the action of cutting conditions. A new surface keeps the definite properties, which are given by its roughness, surface profile, geometry accuracy, intensity and residual stress distribution, respectively microhardness course in surface layer and changes of microstructure in this layer. The surface properties predict the surface behaviour in the real machinery at the dynamical, respectively static loading. At the load, the changes of surface properties proceed, e.g. roughness, residual stress. Simultaneously, changes of surface properties influence the durability of machine part and can also lead to surface damage and machine part breakdown. The slackness can also evoke the cracks, which leads to the fracture. The behaviour of part differs in the operating environment without and with oil or in the corrosion environment.

Structural investigations of human hairs by spectrally resolved ellipsometry

NASA Astrophysics Data System (ADS)

Schulz, Benjamin; Chan, D.; Ruebhausen, M.; Wessel, S.; Wepf, R.

2006-03-01

Human hair is a biological layered system composed of two major layers, the cortex and the cuticle. We show spectrally resolved ellipsometry measurements of the ellipsometric parameters ψ and δ of single human hairs. The spectra reflect the layered nature of hair and the optical anisotropy of the hair’s structure. In addition, measurements on strands of human hair show a high reproducibility of the ellipsometric parameters for different hair fiber bundles from the same person. Based on the measurements, we develop a model of the dielectric function of hair that explains the spectra. This model includes the dielectric properties of the cuticle and cortex as well as their associated layer thicknesses. In addition, surface roughness effects modelled by a roughness layer with an complex refractive index given by an effective medium approach can have a significant effect on the measurements. We derive values for the parameters of the cuticle surface roughness layer of the thickness dACu= 273-360 nm and the air inclusion fA= 0.6 -5.7%. [1] accepted for publication in J. Biomed Opt., 2005

Light interaction in sapphire/MgF2/Al triple-layer omnidirectional reflectors in AlGaN-based near ultraviolet light-emitting diodes

PubMed Central

Lee, Keon Hwa; Moon, Yong-Tae; Song, June-O; Kwak, Joon Seop

2015-01-01

This study examined systematically the mechanism of light interaction in the sapphire/MgF2/Al triple-layer omnidirectional reflectors (ODR) and its effects on the light output power in near ultraviolet light emitting diodes (NUV-LEDs) with the ODR. The light output power of NUV-LEDs with the triple-layer ODR structure increased with decreasing surface roughness of the sapphire backside in the ODR. Theoretical modeling of the roughened surface suggests that the dependence of the reflectance of the triple-layer ODR structure on the surface roughness can be attributed mainly to light absorption by the Al nano-structures and the trapping of scattered light in the MgF2 layer. Furthermore, the ray tracing simulation based upon the theoretical modeling showed good agreement with the measured reflectance of the ODR structure in diffuse mode. PMID:26010378

Light interaction in sapphire/MgF2/Al triple-layer omnidirectional reflectors in AlGaN-based near ultraviolet light-emitting diodes.

PubMed

Lee, Keon Hwa; Moon, Yong-Tae; Song, June-O; Kwak, Joon Seop

2015-05-26

This study examined systematically the mechanism of light interaction in the sapphire/MgF2/Al triple-layer omnidirectional reflectors (ODR) and its effects on the light output power in near ultraviolet light emitting diodes (NUV-LEDs) with the ODR. The light output power of NUV-LEDs with the triple-layer ODR structure increased with decreasing surface roughness of the sapphire backside in the ODR. Theoretical modeling of the roughened surface suggests that the dependence of the reflectance of the triple-layer ODR structure on the surface roughness can be attributed mainly to light absorption by the Al nano-structures and the trapping of scattered light in the MgF2 layer. Furthermore, the ray tracing simulation based upon the theoretical modeling showed good agreement with the measured reflectance of the ODR structure in diffuse mode.

Influence of Under-layer Morphology on Structural and Magnetic Properties of Sputtered Co81Pd19 Films

NASA Astrophysics Data System (ADS)

Ponchaiya, Pairin; Rattanasakulthong, Watcharee

2017-09-01

Sputtered Co81Pd19 films with thickness of about 60 nm were deposited on various under-layers (Co, Ni, Cr and Al) and on glass substrate. Structural, morphological and magnetic properties of Co81Pd19 films were investigated. All of prepared Co81Pd19 film showed CoPd-FCC phase in (111) direction on CoO-FCC (111), NiO-FCC (200), Cr-BCC (200) and (201) and AlO-FCC (200) phases of Co, Ni, Cr and Al under-layer, respectively. AFM images revealed that the film on Cr under-layers and glass substrate exhibited the maximum roughness with the highest grain size and the minimum roughness with the continuous grain size, respectively. Both parallel and perpendicular maximum coercive field were found in the film on glass under-layer and the film on Co-under-layer film showed the highest saturation magnetization from both in-plane and out-of-plane measurements. These results confirmed that the structural and magnetic properties of sputtered Co81Pd19 films were affected by under-layer surface roughness and morphology by the virtue of particle size and distribution on the under-layer film surface.

Refurbishing of carbon contaminated pre-mirror of reflectivity beam line at Indus-1

NASA Astrophysics Data System (ADS)

Yadav, P. K.; Kumar, M.; Gupta, R. K.; Sinha, M.; Patel, H. S.; Modi, M. H.

2018-04-01

In recent days optics contamination and its refurbishing is a serious issue for synchrotron radiation beam line community. Here we refurbished a carbon contaminated mirror by Ar and O2 gas mixed (1:1) radio frequency plasma. For structural analysis pre and post characterization of the mirror was done by Soft X-ray reflectivity (SXRR), Raman Spectroscopy (RS) and Atomic force microscopy (AFM). Before refurbishing mirror, a low density graphitic carbon layer of thickness 400 Å with surface roughness about 55 Å and Au surface roughness 14Å was estimated by SXRR. After one hour RF plasma exposure it is observed by SXRR and Raman spectroscopy that carbon layer is completely removed. The AFM and SXRR results show that roughness of Au surface not increase after plasma exposure.

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.

Au-nanoparticles grafted on plasma treated PE

NASA Astrophysics Data System (ADS)

Švorčík, V.; Chaloupka, A.; Řezanka, P.; Slepička, P.; Kolská, Z.; Kasálková, N.; Hubáček, T.; Siegel, J.

2010-03-01

Polyethylene (PE) surface was treated with Ar plasma. Activated surface was grafted from methanol solution of 1,2-ethanedithiol. Then the sample was immersed into freshly prepared colloid solution of Au-nanoparticles. Finally Au layer was sputtered on the samples. Properties of the modified PE were studied using various methods: AFM, EPR, RBS and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain (AFM) and creation of free radicals by EPR. After grafting with dithiol, the concentration of free radicals declines. The presence of Au and S in the surface layer after the coating with Au-nanoparticles was proved by RBS. Plasma treatment changes PE surface morphology and increases surface roughness, too. Another significant change in surface morphology and roughness was observed after deposition of Au-nanoparticles. Nanoindentation measurements show that the grafting with Au-nanoparticles increases adhesion of subsequently sputtered Au layer.

Effects of surface roughness on an adverse-pressure-gradient separating turbulent boundary layer

NASA Astrophysics Data System (ADS)

Wu, Wen; Piomelli, Ugo; Turbulence Simulation; Modelling Laboratory Team

2017-11-01

Separating turbulent boundary layers over smooth and rough flat plates are investigated by large-eddy simulations. A suction-blowing velocity distribution is imposed at the top boundary to produce an adverse-to-favourable pressure gradient and a closed separation bubble. Sandgrain roughness in the fully-rough regime is modelled by an immersed boundary method. In the rough-wall case, streamline detachment occurs earlier and the separation region is substantially larger due to the momentum deficit caused by the roughness. The adverse pressure gradient decreases the form drag and causes a thin reversed-flow region below the roughness crest, so that Cf = 0 does not coincide with the detachment of the flow from the surface. The wake regions behind roughness elements affect the intermittency of the near-wall flow, so that upstream of the detachment point the flow can be reversed half of the time, but its average is positive. The separated shear layer exhibits higher turbulent kinetic energy (TKE); the growth of the TKE there begins earlier relative to the separation point, and the peak TKE occurs close to the separation point. The momentum deficit caused by the roughness, again, plays a critical role in these changes. The authors acknowledge the support from Hydro-Québec and the NSERC Collaborative Research & Development program (CRDPJ 418786-11). The simulations were performed at CAC Queen't site. UP also thanks the support of Canada Research Chair Program.

Characterization on White Etching Layer Formed During Ceramic Milling of Inconel 718

NASA Astrophysics Data System (ADS)

Kruk, A.; Wusatowska-Sarnek, A. M.; Ziętara, M.; Jemielniak, K.; Siemiątkowski, Z.; Czyrska-Filemonowicz, A.

2018-03-01

A comprehensive characterization of the near surface formed during the interrupted high-speed dry ceramic milling of IN718 was performed using light imaging, SEM/EDX, TEM and nano-hardness methods. It was found out that even an initial cut by a fresh tool creates a sub-surface alteration roughly 20 µm deep. The depth of altered sub-surface progressively changed to a roughly 40 µm when the tool reached an approximately half of its life, and almost 60 µm at the tool's end of the life. In the last two cases, the visible WEL (utilizing a light microscope) of the thickness roughly 6 and 15 µm was created, respectively. The outermost layer of the deformed subsurface was found to be for all three cases approximately 1.5 µm thick and composed of dynamically recrystallized γ phase grains with the average diameter of approximately 150 nm. This layer was free of δ phase and γ' or γ″ precipitates. It was followed by a plastically deformed zone.

Distributed-Roughness Effects on Stability and Transition In Swept-Wing Boundary Layers

NASA Technical Reports Server (NTRS)

Carrillo, Ruben B., Jr.; Reibert, Mark S.; Saric, William S.

1997-01-01

Boundary-layer stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg swept airfoil. The pressure distribution and test conditions are designed to suppress Tollmien-Schlichting disturbances and provide crossflow-dominated transition. The surface of the airfoil is finely polished to a near mirror finish. Under these conditions, submicron surface irregularities cause the naturally occurring stationary crossflow waves to grow to nonuniform amplitudes. Spanwise-uniform stationary crossflow disturbances are generated through careful control of the initial conditions with full-span arrays of micron-high roughness elements near the attachment line. Detailed hot-wire measurements are taken to document the stationary crossflow structure and determine growth rates for the total and individual-mode disturbances. Naphthalene flow visualization provides transition location information. Roughness spacing and roughness height are varied to examine the effects on transition location and all amplified wavelengths. The measurements show that roughness spacings that do not contain harmonics equal to the most unstable wavelength as computed by linear stability theory effectively suppress the most unstable mode. Under certain conditions, subcritical roughness spacing delays transition past that of the corresponding smooth surface.

SiGe derivatization by spontaneous reduction of aryl diazonium salts

NASA Astrophysics Data System (ADS)

Girard, A.; Geneste, F.; Coulon, N.; Cardinaud, C.; Mohammed-Brahim, T.

2013-10-01

Germanium semiconductors have interesting properties for FET-based biosensor applications since they possess high surface roughness allowing the immobilization of a high amount of receptors on a small surface area. Since SiGe combined low cost of Si and intrinsic properties of Ge with high mobility carriers, we focused the study on this particularly interesting material. The comparison of the efficiency of a functionalization process involving the spontaneous reduction of diazonium salts is studied on Si(1 0 0), SiGe and Ge semiconductors. XPS analysis of the functionalized surfaces reveals the presence of a covalent grafted layer on all the substrates that was confirmed by AFM. Interestingly, the modified Ge derivatives have still higher surface roughness after derivatization. To support the estimated thickness by XPS, a step measurement of the organic layers is done by AFM or by profilometer technique after a O2 plasma etching of the functionalized layer. This original method is well-adapted to measure the thickness of thin organic films on rough substrates such as germanium. The analyses show a higher chemical grafting on SiGe substrates compared with Si and Ge semiconductors.

Acoustic Receptivity of a Blasius Boundary Layer with 2-D and Oblique Surface Waviness

NASA Technical Reports Server (NTRS)

King, Rudolph A.; Breuer, Kenneth S.

2000-01-01

An experimental investigation was conducted to examine acoustic receptivity and subsequent boundary-layer instability evolution for a Blasius boundary layer formed on a flat plate in the presence of two-dimensional (2-D) and oblique (3-D) surface waviness. The effect of the non-localized surface roughness geometry and acoustic wave amplitude on the receptivity process was explored. The surface roughness had a well defined wavenumber spectrum with fundamental wavenumber k (sub w). A planar downstream traveling acoustic wave was created to temporally excite the flow near the resonance frequency of an unstable eigenmode corresponding to k (sub ts) = k (sub w). The range of acoustic forcing levels, epsilon, and roughness heights, DELTA h, examined resulted in a linear dependence of receptivity coefficients; however, the larger values of the forcing combination epsilon dot DELTA h resulted in subsequent nonlinear development of the Tollmien-Schlichting (T-S) wave. This study provided the first experimental evidence of a marked increase in the receptivity coefficient with increasing obliqueness of the surface waviness in excellent agreement with theory. Detuning of the 2-D and oblique disturbances was investigated by varying the streamwise wall-roughness wavenumber a,, and measuring the T-S response. For the configuration where laminar-to-turbulent breakdown occurred, the breakdown process was found to be dominated by energy at the fundamental and harmonic frequencies, indicative of K-type breakdown.

Characteristics of the Martian atmosphere surface layer

NASA Technical Reports Server (NTRS)

Clow, G. D.; Haberle, R. M.

1990-01-01

Elements of various terrestrial boundary layer models are extended to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian atmospheric surface ('constant flux') layer. The atmospheric surface layer consists of an interfacial sublayer immediately adjacent to the ground and an overlying fully turbulent surface sublayer where wind-shear production of turbulence dominates buoyancy production. Within the interfacial sublayer, sensible and latent heat are transported by non-steady molecular diffusion into small-scale eddies which intermittently burst through this zone. Both the thickness of the interfacial sublayer and the characteristics of the turbulent eddies penetrating through it depend on whether airflow is aerodynamically smooth or aerodynamically rough, as determined by the Roughness Reynold's number. Within the overlying surface sublayer, similarity theory can be used to express the mean vertical windspeed, temperature, and water vapor profiles in terms of a single parameter, the Monin-Obukhov stability parameter. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed using data from the TPRC Data Series and the first-order Chapman-Cowling expressions; the required collision integrals were approximated using the Lenard-Jones potential. Parameterizations for specific heat and binary diffusivity were also determined. The Brutsart model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the definition of the Monin-Obukhov length was modified to properly account for the buoyancy forces arising from water vapor gradients in the Martian atmospheric boundary layer. It was found that under most Martian conditions, the interfacial and surface sublayers offer roughly comparable resistance to sensible heat and water vapor transport and are thus both important in determining the associated fluxes.

X-33 Hypersonic Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J.; Hollis, Brian R.; Thompson, Richard A.; Hamilton, H. Harris, II

1999-01-01

Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.

The Role of Law-of-the-Wall and Roughness Scale in the Surface Stress Model for LES of the Rough-wall Boundary Layer

NASA Astrophysics Data System (ADS)

Brasseur, James; Paes, Paulo; Chamecki, Marcelo

2017-11-01

Large-eddy simulation (LES) of the high Reynolds number rough-wall boundary layer requires both a subfilter-scale model for the unresolved inertial term and a ``surface stress model'' (SSM) for space-time local surface momentum flux. Standard SSMs assume proportionality between the local surface shear stress vector and the local resolved-scale velocity vector at the first grid level. Because the proportionality coefficient incorporates a surface roughness scale z0 within a functional form taken from law-of-the-wall (LOTW), it is commonly stated that LOTW is ``assumed,'' and therefore ``forced'' on the LES. We show that this is not the case; the LOTW form is the ``drag law'' used to relate friction velocity to mean resolved velocity at the first grid level consistent with z0 as the height where mean velocity vanishes. Whereas standard SSMs do not force LOTW on the prediction, we show that parameterized roughness does not match ``true'' z0 when LOTW is not predicted, or does not exist. By extrapolating mean velocity, we show a serious mismatch between true z0 and parameterized z0 in the presence of a spurious ``overshoot'' in normalized mean velocity gradient. We shall discuss the source of the problem and its potential resolution.

Liquid-Infused Smooth Surface for Improved Condensation Heat Transfer.

PubMed

Tsuchiya, Hirotaka; Tenjimbayashi, Mizuki; Moriya, Takeo; Yoshikawa, Ryohei; Sasaki, Kaichi; Togasawa, Ryo; Yamazaki, Taku; Manabe, Kengo; Shiratori, Seimei

2017-09-12

Control of vapor condensation properties is a promising approach to manage a crucial part of energy infrastructure conditions. Heat transfer by vapor condensation on superhydrophobic coatings has garnered attention, because dropwise condensation on superhydrophobic surfaces with rough structures leads to favorable heat-transfer performance. However, pinned condensed water droplets within the rough structure and a high thermodynamic energy barrier for nucleation of superhydrophobic surfaces limit their heat-transfer increase. Recently, slippery liquid-infused surfaces (SLIPS) have been investigated, because of their high water sliding ability and surface smoothness originating from the liquid layer. However, even on SLIPS, condensed water droplets are eventually pinned to degrade their heat-transfer properties after extended use, because the rough base layer is exposed as infused liquid is lost. Herein, we report a liquid-infused smooth surface named "SPLASH" (surface with π electron interaction liquid adsorption, smoothness, and hydrophobicity) to overcome the problems derived from the rough structures in previous approaches to obtain stable, high heat-transfer performance. The SPLASH displayed a maximum condensation heat-transfer coefficient that was 175% higher than that of an uncoated substrate. The SPLASH also showed higher heat-transfer performance and more stable dropwise condensation than superhydrophobic surfaces and SLIPS from the viewpoints of condensed water droplet mobility and the thermodynamic energy barrier for nucleation. The effects of liquid-infused surface roughness and liquid viscosity on condensation heat transfer were investigated to compare heat-transfer performance. This research will aid industrial applications using vapor condensation.

Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

DOE PAGES

Flippo, K. A.; Doss, F. W.; Kline, J. L.; ...

2016-11-23

While using a large volume high-energy-density fluid shear experiment ( 8.5 cm 3 ) at the National Ignition Facility, we have demonstrated for the first time the ability to significantly alter the evolution of a supersonic sheared mixing layer by controlling the initial conditions of that layer. Furthermore, by altering the initial surface roughness of the tracer foil, we demonstrate the ability to transition the shear mixing layer from a highly ordered system of coherent structures to a randomly ordered system with a faster growing mix layer, indicative of strong mixing in the layer at a temperature of severalmore » tens of electron volts and at near solid density. Moreover, simulations using a turbulent-mix model show good agreement with the experimental results and poor agreement without turbulent mix.« less

Studying Pulsed Laser Deposition conditions for Ni/C-based multi-layers

NASA Astrophysics Data System (ADS)

Bollmann, Tjeerd R. J.

2018-04-01

Nickel carbon based multi-layers are a viable route towards future hard X-ray and soft γ-ray focusing telescopes. Here, we study the Pulsed Laser Deposition growth conditions of such bilayers by Reflective High Energy Electron Diffraction, X-ray Reflectivity and Diffraction, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and cross-sectional Transmission Electron Microscopy analysis, with emphasis on optimization of process pressure and substrate temperature during growth. The thin multi-layers are grown on a treated SiO substrate resulting in Ni and C layers with surface roughnesses (RMS) of ≤0.2 nm. Small droplets resulting during melting of the targets surface increase the roughness, however, and cannot be avoided. The sequential process at temperatures beyond 300 °C results into intermixing between the two layers, being destructive for the reflectivity of the multi-layer.

Pollutant Plume Dispersion in the Atmospheric Boundary Layer over Idealized Urban Roughness

NASA Astrophysics Data System (ADS)

Wong, Colman C. C.; Liu, Chun-Ho

2013-05-01

The Gaussian model of plume dispersion is commonly used for pollutant concentration estimates. However, its major parameters, dispersion coefficients, barely account for terrain configuration and surface roughness. Large-scale roughness elements (e.g. buildings in urban areas) can substantially modify the ground features together with the pollutant transport in the atmospheric boundary layer over urban roughness (also known as the urban boundary layer, UBL). This study is thus conceived to investigate how urban roughness affects the flow structure and vertical dispersion coefficient in the UBL. Large-eddy simulation (LES) is carried out to examine the plume dispersion from a ground-level pollutant (area) source over idealized street canyons for cross flows in neutral stratification. A range of building-height-to-street-width (aspect) ratios, covering the regimes of skimming flow, wake interference, and isolated roughness, is employed to control the surface roughness. Apart from the widely used aerodynamic resistance or roughness function, the friction factor is another suitable parameter that measures the drag imposed by urban roughness quantitatively. Previous results from laboratory experiments and mathematical modelling also support the aforementioned approach for both two- and three-dimensional roughness elements. Comparing the UBL plume behaviour, the LES results show that the pollutant dispersion strongly depends on the friction factor. Empirical studies reveal that the vertical dispersion coefficient increases with increasing friction factor in the skimming flow regime (lower resistance) but is more uniform in the regimes of wake interference and isolated roughness (higher resistance). Hence, it is proposed that the friction factor and flow regimes could be adopted concurrently for pollutant concentration estimate in the UBL over urban street canyons of different roughness.

Incorporation of a high-roughness lower boundary into a mesoscale model for studies of dry deposition over complex terrain

NASA Astrophysics Data System (ADS)

Physick, W. L.; Garratt, J. R.

1995-04-01

For flow over natural surfaces, there exists a roughness sublayer within the atmospheric surface layer near the boundary. In this sublayer (typically 50 z 0 deep in unstable conditions), the Monin-Obukhov (M-O) flux profile relations for homogeneous surfaces cannot be applied. We have incorporated a modified form of the M-O stability functions (Garratt, 1978, 1980, 1983) in a mesoscale model to take account of this roughness sublayer and examined the diurnal variation of the boundary-layer wind and temperature profiles with and without these modifications. We have also investigated the effect of the modified M-O functions on the aerodynamic and laminar-sublayer resistances associated with the transfer of trace gases to vegetation. Our results show that when an observation height or the lowest level in a model is within the roughness sublayer, neglect of the flux-profile modifications leads to an underestimate of resistances by 7% at the most.

Wetting properties of molecularly rough surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Svoboda, Martin; Lísal, Martin, E-mail: lisal@icpf.cas.cz; Department of Physics, Institute of Science, J. E. Purkinje University, 400 96 Ústí n. Lab.

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 bymore » 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.« less

Fundamental studies of nanoarchitectured dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Yang, Zhenzhen

2011-12-01

Dye-sensitized solar cells (DSSCs) are a promising candidate for next-generation photovoltaic panels due to their low cost, easy fabrication processes and relatively high efficiency. Despite the considerable effort on the advancement of DSSCs, the efficiency of DSSCs has been stalled for nearly two decades due to the complex interplay among various DSSC parameters. Particularly, in a conventional DSSC, a thicker semiconductor photovoltaic (PV) layer, i.e., a dye-sensitized TiO2 nanoparticle layer, is required to accommodate more light-induced charge separation centers to enhance light harvesting efficiency. However, a thicker PV layer concurrently increases the charge transport distance in the PV layer; so the system suffers from more charge recombination, leading to significant deterioration in charge collection efficiency. The conflicting demands on the thickness of PV layer by these two critical elementary photoelectrochemical processes becomes a fundamental limitation for further advancement in DSSCs and limits the choice of redox mediators and electrode materials in DSSCs. Hence, the focus of this dissertation research work is to systematically explore a transformative way to fundamentally resolve the conflicting interplay between light harvesting and charge transport. First, our strategy is to allocate part of the roughness factor to the collecting anode instead of imparting all the roughness factors onto the semiconductor PV layer attached to the anode. As a proof of concept, we first synthesized and characterized a microscopically rough Zn collecting anode, on which ZnO nanotips are grown. For the same surface roughness factor, the length of the ZnO nanotips supported on such a rough Zn anode can be much shorter than that of the ZnO nanowires supported on a planar anode. Our Zn-microtip|ZnO-nanotip DSSCs exhibit enhanced fill factor, Voc and Jsc. The investigation of kinetics indicates that the electron collection time is much faster than the electron lifetime due to the short electron transport distance. Apparently, in contrast to the surface roughness factor of a TiO 2 nanoparticulate film, typically well above 1000, the surface roughness factor of our Zn-microtip|ZnO-nanotip electrode is still very low. Thus, we integrated the above idea in the conventional TiO2-based DSSCs such that the advantage of high surface roughness in conventional NP-based DSSC can be retained. We designed and fabricated an array of metal micropillars by a lithographic method as additional electron collection pathways on a planar TCO anode. The surface roughness is distributed between the collecting electrode and the semiconductor layer. The electron transport kinetics was insightfully studied by electrochemical impedance technique, which suggests that the charge collection efficiency can be enhanced without sacrificing the thickness of TiO2 nanoparticle layer. Furthermore, novel TCO nanoarchitectures were explored by converting the 2-D planar TCO to 3-D structure with intentional incorporation of functional optical structures, e.g., photonic crystals in the cell, to synergistically enhance light harvesting efficiency by light trapping effect, while still keep the short charge transport path length at the TCO/semiconductor interface. A novel 3-D nanophotonic crystal TCO electrode was synthesized using a 3-D template-assisted and solution-chemistry-based method. The optical and electrical properties of the 3-D photonic crystal FTO electrodes are studied by UV-Vis transmittance spectroscopy, Hall effect and sheet resistance measurement. In addition, an ultrathin TiO2 layer is coated on all surfaces of the IO-FTO electrodes using the atomic layer deposition technique. Cyclic voltammetry study indicates that the resulting TiO2-coated 3-D FTO shows excellent potentials as electrodes for electrolyte-based DSSCs.

Topography evolution of rough-surface metallic substrates by solution deposition planarization method

NASA Astrophysics Data System (ADS)

Chu, Jingyuan; Zhao, Yue; Liu, Linfei; Wu, Wei; Zhang, Zhiwei; Hong, Zhiyong; Li, Yijie; Jin, Zhijian

2018-01-01

As an emerging technique for surface smoothing, solution deposition planarization (SDP) has recently drawn more attention on the fabrication of the second generation high temperature superconducting (2G-HTS) tapes. In our work, a number of amorphous oxide layers were deposited on electro-polished or mirror-rolled metallic substrates by chemical solution route. Topography evolution of surface defects on these two types of metallic substrates was thoroughly investigated by atomic force microscopy (AFM). It was showed that root mean square roughness values (at 50 × 50 μm2 scanning scale) on both rough substrates reduced to ∼5 nm after coating with SDP-layer. The smoothing effect was mainly attributed to decrease of the depth at grain boundary grooving on the electro-polished metallic substrate. On the mirror-rolled metallic substrates, the amplitude and frequency of the height fluctuation perpendicular to the rolling direction were gradually reduced as depositing more numbers of SDP-layer. A high Jc value of 4.17 MA cm-2 (at 77 K, s.f.) was achieved on a full stack of YBCO/CeO2/IBAD-MgO/SDP-layer/C276 sample. This study enhanced understanding of the topography evolution on the surface defects covered by the SDP-layer, and demonstrated a low-cost route for fabricating IBAD-MgO based YBCO templates with a simplified architecture.

An experimental study on the effects of rough hydrophobic surfaces on the flow around a circular cylinder

NASA Astrophysics Data System (ADS)

Kim, Nayoung; Kim, Hyunseok; Park, Hyungmin

2015-08-01

The present study investigates the effect that rough hydrophobic (or superhydrophobic) surfaces have on the flow separation and subsequent vortex structures in a turbulent wake behind a circular cylinder. The velocity fields were measured using two-dimensional particle image velocimetry in a water tunnel with Reynolds numbers of 0.7-2.3 × 104. The spray-coating of hydrophobic nanoparticles and roughened Teflon was used to produce the rough hydrophobic surfaces, and sandpapers with two different grit sizes were used to sand the Teflon into streamwise and spanwise directions, respectively, in order to examine the effect of the slip direction. The rough hydrophobic surface was found to enhance the turbulence in the flows above the circular cylinder and along the separating shear layers, resulting in a delay of the flow separation and early vortex roll-up in the wake. As a result, the size of the recirculation bubble in the wake was reduced by up to 40%, while the drag reduction of less than 10% is estimated from a wake survey. However, these effects are reversed as the Reynolds number increases. The surface texture normal to the flow direction (spanwise slip) was found to be more effective than that aligned to the flow (streamwise slip), supporting the suggested mechanism. In addition, the superhydrophobic surface is locally applied by varying the installation angle and that applied around the separation point is most effective, indicating that the rough hydrophobic surface directly affects the boundary layer at flow separation. In order to control the flow around a circular cylinder using rough hydrophobic surfaces, it is suggested to have a smaller roughness width, which can stably retain air pockets. In addition, a higher gas fraction and a more uniform distribution of the roughness size are helpful to enhance the performance such as the separation delay and drag reduction.

Effect of Surface Roughness on Polymer Drag Reduction with a High-Reynolds-Number Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Elbing, Brian; Dowling, David; Solomon, Michael; Bian, Sherry; Ceccio, Steven

2007-11-01

A recent experiment at the U.S. Navy's Large Cavitation Channel (LCC) investigated the effect of wall roughness on wall-injection polymer drag reduction (PDR) within a high-Reynolds-number (10^7 to 2x10^8 based on downstream distance) turbulent boundary layer (TBL). Testing was performed in two parts: 1) PDR experiment on a 12.9 m long, 3.05 m wide hydro-dynamically smooth flat plate and 2) PDR experiment on the same model with the entire surface roughened. The roughness was produced by blowing glass beads into epoxy paint that was applied to the entire model. The roughened model had an average roughness height ranging between 307 and 1154 μm. Drag reduction was determined using six, stream-wise located integrated skin-friction balances. In addition to skin-friction measurements, sampling was performed at three stream-wise located ports. The sampling ports were used to determine the amount of degradation, if any, caused by the turbulent flow on the polymer. Both the skin-friction measurements and sampling analysis indicates that wall roughness in a turbulent boundary layer significantly increases degradation of the polymer solution.

Study on Plastic Deformation Characteristics of Shot Peening of Ni-Based Superalloy GH4079

NASA Astrophysics Data System (ADS)

Zhong, L. Q.; Liang, Y. L.; Hu, H.

2017-09-01

In this paper, the X-ray stress diffractometer, surface roughness tester, field emission scanning electron microscope(SEM), dynamic ultra-small microhardness tester were used to measure the surface residual stress and roughness, topography and surface hardness changes of GH4079 superalloy, which was processed by metallographic grinding, turning, metallographic grinding +shot peening and turning + shot peening. Analysized the effects of shot peening parameters on shot peening plastic deformation features; and the effects of the surface state before shot peening on shot peening plastic deformation characteristics. Results show that: the surface residual compressive stress, surface roughness and surface hardness of GH4079 superalloy were increased by shot peening, in addition, the increment of the surface residual compressive stress, surface roughness and surface hardness induced by shot peening increased with increasing shot peening intensity, shot peening time, shot peening pressure and shot hardness, but harden layer depth was not affected considerably. The more plastic deformation degree of before shot peening surface state, the less increment of the surface residual compressive stress, surface roughness and surface hardness induced by shot peening.

Deterministic multi-zone ice accretion modeling

NASA Technical Reports Server (NTRS)

Yamaguchi, K.; Hansman, R. John, Jr.; Kazmierczak, Michael

1991-01-01

The focus here is on a deterministic model of the surface roughness transition behavior of glaze ice. The initial smooth/rough transition location, bead formation, and the propagation of the transition location are analyzed. Based on the hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness.

The internal boundary layer — A review

NASA Astrophysics Data System (ADS)

Garratt, J. R.

1990-03-01

A review is given of relevant work on the internal boundary layer (IBL) associated with: (i) Small-scale flow in neutral conditions across an abrupt change in surface roughness, (ii) Small-scale flow in non-neutral conditions across an abrupt change in surface roughness, temperature or heat/moisture flux, (iii) Mesoscale flow, with emphasis on flow across the coastline for both convective and stably stratified conditions. The major theme in all cases is on the downstream, modified profile form (wind and temperature), and on the growth relations for IBL depth.

Thrust noise minimization in long-term laser ablation of propellant material in the nanosecond and picosecond regime

NASA Astrophysics Data System (ADS)

Lorbeer, Raoul-Amadeus; Scharring, Stefan; Karg, Stephanie; Pastow, Jan; Pastuschka, Lisa; Förster, Daniel Johannes; Eckel, Hans-Albert

2017-01-01

The avoidance of any moving parts in a microthruster exhibits a great potential for low-noise thrust generation in the micronewton range. This is required, e.g., for scientific missions that need attitude and orbit control systems with exquisite precision. Laser ablation propulsion offers the opportunity of permanent inertia-free, electro-optical delivery of laser energy to access the propellant entirely without moving it. New propellant is accessed by ablating the previous surface in layers, essentially damaging the surface with a laser over and over again. The resulting surface properties for different fluences and scanning patterns were investigated for multiple layers of aluminum, copper, and gold. The pulse-length-specific issues of various ablation mechanisms such as vaporization, spallation, and phase explosion are accounted for by the use of a 10-ps laser system and a 500-ps laser system. We show that the surface roughness produced with 500-ps laser pulses is approximately twice the surface roughness generated by using 10-ps laser pulses. Furthermore, with 500-ps pulses, the surface roughness shows low dependency on the fluence for carefully chosen scanning parameters. Therefore, we conclude that laser pulse duration differences in the picosecond and nanosecond regimes will not necessarily alter surface roughness properties.

Smooth e-beam-deposited tin-doped indium oxide for III-nitride vertical-cavity surface-emitting laser intracavity contacts

NASA Astrophysics Data System (ADS)

Leonard, J. T.; Cohen, D. A.; Yonkee, B. P.; Farrell, R. M.; DenBaars, S. P.; Speck, J. S.; Nakamura, S.

2015-10-01

We carried out a series of simulations analyzing the dependence of mirror reflectance, threshold current density, and differential efficiency on the scattering loss caused by the roughness of tin-doped indium oxide (ITO) intracavity contacts for 405 nm flip-chip III-nitride vertical-cavity surface-emitting lasers (VCSELs). From these results, we determined that the ITO root-mean-square (RMS) roughness should be <1 nm to minimize scattering losses in VCSELs. Motivated by this requirement, we investigated the surface morphology and optoelectronic properties of electron-beam (e-beam) evaporated ITO films, as a function of substrate temperature and oxygen flow and pressure. The transparency and conductivity were seen to increase with increasing temperature. Decreasing the oxygen flow and pressure resulted in an increase in the transparency and resistivity. Neither the temperature, nor oxygen flow and pressure series on single-layer ITO films resulted in highly transparent and conductive films with <1 nm RMS roughness. To achieve <1 nm RMS roughness with good optoelectronic properties, a multi-layer ITO film was developed, utilizing a two-step temperature scheme. The optimized multi-layer ITO films had an RMS roughness of <1 nm, along with a high transparency (˜90% at 405 nm) and low resistivity (˜2 × 10-4 Ω-cm). This multi-layer ITO e-beam deposition technique is expected to prevent p-GaN plasma damage, typically observed in sputtered ITO films on p-GaN, while simultaneously reducing the threshold current density and increasing the differential efficiency of III-nitride VCSELs.

Discrete Roughness Effects on Shuttle Orbiter at Mach 6

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Hamilton, H. Harris, II

2002-01-01

Discrete roughness boundary layer transition results on a Shuttle Orbiter model in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed with new boundary layer calculations to provide consistency for comparison to other published results. The experimental results were previously obtained utilizing the phosphor thermography system to monitor the status of the boundary layer via global heat transfer images of the Orbiter windward surface. The size and location of discrete roughness elements were systematically varied along the centerline of the 0.0075-scale model at an angle of attack of 40 deg and the boundary layer response recorded. Various correlative approaches were attempted, with the roughness transition correlations based on edge properties providing the most reliable results. When a consistent computational method is used to compute edge conditions, transition datasets for different configurations at several angles of attack have been shown to collapse to a well-behaved correlation.

Surface roughening of undoped and in situ B-doped SiGe epitaxial layers deposited by using reduced pressure chemical vapor deposition

NASA Astrophysics Data System (ADS)

Kim, Youngmo; Park, Jiwoo; Sohn, Hyunchul

2018-01-01

Si1- x Ge x (:B) epitaxial layers were deposited by using reduced pressure chemical vapor deposition with SiH4, GeH4, and B2H6 source gases, and the dependences of the surface roughness of undoped Si1- x Ge x on the GeH4 flow rate and of Si1- x Ge x :B on the B2H6 flow rate were investigated. The root-mean-square (RMS) roughness value of the undoped Si1- x Ge x at constant thickness increased gradually with increasing Ge composition, resulting from an increase in the amplitude of the wavy surface before defect formation. At higher Ge compositions, the residual strain in Si1- x Ge x significantly decreased through the formation of defects along with an abrupt increase in the RMS roughness. The variation of the surface roughness of Si1- x Ge x :B depended on the boron (B) concentration. At low B concentrations, the RMS roughness of Si1- x Ge x remained constant regardless of Ge composition, which is similar to that of undoped Si1- x Ge x . However, at high B concentrations, the RMS roughness of Si1- x Ge x :B increased greatly due to B islanding. In addition, at very high B concentrations ( 9.9 at%), the RMS roughness of Si1- x Ge x :B decreased due to non-epitaxial growth.

Diffuse reflection from a stochastically bounded, semi-infinite medium

NASA Technical Reports Server (NTRS)

Lumme, K.; Peltoniemi, J. I.; Irvine, W. M.

1990-01-01

In order to determine the diffuse reflection from a medium bounded by a rough surface, the problem of radiative transfer in a boundary layer characterized by a statistical distribution of heights is considered. For the case that the surface is defined by a multivariate normal probability density, the propagation probability for rays traversing the boundary layer is derived and, from that probability, a corresponding radiative transfer equation. A solution of the Eddington (two stream) type is found explicitly, and examples are given. The results should be applicable to reflection from the regoliths of solar system bodies, as well as from a rough ocean surface.

Multiwavelength laser light transmission of hollow optical fiber from the visible to the mid-infrared.

PubMed

Shi, Yi Wei; Ito, Kentaro; Matsuura, Yuji; Miyagi, Mitsunobu

2005-11-01

We report on low-loss multiwavelength laser delivery of hollow optical fiber in a wide wavelength region, from the visible to the infrared. Improved methods of liquid-phase coating were used to fabricate the hollow fiber with inner films of a silver and a cyclic olefin polymer (COP) layer. The surface roughness of the silver layer was reduced dramatically by pretreatment on the inner glass surface with an SnCl2 solution. The COP layer roughness was also decreased by using an ambient atmosphere of tetrahydrofuran (THF) solvent during the COP layer formation. Owing to the smooth surfaces, hollow fiber with optimum COP film thickness for CO2 laser light simultaneously yields low losses for a Er:YAG laser and a red pilot beam. The power durability of CO2 and Er:YAG lasers, as well as the loss properties for the pilot beam, is demonstrated.

Contact mechanics for layered materials with randomly rough surfaces.

PubMed

Persson, B N J

2012-03-07

The contact mechanics model of Persson is applied to layered materials. We calculate the M function, which relates the surface stress to the surface displacement, for a layered material, where the top layer (thickness d) has different elastic properties than the semi-infinite solid below. Numerical results for the contact area as a function of the magnification are presented for several cases. As an application, we calculate the fluid leak rate for laminated rubber seals.

A review of turbulent-boundary-layer heat transfer research at Stanford, 1958-1983

NASA Technical Reports Server (NTRS)

Moffat, R. J.; Kays, W. M.

1984-01-01

For the past 25 years, there has existed in the Thermosciences Laboratory of the Mechanical Engineering Department of Stanford University a research program, primarily experimental, concerned with heat transfer through turbulent boundary layers. In the early phases of the program, the topics considered were the simple zero-pressure-gradient turbulent boundary layer with constant and with varying surface temperature, and the accelerated boundary layer. Later equilibrium boundary layers were considered along with factors affecting the boundary layer, taking into account transpired flows, flows with axial pressure gradients, transpiration, acceleration, deceleration, roughness, full-coverage film cooling, surface curvature, free convection, and mixed convection. A description is provided of the apparatus and techniques used, giving attention to the smooth plate rig, the rough plate rig, the full-coverage film cooling rig, the curvature rig, the concave wall rig, the mixed convection tunnel, and aspects of data reduction and uncertainty analysis.

Simple model of surface roughness for binary collision sputtering simulations

NASA Astrophysics Data System (ADS)

Lindsey, Sloan J.; Hobler, Gerhard; Maciążek, Dawid; Postawa, Zbigniew

2017-02-01

It has been shown that surface roughness can strongly influence the sputtering yield - especially at glancing incidence angles where the inclusion of surface roughness leads to an increase in sputtering yields. In this work, we propose a simple one-parameter model (the "density gradient model") which imitates surface roughness effects. In the model, the target's atomic density is assumed to vary linearly between the actual material density and zero. The layer width is the sole model parameter. The model has been implemented in the binary collision simulator IMSIL and has been evaluated against various geometric surface models for 5 keV Ga ions impinging an amorphous Si target. To aid the construction of a realistic rough surface topography, we have performed MD simulations of sequential 5 keV Ga impacts on an initially crystalline Si target. We show that our new model effectively reproduces the sputtering yield, with only minor variations in the energy and angular distributions of sputtered particles. The success of the density gradient model is attributed to a reduction of the reflection coefficient - leading to increased sputtering yields, similar in effect to surface roughness.

A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers

NASA Astrophysics Data System (ADS)

Fong, Kahei Danny

The current understanding and research efforts on surface roughness effects in hypersonic boundary-layer flows focus, almost exclusively, on how roughness elements trip a hypersonic boundary layer to turbulence. However, there were a few reports in the literature suggesting that roughness elements in hypersonic boundary-layer flows could sometimes suppress the transition process and delay the formation of turbulent flow. These reports were not common and had not attracted much attention from the research community. Furthermore, the mechanisms of how the delay and stabilization happened were unknown. A recent study by Duan et al. showed that when 2-D roughness elements were placed downstream of the so-called synchronization point, the unstable second-mode wave in a hypersonic boundary layer was damped. Since the second-mode wave is typically the most dangerous and dominant unstable mode in a hypersonic boundary layer for sharp geometries at a zero angle of attack, this result has pointed to an explanation on how roughness elements delay transition in a hypersonic boundary layer. Such an understanding can potentially have significant practical applications for the development of passive flow control techniques to suppress hypersonic boundary-layer transition, for the purpose of aero-heating reduction. Nevertheless, the previous study was preliminary because only one particular flow condition with one fixed roughness parameter was considered. The study also lacked an examination on the mechanism of the damping effect of the second mode by roughness. Hence, the objective of the current research is to conduct an extensive investigation of the effects of 2-D roughness elements on the growth of instability waves in a hypersonic boundary layer. The goal is to provide a full physical picture of how and when 2-D roughness elements stabilize a hypersonic boundary layer. Rigorous parametric studies using numerical simulation, linear stability theory (LST), and parabolized stability equation (PSE) are performed to ensure the fidelity of the data and to study the relevant flow physics. All results unanimously confirm the conclusion that the relative location of the synchronization point with respect to the roughness element determines the roughness effect on the second mode. Namely, a roughness placed upstream of the synchronization point amplifies the unstable waves while placing a roughness downstream of the synchronization point damps the second-mode waves. The parametric study also shows that a tall roughness element within the local boundary-layer thickness results in a stronger damping effect, while the effect of the roughness width is relatively insignificant compared with the other roughness parameters. On the other hand, the fact that both LST and PSE successfully predict the damping effect only by analyzing the meanflow suggests the mechanism of the damping is by the meanflow alteration due to the existence of roughness elements, rather than new mode generation. In addition to studying the unstable waves, the drag force and heating with and without roughness have been investigated by comparing the numerical simulation data with experimental correlations. It is shown that the increase in drag force generated by the Mach wave around a roughness element in a hypersonic boundary layer is insignificant compared to the reduction of drag force by suppressing turbulent flow. The study also shows that, for a cold wall flow which is the case for practical flight applications, the Stanton number decreases as roughness elements smooth out the temperature gradient in the wall-normal direction. Based on the knowledge of roughness elements damping the second mode gained from the current study, a novel passive transition control method using judiciously placed roughness elements has been developed, and patented, during the course of this research. The main idea of the control method is that, with a given geometry and flow condition, it is possible to find the most unstable second-mode frequency that can lead to transition. And by doing a theoretical analysis such as LST, the synchronization location for the most unstable frequency can be found. Roughness elements are then strategically placed downstream of the synchronization point to damp out this dangerous second-mode wave, thus stabilizing the boundary layer and suppressing the transition process. This method is later experimentally validated in Purdue's Mach 6 quiet wind tunnel. Overall, this research has not only provided details of when and how 2-D roughness stabilizes a hypersonic boundary layer, it also has led to a successful application of numerical simulation data to the development of a new roughness-based transition delay method, which could potentially have significant contributions to the design of future generation hypersonic vehicles.

ATMOSPHERIC DISPERSION IN THE ARCTIC: WINTERTIME BOUNDARY-LAYER MEASUREMENTS

EPA Science Inventory

The wintertime arctic atmospheric boundary layer was investigated with micro-meteorological and SF6 tracer measurements collected in Prudhoe Bay, AK. he flat, snow-covered tundra surface at this site generates a very small (0.03 cm) surface roughness. he relatively warm maritime ...

Effect of leading-edge roughness on stability and transition of wind turbine blades

NASA Astrophysics Data System (ADS)

Kutz, Douglas; Freels, Justin; Hidore, John; White, Edward

2011-11-01

Over time, wind turbine blades erode due to impacts with sand and other debris. The resulting surface roughness degrades the blades' aerodynamic performance. Experimental studies conducted at the Texas A&M University Low-Speed Wind Tunnel examine roughness effects using a 2D NACA 63-418 airfoil with interchangeable leading edges of varying roughness at chord Reynolds numbers up to 3 . 0 ×106 . These data reveal decreased CL , max and increased CD , min as roughness increases. At very high roughness levels, even the lift curve slope is reduced. To better understand these findings and improve modeling of roughness effects, extensive boundary layer measurements including surface-mounted hotfilms and boundary-layer velocity profiles are used to assess how laminar-to-turbulent transition is promoted by roughness. As expected, roughness accelerates transition. Tollmien-Schlichting (TS) transition is observed only for a smooth leading edge while bypass transition is observed for the moderate and high roughness levels. Results are compared to N-factor transition predictions generated with software used by the wind industry. Predictions are successful for the smooth leading edge but even the low roughness level prevents correct transition prediction using TS-based methods. Support for this work by Vestas Technology Americas, Inc., is gratefully acknowledged as is the support of the wind-energy research group and the Low-Speed Wind Tunnel staff.

Modelling turbulent boundary layer flow over fractal-like multiscale terrain using large-eddy simulations and analytical tools.

PubMed

Yang, X I A; Meneveau, C

2017-04-13

In recent years, there has been growing interest in large-eddy simulation (LES) modelling of atmospheric boundary layers interacting with arrays of wind turbines on complex terrain. However, such terrain typically contains geometric features and roughness elements reaching down to small scales that typically cannot be resolved numerically. Thus subgrid-scale models for the unresolved features of the bottom roughness are needed for LES. Such knowledge is also required to model the effects of the ground surface 'underneath' a wind farm. Here we adapt a dynamic approach to determine subgrid-scale roughness parametrizations and apply it for the case of rough surfaces composed of cuboidal elements with broad size distributions, containing many scales. We first investigate the flow response to ground roughness of a few scales. LES with the dynamic roughness model which accounts for the drag of unresolved roughness is shown to provide resolution-independent results for the mean velocity distribution. Moreover, we develop an analytical roughness model that accounts for the sheltering effects of large-scale on small-scale roughness elements. Taking into account the shading effect, constraints from fundamental conservation laws, and assumptions of geometric self-similarity, the analytical roughness model is shown to provide analytical predictions that agree well with roughness parameters determined from LES.This article is part of the themed issue 'Wind energy in complex terrains'. © 2017 The Author(s).

Validation of SMAP Radar Vegetation Data Cubes from Agricultural Field Measurements

NASA Astrophysics Data System (ADS)

Tsang, L.; Xu, X.; Liao, T.; Kim, S.; Njoku, E. G.

2012-12-01

The NASA Soil Moisture Active/Passive (SMAP) Mission will be launched in October 2014. The objective of the SMAP mission is to provide global measurements of soil moisture and its freeze/thaw state. These measurements will be used to enhance understanding of processes that link the water, energy and carbon cycles, and to extend the capabilities of weather and climate prediction models. In the active algorithm, the retrieval is performed based on the backscattering data cube, which are characterized by two surface parameters, which are soil moisture and soil surface rms height, and one vegetation parameter, the vegetation water content. We have developed a physical-based forward scattering model to generate the data cube for agricultural fields. To represent the agricultural crops, we include a layer of cylinders and disks on top of the rough surface. The scattering cross section of the vegetation layer and its interaction with the underground soil surface were calculated by the distorted Born approximation, which give explicitly three scattering mechanisms. A) The direct volume scattering B) The double bounce effect as, and C) The double bouncing effects. The direct volume scattering is calculated by using the Body of Revolution code. The double bounce effects, exhibited by the interaction of rough surface with the vegetation layer is considered by modifying the rough surface reflectivity using the coherent wave as computed by Numerical solution of Maxwell equations of 3 Dimensional simulations (NMM3D) of bare soil scattering. The rough surface scattering of the soil was calculated by NMM3D. We have compared the physical scattering models with field measurements. In the field campaign, the measurements were made on soil moisture, rough surface rms heights and vegetation water content as well as geometric parameters of vegetation. The three main crops lands are grassland, cornfield and soybean fields. The corresponding data cubes are validated using SGP99, SMEX02 and SMEX 08 field experiments.

Steady Boundary Layer Disturbances Created By Two-Dimensional Surface Ripples

NASA Astrophysics Data System (ADS)

Kuester, Matthew

2017-11-01

Multiple experiments have shown that surface roughness can enhance the growth of Tollmien-Schlichting (T-S) waves in a laminar boundary layer. One of the common observations from these studies is a ``wall displacement'' effect, where the boundary layer profile shape remains relatively unchanged, but the origin of the profile pushes away from the wall. The objective of this work is to calculate the steady velocity field (including this wall displacement) of a laminar boundary layer over a surface with small, 2D surface ripples. The velocity field is a combination of a Blasius boundary layer and multiple disturbance modes, calculated using the linearized Navier-Stokes equations. The method of multiple scales is used to include non-parallel boundary layer effects of O (Rδ- 1) ; the non-parallel terms are necessary, because a wall displacement is mathematically inconsistent with a parallel boundary layer assumption. This technique is used to calculate the steady velocity field over ripples of varying height and wavelength, including cases where a separation bubble forms on the leeward side of the ripple. In future work, the steady velocity field will be the input for stability calculations, which will quantify the growth of T-S waves over rough surfaces. The author would like to acknowledge the support of the Kevin T. Crofton Aerospace & Ocean Engineering Department at Virginia Tech.

Light-induced V{sub oc} increase and decrease in high-efficiency amorphous silicon solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stuckelberger, M., E-mail: michael.stuckelberger@epfl.ch; Riesen, Y.; Despeisse, M.

High-efficiency amorphous silicon (a-Si:H) solar cells were deposited with different thicknesses of the p-type amorphous silicon carbide layer on substrates of varying roughness. We observed a light-induced open-circuit voltage (V{sub oc}) increase upon light soaking for thin p-layers, but a decrease for thick p-layers. Further, the V{sub oc} increase is enhanced with increasing substrate roughness. After correction of the p-layer thickness for the increased surface area of rough substrates, we can exclude varying the effective p-layer thickness as the cause of the substrate roughness dependence. Instead, we explain the observations by an increase of the dangling-bond density in both themore » p-layer—causing a V{sub oc} increase—and in the intrinsic absorber layer, causing a V{sub oc} decrease. We present a mechanism for the light-induced increase and decrease, justified by the investigation of light-induced changes of the p-layer and supported by Advanced Semiconductor Analysis simulation. We conclude that a shift of the electron quasi-Fermi level towards the conduction band is the reason for the observed V{sub oc} enhancements, and poor amorphous silicon quality on rough substrates enhances this effect.« less

Boundary Layer Control for Hypersonic Airbreathing Vehicles

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Nowak, Robert J.; Horvath, Thomas J.

2004-01-01

Active and passive methods for tripping hypersonic boundary layers have been examined in NASA Langley Research Center wind tunnels using a Hyper-X model. This investigation assessed several concepts for forcing transition, including passive discrete roughness elements and active mass addition (or blowing), in the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air Tunnels. Heat transfer distributions obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the Hyper-X nominal Mach 7 flight test-point of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For passive roughness, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The passive roughness study resulted in a swept ramp configuration, scaled to be roughly 0.6 of the calculated boundary layer thickness, being selected for the Mach 7 flight vehicle. For the active blowing study, the manifold pressure was systematically varied (while monitoring the mass flow) for each configuration to determine the jet penetration height, with schlieren, and transition movement, with the phosphor system, for comparison to the passive results. All the blowing concepts tested, which included various rows of sonic orifices (holes), two- and three-dimensional slots, and random porosity, provided transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model surface static pressure, which is adequate to ensure sonic jets. The present results indicate that the jet penetration height for blowing was roughly half the height required with passive roughness elements for an equivalent amount of transition movement.

In vivo measurement of skin surface strain and sub-surface layer deformation induced by natural tissue stretching.

PubMed

Maiti, Raman; Gerhardt, Lutz-Christian; Lee, Zing S; Byers, Robert A; Woods, Daniel; Sanz-Herrera, José A; Franklin, Steve E; Lewis, Roger; Matcher, Stephen J; Carré, Matthew J

2016-09-01

Stratum corneum and epidermal layers change in terms of thickness and roughness with gender, age and anatomical site. Knowledge of the mechanical and tribological properties of skin associated with these structural changes are needed to aid in the design of exoskeletons, prostheses, orthotics, body mounted sensors used for kinematics measurements and in optimum use of wearable on-body devices. In this case study, optical coherence tomography (OCT) and digital image correlation (DIC) were combined to determine skin surface strain and sub-surface deformation behaviour of the volar forearm due to natural tissue stretching. The thickness of the epidermis together with geometry changes of the dermal-epidermal junction boundary were calculated during change in the arm angle, from flexion (90°) to full extension (180°). This posture change caused an increase in skin surface Lagrange strain, typically by 25% which induced considerable morphological changes in the upper skin layers evidenced by reduction of epidermal layer thickness (20%), flattening of the dermal-epidermal junction undulation (45-50% reduction of flatness being expressed as Ra and Rz roughness profile height change) and reduction of skin surface roughness Ra and Rz (40-50%). The newly developed method, DIC combined with OCT imaging, is a powerful, fast and non-invasive methodology to study structural skin changes in real time and the tissue response provoked by mechanical loading or stretching. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Lithography-free glass surface modification by self-masking during dry etching

NASA Astrophysics Data System (ADS)

Hein, Eric; Fox, Dennis; Fouckhardt, Henning

2011-01-01

Glass surface morphologies with defined shapes and roughness are realized by a two-step lithography-free process: deposition of an ~10-nm-thin lithographically unstructured metallic layer onto the surface and reactive ion etching in an Ar/CF4 high-density plasma. Because of nucleation or coalescence, the metallic layer is laterally structured during its deposition. Its morphology exhibits islands with dimensions of several tens of nanometers. These metal spots cause a locally varying etch velocity of the glass substrate, which results in surface structuring. The glass surface gets increasingly rougher with further etching. The mechanism of self-masking results in the formation of surface structures with typical heights and lateral dimensions of several hundred nanometers. Several metals, such as Ag, Al, Au, Cu, In, and Ni, can be employed as the sacrificial layer in this technology. Choice of the process parameters allows for a multitude of different glass roughness morphologies with individual defined and dosed optical scattering.

Surface roughness of Saturn's rings and ring particles inferred from thermal phase curves

NASA Astrophysics Data System (ADS)

Morishima, Ryuji; Turner, Neal J.; Spilker, Linda

2017-10-01

We analyze thermal phase curves of all the main rings of Saturn (the A, B, C rings, and the Cassini division) measured by both the far-IR and mid-IR detectors of the Cassini Composite InfraRed Spectrometer (CIRS). All the rings show temperature increases toward zero phase angle, known as an opposition effect or thermal beaming. For the C ring and Cassini division, which have low optical depths, intra-particle shadowing is considered the dominant mechanism causing the effect. On the other hand, the phase curves of the optically thick B and A rings steepen significantly with decreasing absolute solar elevation angle from 21° to 14°, suggesting inter-particle shadowing plays an important role in these rings. We employ an analytic roughness model to estimate the degrees of surface roughness of the rings or ring particles. For optically thin rings, an isolated particle covered by spherical segment craters is employed while for the thick rings we approximate a packed particle layer as a slab covered by craters. The particles in the thin rings are found to have generally rough surfaces, except in the middle C ring. Across the C ring, the optical depth correlates with the degree of surface roughness. This may indicate that surface roughness comes mainly from particle clumping, while individual particles have rather smooth surfaces. For the optically thick rings, the surface roughness of the particle layer is found to be moderate. The modeled phase curves of optically thick rings are shallow if the phase angle change is primarily due to change of observer azimuthal angle. On the other hand, the phase curves are steep if the phase angle change is due to change of observer elevation angle, as inter-particle shadows become visible at higher observer elevation. In addition, the area of shadowed facets increases with decreasing solar elevation angle. These combined effects explain the large seasonal change of the phase curve steepness observed for the thick rings. The degrees of surface roughness inferred from the thermal phase curves are generally less than those from the phase curves in visible light. This is probably explained by different roughness scales seen in thermal and visible light.

Thin film surface treatments for lowering dust adhesion on Mars Rover calibration targets

NASA Astrophysics Data System (ADS)

Sabri, F.; Werhner, T.; Hoskins, J.; Schuerger, A. C.; Hobbs, A. M.; Barreto, J. A.; Britt, D.; Duran, R. A.

The current generation of calibration targets on Mars Rover serve as a color and radiometric reference for the panoramic camera. They consist of a transparent silicon-based polymer tinted with either color or grey-scale pigments and cast with a microscopically rough Lambertian surface for a diffuse reflectance pattern. This material has successfully withstood the harsh conditions existent on Mars. However, the inherent roughness of the Lambertian surface (relative to the particle size of the Martian airborne dust) and the tackiness of the polymer in the calibration targets has led to a serious dust accumulation problem. In this work, non-invasive thin film technology was successfully implemented in the design of future generation calibration targets leading to significant reduction of dust adhesion and capture. The new design consists of a μm-thick interfacial layer capped with a nm-thick optically transparent layer of pure metal. The combination of these two additional layers is effective in burying the relatively rough Lambertian surface while maintaining diffuse properties of the samples which is central to the correct operation as calibration targets. A set of these targets are scheduled for flight on the Mars Phoenix mission.

Comparison of surface characteristics of retrieved cobalt-chromium femoral heads with and without ion implantation.

PubMed

McGrory, Brian J; Ruterbories, James M; Pawar, Vivek D; Thomas, Reginald K; Salehi, Abraham B

2012-01-01

Nitrogen ion implantation of CoCr is reported to produce increased surface hardness and a lower friction surface. Femoral heads with and without ion implantation retrieved from 1997 to 2003 were evaluated for surface roughness (average surface roughness [Ra], mean peak height [Rpm], and maximum distance from peak to valley [Rmax]), nanohardness, and the ion-treated layer thickness. The difference in average Rmax (P = .033) and average Rpm (P = .008) was statistically significant, but there was no correlation between the average or maximum roughness parameters (average surface roughness, Rmax, and Rpm) and time in vivo (P > .05). Overall, nanohardness was greater for the low-friction ion-treated heads (P < .001); and it decreased with increasing time in vivo (P = .01). Ion treatment produces an increased surface hardness, but the advantage of this increased hardness appears to dissipate over time in vivo. Copyright © 2012 Elsevier Inc. All rights reserved.

Equations for normal-mode statistics of sound scattering by a rough elastic boundary in an underwater waveguide, including backscattering.

PubMed

Morozov, Andrey K; Colosi, John A

2017-09-01

Underwater sound scattering by a rough sea surface, ice, or a rough elastic bottom is studied. The study includes both the scattering from the rough boundary and the elastic effects in the solid layer. A coupled mode matrix is approximated by a linear function of one random perturbation parameter such as the ice-thickness or a perturbation of the surface position. A full two-way coupled mode solution is used to derive the stochastic differential equation for the second order statistics in a Markov approximation.

Relationships between topographic roughness and aeolian processes

NASA Technical Reports Server (NTRS)

Greeley, Ronald; Lancaster, N.; Gaddis, L.; Rasmussen, K. R.; White, B. R.; Saunders, R. S.; Wall, S.; Dobrovolskis, Anthony R.; Iversen, J. D.

1991-01-01

The interaction between winds and desert surfaces has important implications for sediment transport on Earth, Mars, and Venus, and for understanding the relationships between radar backscatter and aerodynamic roughness as part of the NASA Shuttle Imaging radar (SIR-C) Mission. Here, researchers report results from measurements of boundary layer wind profiles and surface roughness at sites in Death Valley and discuss their implications. The sites included a flat to undulating gravel and sand reg, alluvial fans, and a playa. Estimates of average particle size composition of Death Valley sites and arithmetic mean values of aerodynamic roughness are given in tabular form.

Modifying the anti-wetting property of butterfly wings and water strider legs by atomic layer deposition coating: surface materials versus geometry.

PubMed

Ding, Yong; Xu, Sheng; Zhang, Yue; Wang, Aurelia C; Wang, Melissa H; Xiu, Yonghao; Wong, Ching Ping; Wang, Zhong Lin

2008-09-03

Although butterfly wings and water strider legs have an anti-wetting property, their working conditions are quite different. Water striders, for example, live in a wet environment and their legs need to support their weight and bear the high pressure during motion. In this work, we have focused on the importance of the surface geometrical structures in determining their performance. We have applied an atomic layer deposition technique to coat the surfaces of both butterfly wings and water strider legs with a uniform 30 nm thick hydrophilic Al(2)O(3) film. By keeping the surface material the same, we have studied the effect of different surface roughness/structure on their hydrophobic property. After the surface coating, the butterfly wings changed to become hydrophilic, while the water strider legs still remained super-hydrophobic. We suggest that the super-hydrophobic property of the water strider is due to the special shape of the long inclining spindly cone-shaped setae at the surface. The roughness in the surface can enhance the natural tendency to be hydrophobic or hydrophilic, while the roughness in the normal direction of the surface is favorable for forming a composite interface.

2D scaling behavior of nanotextured GaN surfaces: A case study of hillocked and terraced surfaces

NASA Astrophysics Data System (ADS)

Mutta, Geeta Rani; Carapezzi, Stefania

2018-07-01

The 2D scaling properties of GaN surfaces have been studied by means of the 2D height-height correlation function (HHCF). The GaN layers under investigation presented exemplar morphologies, generated by distinct growth methods: a molecular beam epitaxy (MBE) grown surface decorated by hillocks and a metal organic vapor phase epitaxy (MOVPE) grown surface with terraced structure. The 2D statistical analysis of these surfaces has allowed assessing quantitatively the degree of morphological variability along all the different directions across each surface, their corresponding roughness exponents and correlation lengths. A scaling anisotropy as well as correlation length anisotropy has been detected for both hillocked and terraced surfaces. Especially, a marked dependence of correlation length from the direction across the terraced surface has been observed. Additionally, the terraced surfaces showed the lower root mean square (RMS) roughness value and at the same time, the lower roughness exponent value. This could appear as a contradiction, given that a low RMS value is associated to a smooth surface, and usually the roughness exponent is interpreted as a "measure" of the smoothness of the surface, the smoother the surface, the higher (approaching the unity) is the roughness exponent. Our case study is an experimental demonstration in which the roughness exponent should be, more appropriately, interpreted as a quantification of how the roughness changes with length scale.

Effect of film slicks on near-surface wind

NASA Astrophysics Data System (ADS)

Charnotskii, Mikhail; Ermakov, Stanislav; Ostrovsky, Lev; Shomina, Olga

2016-09-01

The transient effects of horizontal variation of sea-surface wave roughness due to surfactant films on near-surface turbulent wind are studied theoretically and experimentally. Here we suggest two practical schemes for calculating variations of wind velocity profiles near the water surface, the average short-wave roughness of which is varying in space and time when a film slick is present. The schemes are based on a generalized two-layer model of turbulent air flow over a rough surface and on the solution of the continuous model involving the equation for turbulent kinetic energy of the air flow. Wave tank studies of wind flow over wind waves in the presence of film slicks are described and compared with theory.

Connections Between the Spring Breakup of the Southern Hemisphere Polar Vortex, Stationary Waves, and Air-sea Roughness

NASA Technical Reports Server (NTRS)

Garfinkel, Chaim I.; Oman, Luke David; Barnes, Elizabeth A.; Waugh, Darryn W.; Hurwitz, Margaret H.; Molod, Andrea M.

2013-01-01

A robust connection between the drag on surface-layer winds and the stratospheric circulation is demonstrated in NASA's Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). Specifically, an updated parameterization of roughness at the air-sea interface, in which surface roughness is increased for moderate wind speeds (4ms to 20ms), leads to a decrease in model biases in Southern Hemispheric ozone, polar cap temperature, stationary wave heat flux, and springtime vortex breakup. A dynamical mechanism is proposed whereby increased surface roughness leads to improved stationary waves. Increased surface roughness leads to anomalous eddy momentum flux convergence primarily in the Indian Ocean sector (where eddies are strongest climatologically) in September and October. The localization of the eddy momentum flux convergence anomaly in the Indian Ocean sector leads to a zonally asymmetric reduction in zonal wind and, by geostrophy, to a wavenumber-1 stationary wave pattern. This tropospheric stationary wave pattern leads to enhanced upwards wave activity entering the stratosphere. The net effect is an improved Southern Hemisphere vortex: the vortex breaks up earlier in spring (i.e., the spring late-breakup bias is partially ameliorated) yet is no weaker in mid-winter. More than half of the stratospheric biases appear to be related to the surface wind speed biases. As many other chemistry climate models use a similar scheme for their surface layer momentum exchange and have similar biases in the stratosphere, we expect that results from GEOSCCM may be relevant for other climate models.

Maintaining the pluripotency of mouse embryonic stem cells on gold nanoparticle layers with nanoscale but not microscale surface roughness.

PubMed

Lyu, Zhonglin; Wang, Hongwei; Wang, Yanyun; Ding, Kaiguo; Liu, Huan; Yuan, Lin; Shi, Xiujuan; Wang, Mengmeng; Wang, Yanwei; Chen, Hong

2014-06-21

Efficient control of the self-renewal and pluripotency maintenance of embryonic stem cell (ESC) is a prerequisite for translating stem cell technologies to clinical applications. Surface topography is one of the most important factors that regulates cell behaviors. In the present study, micro/nano topographical structures composed of a gold nanoparticle layer (GNPL) with nano-, sub-micro-, and microscale surface roughnesses were used to study the roles of these structures in regulating the behaviors of mouse ESCs (mESCs) under feeder-free conditions. The distinctive results from Oct-4 immunofluorescence staining and quantitative real-time polymerase chain reaction (qPCR) demonstrate that nanoscale and low sub-microscale surface roughnesses (Rq less than 392 nm) are conducive to the long-term maintenance of mESC pluripotency, while high sub-microscale and microscale surface roughnesses (Rq greater than 573 nm) result in a significant loss of mESC pluripotency and a faster undirectional differentiation, particularly in long-term culture. Moreover, the likely signalling cascades engaged in the topological sensing of mESCs were investigated and their role in affecting the maintenance of the long-term cell pluripotency was discussed by analyzing the expression of proteins related to E-cadherin mediated cell-cell adhesions and integrin-mediated focal adhesions (FAs). Additionally, the conclusions from MTT, cell morphology staining and alkaline phosphatase (ALP) activity assays show that the surface roughness can provide a potent regulatory signal for various mESC behaviors, including cell attachment, proliferation and osteoinduction.

Evaluation of parameterization for turbulent fluxes of momentum and heat in stably stratified surface layers

NASA Astrophysics Data System (ADS)

Sodemann, H.; Foken, Th.

2003-04-01

General Circulation Models calculate the energy exchange between surface and atmosphere by means of parameterisations for turbulent fluxes of momentum and heat in the surface layer. However, currently implemented parameterisations after Louis (1979) create large discrepancies between predictions and observational data, especially in stably stratified surface layers. This work evaluates a new surface layer parameterisation proposed by Zilitinkevich et al. (2002), which was specifically developed to improve energy flux predictions in stable stratification. The evaluation comprises a detailed study of important surface layer characteristics, a sensitivity study of the parameterisation, and a direct comparison to observational data from Antarctica and predictions by the Louis (1979) parameterisation. The stability structure of the stable surface layer was found to be very complex, and strongly influenced fluxes in the surface layer. The sensitivity study revealed that the new parameterisation depends strongly on the ratio between roughness length and roughness temperature, which were both observed to be very variable parameters. The comparison between predictions and measurements showed good agreement for momentum fluxes, but large discrepancies for heat fluxes. A stability dependent evaluation of selected data showed better agreement for the new parameterisation of Zilitinkevich et al. (2002) than for the Louis (1979) scheme. Nevertheless, this comparison underlines the need for more detailed and physically sound concepts for parameterisations of heat fluxes in stably stratified surface layers. Zilitinkevich, S. S., V. Perov and J. C. King (2002). "Near-surface turbulent fluxes in stable stratification: Calculation techniques for use in General Circulation Models." Q. J. R. Meteorol. Soc. 128(583): 1571--1587. Louis, J. F. (1979). "A Parametric Model of Vertical Eddy Fluxes in the Atmosphere." Bound.-Layer Meteor. 17(2): 187--202.

Smooth- and rough-wall boundary layer structure from high spatial range particle image velocimetry

NASA Astrophysics Data System (ADS)

Squire, D. T.; Morrill-Winter, C.; Hutchins, N.; Marusic, I.; Schultz, M. P.; Klewicki, J. C.

2016-10-01

Two particle image velocimetry arrangements are used to make true spatial comparisons between smooth- and rough-wall boundary layers at high Reynolds numbers across a very wide range of streamwise scales. Together, the arrangements resolve scales ranging from motions on the order of the Kolmogorov microscale to those longer than twice the boundary layer thickness. The rough-wall experiments were obtained above a continuous sandpaper sheet, identical to that used by Squire et al. [J. Fluid Mech. 795, 210 (2016), 10.1017/jfm.2016.196], and cover a range of friction and equivalent sand-grain roughness Reynolds numbers (12 000 ≲δ+≲ 18000, 62 ≲ks+≲104 ). The smooth-wall experiments comprise new and previously published data spanning 6500 ≲δ+≲17 000 . Flow statistics from all experiments show similar Reynolds number trends and behaviors to recent, well-resolved hot-wire anemometry measurements above the same rough surface. Comparisons, at matched δ+, between smooth- and rough-wall two-point correlation maps and two-point magnitude-squared coherence maps demonstrate that spatially the outer region of the boundary layer is the same between the two flows. This is apparently true even at wall-normal locations where the total (inner-normalized) energy differs between the smooth and rough wall. Generally, the present results provide strong support for Townsend's [The Structure of Turbulent Shear Flow (Cambridge University Press, Cambridge, 1956), Vol. 1] wall-similarity hypothesis in high Reynolds number fully rough boundary layer flows.

The influence of surface roughness and high pressure torsion on the growth of anodic titania nanotubes on pure titanium

NASA Astrophysics Data System (ADS)

Hu, Nan; Gao, Nong; Starink, Marco J.

2016-11-01

Anodic titanium dioxide nanotube (TNT) arrays have wide applications in photocatalytic, catalysis, electronics, solar cells and biomedical implants. When TNT coatings are combined with severe plastic deformation (SPD), metal processing techniques which efficiently improve the strength of metals, a new generation of biomedical implant is made possible with both improved bulk and surface properties. This work investigated the effect of processing by high pressure torsion (HPT) and different mechanical preparations on the substrate and subsequently on the morphology of TNT layers. HPT processing was applied to refine the grain size of commercially pure titanium samples and substantially improved their strength and hardness. Subsequent anodization at 30 V in 0.25 wt.% NH4F for 2 h to form TNT layers on sample surfaces prepared with different mechanical preparation methods was carried out. It appeared that the local roughness of the titanium surface on a microscopic level affected the TNT morphology more than the macroscopic surface roughness. For HPT-processed sample, the substrate has to be pre-treated by a mechanical preparation finer than 4000 grit for HPT to have a significant influence on TNTs. During the formation of TNT layers the oxide dissolution rate was increased for the ultrafine-grained microstructure formed due to HPT processing.

Effects of 6 months of aging in water on hardness and surface roughness of two microhybrid dental composites.

PubMed

de Moraes, Rafael Ratto; Marimon, José Laurindo Machado; Schneider, Luis Felipe; Sinhoreti, Mário Alexandre Coelho; Correr-Sobrinho, Lourenço; Bueno, Márcia

2008-06-01

This study assessed the effect of 6 months of aging in water on surface roughness and surface/subsurface hardness of two microhybrid resin composites. Filtek Z250 and Charisma were tested. Cylindrical specimens were obtained and stored in distilled water for 24 hours or 6 months, at 37 degrees C. For Knoop hardness evaluation, the specimens were transversely wet-flattened, and indentations were made on surface and subsurface layers. Data were submitted to three-way ANOVA and Tukey's test (alpha < or = 0.05). Surface roughness baseline measurements were made at 24 hours and repeated after 6 months of storage. Data were submitted to repeated measures ANOVA and Tukey's test (alpha < or = 0.05). Surface hardness (KHN, kg/mm(2)) means (+/- standard deviation) ranged from 55 +/- 1 to 49 +/- 4 for Z250 and from 50 +/- 2 to 41 +/- 3 for Charisma, at 24 hours and 6 months, respectively. Subsurface means ranged from 58 +/- 2 to 61 +/- 3 for Z250 and from 50 +/- 1 to 54 +/- 2 for Charisma, at 24 hours and 6 months. For both composites, the aged specimens presented significantly softer surfaces (p < 0.01). For the subsurface hardness, alteration after storage was detected only for Charisma, which presented a significant rise in hardness (p < 0.01). Z250 presented significantly harder surface and subsurface layers in comparison with Charisma. Surface roughness (Ra, mum) means ranged from 0.07 +/- 0.00 to 0.07 +/- 0.01 for Z250 and from 0.06 +/- 0.01 to 0.07 +/- 0.01 for Charisma, at 24 hours and 6 months, respectively. For both composites, no significant roughness alteration was detected during the study (p= 0.386). The 6-month period of storage in water presented a significant softening effect on the surfaces of the composites, although no significant deleterious alteration was detected for the subsurface hardness. In addition, the storage period had no significant effect on the surface roughness of the materials.

Pt thermal atomic layer deposition for silicon x-ray micropore optics.

PubMed

Takeuchi, Kazuma; Ezoe, Yuichiro; Ishikawa, Kumi; Numazawa, Masaki; Terada, Masaru; Ishi, Daiki; Fujitani, Maiko; Sowa, Mark J; Ohashi, Takaya; Mitsuda, Kazuhisa

2018-04-20

We fabricated a silicon micropore optic using deep reactive ion etching and coated by Pt with atomic layer deposition (ALD). We confirmed that a metal/metal oxide bilayer of Al 2 O 3 ∼10  nm and Pt ∼20  nm was successfully deposited on the micropores whose width and depth are 20 μm and 300 μm, respectively. An increase of surface roughness of sidewalls of the micropores was observed with a transmission electron microscope and an atomic force microscope. X-ray reflectivity with an Al Kα line at 1.49 keV before and after the deposition was measured and compared to ray-tracing simulations. The surface roughness of the sidewalls was estimated to increase from 1.6±0.2  nm rms to 2.2±0.2  nm rms. This result is consistent with the microscope measurements. Post annealing of the Pt-coated optic at 1000°C for 2 h showed a sign of reduced surface roughness and better angular resolution. To reduce the surface roughness, possible methods such as the annealing after deposition and a plasma-enhanced ALD are discussed.

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.

Bacterial plaque retention on oral hard materials: effect of surface roughness, surface composition, and physisorbed polycarboxylate.

PubMed

McConnell, Marla D; Liu, Yu; Nowak, Andrew P; Pilch, Shira; Masters, James G; Composto, Russell J

2010-03-15

Bacterial adhesion to oral hard materials is dependent on various factors, for example, surface roughness and surface composition. In this study, bacteria retention on three oral hard substrates, hydroxyapatite (HAP), enamel, and polished enamel (p-enamel) were investigated. The surface morphology and roughness of the three substrates were measured by scanning probe microscopy. HAP had the roughest surface, followed by enamel and polished enamel. For each individual substrate type, the roughness was shown to increase with scan size up to 50 microm x 50 microm. For HAP and enamel, roughness decreased considerably after formation of a pellicle, while addition of polymer coating to the pellicle layer reduced roughness much less in comparison. Bacterial surface coverage was measured at 30 min, 3 h, and 24 h on both native and surface-modified substrates, which were coated with two different polycarboxylate-based polymers, Gantrez S97 and Carbopol 940. As a result, the polymer coated surfaces had reduced bacteria coverage compared with the native surfaces over all time points and substrates measured. The reduction is the combined effect of electrostatic repulsion and sequestering of Ca(2+) ions at the surface, which plays a key role in the initial adhesion of bacteria to enamel surfaces in models of plaque formation. (c) 2009 Wiley Periodicals, Inc.

Simulations of the kinematic dynamo onset of spherical Couette flows with smooth and rough boundaries.

PubMed

Finke, K; Tilgner, A

2012-07-01

We study numerically the dynamo transition of an incompressible electrically conducting fluid filling the gap between two concentric spheres. In a first series of simulations, the fluid is driven by the rotation of a smooth inner sphere through no-slip boundary conditions, whereas the outer sphere is stationary. In a second series a volume force intended to simulate a rough surface drives the fluid next to the inner sphere within a layer of thickness one-tenth of the gap width. We investigate the effect of the boundary layer thickness on the dynamo threshold in the turbulent regime. The simulations show that the boundary forcing simulating the rough surface lowers the necessary rotation rate, which may help to improve spherical dynamo experiments.

Scaling of Polymer Degradation Rate within a High-Reynolds-Number Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Elbing, Brian; Solomon, Michael; Perlin, Marc; Dowling, David; Ceccio, Steven

2009-11-01

An experiment conducted at the U.S. Navy's Large Cavitation Channel on a 12.9 m long flat-plate test model produced the first quantitative measurements of polymer molecular weight within a turbulent boundary layer. Testing was conducted at speeds to 20 m/s and downstream distance based Reynolds numbers to 220 million. These results showed that the rate of polymer degradation by scission of the polymer chains increases with increased speed, downstream distance and surface roughness. With the surface fully rough at 20 m/s there was no measureable level of drag reduction at the first measurement location (0.56 m downstream of injection). These results are scaled with the assumption that the rate of degradation is dependent on the polymer residence time in the flow and the local shear rate. A successful collapse of the data within the measurement uncertainty was achieved over a range of flow speed (6.6 to 20 m/s), surface roughness (smooth and fully rough) and downstream distance from injection (0.56 to 9.28 m).

Is fault surface roughness indicative of fault mechanisms? Observations from experimental Limestone faults

NASA Astrophysics Data System (ADS)

Sagy, A.; Tesei, T.; Collettini, C.

2016-12-01

Geometrical irregularity of contacting surfaces is a fundamental factor controlling friction and energy dissipation during sliding. We performed direct shear experiments on 20x20 cm limestone surfaces by applying constant normal load (40-200 kN) and sliding velocity 1-300 µm/s. Before shearing, the surfaces were polished with maximal measured amplitudes of less than 0.1 mm. After shear, elongated islands of shear zones are observed, characterized by grooves ploughed into the limestone surfaces and by layers of fine grain wear. These structures indicate that the contact areas during shear are scattered and occupy a limited portion of the entire surface area. The surfaces was scanned by a laser profilometer that measures topography using 640 parallel beams in a single run, offer up to 10 µm accuracy and working ranges of 200 mm. Two distinctive types of topographical end members are defined: rough wavy sections and smooth polished ones. The rough zones display ridges with typical amplitudes of 0.1-1 mm that cross the grooves perpendicular to the slip direction. These features are associated with penetrative brittle damage and with fragmentation. The smoother zones display reflective mirror-like surfaces bordered by topographical sharp steps at heights of 0.3-0.5 mm. These sections are localized inside the wear layer or between the wear layer and the host rock, and are not associated with observed penetrative damage. Preliminary statistical analysis suggests that the roughness of the ridges zones can be characterized using a power-low relationship between profile length and mean roughness, with relatively high values of Hurst exponents (e.g. H > 0.65) parallel to the slip direction. The polished zones, on the other hand, corresponded to lower values of Hurst exponents (e.g. H ≤ 0.6). Both structural and roughness measurements indicate that the distinctive topographic variations on the surfaces reflect competing mechanical processes which occur simultaneously during shear. The wavy ridged zone is the surface expression of penetrative cracking and fragmentation which widen the shear zone, while the smooth zones reflect localized flow and plastic deformation of the wear material. The similarity in topography of shear structures between experimental and natural faults suggests similar mechanical processes.

EM Bias-Correction for Ice Thickness and Surface Roughness Retrievals over Rough Deformed Sea Ice

NASA Astrophysics Data System (ADS)

Li, L.; Gaiser, P. W.; Allard, R.; Posey, P. G.; Hebert, D. A.; Richter-Menge, J.; Polashenski, C. M.

2016-12-01

The very rough ridge sea ice accounts for significant percentage of total ice areas and even larger percentage of total volume. The commonly used Radar altimeter 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. In situ data from multi-instrument airborne and ground campaigns were used to validate the ice thickness and surface roughness retrievals. 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 that the physically-based EMBC algorithm performs fundamentally better than the empirical algorithm over very rough deformed sea ice, suggesting that sea ice surface roughness effects can be modeled and corrected based solely on the radar return waveforms.

An integral wall model for Large Eddy Simulation (iWMLES) and applications to developing boundary layers over smooth and rough plates

NASA Astrophysics Data System (ADS)

Yang, Xiang; Sadique, Jasim; Mittal, Rajat; Meneveau, Charles

2014-11-01

A new wall model for Large-Eddy-Simulations is proposed. It is based on an integral boundary layer method that assumes a functional form for the local mean velocity profile. The method, iWMLES, evaluates required unsteady and advective terms in the vertically integrated boundary layer equations analytically. The assumed profile contains a viscous or roughness sublayer, and a logarithmic layer with an additional linear term accounting for inertial and pressure gradient effects. The iWMLES method is tested in the context of a finite difference LES code. Test cases include developing turbulent boundary layers on a smooth flat plate at various Reynolds numbers, over flat plates with unresolved roughness, and a sample application to boundary layer flow over a plate that includes resolved roughness elements. The elements are truncated cones acting as idealized barnacle-like roughness elements that often occur in biofouling of marine surfaces. Comparisons with data show that iWMLES provides accurate predictions of near-wall velocity profiles in LES while, similarly to equilibrium wall models, its cost remains independent of Reynolds number and is thus significantly lower compared to standard zonal or hybrid wall models. This work is funded by ONR Grant N00014-12-1-0582 (Dr. R. Joslin, program manager).

Influence of Roughness-Induced Slip on Colloid Transport: Experimental and Modelling Insights

NASA Astrophysics Data System (ADS)

Rasmuson, J. A.; Johnson, W. P.

2017-12-01

A limitation of classic colloid filtration theory is that it applies only to smooth surfaces, yet most natural surfaces present some degree of nano- to micro-scale roughness. A large volume of research has been dedicated to understanding the effects of roughness on particle attachment at the nano-scale since these interactions dictate field scale transport behavior. It has been previously demonstrated that roughness imposes a finite slip vector at the surface that causes particles to experience higher near-surface velocities than would be expected over a smooth surface. Slip near a rough surface can affect two primary mechanisms of particle attenuation: 1) interception of the surface (finding a landing spot) and 2) arrest on the surface (sticking the landing). However, a clear designation on how slip affects particle transport near rough surfaces is missing. The goal of this study was to provide a guide for the height of the slip layer and contact surface in reference to the mean-plane for rough surfaces. Direct observation was used to measure near-surface velocities of particles translating near surfaces of varying roughness spanning three orders of magnitude. The influence of roughness on particle transport was investigated using computational fluid dynamics (CFD) modeling with rough surfaces measured with atomic force microscopy (AFM). The CFD and experimental results were used to calibrate a Lagrangian particle transport model that utilizes simple modifications to the flow field for a smooth surface using statistically based roughness parameters. Advantages of the Lagrangian model are significantly decreased computation times and applicability to a wide range of natural surfaces without explicitly simulating individual asperities. The results suggest that the no-slip boundary should be placed at the bottom of the maximum asperity valleys, and that the contact surface should be placed at the root mean square (RMS) roughness above the mean plane. Collector surfaces with the greatest RMS roughness had the highest sensitivity to the placement of the contact surface. These findings highlight the need for accurate and representative AFM measurements and have important implications for future transport models.

The frictional properties of a simulated gouge having a fractal particle distribution

USGS Publications Warehouse

Biegel, R.L.; Sammis, C.G.; Dieterich, J.H.

1989-01-01

The frictional properties of a layer of simulated Westerly granite fault gouge sandwiched between sliding blocks of Westerly granite have been measured in a high-speed servo-controlled double-direct shear apparatus. Most gouge layers were prepared to have a self-similar particle distribution with a fractal dimension of 2.6. The upper fractal limit was varied between 45 and 710 ??m. Some gouges were prepared with all particles in the range between 360 and 710 ??m. In each experiment the sliding velocity was cyclically alternated between 1 and 10 ??ms-1 and the coefficient of friction ??m and its transient parameters a, b and Dc were measured as functions of displacement. In addition to the particle size distribution, the following experimental variables were also investigated: the layer thickness (1 and 3 mm), the roughness of the sliding surfaces (Nos 60 and 600 grit) and the normal stress (10 and 25 MPa). Some of the sample assemblies were epoxy impregnated following a run so the gouge structure could be microscopically examined in thin section. We observed that gouges which were initially non-fractal evolved to a fractal distribution with dimension 2.6. Gouges which had an initial fractal distribution remained fractal. When the sliding blocks had smooth surfaces, the coefficient of friction was relatively low and was independent of the particle distribution. In these cases, strong velocity weakening was observed throughout the experiment and the transient parameters a, b and Dc, remained almost constant. When the sliding blocks had rough surfaces, the coefficient of friction was larger and more dependent on the particle distribution. Velocity strengthening was observed initially but evolved to velocity weakening with increased sliding displacement. All three transient parameters changed with increasing displacement. The a and b values were about three times as large for rough surfaces as for smooth. The characteristic displacement Dc was not sensitive to surface roughness but was the only transient parameter which was sensitive to the normal stress. For the case of rough surfaces, the coefficient of friction of the 1 mm thick gouge was significantly larger than that for the 3 mm thick layers. Many of these observations can be explained by a micromechanical model in which the stress in the gouge layer is heterogeneous. The applied normal and shear stresses are supported by 'grain bridges' which span the layer and which are continually forming and failing. In this model, the frictional properties of the gouge are largely determined by the dominant failure mode of the bridging structures. ?? 1989.

Elastic wave generated by granular impact on rough and erodible surfaces

NASA Astrophysics Data System (ADS)

Bachelet, Vincent; Mangeney, Anne; de Rosny, Julien; Toussaint, Renaud; Farin, Maxime

2018-01-01

The elastic waves generated by impactors hitting rough and erodible surfaces are studied. For this purpose, beads of variable materials, diameters, and velocities are dropped on (i) a smooth PMMA plate, (ii) stuck glass beads on the PMMA plate to create roughness, and (iii) the rough plate covered with layers of free particles to investigate erodible beds. The Hertz model validity to describe impacts on a smooth surface is confirmed. For rough and erodible surfaces, an empirical scaling law that relates the elastic energy to the radius Rb and normal velocity Vz of the impactor is deduced from experimental data. In addition, the radiated elastic energy is found to decrease exponentially with respect to the bed thickness. Lastly, we show that the variability of the elastic energy among shocks increases from some percents to 70% between smooth and erodible surfaces. This work is a first step to better quantify seismic emissions of rock impacts in natural environment, in particular on unconsolidated soils.

Food-safe modification of stainless steel food processing surfaces to reduce bacterial biofilms.

PubMed

Awad, Tarek Samir; Asker, Dalal; Hatton, Benjamin D

2018-06-11

Biofilm formation on stainless steel (SS) surfaces of food processing plants, leading to foodborne illness outbreaks, is enabled by the attachment and confinement within microscale cavities of surface roughness (grooves, scratches). We report Foodsafe Oil-based Slippery Coatings (FOSCs) for food processing surfaces that suppress bacterial adherence and biofilm formation by trapping residual oil lubricant within these surface cavities to block microbial growth. SS surfaces were chemically functionalized with alkylphosphonic acid to preferentially wet a layer of food grade oil. FOSCs reduced the effective surface roughness, the adhesion of organic food residue, and bacteria. FOSCs significantly reduced Pseudomonas aeruginosa biofilm formation on standard roughness SS-316 by 5 log CFU cm-2, and by 3 log CFU cm-2 for mirror-finished SS. FOSCs also enhanced surface cleanability, which we measured by bacterial counts after conventional detergent cleaning. Importantly, both SS grades maintained their anti-biofilm activity after erosion of the oil layer by surface wear with glass beads, which suggests there is a residual volume of oil that remains to block surface cavity defects. These results indicate the potential of such low-cost, scalable approaches to enhance the cleanability of SS food processing surfaces and improve food safety by reducing biofilm growth.

Turbulent Flow over Rough Turbine Airfoils.

DTIC Science & Technology

1985-08-01

SUBJECT TERMS (Continue on reverse if necessary and identify by block number) FIELD GROUP SUB. GR. Turbine blades ’ vanes ; surface roughness...turbulent boundary layer over rough turbine vanes or blades is developed. A new formulation of the mixing length model, expressed in the velocity-space...A-163 005 TURBULENT FLOW OVER ROUGH TURBINE AIRFOILS (U) OHIO 1/ STATE UNIV RESEARCH FOUNDATION COLUMBUS L S HAN AUG B5 OSURF-76357/?i4467 AFWL-TR-95

Bioinspired, roughness-induced, water and oil super-philic and super-phobic coatings prepared by adaptable layer-by-layer technique

PubMed Central

Brown, Philip S.; Bhushan, Bharat

2015-01-01

Coatings with specific surface wetting properties are of interest for anti-fouling, anti-fogging, anti-icing, self-cleaning, anti-smudge, and oil-water separation applications. Many previous bioinspired surfaces are of limited use due to a lack of mechanical durability. Here, a layer-by-layer technique is utilized to create coatings with four combinations of water and oil repellency and affinity. An adapted layer-by-layer approach is tailored to yield specific surface properties, resulting in a durable, functional coating. This technique provides necessary flexibility to improve substrate adhesion combined with desirable surface chemistry. Polyelectrolyte binder, SiO2 nanoparticles, and silane or fluorosurfactant layers are deposited, combining surface roughness and necessary chemistry to result in four different coatings: superhydrophilic/superoleophilic, superhydrophobic/superoleophilic, superhydrophobic/superoleophobic, and superhydrophilic/superoleophobic. The superoleophobic coatings display hexadecane contact angles >150° with tilt angles <5°, whilst the superhydrophobic coatings display water contact angles >160° with tilt angles <2°. One coating combines both oleophobic and hydrophobic properties, whilst others mix and match oil and water repellency and affinity. Coating durability was examined through the use of micro/macrowear experiments. These coatings display transparency acceptable for some applications. Fabrication via this novel combination of techniques results in durable, functional coatings displaying improved performance compared to existing work where either durability or functionality is compromised. PMID:26353971

Effect of substrate nitridation temperature on the persistent photoconductivity of unintentionally-doped GaN layer grown by PAMBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prakash, Nisha, E-mail: prakasnisha@gmail.com; Barvat, Arun; Anand, Kritika

2016-05-23

The surface roughness and defect density of GaN epitaxial layers grown on c-plane sapphire substrate are investigated and found to be dependent on nitridation temperature. GaN epitaxial layers grown after nitridation of sapphire at 200°C have a higher defect density and higher surface roughness compared to the GaN layers grown at 646°C nitridation as confirmed by atomic force microscopy (AFM). The persistent photoconductivity (PPC) was observed in both samples and it was found to be decreasing with decreasing temperature in the range 150-300°C due to long carrier lifetime and high electron mobility at low temperature. The photoresponse of the GaNmore » films grown in this study exhibit improved PPC due to their better surface morphology at 646°C nitrided sample. The point defects or extended microstructure defects limits the photocarrier lifetime and electron mobility at 200°C nitrided sample.« less

An experimental investigation of silicon wafer surface roughness and its effect on the full strength of plated metals

NASA Technical Reports Server (NTRS)

Spiers, G. D.

1981-01-01

Plated silicon wafers with surface roughness ranging from 0.4 to 130 microinches were subjected to tensile pull strength tests. Electroless Ni/electroless Cu/electroplated Cu and electroless Ni/electroplated Cu were the two types of plate contacts tested. It was found that smoother surfaces had higher pull strength than rougher, chemically etched surfaces. The presence of the electroless Cu layer was found to be important to adhesion. The mode of fracture of the contact as it left the silicon was studied, and it was found that in almost all cases separation was due to fracture of the bulk silicon phase. The correlation between surface roughness and mode of contact failure is presented and interpreted.

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.

Superposition of polarized waves at layered media: theoretical modeling and measurement

NASA Astrophysics Data System (ADS)

Finkele, Rolf; Wanielik, Gerd

1997-12-01

The detection of ice layers on road surfaces is a crucial requirement for a system that is designed to warn vehicle drivers of hazardous road conditions. In the millimeter wave regime at 76 GHz the dielectric constant of ice and conventional road surface materials (i.e. asphalt, concrete) is found to be nearly similar. Thus, if the layer of ice is very thin and thus is of the same shape of roughness as the underlying road surface it cannot be securely detected using conventional algorithmic approaches. The method introduced in this paper extents and applies the theoretical work of Pancharatnam on the superposition of polarized waves. The projection of the Stokes vectors onto the Poincare sphere traces a circle due to the variation of the thickness of the ice layer. The paper presents a method that utilizes the concept of wave superposition to detect this trace even if it is corrupted by stochastic variation due to rough surface scattering. Measurement results taken under real traffic conditions prove the validity of the proposed algorithms. Classification results are presented and the results discussed.

Effects of Surface Roughness and Mechanical Properties of Cover-Layer on Near-Field Optical Recording

NASA Astrophysics Data System (ADS)

Kim, Jin-Hong; Lee, Jun-Seok; Lim, Jungshik; Seo, Jung-Kyo

2009-03-01

Narrow gap distance in cover-layer incident near-field recording (NFR) configuration causes a collision problem in the interface between a solid immersion lens and a disk surface. A polymer cover-layer with smooth surface results in a stable gap servo while a nanocomposite cover-layer with high refractive index shows a collision problem during the gap servo test. Even though a dielectric cover-layer, in which the surface is rougher than the polymer, supplements the mechanical properties, an unclear eye pattern due to an unstable gap servo can be obtained after a chemical mechanical polishing. Not only smooth surface but also good mechanical properties of cover-layer are required for the stable gap servo in the NFR.

Fast method to compute scattering by a buried object under a randomly rough surface: PILE combined with FB-SA.

PubMed

Bourlier, Christophe; Kubické, Gildas; Déchamps, Nicolas

2008-04-01

A fast, exact numerical method based on the method of moments (MM) is developed to calculate the scattering from an object below a randomly rough surface. Déchamps et al. [J. Opt. Soc. Am. A23, 359 (2006)] have recently developed the PILE (propagation-inside-layer expansion) method for a stack of two one-dimensional rough interfaces separating homogeneous media. From the inversion of the impedance matrix by block (in which two impedance matrices of each interface and two coupling matrices are involved), this method allows one to calculate separately and exactly the multiple-scattering contributions inside the layer in which the inverses of the impedance matrices of each interface are involved. Our purpose here is to apply this method for an object below a rough surface. In addition, to invert a matrix of large size, the forward-backward spectral acceleration (FB-SA) approach of complexity O(N) (N is the number of unknowns on the interface) proposed by Chou and Johnson [Radio Sci.33, 1277 (1998)] is applied. The new method, PILE combined with FB-SA, is tested on perfectly conducting circular and elliptic cylinders located below a dielectric rough interface obeying a Gaussian process with Gaussian and exponential height autocorrelation functions.

Effects of roughness height, pressure and streamwise distance on stress profiles in the inner part of turbulent boundary layer over super-hydrophobic surfaces

NASA Astrophysics Data System (ADS)

Ling, Hangjian; Katz, Joseph; Srinivasan, Siddarth; McKinley, Gareth; Golovin, Kevin; Tuteja, Anish; Pillutla, Venkata; Abhijeet, Abhijeet; Choi, Wonjae

2016-11-01

Digital holographic microscopy is used for measuring the mean velocity and stress in the inner part of turbulent boundary layers over sprayed or etched super-hydrophobic surfaces (SHSs). The slip velocity and wall friction are calculated directly from the mean velocity and its gradient along with the Reynolds shear stress at the top of SHSs "roughness". Effects of the normalized rms roughness height krms+, facility pressure p and streamwise distance x from the beginning of SHSs on mean flow are examined. For krms+<1 and pkrms / σ <1 (σ is surface tension), the SHSs show 10-28% wall friction reduction, 15-30% slip velocity and λ+ = 3-10 slip length. Increasing Reynolds number and/or krms to establish krms+>1, and increasing p to achieve pkrms / σ >1 suppress the drag reduction, as roughness effects and associated near wall Reynolds stress increase. When the roughness effect is not dominant, the measurements agree with previous theoretical predictions of the relationships between drag reduction and slip velocity. The significance of spanwise slip relative to streamwise slip varies with the SHSs texture. Transitions from a smooth wall to a SHS involve overshoot of Reynolds stress and undershoot of viscous stress, trends that diminish with x. Sponsored by ONR.

Correlation between substratum roughness and wettability, cell adhesion, and cell migration.

PubMed

Lampin, M; Warocquier-Clérout; Legris, C; Degrange, M; Sigot-Luizard, M F

1997-07-01

Cell adhesion and spreading of chick embryo vascular and corneal explants grown on rough and smooth poly (methyl methacrylate) (PMMA) were analyzed to test the cell response specificity to substratum surface properties. Different degrees of roughness were obtained by sand-blasting PMMA with alumina grains. Hydrophilic and hydrophobic components of the surface free energy (SFE) were calculated according to Good-van Oss's model. Contact angles were determined using a computerized angle meter. The apolar component of the SFE gamma s(LW), increased with a slight roughness whereas the basic component, gamma s-, decreased. The acido-basic properties disappeared as roughness increased. Incubation of PMMA in culture medium, performed to test the influence if the biological environment, allowed surface adsorption of medium proteins which annihilated roughness effect and restored hydrophilic properties. An organotypic culture assay was carried out in an attempt to relate the biocompatibility to substratum surface state. Cell migration was calculated from the area of cell layer. Cellular adhesion was determined by measuring the kinetic of release of enzymatically dissociated cells. A slight roughness raised the migration are to an upper extent no matter which cell type. Enhancement of the cell adhesion potential was related to the degree of roughness and the hydrophobicity.

Micro arc oxidized HAp-TiO 2 nanostructured hybrid layers-part I: Effect of voltage and growth time

NASA Astrophysics Data System (ADS)

Abbasi, S.; Bayati, M. R.; Golestani-Fard, F.; Rezaei, H. R.; Zargar, H. R.; Samanipour, F.; Shoaei-Rad, V.

2011-05-01

Micro arc oxidation was employed to grow hydroxyapatite-TiO 2 nanostructured porous composite layers. The layers were synthesized on the titanium substrates in the electrolytes consisting of calcium acetate and sodium β-glycerophosphate salts under different applied voltages for various times. SEM and AFM investigations revealed a porous structure and rough surface where the pores size and the surface roughness were respectively determined as 70-650 nm and 9.8-12.7 nm depending on the voltage and time. Chemical composition and phase structure of the layers were evaluated using EDX, XPS, and XRD methods. The layers consisted of the hydroxyapatite, anatase, α-TCP, and calcium titanatephases with a varying fraction depending on the growth conditions. The hydroxyapatite crystalline size was also determined as ˜42 nm. The sample fabricated under the voltage of 350 V for 3 min exhibited the most appropriate Ca/P ratio (˜1.60) as well as the highest amount of the hydroxyapatite phase. This sample had a fine surface morphology and a high pores density.

The quantitative analysis of silicon carbide surface smoothing by Ar and Xe cluster ions

NASA Astrophysics Data System (ADS)

Ieshkin, A. E.; Kireev, D. S.; Ermakov, Yu. A.; Trifonov, A. S.; Presnov, D. E.; Garshev, A. V.; Anufriev, Yu. V.; Prokhorova, I. G.; Krupenin, V. A.; Chernysh, V. S.

2018-04-01

The gas cluster ion beam technique was used for the silicon carbide crystal surface smoothing. The effect of processing by two inert cluster ions, argon and xenon, was quantitatively compared. While argon is a standard element for GCIB, results for xenon clusters were not reported yet. Scanning probe microscopy and high resolution transmission electron microscopy techniques were used for the analysis of the surface roughness and surface crystal layer quality. The gas cluster ion beam processing results in surface relief smoothing down to average roughness about 1 nm for both elements. It was shown that xenon as the working gas is more effective: sputtering rate for xenon clusters is 2.5 times higher than for argon at the same beam energy. High resolution transmission electron microscopy analysis of the surface defect layer gives values of 7 ± 2 nm and 8 ± 2 nm for treatment with argon and xenon clusters.

Study of the blue-green laser scattering from the rough sea surface with foams by the improved two-scale method

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.

High Stability Pentacene Transistors Using Polymeric Dielectric Surface Modifier.

PubMed

Wang, Xiaohong; Lin, Guangqing; Li, Peng; Lv, Guoqiang; Qiu, Longzhen; Ding, Yunsheng

2015-08-01

1,6-bis(trichlorosilyl)hexane (C6Cl), polystyrene (PS), and cross-linked polystyrene (CPS) were investigated as gate dielectric modified layers for high performance organic transistors. The influence of the surface energy, roughness and morphology on the charge transport of the organic thin-film transistors (OTFTs) was investigated. The surface energy and roughness both affect the grain size of the pentacene films which will control the charge carrier mobility of the devices. Pentacene thin-film transistors fabricated on the CPS modified dielectric layers exhibited charge carrier mobility as high as 1.11 cm2 V-1 s-1. The bias stress stability for the CPS devices shows that the drain current only decays 1% after 1530 s and the mobility never decreases until 13530 s.

Surface roughness of Saturn's rings and ring particles inferred from thermal phase curves

NASA Astrophysics Data System (ADS)

Morishima, Ryuji; Turner, Neal; Spilker, Linda

2017-10-01

We analyze thermal phase curves of all the main rings of Saturn (the A, B, C rings, and the Cassini division) measured by both the far-IR and mid-IR detectors of the Cassini Composite InfraRed Spectrometer (CIRS). All the rings show temperature increases toward zero phase angle, known as an opposition effect or thermal beaming. For the C ring and Cassini division, which have low optical depths, intra-particle shadowing is considered the dominant mechanism causing the effect. On the other hand, the phase curves of the optically thick B and A rings steepen significantly with decreasing absolute solar elevation angle from 21° to 14°, suggesting inter-particle shadowing plays an important role in these rings. We employ an analytic roughness model to estimate the degrees of surface roughness of the rings or ring particles. For optically thin rings, an isolated particle covered by spherical segment craters is employed while for the thick rings we approximate a packed particle layer as a slab covered by craters. The particles in the thin rings are found to have generally rough surfaces, except in the middle C ring. Across the C ring, the optical depth correlates with the degree of surface roughness. This may indicate that surface roughness comes mainly from particle clumping, while individual particles have rather smooth surfaces. For the optically thick rings, the surface roughness of the particle layer is found to be moderate. The modeled phase curves of optically thick rings are shallow if the phase angle change is primarily due to change of observer azimuthal angle. On the other hand, the phase curves are steep if the phase angle change is due to change of observer elevation angle, as inter-particle shadows become visible at higher observer elevation. In addition, the area of shadowed facets increases with decreasing solar elevation angle. These combined effects explain the large seasonal change of the phase curve steepness observed for the thick rings. The degrees of surface roughness inferred from the thermal phase curves are generally less than those from the phase curves in visible light. This is probably explained by different roughness scales seen in thermal and visible light or by dilution of thermal phase curve steepnesses due to particle motion.

Scattering Models and Basic Experiments in the Microwave Regime

NASA Technical Reports Server (NTRS)

Fung, A. K.; Blanchard, A. J. (Principal Investigator)

1985-01-01

The objectives of research over the next three years are: (1) to develop a randomly rough surface scattering model which is applicable over the entire frequency band; (2) to develop a computer simulation method and algorithm to simulate scattering from known randomly rough surfaces, Z(x,y); (3) to design and perform laboratory experiments to study geometric and physical target parameters of an inhomogeneous layer; (4) to develop scattering models for an inhomogeneous layer which accounts for near field interaction and multiple scattering in both the coherent and the incoherent scattering components; and (5) a comparison between theoretical models and measurements or numerical simulation.

SHARAD soundings and surface roughness at past, present, and proposed landing sites on Mars: Reflections at Phoenix may be attributable to deep ground ice

NASA Astrophysics Data System (ADS)

Putzig, Nathaniel E.; Phillips, Roger J.; Campbell, Bruce A.; Mellon, Michael T.; Holt, John W.; Brothers, T. Charles

2014-08-01

We use the Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter to search for subsurface interfaces and characterize surface roughness at the landing sites of Viking Landers 1 and 2, Mars Pathfinder, the Mars Exploration Rovers Spirit and Opportunity, the Phoenix Mars lander, the Mars Science Laboratory Curiosity rover, and three other sites proposed for Curiosity. Only at the Phoenix site do we find clear evidence of subsurface radar returns, mapping out an interface that may be the base of ground ice at depths of ~15-66 m across 2900 km2 in the depression where the lander resides. At the Opportunity, Spirit, and candidate Curiosity sites, images and altimetry show layered materials tens to hundreds of meters thick extending tens to hundreds of kilometers laterally. These scales are well within SHARAD's resolution limits, so the lack of detections is attributable either to low density contrasts in layers of similar composition and internal structure or to signal attenuation within the shallowest layers. At each site, we use the radar return power to estimate surface roughness at scales of 10-100 m, a measure that is important for assessing physical properties, landing safety, and site trafficability. The strongest returns are found at the Opportunity site, indicating that Meridiani Planum is exceptionally smooth. Returns of moderate strength at the Spirit site reflect roughness more typical of Mars. Gale crater, Curiosity's ultimate destination, is the smoothest of the four proposed sites we examined, with Holden crater, Eberswalde crater, and Mawrth Vallis exhibiting progressively greater roughness.

Deposition of gold nano-particles and nano-layers on polyethylene modified by plasma discharge and chemical treatment

NASA Astrophysics Data System (ADS)

Švorčík, V.; Chaloupka, A.; Záruba, K.; Král, V.; Bláhová, O.; Macková, A.; Hnatowicz, V.

2009-08-01

Polyethylene (PE) was treated in Ar plasma discharge and then grafted from methanol solution of 1,2-ethanedithiol to enhance adhesion of gold nano-particles or sputtered gold layers. The modified PE samples were either immersed into freshly prepared colloid solution of Au nano-particles or covered by sputtered, 50 nm thick gold nano-layer. Properties of the plasma modified, dithiol grafted and gold coated PE were studied using XPS, UV-VIS, AFM, EPR, RBS methods and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain, creation of excessive free radicals and conjugated double bonds. After grafting with 1,2-ethanedithiol the concentration of free radicals declined but the concentration of double bonds remained unchanged. Plasma treatment changes PE surface morphology and increases surface roughness too. Another significant change in the surface morphology and roughness was observed after deposition of Au nano-particles. The presence of Au on the sample surface after the coating with Au nano-particles was proved by XPS and RBS methods. Nanoindentation measurements shown that the grafting of plasma activated PE surface with dithiol increases significantly adhesion of sputtered Au nano-layer.

Surface scaling analysis of textured MgO thin films fabricated by energetic particle self-assisted deposition

NASA Astrophysics Data System (ADS)

Feng, Feng; Zhang, Xiangsong; Qu, Timing; Liu, Binbin; Huang, Junlong; Li, Jun; Xiao, Shaozhu; Han, Zhenghe; Feng, Pingfa

2018-04-01

In the fabrication of a high-temperature superconducting coated conductor, the surface roughness and texture of buffer layers can significantly affect the epitaxially grown superconductor layer. A biaxially textured MgO buffer layer fabricated by ion beam assisted deposition (IBAD) is widely used in the coated conductor manufacture due to its low thickness requirement. In our previous study, a new method called energetic particle self-assisted deposition (EPSAD), which employed only a sputtering deposition apparatus without an ion source, was proposed for fabricating biaxially textured MgO films on non-textured substrates. In this study, our aim was to investigate the deposition mechanism of EPSAD-MgO thin films. The behavior of the surface roughness (evaluated by Rq) was studied using atomic force microscopy (AFM) measurements with three scan scales, while the in-plane and out-of-plane textures were measured using X-ray diffraction (XRD). It was found that the variations of surface roughness and textures along with the increase in the thickness of EPSAD-MgO samples were very similar to those of IBAD-MgO reported in the literature, revealing the similarity of their deposition mechanisms. Moreover, fractal geometry was utilized to conduct the scaling analysis of EPSAD-MgO film's surface. Different scaling behaviors were found in two scale ranges, and the indications of the fractal properties in different scale ranges were discussed.

Examination of Surface Roughness on Light Scattering by Long Ice Columns by Use of a Two-Dimensional Finite-Difference Time-Domain Algorithm

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.

Soft X-ray multilayers produced by sputtering and molecular beam epitaxy (MBE) - Substrate and interfacial roughness

NASA Astrophysics Data System (ADS)

Kearney, Patrick A.; Slaughter, J. M.; Powers, K. D.; Falco, Charles M.

1988-01-01

Roughness measurements were made on uncoated silicon wafers and float glass using a WYKO TOPO-3D phase shifting interferometry, and the results are reported. The wafers are found to be slightly smoother than the flat glass. The effects of different cleaning methods and of the deposition of silicon 'buffer layers' on substrate roughness are examined. An acid cleaning method is described which gives more consistent results than detergent cleaning. Healing of the roughness due to sputtered silicon buffer layers was not observed on the length scale probed by the WYKO. Sputtered multilayers are characterized using both the WYKO interferometer and low-angle X-ray diffraction in order to yield information about the roughness of the top surface and of the multilayer interfaces. Preliminary results on film growth using molecular beam epitaxy are also presented.

Manufacturing polymer light emitting diode with high luminance efficiency by solution process

NASA Astrophysics Data System (ADS)

Kim, Miyoung; Jo, SongJin; Yang, Ho Chang; Yoon, Dang Mo; Kwon, Jae-Taek; Lee, Seung-Hyun; Choi, Ju Hwan; Lee, Bum-Joo; Shin, Jin-Koog

2012-06-01

While investigating polymer light emitting diodes (polymer-LEDs) fabricated by solution process, surface roughness influences electro-optical (E-O) characteristics. We expect that E-O characteristics such as luminance and power efficiency related to surface roughness and layer thickness of emitting layer with poly-9-Vinylcarbazole. In this study, we fabricated polymer organic light emitting diodes by solution process which guarantees easy, eco-friendly and low cost manufacturing for flexible display applications. In order to obtain high luminescence efficiency, E-O characteristics of these devices by varying parameters for printing process have been investigated. Therefore, we optimized process condition for polymer-LEDs by adjusting annealing temperatures of emission, thickness of emission layer showing efficiency (10.8 cd/A) at 10 mA/cm2. We also checked wavelength dependent electroluminescence spectrum in order to find the correlation between the variation of efficiency and the thickness of the layer.

Dust Devils on Mars: Effects of Surface Roughness on Particle Threshold

NASA Technical Reports Server (NTRS)

Neakrase, Lynn D.; Greeley, Ronald; Iversen, James D.; Balme, Matthew L.; Foley, Daniel J.; Eddlemon, Eric E.

2005-01-01

Dust devils have been proposed as effective mechanisms for lofting large quantities of dust into the martian atmosphere. Previous work showed that vortices lift dust more easily than simple boundary layer winds. The aim of this study is to determine experimentally the effects of non-erodable roughness elements on vortex particle threshold through laboratory simulations of natural surfaces. Additional information is included in the original extended abstract.

Influence of Cutting Parameters and Tool Wear on the Surface Integrity of Cobalt-Based Stellite 6 Alloy When Machined Under a Dry Cutting Environment

NASA Astrophysics Data System (ADS)

Yingfei, Ge; de Escalona, Patricia Muñoz; Galloway, Alexander

2017-01-01

The efficiency of a machining process can be measured by evaluating the quality of the machined surface and the tool wear rate. The research reported herein is mainly focused on the effect of cutting parameters and tool wear on the machined surface defects, surface roughness, deformation layer and residual stresses when dry milling Stellite 6, deposited by overlay on a carbon steel surface. The results showed that under the selected cutting conditions, abrasion, diffusion, peeling, chipping and breakage were the main tool wear mechanisms presented. Also the feed rate was the primary factor affecting the tool wear with an influence of 83%. With regard to the influence of cutting parameters on the surface roughness, the primary factors were feed rate and cutting speed with 57 and 38%, respectively. In addition, in general, as tool wear increased, the surface roughness increased and the deformation layer was found to be influenced more by the cutting parameters rather than the tool wear. Compressive residual stresses were observed in the un-machined surface, and when machining longer than 5 min, residual stress changed 100% from compression to tension. Finally, results showed that micro-crack initiation was the main mechanism for chip formation.

Error in Radar-Derived Soil Moisture due to Roughness Parameterization: An Analysis Based on Synthetical Surface Profiles

PubMed Central

Lievens, Hans; Vernieuwe, Hilde; Álvarez-Mozos, Jesús; De Baets, Bernard; Verhoest, Niko E.C.

2009-01-01

In the past decades, many studies on soil moisture retrieval from SAR demonstrated a poor correlation between the top layer soil moisture content and observed backscatter coefficients, which mainly has been attributed to difficulties involved in the parameterization of surface roughness. The present paper describes a theoretical study, performed on synthetical surface profiles, which investigates how errors on roughness parameters are introduced by standard measurement techniques, and how they will propagate through the commonly used Integral Equation Model (IEM) into a corresponding soil moisture retrieval error for some of the currently most used SAR configurations. Key aspects influencing the error on the roughness parameterization and consequently on soil moisture retrieval are: the length of the surface profile, the number of profile measurements, the horizontal and vertical accuracy of profile measurements and the removal of trends along profiles. Moreover, it is found that soil moisture retrieval with C-band configuration generally is less sensitive to inaccuracies in roughness parameterization than retrieval with L-band configuration. PMID:22399956

Comparison of different types of phacoemulsification tips. I. Quantitative analysis of elemental composition and tip surface microroughness.

PubMed

Tsaousis, Konstantinos T; Werner, Liliana; Perez, Jesus Paulo; Li, He J; Reiter, Nicholas; Guan, Jia J; Mamalis, Nick

2016-09-01

To evaluate the elemental composition of phacoemulsification tips and their surface roughness in the microscale. John A. Moran Eye Center and Utah Nanofab, College of Engineering, University of Utah, Salt Lake City, Utah, USA. Experimental study. Seven types of phacoemulsification tips were studied. The phaco tips were examined through energy-dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS) for elemental composition. In addition, the roughness of the opening in all tips was assessed through 3-dimensional white-light interferometry. Elemental analysis showed considerable differences in the surface layers between manufacturers. Alcon tips had a thinner oxidized titanium (Ti) layer in their surface. Through XPS, vanadium was not detected in the superficial layers of any tip, but only in deeper levels. The microroughness surface analysis showed comparable results regarding their root-mean-square (RMS) metric. Maximum peak valley distance values varied and appeared to be dependent on the quality of material process rather than the material itself. Phacoemulsification tips are made of Ti alloys and showed differences between models, especially regarding their composition in the superficial layers. Their opening end roughness showed an overall appropriate RMS value of less than 1.0 μm in all cases. The existence of small defected areas highlights the importance of adequate quality control of these critical surgical instruments. None of the authors has a financial or proprietary interest in any material or method mentioned. Copyright © 2016 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

On predicting receptivity to surface roughness in a compressible infinite swept wing boundary layer

NASA Astrophysics Data System (ADS)

Thomas, Christian; Mughal, Shahid; Ashworth, Richard

2017-03-01

The receptivity of crossflow disturbances on an infinite swept wing is investigated using solutions of the adjoint linearised Navier-Stokes equations. The adjoint based method for predicting the magnitude of stationary disturbances generated by randomly distributed surface roughness is described, with the analysis extended to include both surface curvature and compressible flow effects. Receptivity is predicted for a broad spectrum of spanwise wavenumbers, variable freestream Reynolds numbers, and subsonic Mach numbers. Curvature is found to play a significant role in the receptivity calculations, while compressible flow effects are only found to marginally affect the initial size of the crossflow instability. A Monte Carlo type analysis is undertaken to establish the mean amplitude and variance of crossflow disturbances generated by the randomly distributed surface roughness. Mean amplitudes are determined for a range of flow parameters that are maximised for roughness distributions containing a broad spectrum of roughness wavelengths, including those that are most effective in generating stationary crossflow disturbances. A control mechanism is then developed where the short scale roughness wavelengths are damped, leading to significant reductions in the receptivity amplitude.

Surface roughness mediated adhesion forces between borosilicate glass and gram-positive bacteria.

PubMed

Preedy, Emily; Perni, Stefano; Nipiĉ, Damijan; Bohinc, Klemen; Prokopovich, Polina

2014-08-12

It is well-known that a number of surface characteristics affect the extent of adhesion between two adjacent materials. One of such parameters is the surface roughness as surface asperities at the nanoscale level govern the overall adhesive forces. For example, the extent of bacterial adhesion is determined by the surface topography; also, once a bacteria colonizes a surface, proliferation of that species will take place and a biofilm may form, increasing the resistance of bacterial cells to removal. In this study, borosilicate glass was employed with varying surface roughness and coated with bovine serum albumin (BSA) in order to replicate the protein layer that covers orthopedic devices on implantation. As roughness is a scale-dependent process, relevant scan areas were analyzed using atomic force microscope (AFM) to determine Ra; furthermore, appropriate bacterial species were attached to the tip to measure the adhesion forces between cells and substrates. The bacterial species chosen (Staphylococci and Streptococci) are common pathogens associated with a number of implant related infections that are detrimental to the biomedical devices and patients. Correlation between adhesion forces and surface roughness (Ra) was generally better when the surface roughness was measured through scanned areas with size (2 × 2 μm) comparable to bacteria cells. Furthermore, the BSA coating altered the surface roughness without correlation with the initial values of such parameter; therefore, better correlations were found between adhesion forces and BSA-coated surfaces when actual surface roughness was used instead of the initial (nominal) values. It was also found that BSA induced a more hydrophilic and electron donor characteristic to the surfaces; in agreement with increasing adhesion forces of hydrophilic bacteria (as determined through microbial adhesion to solvents test) on BSA-coated substrates.

Helicopter rotor noise investigation during ice accretion

NASA Astrophysics Data System (ADS)

Cheng, Baofeng

An investigation of helicopter rotor noise during ice accretion is conducted using experimental, theoretical, and numerical methods. This research is the acoustic part of a joint helicopter rotor icing physics, modeling, and detection project at The Pennsylvania State University Vertical Lift Research Center of Excellence (VLRCOE). The current research aims to provide acoustic insight and understanding of the rotor icing physics and investigate the feasibility of detecting rotor icing through noise measurements, especially at the early stage of ice accretion. All helicopter main rotor noise source mechanisms and their change during ice accretion are discussed. Changes of the thickness noise, steady loading noise, and especially the turbulent boundary layer - trailing edge (TBL-TE) noise due to ice accretion are identified and studied. The change of the discrete frequency noise (thickness noise and steady loading noise) due to ice accretion is calculated by using PSU-WOPWOP, an advanced rotorcraft acoustic prediction code. The change is noticeable, but too small to be used in icing detection. The small thickness noise change is due to the small volume of the accreted ice compared to that of the entire blade, although a large iced airfoil shape is used. For the loading noise calculation, two simplified methods are used to generate the loading on the rotor blades, which is the input for the loading noise calculation: 1) compact loading from blade element momentum theory, icing effects are considered by increasing the drag coefficient; and 2) pressure loading from the 2-D CFD simulation, icing effects are considered by using the iced airfoil shape. Comprehensive rotor broadband noise measurements are carried out on rotor blades with different roughness sizes and rotation speeds in two facilities: the Adverse Environment Rotor Test Stand (AERTS) facility at The Pennsylvania State University, and The University of Maryland Acoustic Chamber (UMAC). In both facilities the measured high-frequency broadband noise increases significantly with increasing surface roughness heights, which indicates that it is feasible to quantify helicopter rotor ice-induced surface roughness through acoustic measurements. Comprehensive broadband noise measurements based on different accreted ice roughness at AERTS are then used to form the data base from which a correlation between the ice-induced surface roughness and the broadband noise level is developed. Two parameters, the arithmetic average roughness height, Ra, and the averaged roughness height, based on the integrated ice thickness at the blade tip, are introduced to describe the ice-induced surface roughness at the early stage of the ice accretion. The ice roughness measurements are correlated to the measured broadband noise level. Strong correlations (absolute mean deviations of 9.3% and 11.2% for correlation using Ra and the averaged roughness height respectively) between the ice roughness and the broadband noise level are obtained, which can be used as a tool to determine the accreted ice roughness in the AERTS facility through acoustic measurement. It might be possible to use a similar approach to develop an early ice accretion detection tool for helicopters, as well as to quantify the ice-induced roughness at the early stage of rotor ice accretion. Rotor broadband noise source identification is conducted and the broadband noise related to ice accretion is argued to be turbulent boundary layer - trailing edge (TBL-TE) noise. Theory suggests TBL-TE noise scales with Mach number to the fifth power, which is also observed in the experimental data. The trailing edge noise theories developed by Ffowcs Williams and Hall, and Howe both identify two important parameters: boundary layer thickness and turbulence intensity. Numerical studies of 2-D airfoils with different ice-induced surface roughness heights are conducted to investigate the extent that surface roughness impacts the boundary layer thickness and turbulence intensity (and ultimately the TBL-TE noise). The results show that boundary layer thickness and turbulence intensity at the trailing edge increase with the increased roughness height. Using Howe's trailing edge noise model, the increased sound pressure level (SPL) of the trailing edge noise due to the increased displacement thickness and normalized integrated turbulence intensity are 6.2 dB and 1.6 dB for large and small accreted ice roughness heights, respectively. The estimated increased SPL values agree well with the experimental results, which are 5.8 dB and 2.6 dB for large and small roughness height, respectively. Finally a detailed broadband noise spectral scaling for all measured broadband noise in both AERTS and UMAC facilities is conducted. The magnitude and the frequency spectrum of the measured broadband noise are scaled on characteristic velocity and length. The peak of the laminar boundary layer - vortex shedding (LBL-VS) noise coalesces well on the Strouhal scaling in those cases. For the measured broadband noise from a rotor with relatively large roughness heights, no contribution of the LBL-VS noise is observed. The velocity scaling shows that the TBL-TE noise, which is the dominant source mechanism, scales with Mach number to the fifth power based on the absolute frequency. The length scaling shows that the TBL-TE noise scales well on the absolute roughness height based on Howe's TE noise theory.

The effect of repeated firings on the color change and surface roughness of dental ceramics

PubMed Central

Yılmaz, Kerem; Ozturk, Caner

2014-01-01

PURPOSE The color of the ceramic restorations is affected by various factors such as brand, thickness of the layered the ceramic, condensation techniques, smoothness of surface, number of firings, firing temperature and thickness of dentin. The aim of this study was to evaluate the color change and surface roughness in dental porcelain with different thicknesses during repeated firings. MATERIALS AND METHODS Disc-shaped (N=21) metal-ceramic samples (IPS Classic; Ivoclar Vivadent; Shaar, Liechtenstein) with different thickness were exposed to repeated firings. Color measurement of the samples was made using a colorimeter and profilometer was used to determine surface roughness. ANOVA and Tukey tests with repeated measurements were used for statistical analysis. RESULTS The total thickness of the ceramics which is less than 2 mm significantly have detrimental effect on the surface properties and color of porcelains during firings (P<.05). CONCLUSION Repeated firings have effects on the color change and surface roughness of the dental ceramics and should be avoided. PMID:25177475

Surface roughness estimation of MBE grown CdTe/GaAs(211)B by ex-situ spectroscopic ellipsometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karakaya, Merve, E-mail: mervegunnar@iyte.edu.tr; Bilgilisoy, Elif; Arı, Ozan

Spectroscopic ellipsometry (SE) ranging from 1.24 eV to 5.05 eV is used to obtain the film thickness and optical properties of high index (211) CdTe films. A three-layer optical model (oxide/CdTe/GaAs) was chosen for the ex-situ ellipsometric data analysis. Surface roughness cannot be determined by the optical model if oxide is included. We show that roughness can be accurately estimated, without any optical model, by utilizing the correlation between SE data (namely the imaginary part of the dielectric function, or phase angle, ψ) and atomic force microscopy (AFM) roughness. and ψ values at 3.31 eV, which corresponds to E{sub 1}more » critical transition energy of CdTe band structure, are chosen for the correlation since E{sub 1} gives higher resolution than the other critical transition energies. On the other hand, due to the anisotropic characteristic of (211) oriented CdTe surfaces, SE data ( and ψ) shows varieties for different azimuthal angle measurements. For this reason, in order to estimate the surface roughness by considering these correlations, it is shown that SE measurements need to be taken at the same surface azimuthal angle. Estimating surface roughness in this manner is an accurate way to eliminate cumbersome surface roughness measurement by AFM.« less

Message-passing-interface-based parallel FDTD investigation on the EM scattering from a 1-D rough sea surface using uniaxial perfectly matched layer absorbing boundary.

PubMed

Li, J; Guo, L-X; Zeng, H; Han, X-B

2009-06-01

A message-passing-interface (MPI)-based parallel finite-difference time-domain (FDTD) algorithm for the electromagnetic scattering from a 1-D randomly rough sea surface is presented. The uniaxial perfectly matched layer (UPML) medium is adopted for truncation of FDTD lattices, in which the finite-difference equations can be used for the total computation domain by properly choosing the uniaxial parameters. This makes the parallel FDTD algorithm easier to implement. The parallel performance with different processors is illustrated for one sea surface realization, and the computation time of the parallel FDTD algorithm is dramatically reduced compared to a single-process implementation. Finally, some numerical results are shown, including the backscattering characteristics of sea surface for different polarization and the bistatic scattering from a sea surface with large incident angle and large wind speed.

Maintaining the pluripotency of mouse embryonic stem cells on gold nanoparticle layers with nanoscale but not microscale surface roughness

NASA Astrophysics Data System (ADS)

Lyu, Zhonglin; Wang, Hongwei; Wang, Yanyun; Ding, Kaiguo; Liu, Huan; Yuan, Lin; Shi, Xiujuan; Wang, Mengmeng; Wang, Yanwei; Chen, Hong

2014-05-01

Efficient control of the self-renewal and pluripotency maintenance of embryonic stem cell (ESC) is a prerequisite for translating stem cell technologies to clinical applications. Surface topography is one of the most important factors that regulates cell behaviors. In the present study, micro/nano topographical structures composed of a gold nanoparticle layer (GNPL) with nano-, sub-micro-, and microscale surface roughnesses were used to study the roles of these structures in regulating the behaviors of mouse ESCs (mESCs) under feeder-free conditions. The distinctive results from Oct-4 immunofluorescence staining and quantitative real-time polymerase chain reaction (qPCR) demonstrate that nanoscale and low sub-microscale surface roughnesses (Rq less than 392 nm) are conducive to the long-term maintenance of mESC pluripotency, while high sub-microscale and microscale surface roughnesses (Rq greater than 573 nm) result in a significant loss of mESC pluripotency and a faster undirectional differentiation, particularly in long-term culture. Moreover, the likely signalling cascades engaged in the topological sensing of mESCs were investigated and their role in affecting the maintenance of the long-term cell pluripotency was discussed by analyzing the expression of proteins related to E-cadherin mediated cell-cell adhesions and integrin-mediated focal adhesions (FAs). Additionally, the conclusions from MTT, cell morphology staining and alkaline phosphatase (ALP) activity assays show that the surface roughness can provide a potent regulatory signal for various mESC behaviors, including cell attachment, proliferation and osteoinduction.Efficient control of the self-renewal and pluripotency maintenance of embryonic stem cell (ESC) is a prerequisite for translating stem cell technologies to clinical applications. Surface topography is one of the most important factors that regulates cell behaviors. In the present study, micro/nano topographical structures composed of a gold nanoparticle layer (GNPL) with nano-, sub-micro-, and microscale surface roughnesses were used to study the roles of these structures in regulating the behaviors of mouse ESCs (mESCs) under feeder-free conditions. The distinctive results from Oct-4 immunofluorescence staining and quantitative real-time polymerase chain reaction (qPCR) demonstrate that nanoscale and low sub-microscale surface roughnesses (Rq less than 392 nm) are conducive to the long-term maintenance of mESC pluripotency, while high sub-microscale and microscale surface roughnesses (Rq greater than 573 nm) result in a significant loss of mESC pluripotency and a faster undirectional differentiation, particularly in long-term culture. Moreover, the likely signalling cascades engaged in the topological sensing of mESCs were investigated and their role in affecting the maintenance of the long-term cell pluripotency was discussed by analyzing the expression of proteins related to E-cadherin mediated cell-cell adhesions and integrin-mediated focal adhesions (FAs). Additionally, the conclusions from MTT, cell morphology staining and alkaline phosphatase (ALP) activity assays show that the surface roughness can provide a potent regulatory signal for various mESC behaviors, including cell attachment, proliferation and osteoinduction. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr01540a

TaC-coated graphite prepared via a wet ceramic process: Application to CVD susceptors for epitaxial growth of wide-bandgap semiconductors

NASA Astrophysics Data System (ADS)

Nakamura, Daisuke; Kimura, Taishi; Narita, Tetsuo; Suzumura, Akitoshi; Kimoto, Tsunenobu; Nakashima, Kenji

2017-11-01

A novel sintered tantalum carbide coating (SinTaC) prepared via a wet ceramic process is proposed as an approach to reducing the production cost and improving the crystal quality of bulk-grown crystals and epitaxially grown films of wide-bandgap semiconductors. Here, we verify the applicability of the SinTaC components as susceptors for chemical vapor deposition (CVD)-SiC and metal-organic chemical vapor deposition (MOCVD)-GaN epitaxial growth in terms of impurity incorporation from the SinTaC layers and also clarify the surface-roughness controllability of SinTaC layers and its advantage in CVD applications. The residual impurity elements in the SinTaC layers were confirmed to not severely incorporate into the CVD-SiC and MOCVD-GaN epilayers grown using the SinTaC susceptors. The quality of the epilayers was also confirmed to be equivalent to that of epilayers grown using conventional susceptors. Furthermore, the surface roughness of the SinTaC components was controllable over a wide range of average roughness (0.4 ≤ Ra ≤ 5 μm) and maximum height roughness (3 ≤ Rz ≤ 36 μm) through simple additional surface treatment procedures, and the surface-roughened SinTaC susceptor fabricated using these procedures was predicted to effectively reduce thermal stress on epi-wafers. These results confirm that SinTaC susceptors are applicable to epitaxial growth processes and are advantageous over conventional susceptor materials for reducing the epi-cost and improving the quality of epi-wafers.

Designing Pulse Laser Surface Modification of H13 Steel Using Response Surface Method

NASA Astrophysics Data System (ADS)

Aqida, S. N.; Brabazon, D.; Naher, S.

2011-01-01

This paper presents a design of experiment (DOE) for laser surface modification process of AISI H13 tool steel in achieving the maximum hardness and minimum surface roughness at a range of modified layer depth. A Rofin DC-015 diffusion-cooled CO2 slab laser was used to process AISI H13 tool steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, overlap percentage and pulse repetition frequency (PRF). The response surface method with Box-Behnken design approach in Design Expert 7 software was used to design the H13 laser surface modification process. Metallographic study and image analysis were done to measure the modified layer depth. The modified surface roughness was measured using two-dimensional surface profilometer. The correlation of the three laser processing parameters and the modified surface properties was specified by plotting three-dimensional graph. The hardness properties were tested at 981 mN force. From metallographic study, the laser modified surface depth was between 37 μm and 150 μm. The average surface roughness recorded from the 2D profilometry was at a minimum value of 1.8 μm. The maximum hardness achieved was between 728 and 905 HV0.1. These findings are significant to modern development of hard coatings for wear resistant applications.

Wall roughness effect on gas dynamics in supersonic ejector

NASA Astrophysics Data System (ADS)

Aronson, K. E.; Brezgin, D. V.

2016-10-01

The paper presents the numerical simulations results in order to figure out the influence of the wall surface roughness on gas-dynamic processes inside the supersonic ejector. For these purposes two commercial CFD-solvers (Star-CCM+ and Fluent) were used. A detailed comparative study of the built-in tools and approaches in both CFD-packages for evaluation of surface roughness effects on the logarithmic law velocity distribution inside the boundary layer is carried out. Influence of ejector surface roughness is compared with the influence of the backpressure. It is found out that either increasing the backpressure behind the ejector or increasing the surface roughness height, the appearance section of a pressure shock is displaced upstream (closer to the primary nozzle). The numerical simulations results of the ejector with rough walls in both CFD-solvers are well quantitative agreed between each other in terms of the mass flow rates and are well qualitative consistent in terms of the local flow parameters distribution. It is found out that in case of exceeding the "critical roughness height" for the given geometry and boundary conditions, the ejector switches to the "off-design" mode and its performance is significantly reduced.

Comparative Study of Surface Chemical Composition and Oxide Layer Modification upon Oxygen Plasma Cleaning and Piranha Etching on a Novel Low Elastic Modulus Ti25Nb21Hf Alloy

NASA Astrophysics Data System (ADS)

Paredes, Virginia; Salvagni, Emiliano; Rodríguez-Castellón, Enrique; Manero, José María

2017-08-01

Metals are widely employed for many biological artificial replacements, and it is known that the quality and the physical/chemical properties of the surface are crucial for the success of the implant. Therefore, control over surface implant materials and their elastic moduli may be crucial to avoid undesired effects. In this study, surface modification upon cleaning and activation of a low elastic modulus Ti alloy (Ti25Hf21Nb) was investigated. Two different methods, oxygen plasma (OP) cleaning and piranha (PI) solution, were studied and compared. Both surface treatments were effective for organic contaminant removal and to increase the Ti-oxide layer thickness rather than other metal-oxides present at the surface, which is beneficial for biocompatibility of the material. Furthermore, both techniques drastically increased hydrophilicity and introduced oxidation and hydroxylation (OH)-functional groups at the surface that may be beneficial for further chemical modifications. However, these treatments did not alter the surface roughness and bulk material properties. The surfaces were fully characterized in terms of surface roughness, wettability, oxide layer composition, and hydroxyl surface density through analytical techniques (interferometry, X-ray photoelectron spectroscopy (XPS), contact angle, and zinc complexation). These findings provide essential information when planning surface modifications for cleanliness, oxide layer thickness, and surface hydroxyl density, as control over these factors is essential for many applications, especially in biomaterials.

Extreme wettability of nanostructured glass fabricated by non-lithographic, anisotropic etching

PubMed Central

Yu, Eusun; Kim, Seul-Cham; Lee, Heon Ju; Oh, Kyu Hwan; Moon, Myoung-Woon

2015-01-01

Functional glass surfaces with the properties of superhydrophobicity/or superhydrohydrophilicity, anti-condensation or low reflectance require nano- or micro-scale roughness, which is difficult to fabricate directly on glass surfaces. Here, we report a novel non-lithographic method for the fabrication of nanostructures on glass; this method introduces a sacrificial SiO2 layer for anisotropic plasma etching. The first step was to form nanopillars on SiO2 layer-coated glass by using preferential CF4 plasma etching. With continuous plasma etching, the SiO2 pillars become etch-resistant masks on the glass; thus, the glass regions covered by the SiO2 pillars are etched slowly, and the regions with no SiO2 pillars are etched rapidly, resulting in nanopatterned glass. The glass surface that is etched with CF4 plasma becomes superhydrophilic because of its high surface energy, as well as its nano-scale roughness and high aspect ratio. Upon applying a subsequent hydrophobic coating to the nanostructured glass, a superhydrophobic surface was achieved. The light transmission of the glass was relatively unaffected by the nanostructures, whereas the reflectance was significantly reduced by the increase in nanopattern roughness on the glass. PMID:25791414

Strain relaxation of thick (11–22) semipolar InGaN layer for long wavelength nitride-based device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jaehwan; Min, Daehong; Jang, Jongjin

2014-10-28

In this study, the properties of thick stress-relaxed (11–22) semipolar InGaN layers were investigated. Owing to the inclination of growth orientation, misfit dislocations (MDs) occurred at the heterointerface when the strain state of the (11–22) semipolar InGaN layers reached the critical point. We found that unlike InGaN layers based on polar and nonpolar growth orientations, the surface morphologies of the stress-relaxed (11–22) semipolar InGaN layers did not differ from each other and were similar to the morphology of the underlying GaN layer. In addition, misfit strain across the whole InGaN layer was gradually relaxed by MD formation at the heterointerface.more » To minimize the effect of surface roughness and defects in GaN layers on the InGaN layer, we conducted further investigation on a thick (11–22) semipolar InGaN layer grown on an epitaxial lateral overgrown GaN template. We found that the lateral indium composition across the whole stress-relaxed InGaN layer was almost uniform. Therefore, thick stress-relaxed (11–22) semipolar InGaN layers are suitable candidates for use as underlying layers in long-wavelength devices, as they can be used to control strain accumulation in the heterostructure active region without additional influence of surface roughness.« less

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.

A Tower-based Prototype VHF/UHF Radar for Subsurface Sensing: System Description and Data Inversion Results

NASA Technical Reports Server (NTRS)

Moghaddam, Mahta; Pierce, Leland; Tabatabaeenejad, Alireza; Rodriguez, Ernesto

2005-01-01

Knowledge of subsurface characteristics such as permittivity variations and layering structure could provide a breakthrough in many terrestrial and planetary science disciplines. For Earth science, knowledge of subsurface and subcanopy soil moisture layers can enable the estimation of vertical flow in the soil column linking surface hydrologic processes with that in the subsurface. For planetary science, determining the existence of subsurface water and ice is regarded as one of the most critical information needs for the study of the origins of the solar system. The subsurface in general can be described as several near-parallel layers with rough interfaces. Each homogenous rough layer can be defined by its average thickness, permittivity, and rms interface roughness assuming a known surface spectral distribution. As the number and depth of layers increase, the number of measurements needed to invert for the layer unknowns also increases, and deeper penetration capability would be required. To nondestructively calculate the characteristics of the rough layers, a multifrequency polarimetric radar backscattering approach can be used. One such system is that we have developed for data prototyping of the Microwave Observatory of Subcanopy and Subsurface (MOSS) mission concept. A tower-mounted radar makes backscattering measurements at VHF, UHF, and L-band frequencies. The radar is a pulsed CW system, which uses the same wideband antenna to transmit and receive the signals at all three frequencies. To focus the beam at various incidence angles within the beamwidth of the antenna, the tower is moved vertically and measurements made at each position. The signals are coherently summed to achieve focusing and image formation in the subsurface. This requires an estimate of wave velocity profiles. To solve the inverse scattering problem for subsurface velocity profile simultaneously with radar focusing, we use an iterative technique based on a forward numerical solution of the layered rough surface problem. The layers are each defined in terms of a small number of unknown distributions as given above. An a priori estimate of the solution is first assumed, based on which the forward problem is solved for the backscattered measurements. This is compared with the measured data and using iterative techniques an update to the solution for the unknowns is calculated. The process continues until convergence is achieved. Numerical results will be shown using actual radar data acquired with the MOSS tower radar system in Arizona in Fall 2003, and compared with in-situ measurements.

Incorporation of interfacial roughness into recursion matrix formalism of dynamical X-ray diffraction in multilayers and superlattices.

PubMed

Lobach, Ihar; Benediktovitch, Andrei; Ulyanenkov, Alexander

2017-06-01

Diffraction in multilayers in the presence of interfacial roughness is studied theoretically, the roughness being considered as a transition layer. Exact (within the framework of the two-beam dynamical diffraction theory) differential equations for field amplitudes in a crystalline structure with varying properties along its surface normal are obtained. An iterative scheme for approximate solution of the equations is developed. The presented approach to interfacial roughness is incorporated into the recursion matrix formalism in a way that obviates possible numerical problems. Fitting of the experimental rocking curve is performed in order to test the possibility of reconstructing the roughness value from a diffraction scan. The developed algorithm works substantially faster than the traditional approach to dealing with a transition layer (dividing it into a finite number of thin lamellae). Calculations by the proposed approach are only two to three times longer than calculations for corresponding structures with ideally sharp interfaces.

A wind tunnel study of flows over idealised urban surfaces with roughness sublayer corrections

NASA Astrophysics Data System (ADS)

Ho, Yat-Kiu; Liu, Chun-Ho

2017-10-01

Dynamics in the roughness (RSLs) and inertial (ISLs) sublayers in the turbulent boundary layers (TBLs) over idealised urban surfaces are investigated analytically and experimentally. In this paper, we derive an analytical solution to the mean velocity profile, which is a continuous function applicable to both RSL and ISL, over rough surfaces in isothermal conditions. Afterwards, a modified mixing-length model for RSL/ISL transport is developed that elucidates how surface roughness affects the turbulence motions. A series of wind tunnel experiments are conducted to measure the vertical profiles of mean and fluctuating velocities, together with momentum flux over various configurations of surface-mounted ribs in cross flows using hot-wire anemometry (HWA). The analytical solution agrees well with the wind tunnel result that improves the estimate to mean velocity profile over urban surfaces and TBL dynamics as well. The thicknesses of RSL and ISL are calculated by monitoring the convergence/divergence between the temporally averaged and spatio-temporally averaged profiles of momentum flux. It is found that the height of RSL/ISL interface is a function of surface roughness. Examining the direct, physical influence of roughness elements on near-surface RSL flows reveals that the TBL flows over rough surfaces exhibit turbulence motions of two different length scales which are functions of the RSL and ISL structure. Conclusively, given a TBL, the rougher the surface, the higher is the RSL intruding upward that would thinner the ISL up to 50 %. Therefore, the conventional ISL log-law approximation to TBL flows over urban surfaces should be applied with caution.

Characterizing near-surface firn using the scattered signal component of the glacier surface return from airborne radio-echo sounding

NASA Astrophysics Data System (ADS)

Rutishauser, Anja; Grima, Cyril; Sharp, Martin; Blankenship, Donald D.; Young, Duncan A.; Cawkwell, Fiona; Dowdeswell, Julian A.

2016-12-01

We derive the scattered component (hereafter referred to as the incoherent component) of glacier surface echoes from airborne radio-echo sounding measurements over Devon Ice Cap, Arctic Canada, and compare the scattering distribution to firn stratigraphy observations from ground-based radar data. Low scattering correlates to laterally homogeneous firn above 1800 m elevation containing thin, flat, and continuous ice layers and below 1200 m elevation where firn predominantly consists of ice. Increased scattering between elevations of 1200-1800 m corresponds to firn with inhomogeneous, undulating ice layers. No correlation was found to surface roughness and its theoretical incoherent backscattering values. This indicates that the scattering component is mainly influenced by the near-surface firn stratigraphy, whereas surface roughness effects are minor. Our results suggest that analyzing the scattered signal component of glacier surface echoes is a promising approach to characterize the spatial heterogeneity of firn that is affected by melting and refreezing processes.

Ni-P/Zn-Ni compositionally modulated multilayer coatings - Part 1: Electrodeposition and growth mechanism, composition, morphology, roughness and structure

NASA Astrophysics Data System (ADS)

Bahadormanesh, Behrouz; Ghorbani, Mohammad

2018-06-01

The Ni-P/Zn-Ni compositionally modulated multilayer coatings CMMCs were electrodeposited from a single bath by switching the cathodic current density. The composition, surface morphology, roughness, layers growth pattern as well as the phase structure of deposits were extensively studied via SEM, EDS, AFM and XRD analysis. Effects of bath ingredients on the electrodeposition behavior were analyzed through cathodic linear sweep voltammetry. Although the concentration of Zn2+ in bath was 13 times higher than Ni2+, the Zn-Ni deposition potential was much nearer to Ni deposition potential rather than that of Zn. Addition of NaH2PO2 to the Ni deposition bath considerably raised the current density and shifted the crystallization potential of Ni to more nobble values. Codeposition of P with Zn-Ni alloy lead to crack formation in the monolayer that was deposited in 60 mA/cm2. However, the cracks were not observed in the Zn-Ni layers of multilayers. Zn-Ni layers in CMMCs exhibited a three-dimensional pattern of growth while that of Ni-P layers was two-dimensional. Also, the Ni-P deposits tends to fill the discontinuities in Zn-Ni layers and performed leveling properties and lowered the surface roughness of Zn-Ni layers and CMMCs. Structural analysis demonstrated that Ni-P layers were amorphous and the Zn-Ni layers exhibited crystallite phase of Zn11Ni2. Thus, the Ni-P/Zn-Ni CMMCs comprised of alternate layers of amorphous Ni-P and nanocrystalline Zn Ni.

Investigation of the Dissolution-Reformation Cycle of the Passive Oxide Layer on NiTi Orthodontic Archwires

NASA Astrophysics Data System (ADS)

Uzer, B.; Birer, O.; Canadinc, D.

2017-09-01

Dissolution-reformation cycle of the passive oxide layer on the nickel-titanium (NiTi) orthodontic archwires was investigated, which has recently been recognized as one of the key parameters dictating the biocompatibility of archwires. Specifically, commercially available NiTi orthodontic archwires were immersed in artificial saliva solutions of different pH values (2.3, 3.3, and 4.3) for four different immersion periods: 1, 7, 14, and 30 days. Characterization of the virgin and tested samples revealed that the titanium oxide layer on the NiTi archwire surfaces exhibit a dissolution-reformation cycle within the first 14 days of the immersion period: the largest amount of Ni ion release occurred within the first week of immersion, while it significantly decreased during the reformation period from day 7 to day 14. Furthermore, the oxide layer reformation was catalyzed on the grooves within the peaks and valleys due to relatively larger surface energy of these regions, which eventually decreased the surface roughness significantly within the reformation period. Overall, the current results clearly demonstrate that the analyses of dissolution-reformation cycle of the oxide layer in orthodontic archwires, surface roughness, and ion release behavior constitute utmost importance in order to ensure both the highest degree of biocompatibility and an efficient medical treatment.

Eggshell structure in Caiman latirostris eggs improves embryo survival during nest inundation.

PubMed

Cedillo-Leal, César; Simoncini, Melina S; Leiva, Pamela M L; Larriera, Alejandro; Lang, Jeffrey W; Piña, Carlos I

2017-05-17

Egg inundation often results in poor hatching success in crocodylians. However, how tolerant eggs are to submergence, and/or how eggshell ultrastructure may affect embryo survival when inundated, are not well understood. In this study, our objective was to determine if embryo survival in Caiman latirostris is affected by eggshell surface roughness, when eggs are submerged under water. Tolerance to inundation was tested early (day 30) versus late (day 60) in development, using eight clutches (four per time treatments), subdivided into four groups: ( N = 9 per clutch per treatment; 9 × 4 = 36 eggs per group). 'Rough' eggshell represented the natural, unmodified eggshell surface structure. 'Smooth' eggshell surface structure was created by mechanically sanding the natural rough surface to remove surface columnar elements and secondary layer features, e.g. irregularities that result in 'roughness'. When inundated by submerging eggs under water for 10 h at day 30, 'smooth' eggshell structure resulted in more than twice as many dead embryos (16 versus 6, smooth versus rough; N = 36), and fewer than half as many healthy embryos (6 versus 13, smooth versus rough, respectively; N = 36). By contrast, at day 60, inundation resulted in very low hatching success, regardless of eggshell surface structure. Only two hatchlings survived the inundation, notably in the untreated group with intact, rough eggshells. Inundation produced a high rate of malformations (58% at day 30), but did not affect hatchling size. Our results indicate that eggshell roughness enhances embryo survival when eggs are inundated early in development, but not late in development. Apparently, the natural surface 'roughness' entraps air bubbles at the eggshell surface during inundation, thereby facilitating gas exchange through the eggshell even when the egg is submerged under water. © 2017 The Author(s).

On the sensitivity of mesoscale models to surface-layer parameterization constants

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Pielke, R. A.

1989-09-01

The Colorado State University standard mesoscale model is used to evaluate the sensitivity of one-dimensional (1D) and two-dimensional (2D) fields to differences in surface-layer parameterization “constants”. Such differences reflect the range in the published values of the von Karman constant, Monin-Obukhov stability functions and the temperature roughness length at the surface. The sensitivity of 1D boundary-layer structure, and 2D sea-breeze intensity, is generally less than that found in published comparisons related to turbulence closure schemes generally.

Effect of the seed layer on the Y0.5Gd0.5Ba2Cu3O7-σ film fabricated by PLD

NASA Astrophysics Data System (ADS)

Yao, Yanjie; Wang, Wei; Liu, Linfei; Lu, Saidan; Wu, Xiang; Zheng, Tong; Liu, Shunfan; Li, Yijie

2018-06-01

The surface morphology and internal residual stress have influence on the critical current density (Jc) of REBa2Cu3O7-σ (REBCO) coated conductor. In order to modulate them, a series of Y0.5Gd0.5Ba2Cu3O7-σ (YGBCO) films were prepared by pulsed laser deposition (PLD) through introducing a seed layer in this paper. The thicknesses of seed layer changes from about 2 nm to 30 nm. For comparison, a standard sample without seed layer was fabricated at the same deposition condition. The surface morphology was illustrated by Scanning electron microscopy (SEM). The surface roughness was scanned by Atomic force microscopy (AFM). The microstructure and internal strain were measured by X-ray Diffraction (XRD). DC four-probe method was used to measure the critical current of the samples at 77 K and self-field. As a result, all samples have high Jc of about 4 MA/cm2, while the self-field Jc of the YGBCO films can be promoted by the seed layer. The results of our research work are as follows. First of all, seed layer makes the deposition of the YGBCO layer much easier to control. By this way, we can decrease the surface roughness of the samples. Furthermore, the internal residual stress of the YGBCO films with seed layer decrease. Finally, the best thickness of the seed layer was found by summarizing and analyzing the conditions of seed layer.

Receptivity of the Boundary Layer to Vibrations of the Wing Surface

NASA Astrophysics Data System (ADS)

Bernots, Tomass; Ruban, Anatoly; Pryce, David; Laminar Flow Control UK Group Team

2014-11-01

In this work we study generation of Tollmien-Schlichting (T-S) waves in the boundary layer due to elastic vibrations of the wing surface. The flow is investigated based on the asymptotic analysis of the Navier-Stokes equations at large values of the Reynolds number. It is assumed that in the spectrum of the wing vibrations there is a harmonic which comes in resonance with the T-S wave on the lower branch of the stability curve. It was found that the vibrations of the wing surface produce pressure perturbations in the flow outside the boundary layer which can be calculated with the help of the piston theory. As the pressure perturbations penetrate into the boundary layer, a Stokes layer forms on the wing surface which appears to be influenced significantly by the compressibility of the flow, and is incapable of producing the T-S waves. The situation changes when the Stokes layer encounters an roughness; near which the flow is described using the triple-deck theory. The solution of the triple-deck problem can be found in an analytic form. Our main concern is with the flow behaviour downstream of the roughness and, in particular, with the amplitude of the generated Tollmien-Schlichting waves. This research was performed in the Laminar Flow Control Centre (LFC-UK) at Imperial College London. The centre is supported by EPSRC, Airbus UK and EADS Innovation Works.

Effect of nanocomposite gate-dielectric properties on pentacene microstructure and field-effect transistor characteristics.

PubMed

Lee, Wen-Hsi; Wang, Chun-Chieh

2010-02-01

In this study, the effect of surface energy and roughness of the nanocomposite gate dielectric on pentacene morphology and electrical properties of pentacene OTFT are reported. Nanoparticles TiO2 were added in the polyimide matrix to form a nanocomposite which has a significantly different surface characteristic from polyimide, leading to a discrepancy in the structural properties of pentacene growth. A growth mode of pentacene deposited on the nanocomposite is proposed to explain successfully the effect of surface properties of nanocomposite gate dielectric such as surface energy and roughness on the pentacene morphology and electrical properties of OTFT. To obtain the lower surface energy and smoother surface of nanocomposite gate dielectric that is responsible for the desired crystalline, microstructure of pentacene and electrical properties of device, a bottom contact OTFT-pentacene deposited on the double-layer nanocomposite gate dielectric consisting of top smoothing layer of the neat polyimide and bottom layer of (PI+ nano-TiO2 particles) nanocomposite has been successfully demonstrated to exhibit very promising performance including high current on to off ratio of about 6 x 10(5), threshold voltage of -10 V and moderately high filed mobility of 0.15 cm2V(-1)s(-1).

Corroded surface roughness of copper analyzed by Fourier transform infrared mapping microscopy and optical profilometric study.

PubMed

Kasperek, J; Lefez, B; Beucher, E

2004-02-01

This study shows the effects of roughness on infrared spectra shapes of thin corrosion products on metallic substrates. The calculated spectra show that the baseline is mainly affected by increasing roughness and that such effects do not shift the position of the absorption bands. The model obtained has been used to extract data of artificial patina on a copper surface. Surface defects of copper substrates can be distinguished on the whole surface, from the morphological and chemical points of view, using optical profilometry and infrared microspectroscopy. An homogeneous layer of cuprite covers the surface except in the linear defects. Fourier transform infrared (FT-IR) analysis indicates that a mixture of atacamite and clinoatacamite is mainly located in these scratches. The width of these particular areas is in good agreement with profilometric observations.

Surface Forces Apparatus Measurements of Interactions between Rough and Reactive Calcite Surfaces.

PubMed

Dziadkowiec, Joanna; Javadi, Shaghayegh; Bratvold, Jon E; Nilsen, Ola; Røyne, Anja

2018-06-26

nm-Range forces acting between calcite surfaces in water affect macroscopic properties of carbonate rocks and calcite-based granular materials and are significantly influenced by calcite surface recrystallization. We suggest that the repulsive mechanical effects related to nm-scale surface recrystallization of calcite in water could be partially responsible for the observed decrease of cohesion in calcitic rocks saturated with water. Using the surface forces apparatus, we simultaneously followed the calcite reactivity and measured the forces in water in two surface configurations: between two rough calcite surfaces (CC) and between rough calcite and a smooth mica surface (CM). We used nm-scale rough, polycrystalline calcite films prepared by atomic layer deposition. We measured only repulsive forces in CC in CaCO 3 -saturated water, which was related to roughness and possibly to repulsive hydration effects. Adhesive or repulsive forces were measured in CM in CaCO 3 -saturated water depending on calcite roughness, and the adhesion was likely enhanced by electrostatic effects. The pull-off adhesive force in CM became stronger with time, and this increase was correlated with a decrease of roughness at contacts, the parameter which could be estimated from the measured force-distance curves. That suggested a progressive increase of real contact areas between the surfaces, caused by gradual pressure-driven deformation of calcite surface asperities during repeated loading-unloading cycles. Reactivity of calcite was affected by mass transport across nm- to μm-thick gaps between the surfaces. Major roughening was observed only for the smoothest calcite films, where gaps between two opposing surfaces were nm-thick over μm-sized areas and led to force of crystallization that could overcome confining pressures of the order of MPa. Any substantial roughening of calcite caused a significant increase of the repulsive mechanical force contribution.

Direct numerical simulation of instabilities in parallel flow with spherical roughness elements

NASA Technical Reports Server (NTRS)

Deanna, R. G.

1992-01-01

Results from a direct numerical simulation of laminar flow over a flat surface with spherical roughness elements using a spectral-element method are given. The numerical simulation approximates roughness as a cellular pattern of identical spheres protruding from a smooth wall. Periodic boundary conditions on the domain's horizontal faces simulate an infinite array of roughness elements extending in the streamwise and spanwise directions, which implies the parallel-flow assumption, and results in a closed domain. A body force, designed to yield the horizontal Blasius velocity in the absence of roughness, sustains the flow. Instabilities above a critical Reynolds number reveal negligible oscillations in the recirculation regions behind each sphere and in the free stream, high-amplitude oscillations in the layer directly above the spheres, and a mean profile with an inflection point near the sphere's crest. The inflection point yields an unstable layer above the roughness (where U''(y) is less than 0) and a stable region within the roughness (where U''(y) is greater than 0). Evidently, the instability begins when the low-momentum or wake region behind an element, being the region most affected by disturbances (purely numerical in this case), goes unstable and moves. In compressible flow with periodic boundaries, this motion sends disturbances to all regions of the domain. In the unstable layer just above the inflection point, the disturbances grow while being carried downstream with a propagation speed equal to the local mean velocity; they do not grow amid the low energy region near the roughness patch. The most amplified disturbance eventually arrives at the next roughness element downstream, perturbing its wake and inducing a global response at a frequency governed by the streamwise spacing between spheres and the mean velocity of the most amplified layer.

The Effect of Humidity and Particle Characteristics on Friction and Stick-slip Instability in Granular Fault Gouge

NASA Astrophysics Data System (ADS)

Anthony, J. L.; Marone, C. J.

2003-12-01

Previous studies have shown that particle characteristics such as shape, dimension, and roughness affect friction in granular shear zones. Other work shows that humidity plays a key role in frictional healing and rate/state dependence within granular gouge. In order to improve our understanding of grain-scale deformation mechanisms within fault gouge, we performed laboratory experiments using a double-direct-shear testing apparatus. This assembly includes three rigid forcing blocks with two gouge layers sandwiched between rough or smooth surfaces. Roughened surfaces were triangular grooves 0.8 mm deep and 1 mm wavelength. These promote distributed shear throughout the layer undergoing cataclastic deformation. Smooth surfaces were mirror-finished hardened steel and were used to promote and isolate grain boundary sliding. The center block is forced at controlled displacement rate between the two side blocks to create frictional shear. We studied gouge layers 3-7 mm thick, consisting of either quartz rods sheared in 1-D and 2-D configurations and smooth glass beads mixed with varying amounts of rough sand particles. We report on particle diameters that range from 0.050-0.210 mm, and quartz rods 1 mm in diameter and 100 mm long. The experiments are run at room temperature, controlled relative humidity ranging from 5 to 100%, and shear displacement rates from 0.1 to 300 microns per second. Experiments are carried out under a normal stress of 5 MPa, a non-fracture loading regime where sliding friction for smooth spherical particles is measurably lower than for rough angular particles. We compare results from shear between smooth boundaries, where we hypothesize that grain boundary sliding is the mechanism influencing granular friction, to rough sample experiments where shear undergoes a transition from distributed, pervasive shear to progressively localized as a function of increasing strain. For shear within rough surfaces, stick-slip instability occurs in gouge that consists of less than 30% angular grains and begins once the coefficient of friction (shear stress divided by normal stress) reaches a value of 0.35-0.40. Peak friction during stick-slip cycles is 0.40-0.45. Each stick-slip event involves a small amount of quasi-static displacement prior to failure, which we refer to as pre-seismic slip. For unstable sliding regimes, we measure the amount of pre-seismic slip and the magnitude of dynamic stress drop. These parameters vary systematically with sliding velocity, particle characteristics, and bounding roughness. For shear within smooth surfaces, friction is very low (0.15-0.16 for spherical particles) and sliding is stable, without stick-slip instability. As more angular grains are mixed with spherical beads the coefficient of friction increases. This holds true for both the rough and smooth sample experiments. We expand on previous work done by Frye and Marone 2002 (JGR) to study the effect of humidity on 1-D, 2-D, and 3-D gouge layer configurations. Our data show that humidity has a significant effect on frictional strength and stability and that this effect is observed for both smooth surfaces, where grain boundary sliding is the dominant deformation mechanisms, and for shear within rough surfaces where gouge deformation occurs by rolling, dilation, compaction, and grain boundary sliding.

X-Ray-Based Imaging for Characterizing Heterogeneous Gas Diffusion Layers for Polymer Electrolyte Membrane Fuel Cells

NASA Astrophysics Data System (ADS)

George, Michael G.

Characterization of gas diffusion layers (GDLs) for polymer electrolyte membrane (PEM) fuel cells informs modeling studies and the manufacturers of next generation fuel cell materials. Identifying the physical properties related to the primary functions of the modern GDL (thermal, electrical, and mass transport) is necessary for understanding the impact of GDL design choices. X-ray micro-computed tomographic reconstructions of GDLs were studied to isolate GDL surface morphologies. Surface roughness was measured for a wide variety of samples and a sensitivity study highlighted the scale-dependence of surface roughness measurements. Furthermore, a spatially resolved distribution map of polytetrafluoroethylene (PTFE) in the microporous layer (MPL), critical for water management and mass transport, was identified and the existence of PTFE agglomerations was highlighted. Finally, the impact of accelerated degradation on GDL wettability and water transport increases in liquid water accumulation and oxygen mass transport resistance were quantified as a result of accelerated GDL degradation.

Assessment of a surface-layer parameterization scheme in an atmospheric model for varying meteorological conditions

NASA Astrophysics Data System (ADS)

Anurose, T. J.; Bala Subrahamanyam, D.

2014-06-01

The performance of a surface-layer parameterization scheme in a high-resolution regional model (HRM) is carried out by comparing the model-simulated sensible heat flux (H) with the concurrent in situ measurements recorded at Thiruvananthapuram (8.5° N, 76.9° E), a coastal station in India. With a view to examining the role of atmospheric stability in conjunction with the roughness lengths in the determination of heat exchange coefficient (CH) and H for varying meteorological conditions, the model simulations are repeated by assigning different values to the ratio of momentum and thermal roughness lengths (i.e. z0m/z0h) in three distinct configurations of the surface-layer scheme designed for the present study. These three configurations resulted in differential behaviour for the varying meteorological conditions, which is attributed to the sensitivity of CH to the bulk Richardson number (RiB) under extremely unstable, near-neutral and stable stratification of the atmosphere.

Comparing DNS and Experiments of Subcritical Flow Past an Isolated Surface Roughness Element

NASA Astrophysics Data System (ADS)

Doolittle, Charles; Goldstein, David

2009-11-01

Results are presented from computational and experimental studies of subcritical roughness within a Blasius boundary layer. This work stems from discrepancies presented by Stephani and Goldstein (AIAA Paper 2009-585) where DNS results did not agree with hot-wire measurements. The near wake regions of cylindrical surface roughness elements corresponding to roughness-based Reynolds numbers Rek of about 202 are of specific concern. Laser-Doppler anemometry and flow visualization in water, as well as the same spectral DNS code used by Stephani and Goldstein are used to obtain both quantitative and qualitative comparisons with previous results. Conclusions regarding previous studies will be presented alongside discussion of current work including grid resolution studies and an examination of vorticity dynamics.

Surface smoothening of the inherent roughness of micro-lenses fabricated with 2-photon lithography

NASA Astrophysics Data System (ADS)

Schift, Helmut; Kirchner, Robert; Chidambaram, Nachiappan; Altana, Mirco

2018-01-01

Two-photon polymerization by direct laser writing enables to write refractive micro-optical elements with sub-μm precision. The trajectories and layering during the direct writing process often result in roughness in the range of the writing increment, which has adverse effects for optical applications. Instead of increasing overlap between adjacent voxels, roughness in the range of 100 nm can be smoothed out by post-processing. For this a method known as TASTE was developed, which allows polishing of surfaces without changing the structural details or the overall shape. It works particularly well with thermoplastic polymers and enables sub-10 nm roughness. The optical quality was confirmed for an array with several 100 microlenses.

High efficiency replicated x-ray optics and fabrication method

DOEpatents

Barbee, Jr., Troy W.; Lane, Stephen M.; Hoffman, Donald E.

2001-01-01

Replicated x-ray optics are fabricated by sputter deposition of reflecting layers on a super-polished reusable mandrel. The reflecting layers are strengthened by a supporting multilayer that results in stronger stress-relieved reflecting surfaces that do not deform during separation from the mandrel. The supporting multilayer enhances the ability to part the replica from the mandrel without degradation in surface roughness. The reflecting surfaces are comparable in smoothness to the mandrel surface. An outer layer is electrodeposited on the supporting multilayer. A parting layer may be deposited directly on the mandrel before the reflecting surface to facilitate removal of the layered, tubular optic device from the mandrel without deformation. The inner reflecting surface of the shell can be a single layer grazing reflection mirror or a resonant multilayer mirror. The resulting optics can be used in a wide variety of applications, including lithography, microscopy, radiography, tomography, and crystallography.

Modeling of normal contact of elastic bodies with surface relief taken into account

NASA Astrophysics Data System (ADS)

Goryacheva, I. G.; Tsukanov, I. Yu

2018-04-01

An approach to account the surface relief in normal contact problems for rough bodies on the basis of an additional displacement function for asperities is considered. The method and analytic expressions for calculating the additional displacement function for one-scale and two-scale wavy relief are presented. The influence of the microrelief geometric parameters, including the number of scales and asperities density, on additional displacements of the rough layer is analyzed.

Use of CFD Analyses to Predict Disk Friction Loss of Centrifugal Compressor Impellers

NASA Astrophysics Data System (ADS)

Cho, Leesang; Lee, Seawook; Cho, Jinsoo

To improve the total efficiency of centrifugal compressors, it is necessary to reduce disk friction loss, which is expressed as the power loss. In this study, to reduce the disk friction loss due to the effect of axial clearance and surface roughness is analyzed and methods to reduce disk friction loss are proposed. The rotating reference frame technique using a commercial CFD tool (FLUENT) is used for steady-state analysis of the centrifugal compressor. Numerical results of the CFD analysis are compared with theoretical results using established experimental empirical equations. The disk friction loss of the impeller is decreased in line with increments in axial clearance until the axial clearance between the impeller disk and the casing is smaller than the boundary layer thickness. In addition, the disk friction loss of the impeller is increased in line with the increments in surface roughness in a similar pattern as that of existing experimental empirical formulas. The disk friction loss of the impeller is more affected by the surface roughness than the change of the axial clearance. To minimize disk friction loss on the centrifugal compressor impeller, the axial clearance and the theoretical boundary layer thickness should be designed to be the same. The design of the impeller requires careful consideration in order to optimize axial clearance and minimize surface roughness.

Bifurcation parameters of a reflected shock wave in cylindrical channels of different roughnesses

NASA Astrophysics Data System (ADS)

Penyazkov, O.; Skilandz, A.

2018-03-01

To investigate the effect of bifurcation on the induction time in cylindrical shock tubes used for chemical kinetic experiments, one should know the parameters of the bifurcation structure of a reflected shock wave. The dynamics and parameters of the shock wave bifurcation, which are caused by reflected shock wave-boundary layer interactions, are studied experimentally in argon, in air, and in a hydrogen-nitrogen mixture for Mach numbers M = 1.3-3.5 in a 76-mm-diameter shock tube without any ramp. Measurements were taken at a constant gas density behind the reflected shock wave. Over a wide range of experimental conditions, we studied the axial projection of the oblique shock wave and the pressure distribution in the vicinity of the triple Mach configuration at 50, 150, and 250 mm from the endwall, using side-wall schlieren and pressure measurements. Experiments on a polished shock tube and a shock tube with a surface roughness of 20 {μ }m Ra were carried out. The surface roughness was used for initiating small-scale turbulence in the boundary layer behind the incident shock wave. The effect of small-scale turbulence on the homogenization of the transition zone from the laminar to turbulent boundary layer along the shock tube perimeter was assessed, assuming its influence on a subsequent stabilization of the bifurcation structure size versus incident shock wave Mach number, as well as local flow parameters behind the reflected shock wave. The influence of surface roughness on the bifurcation development and pressure fluctuations near the wall, as well as on the Mach number, at which the bifurcation first develops, was analyzed. It was found that even small additional surface roughness can lead to an overshoot in pressure growth by a factor of two, but it can stabilize the bifurcation structure along the shock tube perimeter.

Modeling quantum yield, emittance, and surface roughness effects from metallic photocathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimitrov, D. A.; Bell, G. I.; Smedley, J.

Here, detailed measurements of momentum distributions of emitted electrons have allowed the investigation of the thermal limit of the transverse emittance from metal photocathodes. Furthermore, recent developments in material design and growth have resulted in photocathodes that can deliver high quantum efficiency and are sufficiently robust to use in high electric field gradient photoinjectors and free electron lasers. The growth process usually produces photoemissive material layers with rough surface profiles that lead to transverse accelerating fields and possible work function variations, resulting in emittance growth. To better understand the effects of temperature, density of states, and surface roughness on themore » properties of emitted electrons, we have developed realistic three-dimensional models for photocathode materials with grated surface structures. They include general modeling of electron excitation due to photon absorption, charge transport, and emission from flat and rough metallic surfaces. The models also include image charge and field enhancement effects. We report results from simulations with flat and rough surfaces to investigate how electron scattering, controlled roughness, work function variation, and field enhancement affect emission properties. Comparison of simulation results with measurements of the quantum yield and transverse emittance from flat Sb emission surfaces shows the importance of including efficient modeling of photon absorption, temperature effects, and the material density of states to achieve agreement with the experimental data.« less

Modeling quantum yield, emittance, and surface roughness effects from metallic photocathodes

DOE PAGES

Dimitrov, D. A.; Bell, G. I.; Smedley, J.; ...

2017-10-26

Here, detailed measurements of momentum distributions of emitted electrons have allowed the investigation of the thermal limit of the transverse emittance from metal photocathodes. Furthermore, recent developments in material design and growth have resulted in photocathodes that can deliver high quantum efficiency and are sufficiently robust to use in high electric field gradient photoinjectors and free electron lasers. The growth process usually produces photoemissive material layers with rough surface profiles that lead to transverse accelerating fields and possible work function variations, resulting in emittance growth. To better understand the effects of temperature, density of states, and surface roughness on themore » properties of emitted electrons, we have developed realistic three-dimensional models for photocathode materials with grated surface structures. They include general modeling of electron excitation due to photon absorption, charge transport, and emission from flat and rough metallic surfaces. The models also include image charge and field enhancement effects. We report results from simulations with flat and rough surfaces to investigate how electron scattering, controlled roughness, work function variation, and field enhancement affect emission properties. Comparison of simulation results with measurements of the quantum yield and transverse emittance from flat Sb emission surfaces shows the importance of including efficient modeling of photon absorption, temperature effects, and the material density of states to achieve agreement with the experimental data.« less

Boundary-layer cumulus over land: Some observations and conceptual models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stull, R.B.

1993-09-01

Starting in 1980, the Boundary Layer Research Team at the University of Wisconsin has been systematically studying the formation and evolution of nonprecipitating boundary-layer cumulus clouds (BLCu) in regions of fair weather (anticyclones) over land (Stull, 1980). Our approach is to quantify the average statistical characteristics of the surface, thermals, boundary layer, and clouds over horizontal regions of roughly 20 km in diameter. Within such a region over land, there is typically quite a variation in land use, and associated variations in surface albedo and moisture.

Transition Experiments on Large Bluntness Cones with Distributed Roughness in Hypersonic Flight

NASA Technical Reports Server (NTRS)

Reda, Daniel. C.; Wilder, Michael C.; Prabhu, Dinesh K.

2012-01-01

Large bluntness cones with smooth nosetips and roughened frusta were flown in the NASA Ames hypersonic ballistic range at a Mach number of 10 through quiescent air environments. Global surface intensity (temperature) distributions were optically measured and analyzed to determine transition onset and progression over the roughened surface. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted to predict values of key dimensionless parameters used to correlate transition on such configurations in hypersonic flow. For these large bluntness cases, predicted axial distributions of the roughness Reynolds number showed (for each specified freestream pressure) that this parameter was a maximum at the physical beginning of the roughened zone and decreased with increasing run length along the roughened surface. Roughness-induced transition occurred downstream of this maximum roughness Reynolds number location, and progressed upstream towards the beginning of the roughened zone as freestream pressure was systematically increased. Roughness elements encountered at the upstream edge of the roughened frusta thus acted like a finite-extent trip array, consistent with published results concerning the tripping effectiveness of roughness bands placed on otherwise smooth surfaces.

Numerical Computations of Hypersonic Boundary-Layer over Surface Irregularities

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan M.; Li, Fei

2010-01-01

Surface irregularities such as protuberances inside a hypersonic boundary layer may lead to premature transition on the vehicle surface. Early transition in turn causes large localized surface heating that could damage the thermal protection system. Experimental measurements as well as numerical computations aimed at building a knowledge base for transition Reynolds numbers with respect to different protuberance sizes and locations have been actively pursued in recent years. This paper computationally investigates the unsteady wake development behind large isolated cylindrical roughness elements and the scaled wind-tunnel model of the trip used in a recent flight measurement during the reentry of space shuttle Discovery. An unstructured mesh, compressible flow solver based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for the flow past a roughness element under several wind-tunnel conditions. For a cylindrical roughness element with a height to the boundary-layer thickness ratio from 0.8 to 2.5, the wake flow is characterized by a mushroom-shaped centerline streak and horse-shoe vortices. While time-accurate solutions converged to a steady-state for a ratio of 0.8, strong flow unsteadiness is present for a ratio of 1.3 and 2.5. Instability waves marked by distinct disturbance frequencies were found in the latter two cases. Both the centerline streak and the horse-shoe vortices become unstable downstream. The oscillatory vortices eventually reach an early breakdown stage for the largest roughness element. Spectral analyses in conjunction with the computed root mean square variations suggest that the source of the unsteadiness and instability waves in the wake region may be traced back to possible absolute instability in the front-side separation region.

Analysis of the influence of chemical treatment to the strength and surface roughness of FDM

NASA Astrophysics Data System (ADS)

Hambali, R. H.; Cheong, K. M.; Azizan, N.

2017-06-01

The applications of Additive Manufacturing (AM) technology have a greater functionality and wider range of application beyond an intention of prototyping. AM is the process of joining materials to form objects from Computer-Aided Design (CAD) models via layer upon layer process. One of AM technologies is the Fused Deposition Modelling (FDM), which use an extrusion method to create a part. FDM has been applied in many manufacturing applications includes an end-used parts. However, FDM tends to have bad surface quality due to staircase effect and post treatment is required. This chemical treatment is one of a way to improve the surface roughness of FDM fabricated parts. This method is one of economical and faster method. In order to enhance the surface finish of Acrylonitrile-Butadiene-Styrene (ABS) FDM parts by performing chemical treatment in an acetone solution as acetone has very low toxicity, high diffusion and low cost chemical solution. Therefore, the aim of this research is to investigate the influence of chemical treatment to the FDM used part in terms of surface roughness as well as the strength. In this project, ten specimens of standard ASTM D638 dogbone specimens have been fabricated using MOJO 3D printer. Five specimens from the dogbone were tested for surface roughness and tensile testing while another five were immersed in the chemical solution before the same testing. Based on results, the surface roughness of chemically treated dogbone has dramatically improved, compared to untreated dogbone with 97.2% of improvement. However, in term of strength, the tensile strength of dogbone is reduced 42.58% due to the rearrange of material properties and chemical effects to the joining of the filaments. In conclusion, chemical treatment is an economical and sustainable approach to enhance the surface quality of AM parts.

Optimization of the buffer surface of CoFeB/MgO/CoFeB-based magnetic tunnel junctions by ion beam milling

NASA Astrophysics Data System (ADS)

Martins, L.; Ventura, J.; Ferreira, R.; Freitas, P. P.

2017-12-01

Due to their high tunnel magnetoresistance (TMR) ratios at room temperature, magnetic tunnel junctions (MTJs) with a crystalline MgO insulating barrier and CoFeB ferromagnetic (FM) layers are the best candidates for novel magnetic memory applications. To overcome impedance matching problems in electronic circuits, the MgO barrier must have an ultra-low thickness (∼1 nm). Therefore, it is mandatory to optimize the MTJ fabrication process, in order to prevent relevant defects in the MgO barrier that could affect the magnetic and electrical MTJ properties. Here, a smoothing process aiming to decrease the roughness of the buffer surface before the deposition of the full MTJ stack is proposed. An ion beam milling process was used to etch the surface of an MTJ buffer structure with a Ru top layer. The morphologic results prove an effective decrease of the Ru surface roughness with the etching time. The electrical and magnetic results obtained for MTJs with smoothed buffer structures show a direct influence of the buffer roughness and coupling field on the improvement of the TMR ratio.

Effect of surface pre-treatments on biocompatibility of magnesium.

PubMed

Lorenz, Carla; Brunner, Johannes G; Kollmannsberger, Philip; Jaafar, Leila; Fabry, Ben; Virtanen, Sannakaisa

2009-09-01

This study reports the influence of Mg surface passivation on the survival rate of human HeLa cells and mouse fibroblasts in cell culture experiments. Polished samples of commercially pure Mg show high reactivity in the cell culture medium, leading to a pH shift in the alkaline direction, and therefore cell adhesion and survival is strongly impaired. Passivation of the Mg surface in 1M NaOH can strongly enhance cell survival. The best initial cell adhesion is observed for Mg samples incubated in simulated body fluid (M-SBF), which leads to the formation of a biomimetic, amorphous Ca/Mg-phosphate layer with high surface roughness. This surface layer, however, passivates and seals the Mg surface only partially. Subsequent Mg dissolution leads to a significantly stronger pH increase compared to NaOH-passivated samples, which prevents long-term cell survival. These results demonstrate that surface passivation with NaOH and M-SBF together with the associated changes of surface reactivity, chemistry and roughness provide a viable strategy to facilitate cell survival on otherwise non-biocompatible Mg surfaces.

Transparent superwetting nanofilms with enhanced durability at model physiological condition

PubMed Central

Hwangbo, Sunghee; Heo, Jiwoong; Lin, Xiangde; Choi, Moonhyun; Hong, Jinkee

2016-01-01

There have been many studies on superwetting surfaces owing to the variety of their potential applications. There are some drawbacks to developing these films for biomedical applications, such as the fragility of the microscopic roughness feature that is vital to ensure superwettability. But, there are still only a few studies that have shown an enhanced durability of nanoscale superwetting films at certain extreme environment. In this study, we fabricated intrinsically stable superwetting films using the organosilicate based layer-by-layer (LbL) self-assembly method in order to control nano-sized roughness of the multilayer structures. In order to develop mechanically and chemically robust surfaces, we successfully introduced polymeric silsesquioxane as a building block for LbL assembly with desired fashion. Even in the case that the superhydrophobic outer layers were damaged, the films maintained their superhydrophobicity because of the hydrophobic nature of their inner layers. As a result, we successfully fabricated superwetting nano-films and evaluated their robustness and stability. PMID:26764164

Impact of thickness on the structural properties of high tin content GeSn layers

NASA Astrophysics Data System (ADS)

Aubin, J.; Hartmann, J. M.; Gassenq, A.; Milord, L.; Pauc, N.; Reboud, V.; Calvo, V.

2017-09-01

We have grown various thicknesses of GeSn layers in a 200 mm industrial Reduced Pressure - Chemical Vapor Deposition cluster tool using digermane (Ge2H6) and tin tetrachloride (SnCl4). The growth pressure (100 Torr) and the F(Ge2H6)/F(SnCl4) mass-flow ratio were kept constant, and incorporation of tin in the range of 10-15% was achieved with a reduction in temperature: 325 °C for 10% to 301 °C for 15% of Sn. The layers were grown on 2.5 μm thick Ge Strain Relaxed Buffers, themselves on Si(0 0 1) substrates. We used X-ray Diffraction, Atomic Force Microscopy, Raman spectroscopy and Scanning Electron Microscopy to measure the Sn concentration, the strain state, the surface roughness and thickness as a function of growth duration. A dramatic degradation of the film was seen when the Sn concentration and layer thickness were too high resulting in rough/milky surfaces and significant Sn segregation.

Real time measurements of surface growth evolution in magnetron sputtered single crystal Mo/V superlattices using in situ reflection high energy electron diffraction analysis

NASA Astrophysics Data System (ADS)

Svedberg, E. B.; Birch, J.; Edvardsson, C. N. L.; Sundgren, J.-E.

1999-07-01

The use of video recording of reflection high energy electron diffraction (RHEED) patterns for assessing the dynamic evolution of the surface morphology and crystallinity during growth was evaluated. As an example, Mo/V(001) superlattices with varying layer thickness (with periods Λ of 2.5 to 8.9 nm and a constant Mo:V ratio of 1:1) were examined. During the deposition, changes from two- to three-dimensional growth were observed in situ. From prior transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies, it is known that this transition is associated with a critical thickness and concurrent roughening of the V layer. Video recording and subsequent image and data processing allowed the surface morphology to be continuously followed during growth. Post-growth analyses of the recorded data provided the evolution of surface lattice parameters and short range [1-2 monolayer (ML)] surface roughnesses with a time resolution of 200-400 ms (0.02-0.04 nm thickness resolution). During growth of Mo, a smoothening effect could be observed while the growth of V evidently increased the surface roughness from 1 to 2 ML. Furthermore, the onset of coherency strain relaxation of the topmost growing layers was observed to occur at 2.0-2.5 nm layer thicknesses for both materials, which is in qualitative agreement with theoretical predictions.

Optimization of Al2O3/TiO2/Al 2O3 Multilayer Antireflection Coating With X-Ray Scattering Techniques

NASA Astrophysics Data System (ADS)

Li, Chao

Broadband multilayer antireflection coatings (ARCs) are keys to improving solar cell efficiencies. The goal of this dissertation is to optimize the multilayer Al2O3/TiO2/Al2O 3 ARC designed for a III-V space multi-junction solar cell with understanding influences of post-annealing and varying deposition parameters on the optical properties. Accurately measuring optical properties is important in accessing optical performances of ARCs. The multilayer Al2O3/TiO 2/Al2O3 ARC and individual Al2O 3 and TiO2 layers were characterized by a novel X-ray reflectivity (XRR) method and a combined method of grazing-incidence small angle X-ray scattering (GISAXS), atomic force microscopy (AFM), and XRR developed in this study. The novel XRR method combining an enhanced Fourier analysis with specular XRR simulation effectively determines layer thicknesses and surface and interface roughnesses and/or grading with sub-nanometer precision, and densities less than three percent uncertainty. Also, the combined method of GISAXS, AFM, and XRR characterizes the distribution of pore size with one-nanometer uncertainty. Unique to this method, the diffuse scattering from surface and interface roughnesses is estimated with surface parameters (root mean square roughness sigma, lateral correlation length ξ, and Hurst parameter h) obtained from AFM, and layer densities, surface grading and interface roughness/grading obtained from specular XRR. It is then separated from pore scattering. These X-ray scattering techniques obtained consistent results and were validated by other techniques including optical reflectance, spectroscopic ellipsometry (SE), glancing incidence X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy. The ARCs were deposited by atomic layer deposition with standard parameters at 200 °C. The as-deposited individual Al2O3 layer on Si is porous and amorphous as indicated by the combined methods of GISAXS, AFM, and XRR. Both post-annealing at 400 °C for 40 min in air and varying ALD parameters can eliminate pores, and lead to consistent increases in density and refractive index determined by the XRR method, SE, and optical reflectance measurements. After annealing, the layer remains amorphous. On the other hand, the as-deposited TiO 2 layer is non-porous and amorphous. It is densified and crystallized after annealing at 400 °C for 10 min in air. The multilayer Al2O 3/TiO2/Al2O3 ARC deposited on Si has surface and interface roughnesses and/or grading on the order of one nanometer. Annealing at 400 °C for 10 min in air induces densification and crystallization of the amorphous TiO2 layer as well as possible chemical reactions between TiO2 and Si diffusing from the substrate. On the other hand, Al2O3 layers remain amorphous after annealing. The thickness of the top Al2O3 layer decreases - likely due to interdiffusion between the top two layers and loss of hydrogen from hydroxyl groups initially present in the ALD layers. The thickness of the bottom Al2O3 layer increases, probably due to the diffusion of Si atoms into the bottom layer. In addition, the multilayer Al 2O3/TiO2/Al2O3 ARC was deposited on AlInP (30nm) / GaInP (100nm) / GaAs that includes the topmost layers of III-V multi-junction solar cells. Reflectance below 5 % is achieved within nearly the whole wavelength range of the current-limiting sub-cell. Also, internal scattering occurs in the TiO2 layer possibly associated with the initiated crystallization in the TiO2 layer while absent in the amorphous Al2O3 layers.

Laser shock peening studies on SS316LN plate with various sacrificial layers

NASA Astrophysics Data System (ADS)

Yella, Pardhu; Venkateswarlu, P.; Buddu, Ramesh K.; Vidyasagar, D. V.; Sankara Rao, K. Bhanu; Kiran, P. Prem; Rajulapati, Koteswararao V.

2018-03-01

Laser shock peening (LSP) has been utilized to modify the surface characteristics of SS316LN plates of 6 mm thickness. Laser pulse widths employed are 30 ps and 7 ns and the laser energy was varied in the range 5-90 mJ. Peening was performed in direct ablation mode as well as with various sacrificial layers such as black paint, transparent adhesive tape and absorbing adhesive tape. The surface characteristics were greatly influenced by the type of sacrificial layer employed. The average surface roughness values are about 0.4 μm when the black paint and transparent adhesive tape were used as sacrificial layers. In contrast to this, using absorbent adhesive tape as a sacrificial layer has resulted in an average surface roughness of about 0.04 μm. Irrespective of pulse durations (30 ps or 7 ns), absorbent adhesive tape has always resulted in compressive residual stresses whereas other layers appear to be not that effective. In case of 30 ps pulse, as the laser energy was increased from 5 mJ to 25 mJ, there was a texture observed in (111) reflection of X-ray diffractograms and the center of the peak has also gradually shifted to left. X-ray line profile analysis suggests that with the increase in laser energy, lattice microstrain also has increased. This lattice microstrain appears to be resulting from the increased dislocation density in the peened sample as evidenced during transmission electron microscopic investigations. Cross-sectional scanning electron microscopy performed on peened samples suggests that absorbing adhesive tape brings no surface damage to the samples whereas other sacrificial layers have resulted in some surface damage. Based on all these structural and microstructural details, it is recommended that absorbent tape could be used as a sacrificial layer during LSP process which induces surface residual stresses with no damage to the sample surface.

Surface pre-treatment for barrier coatings on polyethylene terephthalate

NASA Astrophysics Data System (ADS)

Bahre, H.; Bahroun, K.; Behm, H.; Steves, S.; Awakowicz, P.; Böke, M.; Hopmann, Ch; Winter, J.

2013-02-01

Polymers have favourable properties such as light weight, flexibility and transparency. Consequently, this makes them suitable for food packaging, organic light-emitting diodes and flexible solar cells. Nonetheless, raw plastics do not possess sufficient barrier functionality against oxygen and water vapour, which is of paramount importance for most applications. A widespread solution is to deposit thin silicon oxide layers using plasma processes. However, silicon oxide layers do not always fulfil the requirements concerning adhesion and barrier performance when deposited on films. Thus, plasma pre-treatment is often necessary. To analyse the influence of a plasma-based pre-treatment on barrier performance, different plasma pre-treatments on three reactor setups were applied to a very smooth polyethylene terephthalate film before depositing a silicon oxide barrier layer. In this paper, the influence of oxygen and argon plasma pre-treatments towards the barrier performance is discussed examining the chemical and topological change of the film. It was observed that a short one-to-ten-second plasma treatment can reduce the oxygen transmission rate by a factor of five. The surface chemistry and the surface topography change significantly for these short treatment times, leading to an increased surface energy. The surface roughness rises slowly due to the development of small spots in the nanometre range. For very long treatment times, surface roughness of the order of the barrier layer's thickness results in a complete loss of barrier properties. During plasma pre-treatment, the trade-off between surface activation and roughening of the surface has to be carefully considered.

Epitaxial ZnO/LiNbO{sub 3}/ZnO stacked layer waveguide for application to thin-film Pockels sensors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akazawa, Housei, E-mail: akazawa.housei@lab.ntt.co.jp; Fukuda, Hiroshi

We produced slab waveguides consisting of a LiNbO{sub 3} (LN) core layer that was sandwiched with Al-doped ZnO cladding layers. The ZnO/LN/ZnO stacked layers were grown on sapphire C-planes by electron cyclotron resonance (ECR) plasma sputtering and were subjected to structural, electrical, and optical characterizations. X-ray diffraction confirmed that the ZnO and LN layers were epitaxial without containing misoriented crystallites. The presence of 60°-rotational variants of ZnO and LN crystalline domains were identified from X-ray pole figures. Cross-sectional transmission electron microscopy images revealed a c-axis orientated columnar texture for LN crystals, which ensured operation as electro-optic sensors based on opticalmore » anisotropy along longitudinal and transversal directions. The interfacial roughness between the LN core and ZnO bottom layers as well as that between the ZnO top and the LN core layers was less than 20 nm, which agreed with surface images observed with atomic force microscopy. Outgrowth of triangular LN crystalline domains produced large roughness at the LN film surface. The RMS roughness of the LN film surface was twice that of the same structure grown on sapphire A-planes. Vertical optical transmittance of the stacked films was higher than 85% within the visible and infrared wavelength range. Following the approach adopted by Teng and Man [Appl. Phys. Lett. 56, 1734 (1990)], ac Pockels coefficients of r{sub 33} = 24-28 pm/V were derived for c-axis oriented LN films grown on low-resistive Si substrates. Light propagation within a ZnO/LN/ZnO slab waveguide as well as within a ZnO single layer waveguide was confirmed. The birefringence of these waveguides was 0.11 for the former and 0.05 for the latter.« less

Impact of Aspect Ratio, Incident Angle, and Surface Roughness on Windbreak Wakes

NASA Astrophysics Data System (ADS)

Tobin, Nicolas; Chamorro, Leonardo P.

2017-11-01

Wind-tunnel results are presented on the wakes behind three-dimensional windbreaks in a simulated atmospheric boundary layer. Sheltering by upwind windbreaks, and surface-mounted obstacles (SMOs) in general, is parameterized by the wake-moment coefficient C h , which is a complex function of obstacle geometry and flow conditions. Values of C h are presented for several windbreak aspect ratios, incident angles, and windbreak-height-to-surface-roughness ratios. Lateral wake deflection is further presented for several incident angles and aspect ratios, and compared to a simple analytical formulation including a near- and far-wake solution. It is found that C h does not change with aspect ratios of 10 or greater, though C h may be lower for an aspect ratio of 5. C h is found to change roughly with the cosine of the incident angle, and to depend strongly on windbreak-height-to-surface-roughness ratio. The data broadly support the proposed wake-deflection model.

Bistatic scattering from a three-dimensional object above a two-dimensional randomly rough surface modeled with the parallel FDTD approach.

PubMed

Guo, L-X; Li, J; Zeng, H

2009-11-01

We present an investigation of the electromagnetic scattering from a three-dimensional (3-D) object above a two-dimensional (2-D) randomly rough surface. A Message Passing Interface-based parallel finite-difference time-domain (FDTD) approach is used, and the uniaxial perfectly matched layer (UPML) medium is adopted for truncation of the FDTD lattices, in which the finite-difference equations can be used for the total computation domain by properly choosing the uniaxial parameters. This makes the parallel FDTD algorithm easier to implement. The parallel performance with different number of processors is illustrated for one rough surface realization and shows that the computation time of our parallel FDTD algorithm is dramatically reduced relative to a single-processor implementation. Finally, the composite scattering coefficients versus scattered and azimuthal angle are presented and analyzed for different conditions, including the surface roughness, the dielectric constants, the polarization, and the size of the 3-D object.

Effect of substrate chemical pretreatment on the tribological properties of graphite films

NASA Technical Reports Server (NTRS)

Fusaro, R. L.

1984-01-01

Rubbed films of natural flake Madagascar graphite were applied to ASTM A-355(D) steel with chemical surface pretreatments of zinc phosphate, gas nitride, salt nitride, sulfo-nitride, and with mechanical pretreatment (sandblasting). SAE 1045 steel pins were slid against these films using a pin-on-disk tribometer. The results indicate that two different lubricating mechanisms can occur. In the chemical surface pretreatment, the graphite can mix together to form a surface layer of the two constituents and this plasticity flowing layer provides the lubrication. The longest endurance lives and the lowest pin wear rates were obtained with this mechanism. In the other, surface topography appeared to control the mechanism. A rough surface was necessary to serve as a reservoir to supply the graphite to the flat metallic plateaus where it was sheared in very thin films between the plateaus and the sliding pin surface. For this mechanism, chemical pretreatment seemed to do little more than serve as a means for roughening the surface. Mean friction was not significantly influenced by chemical pretreatment, but surface roughness effects were observed.

Assessment of Surface Area Characteristics of Dental Implants with Gradual Bioactive Surface Treatment

NASA Astrophysics Data System (ADS)

Czan, Andrej; Babík, Ondrej; Miklos, Matej; Záušková, Lucia; Mezencevová, Viktória

2017-10-01

Since most of the implant surface is in direct contact with bone tissue, shape and integrity of said surface has great influence on successful osseointegration. Among other characteristics that predetermine titanium of different grades of pureness as ideal biomaterial, titanium shows high mechanical strength making precise miniature machining increasingly difficult. Current titanium-based implants are often anodized due to colour coding. This anodized layer has important functional properties for right usage and also bio-compatibility of dental implants. Physical method of anodizing and usage of anodizing mediums has a significant influence on the surface quality and itself functionality. However, basic requirement of the dental implant with satisfactory properties is quality of machined surface before anodizing. Roughness, for example, is factor affecting of time length of anodizing operation and so whole productivity. The paper is focused on monitoring of surface and area characteristics, such as roughness or surface integrity after different cutting conditions of miniature machining of dental implants and their impact on suitability for creation of satisfactory anodized layer with the correct biocompatible functional properties.

On the modeling of wave-enhanced turbulence nearshore

NASA Astrophysics Data System (ADS)

Moghimi, Saeed; Thomson, Jim; Özkan-Haller, Tuba; Umlauf, Lars; Zippel, Seth

2016-07-01

A high resolution k-ω two-equation turbulence closure model, including surface wave forcing was employed to fully resolve turbulence dissipation rate profiles close to the ocean surface. Model results were compared with observations from Surface Wave Instrument Floats with Tracking (SWIFTs) in the nearshore region at New River Inlet, North Carolina USA, in June 2012. A sensitivity analysis for different physical parameters and wave and turbulence formulations was performed. The flux of turbulent kinetic energy (TKE) prescribed by wave dissipation from a numerical wave model was compared with the conventional prescription using the wind friction velocity. A surface roughness length of 0.6 times the significant wave height was proposed, and the flux of TKE was applied at a distance below the mean sea surface that is half of this roughness length. The wave enhanced layer had a total depth that is almost three times the significant wave height. In this layer the non-dimensionalized Terray scaling with power of - 1.8 (instead of - 2) was applicable.

Assessment of surface turbulent fluxes using geostationary satellite surface skin temperatures and a mixed layer planetary boundary layer scheme

NASA Technical Reports Server (NTRS)

Diak, George R.; Stewart, Tod R.

1989-01-01

A method is presented for evaluating the fluxes of sensible and latent heating at the land surface, using satellite-measured surface temperature changes in a composite surface layer-mixed layer representation of the planetary boundary layer. The basic prognostic model is tested by comparison with synoptic station information at sites where surface evaporation climatology is well known. The remote sensing version of the model, using satellite-measured surface temperature changes, is then used to quantify the sharp spatial gradient in surface heating/evaporation across the central United States. An error analysis indicates that perhaps five levels of evaporation are recognizable by these methods and that the chief cause of error is the interaction of errors in the measurement of surface temperature change with errors in the assigment of surface roughness character. Finally, two new potential methods for remote sensing of the land-surface energy balance are suggested which will relay on space-borne instrumentation planned for the 1990s.

Hierarchical roughness of sticky and non-sticky superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Raza, Muhammad; Kooij, Stefan; van Silfhout, Arend; Zandvliet, Harold; Poelsema, Bene

2011-11-01

The importance of superhydrophobic substrates (contact angle >150° with sliding angle <10°) in modern technology is undeniable. We present a simple colloidal route to manufacture superstructured arrays with single- and multi-length-scaled roughness to obtain sticky and non-sticky superhydrophobic surfaces. The largest length scale is provided by (multi-)layers of silica spheres (1 μm, 500nm and 150nm diameter). Decoration with gold nanoparticles (14nm, 26nm and 47nm) gives rise to a second length scale. To lower the surface energy, gold nanoparticles are functionalized with dodecanethiol and the silica spheres by perfluorooctyltriethoxysilane. The morphology was examined by helium ion microscopy (HIM), while wettability measurements were performed by using the sessile drop method. We conclude that wettability can be controlled by changing the surface chemistry and/or length scales of the structures. To achieve truly non-sticky superhydrophobic surfaces, hierarchical roughness plays a vital role.

Importance of tread inertia and damping on the tyre/road contact stiffness

NASA Astrophysics Data System (ADS)

Winroth, J.; Andersson, P. B. U.; Kropp, W.

2014-10-01

Predicting tyre/road interaction processes like roughness excitation, stick-slip, stick-snap, wear and traction requires detailed information about the road surface, the tyre dynamics and the local deformation of the tread at the interface. Aspects of inertia and damping when the tread is locally deformed are often neglected in many existing tyre/road interaction models. The objective of this paper is to study how the dynamic features of the tread affect contact forces and contact stiffness during local deformation. This is done by simulating the detailed contact between an elastic layer and a rough road surface using a previously developed numerical time domain contact model. Road roughness on length scales smaller than the discretisation scale is included by the addition of nonlinear contact springs between each pair of contact elements. The dynamic case, with an elastic layer impulse response extending in time, is compared with the case where the corresponding quasi-static response is used. Results highlight the difficulty of estimating a constant contact stiffness as it increases during the indentation process between the elastic layer and the rough road surface. The stiffness-indentation relation additionally depends on how rapidly the contact develops; a faster process gives a stiffer contact. Material properties like loss factor and density also alter the contact development. This work implies that dynamic properties of the local tread deformation may be of importance when simulating contact details during normal tyre/road interaction conditions. There are however indications that the significant effect of damping could approximately be included as an increased stiffness in a quasi-static tread model.

Slippery surfaces of pitcher plants: Nepenthes wax crystals minimize insect attachment via microscopic surface roughness.

PubMed

Scholz, I; Bückins, M; Dolge, L; Erlinghagen, T; Weth, A; Hischen, F; Mayer, J; Hoffmann, S; Riederer, M; Riedel, M; Baumgartner, W

2010-04-01

Pitcher plants of the genus Nepenthes efficiently trap and retain insect prey in highly specialized leaves. Besides a slippery peristome which inhibits adhesion of insects they employ epicuticular wax crystals on the inner walls of the conductive zone of the pitchers to hamper insect attachment by adhesive devices. It has been proposed that the detachment of individual crystals and the resulting contamination of adhesive organs is responsible for capturing insects. However, our results provide evidence in favour of a different mechanism, mainly based on the stability and the roughness of the waxy surface. First, we were unable to detect a large quantity of crystal fragments on the pads of insects detached from mature pitcher surfaces of Nepenthes alata. Second, investigation of the pitcher surface by focused ion beam treatment showed that the wax crystals form a compact 3D structure. Third, atomic force microscopy of the platelet-shaped crystals revealed that the crystals are mechanically stable, rendering crystal detachment by insect pads unlikely. Fourth, the surface profile parameters of the wax layer showed striking similarities to those of polishing paper with low grain size. By measuring friction forces of insects on this artificial surface we demonstrate that microscopic roughness alone is sufficient to minimize insect attachment. A theoretical model shows that surface roughness within a certain length scale will prevent adhesion by being too rough for adhesive pads but not rough enough for claws.

Influence of Wall Porosity and Surfaces Roughness on the Steady Performance of an Externally Pressurized Hydrostatic Conical Bearing Lubricated by a Rabinowitsch Fluid

NASA Astrophysics Data System (ADS)

Walicka, A.; Walicki, E.; Jurczak, P.; Falicki, J.

2017-08-01

In the paper, the influence of both the bearing surfaces roughness as well as porosity of one bearing surface on the pressure distribution and load-carrying capacity of a curvilinear, externally pressurized, thrust bearing is discussed. The equations of motion of a pseudo-plastic Rabinowitsch fluid are used to derive the Reynolds equation. After general considerations on the flow in a bearing clearance and in a porous layer using the Morgan-Cameron approximation and Christensen theory of hydrodynamic lubrication with rough bearing surfaces the modified Reynolds equation is obtained. The analytical solution is presented; as a result one obtains the formulae expressing the pressure distribution and load-carrying capacity. Thrust radial and conical bearings, externally pressurized, are considered as numerical examples.

[A surface reacted layer study of titanium-zirconium alloy after dental casting].

PubMed

Zhang, Y; Guo, T; Li, Z; Li, C

2000-10-01

To investigate the influence of the mold temperature on the surface reacted layer of Ti-Zr alloy castings. Ti-Zr alloy was casted into a mold which was made of a zircon (ZrO2.SiO2) for inner coating and a phosphate-bonded material for outer investing with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was casted separately. The surface roughness of the castings was calculated by instrument of smooth finish (China). From the surface to the inner part the Knoop hardness and thickness in reacted layer of Ti-Zr alloy casting was measured. The structure of the surface reacted layer was analysed by SEM. Elemental analyses of the interfacial zone of the casting was made by element line scanning observation. The surface roughness of the castings was increased significantly with the mold temperature increasing. At a higher mold temperature the Knoop hardness of the reactive layer was increased. At the three mold temperature the outmost surface was very hard, and microhardness data decreased rapidly where they reached constant values. The thickness was about 85 microns for castings at room temperature and 300 degrees C, 105 microns for castings at 600 degrees C. From the SEM micrograph of the Ti-Zr alloy casting, the surface reacted layer could be divided into three different layers. The first layer was called non-structure layer, which thickness was about 10 microns for room temperature group, 20 microns for 300 degrees C and 25 microns for 600 degrees C. The second layer was characterized by coarse-grained acicular crystal, which thickness was about 50 microns for three mold temperatures. The third layer was Ti-Zr alloy. The element line scanning showed non-structure layer with higher level of element of O, Al, Si and Zr, The higher the mold temperature during casting, the deeper the Si permeating and in the second layer the element Si could also be found. The mold temperature is one of the major factors influencing to casting quality. In order to reduce the surface reacted layer of Ti-Zr alloy castings, the lower mold temperature and the investment without Si should be chosen.

Osteoblast response to magnesium ion-incorporated nanoporous titanium oxide surfaces.

PubMed

Park, Jin-Woo; Kim, Youn-Jeong; Jang, Je-Hee; Song, Hwangjun

2010-11-01

This study investigated the surface characteristics and in vitro osteoconductivity of a titanium (Ti) surface incorporated with the magnesium ions (Mg) produced by hydrothermal treatment for future application as an endosseous implant surface. Mg-incorporated Ti oxide surfaces were produced by hydrothermal treatment using Mg-containing solution on two different microstructured surfaces--abraded minimally rough (Ma) or grit-blasted moderately rough (RBM) samples. The surface characteristics were evaluated using scanning electron microscopy, thin-film X-ray diffractometry, X-ray photoelectron spectroscopy, optical profilometry, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). MC3T3-E1 pre-osteoblast cell attachment, proliferation, alkaline phosphatase (ALP) activity, and quantitative analysis of osteoblastic gene expression on Ma, RBM, Mg-incorporated Ma (Mg), and Mg-incorporated grit-blasted (RBM/Mg) Ti surfaces were evaluated. Hydrothermal treatment produced an Mg-incorporated Ti oxide layer with nanoporous surface structures. Mg-incorporated surfaces showed surface morphologies and surface roughness values almost identical to those of untreated smooth or micro-rough surfaces at the micron scale. ICP-AES analysis showed Mg ions released from treated surfaces into the solution. Mg incorporation significantly increased cellular attachment (P=0 at 0.5 h, P=0.01 at 1 h) on smooth surfaces, but no differences were found on micro-rough surfaces. Mg incorporation further increased ALP activity in cells grown on both smooth and micro-rough surfaces at 7 and 14 days of culture (P=0). Real-time polymerase chain reaction analysis showed higher mRNA expressions of the osteoblast transcription factor gene (Dlx5), various integrins, and the osteoblast phenotype genes (ALP, bone sialoprotein and osteocalcin) in cells grown on micro-rough (RBM) and Mg-incorporated (Mg and RBM/Mg) surfaces than those on Ma surfaces. Mg incorporation further increased the mRNA expressions of key osteoblast genes and integrins (α1, α2, α5, and β1) in cells grown on both the smooth and the micro-rough surfaces. These results indicate that an Mg-incorporated nanoporous Ti oxide surface produced by hydrothermal treatment may improve implant bone healing by enhancing the attachment and differentiation of osteoblastic cells. © 2010 John Wiley & Sons A/S.

Experimental Investigation of Roughness Effects on Transition Onset and Turbulent Heating Augmentation on a Hemisphere at Mach 6 and Mach 10

NASA Technical Reports Server (NTRS)

Hollis, Brian R.

2017-01-01

An experimental investigation of the effects of distributed surface roughness on boundary-layer transition and turbulent heating has been conducted. Hypersonic wind tunnel testing was performed using hemispherical models with surface roughness patterns simulating those produced by heat shield ablation. Global aeroheating and transition onset data were obtained using phosphor thermography at Mach 6 and Mach 10 over a range of roughness heights and free stream Reynolds numbers sufficient to produce laminar, transitional and turbulent flow. Upstream movement of the transition onset location and increasing heating augmentation over predicted smooth-wall levels were observed with both increasing roughness heights and increasing free stream Reynolds numbers. The experimental heating data are presented herein, as are comparisons to smooth-wall heat transfer distributions from computational flow-field simulations. The transition onset data are also tabulated, and correlations of these data are presented.

Synthesis of antireflective silica coatings through the synergy of polypeptide layer-by-layer assemblies and biomineralization

NASA Astrophysics Data System (ADS)

Lee, Yung-Lun; Lin, Ting-Xuan; Hsu, Feng-Ming; Jan, Jeng-Shiung

2016-01-01

We report a versatile approach to synthesize silica coatings with antireflective (AR) characteristics through the combination of a layer-by-layer (LbL) assembly technique and biomineralization. LbL assembled decanoyl-modified poly(l-lysine)/poly(l-glutamic acid) (PLL-g-Dec/PLGA) multilayer films were used as templates for silica mineralization, followed by calcination. The specific deposition of silica onto the LbL polypeptide assemblies through amine-catalyzed polycondensation resulted in silica coatings that exhibited the transcription of the nano-/microstructured polypeptide films and their film thickness and porosity can be tuned by varying the number of bilayers, degree of substitution, and PLL molecular weight. AR silica coatings exhibiting more than 6% increase in transmittance in the near UV/visible spectral range can be obtained at an optimized refractive index, thickness, and surface roughness. The abrasion test showed that the silica coatings exhibited sufficient structural durability due to continuous silica nanostructures and low surface roughness. This study demonstrated that nanostructured thin films can be synthesized for AR coatings using the synergy between the LbL assembly technique and biomineralization.We report a versatile approach to synthesize silica coatings with antireflective (AR) characteristics through the combination of a layer-by-layer (LbL) assembly technique and biomineralization. LbL assembled decanoyl-modified poly(l-lysine)/poly(l-glutamic acid) (PLL-g-Dec/PLGA) multilayer films were used as templates for silica mineralization, followed by calcination. The specific deposition of silica onto the LbL polypeptide assemblies through amine-catalyzed polycondensation resulted in silica coatings that exhibited the transcription of the nano-/microstructured polypeptide films and their film thickness and porosity can be tuned by varying the number of bilayers, degree of substitution, and PLL molecular weight. AR silica coatings exhibiting more than 6% increase in transmittance in the near UV/visible spectral range can be obtained at an optimized refractive index, thickness, and surface roughness. The abrasion test showed that the silica coatings exhibited sufficient structural durability due to continuous silica nanostructures and low surface roughness. This study demonstrated that nanostructured thin films can be synthesized for AR coatings using the synergy between the LbL assembly technique and biomineralization. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06948c

Formation of pentacene wetting layer on the SiO2 surface and charge trap in the wetting layer.

PubMed

Kim, Chaeho; Jeon, D

2008-09-01

We studied the early-stage growth of vacuum-evaporated pentacene film on a native SiO(2) surface using atomic force microscopy and in-situ spectroscopic ellipsometry. Pentacene deposition prompted an immediate change in the ellipsometry spectra, but atomic force microscopy images of the early stage films did not show a pentacene-related morphology other than the decrease in the surface roughness. This suggested that a thin pentacene wetting layer was formed by pentacene molecules lying on the surface before the crystalline islands nucleated. Growth simulation based on the in situ spectroscopic ellipsometry spectra supported this conclusion. Scanning capacitance microscopy measurement indicated the existence of trapped charges in the SiO(2) and pentacene wetting layer.

Characteristics of the Martian atmosphere surface layer

NASA Technical Reports Server (NTRS)

Clow, G. D.; Haberle, R. M.

1991-01-01

Researchers extend elements of various terrestrial boundary layer models to Mars in order to estimate sensible heat, latent heat, and momentum fluxes within the Martian atmospheric surface layer. To estimate the molecular viscosity and thermal conductivity of a CO2-H2O gas mixture under Martian conditions, parameterizations were developed. Parameterizations for specific heat and and binary diffusivity were also determined. The Prandtl and Schmidt numbers derived from these thermophysical properties were found to range from 0.78 - 1.0 and 0.47 - 0.70, respectively, for Mars. Brutsaert's model for sensible and latent heat transport within the interfacial sublayer for both aerodynamically smooth and rough airflow was experimentally tested under similar conditions, validating its application to Martian conditions. For the surface sublayer, the researchers modified the definition of the Monin-Obukhov length to properly account for the buoyancy forces arising from water vapor gradients in the Martian atmospheric boundary layer. This length scale was then utilized with similarity theory turbulent flux profiles with the same form as those used by Businger et al. and others. It was found that under most Martian conditions, the interfacial and surface sublayers offer roughly comparable resistance to sensible heat and water vapor transport and are thus both important in determining the associated fluxes.

Effect of sealer coating and storage methods on the surface roughness of soft liners.

PubMed

Usta Kutlu, Ilknur; Yanikoğlu, Nuran Dinckal; Kul, Esra; Duymuş, Zeynep Yesïl; Sağsöz, Nurdan Polat

2016-03-01

A soft lining is applied under a removable prosthesis for various reasons. The porosity of the lining material may increase colonization by microorganisms and cause tissue inflammation. The purpose of this in vitro study was to evaluate the effect of sealer coating on the surface roughness of soft lining materials under 4 different conditions. A total of 125 specimens were prepared. One high-temperature silicone-based soft lining material and 2 room-temperature-polymerized soft lining materials (1 silicone-based and 1 methacrylate-based) were used. Twenty-five specimens of each room-temperature soft lining material were coated with 2 layers of surface sealer. Additionally, 5 specimens of each material were stored in either distilled water, Coca-Cola, denture cleanser, saliva, or air. The surface roughness was measured at baseline and after 1, 7, 14, and 28 days. Surface roughness values were analyzed with repeated measures analysis of variance, and the Bonferroni multiple comparison test was performed using time-dependent groups and storage methods. In the time-dependent groups, methacrylate-based sealer-coated soft liners exhibited a significant increase in roughness (1.74-2.09 μm, P<.001), and silicone-based sealer-coated soft liners exhibited a decrease in roughness, but it was not significant (2.16-2.02 μm, P>.05). Therefore, the sealer coating was not effective in reducing surface roughness. Among the time-dependent storage methods, the denture cleanser exhibited an almost significant increase in roughness (1.83-1.99 μm, P=.054). Coca-Cola and artificial saliva did not show a significant difference (P>.05). However, a significant decrease in roughness was found with distilled water (P=.02) and air (P<.001). Statistically significant differences in surface roughness were found among the different types of soft liners. The sealer coating had no significant effect, and denture cleanser slightly increased the surface roughness. Contrary to expectations, the roughness did not increase in all groups over time. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Aeroheating Measurement of Apollo Shaped Capsule with Boundary Layer Trip in the Free-piston Shock Tunnel HIEST

NASA Technical Reports Server (NTRS)

Hideyuki, TANNO; Tomoyuki, KOMURO; Kazuo, SATO; Katsuhiro, ITOH; Lillard, Randolph P.; Olejniczak, Joseph

2013-01-01

An aeroheating measurement test campaign of an Apollo capsule model with laminar and turbulent boundary layer was performed in the free-piston shock tunnel HIEST at JAXA Kakuda Space Center. A 250mm-diameter 6.4%-scaled Apollo CM capsule model made of SUS-304 stainless steel was applied in this study. To measure heat flux distribution, the model was equipped with 88 miniature co-axial Chromel-Constantan thermocouples on the heat shield surface of the model. In order to promote boundary layer transition, a boundary layer trip insert with 13 "pizza-box" isolated roughness elements, which have 1.27mm square, were placed at 17mm below of the model geometric center. Three boundary layer trip inserts with roughness height of k=0.3mm, 0.6mm and 0.8mm were used to identify the appropriate height to induce transition. Heat flux records with or without roughness elements were obtained for model angles of attack 28º under stagnation enthalpy between H(sub 0)=3.5MJ/kg to 21MJ/kg and stagnation pressure between P(sub 0)=14MPa to 60MPa. Under the condition above, Reynolds number based on the model diameter was varied from 0.2 to 1.3 million. With roughness elements, boundary layer became fully turbulent less than H(sub 0)=9MJ/kg condition. However, boundary layer was still laminar over H(sub 0)=13MJ/kg condition even with the highest roughness elements. An additional experiment was also performed to correct unexpected heat flux augmentation observed over H(sub 0)=9MJ/kg condition.

Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

NASA Technical Reports Server (NTRS)

Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

1988-01-01

The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

Effect of pulsed laser parameters on the corrosion limitation for electric connector coatings

NASA Astrophysics Data System (ADS)

Georges, C.; Semmar, N.; Boulmer-Leborgne, C.

2006-12-01

Materials used in electrical contact applications are usually constituted of multilayered compounds (e.g.: copper alloy electroplated with a nickel layer and finally by a gold layer). After the electro-deposition, micro-channels and pores within the gold layer allow undesirable corrosion of the underlying protection. In order to modify the gold-coating microstructure, a laser surface treatment was applied. The laser treatment suppressing porosity and smoothing the surface sealed the original open structure as a low roughness allows a good electrical contact. Corrosion tests were carried out in humid synthetic air containing three polluting gases. SEM characterization of cross-sections was performed to estimate the gold melting depth and to observe the modifications of gold structure obtained after laser treatment. The effects of the laser treatment were studied according to different surface parameters (roughness of the substrate and thickness of the gold layer) and different laser parameters (laser wavelength, laser fluence, pulse duration and number of pulses). A thermokinetic model was used to understand the heating and melting mechanism of the multilayered coating to optimize the process in terms of laser wavelength, energy and time of interaction.

Phase formation in selected surface-roughened plasma-nitrided 304 austenite stainless steel.

PubMed

Singh, Gajendra Prasad; Joseph, Alphonsa; Raole, Prakash Manohar; Barhai, Prema Kanta; Mukherjee, Subroto

2008-04-01

Direct current (DC) glow discharge plasma nitriding was carried out on three selected surface-roughened AISI 304 stainless steel samples at 833 K under 4 mbar pressures for 24 h in the presence of N 2 :H 2 gas mixtures of 50 : 50 ratios. After plasma nitriding, the phase formation, case depth, surface roughness, and microhardness of a plasma-nitrided layer were evaluated by glancing angle x-ray diffractogram, optical microscope, stylus profilometer, and Vickers microhardness tester techniques. The case depth, surface hardness, and phase formation variations were observed with a variation in initial surface roughness. The diffraction patterns of the plasma-nitrided samples showed the modified intensities of the α and γ phases along with those of the CrN, Fe 4 N, and Fe 3 N phases. Hardness and case depth variations were observed with a variation in surface roughness. A maximum hardness of 1058 Hv and a case depth of 95 μm were achieved in least surface-roughened samples.

Influence of SMAT Parameters on Microstructural and Mechanical Properties of Al-Mg-Si Alloy AA 6061

NASA Astrophysics Data System (ADS)

Anand Kumar, S.; Satish Kumar, P.; Ganesh Sundara Raman, S.; Sankara Narayanan, T. S. N.

2017-04-01

In the present work, the influence of surface mechanical attrition treatment (SMAT) parameters on the microstructural and mechanical properties of an aluminum-magnesium-silicon alloy AA 6061 was studied using design of experiment technique. Balls of three different diameters were used, and SMAT was done for three different durations. The microstructural features of the surface layer fabricated by SMAT were characterized by cross-sectional scanning electron microscopic observations, x-ray diffraction technique and transmission electron microscopy. The microindentation hardness, nanoindentation hardness and surface roughness were determined. Due to SMAT, nanocrystallites formed on the surface and near-surface regions, and hardness and surface roughness increased. The ball diameter was the most influencing SMAT parameter compared to the treatment duration. However, interaction between ball diameter and treatment duration could not be ignored. Regression equations were developed relating the process parameters to the surface properties. The ball diameter and treatment duration could thus be properly selected as per the required values of roughness and/or the hardness.

Effect of fabrication parameters on morphological and optical properties of highly doped p-porous silicon

NASA Astrophysics Data System (ADS)

Zare, Maryam; Shokrollahi, Abbas; Seraji, Faramarz E.

2011-09-01

Porous silicon (PS) layers were fabricated by anodization of low resistive (highly doped) p-type silicon in HF/ethanol solution, by varying current density, etching time and HF concentration. Atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) analyses were used to investigate the physical properties and reflection spectrum was used to investigate the optical behavior of PS layers in different fabrication conditions. Vertically aligned mesoporous morphology is observed in fabricated films and with HF concentration higher than 20%. The dependence of porosity, layer thickness and rms roughness of the PS layer on current density, etching time and composition of electrolyte is also observed in obtained results. Correlation between reflectivity and fabrication parameters was also explored. Thermal oxidation was performed on some mesoporous layers that resulted in changes of surface roughness, mean height and reflectivity of the layers.

Organic photosensitive cells grown on rough electrode with nano-scale morphology control

DOEpatents

Yang, Fan [Piscataway, NJ; Forrest, Stephen R [Ann Arbor, MI

2011-06-07

An optoelectronic device and a method for fabricating the optoelectronic device includes a first electrode disposed on a substrate, an exposed surface of the first electrode having a root mean square roughness of at least 30 nm and a height variation of at least 200 nm, the first electrode being transparent. A conformal layer of a first organic semiconductor material is deposited onto the first electrode by organic vapor phase deposition, the first organic semiconductor material being a small molecule material. A layer of a second organic semiconductor material is deposited over the conformal layer. At least some of the layer of the second organic semiconductor material directly contacts the conformal layer. A second electrode is deposited over the layer of the second organic semiconductor material. The first organic semiconductor material is of a donor-type or an acceptor-type relative to the second organic semiconductor material, which is of the other material type.

The effect of bed roughness on the free surface of an open channel flow and implications for remotely monitoring river discharge

NASA Astrophysics Data System (ADS)

Johnson, Erika; Cowen, Edwin

2013-11-01

The effect of increased bed roughness on the free surface turbulence signature of an open channel flow is investigated with the goal of incorporating the findings into a methodology to remotely monitor volumetric flow rates. Half of a wide (B = 2 m) open channel bed is covered with a 3 cm thick layer of loose gravel (D50 = 0.6 cm). Surface PIV (particle image velocimetry) experiments are conducted for a range of flow depths (B/H = 10-30) and Reynolds numbers (ReH = 10,000-60,000). It is well established that bed roughness in wall-bounded flows enhances the vertical velocity fluctuations (e.g. Krogstad et al. 1992). When the vertical velocity fluctuations approach the free surface they are redistributed (e.g. Cowen et al. 1995) to the surface parallel component directions. It is anticipated and confirmed that the interaction of these two phenomena result in enhanced turbulence at the free surface. The effect of the rough bed on the integral length scales and the second order velocity structure functions calculated at the free surface are investigated. These findings have important implications for developing new technologies in stream gaging.

Scale growth of structures in the turbulent boundary layer with a rod-roughened wall

NASA Astrophysics Data System (ADS)

Lee, Jin; Kim, Jung Hoon; Lee, Jae Hwa

2016-01-01

Direct numerical simulation of a turbulent boundary layer over a rod-roughened wall is performed with a long streamwise domain to examine the streamwise-scale growth mechanism of streamwise velocity fluctuating structures in the presence of two-dimensional (2-D) surface roughness. An instantaneous analysis shows that there is a slightly larger population of long structures with a small helix angle (spanwise inclinations relative to streamwise) and a large spanwise width over the rough-wall compared to that over a smooth-wall. Further inspection of time-evolving instantaneous fields clearly exhibits that adjacent long structures combine to form a longer structure through a spanwise merging process over the rough-wall; moreover, spanwise merging for streamwise scale growth is expected to occur frequently over the rough-wall due to the large spanwise scales generated by the 2-D roughness. Finally, we examine the influence of a large width and a small helix angle of the structures over the rough-wall with regard to spatial two-point correlation. The results show that these factors can increase the streamwise coherence of the structures in a statistical sense.

Micro PIV measurements of turbulent flow over 2D structured roughness

NASA Astrophysics Data System (ADS)

Hartenberger, Joel; Perlin, Marc

2015-11-01

We investigate the turbulent boundary layer over surfaces with 2D spanwise square and triangular protrusions having nominal heights of 100 - 300 microns for Reynolds numbers ranging from Reτ ~ 1500 through Reτ ~ 4500 using a high speed, high magnification imaging system. Micro PIV analysis gives finely resolved velocity fields of the flow (on the order of 10 microns between vectors) enabling a detailed look at the inner region as well as the flow in the immediate vicinity of the roughness elements. Additionally, planar PIV with lower resolution is performed to capture the remainder of the boundary layer to the freestream flow. Varying the streamwise distance between individual roughness elements from one to ten times the nominal heights allows investigation of k-type and d-type roughness in both the transitionally rough and fully rough regimes. Preliminary results show a shift in the mean velocity profile similar to the results of previous studies. Turbulent statistics will be presented also. The authors would like to acknowledge the support of NAVSEA which funded this project through the Naval Engineering Education Center (NEEC).

Effect of sound on boundary layer stability

NASA Technical Reports Server (NTRS)

Saric, William S. (Principal Investigator); Spencer, Shelly Anne

1993-01-01

Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-travelling, sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2(lambda)(sub TS)/pi, of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations and the Stokes wave subtracted) show the generation of 3-D-T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modelling are observed.

Effect of sound on boundary layer stability

NASA Technical Reports Server (NTRS)

Saric, William S.; Spencer, Shelly Anne

1993-01-01

Experiments are conducted in the Arizona State University Unsteady Wind Tunnel with a zero-pressure-gradient flat-plate model that has a 67:1 elliptical leading edge. Boundary-layer measurements are made of the streamwise fluctuating-velocity component in order to identify the amplified T-S waves that are forced by downstream-traveling sound waves. Measurements are taken with circular 3-D roughness elements placed at the Branch 1 neutral stability point for the frequency under consideration, and then with the roughness element downstream of Branch 1. These roughness elements have a principal chord dimension equal to 2 lambda(sub TS)/pi of the T-S waves under study and are 'stacked' in order to resemble a Gaussian height distribution. Measurements taken just downstream of the roughness (with leading-edge T-S waves, surface roughness T-S waves, instrumentation sting vibrations, and the Stokes wave subtracted) show the generation of 3-D T-S waves, but not in the characteristic heart-shaped disturbance field predicted by 3-D asymptotic theory. Maximum disturbance amplitudes are found on the roughness centerline. However, some near-field characteristics predicted by numerical modeling are observed.

Multi-hybrid method for investigation of EM scattering from inhomogeneous object above a dielectric rough surface

NASA Astrophysics Data System (ADS)

Li, Jie; Guo, LiXin; He, Qiong; Wei, Bing

2012-10-01

An iterative strategy combining Kirchhoff approximation^(KA) with the hybrid finite element-boundary integral (FE-BI) method is presented in this paper to study the interactions between the inhomogeneous object and the underlying rough surface. KA is applied to study scattering from underlying rough surfaces, whereas FE-BI deals with scattering from the above target. Both two methods use updated excitation sources. Huygens equivalence principle and an iterative strategy are employed to consider the multi-scattering effects. This hybrid FE-BI-KA scheme is an improved and generalized version of previous hybrid Kirchhoff approximation-method of moments (KA-MoM). This newly presented hybrid method has the following advantages: (1) the feasibility of modeling multi-scale scattering problems (large scale underlying surface and small scale target); (2) low memory requirement as in hybrid KA-MoM; (3) the ability to deal with scattering from inhomogeneous (including coated or layered) scatterers above rough surfaces. The numerical results are given to evaluate the accuracy of the multi-hybrid technique; the computing time and memory requirements consumed in specific numerical simulation of FE-BI-KA are compared with those of MoM. The convergence performance is analyzed by studying the iteration number variation caused by related parameters. Then bistatic scattering from inhomogeneous object of different configurations above dielectric Gaussian rough surface is calculated and the influences of dielectric compositions and surface roughness on the scattering pattern are discussed.

Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition

PubMed Central

Liao, Yu-Kuang; Liu, Yung-Tsung; Hsieh, Dan-Hua; Shen, Tien-Lin; Hsieh, Ming-Yang; Tzou, An-Jye; Chen, Shih-Chen; Tsai, Yu-Lin; Lin, Wei-Sheng; Chan, Sheng-Wen; Shen, Yen-Ping; Cheng, Shun-Jen; Chen, Chyong-Hua; Wu, Kaung-Hsiung; Chen, Hao-Ming; Kuo, Shou-Yi; Charlton, Martin D. B.; Hsieh, Tung-Po; Kuo, Hao-Chung

2017-01-01

Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin films with the thickness of a few nanometers on rough surfaces. We present a new ”paradigm shift” non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In,Ga)Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase. PMID:28383488

The Budget of Turbulent Kinetic Energy in the Urban Roughness Sublayer

NASA Astrophysics Data System (ADS)

Christen, Andreas; Rotach, Mathias W.; Vogt, Roland

2009-05-01

Full-scale observations from two urban sites in Basel, Switzerland were analysed to identify the magnitude of different processes that create, relocate, and dissipate turbulent kinetic energy (TKE) in the urban atmosphere. Two towers equipped with a profile of six ultrasonic anemometers each sampled the flow in the urban roughness sublayer, i.e. from street canyon base up to roughly 2.5 times the mean building height. This observational study suggests a conceptual division of the urban roughness sublayer into three layers: (1) the layer above the highest roofs, where local buoyancy production and local shear production of TKE are counterbalanced by local viscous dissipation rate and scaled turbulence statistics are close to to surface-layer values; (2) the layer around mean building height with a distinct inflexional mean wind profile, a strong shear and wake production of TKE, a more efficient turbulent exchange of momentum, and a notable export of TKE by transport processes; (3) the lower street canyon with imported TKE by transport processes and negligible local production. Averaged integral velocity variances vary significantly with height in the urban roughness sublayer and reflect the driving processes that create or relocate TKE at a particular height. The observed profiles of the terms of the TKE budget and the velocity variances show many similarities to observations within and above vegetation canopies.

Establishing Antibacterial Multilayer Films on the Surface of Direct Metal Laser Sintered Titanium Primed with Phase-Transited Lysozyme

PubMed Central

Guan, Binbin; Wang, Haorong; Xu, Ruiqing; Zheng, Guoying; Yang, Jie; Liu, Zihao; Cao, Man; Wu, Mingyao; Song, Jinhua; Li, Neng; Li, Ting; Cai, Qing; Yang, Xiaoping; Li, Yanqiu; Zhang, Xu

2016-01-01

Direct metal laser sintering is a technology that allows the fabrication of titanium (Ti) implants with a functional gradation of porosity and surface roughness according to three-dimensional (3D) computer data. The surface roughness of direct metal laser sintered titanium (DMLS-Ti) implants may provide abundant binding sites for bacteria. Bacterial colonization and subsequent biofilm formation can cause unsatisfactory cell adhesion and implant-related infections. To prevent such infections, a novel phase-transited lysozyme (PTL) was utilized as an initial functional layer to simply and effectively prime DMLS-Ti surfaces for subsequent coating with antibacterial multilayers. The purpose of the present study was to establish a surface with dual biological functionality. The minocycline-loaded polyelectrolyte multilayers of hyaluronic acid (HA) and chitosan (CS) formed via a layer-by-layer (LbL) self-assembly technique on PTL-functionalized DMLS-Ti were designed to inhibit pathogenic microbial infections while allowing the DMLS-Ti itself and the modified coatings to retain acceptable biocompatibility. The experimental results indicate that the DMLS-Ti and the hydrogel treated surfaces can inhibit early bacterial adhesion while completely preserving osteoblast functions. This design is expected to gain considerable interest in the medical field and to have good potential for applications in multifunctional DMLS-Ti implants. PMID:27821857

Establishing Antibacterial Multilayer Films on the Surface of Direct Metal Laser Sintered Titanium Primed with Phase-Transited Lysozyme.

PubMed

Guan, Binbin; Wang, Haorong; Xu, Ruiqing; Zheng, Guoying; Yang, Jie; Liu, Zihao; Cao, Man; Wu, Mingyao; Song, Jinhua; Li, Neng; Li, Ting; Cai, Qing; Yang, Xiaoping; Li, Yanqiu; Zhang, Xu

2016-11-08

Direct metal laser sintering is a technology that allows the fabrication of titanium (Ti) implants with a functional gradation of porosity and surface roughness according to three-dimensional (3D) computer data. The surface roughness of direct metal laser sintered titanium (DMLS-Ti) implants may provide abundant binding sites for bacteria. Bacterial colonization and subsequent biofilm formation can cause unsatisfactory cell adhesion and implant-related infections. To prevent such infections, a novel phase-transited lysozyme (PTL) was utilized as an initial functional layer to simply and effectively prime DMLS-Ti surfaces for subsequent coating with antibacterial multilayers. The purpose of the present study was to establish a surface with dual biological functionality. The minocycline-loaded polyelectrolyte multilayers of hyaluronic acid (HA) and chitosan (CS) formed via a layer-by-layer (LbL) self-assembly technique on PTL-functionalized DMLS-Ti were designed to inhibit pathogenic microbial infections while allowing the DMLS-Ti itself and the modified coatings to retain acceptable biocompatibility. The experimental results indicate that the DMLS-Ti and the hydrogel treated surfaces can inhibit early bacterial adhesion while completely preserving osteoblast functions. This design is expected to gain considerable interest in the medical field and to have good potential for applications in multifunctional DMLS-Ti implants.

Establishing Antibacterial Multilayer Films on the Surface of Direct Metal Laser Sintered Titanium Primed with Phase-Transited Lysozyme

NASA Astrophysics Data System (ADS)

Guan, Binbin; Wang, Haorong; Xu, Ruiqing; Zheng, Guoying; Yang, Jie; Liu, Zihao; Cao, Man; Wu, Mingyao; Song, Jinhua; Li, Neng; Li, Ting; Cai, Qing; Yang, Xiaoping; Li, Yanqiu; Zhang, Xu

2016-11-01

Direct metal laser sintering is a technology that allows the fabrication of titanium (Ti) implants with a functional gradation of porosity and surface roughness according to three-dimensional (3D) computer data. The surface roughness of direct metal laser sintered titanium (DMLS-Ti) implants may provide abundant binding sites for bacteria. Bacterial colonization and subsequent biofilm formation can cause unsatisfactory cell adhesion and implant-related infections. To prevent such infections, a novel phase-transited lysozyme (PTL) was utilized as an initial functional layer to simply and effectively prime DMLS-Ti surfaces for subsequent coating with antibacterial multilayers. The purpose of the present study was to establish a surface with dual biological functionality. The minocycline-loaded polyelectrolyte multilayers of hyaluronic acid (HA) and chitosan (CS) formed via a layer-by-layer (LbL) self-assembly technique on PTL-functionalized DMLS-Ti were designed to inhibit pathogenic microbial infections while allowing the DMLS-Ti itself and the modified coatings to retain acceptable biocompatibility. The experimental results indicate that the DMLS-Ti and the hydrogel treated surfaces can inhibit early bacterial adhesion while completely preserving osteoblast functions. This design is expected to gain considerable interest in the medical field and to have good potential for applications in multifunctional DMLS-Ti implants.

A Generalized Wall Function

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Povinelli, Louis A.; Liu, Nan-Suey; Potapczuk, Mark G.; Lumley, J. L.

1999-01-01

The asymptotic solutions, described by Tennekes and Lumley (1972), for surface flows in a channel, pipe or boundary layer at large Reynolds numbers are revisited. These solutions can be extended to more complex flows such as the flows with various pressure gradients, zero wall stress and rough surfaces, etc. In computational fluid dynamics (CFD), these solutions can be used as the boundary conditions to bridge the near-wall region of turbulent flows so that there is no need to have the fine grids near the wall unless the near-wall flow structures are required to resolve. These solutions are referred to as the wall functions. Furthermore, a generalized and unified law of the wall which is valid for whole surface layer (including viscous sublayer, buffer layer and inertial sublayer) is analytically constructed. The generalized law of the wall shows that the effect of both adverse and favorable pressure gradients on the surface flow is very significant. Such as unified wall function will be useful not only in deriving analytic expressions for surface flow properties but also bringing a great convenience for CFD methods to place accurate boundary conditions at any location away from the wall. The extended wall functions introduced in this paper can be used for complex flows with acceleration, deceleration, separation, recirculation and rough surfaces.

Turbulent boundary layer over roughness transition with variation in spanwise roughness length scale

NASA Astrophysics Data System (ADS)

Westerweel, Jerry; Tomas, Jasper; Eisma, Jerke; Pourquie, Mathieu; Elsinga, Gerrit; Jonker, Harm

2016-11-01

Both large-eddy simulations (LES) and water-tunnel experiments, using simultaneous stereoscopic PIV and LIF were done to investigate pollutant dispersion in a region where the surface changes from rural to urban roughness. This consists of rectangular obstacles where we vary the spanwise aspect ratio of the obstacles. A line source of passive tracer was placed upstream of the roughness transition. The objectives of the study are: (i) to determine the influence of the aspect ratio on the roughness-transition flow, and (ii) to determine the dominant mechanisms of pollutant removal from street canyons in the transition region. It is found that for a spanwise aspect ratio of 2 the drag induced by the roughness is largest of all considered cases, which is caused by a large-scale secondary flow. In the roughness transition the vertical advective pollutant flux is the main ventilation mechanism in the first three streets. Furthermore, by means of linear stochastic estimation the mean flow structure is identied that is responsible for exchange of the fluid between the roughness obstacles and the outer part of the boundary layer. Furthermore, it is found that the vertical length scale of this structure increases with increasing aspect ratio of the obstacles in the roughness region.

Sol-gel layers for ceramic microsystems application

NASA Astrophysics Data System (ADS)

Czok, Mateusz; Golonka, Leszek

2016-11-01

This paper describes research on sol-gel solutions preparation process. Utilize of a sol-gel layers in the LTCC technology for reduction of surface roughness and influence on the ceramics properties is examined and described. The influence of sol-gel layer on possible sedimentation of dyes or biological substances in channels, mixers or chambers of ceramic microfluidic structures was investigated. Moreover, properties of sol-gel coated surfaces have been precisely examined and described. Finally, positive results of conducted experiments made it possible to design and manufacture a simple microfluidic ceramic structure, with embedded protective layer of sol-gel, for fluorescence measurements.

Polymer based organic solar cells using ink-jet printed active layers

NASA Astrophysics Data System (ADS)

Aernouts, T.; Aleksandrov, T.; Girotto, C.; Genoe, J.; Poortmans, J.

2008-01-01

Ink-jet printing is used to deposit polymer:fullerene blends suitable as active layer for organic solar cells. We show that merging of separately deposited ink droplets into a continuous, pinhole-free organic thin film results from a balance between ink viscosity and surface wetting, whereas for certain of the studied solutions clear coffee drop effect occurs for single droplets; this can be minimized for larger printed areas, yielding smooth layers with minimal surface roughness. Resulting organic films are used as active layer for solar cells with power conversion efficiency of 1.4% under simulated AM1.5 solar illumination.

Shallow convection on day 261 of GATE - Mesoscale arcs

NASA Technical Reports Server (NTRS)

Warner, C.; Simpson, J.; Martin, D. W.; Suchman, D.; Mosher, F. R.; Reinking, R. F.

1979-01-01

Cloudy convection in the moist layer of a cloud cluster growing in the GATE ship array is examined. Analyses suggest that the moist layer was dominated by features of horizontal dimension roughly 40 km and lifetime roughly 2 h, with arc patterns triggered by dense downdraft air accompanying rainfall, and composed of many small cumulus clouds. Aircraft recorded data on thermodynamic quantities and winds, indicating that the arcs persisted as mesoscale circulations driven by the release of latent heat in the clouds, rather than being driven by the original density current at the surface. It is also suggested that the mesoscale cloud patterns of the moist layer play a primary role in heat transfer upward within this layer, and contribute to the forcing of showering midtropospheric clouds.

Osteoinduction on Acid and Heat Treated Porous Ti Metal Samples in Canine Muscle

PubMed Central

Kawai, Toshiyuki; Takemoto, Mitsuru; Fujibayashi, Shunsuke; Akiyama, Haruhiko; Tanaka, Masashi; Yamaguchi, Seiji; Pattanayak, Deepak K.; Doi, Kenji; Matsushita, Tomiharu; Nakamura, Takashi; Kokubo, Tadashi; Matsuda, Shuichi

2014-01-01

Samples of porous Ti metal were subjected to different acid and heat treatments. Ectopic bone formation on specimens embedded in dog muscle was compared with the surface characteristics of the specimen. Treatment of the specimens by H2SO4/HCl and heating at 600°C produced micrometer-scale roughness with surface layers composed of rutile phase of titanium dioxide. The acid- and heat-treated specimens induced ectopic bone formation within 6 months of implantation. A specimen treated using NaOH followed by HCl acid and then heat treatment produced nanometer-scale surface roughness with a surface layer composed of both rutile and anatase phases of titanium dioxide. These specimens also induced bone formation after 6 months of implantation. Both these specimens featured positive surface charge and good apatite-forming abilities in a simulated body fluid. The amount of the bone induced in the porous structure increased with apatite-forming ability and higher positive surface charge. Untreated porous Ti metal samples showed no bone formation even after 12 months. Specimens that were only heat treated featured a smooth surface composed of rutile. A mixed acid treatment produced specimens with micrometer-scale rough surfaces composed of titanium hydride. Both of them also showed no bone formation after 12 months. The specimens that showed no bone formation also featured almost zero surface charge and no apatite-forming ability. These results indicate that osteoinduction of these porous Ti metal samples is directly related to positive surface charge that facilitates formation of apatite on the metal surfaces in vitro. PMID:24520375

Effect of Pd Surface Roughness on the Bonding Process and High Temperature Reliability of Au Ball Bonds

NASA Astrophysics Data System (ADS)

Huang, Y.; Kim, H. J.; McCracken, M.; Viswanathan, G.; Pon, F.; Mayer, M.; Zhou, Y. N.

2011-06-01

A 0.3- μm-thick electrolytic Pd layer was plated on 1 μm of electroless Ni on 1 mm-thick polished and roughened Cu substrates with roughness values ( R a) of 0.08 μm and 0.5 μm, respectively. The rough substrates were produced with sand-blasting. Au wire bonding on the Ni/Pd surface was optimized, and the electrical reliability was investigated under a high temperature storage test (HTST) during 800 h at 250°C by measuring the ball bond contact resistance, R c. The average value of R c of optimized ball bonds on the rough substrate was 1.96 mΩ which was about 40.0% higher than that on the smooth substrate. The initial bondability increased for the rougher surface, so that only half of the original ultrasonic level was required, but the reliability was not affected by surface roughness. For both substrate types, HTST caused bond healing, reducing the average R c by about 21% and 27%, respectively. Au diffusion into the Pd layer was observed in scanning transmission electron microscopy/ energy dispersive spectroscopy (STEM-EDS) line-scan analysis after HTST. It is considered that diffusion of Au or interdiffusion between Au and Pd can provide chemically strong bonding during HTST. This is supported by the R c decrease measured as the aging time increased. Cu migration was indicated in the STEM-EDS analysis, but its effect on reliability can be ignored. Au and Pd tend to form a complete solid solution at the interface and can provide reliable interconnection for high temperature (250°C) applications.

The surface roughness effect on the performance of supersonic ejectors

NASA Astrophysics Data System (ADS)

Brezgin, D. V.; Aronson, K. E.; Mazzelli, F.; Milazzo, A.

2017-07-01

The paper presents the numerical simulation results of the surface roughness influence on gas-dynamic processes inside flow parts of a supersonic ejector. These simulations are performed using two commercial CFD solvers (Star- CCM+ and Fluent). The results are compared to each other and verified by a full-scale experiment in terms of global flow parameters (the entrainment ratio: the ratio between secondary to primary mass flow rate - ER hereafter) and local flow parameters distribution (the static pressure distribution along the mixing chamber and diffuser walls). A detailed comparative study of the employed methods and approaches in both CFD packages is carried out in order to estimate the roughness effect on the logarithmic law velocity distribution inside the boundary layer. Influence of the surface roughness is compared with the influence of the backpressure (static pressure at the ejector outlet). It has been found out that increasing either the ejector backpressure or the surface roughness height, the shock position displaces upstream. Moreover, the numerical simulation results of an ejector with rough walls in the both CFD solvers are well quantitatively agreed with each other in terms of the mean ER and well qualitatively agree in terms of the local flow parameters distribution. It is found out that in the case of exceeding the "critical roughness height" for the given boundary conditions and ejector's geometry, the ejector switches to the "off-design" mode and its performance decreases considerably.

Technological capabilities of surface layers formation on implant made of Ti-6Al-4V ELI alloy.

PubMed

Kiel-Jamrozik, Marta; Szewczenko, Janusz; Basiaga, Marcin; Nowińska, Katarzyna

2015-01-01

The aim of the presented research was to find a combination of surface modification methods of implants made of the Ti-6Al-4V ELI alloy, that lead to formation of effective barrier for metallic ions that may infiltrate into solution. To this end, the following tests were carried out: roughness measurement, the voltamperometric tests (potentiodynamic and potentiostatic), and the ion infiltration test. The electropolishing process resulted in the lowering of surface roughness in comparison with mechanical treatment of the surface layer. The anodization process and steam sterilization increased corrosion resistance regardless of the mechanical treatment or electropolishing. The crevice corrosion tests revealed that independent of the modification method applied, the Ti-6Al-4V ELI alloy has excellent crevice corrosion resistance. The smallest quantity of ions infiltrated to the solution was observed for surface modification consisting in the mechanical treatment and anodization with the potential of 97 V. Electric parameters deter- mined during studies were the basis for effectiveness estimation of particular surface treatment methods. The research has shown that the anodization process significantly influences the pitting corrosion resistance of the Ti-6Al-4V ELI alloy independent of the previous surface treatment methods (mechanical and electrochemical). The surface layer after such modification is a protective barrier for metallic ions infiltrated to solution and protects titanium alloy against corrosive environment influence.

Quantitative Mapping of Surface Texture on the Northern Polar Residual Cap of Mars

NASA Astrophysics Data System (ADS)

Milkovich, S. M.; Byrne, S.; Russell, P. S.

2010-12-01

The northern polar residual cap (NPRC) of Mars is a water ice deposit with a rough surface made up of pits, knobs, and linear depressions on scales of tens of meters [1]. This roughness manifests as a series of bright and dark patches in visible images. Spectral data indicate that the surface of the NPRC is composed of large-grained (and therefore old) water ice. Due to the presence of this old ice, it is thought that the NPRC is in a current state of net loss of material [2]. The NPRC provides a link between the current martian climate and the historical climate recorded within the layers of the underlying north polar layered deposits. By characterizing and mapping the variations in surface texture of the NPRC, we seek to understand what factors (distance from the pole, GCM and mesoscale wind direction predictions, etc) are currently at work in resurfacing the deposit, and may have been at work in shaping the layers below. Maps of NPRC texture wavelength and orientation are being produced from HiRISE images. Two-dimensional Fourier analysis is performed upon a 256 meter x 256 meter region (corresponding to 512 x 512 pixels in 0.5 cm/pxl images, or 1024 x 1024 pixels in 0.25 cm/pxl images) within each image analyzed. The dominant wavelength of the resulting peak power spectrum corresponds to the average size of a pit-knob pair in the image, and so is a proxy for the scale of the surface roughness. The orientation of the surface roughness (i.e., the orientation of a chain of pits and mounds) is measured from a narrow range of wavelengths encompassing the dominant wavelength. We will report on how the dominant wavelengths and orientations of this surface texture vary with location and what that implies for the processes currently shaping this landscape. [1] P. C. Thomas et al, Nature 404, 161-164, 2000 [2]Y. Langevin et al, Science 307, 5715, 1581-1584, 2005.

Novel fabrication method for 3D microstructures using surface-activated bonding and its application to micro-mechanical parts

NASA Astrophysics Data System (ADS)

Yamada, Takayuki; Takahashi, Mutsuya; Ozawa, Takashi; Tawara, Satoshi; Goto, Takayuki

2002-11-01

The purpose of this work is to demonstrate that a novel fabrication method for 3-D microstructures (FORMULA) is applicable to fabrication of micro mechanical parts with a large flexibility. This method is a kind of layer manufacturing method of thin films for metallic or dielectric microstructures using surface-activated bonding (SAB). The bonding interfaces of thin films are investigated by transmission electron microscope (TEM). Voids were observed at the interfaces of both pure aluminum films and Al-Cu alloy films. The ratio of void on the Al-Cu/Al-Cu interface is much larger than that of Al/Al interface, although the films have the same surface roughness of 3nm in Ra (average roughness). And approximately 10nm-thick amorphous intermediate layers were found at the interfaces. Furthermore, we have fabricated a micro gear of 900μm in diameter and 200μm in height, which is about ten times as large as our previous test pieces. Overhung structures such as a bridge structure and a cantilever were also fabricated without supporting layers beneath them.

Flow Measurements over a Biomimetic Surface Roughness Microgeometry

NASA Astrophysics Data System (ADS)

Lang, Amy; Hidalgo, Pablo; Westcott, Matthew

2007-11-01

Certain species of sharks (e.g. shortfin mako) have a skin structure that results in a bristling of their denticles (scales) during increased swimming speeds. This unique surface geometry results in the formation of a 3D array of cavities* (d-type roughness geometry) within the shark skin, thus causing it to potentially act as a means of boundary layer control. 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 over a shark skin model. The hypothesized formation of cavity vortices within the shark skin replica has been measured using DPIV. We have also shown that with the sufficient growth of a boundary layer upstream of the model (local Re = 200,000), transition is not tripped by the surface and the flow skips over the cavities. Support for this research by a NSF SGER grant (CTS-0630489), Lindbergh Foundation Grant and a University of Alabama RAC grant is gratefully acknowledged. * Patent pending.

Electrografted diazonium salt layers for antifouling on the surface of surface plasmon resonance biosensors.

PubMed

Zou, Qiongjing; Kegel, Laurel L; Booksh, Karl S

2015-02-17

Electrografted diazonium salt layers on the surface of surface plasmon resonance (SPR) sensors present potential for a significant improvement in antifouling coatings. A pulsed potential deposition profile was used in order to circumvent mass-transport limitations for layer deposition rate. The influence of number of pulses with respect to antifouling efficacy was evaluated by nonspecific adsorption surface coverage of crude bovine serum proteins. Instead of using empirical and rough estimated values, the penetration depth and sensitivity of the SPR instrument were experimentally determined for the calculation of nonspecific adsorption surface coverage. This provides a method to better examine antifouling surface coatings and compare crossing different coatings and experimental systems. Direct comparison of antifouling performance of different diazonium salts was facilitated by a tripad SPR sensor design. The electrografted 4-phenylalanine diazonium chloride (4-APhe) layers with zwitterionic characteristic demonstrate ultralow fouling.

Faraday instability on patterned surfaces

NASA Astrophysics Data System (ADS)

Feng, Jie; Rubinstein, Gregory; Jacobi, Ian; Stone, Howard

2013-11-01

We show how micro-scale surface patterning can be used to control the onset of the Faraday instability in thin liquid films. It is well known that when a liquid film on a planar substrate is subject to sufficient vibrational accelerations, the free surface destabilizes, exhibiting a family of non-linear standing waves. This instability remains a canonical problem in the study of spontaneous pattern formation, but also has practical uses. For example, the surface waves induced by the Faraday instability have been studied as a means of enhanced damping for mechanical vibrations (Genevaux et al. 2009). Also the streaming within the unstable layer has been used as a method for distributing heterogeneous cell cultures on growth medium (Takagi et al. 2002). In each of these applications, the roughness of the substrate significantly affects the unstable flow field. We consider the effect of patterned substrates on the onset and behavior of the Faraday instability over a range of pattern geometries and feature heights where the liquid layer is thicker than the pattern height. Also, we describe a physical model for the influence of patterned roughness on the destabilization of a liquid layer in order to improve the design of practical systems which exploit the Faraday instability.

Assessing sea wave and spray effects on Marine Boundary Layer structure

NASA Astrophysics Data System (ADS)

Stathopoulos, Christos; Galanis, George; Patlakas, Platon; Kallos, George

2017-04-01

Air sea interface is characterized by several mechanical and thermodynamical processes. Heat, moisture and momentum exchanges increase the complexity in modeling the atmospheric-ocean system. Near surface atmospheric levels are subject to sea surface roughness and sea spray. Sea spray fluxes can affect atmospheric stability and induce microphysical processes such as sea salt particle formation and condensation/evaporation of water in the boundary layer. Moreover, presence of sea spray can alter stratification over the ocean surface with further insertion of water vapor. This can lead to modified stability conditions and to wind profiles that deviate significantly from the logarithmic approximation. To model these effects, we introduce a fully coupled system consisting of the mesoscale atmospheric model RAMS/ICLAMS and the wave model WAM. The system encompasses schemes for ocean surface roughness, sea salt aerosols and droplet thermodynamic processes and handles sea salt as predictive quantity. Numerical experiments using the developed atmospheric-ocean system are performed over the Atlantic and Mediterranean shoreline. Emphasis is given to the quantification of the improvement obtained in the description of the marine boundary layer, particularly in its lower part as well as in wave characteristics.

Perspectives of mid-infrared optical coherence tomography for inspection and micrometrology of industrial ceramics

PubMed Central

Su, Rong; Kirillin, Mikhail; Chang, Ernest W.; Sergeeva, Ekaterina; Yun, Seok H.; Mattsson, Lars

2014-01-01

Optical coherence tomography (OCT) is a promising tool for detecting micro channels, metal prints, defects and delaminations embedded in alumina and zirconia ceramic layers at hundreds of micrometers beneath surfaces. The effect of surface roughness and scattering of probing radiation within sample on OCT inspection is analyzed from the experimental and simulated OCT images of the ceramic samples with varying surface roughnesses and operating wavelengths. By Monte Carlo simulations of the OCT images in the mid-IR the optimal operating wavelength is found to be 4 µm for the alumina samples and 2 µm for the zirconia samples for achieving sufficient probing depth of about 1 mm. The effects of rough surfaces and dispersion on the detection of the embedded boundaries are discussed. Two types of image artefacts are found in OCT images due to multiple reflections between neighboring boundaries and inhomogeneity of refractive index. PMID:24977838

Large-Eddy Simulations of Fully Developed Turbulent Channel and Pipe Flows with Smooth and Rough Walls

NASA Astrophysics Data System (ADS)

Saito, Namiko

Studies in turbulence often focus on two flow conditions, both of which occur frequently in real-world flows and are sought-after for their value in advancing turbulence theory. These are the high Reynolds number regime and the effect of wall surface roughness. In this dissertation, a Large-Eddy Simulation (LES) recreates both conditions over a wide range of Reynolds numbers Retau = O(102) - O(108) and accounts for roughness by locally modeling the statistical effects of near-wall anisotropic fine scales in a thin layer immediately above the rough surface. A subgrid, roughness-corrected wall model is introduced to dynamically transmit this modeled information from the wall to the outer LES, which uses a stretched-vortex subgrid-scale model operating in the bulk of the flow. Of primary interest is the Reynolds number and roughness dependence of these flows in terms of first and second order statistics. The LES is first applied to a fully turbulent uniformly-smooth/rough channel flow to capture the flow dynamics over smooth, transitionally rough and fully rough regimes. Results include a Moody-like diagram for the wall averaged friction factor, believed to be the first of its kind obtained from LES. Confirmation is found for experimentally observed logarithmic behavior in the normalized stream-wise turbulent intensities. Tight logarithmic collapse, scaled on the wall friction velocity, is found for smooth-wall flows when Re tau ≥ O(106) and in fully rough cases. Since the wall model operates locally and dynamically, the framework is used to investigate non-uniform roughness distribution cases in a channel, where the flow adjustments to sudden surface changes are investigated. Recovery of mean quantities and turbulent statistics after transitions are discussed qualitatively and quantitatively at various roughness and Reynolds number levels. The internal boundary layer, which is defined as the border between the flow affected by the new surface condition and the unaffected part, is computed, and a collapse of the profiles on a length scale containing the logarithm of friction Reynolds number is presented. Finally, we turn to the possibility of expanding the present framework to accommodate more general geometries. As a first step, the whole LES framework is modified for use in the curvilinear geometry of a fully-developed turbulent pipe flow, with implementation carried out in a spectral element solver capable of handling complex wall profiles. The friction factors have shown favorable agreement with the superpipe data, and the LES estimates of the Karman constant and additive constant of the log-law closely match values obtained from experiment.

A phase field crystal model simulation of morphology evolution and misfit dislocation generation in nanoheteroepitaxy

NASA Astrophysics Data System (ADS)

Zhang, J.; Chen, Z.; Cheng, C.; Wang, Y. X.

2017-10-01

A phase field crystal (PFC) model is employed to study morphology evolution of nanoheteroepitaxy and misfit dislocation generation when applied with enhanced supercooling, lattice mismatch and substrate vicinal angle conditions. Misfit strain that rises due to lattice mismatch causes rough surfaces or misfit dislocations, deteriorates film properties, hence, efforts taken to reveal their microscopic mechanism are significant for film quality improvement. Uniform islands, instead of misfit dislocations, are developed in subcritical thickness film, serving as a way of strain relief by surface mechanism. Misfit dislocations generate when strain relief by surface mechanism is deficient in higher supercooling, multilayers of misfit dislocations dominate, but the number of layers reduces gradually when the supercooling is further enhanced. Rough surfaces like islands or cuspate pits are developed which is ascribed to lattice mismatch, multilayers of misfit dislocations generate to further enhance lattice mismatch. Layers of misfit dislocations generate at a thickening position at enhanced substrate vicinal angle, this further enhancing the angle leading to sporadic generation of misfit dislocations.

Prediction of Laminar and Turbulent Boundary Layer Flow Separation in V/STOL Engine Inlets

NASA Technical Reports Server (NTRS)

Chou, D. C.; Luidens, R. W.; Stockman, N. O.

1977-01-01

A description is presented of the development of the boundary layer on the lip and diffuser surface of a subsonic inlet at arbitrary operating conditions of mass flow rate, free stream velocity and incidence angle. Both laminar separation on the lip and turbulent separation in the diffuser are discussed. The agreement of the theoretical results with model experimental data illustrates the capability of the theory to predict separation. The effects of throat Mach number, inlet size, and surface roughness on boundary layer development and separation are illustrated.

Modifying mixing and instability growth through the adjustment of initial conditions in a high-energy-density counter-propagating shear experiment on OMEGA

DOE PAGES

Merritt, E. C.; Doss, F. W.; Loomis, E. N.; ...

2015-06-24

Counter-propagating shear experiments conducted at the OMEGA Laser Facility have been evaluating the effect of target initial conditions, specifically the characteristics of a tracer foil located at the shear boundary, on Kelvin-Helmholtz instability evolution and experiment transition toward nonlinearity and turbulence in the high-energy-density (HED) regime. Experiments are focused on both identifying and uncoupling the dependence of the model initial turbulent length scale in variable-density turbulence models of k-ϵ type on competing physical instability seed lengths as well as developing a path toward fully developed turbulent HED experiments. We present results from a series of experiments controllably and independently varyingmore » two initial types of scale lengths in the experiment: the thickness and surface roughness (surface perturbation scale spectrum) of a tracer layer at the shear interface. We show that decreasing the layer thickness and increasing the surface roughness both have the ability to increase the relative mixing in the system, and thus theoretically decrease the time required to begin transitioning to turbulence in the system. In addition, we also show that we can connect a change in observed mix width growth due to increased foil surface roughness to an analytically predicted change in model initial turbulent scale lengths.« less

Optical constants of electroplated gold from spectroscopic ellipsometry

NASA Astrophysics Data System (ADS)

Synowicki, R. A.; Herzinger, Craig M.; Hall, James T.; Malingowski, Andrew

2017-11-01

The optical constants of an opaque electroplated gold film (Laser Gold from Epner Technology Inc.), were determined by spectroscopic ellipsometry at room temperature over the spectral range from 0.142 μm in the vacuum ultraviolet to 36 μm in the infrared (photon energy range 0.034-8.75 eV). Data from two separate ellipsometer instruments covering different spectral ranges were analyzed simultaneously. The optical constants n&k or ε1&ε2 were determined by fitting an oscillator dispersion model combining Drude, Gaussian, and Sellmeier dispersion functions to the experimental Ψ and Δ data. The data were analyzed using both an ideal bulk substrate model and a simple overlayer model to account for surface roughness. Including the optical surface roughness layer improved ellipsometric data fits in the UV, and using a separate Drude function for the surface layer improved fits in the infrared. The surface roughness was also characterized using an Atomic Force Microscope. Using an oscillator dispersion model for the optical constants determined in this work allows for more realistic extrapolation to longer infrared wavelengths. Extending optical constants out to 50 μm and beyond is important for calibrating far-infrared reflectance measurements. Applications include understanding the thermal performance of cryogenic space-based instruments, such as the James Webb Space Telescope (JWST).

Tuning Wettability and Adhesion of Structured Surfaces

NASA Astrophysics Data System (ADS)

Badge, Ila

Structured surfaces with feature size ranging from a few micrometers down to nanometers are of great interest in the applications such as design of anti-wetting surfaces, tissue engineering, microfluidics, filtration, microelectronic devices, anti-reflective coatings and reversible adhesives. A specific surface property demands particular roughness geometry along with suitable surface chemistry. Plasma Enhanced Chemical Vapor Deposition (PECVD) is a technique that offers control over surface chemistry without significantly affecting the roughness and thus, provides a flexibility to alter surface chemistry selectively for a given structured surface. In this study, we have used PECVD to fine tune wetting and adhesion properties. The research presented focuses on material design aspects as well as the fundamental understanding of wetting and adhesion phenomena of structured surfaces. In order to study the effect of surface roughness and surface chemistry on the surface wettability independently, we developed a model surface by combination of colloidal lithography and PECVD. A systematically controlled hierarchical roughness using spherical colloidal particles and surface chemistry allowed for quantitative prediction of contact angles corresponding to metastable and stable wetting states. A well-defined roughness and chemical composition of the surface enabled establishing a correlation between theory predictions and experimental measurements. We developed an extremely robust superhydrophobic surface based on Carbon-Nanotubes (CNT) mats. The surface of CNTs forming a nano-porous mesh was modified using PECVD to deposit a layer of hydrophobic coating (PCNT). The PCNT surface thus formed is superhydrophobic with almost zero contact angle hysteresis. We demonstrated that the PCNT surface is not wetted under steam condensation even after prolonged exposure and also continues to retain its superhydrophobicity after multiple frosting-defrosting cycles. The anti-wetting behavior of PCNT surface is consistent with our model predictions, derived based on thermodynamic theory of wetting. The surface of gecko feet is a very unique natural structured surface. The hierarchical surface structure of a Gecko toe pad is responsible for its reversible adhesive properties and superhydrophobicity. van der Waals interactions is known to be the key mechanism behind Gecko adhesion. However, we found that the wettability, thus the surface chemistry plays a significant role in Gecko adhesion mechanism, especially in the case of underwater adhesion. We used PECVD process to deposit a layer of coating with known chemistry on the surface of sheds of gecko toes to study the effect that wettability of the toe surface has on its adhesion. In summary, we demonstrated that PECVD can be effectively used as means of surface chemistry control for tunable structure-property relationship of three types of structured surfaces; each having unique surface features.

Variation in bed level shear stress on surfaces sheltered by nonerodible roughness elements

NASA Astrophysics Data System (ADS)

Sutton, Stephen L. F.; McKenna-Neuman, Cheryl

2008-09-01

Direct bed level observations of surface shear stress, pressure gradient variability, turbulence intensity, and fluid flow patterns were carried out in the vicinity of cylindrical roughness elements mounted in a boundary layer wind tunnel. Paired corkscrew vortices shed from each of the elements result in elevated shear stress and increased potential for the initiation of particle transport within the far wake. While the size and shape of these trailing vortices change with the element spacing, they persist even for large roughness densities. Wake interference coincides with the impingement of the upwind horseshoe vortices upon one another at a point when their diameter approaches half the distance between the roughness elements. While the erosive capability of the horseshoe vortex has been suggested for a variety of settings, the present study shows that the fluid stress immediately beneath this coherent structure is actually small in comparison to that caused by compression of the incident flow as it is deflected around the element and attached vortex. Observations such as these are required for further refinement of models of stress partitioning on rough surfaces.

Convective Enhancement of Icing Roughness Elements in Stagnation Region Flows

NASA Technical Reports Server (NTRS)

Hughes, Michael T.; McClain, Stephen T.; Vargas, Mario; Broeren, Andy

2015-01-01

To improve existing ice accretion simulation codes, more data regarding ice roughness and its effects on convective heat transfer are required. To build on existing research on this topic, this study used the Vertical Icing Studies Tunnel (VIST) at NASA Glenn Research to model realistic ice roughness in the stagnation region of a NACA 0012 airfoil. Using the VIST, a test plate representing the leading 2% chord of the airfoil was subjected to flows of 7.62 m/s (25 ft/s), 12.19 m/s (40 ft/s), and 16.76 m/s (55 ft/s). The test plate was fitted with 3 surfaces, each with a different representation of ice roughness: 1) a control surface with no ice roughness, 2) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 10x, and 3) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 25x. Temperature data from the tests were recorded using an infrared camera and thermocouples imbedded in the test plate. From the temperature data, a convective heat transfer coefficient map was created for each case. Additional testing was also performed to validate the VIST's flow quality. These tests included five-hole probe and hot-wire probe velocity traces to provide flow visualization and to study boundary layer formation on the various test surfaces. The knowledge gained during the experiments will help improve ice accretion codes by providing heat transfer coefficient validation data and by providing flow visualization data helping understand current and future experiments performed in the VIST.

CF4 plasma treatment of poly(dimethylsiloxane): effect of fillers and its application to high-aspect-ratio UV embossing.

PubMed

Yan, Y H; Chan-Park, M B; Yue, C Y

2005-09-13

Surface modification of poly(dimethylsiloxane) (PDMS) was carried out via CF4 plasma treatment. The test PDMS used contains significant amounts of quartz and silica fillers, while the control material is the same PDMS with quartz removed by centrifugation. Fluorination accompanied with roughening was produced on both PDMS surfaces. With short plasma times (15 min or less), a macromolecular fluorocarbon layer was formed on the PDMS surfaces because of the dominant fluorination, leading to significant increase in F concentration, decrease of surface energy, and some roughening. With intermediate plasma times (15-30 min), dynamic balance between fluorination and ablation was achieved, leading to a plateau of the surface roughness, fluorine content, and [F-Si]/[F-C] ratio. At our longest investigated plasma time of 45 min, the plasma ablated the fluorinated covering layer on the PDMS surfaces, leading to significant increase in roughness and [F-Si]/[F-C] ratio and decrease of surface F concentration. The effect of additional quartz in the test PDMS on surface F concentration, [F-Si]/[F-C] ratio, and roughness was dramatic only when ablation was significant (i.e., 45 min). The obtained Teflon-like surface displays long-term stability as opposed to hydrophobic recovery of other plasma-treated PDMS surfaces to increase hydrophilicity. On the basis of the optimized plasma treatment time of 15 min, a microstructured PDMS mold was plasma treated and successfully used for multiple high-aspect-ratio (about 8) UV embossing of nonpolar polypropylene glycol diacrylate (PPGDA) resin.

Biomimetic Deposition of Hydroxyapatite by Mixed Acid Treatment of Titanium Surfaces.

PubMed

Zhao, J M; Park, W U; Hwang, K H; Lee, J K; Yoon, S Y

2015-03-01

A simple chemical method was established for inducing bioactivity of Ti metal. In the present study, two kinds of mixed acid solutions were used to treat Ti specimens to induce Ca-P formation. Following a strong mixed acid activation process, Ca-P coatings successfully formed on the Ti surfaces in the simulated body fluid. Strong mixed acid etching was used to increase the roughness of the metal surface, because the porous and rough surfaces allow better adhesion between Ca-P coatings and substrate. Nano-scale modification of titanium surfaces can alter cellular and tissue responses, which may benefit osseointegration and dental implant therapy. Some specimens were treated with a 5 M NaOH aqueous solution, and then heat treated at 600 °C in order to form an amorphous sodium titanate layer on their surface. This treated titanium metal is believed to form a dense and uniform bone-like apatite layer on its surface in a simulated body fluid (SBF). This study proved that mixed acid treatment is not only important for surface passivation but is also another bioactive treatment for titanium surfaces, an alternative to alkali treatment. In addition, mixed acid treatment uses a lower temperature and shorter time period than alkali treatment.

Design and characterization of thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Schulte, K. L.; Zutter, B. T.; Wood, A. W.; Babcock, S. E.; Kuech, T. F.

2014-03-01

Thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) were studied. Relationships between MBL properties and growth parameters such as grading rate, cap layer thickness, final xInAs, and deposition temperature (TD) were explored. The MBLs were characterized by measurement of in-plane residual strain (ɛ¦¦), surface etch pit density (EPD), and surface roughness. Capping layer thickness had a strong effect on strain relaxation, with thickly capped samples exhibiting the lowest ɛ¦¦. EPD was higher in samples with thicker caps, reflecting their increased relaxation through dislocation generation. ɛ¦¦ and EPD were weakly affected by the grading rate, making capping layer thickness the primary structural parameter which controls these properties. MBLs graded in discrete steps had similar properties to MBLs with continuous grading. In samples with identical thickness and 10-step grading style, ɛ¦¦ increased almost linearly with final xInAs, while total relaxation stayed relatively constant. Relaxation as a function of xInAs could be described by an equilibrium model in which dislocation nucleation is impeded by the energy of the existing dislocation array. EPD was constant from xInAs = 0 to 0.24 then increased exponentially, which is related to the increased dislocation interaction and blocking seen at higher dislocation densities. RMS roughness increased with xInAs above a certain strain rate (0.15%/µm) samples grown below this level possessed large surface hillocks and high roughness values. The elimination of hillocks at higher values of xInAs is attributed to increased density of surface steps and is related to the out-of-plane component of the burgers vector of the dominant type of 60° dislocation. TD did not affect ɛ¦¦ for samples with a given xInAs. EPD tended to increase with TD, indicating dislocation glide likely is impeded at higher temperatures.

Control of the Pore Texture in Nanoporous Silicon via Chemical Dissolution.

PubMed

Secret, Emilie; Wu, Chia-Chen; Chaix, Arnaud; Galarneau, Anne; Gonzalez, Philippe; Cot, Didier; Sailor, Michael J; Jestin, Jacques; Zanotti, Jean-Marc; Cunin, Frédérique; Coasne, Benoit

2015-07-28

The surface and textural properties of porous silicon (pSi) control many of its physical properties essential to its performance in key applications such as optoelectronics, energy storage, luminescence, sensing, and drug delivery. Here, we combine experimental and theoretical tools to demonstrate that the surface roughness at the nanometer scale of pSi can be tuned in a controlled fashion using partial thermal oxidation followed by removal of the resulting silicon oxide layer with hydrofluoric acid (HF) solution. Such a process is shown to smooth the pSi surface by means of nitrogen adsorption, electron microscopy, and small-angle X-ray and neutron scattering. Statistical mechanics Monte Carlo simulations, which are consistent with the experimental data, support the interpretation that the pore surface is initially rough and that the oxidation/oxide removal procedure diminishes the surface roughness while increasing the pore diameter. As a specific example considered in this work, the initial roughness ξ ∼ 3.2 nm of pSi pores having a diameter of 7.6 nm can be decreased to 1.0 nm following the simple procedure above. This study allows envisioning the design of pSi samples with optimal surface properties toward a specific process.

Investigation of the atmospheric boundary layer characteristics on gust factor for the calculation of wind load

NASA Astrophysics Data System (ADS)

Ghanadi, Farzin; Emes, Matthew; Yu, Jeremy; Arjomandi, Maziar; Kelso, Richard

2017-06-01

Dynamic amplification and gust effects from turbulence can increase wind loads significantly over and above the static wind loads that have been used for heliostat design. This paper presents the results of analyzing the relationship between gust factor and turbulence intensity within the atmospheric boundary layer (ABL) based on the high fidelity measurements of wind velocity at the SLTEST facility in the Utah desert. Results showed that there are distinct characteristics of a low roughness ABL that deviate from semi-empirical relationships derived for open country and urban terrains with larger surface roughness heights. The analysis also indicated that gust factor is increased by 2.4% when lowering the gust period from 3s to 1s in the low roughness field experiment ABL, compared to a 3.6% increase in a suburban terrain at a 10m height. Although 3s gust periods are recommended in AS/NZS 1170.2 [1], comparison of gust factor data with a 1s gust period is recommended particularly in high roughness ABLs such as in urban areas, to ensure that buildings are adequately designed to withstand higher frequency gusts. This research proved the strength of the correlation between gust factor and turbulence intensity is dependent on the surface roughness height of the terrain. It is recommended that the coefficient in the previous semi-empirical equation must be adjusted to be fitted to the low roughness desert terrain in the field experiment ABL.

Could Crop Roughness Impact the Wind Resource at Agriculturally Productive Wind Farm Sites?

NASA Astrophysics Data System (ADS)

Vanderwende, B. J.; Lundquist, J. K.

2014-12-01

The high concentration of both large-scale agriculture and wind power production in the United States Midwest region raises new questions concerning the interaction of the two activities. For instance, it is known from internal boundary layer theory that changes in the roughness of the land-surface resulting from crop choices could modify the momentum field aloft. Upward propagation of such an effect might impact the properties of the winds encountered by modern turbines, which typically span a layer from about 40 to 120 meters above the surface. As direct observation of such interaction would require impractical interference in the planting schedules of farmers, we use numerical modeling to quantify the magnitude of crop-roughness effects. To simulate a collocated farm and turbine array, we use version 3.4.1 of the Weather Research and Forecasting model (WRF). The hypothetical farm is inserted near the real location of the 2013 Crop Wind Energy Experiment (CWEX). Reanalyses provide representative initial and boundary conditions. A month-long period spanning August 2013 is used to evaluate the differences in flows above corn (maize) and soybean crops at the mature, reproductive stage. Simulations are performed comparing the flow above each surface regime, both in the absence and presence of a wind farm, which consists of a parameterized 11x11 array of 1.8 MW Vestas V90 turbines. Appreciable differences in rotor-layer wind speeds emerge. The use of soybeans results in an increase in wind speeds and a corresponding reduction in rotor-layer shear when compared to corn. Despite the turbulent nature of flow within a wind farm, high stability reduces the impact of crop roughness on the flow aloft, particularly in the upper portion of the rotor disk. We use these results to estimate the economic impact of crop selection on wind power producers.

Surface modification of poly(vinylidene fluoride) hollow fibre membranes for biogas purification in a gas-liquid membrane contactor system.

PubMed

Jin, Pengrui; Huang, Chuan; Li, Jiaxiang; Shen, Yadong; Wang, Liao

2017-11-01

The wetting of hollow fibre membranes decreases the performance of the liquid-gas membrane contactor for CO 2 capture in biogas upgrading. To solve this problem, in this work, a poly(vinylidene fluoride) (PVDF) hollow fibre membrane for a liquid-gas membrane contactor was coated with a superhydrophobic layer composed of a combination of hydrophobic SiO 2 nanoparticles and polydimethylsiloxane (PDMS) by the method of spray deposition. A rough layer of SiO 2 deposited on the PVDF membrane resulted in an enhanced surface hydrophobicity. The surface structure of the pristine PVDF significantly affected the homogeneity of the generated SiO 2 layer. A uniform surface coating on the PVDF upper layer resulted from the presence of micrometre and nanometre-sized roughness on the surface of the PVDF membrane, which was achieved with a SiO 2 concentration of 4.44 mg ml -1 (0.2 g/45 ml) in the coating solution. As a result, the water contact angle of the modified surface was recorded as 155 ± 3°, which is higher than that of the pristine surface. The high contact angle is advantageous for reducing the wetting of the membrane. Additional mass transfer resistance was introduced by the superhydrophobic layer. In addition, continuous CO 2 absorption tests were carried out in original and modified PVDF hollow fibre membrane contactors, using monoethanolamine (MEA) solution as the absorbent. A long-term stability test revealed that the modified PVDF hollow fibre membrane contactor was able to outperform the original membrane contactor and demonstrated outstanding long-term stability, suggesting that spray deposition is a promising approach to obtain superhydrophobic PVDF membranes for liquid-gas membrane absorption.

Surface modification of poly(vinylidene fluoride) hollow fibre membranes for biogas purification in a gas–liquid membrane contactor system

PubMed Central

Huang, Chuan; Li, Jiaxiang; Shen, Yadong; Wang, Liao

2017-01-01

The wetting of hollow fibre membranes decreases the performance of the liquid–gas membrane contactor for CO2 capture in biogas upgrading. To solve this problem, in this work, a poly(vinylidene fluoride) (PVDF) hollow fibre membrane for a liquid–gas membrane contactor was coated with a superhydrophobic layer composed of a combination of hydrophobic SiO2 nanoparticles and polydimethylsiloxane (PDMS) by the method of spray deposition. A rough layer of SiO2 deposited on the PVDF membrane resulted in an enhanced surface hydrophobicity. The surface structure of the pristine PVDF significantly affected the homogeneity of the generated SiO2 layer. A uniform surface coating on the PVDF upper layer resulted from the presence of micrometre and nanometre-sized roughness on the surface of the PVDF membrane, which was achieved with a SiO2 concentration of 4.44 mg ml−1 (0.2 g/45 ml) in the coating solution. As a result, the water contact angle of the modified surface was recorded as 155 ± 3°, which is higher than that of the pristine surface. The high contact angle is advantageous for reducing the wetting of the membrane. Additional mass transfer resistance was introduced by the superhydrophobic layer. In addition, continuous CO2 absorption tests were carried out in original and modified PVDF hollow fibre membrane contactors, using monoethanolamine (MEA) solution as the absorbent. A long-term stability test revealed that the modified PVDF hollow fibre membrane contactor was able to outperform the original membrane contactor and demonstrated outstanding long-term stability, suggesting that spray deposition is a promising approach to obtain superhydrophobic PVDF membranes for liquid–gas membrane absorption. PMID:29291117

Benchmarking the x-ray phase contrast imaging for ICF DT ice characterization using roughened surrogates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dewald, E; Kozioziemski, B; Moody, J

2008-06-26

We use x-ray phase contrast imaging to characterize the inner surface roughness of DT ice layers in capsules planned for future ignition experiments. It is therefore important to quantify how well the x-ray data correlates with the actual ice roughness. We benchmarked the accuracy of our system using surrogates with fabricated roughness characterized with high precision standard techniques. Cylindrical artifacts with azimuthally uniform sinusoidal perturbations with 100 um period and 1 um amplitude demonstrated 0.02 um accuracy limited by the resolution of the imager and the source size of our phase contrast system. Spherical surrogates with random roughness close tomore » that required for the DT ice for a successful ignition experiment were used to correlate the actual surface roughness to that obtained from the x-ray measurements. When comparing average power spectra of individual measurements, the accuracy mode number limits of the x-ray phase contrast system benchmarked against surface characterization performed by Atomic Force Microscopy are 60 and 90 for surrogates smoother and rougher than the required roughness for the ice. These agreement mode number limits are >100 when comparing matching individual measurements. We will discuss the implications for interpreting DT ice roughness data derived from phase-contrast x-ray imaging.« less

Preliminary results on complex ceramic layers deposition by atmospheric plasma spraying

NASA Astrophysics Data System (ADS)

Florea, Costel; Bejinariu, Costicǎ; Munteanu, Corneliu; Cimpoeşu, Nicanor

2017-04-01

In this article we obtain thin layers from complex ceramic powders using industrial equipment based on atmospheric plasma spraying. We analyze the influence of the substrate material roughness on the quality of the thin layers using scanning electron microscopy (SEM) and X-ray dispersive energy analyze (EDAX). Preliminary results present an important dependence between the surface state and the structural and chemical homogeneity.

Surface Coating of Gypsum-Based Molds for Maxillofacial Prosthetic Silicone Elastomeric Material: The Surface Topography.

PubMed

Khalaf, Salah; Ariffin, Zaihan; Husein, Adam; Reza, Fazal

2015-07-01

This study aimed to compare the surface roughness of maxillofacial silicone elastomers fabricated in noncoated and coated gypsum materials. This study was also conducted to characterize the silicone elastomer specimens after surfaces were modified. A gypsum mold was coated with clear acrylic spray. The coated mold was then used to produce modified silicone experimental specimens (n = 35). The surface roughness of the modified silicone elastomers was compared with that of the control specimens, which were prepared by conventional flasking methods (n = 35). An atomic force microscope (AFM) was used for surface roughness measurement of silicone elastomer (unmodified and modified), and a scanning electron microscope (SEM) was used to evaluate the topographic conditions of coated and noncoated gypsum and silicone elastomer specimens (unmodified and modified) groups. After the gypsum molds were characterized, the fabricated silicone elastomers molded on noncoated and coated gypsum materials were evaluated further. Energy-dispersive X-ray spectroscopy (EDX) analysis of gypsum materials (noncoated and coated) and silicone elastomer specimens (unmodified and modified) was performed to evaluate the elemental changes after coating was conducted. Independent t test was used to analyze the differences in the surface roughness of unmodified and modified silicone at a significance level of p < 0.05. Roughness was significantly reduced in the silicone elastomers processed against coated gypsum materials (p < 0.001). The AFM and SEM analysis results showed evident differences in surface smoothness. EDX data further revealed the presence of the desired chemical components on the surface layer of unmodified and modified silicone elastomers. Silicone elastomers with lower surface roughness of maxillofacial prostheses can be obtained simply by coating a gypsum mold. © 2014 by the American College of Prosthodontists.

Shuttle Return To Flight Experimental Results: Protuberance Effects on Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Berry, Scott A.; Horvath, Thomas J.

2006-01-01

The effect of isolated roughness elements on the windward boundary layer of the Shuttle Orbiter has been experimentally examined in the Langley Aerothermodynamic Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for return to flight. This experimental effort was initiated to provide a roughness effects database for developing transition criteria to support on-orbit decisions to repair damage to the thermal protection system. Boundary layer transition results were obtained using trips of varying heights and locations along the centerline and attachment lines of 0.0075-scale models. Global heat transfer images using phosphor thermography of the Orbiter windward surface and the corresponding heating distributions were used to infer the state of the boundary layer (laminar, transitional, or turbulent). The database contained within this report will be used to formulate protuberance-induced transition correlations using predicted boundary layer edge parameters.

Roughness Effects on Wind-Turbine Wake Dynamics in a Boundary-Layer Wind Tunnel

NASA Astrophysics Data System (ADS)

Barlas, E.; Buckingham, S.; van Beeck, J.

2016-01-01

Increasing demand in wind energy has resulted in increasingly clustered wind farms, and raised the interest in wake research dramatically in the last couple of years. To this end, the present work employs an experimental approach with scaled three-bladed wind-turbine models in a large boundary-layer wind-tunnel. Time-resolved measurements are carried out with a three-component hot-wire anemometer in the mid-vertical plane of the wake up to a downstream distance of eleven turbine diameters. The major issue addressed is the wake dynamics i.e. the flow and turbulence characteristics as well as spectral content under two different neutral boundary-layer inflow conditions. The wind tunnel is arranged with and without roughened surfaces in order to mimic moderately rough and smooth conditions. The inflow characterization is carried out by using all three velocity components, while the rest of the study is focused on the streamwise component's evolution. The results show an earlier wake recovery, i.e. the velocity deficit due to the turbine is less persistent for the rough case due to higher incoming turbulence levels. This paves the way for enhanced mixing from higher momentum regions of the boundary layer towards the centre of the wake. The investigation on the turbulent shear stresses is in line with this observation as well. Moreover, common as well as distinguishing features of the turbulent-scales evolution are detected for rough and smooth inflow boundary-layer conditions. Wake meandering disappears for rough inflow conditions but persists for smooth case with a Strouhal number similar to that of a solid disk wake.

Mars Science Laboratory Heatshield Aerothermodynamics: Design and Reconstruction

NASA Technical Reports Server (NTRS)

Edquist, Karl T.; Hollis, Brian R.; Johnston, Christopher O.; Bose, Deepak; White, Todd R.; Mahzari, Milad

2013-01-01

The Mars Science Laboratory heatshield was designed to withstand a fully turbulent heat pulse based on test results and computational analysis on a pre-flight design trajectory. Instrumentation on the flight heatshield measured in-depth temperatures in the thermal protection system. The data indicate that boundary layer transition occurred at 5 of 7 thermocouple locations prior to peak heating. Data oscillations at 3 pressure measurement locations may also indicate transition. This paper presents the heatshield temperature and pressure data, possible explanations for the timing of boundary layer transition, and a qualitative comparison of reconstructed and computational heating on the as-flown trajectory. Boundary layer Reynolds numbers that are typically used to predict transition are compared to observed transition at various heatshield locations. A uniform smooth-wall transition Reynolds number does not explain the timing of boundary layer transition observed during flight. A roughness-based Reynolds number supports the possibility of transition due to discrete or distributed roughness elements on the heatshield. However, the distributed roughness height would have needed to be larger than the pre-flight assumption. The instrumentation confirmed the predicted location of maximum turbulent heat flux near the leeside shoulder. The reconstructed heat flux at that location is bounded by smooth-wall turbulent calculations on the reconstructed trajectory, indicating that augmentation due to surface roughness probably did not occur. Turbulent heating on the downstream side of the heatshield nose exceeded smooth-wall computations, indicating that roughness may have augmented heating. The stagnation region also experienced heating that exceeded computational levels, but shock layer radiation does not fully explain the differences.

Analysis of Turbulent Boundary-Layer over Rough Surfaces with Application to Projectile Aerodynamics

DTIC Science & Technology

1988-12-01

12 V. APPLICATION IN COMPONENT BUILD-UP METHODOLOGIES ....................... 12 1. COMPONENT BUILD-UP IN DRAG...dimensional roughness. II. CLASSIFICATION OF PREDICTION METHODS Prediction methods can be classified into two main approache-: 1) Correlation methodologies ...data are availaNe. V. APPLICATION IN COMPONENT BUILD-UP METHODOLOGIES 1. COMPONENT BUILD-UP IN DRAG The new correlation can be used for an engine.ring

Study on River Snail Shells Unearthed from Laoniupo Shang Dynasty Site.

PubMed

Zhang, Rui; Yue, Lianjian; Yang, Junchang

2016-03-01

The samples of river snail shell pieces, unearthed from Laoniupo Shang dynasty site, were observed and characterized by SEM, Raman and IR to obtain the information about their chemical component and crystal structure. The uneven surface of the cuticle was covered with nanoparticles, which formed rough surface of the shells. The surface of pearl layer was combined with nano-sized flakes and kept smooth on the whole. The insection of shell was composed of three layers: the cuticle (100-120 μm in thickness), the prismatic layer (-130-140 μm in thickness), and the thickest pearl layer (280-300 μm in thickness). All layers had the component of calcium carbonate with aragonite structure and they were different in nanostructures because of different biomineralization processes.

Different Effects of Roughness (Granularity) and Hydrophobicity

NASA Astrophysics Data System (ADS)

Shirtcliffe, Neil; McHale, Glen; Hamlett, Christopher; Newton, Michael

2010-05-01

With thanks to Stefan Doerr and Jorge Mataix-Solera for their invitation Superhydrophobicity is an interesting effect that appears to be simple on the outset; increased surface area from roughness increases interfacial area and therefore energy loss or gain. More extreme roughness prevents total wetting, resulting in gas pockets present at the surface and a drastic change in the properties of the system. Increases in complexity of the system, by adding porosity (granularity), allowing the structures to move, varying the shape of the roughness or the composition of the liquid used often has unexpected effects. Here we will consider a few of these related to complex topography. Overhanging features are commonly used in test samples as they perform better in some tests than simple roughness. It has been shown to be a prerequisite for superoleophobic surfaces as it allows liquids to be suspended for contact angles considerably below 90°. It also allows trapping of gas in lower layers even if the first layer is flooded. This is important in soils as a fixed bed of granules behaves just like a surface with overhanging roughness. Using simple geometry it is possible to predict at what contact angle penetration will occur. Plants have some structured superhydrophobic surfaces and we have shown that some use them in conjunction with other structured surfaces to control water flows. This allows some plants to survive in difficult environments and shows us how subtly different structures interact completely differently with water. Long fibres can either cause water droplets to roll over a plant surface or halt it in its tracks. Implications of this in soils include predicting when particles will adhere more strongly to water drops and why organic fibrous material may play a greater role in the behaviour of water in soils than may be expected from the amount present. The garden snail uses a biosurfactant that is very effective at wetting surfaces and can crawl over most superhydrophobic surfaces. There are some, however, that defeat even the snail's complex slime. Looking at these surfaces in more detail reveals that some superhydrophobic surfaces are much more resistant to the effects of surfactants than others. As mentioned above, overhanging structures, such as those found in granular materials are particularly effective at suspending liquids. This does not, however, always translate to them being more effective against surfactants, unfortunately, however, surfactants are not always as effective as we would like them to be, although drops do not skate across superhydrophobic surfaces they often do not penetrate into them fully either.

Differential response of surface temperature and atmospheric temperature to the biogeophysical effects of deforestation

NASA Astrophysics Data System (ADS)

Winckler, J.; Reick, C. H.; Lejeune, Q.; Pongratz, J.

2017-12-01

Deforestation influences temperature locally by changing the water, energy and momentum balance. While most observation-based studies and some modeling studies focused on the effects on surface temperature, other studies focused on the effects on near-surface air temperature. However, these two variables may respond differently to deforestation because changes in albedo and surface roughness may alter the land-atmosphere coupling and thus the vertical temperature distribution. Thus it is unclear whether it is possible to compare studies that assess the impacts of deforestation on these two different variables. Here, we analyze the biogeophysical effects of global-scale deforestation in the climate model MPI-ESM separately for surface temperature, 2m-air temperature and temperature the lowest atmospheric model layer. We investigate why the response of these variables differs by isolating the effects of only changing surface albedo and only changing surface roughness and by separating effects that are induced at the location of deforestation (local effects) from effects that are induced by advection and changes in circulation (nonlocal effects). Concerning surface temperature, we find that the local effects of deforestation lead to a global mean warming which is overcompensated by the nonlocal effects (up to 0.1K local warming versus -0.3K nonlocal cooling). The surface warming in the local effects is largely driven by the change in surface roughness while the cooling in the nonlocal effects is largely driven by the change in surface albedo. The nonlocal effects are largely consistent across surface temperature, 2m-air temperature, and the temperature of the lowest atmospheric layer. However, the local effects strongly differ across the three considered variables. The local effects are strong for surface temperature, but substantially weaker in the 2m-air temperature and largely absent in the lowest atmospheric layer. We conclude that studies focusing on the deforestation effects on surface temperature should not be compared to studies focusing on the effects on air temperature. While the local effects on surface temperature are useful for model evaluation, they might be less relevant for local adaptation and mitigation than previously thought because they might largely be absent in the atmosphere.

Turbulent Flow Over Large Roughness Elements: Effect of Frontal and Plan Solidity on Turbulence Statistics and Structure

NASA Astrophysics Data System (ADS)

Placidi, M.; Ganapathisubramani, B.

2018-04-01

Wind-tunnel experiments were carried out on fully-rough boundary layers with large roughness (δ /h ≈ 10, where h is the height of the roughness elements and δ is the boundary-layer thickness). Twelve different surface conditions were created by using LEGO™ bricks of uniform height. Six cases are tested for a fixed plan solidity (λ _P) with variations in frontal density (λ _F), while the other six cases have varying λ _P for fixed λ _F. Particle image velocimetry and floating-element drag-balance measurements were performed. The current results complement those contained in Placidi and Ganapathisubramani (J Fluid Mech 782:541-566, 2015), extending the previous analysis to the turbulence statistics and spatial structure. Results indicate that mean velocity profiles in defect form agree with Townsend's similarity hypothesis with varying λ _F, however, the agreement is worse for cases with varying λ _P. The streamwise and wall-normal turbulent stresses, as well as the Reynolds shear stresses, show a lack of similarity across most examined cases. This suggests that the critical height of the roughness for which outer-layer similarity holds depends not only on the height of the roughness, but also on the local wall morphology. A new criterion based on shelter solidity, defined as the sheltered plan area per unit wall-parallel area, which is similar to the `effective shelter area' in Raupach and Shaw (Boundary-Layer Meteorol 22:79-90, 1982), is found to capture the departure of the turbulence statistics from outer-layer similarity. Despite this lack of similarity reported in the turbulence statistics, proper orthogonal decomposition analysis, as well as two-point spatial correlations, show that some form of universal flow structure is present, as all cases exhibit virtually identical proper orthogonal decomposition mode shapes and correlation fields. Finally, reduced models based on proper orthogonal decomposition reveal that the small scales of the turbulence play a significant role in assessing outer-layer similarity.

The nanostructure and microstructure of SiC surface layers deposited by MWCVD and ECRCVD

NASA Astrophysics Data System (ADS)

Dul, K.; Jonas, S.; Handke, B.

2017-12-01

Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to investigate ex-situ the surface topography of SiC layers deposited on Si(100) by Microwave Chemical Vapour Deposition (MWCVD) -S1,S2 layers and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) - layers S3,S4, using silane, methane, and hydrogen. The effects of sample temperature and gas flow on the nanostructure and microstructure have been investigated. The nanostructure was described by three-dimensional surface roughness analysis based on digital image processing, which gives a tool to quantify different aspects of surface features. A total of 13 different numerical parameters used to describe the surface topography were used. The scanning electron image (SEM) of the microstructure of layers S1, S2, and S4 was similar, however, layer S3 was completely different; appearing like grains. Nonetheless, it can be seen that no grain boundary structure is present in the AFM images.

Perturbation Theory for Scattering from Multilayers with Randomly Rough Fractal Interfaces: Remote Sensing Applications.

PubMed

Imperatore, Pasquale; Iodice, Antonio; Riccio, Daniele

2017-12-27

A general, approximate perturbation method, able to provide closed-form expressions of scattering from a layered structure with an arbitrary number of rough interfaces, has been recently developed. Such a method provides a unique tool for the characterization of radar response patterns of natural rough multilayers. In order to show that, here, for the first time in a journal paper, we describe the application of the developed perturbation theory to fractal interfaces; we then employ the perturbative method solution to analyze the scattering from real-world layered structures of practical interest in remote sensing applications. We focus on the dependence of normalized radar cross section on geometrical and physical properties of the considered scenarios, and we choose two classes of natural stratifications: wet paleosoil covered by a low-loss dry sand layer and a sea-ice layer above water with dry snow cover. Results are in accordance with the experimental evidence available in the literature for the low-loss dry sand layer, and they may provide useful indications about the actual ability of remote sensing instruments to perform sub-surface sensing for different sensor and scene parameters.

Perturbation Theory for Scattering from Multilayers with Randomly Rough Fractal Interfaces: Remote Sensing Applications

PubMed Central

2017-01-01

A general, approximate perturbation method, able to provide closed-form expressions of scattering from a layered structure with an arbitrary number of rough interfaces, has been recently developed. Such a method provides a unique tool for the characterization of radar response patterns of natural rough multilayers. In order to show that, here, for the first time in a journal paper, we describe the application of the developed perturbation theory to fractal interfaces; we then employ the perturbative method solution to analyze the scattering from real-world layered structures of practical interest in remote sensing applications. We focus on the dependence of normalized radar cross section on geometrical and physical properties of the considered scenarios, and we choose two classes of natural stratifications: wet paleosoil covered by a low-loss dry sand layer and a sea-ice layer above water with dry snow cover. Results are in accordance with the experimental evidence available in the literature for the low-loss dry sand layer, and they may provide useful indications about the actual ability of remote sensing instruments to perform sub-surface sensing for different sensor and scene parameters. PMID:29280979

Surface morphological evolution of epitaxial CrN(001) layers

NASA Astrophysics Data System (ADS)

Frederick, J. R.; Gall, D.

2005-09-01

CrN layers, 57 and 230 nm thick, were grown on MgO(001) at Ts=600-800 °C by ultrahigh-vacuum magnetron sputter deposition in pure N2 discharges from an oblique deposition angle α=80°. Layers grown at 600 °C nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. The surface morphology of epitaxial CrN(001) grown at 700 °C is characterized by dendritic ridge patterns extending along the orthogonal <110> directions superposed by square-shaped super mounds with <100> edges. The ridge patterns are attributed to a Bales-Zangwill instability while the supermounds form due to atomic shadowing which leads to the formation of epitaxial inverted pyramids that are separated from the surrounding layer by tilted nanovoids. Growth at 800 °C yields complete single crystals with smooth surfaces. The root-mean-square surface roughness for 230-nm-thick layers decreases from 18.8 to 9.3 to 1.1 nm as Ts is raised from 600 to 700 to 800 °C. This steep decrease is due to a transition in the roughening mechanism from atomic shadowing to kinetic roughening. Atomic shadowing is dominant at 600 and 700 °C, where misoriented grains and supermounds, respectively, capture a larger fraction of the oblique deposition flux in comparison to the surrounding epitaxial matrix, resulting in a high roughening rate that is described by a power law with an exponent β>0.5. In contrast, kinetic roughening controls the surface morphology for Ts=800 °C, as well as the epitaxial fraction of the layers grown at 600 and 700 °C, yielding relatively smooth surfaces and β<=0.27.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Sijun, E-mail: sluo1@tulane.edu; Riggs, Brian C.; Shipman, Joshua T.

Direct integration of proton conductor films on Pt-coated substrates opens the way to film-based proton transport devices. Columnar SrZr{sub 0.95}Y{sub 0.05}O{sub 3−δ} (SZY) films with dense microstructure were deposited on Pt-coated MgO(100) substrates at 830 °C by pulsed laser deposition. The optimal window of ambient O{sub 2} pressure for good crystallinity of SZY films is from 400 to 600 mTorr. The ambient O{sub 2} compresses the plasma plume of SZY and increases the deposition rate. The 10 nm thick Ti adhesion layer on MgO(100) greatly affects the orientation of the sputtered Pt layers. Pt deposited directly on MgO shows a highly (111)-preferredmore » orientation and leads to preferentially oriented SZY films while the addition of a Ti adhesion layer makes Pt show a less preferential orientation that leads to randomly oriented SZY films. The RMS surface roughness of preferentially oriented SZY films is larger than that of randomly oriented SZY films deposited under the same ambient O{sub 2} pressure. As the O{sub 2} pressure increased, the RMS surface roughness of preferentially oriented SZY films increased, reaching 45.7 nm (2.61% of film thickness) at 600 mTorr. This study revealed the ambient O{sub 2} pressure and orientation dependent surface roughness of SZY films grown on Pt-coated MgO substrates, which provides the potential to control the surface microstructure of SZY films for electrochemical applications in film-based hydrogen devices.« less

Nanoscale electro-structural characterisation of ohmic contacts formed on p-type implanted 4H-SiC

NASA Astrophysics Data System (ADS)

Frazzetto, Alessia; Giannazzo, Filippo; Lo Nigro, Raffaella; di Franco, Salvatore; Bongiorno, Corrado; Saggio, Mario; Zanetti, Edoardo; Raineri, Vito; Roccaforte, Fabrizio

2011-12-01

This work reports a nanoscale electro-structural characterisation of Ti/Al ohmic contacts formed on p-type Al-implanted silicon carbide (4H-SiC). The morphological and the electrical properties of the Al-implanted layer, annealed at 1700°C with or without a protective capping layer, and of the ohmic contacts were studied using atomic force microscopy [AFM], transmission line model measurements and local current measurements performed with conductive AFM. The characteristics of the contacts were significantly affected by the roughness of the underlying SiC. In particular, the surface roughness of the Al-implanted SiC regions annealed at 1700°C could be strongly reduced using a protective carbon capping layer during annealing. This latter resulted in an improved surface morphology and specific contact resistance of the Ti/Al ohmic contacts formed on these regions. The microstructure of the contacts was monitored by X-ray diffraction analysis and a cross-sectional transmission electron microscopy, and correlated with the electrical results.

Geometrical and Structural Asperities on Fault Surfaces

NASA Astrophysics Data System (ADS)

Sagy, A.; Brodsky, E. E.; van der Elst, N.; Agosta, F.; di Toro, G.; Collettini, C.

2007-12-01

Earthquake dynamics are strongly affected by fault zone structure and geometry. Fault surface irregularities and the nearby structure control the rupture nucleation and propagation, the fault strength, the near-field stress orientations and the hydraulic properties. New field observations demonstrate the existence of asperities in faults as displayed by topographical bumps on the fault surface and hardening of the internal structure near them. Ground-based LIDAR measurements on more than 30 normal and strike slip faults in different lithologies demonstrate that faults are not planar surfaces and roughness is strongly dependent on fault displacement. In addition to the well-understood roughness exemplified by abrasive striations and fracture segmentation, we found semi-elliptical topographical bumps with wavelengths of a few meters. In many faults the bumps are not spread equally on the surface and zones can be bumpier than others. The bumps are most easily identified on faults with total displacement of dozens to hundreds of meters. Smaller scale roughness on these faults is smoothed by abrasive processes. A key site in southern Oregon shows that the topographic bumps are closely tied to the internal structure of the fault zone. At this location, we combine LiDAR data with detailed structural analysis of the fault zone embedded in volcanic rocks. Here the bumps correlate with an abrupt change in the width of the cohesive cataclasite layer that is exposed under a thin ultracataclasite zone. In most of the exposures the cohesive layer thickness is 10-20 cm. However, under protruding bumps the layer is always thickened and the width can locally exceed one meter. Field and microscopic analyses show that the layer contains grains with dimensions ranging from less than 10 μ up to a few centimeters. There is clear evidence of internal flow, rotation and fracturing of the grains in the layer. X-Ray diffraction measurements of samples from the layer show that the bulk mineralogy is identical to that of the host rock, although thin section analysis suggests that some alteration and secondary mineralization of the grains also occurs. We infer that the cohesiveness of the layer is a consequence of repacking and cementation similar to deformation bands in granular material. By comparing the thickness of the cohesive layer on several secondary faults in this fault area we found that the average thickness of the layer increases with total slip. The correlation is nonlinear and the thickening rate decreases with increasing slip. We conclude that granular flow decreasing with increasing slip and thus the deformation is continually localized.

Surface roughening transition and critical layer thickness in strained-layer heteroepitaxy of EuTe on PbTe (111)

NASA Astrophysics Data System (ADS)

Springholz, G.; Frank, N.; Bauer, G.

1994-05-01

Heteroepitaxial growth of 2% lattice-mismatched EuTe on PbTe (111) by molecular beam epitaxy is investigated in the two-dimensional layer-by-layer growth regime combining in situ reflection high-energy electron diffraction and scanning tunneling microscopy (STM). At the critical layer thickness a distinct surface roughening is observed. The quantitative analysis of STM images yields an increase of the root mean square roughness by a factor of 4 at this roughening transition. Strong evidence is presented that for the used growth conditions this roughening is not caused by strain induced coherent islanding but by misfit dislocations at the onset of strain relaxation.

Effect of multipath laser shock processing on microhardness, surface roughness, and wear resistance of 2024-T3 Al alloy.

PubMed

Kadhim, Abdulhadi; Salim, Evan T; Fayadh, Saeed M; Al-Amiery, Ahmed A; Kadhum, Abdul Amir H; Mohamad, Abu Bakar

2014-01-01

Laser shock processing (LSP) is an innovative surface treatment technique with high peak power, short pulse, and cold hardening for strengthening metal materials. LSP is based on the application of a high intensity pulsed laser beam (I > 1 GW/cm(2); t < 50 ns) at the interface between the metallic target and the surrounding medium (a transparent confining material, normally water) forcing a sudden vaporization of the metallic surface into a high temperature and density plasma that immediately develops inducing a shock wave propagating into the material. The shock wave induces plastic deformation and a residual stress distribution in the target material. In this paper we study the increase of microhardness and surface roughness with the increase of laser pulse energy in 2024-T3 Al alloy. The influence of the thickness of the confining layer (water) on microhardness and surface roughness is also studied. In addition, the effect of LSP treatment with best conditions on wear behaviors of the alloy was investigated.

Sensitivity of turbine-height wind speeds to parameters in planetary boundary-layer and surface-layer schemes in the weather research and forecasting model

DOE PAGES

Yang, Ben; Qian, Yun; Berg, Larry K.; ...

2016-07-21

We evaluate the sensitivity of simulated turbine-height wind speeds to 26 parameters within the Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary-layer scheme and MM5 surface-layer scheme of the Weather Research and Forecasting model over an area of complex terrain. An efficient sampling algorithm and generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of simulated turbine-height wind speeds. The results indicate that most of the variability in the ensemble simulations is due to parameters related to the dissipation of turbulent kinetic energy (TKE), Prandtl number, turbulent length scales, surface roughness, and the von Kármán constant. Themore » parameter associated with the TKE dissipation rate is found to be most important, and a larger dissipation rate produces larger hub-height wind speeds. A larger Prandtl number results in smaller nighttime wind speeds. Increasing surface roughness reduces the frequencies of both extremely weak and strong airflows, implying a reduction in the variability of wind speed. All of the above parameters significantly affect the vertical profiles of wind speed and the magnitude of wind shear. Lastly, the relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability.« less

Sensitivity of turbine-height wind speeds to parameters in planetary boundary-layer and surface-layer schemes in the weather research and forecasting model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Ben; Qian, Yun; Berg, Larry K.

We evaluate the sensitivity of simulated turbine-height wind speeds to 26 parameters within the Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary-layer scheme and MM5 surface-layer scheme of the Weather Research and Forecasting model over an area of complex terrain. An efficient sampling algorithm and generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of simulated turbine-height wind speeds. The results indicate that most of the variability in the ensemble simulations is due to parameters related to the dissipation of turbulent kinetic energy (TKE), Prandtl number, turbulent length scales, surface roughness, and the von Kármán constant. Themore » parameter associated with the TKE dissipation rate is found to be most important, and a larger dissipation rate produces larger hub-height wind speeds. A larger Prandtl number results in smaller nighttime wind speeds. Increasing surface roughness reduces the frequencies of both extremely weak and strong airflows, implying a reduction in the variability of wind speed. All of the above parameters significantly affect the vertical profiles of wind speed and the magnitude of wind shear. Lastly, the relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability.« less

Nanocryl Coating of PMMA Complete Denture Base Materials to Prevent Scratching.

PubMed

Fathi, Hawa M; Benonn, Hajer A; Johnson, Anthony

2017-09-01

The surface of polymethylmethacrylate (PMMA) is vulnerable to indentation by hard objects that may contribute to abrade the material surface and subject it to wear. This phenomenon promotes an increase in the surface roughness leading to microbial colonisation which can endanger the general health of wearers and damage the intra-oral prosthesis. The aim of this study is to investigate the effect of three different nanocryl coating agents (Easy Glaze, G-Coat Plus and Formulation XP) on surface roughness and thickness of PMMA material after a simulating cleaning process utilizing an electric toothbrush and three different dentifrices (pastes and immersion). Acrylic uncoated discs were used as a control group. The results showed that the G-Coat Plus coating agent had less changes in the surface roughness and thickness layer whereas the immersion cleaner revealed less abrasion effect compared with the paste cleaners which could be considered the most suitable cleaner to provide lower abrasivenes and good removal of organic debris. However, using nanofilled sealants did not demonstrate significant improvement in reducing surface roughness p ⟩ 0.05. Nevertheless, it could provide some protection against wearing to the acrylic resin surface during tooth brushing and may provide better resistance to microbial colonisation. Copyright© 2017 Dennis Barber Ltd.

Characterization of Cu(In,Ga)Se 2 (CIGS) films with varying gallium ratios

DOE PAGES

Claypoole, Jesse; Peace, Bernadette; Sun, Neville; ...

2015-09-05

Cu(In 1–x,Ga x)Se 2 (CIGS) absorber layers were deposited on molybdenum (Mo) coated soda-lime glass substrates with varying Ga content (described as Ga/(In + Ga) ratios) with respect to depth. As the responsible mechanisms for the limitation of the performance of the CIGS solar cells with high Ga contents are not well understood, the goal of this work was to investigate different properties of CIGS absorber films with Ga/(In + Ga) ratios varied between 0.29 and 0.41 (as determined by X-ray florescence spectroscopy (XRF)) in order to better understand the role that the Ga content has on film quality. Themore » Ga grading in the CIGS layer has the effect causing a higher band gap toward the surface and Mo contact while the band gap in the middle of the CIGS layer is lower. Also, a wider and larger Ga/(In + Ga) grading dip located deeper in the CIGS absorber layers tend to produce larger grains in the regions of the films that have lower Ga/(In + Ga) ratios. Moreover, it was found that surface roughness decreases from 51.2 nm to 41.0 nm with increasing Ga/(In + Ga) ratios. Furthermore, the surface roughness generally decreases if the Ga grading occurs deeper in the absorber layer.« less

An Optimal Estimation Method to Obtain Surface Layer Turbulent Fluxes from Profile Measurements

NASA Astrophysics Data System (ADS)

Kang, D.

2015-12-01

In the absence of direct turbulence measurements, the turbulence characteristics of the atmospheric surface layer are often derived from measurements of the surface layer mean properties based on Monin-Obukhov Similarity Theory (MOST). This approach requires two levels of the ensemble mean wind, temperature, and water vapor, from which the fluxes of momentum, sensible heat, and water vapor can be obtained. When only one measurement level is available, the roughness heights and the assumed properties of the corresponding variables at the respective roughness heights are used. In practice, the temporal mean with large number of samples are used in place of the ensemble mean. However, in many situations the samples of data are taken from multiple levels. It is thus desirable to derive the boundary layer flux properties using all measurements. In this study, we used an optimal estimation approach to derive surface layer properties based on all available measurements. This approach assumes that the samples are taken from a population whose ensemble mean profile follows the MOST. An optimized estimate is obtained when the results yield a minimum cost function defined as a weighted summation of all error variance at each sample altitude. The weights are based one sample data variance and the altitude of the measurements. This method was applied to measurements in the marine atmospheric surface layer from a small boat using radiosonde on a tethered balloon where temperature and relative humidity profiles in the lowest 50 m were made repeatedly in about 30 minutes. We will present the resultant fluxes and the derived MOST mean profiles using different sets of measurements. The advantage of this method over the 'traditional' methods will be illustrated. Some limitations of this optimization method will also be discussed. Its application to quantify the effects of marine surface layer environment on radar and communication signal propagation will be shown as well.

Bacterial adhesion on conventional and self-ligating metallic brackets after surface treatment with plasma-polymerized hexamethyldisiloxane.

PubMed

Tupinambá, Rogerio Amaral; Claro, Cristiane Aparecida de Assis; Pereira, Cristiane Aparecida; Nobrega, Celestino José Prudente; Claro, Ana Paula Rosifini Alves

2017-01-01

Plasma-polymerized film deposition was created to modify metallic orthodontic brackets surface properties in order to inhibit bacterial adhesion. Hexamethyldisiloxane (HMDSO) polymer films were deposited on conventional (n = 10) and self-ligating (n = 10) stainless steel orthodontic brackets using the Plasma-Enhanced Chemical Vapor Deposition (PECVD) radio frequency technique. The samples were divided into two groups according to the kind of bracket and two subgroups after surface treatment. Scanning Electron Microscopy (SEM) analysis was performed to assess the presence of bacterial adhesion over samples surfaces (slot and wings region) and film layer integrity. Surface roughness was assessed by Confocal Interferometry (CI) and surface wettability, by goniometry. For bacterial adhesion analysis, samples were exposed for 72 hours to a Streptococcus mutans solution for biofilm formation. The values obtained for surface roughness were analyzed using the Mann-Whitney test while biofilm adhesion were assessed by Kruskal-Wallis and SNK test. Significant statistical differences (p< 0.05) for surface roughness and bacterial adhesion reduction were observed on conventional brackets after surface treatment and between conventional and self-ligating brackets; no significant statistical differences were observed between self-ligating groups (p> 0.05). Plasma-polymerized film deposition was only effective on reducing surface roughness and bacterial adhesion in conventional brackets. It was also noted that conventional brackets showed lower biofilm adhesion than self-ligating brackets despite the absence of film.

Understanding the creation of & reducing surface microroughness during polishing & post-processing of glass optics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suratwala, Tayyab

2016-09-22

In the follow study, we have developed a detailed understanding of the chemical and mechanical microscopic interactions that occur during polishing affecting the resulting surface microroughness of the workpiece. Through targeted experiments and modeling, the quantitative relationships of many important polishing parameters & characteristics affecting surface microroughness have been determined. These behaviors and phenomena have been described by a number of models including: (a) the Ensemble Hertzian Multi Gap (EHMG) model used to predict the removal rate and roughness at atomic force microscope (AFM) scale lengths as a function of various polishing parameters, (b) the Island Distribution Gap (IDG) modelmore » used to predict the roughness at larger scale lengths, (c) the Deraguin-Verwey-Landau-Overbeek (DLVO) 3-body electrostatic colloidal model used to predict the interaction of slurry particles at the interface and roughness behavior as a function of pH, and (d) a diffusion/chemical reaction rate model of the incorporation of impurities species into the polishing surface layer (called the Bielby layer). Based on this improved understanding, novel strategies to polish the workpiece have been developed simultaneously leading to both ultrasmooth surfaces and high material removal rates. Some of these strategies include: (a) use of narrow PSD slurries, (b) a novel diamond conditioning recipe of the lap to increase the active contact area between the workpiece and lap without destroying its surface figure, (c) proper control of pH for a given glass type to allow for a uniform distribution of slurry particles at the interface, and (d) increase in applied load just up to the transition between molecular to plastic removal regime for a single slurry particle. These techniques have been incorporated into a previously developed finishing process called Convergent Polishing leading to not just economical finishing process with improved surface figure control, but also simultaneously leading to low roughness surface with high removal rates.« less

Effect of Electropulsing-Assisted Ultrasonic Nanocrystalline Surface Modification on the Surface Mechanical Properties and Microstructure of Ti-6Al-4V Alloy

NASA Astrophysics Data System (ADS)

Ye, Yongda; Wang, Haibo; Tang, Guoyi; Song, Guolin

2018-05-01

The effect of electropulsing-assisted ultrasonic nanocrystalline surface modification (EP-UNSM) on surface mechanical properties and microstructure of Ti-6Al-4V alloy is investigated. Compared to conventional ultrasonic nanocrystalline surface modification (UNSM), EP-UNSM can effectively facilitate surface roughness and morphology, leading to excellent surface roughness (reduced from Ra 0.918 to Ra 0.028 μm by UNSM and Ra 0.019 μm by EP-UNSM) and smoother morphology with less cracks and defects. Surface friction coefficients are enhanced, resulting in lower and smoother friction coefficients. In addition, the surface-strengthened layer and ultra-refined grains are significantly enhanced with more severe plastic deformation and a greater surface hardness (a maximum hardness value of 407 HV and an effective depth of 550 μm, in comparison with the maximum hardness value of 364 HV and effective depth of 300 μm obtained by conventional UNSM). Remarkable enhancement of surface mechanical properties can be attributed to the refined gradient microstructure and the enhanced severe plastic deformation layer induced by coupling the effects of UNSM and electropulsing. The accelerated dislocation mobility and atom diffusion caused by the thermal and athermal effects of electropulsing treatment may be the primary intrinsic reasons for these improvements.

Analysis of the coherent and turbulent stresses of a numerically simulated rough wall pipe

NASA Astrophysics Data System (ADS)

Chan, L.; MacDonald, M.; Chung, D.; Hutchins, N.; Ooi, A.

2017-04-01

A turbulent rough wall flow in a pipe is simulated using direct numerical simulation (DNS) where the roughness elements consist of explicitly gridded three-dimensional sinusoids. Two groups of simulations were conducted where the roughness semi-amplitude h+ and the roughness wavelength λ+ are systematically varied. The triple decomposition is applied to the velocity to separate the coherent and turbulent components. The coherent or dispersive component arises due to the roughness and depends on the topological features of the surface. The turbulent stress on the other hand, scales with the friction Reynolds number. For the case with the largest roughness wavelength, large secondary flows are observed which are similar to that of duct flows. The occurrence of these large secondary flows is due to the spanwise heterogeneity of the roughness which has a spacing approximately equal to the boundary layer thickness δ.

Laser-Hardened and Ultrasonically Peened Surface Layers on Tool Steel AISI D2: Correlation of the Bearing Curves' Parameters, Hardness and Wear

NASA Astrophysics Data System (ADS)

Lesyk, D. A.; Martinez, S.; Mordyuk, B. N.; Dzhemelinskyi, V. V.; Lamikiz, A.; Prokopenko, G. I.; Grinkevych, K. E.; Tkachenko, I. V.

2018-02-01

This paper is focused on the effects of the separately applied laser heat treatment (LHT) and ultrasonic impact treatment (UIT) and the combined LHT + UIT process on the wear and friction behaviors of the hardened surface layers of the tool steel AISI D2. In comparison with the initial state, wear losses of the treated specimens after long-term wear tests were decreased by 68, 41, and 77% at the LHT, UIT, and combined LHT + UIT processes, respectively. The Abbott-Firestone bearing curves were used to analyze the material ratio and functional characterization (bearing capacity and oil capacitance) of the studied surface specimens. The wear losses registered after short (15 min) tests correlate well with the changes in experimental surface roughness Ra, and the predictive Rpk, and bearing capacity B C parameters, respectively, evaluated using the Abbott-Firestone curves and Kragelsky-Kombalov formula. The wear losses after the long-term (45 min) tests are in good correlation with the reciprocal surface microhardness HV and with the W L and W P wear parameters, respectively, estimated using Archard-Rabinowicz formula and complex roughness-and-strength approach. The observed HV increase is supported by nanotwins (LHT), by dense dislocation nets (UIT), and by dislocation cells/nanograins fixed with fine carbides (LHT + UIT) formed in the surface layers of the steel.

Separating local topography from snow effects on momentum roughness in mountain regions

NASA Astrophysics Data System (ADS)

Diebold, M.; Katul, G. G.; Calaf, M.; Lehning, M.; Parlange, M. B.

2013-12-01

Parametrization of momentum surface roughness length in mountainous regions continues to be an active research topic given its application to improved weather forecasting and sub-grid scale representation of mountainous regions in climate models. A field campaign was conducted in the Val Ferret watershed (Swiss Alps) to assess the role of topographic variability and snow cover on momentum roughness. To this end, turbulence measurements in a mountainous region with and without snow cover have been analyzed. A meteorological mast with four sonic anemometers together with temperature and humidity sensors was installed at an elevation of 2500 m and data were obtained from October 2011 until May 2012. Because of the long-term nature of these experiments, natural variability in mean wind direction allowed a wide range of terrain slopes and snow depths to be sampled. A theoretical framework that accounted only for topographically induced pressure perturbations in the mean momentum balance was used to diagnose the role of topography on the effective momentum roughness height as inferred from the log-law. Surface roughness depended systematically on wind direction but was not significantly influenced by the presence of snow depth variation. Moreover, the wind direction and so the surface roughness influenced the normalized turbulent kinetic energy, which in theory should not depend on these factors in the near-neutral atmospheric surface layer. The implications of those findings to modeling momentum roughness heights and turbulent kinetic energy (e.g. in conventional K-epsilon closure) in complex terrain are briefly discussed.

High Temperature Superconducting Thick Films

DOEpatents

Arendt, Paul N.; Foltyn, Stephen R.; Groves, James R.; Holesinger, Terry G.; Jia, Quanxi

2005-08-23

An article including a substrate, a layer of an inert oxide material upon the surface of the substrate, (generally the inert oxide material layer has a smooth surface, i.e., a RMS roughness of less than about 2 nm), a layer of an amorphous oxide or oxynitride material upon the inert oxide material layer, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the amorphous oxide material layer is provided together with additional layers such as at least one layer of a buffer material upon the oriented cubic oxide material layer or a HTS top-layer of YBCO directly upon the oriented cubic oxide material layer. With a HTS top-layer of YBCO upon at least one layer of a buffer material in such an article, Jc's of 1.4×106 A/cm2 have been demonstrated with projected Ic's of 210 Amperes across a sample 1 cm wide.

Metal deposition using seed layers

DOEpatents

Feng, Hsein-Ping; Chen, Gang; Bo, Yu; Ren, Zhifeng; Chen, Shuo; Poudel, Bed

2013-11-12

Methods of forming a conductive metal layers on substrates are disclosed which employ a seed layer to enhance bonding, especially to smooth, low-roughness or hydrophobic substrates. In one aspect of the invention, the seed layer can be formed by applying nanoparticles onto a surface of the substrate; and the metallization is achieved by electroplating an electrically conducting metal onto the seed layer, whereby the nanoparticles serve as nucleation sites for metal deposition. In another approach, the seed layer can be formed by a self-assembling linker material, such as a sulfur-containing silane material.

Synthesis and Characterization of Hydrophobic Silica Thin Layer Derived from Methyltrimethoxysilane (MTMS)

NASA Astrophysics Data System (ADS)

Darmawan, Adi; Utari, Riyadini; Eka Saputra, Riza; Suhartana; Astuti, Yayuk

2018-01-01

This study investigated the synthesis and characterization of MTMS hydrophobic silica prepared by sol-gel method. In principle, silica xerogels and silica thin layer were obtained by reacting MTMS in ethanol solvent in some pH variations. The MTMS solution was used to modify the surface of the ceramic plate by dipcoating method to further be calcined at two different temperatures of 350°C and 500°C. The silica xerogels were analysed by FTIR, TGA-DSC and GSA to determine functional group characteristics, thermal properties and pore morphology respectively. Meanwhile, the silica thin layers were analysed their hydrophobic properties using water contact angle measurement and surface roughness determination using SEM. The results showed that the higher the pH used in the MTMS solution, the higher the resulting contact angle. The highest contact angle was obtained at pH 8.12 which reached 94.7° and 79.5° for silica thin layer calcined at 350°C and 500°C, respectively. The TGA results indicated that the methyl group survived up to 400°C and disappeared at 500°C which had implications on silica thin layer hydrophobic nature. GSA result exhibited that the silica xerogel had a close structure with a very low pore volume. While the SEM-EDX results displayed that the silica thin layer prepared at acidic pH had smoother surface morphology and became rough when prepared at an alkaline pH.

Multigrid methods for flow transition in three-dimensional boundary layers with surface roughness

NASA Technical Reports Server (NTRS)

Liu, Chaoqun; Liu, Zhining; Mccormick, Steve

1993-01-01

The efficient multilevel adaptive method has been successfully applied to perform direct numerical simulations (DNS) of flow transition in 3-D channels and 3-D boundary layers with 2-D and 3-D isolated and distributed roughness in a curvilinear coordinate system. A fourth-order finite difference technique on stretched and staggered grids, a fully-implicit time marching scheme, a semi-coarsening multigrid method associated with line distributive relaxation scheme, and an improved outflow boundary-condition treatment, which needs only a very short buffer domain to damp all order-one wave reflections, are developed. These approaches make the multigrid DNS code very accurate and efficient. This allows us not only to be able to do spatial DNS for the 3-D channel and flat plate at low computational costs, but also to do spatial DNS for transition in the 3-D boundary layer with 3-D single and multiple roughness elements, which would have extremely high computational costs with conventional methods. Numerical results show good agreement with the linear stability theory, the secondary instability theory, and a number of laboratory experiments. The contribution of isolated and distributed roughness to transition is analyzed.

Coupled three-layer model for turbulent flow over large-scale roughness: On the hydrodynamics of boulder-bed streams

NASA Astrophysics Data System (ADS)

Pan, Wen-hao; Liu, Shi-he; Huang, Li

2018-02-01

This study developed a three-layer velocity model for turbulent flow over large-scale roughness. Through theoretical analysis, this model coupled both surface and subsurface flow. Flume experiments with flat cobble bed were conducted to examine the theoretical model. Results show that both the turbulent flow field and the total flow characteristics are quite different from that in the low gradient flow over microscale roughness. The velocity profile in a shallow stream converges to the logarithmic law away from the bed, while inflecting over the roughness layer to the non-zero subsurface flow. The velocity fluctuations close to a cobble bed are different from that of a sand bed, and it indicates no sufficiently large peak velocity. The total flow energy loss deviates significantly from the 1/7 power law equation when the relative flow depth is shallow. Both the coupled model and experiments indicate non-negligible subsurface flow that accounts for a considerable proportion of the total flow. By including the subsurface flow, the coupled model is able to predict a wider range of velocity profiles and total flow energy loss coefficients when compared with existing equations.

The role of electro-explosion alloying with titanium diboride and treatment with pulsed electron beam in the surface modification of VT6 alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konovalov, Sergey, E-mail: konovserg@gmail.com; Gromov, Victor, E-mail: gromov@physics.sibsiu.ru; Kobzareva, Tatyana

The paper presents the results of the investigation of VT6 titanium alloy subjected to electro-explosion alloying with TiB{sub 2} and irradiation with pulsed electron beam. It was established that electro-explosion alloying resulted in a high level of roughness of the surface layer with high adhesion of the modified layer and matrix. Further irradiation of the material with electron beam resulted in the smoothing of the surface of alloying and formation of a porous structure with various scale levels in the surface layer. It was also established that the energetic exposure causes the formation of a gradient structure with a changingmore » elemental composition along the direction from the surface of alloying.« less

The influence of nano-oxide layer on magnetostriction of sensing layer in bottom spin valves

NASA Astrophysics Data System (ADS)

Qiu, J. J.; Han, G. C.; Li, K. B.; Liu, Z. Y.; Zong, B. Y.; Wu, Y. H.

2006-05-01

The magnetostriction coefficient (λs) of ultrathin sputtered polycrystalline as-deposited and annealed Ta/Ni81Fe19(t)/Ta films was studied as a function of the thickness. λs and magnetoresistance (MR) of bottom-type spin valves (SVs) with nano-oxide layer (NOL) added in the pinned layer were investigated by using NiFe, Co90Fe10, and CoFe/NiFe/CoFe layers as free layer (FL), respectively. λs of SV with NOL increased slightly except that of CoFe FL. NOLs were added at different positions to study the effects of NOL on λs of CoFe FL. All λs of CoFe FL change from negative to positive and its absolute value also increases significantly with CoFeOx related NOL added below. Our λs and surface roughness results indicated that the structure of the film not the roughness dominates λs of ultrathin FL in SVs.

Hypersonic Viscous Flow Over Large Roughness Elements

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan M.

2009-01-01

Viscous flow over discrete or distributed surface roughness has great implications for hypersonic flight due to aerothermodynamic considerations related to laminar-turbulent transition. Current prediction capability is greatly hampered by the limited knowledge base for such flows. To help fill that gap, numerical computations are used to investigate the intricate flow physics involved. An unstructured mesh, compressible Navier-Stokes code based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for two roughness shapes investigated in wind tunnel experiments at NASA Langley Research Center. It was found through 2D parametric study that at subcritical Reynolds numbers of the boundary layers, absolute instability resulting in vortex shedding downstream, is likely to weaken at supersonic free-stream conditions. On the other hand, convective instability may be the dominant mechanism for supersonic boundary layers. Three-dimensional calculations for a rectangular or cylindrical roughness element at post-shock Mach numbers of 4.1 and 6.5 also confirm that no self-sustained vortex generation is present.

Boundary-layer transition on cones at angle of attack in a Mach-6 Quiet Tunnel

NASA Astrophysics Data System (ADS)

Swanson, Erick O.

It is desirable for the boundary layer on a re-entry vehicle (RV) to be laminar during as much of its flight as possible, since a turbulent boundary layer causes several problems, such as high heat flux to the vehicle and larger drag forces. Nosetip roughness can cause the boundary layer to transition downstream on the cone. Surface roughness and nosetip bluntness may cause windside-forward transition on maneuvering RVs. The crossflow instability may also influence transition on yawed RVs. The mechanisms through which these phenomena induce transition are poorly understood. Several experiments have been conducted to study these phenomena. The temperature-sensitive-paint (TSP) and oil-flow techniques were used to observe transition and crossflow vortices on cones at angle of attack in the Purdue Boeing/AFOSR Mach-6 Quiet Tunnel. The high-Reynolds number capability of the tunnel was developed to facilitate these experiments. Improvements were made in the use of the temperature-sensitive-paint technique in the Purdue Mach-6 Quiet Tunnel. The measured heat transfer to cones with sharp and spherically-blunt nosetips at 0° angle-of-attack was within 60% of the values from Navier-Stokes computations. Transition was observed on sharp and spherically-blunt cones at 6° angle-of-attack in noisy flow. Crossflow vortices were observed with both TSP and oil flow under noisy conditions in the turbulent boundary layer on a sharp cone. The vortex angles were about 50% of the surface-streamline angles observed using oil dots. TSP was also used to observe crossflow vortices in quiet flow. The vortices were similar to those seen in noisy flow. An array of roughness elements at x = 2 inches (axially) with a spacing of 9° on a yawed sharp cone in noisy flow influenced transition that was apparently induced by the crossflow instability. No influence of the roughness array was observed in quiet flow.

Surface modification of paper on a continuous atmospheric-pressure-plasma system

NASA Astrophysics Data System (ADS)

Cruz-Barba, Luis Emilio

Plasma technologies for the continuous modification of materials in atmospheric-pressure-plasma conditions were used to evaluate the surface modification of paper under different plasma conditions. The generation of hydrophobic layers was used to characterize the efficiency of the originally designed system for future application in the paper industry. Generation of hydrophobic layers was carried out by deposition of thin layers from fluorine containing gases, as well as cross-linking of pre-deposited thin layers of hydrophobic materials, such as fluoropolymers and silicones, in a continuous system plasma reactor (CSPR). Physical and chemical characterization of these layers was carried out by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), contact angle goniometry, and water absorption evaluations. Pure gaseous CF4 and a CF4/CH4 mixture were used to deposit fluorinated layers, rendering paper surfaces with low to moderate relative surface atomic contents of fluorine (2.5 to 16.3%). Morphological characterization revealed that the deposition consists of small clusters of fluorinated species scattered on the surface. Contact angle evaluations (50°--70°) indicated a reduction in the water affinity of the paper. Thin layers of fluoropolymer pre-deposited on paper surfaces were cross-linked in the presence of CF4, CF4/CH4, and NH 3 plasmas. All of the gases proved to be effective for the cross-linking under different conditions. These cross-linked layers were determined to maintain the original polymer structure, consisting mainly of CF2-CF 2 and small quantities of CFx. Surface characterization by AFM indicated lower roughness values compared to the untreated additive-free paper (45.1 vs 67.1 nm). Paper samples treated by this approach showed a highly hydrophobic character with up to 160° contact angles, and water absorption was reduced by as much as 61.6%. Silicone layers were cross-linked in the presence of argon and oxygen plasmas. Characterization of the silicone-coated paper indicated, as in the case of fluoropolymers, the retention of the original chemical structure. Surface roughness values (AFM) were in the range of 11.8 to 18.2 nm, evidence of a very smooth surface. High hydrophobicity levels were reached, as shown by contact angles of up to 126°, and water absorption showed a maximum reduction of 76.8%.

Impact of cleaning methods on the structural properties and morphology of SrTiO3 surface

NASA Astrophysics Data System (ADS)

Arnay, Iciar; Rubio-Zuazo, Juan; Castro, German R.

2018-01-01

SrTiO3 is a widely used substrate for the epitaxial growth of complex systems. Nevertheless, in order to get good quality interface and avoid the formation of defects in the adsorbed layer it is essential to prepare the surface of the substrate prior to the deposition. Thermal and chemical treatments are mostly used to eliminate superficial contamination and improve the surface quality. However, there is a lack of information regarding the impact of these treatments on the formation of structural defects at the SrTiO3 surface. In this work we present a detailed characterization of the SrTiO3 surface for the different cleaning methods paying special attention to the formation of oxygen vacancies, large surface mosaicity and roughness. We prove that thermal treatment induces large surface roughness and that chemical etching produces important structural defects at the surface. Our results show that mechanical polishing provided the best compromise in terms of large surface domains, low roughness, absence of oxygen vacancies and absence of atomic structure modification, although with the presence of low level of contaminants at the SrTiO3 surface.

Dissolution of minerals with rough surfaces

NASA Astrophysics Data System (ADS)

de Assis, Thiago A.; Aarão Reis, Fábio D. A.

2018-05-01

We study dissolution of minerals with initial rough surfaces using kinetic Monte Carlo simulations and a scaling approach. We consider a simple cubic lattice structure, a thermally activated rate of detachment of a molecule (site), and rough surface configurations produced by fractional Brownian motion algorithm. First we revisit the problem of dissolution of initial flat surfaces, in which the dissolution rate rF reaches an approximately constant value at short times and is controlled by detachment of step edge sites. For initial rough surfaces, the dissolution rate r at short times is much larger than rF ; after dissolution of some hundreds of molecular layers, r decreases by some orders of magnitude across several time decades. Meanwhile, the surface evolves through configurations of decreasing energy, beginning with dissolution of isolated sites, then formation of terraces with disordered boundaries, their growth, and final smoothing. A crossover time to a smooth configuration is defined when r = 1.5rF ; the surface retreat at the crossover is approximately 3 times the initial roughness and is temperature-independent, while the crossover time is proportional to the initial roughness and is controlled by step-edge site detachment. The initial dissolution process is described by the so-called rough rates, which are measured for fixed ratios between the surface retreat and the initial roughness. The temperature dependence of the rough rates indicates control by kink site detachment; in general, it suggests that rough rates are controlled by the weakest microscopic bonds during the nucleation and formation of the lowest energy configurations of the crystalline surface. Our results are related to recent laboratory studies which show enhanced dissolution in polished calcite surfaces. In the application to calcite dissolution in alkaline environment, the minimal values of recently measured dissolution rate spectra give rF ∼10-9 mol/(m2 s), and the calculated rate laws of our model give rough rates in the range 10-6 -10-5 mol/(m2 s). This estimate is consistent with the range of calcite dissolution rates obtained in a recent work after treatment of literature data, which suggests the universal control of kink site dissolution in short term laboratory works. The weak effects of lattice size on our results also suggest that smoothing of mineral grain surfaces across geological times may be a microscopic explanation for the difference of chemical weathering rate of silicate minerals in laboratory and in the environment.

Investigation of wall-bounded turbulence over regularly distributed roughness

NASA Astrophysics Data System (ADS)

Placidi, Marco; Ganapathisubramani, Bharathram

2012-11-01

The effects of regularly distributed roughness elements on the structure of a turbulent boundary layer are examined by performing a series of Planar (high resolution l+ ~ 30) and Stereoscopic Particle Image Velocimetry (PIV) experiments in a wind tunnel. An adequate description of how to best characterise a rough wall, especially one where the density of roughness elements is sparse, is yet to be developed. In this study, rough surfaces consisting of regularly and uniformly distributed LEGO® blocks are used. Twelve different patterns are adopted in order to systematically examine the 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 the turbulence structure. The Karman number, Reτ , is approximately 4000 across the different cases. Spanwise 3D vector fields at two different wall-normal locations (top of the canopy and within the log-region) are also compared to examine the spanwise homogeneity of the flow across different surfaces. In the talk, a detailed analysis of mean and rms velocity profiles, Reynolds stresses, and quadrant decomposition for the different patterns will be presented.

Effects of bio-inspired microscale roughness on macroscale flow structures

NASA Astrophysics Data System (ADS)

Bocanegra Evans, Humberto; Hamed, Ali M.; Gorumlu, Serdar; Doosttalab, Ali; Aksak, Burak; Chamorro, Leonardo P.; Castillo, Luciano

2016-11-01

The interaction between rough surfaces and flows is a complex physical situation that produces rich flow phenomena. While random roughness typically increases drag, properly engineered roughness patterns may produce positive results, e.g. dimples in a golf ball. Here we present a set of PIV measurements in an index matched facility of the effect of a bio-inspired surface that consists of an array of mushroom-shaped micro-pillars. The experiments are carried out-under fully wetted conditions-in a flow with adverse pressure gradient, triggering flow separation. The introduction of the micro-pillars dramatically decreases the size of the recirculation bubble; the area with backflow is reduced by approximately 60%. This suggests a positive impact on the form drag generated by the fluid. Furthermore, a negligible effect is seen on the turbulence production terms. The micro-pillars affect the flow by generating low and high pressure perturbations at the interface between the bulk and roughness layer, in a fashion comparable to that of synthetic jets. The passive approach, however, facilitates the implementation of this coating. As the mechanism does not rely on surface hydrophobicity, it is well suited for underwater applications and its functionality should not degrade over time.

Quantitative evaluation of sputtering induced surface roughness and its influence on AES depth profiles of polycrystalline Ni/Cu multilayer thin films

NASA Astrophysics Data System (ADS)

Yan, X. L.; Coetsee, E.; Wang, J. Y.; Swart, H. C.; Terblans, J. J.

2017-07-01

The polycrystalline Ni/Cu multilayer thin films consisting of 8 alternating layers of Ni and Cu were deposited on a SiO2 substrate by means of electron beam evaporation in a high vacuum. Concentration-depth profiles of the as-deposited multilayered Ni/Cu thin films were determined with Auger electron spectroscopy (AES) in combination with Ar+ ion sputtering, under various bombardment conditions with the samples been stationary as well as rotating in some cases. The Mixing-Roughness-Information depth (MRI) model used for the fittings of the concentration-depth profiles accounts for the interface broadening of the experimental depth profiling. The interface broadening incorporates the effects of atomic mixing, surface roughness and information depth of the Auger electrons. The roughness values extracted from the MRI model fitting of the depth profiling data agrees well with those measured by atomic force microscopy (AFM). The ion sputtering induced surface roughness during the depth profiling was accordingly quantitatively evaluated from the fitted MRI parameters with sample rotation and stationary conditions. The depth resolutions of the AES depth profiles were derived directly from the values determined by the fitting parameters in the MRI model.

Polyimide surface modification by using microwave plasma for adhesion enhancement of Cu electroless plating.

PubMed

Cho, Sang-Jin; Nguyen, Trieu; Boo, Jin-Hyo

2011-06-01

Microwave (MW) plasma was applied to the surface of polyimide (PI) films as a treatment to enhance the adhesion between copper deposition layer and PI surface for electroless plating. The influences of nitrogen MW plasma treatment on chemical composition of the PI surface were investigated by using X-Ray photoelectron spectroscopy (XPS). The wettability was also investigated by water contact angle measurement. The surface morphologies of PI films before and after treatment were characterized with atomic force microscopy (AFM). The contact angle results show that was dramatically decreased to 16.1 degrees at the optimal treatment condition from 72.1 degrees (untreated PI). However, the root mean square (RMS) roughness of treated PI film was almost unchanged. The AFM roughness was stayed from 1.0 to 1.2 with/without plasma treatment. XPS data show a nitrogen increase when PI films exposed to N2 MW plasma. Electroless copper depositions were carried out with the free-formaldehyde method using glyoxylic acid as the reducing reagent and mixture palladium chloride, tin chloride as activation solution. Adhesion property between polyimide surface and copper layer was investigated by tape test.

Observation of surface layering in a nonmetallic liquid

NASA Astrophysics Data System (ADS)

Mo, Haiding; Evmenenko, Guennadi; Kewalramani, Sumit; Kim, Kyungil; Dutta, Pulak; Ehrlich, Steven

2006-03-01

Non-monotonic density profiles (layers) have previously been observed at the free surfaces of many metallic liquids, but not in isotropic dielectric liquids. Whether the presence of an electron gas is necessary for surface layering has been the subject of debate. Until recently, MD simulations have suggested that layering at free liquid interface may be a generic phenomenon and is not limited to the metallic liquids^1. The theories predict that if normal liquids can be cooled down to temperatures low enough, layering structure should be observed experimentally. However, this is difficult for most molecular liquids because these liquids freeze well above the temperature necessary for observing the layering structure. By studying the surface structure of liquid TEHOS (tetrakis(2-ethylhexoxy)silane), which combines relatively low freezing point and high boiling point compared to that of most molecular liquids, we have observed the evidence of layering at the free interface of liquid TEHOS using x-ray reflectivity. When cooled to T/Tc 0.25 (well above the bulk freezing point, Tc is the critical temperature of TEHOS), the surface roughness drops sharply and density oscillations appear near the surface. Lateral ordering of the surface layers is liquid-like, just as at liquid metal surfaces. 1. E. Chac'on and P. Tarazona, Phys. Rev. Lett. 91 166103-1 (2003)

Effect of applied voltage on surface properties of anodised titanium in mixture of β-glycerophosphate (β-GP) and calcium acetate (CA)

NASA Astrophysics Data System (ADS)

Chuan, Lee Te; Rathi, Muhammad Fareez Mohamad; Abidin, Muhamad Yusuf Zainal; Abdullah, Hasan Zuhudi; Idris, Maizlinda Izwana

2015-07-01

Anodic oxidation is a surface modification method which combines electric field driven metal and oxygen ion diffusion for formation of oxide layer on the anode surface. This method has been widely used to modify the surface morphology of biomaterial especially titanium. This study aimed to investigate the effect of applied voltage on titanium. Specifically, the titanium foil was anodised in mixture of β-glycerophosphate disodium salt pentahydrate (β-GP) and calcium acetate monohydrate (CA) with different applied voltage (50-350 V), electrolyte concentration (0.04 M β-GP + 0.4 M CA), anodising time (10minutes) and current density (50 and 70 mA.cm-2) at room temperature. Surface oxide properties of anodised titanium were characterised by digital single-lens reflex camera (DSLR camera), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). At lower applied voltage (≤150 V), surface of titanium foils were relatively smooth. With increasing applied voltage (≥250 V), the oxide layer became more porous and donut-shaped pores were formed on the surface of titanium foils. The AFM results indicated that the surface roughness of anodised titanium increases with increasing of applied voltage. The porous and rough surface is able to promote the osseointegration and reduce the suffering time of patient.

Defining the Post-Machined Sub-surface in Austenitic Stainless Steels

NASA Astrophysics Data System (ADS)

Srinivasan, N.; Sunil Kumar, B.; Kain, V.; Birbilis, N.; Joshi, S. S.; Sivaprasad, P. V.; Chai, G.; Durgaprasad, A.; Bhattacharya, S.; Samajdar, I.

2018-04-01

Austenitic stainless steels grades, with differences in chemistry, stacking fault energy, and thermal conductivity, were subjected to vertical milling. Anodic potentiodynamic polarization was able to differentiate (with machining speed/strain rate) between different post-machined sub-surfaces in SS 316L and Alloy A (a Cu containing austenitic stainless steel: Sanicroe 28™), but not in SS 304L. However, such differences (in the post-machined sub-surfaces) were revealed in surface roughness, sub-surface residual stresses and misorientations, and in the relative presence of sub-surface Cr2O3 films. It was shown, quantitatively, that higher machining speed reduced surface roughness and also reduced the effective depths of the affected sub-surface layers. A qualitative explanation on the sub-surface microstructural developments was provided based on the temperature-dependent thermal conductivity values. The results herein represent a mechanistic understanding to rationalize the corrosion performance of widely adopted engineering alloys.

Defining the Post-Machined Sub-surface in Austenitic Stainless Steels

NASA Astrophysics Data System (ADS)

Srinivasan, N.; Sunil Kumar, B.; Kain, V.; Birbilis, N.; Joshi, S. S.; Sivaprasad, P. V.; Chai, G.; Durgaprasad, A.; Bhattacharya, S.; Samajdar, I.

2018-06-01

Austenitic stainless steels grades, with differences in chemistry, stacking fault energy, and thermal conductivity, were subjected to vertical milling. Anodic potentiodynamic polarization was able to differentiate (with machining speed/strain rate) between different post-machined sub-surfaces in SS 316L and Alloy A (a Cu containing austenitic stainless steel: Sanicroe 28™), but not in SS 304L. However, such differences (in the post-machined sub-surfaces) were revealed in surface roughness, sub-surface residual stresses and misorientations, and in the relative presence of sub-surface Cr2O3 films. It was shown, quantitatively, that higher machining speed reduced surface roughness and also reduced the effective depths of the affected sub-surface layers. A qualitative explanation on the sub-surface microstructural developments was provided based on the temperature-dependent thermal conductivity values. The results herein represent a mechanistic understanding to rationalize the corrosion performance of widely adopted engineering alloys.

Use of a liquid-crystal, heater-element composite for quantitative, high-resolution heat transfer coefficients on a turbine airfoil, including turbulence and surface roughness effects

NASA Astrophysics Data System (ADS)

Hippensteele, Steven A.; Russell, Louis M.; Torres, Felix J.

1987-05-01

Local heat transfer coefficients were measured along the midchord of a three-times-size turbine vane airfoil in a static cascade operated at roon temperature over a range of Reynolds numbers. The test surface consisted of a composite of commercially available materials: a Mylar sheet with a layer of cholestric liquid crystals, which change color with temperature, and a heater made of a polyester sheet coated with vapor-deposited gold, which produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat transfer coefficients were mapped over the airfoil surface. Tests were conducted at two free-stream turbulence intensities: 0.6 percent, which is typical of wind tunnels; and 10 percent, which is typical of real engine conditions. In addition to a smooth airfoil, the effects of local leading-edge sand roughness were also examined for a value greater than the critical roughness. The local heat transfer coefficients are presented for both free-stream turbulence intensities for inlet Reynolds numbers from 1.20 to 5.55 x 10 to the 5th power. Comparisons are also made with analytical values of heat transfer coefficients obtained from the STAN5 boundary layer code.

Use of a liquid-crystal and heater-element composite for quantitative, high-resolution heat-transfer coefficients on a turbine airfoil including turbulence and surface-roughness effects

NASA Astrophysics Data System (ADS)

Hippensteele, S. A.; Russell, L. M.; Torres, F. J.

Local heat transfer coefficients were measured along the midchord of a three-times-size turbine vane airfoil in a static cascade operated at room temperature over a range of Reynolds numbers. The test surface consisted of a composite of commercially available materials: a Mylar sheet with a layer of cholestric liquid crystals, which change color with temperature, and a heater made of a polyester sheet coated with vapor-deposited gold, which produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat transfer coefficients were mapped over the airfoil surface. Tests were conducted at two free-stream turbulence intensities: 0.6 percent, which is typical of wind tunnels; and 10 percent, which is typical of real engine conditions. In addition to a smooth airfoil, the effects of local leading-edge sand roughness were also examined for a value greater than the critical roughness. The local heat transfer coefficients are presented for both free-stream turbulence intensities for inlet Reynolds numbers from 1.20 to 5.55 x 10 to the 5th power. Comparisons are also made with analytical values of heat transfer coefficients obtained from the STAN5 boundary layer code.

Use of a liquid-crystal, heater-element composite for quantitative, high-resolution heat transfer coefficients on a turbine airfoil, including turbulence and surface roughness effects

NASA Technical Reports Server (NTRS)

Hippensteele, Steven A.; Russell, Louis M.; Torres, Felix J.

1987-01-01

Local heat transfer coefficients were measured along the midchord of a three-times-size turbine vane airfoil in a static cascade operated at roon temperature over a range of Reynolds numbers. The test surface consisted of a composite of commercially available materials: a Mylar sheet with a layer of cholestric liquid crystals, which change color with temperature, and a heater made of a polyester sheet coated with vapor-deposited gold, which produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat transfer coefficients were mapped over the airfoil surface. Tests were conducted at two free-stream turbulence intensities: 0.6 percent, which is typical of wind tunnels; and 10 percent, which is typical of real engine conditions. In addition to a smooth airfoil, the effects of local leading-edge sand roughness were also examined for a value greater than the critical roughness. The local heat transfer coefficients are presented for both free-stream turbulence intensities for inlet Reynolds numbers from 1.20 to 5.55 x 10 to the 5th power. Comparisons are also made with analytical values of heat transfer coefficients obtained from the STAN5 boundary layer code.

Superhydrophobic Surface Based on a Coral-Like Hierarchical Structure of ZnO

PubMed Central

Wu, Jun; Xia, Jun; Lei, Wei; Wang, Baoping

2010-01-01

Background Fabrication of superhydrophobic surfaces has attracted much interest in the past decade. The fabrication methods that have been studied are chemical vapour deposition, the sol-gel method, etching technique, electrochemical deposition, the layer-by-layer deposition, and so on. Simple and inexpensive methods for manufacturing environmentally stable superhydrophobic surfaces have also been proposed lately. However, work referring to the influence of special structures on the wettability, such as hierarchical ZnO nanostructures, is rare. Methodology This study presents a simple and reproducible method to fabricate a superhydrophobic surface with micro-scale roughness based on zinc oxide (ZnO) hierarchical structure, which is grown by the hydrothermal method with an alkaline aqueous solution. Coral-like structures of ZnO were fabricated on a glass substrate with a micro-scale roughness, while the antennas of the coral formed the nano-scale roughness. The fresh ZnO films exhibited excellent superhydrophilicity (the apparent contact angle for water droplet was about 0°), while the ability to be wet could be changed to superhydrophobicity after spin-coating Teflon (the apparent contact angle greater than 168°). The procedure reported here can be applied to substrates consisting of other materials and having various shapes. Results The new process is convenient and environmentally friendly compared to conventional methods. Furthermore, the hierarchical structure generates the extraordinary solid/gas/liquid three-phase contact interface, which is the essential characteristic for a superhydrophobic surface. PMID:21209931

Melt layer behavior of metal targets irradiatead by powerful plasma streams

NASA Astrophysics Data System (ADS)

Bandura, A. N.; Byrka, O. V.; Chebotarev, V. V.; Garkusha, I. E.; Makhlaj, V. A.; Solyakov, D. G.; Tereshin, V. I.; Wuerz, H.

2002-12-01

In this paper melt layer erosion of metal targets under pulsed high-heat loads is studied. Experiments with steel, copper, aluminum and titanium samples were carried out in two plasma accelerator devices with different time durations of the heat load. The surfaces of the resolidified melt layers show a considerable roughness with microcraters and ridge like relief on the surface. For each material the mass loss was determined. Melt layer erosion by melt motion was clearly identified. However it is masked by boiling, bubble expansion and bubble collapse and by formation of a Kelvin-Helmholtz instability. The experimental results can be used for validation of numerical codes which model melt layer erosion of metallic armour materials in off-normal events, in tokamaks.

Superfluid Boundary Layer.

PubMed

Stagg, G W; Parker, N G; Barenghi, C F

2017-03-31

We model the superfluid flow of liquid helium over the rough surface of a wire (used to experimentally generate turbulence) profiled by atomic force microscopy. Numerical simulations of the Gross-Pitaevskii equation reveal that the sharpest features in the surface induce vortex nucleation both intrinsically (due to the raised local fluid velocity) and extrinsically (providing pinning sites to vortex lines aligned with the flow). Vortex interactions and reconnections contribute to form a dense turbulent layer of vortices with a nonclassical average velocity profile which continually sheds small vortex rings into the bulk. We characterize this layer for various imposed flows. As boundary layers conventionally arise from viscous forces, this result opens up new insight into the nature of superflows.

Effects of Cavities and Protuberances on Transition over Hypersonic Vehicles

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan M.; Li, Fei; Venkatachari, Balaji

2011-01-01

Surface protuberances and cavities on a hypersonic vehicle are known to cause several aerodynamic or aerothermodynamic issues. Most important of all, premature transition due to these surface irregularities can lead to a significant rise in surface heating. To help understand laminar-turbulent transition induced by protuberances or cavities on a Crew Exploration Vehicle (CEV) surface, high-fidelity numerical simulations are carried out for both types of trips on a CEV wind tunnel model. Due to the large bluntness, these surface irregularities reside in an accelerating subsonic boundary layer. For the Mach 6 wind tunnel conditions with a roughness Reynolds number Re(sub kk) of 800, it was found that a protuberance with a height to boundary layer thickness ratio of 0.73 leads to strong wake instability and spontaneous vortex shedding, while a cavity with identical geometry only causes a rather weak flow unsteadiness. The same cavity with a larger Reynolds number also leads to similar spontaneous vortex shedding and wake instability. The wake development and the formation of hairpin vortices for both protuberance and cavity were found to be qualitatively similar to that observed for an isolated hemisphere submerged in a subsonic, low speed flat-plate boundary layer. However, the shed vortices and their accompanying instability waves were found to be slightly stabilized downstream by the accelerating boundary layer along the CEV surface. Despite this stabilizing influence, it was found that the wake instability spreads substantially in both wall-normal and azimuthal directions as the flow is evolving towards a transitional state. Similarities and differences between the wake instability behind a protuberance and a cavity are investigated. Computations for the Mach 6 boundary layer over a slender cylindrical roughness element with a height to the boundary layer thickness of about 1.1 also shows spontaneous vortex shedding and strong wake instability. Comparisons of detailed flow structures associated with protuberances at subsonic and supersonic edge Mach numbers indicate distinctively different instability mechanisms.

Shot-Peening Effect on High Cycling Fatigue of Al-Cu Alloy

NASA Astrophysics Data System (ADS)

Fouad, Yasser; Metwally, Mostafa El

2013-12-01

The present work was aimed at evaluating the effects of shot-peening on the high cycle fatigue performance of the age-hardening aircraft alloy Al 2024 at different almen intensities. Shot-peening to full coverage (100 pct) was performed using spherically conditioned cut wire (SCCW 14) with an average shot size of 0.36 mm and at almen intensities of 0.1, 0.2, and 0.3 mmA. After applying the various mechanical surface treatments, the changes in the surface and near-surface layer properties such as microhardness, residual stress-depth profiles, and surface roughness were determined. The microhardness, surface roughness, and the residual stresses increased proportionally with the almen intensity. Electropolitically polished conditions were used as reference in the mechanically surface treated specimens. A significant improvement was seen in the fatigue performance of the 0.1 mmA.

Effects of surface cooling and of roughness on the heating (including transition) to the windward plane-of-symmetry of the shuttle orbiter

NASA Technical Reports Server (NTRS)

Bertin, J. J.; Idar, E. S., III; Galanski, S. R.

1977-01-01

The theoretical heat-transfer distributions are compared with experimental heat-transfer distributions obtained in Tunnel B at AEDC using a 0.0175 scale model of the space shuttle orbiter configuration for which the first 80% of the windward surface was roughened by a simulated tile misalignment. The theoretical solutions indicate that thinning the boundary layer by surface cooling increased the nondimensionalized value of the local heat-transfer coefficient. Tile misalignment did not significantly affect the heat-transfer rate in regions where the boundary layer was either laminar or turbulent.

Atmospheric stability analysis over statically and dynamically rough surfaces

NASA Astrophysics Data System (ADS)

Maric, Emina; Metzger, Meredith; Singha, Arindam; Sadr, Reza

2011-11-01

The ratio of buoyancy flux to turbulent kinetic energy production in the atmospheric surface layer is investigated experimentally for air flow over two types of surfaces characterized by static and dynamic roughness. In this study, ``static'' refers to the time-invariant nature of naturally-occurring roughness over a mud/salt playa; while, ``dynamic'' refers to the behavior of water waves along an air-water interface. In both cases, time-resolved measurements of the momentum and heat fluxes were acquired from synchronized 3D sonic anemometers mounted on a vertical tower. Field campaigns were conducted at two sites, representing the ``statically'' and ``dynamically'' rough surfaces, respectively: (1) the SLTEST facility in Utah's western desert, and (2) the new Doha airport in Qatar under construction along the coast of the Persian Gulf. Note, at site 2, anemometers were located directly above the water by extension from a tower secured to the end of a 1 km-long pier. Comparisons of the Monin-Obukhov length, flux Richardson number, and gradient Richardson number are presented, and discussed in the context of the observed evolution of the turbulent spectra in response to diurnal variations of atmospheric stability. Supported by the Qatar National Research Fund.

Mirage is an image in a flat ground surface.

PubMed

Tavassoly, M Taghi; Osanloo, Soghra; Salehpour, Ali

2015-04-01

Mirage is a fascinating phenomenon that has attracted many scientists to report their observations and descriptions about it. There are two different approaches to mirage formation. The more popular one is attributed to total internal reflection that occurs in the near ground air layers on hot sunny days. According to the other approach, mirage is an image in a rough surface that is observed at grazing angles of incidence. Most of the existing descriptions are qualitative and some include calculations based on guessing temperature change with no concrete experiments. In this report, first we show that Fermat's principle also concerns the wave nature of light and covers the constructive and destructive interference that is essential for image formation. Then, we provide a brief review of the image formation theory in a rough plane and demonstrate by experiments in the lab and deserts that the temperature gradient in the near ground air layers does not lead to mirage formation.

Growth of magnesium diboride thin films on boron buffered Si and silicon-on-insulator substrates by hybrid physical chemical vapor deposition

NASA Astrophysics Data System (ADS)

Withanage, Wenura K.; Penmatsa, Sashank V.; Acharya, Narendra; Melbourne, Thomas; Cunnane, D.; Karasik, B. S.; Xi, X. X.

2018-07-01

We report on the growth of high quality MgB2 thin films on silicon and silicon-on-insulator substrates by hybrid physical chemical vapor deposition. A boron buffer layer was deposited on all sides of the Si substrate to prevent the reaction of Mg vapor and Si. Ar ion milling at a low angle of 1° was used to reduce the roughness of the boron buffer layer before the MgB2 growth. An Ar ion milling at low angle of 1° was also applied to the MgB2 surface to reduce its roughness. The resultant MgB2 films showed excellent superconducting properties and a smooth surface. The process produces thin MgB2 films suitable for waveguide-based superconducting hot electron bolometers and other MgB2-based electronic devices.

The effect of aluminium nanocoating and water pH value on the wettability behavior of an aluminium surface

NASA Astrophysics Data System (ADS)

Ali, Naser; Teixeira, Joao A.; Addali, Abdulmajid; Al-Zubi, Feras; Shaban, Ehab; Behbehani, Ismail

2018-06-01

Experimental investigation was performed to highlight the influence of ionic bounding and surface roughness effects on the surface wettability. Nanocoating technique via e-beam physical vapor deposition process was used to fabricate aluminium (Al) film of 50, 100, and 150 nm on the surface of an Al substrate. Microstructures of the samples before and after deposition were observed using an atomic force microscopy. A goniometer device was later on used to examine the influence of surface topography on deionised water of pH 4, 7 and 9 droplets at a temperature ranging from 10 °C to 60 °C through their contact angles with the substrate surface, for both coated and uncoated samples. It was found that, although the coated layer has reduced the mean surface roughness of the sample from 10.7 nm to 4.23 nm, by filling part of the microstructure gaps with Al nanoparticles, the wettability is believed to be effected by the ionic bounds between the surface and the free anions in the fluid. As the deionised water of pH 4, and 9 gave an increase in the average contact angles with the increase of the coated layer thickness. On the other hand, the deionised water of pH 7 has showed a negative relation with the film thickness, where the contact angle reduced as the thickness of the coated layer was increased. The results from the aforementioned approach had showed that nanocoating can endorse the hydrophobicity (unwitting) nature of the surface when associated with free ions hosted by the liquid.

Improvement of resist profile roughness in bilayer resist process

NASA Astrophysics Data System (ADS)

Jeong, Chang-Young; Ryu, Sang-Wook; Park, Ki-Yeop; Lee, Won-Kyu; Lee, Seung-Woog; Lee, Dai-Hoon

2000-06-01

The bi-layer resist (BLR) process, which first accomplish imaging on a thin top layer and transfer it down to a thick organic layer, is one of newly emerging patterning techniques in silicon processing. In this work, we studied the lithographic performance of the BLR process adopting FK- SPTM (Fujifilm Olin Co.) as top layer material and various organic material as bottom layer. Generally, considerable advantages of planarization, reduced substrate reflection, improved process latitude, and of enhanced resolution are achieved. However, the resolution and the process latitude are highly affected by surface interaction between the top resist and the bottom material. Moreover, the BLR process has a sidewall roughness problem related to the material factors of the resist and the degraded aerial image contrast, which can affect the reliability of the device. We found that thermal curing treatment applied after development with the consideration of the glass transition temperature are very effective in reducing the line edge roughness. More smooth and steep patterning is achieved by the thermal treatment. The linewidth controllability is below 10 nm and the k1 value is reduced from 0.5 down to 0.32 in this process. The reactive ion etching adopting O2 gas demonstrated selectivity of the top resist over bottom material more than 15:1, together with residue-free and vertical wall profile.

Layer-by-layer assembled hydrophobic coatings for cellulose nanofibril films and textiles, made of polylysine and natural wax particles.

PubMed

Forsman, Nina; Lozhechnikova, Alina; Khakalo, Alexey; Johansson, Leena-Sisko; Vartiainen, Jari; Österberg, Monika

2017-10-01

Herein we present a simple method to render cellulosic materials highly hydrophobic while retaining their breathability and moisture buffering properties, thus allowing for their use as functional textiles. The surfaces are coated via layer-by-layer deposition of two natural components, cationic poly-l-lysine and anionic carnauba wax particles. The combination of multiscale roughness, open film structure, and low surface energy of wax colloids, resulted in long-lasting superhydrophobicity on cotton surface already after two bilayers. Atomic force microscopy, interference microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy were used to decouple structural effects from changes in surface energy. Furthermore, the effect of thermal annealing on the coating was evaluated. The potential of this simple and green approach to enhance the use of natural cellulosic materials is discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.

A scheme for computing surface layer turbulent fluxes from mean flow surface observations

NASA Technical Reports Server (NTRS)

Hoffert, M. I.; Storch, J.

1978-01-01

A physical model and computational scheme are developed for generating turbulent surface stress, sensible heat flux and humidity flux from mean velocity, temperature and humidity at some fixed height in the atmospheric surface layer, where conditions at this reference level are presumed known from observations or the evolving state of a numerical atmospheric circulation model. The method is based on coupling the Monin-Obukov surface layer similarity profiles which include buoyant stability effects on mean velocity, temperature and humidity to a force-restore formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux and surface temperature. A self-contained formulation is presented including parameterizations for solar and infrared radiant fluxes at the surface. Additional parameters needed to implement the scheme are the thermal heat capacity of the soil per unit surface area, surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity and atmospheric transmissivity to solar radiation.

Surface Features Parameterization and Equivalent Roughness Height Estimation of a Real Subglacial Conduit in the Arctic

NASA Astrophysics Data System (ADS)

Chen, Y.; Liu, X.; Mankoff, K. D.; Gulley, J. D.

2016-12-01

The surfaces of subglacial conduits are very complex, coupling multi-scale roughness, large sinuosity, and cross-sectional variations together. Those features significantly affect the friction law and drainage efficiency inside the conduit by altering velocity and pressure distributions, thus posing considerable influences on the dynamic development of the conduit. Parameterizing the above surface features is a first step towards understanding their hydraulic influences. A Matlab package is developed to extract the roughness field, the conduit centerline, and associated area and curvature data from the conduit surface, acquired from 3D scanning. By using those data, the characteristic vertical and horizontal roughness scales are then estimated based on the structure functions. The centerline sinuosities, defined through three concepts, i.e., the traditional definition of a fluvial river, entropy-based sinuosity, and curvature-based sinuosity, are also calculated and compared. The cross-sectional area and equivalent circular diameter along the centerline are also calculated. Among those features, the roughness is especially important due to its pivotal role in determining the wall friction, and thus an estimation of the equivalent roughness height is of great importance. To achieve such a goal, the original conduit is firstly simplified into a straight smooth pipe with the same volume and centerline length, and the roughness field obtained above is then reconstructed into the simplified pipe. An OpenFOAM-based Large-eddy-simulation (LES) is then performed based on the reconstructed pipe. Considering that the Reynolds number is of the order 106, and the relative roughness is larger than 5% for 60% of the conduit, we test the validity of the resistance law for completely rough pipe. The friction factor is calculated based on the pressure drop and mean velocity in the simulation. Working together, the equivalent roughness height can be calculated. However, whether the assumption is applicable for the current case, i.e., high relative roughness, is a question. Two other roughness heights, i.e., the vertical roughness scale based on structure functions and viscous sublayer thickness determined from the wall boundary layer are also calculated and compared with the equivalent roughness height.

Bacterial adhesion on conventional and self-ligating metallic brackets after surface treatment with plasma-polymerized hexamethyldisiloxane

PubMed Central

Tupinambá, Rogerio Amaral; Claro, Cristiane Aparecida de Assis; Pereira, Cristiane Aparecida; Nobrega, Celestino José Prudente; Claro, Ana Paula Rosifini Alves

2017-01-01

ABSTRACT Introduction: Plasma-polymerized film deposition was created to modify metallic orthodontic brackets surface properties in order to inhibit bacterial adhesion. Methods: Hexamethyldisiloxane (HMDSO) polymer films were deposited on conventional (n = 10) and self-ligating (n = 10) stainless steel orthodontic brackets using the Plasma-Enhanced Chemical Vapor Deposition (PECVD) radio frequency technique. The samples were divided into two groups according to the kind of bracket and two subgroups after surface treatment. Scanning Electron Microscopy (SEM) analysis was performed to assess the presence of bacterial adhesion over samples surfaces (slot and wings region) and film layer integrity. Surface roughness was assessed by Confocal Interferometry (CI) and surface wettability, by goniometry. For bacterial adhesion analysis, samples were exposed for 72 hours to a Streptococcus mutans solution for biofilm formation. The values obtained for surface roughness were analyzed using the Mann-Whitney test while biofilm adhesion were assessed by Kruskal-Wallis and SNK test. Results: Significant statistical differences (p< 0.05) for surface roughness and bacterial adhesion reduction were observed on conventional brackets after surface treatment and between conventional and self-ligating brackets; no significant statistical differences were observed between self-ligating groups (p> 0.05). Conclusion: Plasma-polymerized film deposition was only effective on reducing surface roughness and bacterial adhesion in conventional brackets. It was also noted that conventional brackets showed lower biofilm adhesion than self-ligating brackets despite the absence of film. PMID:28902253

Durable high strength cement concrete topping for asphalt roads

NASA Astrophysics Data System (ADS)

Vyrozhemskyi, Valerii; Krayushkina, Kateryna; Bidnenko, Nataliia

2017-09-01

Work on improving riding qualities of pavements by means of placing a thin cement layer with high roughness and strength properties on the existing asphalt pavement were conducted in Ukraine for the first time. Such pavement is called HPCM (High Performance Cementitious Material). This is a high-strength thin cement-layer pavement of 8-9 mm thickness reinforced with metal or polymer fiber of less than 5 mm length. Increased grip properties are caused by placement of stone material of 3-5 mm fraction on the concrete surface. As a result of the research, the preparation and placement technology of high-strength cement thin-layer pavement reinforced with fiber was developed to improve friction properties of existing asphalt pavements which ensures their roughness and durability. It must be emphasized that HPCM is a fundamentally new type of thin-layer pavement in which a rigid layer of 10 mm thickness is placed on a non-rigid base thereby improving riding qualities of asphalt pavement at any season of a year.

Improved Modeling of Surface Layer Parameters in a AGCM Using Refined Vertical Resolution in the Surface Layer

NASA Astrophysics Data System (ADS)

Shin, H. H.; Zhao, M.; Ming, Y.; Chen, X.; Lin, S. J.

2017-12-01

Surface layer (SL) parameters in atmospheric models - such as 2-m air temperature (T2), 10-m wind speed (U10), and surface turbulent fluxes - are computed by applying the Monin-Obukhov Similarity Theory (MOST) to the lowest model level height (LMH) in the models. The underlying assumption is that LMH is within surface layer height (SLH), but most AGCMs hardly meet the condition in stable boundary layers (SBLs) over land. To assess the errors in modeled SL parameters caused by this, offline computations of the MOST are performed with different LMHs from 1 to 100 m, for an idealized SBL case with prescribed surface parameters (surface temperature, roughness length and Obukhov length), and vertical profiles of temperature and winds. The results show that when LMH is higher than SLH, T2 and U10 are underestimated by O(1 K) and O(1 m/s), respectively, and the biases increase as LMH increases. Based on this, the refined vertical resolution with an additional layer in the SL is applied to the GFDL AGCM, and it reduces the systematic cold biases in T2 and the systematic underestimation of U10.

Control of surface topography in biomimetic calcium phosphate coatings.

PubMed

Costa, Daniel O; Allo, Bedilu A; Klassen, Robert; Hutter, Jeffrey L; Dixon, S Jeffrey; Rizkalla, Amin S

2012-02-28

The behavior of cells responsible for bone formation, osseointegration, and bone bonding in vivo are governed by both the surface chemistry and topography of scaffold matrices. Bone-like apatite coatings represent a promising method to improve the osteoconductivity and bonding of synthetic scaffold materials to mineralized tissues for regenerative procedures in orthopedics and dentistry. Polycaprolactone (PCL) films were coated with calcium phosphates (CaP) by incubation in simulated body fluid (SBF). We investigated the effect of SBF ion concentration and soaking time on the surface properties of the resulting apatite coatings. CaP coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and energy dispersive X-ray spectrometry (EDX). Young's modulus (E(s)) was determined by nanoindentation, and surface roughness was assessed by atomic force microscopy (AFM) and mechanical stylus profilometry. CaP such as carbonate-substituted apatite were deposited onto PCL films. SEM and AFM images of the apatite coatings revealed an increase in topographical complexity and surface roughness with increasing ion concentration of SBF solutions. Young's moduli (E(s)) of various CaP coatings were not significantly different, regardless of the CaP phase or surface roughness. Thus, SBF with high ion concentrations may be used to coat synthetic polymers with CaP layers of different surface topography and roughness to improve the osteoconductivity and bone-bonding ability of the scaffold. © 2012 American Chemical Society

RMS roughness-independent tuning of surface wettability by tailoring silver nanoparticles with a fluorocarbon plasma polymer.

PubMed

Choukourov, A; Kylián, O; Petr, M; Vaidulych, M; Nikitin, D; Hanuš, J; Artemenko, A; Shelemin, A; Gordeev, I; Kolská, Z; Solař, P; Khalakhan, I; Ryabov, A; Májek, J; Slavínská, D; Biederman, H

2017-02-16

A layer of 14 nm-sized Ag nanoparticles undergoes complex transformation when overcoated by thin films of a fluorocarbon plasma polymer. Two regimes of surface evolution are identified, both with invariable RMS roughness. In the early regime, the plasma polymer penetrates between and beneath the nanoparticles, raising them above the substrate and maintaining the multivalued character of the surface roughness. The growth (β) and the dynamic (1/z) exponents are close to zero and the interface bears the features of self-affinity. The presence of inter-particle voids leads to heterogeneous wetting with an apparent water contact angle θ a = 135°. The multivalued nanotopography results in two possible positions for the water droplet meniscus, yet strong water adhesion indicates that the meniscus is located at the lower part of the spherical nanofeatures. In the late regime, the inter-particle voids become filled and the interface acquires a single valued character. The plasma polymer proceeds to grow on the thus-roughened surface whereas the nanoparticles keep emerging away from the substrate. The RMS roughness remains invariable and lateral correlations propagate with 1/z = 0.27. The surface features multiaffinity which is given by different evolution of length scales associated with the nanoparticles and with the plasma polymer. The wettability turns to the homogeneous wetting state.

Characterization of surface roughness of laser deposited titanium alloy and copper using AFM

NASA Astrophysics Data System (ADS)

Erinosho, M. F.; Akinlabi, E. T.; Johnson, O. T.

2018-03-01

Laser Metal Deposition (LMD) is the process of using the laser beam of a nozzle to produce a melt pool on a metal surface usually the substrate and metal powder is been deposited into it thereby creating a fusion bond with the substrate to form a new material layer against the force gravity. A good metal laminate is formed when the wettability between the dropping metal powder and the substrate adheres. This paper reports the surface roughness of laser deposited titanium alloy and copper (Ti6Al4V + Cu) using the Atomic Force Microscopy (AFM). This AFM is employed in order to sense the surface and produce different manipulated images using the micro-fabricated mechanical tip under a probe cartridge of high resolution. The process parameters employed during the deposition routine determines the output of the deposit. A careful attention is given to the laser deposited Ti6Al4V + Cu samples under the AFM probe because of their single tracked layers with semi-circular pattern of deposition. This research work can be applicable in the surface modification of laser deposited samples for the marine industry.

Electrical activity of ferroelectric biomaterials and its effects on the adhesion, growth and enzymatic activity of human osteoblast-like cells

NASA Astrophysics Data System (ADS)

Vaněk, P.; Kolská, Z.; Luxbacher, T.; García, J. A. L.; Lehocký, M.; Vandrovcová, M.; Bačáková, L.; Petzelt, J.

2016-05-01

Ferroelectrics have been, among others, studied as electroactive implant materials. Previous investigations have indicated that such implants induce improved bone formation. If a ferroelectric is immersed in a liquid, an electric double layer and a diffusion layer are formed at the interface. This is decisive for protein adsorption and bioactive behaviour, particularly for the adhesion and growth of cells. The charge distribution can be characterized, in a simplified way, by the zeta potential. We measured the zeta potential in dependence on the surface polarity on poled ferroelectric single crystalline LiNbO3 plates. Both our results and recent results of colloidal probe microscopy indicate that the charge distribution at the surface can be influenced by the surface polarity of ferroelectrics under certain ‘ideal’ conditions (low ionic strength, non-contaminated surface, very low roughness). However, suggested ferroelectric coatings on the surface of implants are far from ideal: they are rough, polycrystalline, and the body fluid is complex and has high ionic strength. In real cases, it can therefore be expected that there is rather low influence of the sign of the surface polarity on the electric diffusion layer and thus on the specific adsorption of proteins. This is supported by our results from studies of the adhesion, growth and the activity of alkaline phosphatase of human osteoblast-like Saos-2 cells on ferroelectric LiNbO3 plates in vitro.

Characteristics of subgrid-resolved-scale dynamics in anisotropic turbulence, with application to rough-wall boundary layers

NASA Astrophysics Data System (ADS)

Juneja, Anurag; Brasseur, James G.

1999-10-01

Large-eddy simulation (LES) of the atmospheric boundary layer (ABL) using eddy viscosity subgrid-scale (SGS) models is known to poorly predict mean shear at the first few grid cells near the ground, a rough surface with no viscous sublayer. It has recently been shown that convective motions carry this localized error vertically to infect the entire ABL, and that the error is more a consequence of the SGS model than grid resolution in the near-surface inertial layer. Our goal was to determine what first-order errors in the predicted SGS terms lead to spurious expectation values, and what basic dynamics in the filtered equation for resolved scale (RS) velocity must be captured by SGS models to correct the deficiencies. Our analysis is of general relevance to LES of rough-wall high Reynolds number boundary layers, where the essential difficulty in the closure is the importance of the SGS acceleration terms, a consequence of necessary under-resolution of relevant energy-containing motions at the first few grid levels, leading to potentially strong couplings between the anisotropies in resolved velocity and predicted SGS dynamics. We analyze these two issues (under-resolution and anisotropy) in the absence of a wall using two direct numerical simulation datasets of homogeneous turbulence with very different anisotropic structure characteristic of the near-surface ABL: shear- and buoyancy-generated turbulence. We uncover three important issues which should be addressed in the design of SGS closures near rough walls and we provide a priori tests for the SGS model. First, we identify a strong spurious coupling between the anisotropic structure of the resolved velocity field and predicted SGS dynamics which can create a feedback loop to incorrectly enhance certain components of the predicted velocity field. Second, we find that eddy viscosity and "similarity" SGS models do not contain enough degrees of freedom to capture, at a sufficient level of accuracy, both RS-SGS energy flux and SGS-RS dynamics. Third, to correctly capture pressure transport near a wall, closures must be made more flexible to accommodate proper partitioning between SGS stress divergence and SGS pressure gradient.

Structural features of the adsorption layer of pentacene on the graphite surface and the PMMA/graphite hybrid surface

NASA Astrophysics Data System (ADS)

Fadeeva, A. I.; Gorbunov, V. A.; Litunenko, T. A.

2017-08-01

Using the molecular dynamics and the Monte Carlo methods, we have studied the structural features and growth mechanism of the pentacene film on graphite and polymethylmethacrylate /graphite surfaces. Monolayer capacity and molecular area, optimal angles between the pentacene molecules and graphite and PMMA/graphite surfaces as well as the characteristic angles between the neighboring pentacene molecules in the adsorption layer were estimated. It is shown that the orientation of the pentacene molecules in the film is determined by a number of factors, including the surface concentration of the molecules, relief of the surface, presence or absence of the polymer layer and its thickness. The pentacene molecules adsorbed on the graphite surface keep a horizontal position relative to the long axis at any surface coverage/thickness of the film. In the presence of the PMMA layer on the graphite, the increase of the number of pentacene molecules as well as the thickness of the PMMA layer induce the change of molecular orientation from predominantly horizontal to vertical one. The reason for such behavior is supposed to be the roughness of the PMMA surface.

Effect of Multipath Laser Shock Processing on Microhardness, Surface Roughness, and Wear Resistance of 2024-T3 Al Alloy

PubMed Central

Kadhim, Abdulhadi; Salim, Evan T.; Fayadh, Saeed M.; Al-Amiery, Ahmed A.; Kadhum, Abdul Amir H.; Mohamad, Abu Bakar

2014-01-01

Laser shock processing (LSP) is an innovative surface treatment technique with high peak power, short pulse, and cold hardening for strengthening metal materials. LSP is based on the application of a high intensity pulsed laser beam (I > 1 GW/cm2; t < 50 ns) at the interface between the metallic target and the surrounding medium (a transparent confining material, normally water) forcing a sudden vaporization of the metallic surface into a high temperature and density plasma that immediately develops inducing a shock wave propagating into the material. The shock wave induces plastic deformation and a residual stress distribution in the target material. In this paper we study the increase of microhardness and surface roughness with the increase of laser pulse energy in 2024-T3 Al alloy. The influence of the thickness of the confining layer (water) on microhardness and surface roughness is also studied. In addition, the effect of LSP treatment with best conditions on wear behaviors of the alloy was investigated. PMID:24737973

Characterization and analysis of surface notches on Ti-alloy plates fabricated by additive manufacturing techniques

NASA Astrophysics Data System (ADS)

Chan, Kwai S.

2015-12-01

Rectangular plates of Ti-6Al-4V with extra low interstitial (ELI) were fabricated by layer-by-layer deposition techniques that included electron beam melting (EBM) and laser beam melting (LBM). The surface conditions of these plates were characterized using x-ray micro-computed tomography. The depth and radius of surface notch-like features on the LBM and EBM plates were measured from sectional images of individual virtual slices of the rectangular plates. The stress concentration factors of individual surface notches were computed and analyzed statistically to determine the appropriate distributions for the notch depth, notch radius, and stress concentration factor. These results were correlated with the fatigue life of the Ti-6Al-4V ELI alloys from an earlier investigation. A surface notch analysis was performed to assess the debit in the fatigue strength due to the surface notches. The assessment revealed that the fatigue lives of the additively manufactured plates with rough surface topographies and notch-like features are dominated by the fatigue crack growth of large cracks for both the LBM and EBM materials. The fatigue strength reduction due to the surface notches can be as large as 60%-75%. It is concluded that for better fatigue performance, the surface notches on EBM and LBM materials need to be removed by machining and the surface roughness be improved to a surface finish of about 1 μm.

The Effect of an Isogrid on Cryogenic Propellant Behavior and Thermal Stratification

NASA Technical Reports Server (NTRS)

Oliveira, Justin; Kirk, Daniel R.; Chintalapati, Sunil; Schallhorn, Paul A.; Piquero, Jorge L.; Campbell, Mike; Chase, Sukhdeep

2007-01-01

All models for thermal stratification available in the presentation are derived using smooth, flat plate laminar and turbulent boundary layer models. This study examines the effect of isogrid (roughness elements) on the surface of internal tank walls to mimic the effects of weight-saving isogrid, which is located on the inside of many rocket propellant tanks. Computational Fluid Dynamics (CFD) is used to study the momentum and thermal boundary layer thickness for free convection flows over a wall with generic roughness elements. This presentation makes no mention of actual isogrid sizes or of any specific tank geometry. The magnitude of thermal stratification is compared for smooth and isogrid-lined walls.

Complexation of lysozyme with adsorbed PtBS-b-SCPI block polyelectrolyte micelles on silver surface.

PubMed

Papagiannopoulos, Aristeidis; Christoulaki, Anastasia; Spiliopoulos, Nikolaos; Vradis, Alexandros; Toprakcioglu, Chris; Pispas, Stergios

2015-01-20

We present a study of the interaction of the positively charged model protein lysozyme with the negatively charged amphiphilic diblock polyelectrolyte micelles of poly(tert-butylstyrene-b-sodium (sulfamate/carboxylate)isoprene) (PtBS-b-SCPI) on the silver/water interface. The adsorption kinetics are monitored by surface plasmon resonance, and the surface morphology is probed by atomic force microscopy. The micellar adsorption is described by stretched-exponential kinetics, and the micellar layer morphology shows that the micelles do not lose their integrity upon adsorption. The complexation of lysozyme with the adsorbed micellar layers depends on the micelles arrangement and density in the underlying layer, and lysozyme follows the local morphology of the underlying roughness. When the micellar adsorbed amount is small, the layers show low capacity in protein complexation and low resistance in loading. When the micellar adsorbed amount is high, the situation is reversed. The adsorbed layers both with or without added protein are found to be irreversibly adsorbed on the Ag surface.

Characterizing near-surface firn from the scattered signal component of glacier surface reflections detected in airborne radio-echo sounding measurements

NASA Astrophysics Data System (ADS)

Rutishauser, A.; Grima, C.; Sharp, M. J.; Blankenship, D. D.; Young, D. A.; Cawkwell, F.; Dowdeswell, J. A.

2016-12-01

With recent summer warming, surface melt on Canadian Arctic ice caps has intensified and extended to higher elevations in ice cap accumulation areas. Consequently, more meltwater percolates into the near-surface firn, and refreezes as ice layers where firn temperatures are below freezing. This process can increase firn densification rates, causing a lowering of the glacier surface height even in the absence of mass changes. Thus, knowledge of spatio-temporal variations in the near-surface firn stratigraphy is important for interpreting altimetrically-derived estimates of ice cap mass balance. We investigate the use of the scattering signal component of glacier surface reflections in airborne radio-echo sounding (RES) measurements to characterize the near-surface firn stratigraphy. The scattering signal distribution over Devon Ice Cap is compared to firn stratigraphy derived from ground-based radar data. We identify three distinct firn facies zones at different elevation ranges. The scattered signal component changes significantly between the different firn facies zones: low scattering correlates to laterally homogeneous firn containing thin, flat and continuous ice layers at elevations above 1800 m and below 1200 m, where firn consists mainly of ice. Higher scattering values are found from 1200-1800 m where the firn contains discrete, undulating ice layers. No correlation was found between the scattering component and surface roughness. Modelled scattering values for the measured roughness were significantly less than the observed values, and did not reproduce their observed spatial distribution. This indicates that the scattering component is determined mainly by the structure of near-surface firn. Our results suggest that the scattering component of surface reflections from airborne RES measurements has potential for characterizing heterogeneity in the spatial structure of firn that is affected by melting and refreezing processes.

Investigation of wall-bounded turbulence over sparsely distributed roughness

NASA Astrophysics Data System (ADS)

Placidi, Marco; Ganapathisubramani, Bharath

2011-11-01

The effects of sparsely distributed roughness elements on the structure of a turbulent boundary layer are examined by performing a series of Particle Image Velocimetry (PIV) experiments in a wind tunnel. From the literature, the best way to characterise a rough wall, especially one where the density of roughness elements is sparse, is unclear. In this study, rough surfaces consisting of sparsely and uniformly distributed LEGO® blocks are used. Five different patterns are adopted in order to examine the effects of frontal solidity (λf, frontal area of the roughness elements per unit wall-parallel area), plan solidity (λp, plan area of roughness elements per unit wall-parallel area) and the geometry of the roughness element (square and cylindrical elements), on the turbulence structure. The Karman number, Reτ , has been matched, at the value of approximately 2300, in order to compare across the different cases. In the talk, we will present detailed analysis of mean and rms velocity profiles, Reynolds stresses and quadrant decomposition.

Laser induced nanostructures created from Au layer on polyhydroxybutyrate

NASA Astrophysics Data System (ADS)

Michaljaničová, I.; Slepička, P.; Juřík, P.; Švorčík, V.

2017-11-01

Nanostructures as well as composite materials expand the range of materials properties and allow use of these materials in new and highly specific applications. In this paper, we described laser modification of polyhydroxybutyrate films covered with thin gold layer, which led to the formation of various composite structures. The crucial for the composite structures creation was setting of appropriate laser parameters; 15 mJ cm-2 laser fluence and 6 000 pulses were recognized as the best. The morphology of structures was determined by the thickness of the Au layer. The most interesting formations, very porous with the biggest roughness, were observed after treatment of foils covered with 10 nm of Au. The morphology was observed by atomic force microscopy. The influence on roughness and the difference between projected area and surface area was also determined.

Optimization of Surface Roughness Parameters of Al-6351 Alloy in EDC Process: A Taguchi Coupled Fuzzy Logic Approach

NASA Astrophysics Data System (ADS)

Kar, Siddhartha; Chakraborty, Sujoy; Dey, Vidyut; Ghosh, Subrata Kumar

2017-10-01

This paper investigates the application of Taguchi method with fuzzy logic for multi objective optimization of roughness parameters in electro discharge coating process of Al-6351 alloy with powder metallurgical compacted SiC/Cu tool. A Taguchi L16 orthogonal array was employed to investigate the roughness parameters by varying tool parameters like composition and compaction load and electro discharge machining parameters like pulse-on time and peak current. Crucial roughness parameters like Centre line average roughness, Average maximum height of the profile and Mean spacing of local peaks of the profile were measured on the coated specimen. The signal to noise ratios were fuzzified to optimize the roughness parameters through a single comprehensive output measure (COM). Best COM obtained with lower values of compaction load, pulse-on time and current and 30:70 (SiC:Cu) composition of tool. Analysis of variance is carried out and a significant COM model is observed with peak current yielding highest contribution followed by pulse-on time, compaction load and composition. The deposited layer is characterised by X-Ray Diffraction analysis which confirmed the presence of tool materials on the work piece surface.

A Comparison of Active and Passive Methods for Control of Hypersonic Boundary Layers on Airbreathing Configurations

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Nowak, Robert J.

2003-01-01

Active and passive methods for control of hypersonic boundary layers have been experimentally examined in NASA Langley Research Center wind tunnels on a Hyper-X model. Several configurations for forcing transition using passive discrete roughness elements and active mass addition, or blowing, methods were compared in two hypersonic facilities, the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air tunnels. Heat transfer distributions, obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the nominal Mach 7 flight trajectory of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For the passive roughness examination, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The prior passive roughness study resulted in a swept ramp configuration being selected for the Mach 7 flight vehicle that was scaled to be roughly 0.6 of the calculated boundary layer thickness. For the active jet blowing study, the blowing manifold pressure was systematically varied for each configuration, while monitoring the mass flow, to determine the jet penetration height with schlieren and transition movement with the phosphor system for comparison to the passive results. All the blowing concepts tested were adequate for providing transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model static pressure or higher.

The Effects of Land Surface Heating And Roughness Elements on the Structure and Scaling Laws of Atmospheric Boundary Layer Turbulence

NASA Astrophysics Data System (ADS)

Ghannam, Khaled

The atmospheric boundary-layer is the lowest 500-2000 m of the Earth's atmosphere where much of human life and ecosystem services reside. This layer responds to land surface (e.g. buoyancy and roughness elements) and slowly evolving free tropospheric (e.g. temperature and humidity lapse rates) conditions that arguably mediate and modulate biosphere-atmosphere interactions. Such response often results in spatially- and temporally-rich turbulence scales that continue to be the subject of inquiry given their significance to a plethora of applications in environmental sciences and engineering. The work here addresses key aspects of boundary layer turbulence with a focus on the role of roughness elements (vegetation canopies) and buoyancy (surface heating) in modifying the well-studied picture of shear-dominated wall-bounded turbulence. A combination of laboratory channel experiments, field experiments, and numerical simulations are used to explore three distinct aspects of boundary layer turbulence. These are: • The concept of ergodicity in turbulence statistics within canopies: It has been long-recognized that homogeneous and stationary turbulence is ergodic, but less is known about the effects of inhomogeneity introduced by the presence of canopies on the turbulence statistics. A high resolution (temporal and spatial) flume experiment is used here to test the convergence of the time statistics of turbulent scalar concentrations to their ensemble (spatio-temporal) counterpart. The findings indicate that within-canopy scalar statistics have a tendency to be ergodic, mostly in shallow layers (close to canopy top) where the sweeping flow events appear to randomize the statistics. Deeper layers within the canopy are dominated by low-dimensional (quasi-deterministic) von Karman vortices that tend to break ergodicity. • Scaling laws of turbulent velocity spectra and structure functions in near-surface atmospheric turbulence: the existence of a logarithmic scaling in the structure function of the longitudinal and vertical velocity components is examined using five experimental data sets that span the roughness sub-layer above vegetation canopies, the atmospheric surface-layer above a lake and a grass field, and an open channel experiment. The results indicate that close to the wall/surface, this scaling exists in the longitudinal velocity structure function only, with the vertical velocity counterpart exhibiting a much narrower extent of this range due to smaller separation of scales. Phenomenological aspects of the large-scale eddies show that the length scale formed by the friction velocity and energy dissipation acts as a dominant similarity length scale in collapsing experimental data at different heights, mainly due to the imbalance between local production and dissipation of turbulence kinetic energy. • Nonlocal heat transport in the convective atmospheric boundary-layer: Failure of the mean gradient-diffusion (K-theory) in the convective boundary-layer is explored. Using large eddy simulation runs for the atmospheric boundary layer spanning weakly to strongly convective conditions, a generic diagnostic framework that encodes the role of third-order moments in nonlocal heat transport is developed and tested. The premise is that these nonlocal effects are responsible for the inherent asymmetry in vertical transport, and hence the necessary non-Gaussian nature of the joint probability density function (JPDF) of vertical velocity and potential temperature must account for these effects. Conditional sampling (quadrant analysis) of this function and the imbalance between the flow mechanisms of ejections and sweeps are used to characterize this asymmetry, which is then linked to the third-order moments using a cumulant-discard method for the Gram-Charlier expansion of the JPDF. The connection between the ejection-sweep events and the third-order moments shows that the concepts of bottom-up/top-down diffusion, or updraft/downdraft models, are accounted for by various quadrants of this joint probability density function. To this end, future research directions that build upon this work are also discussed.

Structural changes of anodic layer on titanium in sulfate solution as a function of anodization duration in constant current mode

NASA Astrophysics Data System (ADS)

Komiya, Shinji; Sakamoto, Kouta; Ohtsu, Naofumi

2014-03-01

The present study investigated the effect of anodization time, in constant current mode, on the anodic oxide layer formed on titanium (Ti). Anodization of the Ti substrate was　carried out in a 0.1 M (NH4)2SO4 aqueous solution with reaction times of various durations, after which the characteristics and photocatalytic activity were investigated in detail. The TiO2 layer fabricated in a short duration exhibited comparatively flat surface morphology and an anatase-type crystal structure. This layer acted as a photocatalyst only under ultraviolet light (UV) illumination. Upon prolonging the anodization, the layer structure changed drastically. The surface morphology became rough, and the crystal structure changed to rutile-type TiO2. Furthermore, the layer showed photocatalytic activity both under UV and visible light illumination. Further anodization increased the amount of methylene blue (MB) adsorbed on the surface, but did not cause additional change to the structure of the anodic layer. The surface morphology and crystal structure of the anodic layer were predominantly controlled by the anodization time; thus, the anodization time is an important parameter for controlling the characteristics of the anodic layer.

An intermittency model for predicting roughness induced transition

NASA Astrophysics Data System (ADS)

Ge, Xuan; Durbin, Paul

2014-11-01

An extended model for roughness-induced transition is proposed based on an intermittency transport equation for RANS modeling formulated in local variables. To predict roughness effects in the fully turbulent boundary layer, published boundary conditions for k and ω are used, which depend on the equivalent sand grain roughness height, and account for the effective displacement of wall distance origin. Similarly in our approach, wall distance in the transition model for smooth surfaces is modified by an effective origin, which depends on roughness. Flat plate test cases are computed to show that the proposed model is able to predict the transition onset in agreement with a data correlation of transition location versus roughness height, Reynolds number, and inlet turbulence intensity. Experimental data for a turbine cascade are compared with the predicted results to validate the applicability of the proposed model. Supported by NSF Award Number 1228195.

Surface Morphology of Liquid and Solid Thin Films via X-Ray Reflectivity.

NASA Astrophysics Data System (ADS)

Shindler, Joseph Daniel

X-ray reflectivity can be used to measure the spatial variations in the electron density on length scales from Angstroms to microns. It is sensitive to atomic scale roughness, interdiffusion in buried layers, the thickness of multilayer stacks, and in-plane correlations in each of these cases. We have pioneered the use of a high intensity, moderate resolution configuration for x-ray reflectivity which utilizes a bent crystal graphite monochromator. With this technique we can obtain a beam intensity one hundred times greater than is possible using the high resolution rotating anode configuration, while we have shown that the resulting instrumental resolution is appropriate for the vast majority of thin film work. For all of the systems studied, we were able to measure the weak diffuse scattering signal to probe the in-plane length scales of interfacial roughness, a measurement which had previously only been attempted at synchrotron sources. Studied systems include thin films and surfaces with a wide range of structural order and surface morphologies. Interest in liquid films has been of a fundamental nature. Theories on the expected film evolution with changing thickness and temperature are currently being tested with scattering experiments. We have pursued the issues of film/substrate wetting and conformality, focussing on the temperature dependence of these phenomena near the triple point. Despite the heterogeneity of the substrate potential, we see a very sharp wetting transition at or near the triple point, although below the triple point the film is still smooth, consistent with a uniform layer. We also see a loss of conformality as the fluid films thicken; this is consistent with theory and with other recent experiments. The properties of a multilayer solid film depend not only on the magnitude of the roughness of each interface, but also on the conformality between interfaces and the length scales of the roughness--i.e., whether the roughness is on the atomic lengths of interdiffusion, crystalline order lengths of faceting, or even longer lengths due to other processes. In a joint project with Alcoa, we combined the methods of x-ray Bragg diffraction and small angle reflectivity to probe aluminum thin films as precursors to true multilayer films, correlating grain size and orientation with the magnitude and length-scales of surface roughness. We also correlated all film properties with such parameters as the deposition method, substrate roughness, and film thickness.

Early Onset of Kinetic Roughening due to a Finite Step Width in Hematin Crystallization

NASA Astrophysics Data System (ADS)

Olafson, Katy N.; Rimer, Jeffrey D.; Vekilov, Peter G.

2017-11-01

The structure of the interface of a growing crystal with its nutrient phase largely determines the growth dynamics. We demonstrate that hematin crystals, crucial for the survival of malaria parasites, transition from faceted to rough growth interfaces at increasing thermodynamic supersaturation Δ μ . Contrary to theoretical predictions and previous observations, this transition occurs at moderate values of Δ μ . Moreover, surface roughness varies nonmonotonically with Δ μ , and the rate constant for rough growth is slower than that resulting from nucleation and spreading of layers. We attribute these unexpected behaviors to the dynamics of step growth dominated by surface diffusion and the loss of identity of nuclei separated by less than the step width w . We put forth a general criterion for the onset of kinetic roughening using w as a critical length scale.

Scale resolving computation of submerged wall jets on flat wall with different roughness heights

NASA Astrophysics Data System (ADS)

Paik, Joongcheol; Bombardelli, Fabian

2014-11-01

Scale-adaptive simulation is used to investigate the response of velocity and turbulence in submerged wall jets to abrupt changes from smooth to rough beds. The submerged wall jets were experimentally investigated by Dey and Sarkar [JFM, 556, 337, 2006] at the Reynolds number of 17500 the Froude number of 4.09 and the submergence ratio of 1.12 on different rough beds that were generated by uniform sediments of different median diameters The SAS is carried out by means of a second-order-accurate finite volume method in space and time and the effect of bottom roughness is treated by the approach of Cebeci (2004). The evolution of free surface is captured by employing the two-phase volume of fluid (VOF) technique. The numerical results obtained by the SAS approach, incorporated with the VOF and the rough wall treatment, are in good agreement with the experimental measurements. The computed turbulent boundary layer grows more quickly and the depression of the free surface is more increased on the rough wall than those on smooth wall. The size of the fully developed zone shrinks and the decay rate of maximum streamwise velocity and Reynolds stress components are faster with increase in the wall roughness. Supported by NSF and NRF of Korea.

Colloidal quantum dot active layers for light emitting diodes

NASA Astrophysics Data System (ADS)

Pagan, Jennifer G.; Stokes, Edward B.; Patel, Kinnari; Burkhart, Casey C.; Ahrens, Michael T.; Barletta, Philip T.; O'Steen, Mark

2006-07-01

In this paper the preliminary results of incorporating a novel active layer into a GaN light emitting diode (LED) are discussed. Integration of colloidal CdSe quantum dots into a GaN LED active layer is demonstrated. Properties of p-type Mg doped overgrowth GaN are examined via circular transmission line method (CTLM). Effects on surface roughness due to the active layer incorporation are examined using atomic force microscopy (AFM). Electroluminescence of LED test structures is reported, and an ideality factor of n = 1.6 is demonstrated.

Effect of Build Angle on Surface Properties of Nickel Superalloys Processed by Selective Laser Melting

NASA Astrophysics Data System (ADS)

Covarrubias, Ernesto E.; Eshraghi, Mohsen

2018-03-01

Aerospace, automotive, and medical industries use selective laser melting (SLM) to produce complex parts through solidifying successive layers of powder. This additive manufacturing technique has many advantages, but one of the biggest challenges facing this process is the resulting surface quality of the as-built parts. The purpose of this research was to study the surface properties of Inconel 718 alloys fabricated by SLM. The effect of build angle on the surface properties of as-built parts was investigated. Two sets of sample geometries including cube and rectangular artifacts were considered in the study. It was found that, for angles between 15° and 75°, theoretical calculations based on the "stair-step" effect were consistent with the experimental results. Downskin surfaces showed higher average roughness values compared to the upskin surfaces. No significant difference was found between the average roughness values measured from cube and rectangular test artifacts.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drozdov, Yu. N., E-mail: drozdyu@ipmras.ru; Drozdov, M. N.; Yunin, P. A.

It is demonstrated using X-ray diffraction and atomic force microscopy that elastic stresses in GeSi layers on Si (115) substrates relax more effectively than in the same layers on Si (001) substrates. This fact is attributed to the predominant contribution of one of the (111) slip planes on the (115) cut. The atomicforce-microscopy image of the GeSi/Si(115) surface reveals unidirectional slip planes, while the GeSi/Si(001) image contains a grid of orthogonal lines and defects at the points of their intersection. As a result, thick GeSi layers on Si (115) have a reduced surface roughness. A technique for calculating the parametersmore » of relaxation of the layer on the Si (115) substrate using X-ray diffraction data is discussed.« less

Wear and corrosion resistance of electroforming layer after WEDM for 7075 aluminum alloy

NASA Astrophysics Data System (ADS)

Xu, Jinkai; Qiu, Rongxian; Lian, Zhongxu; Yu, Zhanjiang; Yu, Peng; Ren, Wanfei; Yu, Huadong

2018-06-01

In order to investigate the influence of the recast layer obtained by wire electrical discharge machining (WEDM) for 7075 aluminum alloy on the mechanical physical properties of the workpiece, we carried out research on the geometry parameters, microstructure, adhesion, wear resistance and corrosion resistance of the recast layer. The results show that the unit thermal power density decreases, the surface roughness Ra value increases, and the amount of the electric erosion craters and the micro/nano pits decrease with the increase of current and voltage. In the meantime, the thickness and hardness of the recast layer are increased, so the wear resistance and corrosion resistance are significantly improved. In addition, the surface hardness plays a major role in increasing wear resistance.

Interface morphology of a Cr(001)/Fe(001) superlattice determined by scanning tunneling microscopy and x-ray diffraction: A comparison

NASA Astrophysics Data System (ADS)

Schmidt, C. M.; Bürgler, D. E.; Schaller, D. M.; Meisinger, F.; Güntherodt, H.-J.; Temst, K.

2001-01-01

A Cr(001)/Fe(001) superlattice with ten bilayers grown by molecular beam epitaxy on a Ag(001) substrate is studied by in situ scanning tunneling microscopy (STM) and ex situ x-ray diffraction (XRD). Layer-resolved roughness parameters determined from STM images taken in various stages of the superlattice fabrication are compared with average values reported in the literature or obtained from the fits of our XRD data. Good agreement is found for the rms roughnesses describing vertical roughness and for the lateral correlation lengths characterizing correlated as well as uncorrelated interface roughness if peculiarities of STM and XRD are taken into account. We discuss in detail (i) the possible differences between the STM topography of a free surface and the morphology of a subsequently formed interface, (ii) contributions due to chemical intermixing at the interfaces, (iii) the comparison of XRD parameters averaged over all interfaces versus layer-resolved STM parameters, and (iv) the question of the coherent field of view for the determination of rms values.

Effects of roughness and compressibility of flooring on cow locomotion.

PubMed

Rushen, J; de Passillé, A M

2006-08-01

We examined the effects of roughness and degree of compressibility of flooring on the locomotion of dairy cows. We observed 16 cows walking down specially constructed walkways with materials that differed in surface roughness and degree of compressibility. Use of a commercially available soft rubber flooring material decreased slipping, number of strides, and time to traverse the corridor. These effects were most apparent at difficult sections of the corridor, such as at the start, at a right-angle turn, and across a gutter. Covering the walkway with a thin layer of slurry increased frequency of slipping, number of strides, and time taken to traverse the walkway. Effects of adding slurry were not overcome by increasing surface roughness or compressibility. Placing more compressible materials under a slip-resistant material reduced the time and number of steps needed to traverse the corridor but did not reduce slips, and the effects on cow locomotion varied nonlinearly with the degree of compressibility of the floor. Use of commercially available rubber floors improved cow locomotion compared with concrete floors. However, standard engineering measures of the floor properties may not predict effects of the floor on cow behavior well. Increasing compressibility of the flooring on which cows walk, independently of the roughness of the surface, can improve cow locomotion.

Vancomycin incorporated chitosan/gelatin coatings coupled with TiO2-SrHAP surface modified cp-titanium for osteomyelitis treatment.

PubMed

D, Nancy; N, Rajendran

2018-04-15

Commercially pure Titanium (Cp-Ti) was electrophoretically modified using double layer coatings consisting of TiO 2 -SrHAP as the first layer (TH) followed by vancomycin incorporated Chitosan/Gelatin as the second layer (THV). The nano crystalline phase of coated Strontium incorporated hydroxyapatite (Sr-HAP) confirmed through X-ray diffraction studies (XRD). The polyelectrolyte complex formation between chitosan and gelatin, the stability of the drug, the bonding between chitosan and Sr-HAP were confirmed through infra-red spectroscopic studies (IR). The average roughness (R a ) value calculated from atomic force microscopy (AFM) corroborates with the water contact angle data, which clearly confirms the tuning property of the surface in relation to the surface energy and roughness of the coated samples. The total amount of vancomycin encapsulated was calculated to be 11.5 μg. Antibacterial activity was found against both Staphylococcus aureus strains methicillin resistant Staphylococcus aureus (MRSA) and methicillin sensitive Staphylococcus aureus (MRSA) for a drug concentration of 2.74 μg released after 12 h of immersion. The in-vitro cell culture studies showed enhanced cellular activity for THV samples. Thus, THV samples have a dual action at the surface, by resisting the bacterial adhesion and enhancing cellular interaction at the bio-interface, making it a promising candidate to treat osteomyelitis infection. Copyright © 2018. Published by Elsevier B.V.

Control of crystallographic texture and surface morphology of Pt/Tio2 templates for enhanced PZT thin film texture.

PubMed

Fox, Austin J; Drawl, Bill; Fox, Glen R; Gibbons, Brady J; Trolier-McKinstry, Susan

2015-01-01

Optimized processing conditions for Pt/TiO2/SiO2/Si templating electrodes were investigated. These electrodes are used to obtain [111] textured thin film lead zirconate titanate (Pb[ZrxTi1-x ]O3 0 ≤ x ≤ 1) (PZT). Titanium deposited by dc magnetron sputtering yields [0001] texture on a thermally oxidized Si wafer. It was found that by optimizing deposition time, pressure, power, and the chamber pre-conditioning, the Ti texture could be maximized while maintaining low surface roughness. When oxidized, titanium yields [100]-oriented rutile. This seed layer has as low as a 4.6% lattice mismatch with [111] Pt; thus, it is possible to achieve strongly oriented [111] Pt. The quality of the orientation and surface roughness of the TiO2 and the Ti directly affect the achievable Pt texture and surface morphology. A transition between optimal crystallographic texture and the smoothest templating surface occurs at approximately 30 nm of original Ti thickness (45 nm TiO2). This corresponds to 0.5 nm (2 nm for TiO2) rms roughness as determined by atomic force microscopy and a full-width at half-maximum (FWHM) of the rocking curve 0002 (200) peak of 5.5/spl degrees/ (3.1/spl degrees/ for TiO2). A Pb[Zr0.52Ti 0.48]O3 layer was deposited and shown to template from the textured Pt electrode, with a maximum [111] Lotgering factor of 87% and a minimum 111 FWHM of 2.4/spl degrees/ at approximately 30 nm of original Ti.

Polarized Neutron Reflectometry of Nickel Corrosion Inhibitors.

PubMed

Wood, Mary H; Welbourn, Rebecca J L; Zarbakhsh, Ali; Gutfreund, Philipp; Clarke, Stuart M

2015-06-30

Polarized neutron reflectometry has been used to investigate the detailed adsorption behavior and corrosion inhibition mechanism of two surfactants on a nickel surface under acidic conditions. Both the corrosion of the nickel surface and the structure of the adsorbed surfactant layer could be monitored in situ by the use of different solvent contrasts. Layer thicknesses and roughnesses were evaluated over a range of pH values, showing distinctly the superior corrosion inhibition of one negatively charged surfactant (sodium dodecyl sulfate) compared to a positively charged example (dodecyl trimethylammonium bromide) due to its stronger binding interaction with the surface. It was found that adequate corrosion inhibition occurs at significantly less than full surface coverage.

Semiconductor light-emitting devices having concave microstructures providing improved light extraction efficiency and method for producing same

DOEpatents

Tansu, Nelson; Gilchrist, James F; Ee, Yik-Khoon; Kumnorkaew, Pisist

2013-11-19

A conventional semiconductor LED is modified to include a microlens layer over its light-emitting surface. The LED may have an active layer including at least one quantum well layer of InGaN and GaN. The microlens layer includes a plurality of concave microstructures that cause light rays emanating from the LED to diffuse outwardly, leading to an increase in the light extraction efficiency of the LED. The concave microstructures may be arranged in a substantially uniform array, such as a close-packed hexagonal array. The microlens layer is preferably constructed of curable material, such as polydimethylsiloxane (PDMS), and is formed by soft-lithography imprinting by contacting fluid material of the microlens layer with a template bearing a monolayer of homogeneous microsphere crystals, to cause concave impressions, and then curing the material to fix the concave microstructures in the microlens layer and provide relatively uniform surface roughness.

An operational large-scale marine planetary boundary layer model

NASA Technical Reports Server (NTRS)

Brown, R. A.; Liu, W. T.

1982-01-01

A marine planetary boundary layer (PBL) model is presented and compared with data from sea-based experiments. The PBL model comprises two layers, the outer an Ekman-Taylor layer with stratification-dependent secondary flow, and the logarithmic surface layer corrected for stratification and humidity effects and variable surface roughness. Corrections are noted for air much warmer than water in stable conditions and for low wind speeds. The layers are analytically defined along with similarity relations and a resistance law for inclusion in a program. An additional interfacial layer correction is developed and shown to be significant for heat flux calculations. Experimental data from GOASEX were used to predict the windfield in the Gulf of Alaska, and JASIN data was used for windfields SE of Iceland. The JASIN-derived wind field predictions were accurate to within 1 m/sec and 10 deg in a 200 km triangle.

A high-resolution model of the planetary boundary layer - Sensitivity tests and comparisons with SESAME-79 data

NASA Technical Reports Server (NTRS)

Zhang, D.; Anthes, R. A.

1982-01-01

A one-dimensional, planetary boundary layer (PBL) model is presented and verified using April 10, 1979 SESAME data. The model contains two modules to account for two different regimes of turbulent mixing. Separate parameterizations are made for stable and unstable conditions, with a predictive slab model for surface temperature. Atmospheric variables in the surface layer are calculated with a prognostic model, with moisture included in the coupled surface/PBL modeling. Sensitivity tests are performed for factors such as moisture availability, albedo, surface roughness, and thermal capacity, and a 24 hr simulation is summarized for day and night conditions. The comparison with the SESAME data comprises three hour intervals, using a time-dependent geostrophic wind. Close correlations were found with daytime conditions, but not in nighttime thermal structure, while the turbulence was faithfully predicted. Both geostrophic flow and surface characteristics were shown to have significant effects on the model predictions

Preparation of Superhydrophobic Film on Ti Substrate and Its Anticorrosion Property

PubMed Central

Zhu, Min; Tang, Wenchuan; Huang, Luyao; Zhang, Dawei; Du, Cuiwei; Yu, Gaohong; Chen, Ming; Chowwanonthapunya, Thee

2017-01-01

Superhydrophobic films were fabricated on a titanium substrate with or without anodizing by using a self-assembling method. Firstly, the pretreatments of mechanical polishing/anodizing or mechanical polishing only were conducted, respectively. Subsequently, the preparation of polydopamine film layer, deposition of nano-silver particles, and post modification of 1H,1H,2H,2H-perfluorodecanethiol were performed on the surface of the pretreated substrate. The surface morphologies, compositions, wettability, and corrosion resistance of the films were investigated with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), water contact angle measurements, and electrochemical tests, respectively. Meanwhile, the effect of the deposition time in the silver nitrate solution on the hydrophobicity of the specimen surface was investigated. The result showed that with the increase of deposition time, the hydrophobic property enhanced gradually. The surface deposited for 7 h exhibited an optimum hydrophobic effect, which was characterized with a large water contact angle (WCA) of 154°, and the surface was rather rough and covered by a relatively uniform layer of micro-nano silver particles. The excellent hydrophobicity was attributed to a rough stratified microstructure along with the low surface energy. The electrochemical measurements showed that the existence of the superhydrophobic film can effectively enhance the corrosion resistance of Ti samples. PMID:28772987

Preparation of Superhydrophobic Film on Ti Substrate and Its Anticorrosion Property.

PubMed

Zhu, Min; Tang, Wenchuan; Huang, Luyao; Zhang, Dawei; Du, Cuiwei; Yu, Gaohong; Chen, Ming; Chowwanonthapunya, Thee

2017-06-08

Superhydrophobic films were fabricated on a titanium substrate with or without anodizing by using a self-assembling method. Firstly, the pretreatments of mechanical polishing/anodizing or mechanical polishing only were conducted, respectively. Subsequently, the preparation of polydopamine film layer, deposition of nano-silver particles, and post modification of 1H,1H,2H,2H-perfluorodecanethiol were performed on the surface of the pretreated substrate. The surface morphologies, compositions, wettability, and corrosion resistance of the films were investigated with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), water contact angle measurements, and electrochemical tests, respectively. Meanwhile, the effect of the deposition time in the silver nitrate solution on the hydrophobicity of the specimen surface was investigated. The result showed that with the increase of deposition time, the hydrophobic property enhanced gradually. The surface deposited for 7 h exhibited an optimum hydrophobic effect, which was characterized with a large water contact angle (WCA) of 154°, and the surface was rather rough and covered by a relatively uniform layer of micro-nano silver particles. The excellent hydrophobicity was attributed to a rough stratified microstructure along with the low surface energy. The electrochemical measurements showed that the existence of the superhydrophobic film can effectively enhance the corrosion resistance of Ti samples.

Relationships between structure and activity of carbon as a multifunctional support for electrocatalysts.

PubMed

Stevanović, Sanja I; Panić, Vladimir V; Dekanski, Aleksandar B; Tripković, Amalija V; Jovanović, Vladislava M

2012-07-14

We report on new insights into the relationships between structure and activity of glassy carbon (GC), as a model material for electrocatalyst support, during its anodization in acid solution. Our investigation strongly confirms the role of CFGs in promotion of Pt activity by the "spill-over" effect related to CO(ads) for methanol electrooxidation (MEO) on a carbon-supported Pt catalyst. Combined analysis of voltammetric and impedance behaviour as well as changes in GC surface morphology induced by intensification of anodizing conditions reveal an intrinsic influence of the carbon functionalization and the structure of a graphene oxide (GO) layer on the electrical and electrocatalytic properties of activated GC. Although GO continuously grows during anodization, it structurally changes from being a graphite inter-layer within graphite ribbons toward a continuous GO surface layer that deteriorates the native structure of GC. As a consequence of the increased distance between GO-spaced graphite layers, the GC conductivity decreases until the case of profound GO exfoliation under drastic anodizing conditions. This exposes the native, yet abundantly functionalized, GC texture. While GC capacitance continuously increases with intensification of anodizing conditions, the surface nano-roughness and GO resistance reach the highest values at modest anodizing conditions, and then decrease upon drastic anodization due to the onset of GO exfoliation. We found for the first time that the activity of a GC-supported Pt catalyst in MEO, as one of the promising half-reactions in polymer electrolyte fuel cells, strictly follows the changes in GC nano-roughness and GO-induced GC resistance. The highest GC/Pt MEO activity is reached when optimal distance between graphite layers and optimal degree of GC functionalization bring the highest amount of CFGs into intimate contact with the Pt surface. This confirms the promoting role of CFGs in MEO catalysis.

Free convection in the Matian atmosphere

NASA Technical Reports Server (NTRS)

Clow, G. D.; Haberle, R. M.

1990-01-01

The 'free convective' regime for the Martian atmospheric boundary layer (ABL) was investigated. This state occurs when the mean windspeed at the top of the ABL drops below some critical value U(sub c) and positive buoyant forces are present. Such forces can arise either from vertical temperature or water vapor gradients across the atmospheric surface layer. During free convection, buoyant forces drive narrow plumes that ascend to the inversion height with a return circulation consisting of broad slower-moving downdraughts. Horizontal pressure, temperature, windspeed, and water vapor fluctuations resulting form this circulation pattern can be quite large adjacent to the ground (within the surface layer). The local turbulent fluctuations cause non-zero mean surface stresses, sensible heat fluxes, and latent heat fluxes, even when the mean regional windspeed is zero. Although motions above the surface layer are insensitive to the nature of the surface, the sensible and latent heat fluxes are primarily controlled by processes within the interfacial sublayer immediately adjacent to the ground during free convection. Thus the distinction between aerodynamically smooth and rough airflow within the interfacial sublayer is more important than for the more typical situation where the mean regional windspeed is greater than U(sub c). Buoyant forces associated with water vapor gradients are particularly large on Mars at low pressures and high temperatures when the surface relative humidity is 100 percent, enhancing the likelihood of free convection under these conditions. On this basis, Ingersol postulated the evaporative heat losses from an icy surface on Mars at 237 K and current pressures would exceed the available net radiative flux at the surface, thus prohibiting ice from melting at low atmospheric pressures. Schumann has developed equations describing the horizontal fluctuations and mean vertical gradients occurring during free convection. Schumann's model was generalized to include convection driven by water vapor gradients and to include the effects of circulation above both aerodynamically smooth and rough surfaces.

Experimental Study of Aligned and Staggered Wind Farms in a Convective Boundary Layer

NASA Astrophysics Data System (ADS)

Markfort, Corey; Zhang, Wei; Porte-Agel, Fernando

2011-11-01

Wind farm-atmosphere interaction is complicated by turbine configuration and thermal effects on momentum and kinetic energy fluxes. Wind farms of finite length have been modeled as increased surface roughness or as a sparse canopy; however it is not clear which approach is more appropriate. Experiments were conducted in a thermally controlled boundary layer wind tunnel, using a custom x-wire/cold wire and surface heat flux sensors, to understand the effect of aligned versus staggered turbine configurations on momentum absorption and flow adjustment in a convective boundary layer (CBL). Results for experiments of a large farm show the span-wise averaged flow statistics exhibit similar turbulent transport properties to that of canopy flows. The wake adjusts within and grows over the farm more quickly for a staggered compared to an aligned farm. Using canopy flow scaling, we show that the flow equilibrates faster and the overall momentum absorption is higher in a staggered compared to an aligned farm. Wake recovery behind a single turbine is facilitated by buoyancy in a CBL (Zhang et al. under review). We find a similar effect in wind farms resulting in reduced effective roughness and momentum absorption. We also find a reduction of surface heat flux for both wind farms, but greater for the staggered farm.

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

NASA Astrophysics Data System (ADS)

Brennan, Joseph C.; Geraldi, Nicasio R.; Morris, Robert H.; Fairhurst, David J.; McHale, Glen; Newton, Michael I.

2015-05-01

In recent years extensive work has been focused onto using superhydrophobic surfaces for drag reduction applications. Superhydrophobic surfaces retain a gas layer, called a plastron, when submerged underwater in the Cassie-Baxter state with water in contact with the tops of surface roughness features. In this state the plastron allows slip to occur across the surface which results in a drag reduction. In this work we report flexible and relatively large area superhydrophobic surfaces produced using two different methods: Large roughness features were created by electrodeposition on copper meshes; Small roughness features were created by embedding carbon nanoparticles (soot) into Polydimethylsiloxane (PDMS). Both samples were made into cylinders with a diameter under 12 mm. To characterize the samples, scanning electron microscope (SEM) images and confocal microscope images were taken. The confocal microscope images were taken with each sample submerged in water to show the extent of the plastron. The hydrophobized electrodeposited copper mesh cylinders showed drag reductions of up to 32% when comparing the superhydrophobic state with a wetted out state. The soot covered cylinders achieved a 30% drag reduction when comparing the superhydrophobic state to a plain cylinder. These results were obtained for turbulent flows with Reynolds numbers 10,000 to 32,500.

[Comparison of surface roughness of nanofilled and microhybrid composite resins after curing and polishing].

PubMed

Jiang, Hong; Lv, Da; Liu, Kailei; Zhang, Weisheng; Yao, Yao; Liao, Chuhong

2014-05-01

To compare the surface roughness of nanofilled dental composite resin and microhybrid composite resins after curing and polishing. A nanofilled composite (Z350) and 4 microhybrid composites (P60, Z250, Spectrum, and AP-X) were fabricated from the lateral to the medial layers to prepare 8 mm×8 mm×5 mm cubical specimens. The 4 lateral surfaces of each specimens were polished with abrasive disks (Super-Snap). Profilometer was used to test the mean surface roughness (Ra) after polishing. P60 had the lowest Ra (0.125∓0.030 µm) followed by Z250 and Spectrum. The Ra of Z350 (0.205∓0.052 µm) was greater than that of the other 3 resins, and AP-X had the roughest surfaces. Under scanning electron microscope, the polished faces of P60 resin were characterized by minor, evenly distributed particles with fewer scratches; the polished faces of Z350 presented with scratches where defects of the filling material could be seen. The nanofilled composite Z350 has smooth surface after polishing by abrasive disks, but its smoothness remains inferior to that of other micro-hybrid composite resins.

Ordered roughness effects on NACA 0026 airfoil

NASA Astrophysics Data System (ADS)

Harun, Z.; Abbas, A. A.; Dheyaa, R. Mohammed; Ghazali, M. I.

2016-10-01

The effects of highly-ordered rough surface - riblets, applied onto the surface of a NACA 0026 airfoil, are investigated experimentally using wind tunnel. The riblets are arranged in directionally converging - diverging pattern with dimensions of height, h = 1 mm, pitch or spacing, s = 1 mm, yaw angle α = 0o and 10o The airfoil with external geometry of 500 mm span, 600 mm chord and 156 mm thickness has been built using mostly woods and aluminium. Turbulence quantities are collected using hotwire anemometry. Hotwire measurements show that flows past converging and diverging pattern inherit similar patterns in the near-wall region for both mean velocity and turbulence intensities profiles. The mean velocity profiles in logarithmic regions for both flows past converging and diverging riblet pattern are lower than that with yaw angle α = 0o. Converging riblets cause the boundary layer to thicken and the flow with yaw angle α = 0o produces the thinnest boundary layer. Both the converging and diverging riblets cause pronounced outer peaks in the turbulence intensities profiles. Most importantly, flows past converging and diverging pattern experience 30% skin friction reductions. Higher order statistics show that riblet surfaces produce similar effects due to adverse pressure gradient. It is concluded that a small strip of different ordered roughness features applied at a leading edge of an airfoil can change the turbulence characteristics dramatically.

Orbiter windward surface entry Heating: Post-orbital flight test program update

NASA Technical Reports Server (NTRS)

Harthun, M. H.; Blumer, C. B.; Miller, B. A.

1983-01-01

Correlations of orbiter windward surface entry heating data from the first five flights are presented with emphasis on boundary layer transition and the effects of catalytic recombination. Results show that a single roughness boundary layer transition correlation developed for spherical element trips works well for the orbiter tile system. Also, an engineering approach for predicting heating in nonequilibrium flow conditions shows good agreement with the flight test data in the time period of significant heating. The results of these correlations, when used to predict orbiter heating for a high cross mission, indicate that the thermal protection system on the windward surface will perform successfully in such a mission.

Wind Characteristics of Coastal and Inland Surface Flows

NASA Astrophysics Data System (ADS)

Subramanian, Chelakara; Lazarus, Steven; Jin, Tetsuya

2015-11-01

Lidar measurements of the winds in the surface layer (up to 80 m) inland and near the beach are studied to better characterize the velocity profile and the effect of roughness. Mean and root-mean-squared profiles of horizontal and vertical wind components are analyzed. The effects of variable time (18, 60 and 600 seconds) averaging on the above profiles are discussed. The validity of common surface layer wind profile models to estimate skin friction drag is assessed in light of these measurements. Other turbulence statistics such as auto- and cross- correlations in spatial and temporal domains are also presented. The help of FIT DMES field measurement crew is acknowledged.

Sensitivity of Climate Simulations to Land-Surface and Atmospheric Boundary-Layer Treatments-A Review.

NASA Astrophysics Data System (ADS)

Garratt, J. R.

1993-03-01

Aspects of the land-surface and boundary-layer treatments in some 20 or so atmospheric general circulation models (GCMS) are summarized. In only a small fraction of these have significant sensitivity studies been carried out and published. Predominantly, the sensitivity studies focus upon the parameterization of land-surface processes and specification of land-surface properties-the most important of these include albedo, roughness length, soil moisture status, and vegetation density. The impacts of surface albedo and soil moisture upon the climate simulated in GCMs with bare-soil land surfaces are well known. Continental evaporation and precipitation tend to decrease with increased albedo and decreased soil moisture availability. For example, results from numerous studies give an average decrease in continental precipitation of 1 mm day1 in response to an average albedo increase of 0.13. Few conclusive studies have been carried out on the impact of a gross roughness-length change-the primary study included an important statistical assessment of the impact upon the mean July climate around the globe of a decreased continental roughness (by three orders of magnitude). For example, such a decrease reduced the precipitation over Amazonia by 1 to 2 mm day1.The inclusion of a canopy scheme in a GCM ensures the combined impacts of roughness (canopies tend to be rougher than bare soil), albedo (canopies tend to be less reflective than bare soil), and soil-moisture availability (canopies prevent the near-surface soil region from drying out and can access the deep soil moisture) upon the simulated climate. The most revealing studies to date involve the regional impact of Amazonian deforestation. The results of four such studies show that replacing tropical forest with a degraded pasture results in decreased evaporation ( 1 mm day1) and precipitation (1-2 mm day1), and increased near-surface air temperatures (2 K).Sensitivity studies as a whole suggest the need for a realistic surface representation in general circulation models of the atmosphere. It is not yet clear how detailed this representation needs to be, but even allowing for the importance of surface processes, the parameterization of boundary-layer and convective clouds probably represents a greater challenge to improved climate simulations. This is illustrated in the case of surface net radiation for Aniazonia, which is not well simulated and tends to be overestimated, leading to evaporation rates that are too large. Underestimates in cloudiness, cloud albedo, and clear-sky shortwave absorption, rather than in surface albedo, appear to be the main culprits.There are three major tasks that confront the researcher so far as the development and validation of atmospheric boundary-layer (ABL) and surface schemes in GCMs are concerned:(i) There is a need to as' critically the impact of `improved' parameterization schemes on WM simulations, taking into account the problem of natural variability and hence the statistical significance of the induced changes.(ii) There is a need to compare GCM simulations of surface and ABL behavior (particularly regarding the diurnal cycle of surface fluxes, air temperature, and ABL depth) with observations over a range of surface types (vegetation, desert, ocean). In this context, area-average values of surface fluxes will be required to calibrate directly the ABL/land-surface scheme in the GCM.(iii) There is a need for intercomparisons of ABL and land-surface schemes used in GCMS, both for one- dimensional stand-alone models and for GCMs that incorporate the respective schemes.

Advanced light-scattering materials: Double-textured ZnO:B films grown by LP-MOCVD

NASA Astrophysics Data System (ADS)

Addonizio, M. L.; Spadoni, A.; Antonaia, A.

2013-12-01

Double-textured ZnO:B layers with enhanced optical scattering in both short and long wavelength regions have been successfully fabricated using MOCVD technique through a three step process. Growth of double-textured structures has been induced by wet etching on polycrystalline ZnO surface. Our double-layer structure consists of a first ZnO:B layer wet etched and subsequently used as substrate for a second ZnO:B layer deposition. Polycrystalline ZnO:B layers were etched by utilizing diluted solutions of fluoridic acid (HF), chloridric acid (HCl) and phosphoric acid (H3PO4) and their effect on surface morphology modification was systematically investigated. The morphology of the second deposited ZnO layer strongly depended on the surface properties of the etched ZnO first layer. Growth of cauliflower-like texture was induced by protrusions presence on the HCl etched surface. Optimized double-layer structure shows a cauliflower-like double texture with higher RMS roughness and increased spectral haze values in both short and long wavelength regions, compared to conventional pyramidal-like single texture. Furthermore, this highly scattering structure preserves excellent optical and electrical properties.

Electronic absorption band broadening and surface roughening of phthalocyanine double layers by saturated solvent vapor treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jinhyun; Yim, Sanggyu, E-mail: sgyim@kookmin.ac.kr

2012-10-15

Variations in the electronic absorption (EA) and surface morphology of three types of phthalocyanine (Pc) thin film systems, i.e. copper phthalocyanine (CuPc) single layer, zinc phthalocyanine (ZnPc) single layer, and ZnPc on CuPc (CuPc/ZnPc) double layer film, treated with saturated acetone vapor were investigated. For the treated CuPc single layer film, the surface roughness slightly increased and bundles of nanorods were formed, while the EA varied little. In contrast, for the ZnPc single layer film, the relatively high solubility of ZnPc led to a considerable shift in the absorption bands as well as a large increase in the surface roughnessmore » and formation of long and wide nano-beams, indicating a part of the ZnPc molecules dissolved in acetone, which altered their molecular stacking. For the CuPc/ZnPc film, the saturated acetone vapor treatment resulted in morphological changes in mainly the upper ZnPc layer due to the significantly low solubility of the underlying CuPc layer. The treatment also broadened the EA band, which involved a combination of unchanged CuPc and changed ZnPc absorption.« less

Effects of image charges, interfacial charge discreteness, and surface roughness on the zeta potential of spherical electric double layers.

PubMed

Gan, Zecheng; Xing, Xiangjun; Xu, Zhenli

2012-07-21

We investigate the effects of image charges, interfacial charge discreteness, and surface roughness on spherical electric double layer structures in electrolyte solutions with divalent counterions in the setting of the primitive model. By using Monte Carlo simulations and the image charge method, the zeta potential profile and the integrated charge distribution function are computed for varying surface charge strengths and salt concentrations. Systematic comparisons were carried out between three distinct models for interfacial charges: (1) SURF1 with uniform surface charges, (2) SURF2 with discrete point charges on the interface, and (3) SURF3 with discrete interfacial charges and finite excluded volume. By comparing the integrated charge distribution function and the zeta potential profile, we argue that the potential at the distance of one ion diameter from the macroion surface is a suitable location to define the zeta potential. In SURF2 model, we find that image charge effects strongly enhance charge inversion for monovalent interfacial charges, and strongly suppress charge inversion for multivalent interfacial charges. For SURF3, the image charge effect becomes much smaller. Finally, with image charges in action, we find that excluded volumes (in SURF3) suppress charge inversion for monovalent interfacial charges and enhance charge inversion for multivalent interfacial charges. Overall, our results demonstrate that all these aspects, i.e., image charges, interfacial charge discreteness, their excluding volumes, have significant impacts on zeta potentials of electric double layers.

Definition of criteria for estimating alternative technologies of increasing quality of rotor shaft neck by electroerosive alloying and surface plastic deformation methods

NASA Astrophysics Data System (ADS)

Martsynkovskyy, V.; Kirik, G.; Tarelnyk, V.; Zharkov, P.; Konoplianchenko, Ie; Dovzhyk, M.

2017-08-01

There are represented the results of influence of the surface plastic deformation (SPD) methods, namely, diamond smoothing (DS) and ball-rolling surface roughness generation (BSRG) ones on the qualitative parameters (residual stresses, fatigue strength and wear resistance values) of the steel substrate surface layers formed by the electroerosive alloying (EEA) method. There are proposed the most rational methods of deformation and also the composition for electroerosive coatings providing the presence of the favorable residual compressive stresses in the surface layer, increasing fatigue strength and wear resistance values. There are stated the criteria for estimating the alternative variants of the combined technologies and choosing the most rational ones thereof.

Annealing effects on electron-beam evaporated Al 2O 3 films

NASA Astrophysics Data System (ADS)

Shuzhen, Shang; Lei, Chen; Haihong, Hou; Kui, Yi; Zhengxiu, Fan; Jianda, Shao

2005-04-01

The effects of post-deposited annealing on structure and optical properties of electron-beam evaporated Al 2O 3 single layers were investigated. The films were annealed in air for 1.5 h at different temperatures from 250 to 400 °C. The optical constants and cut-off wavelength were deduced. Microstructure of the samples was characterized by X-ray diffraction (XRD). Profile and surface roughness measurement instrument was used to determine the rms surface roughness. It was found that the cut-off wavelength shifted to short wavelength as the annealing temperature increased and the total optical loss decreased. The film structure remained amorphous even after annealing at 400 °C temperature and the samples annealed at higher temperature had the higher rms surface roughness. The decreasing total optical loss with annealing temperature was attributed to the reduction of absorption owing to oxidation of the film by annealing. Guidance to reduce the optical loss of excimer laser mirrors was given.

Wind-Tunnel Study of Scalar Transfer Phenomena for Surfaces of Block Arrays and Smooth Walls with Dry Patches

NASA Astrophysics Data System (ADS)

Chung, Juyeon; Hagishima, Aya; Ikegaya, Naoki; Tanimoto, Jun

2015-11-01

We report the result of a wind-tunnel experiment to measure the scalar transfer efficiency of three types of surfaces, wet street surfaces of cube arrays, wet smooth surfaces with dry patches, and fully wet smooth surfaces, to examine the effects of roughness topography and scalar source allocation. Scalar transfer coefficients defined by the source area {C}_{E wet} for an underlying wet street surface of dry block arrays show a convex trend against the block density λ _p. Comparison with past data, and results for wet smooth surfaces including dry patches, reveal that the positive peak of {C}_{E wet} with increasing λ _p is caused by reduced horizontal advection due to block roughness and enhanced evaporation due to a heterogeneous scalar source distribution. In contrast, scalar transfer coefficients defined by a lot-area including wet and dry areas {C}_{E lot} for smooth surfaces with dry patches indicate enhanced evaporation compared to the fully wet smooth surface (the oasis effect) for all three conditions of dry plan-area ratio up to 31 %. Relationships between the local Sherwood and Reynolds numbers derived from experimental data suggest that attenuation of {C}_{E wet} for a wet street of cube arrays against streamwise distance is weaker than for a wet smooth surface because of canopy flow around the blocks. Relevant parameters of ratio of roughness length for momentum to scalar {B}^{-1} were calculated from observational data. The result implies that {B}^{-1} possibly increases with block roughness, and decreases with the partitioning of the scalar boundary layer because of dry patches.

Effect of applied voltage on surface properties of anodised titanium in mixture of β-glycerophosphate (β-GP) and calcium acetate (CA)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chuan, Lee Te, E-mail: gd130079@siswa.uthm.edu.my; Rathi, Muhammad Fareez Mohamad, E-mail: cd110238@siswa.uthm.edu.my; Abidin, Muhamad Yusuf Zainal, E-mail: cd110221@siswa.uthm.edu.my

Anodic oxidation is a surface modification method which combines electric field driven metal and oxygen ion diffusion for formation of oxide layer on the anode surface. This method has been widely used to modify the surface morphology of biomaterial especially titanium. This study aimed to investigate the effect of applied voltage on titanium. Specifically, the titanium foil was anodised in mixture of β-glycerophosphate disodium salt pentahydrate (β-GP) and calcium acetate monohydrate (CA) with different applied voltage (50-350 V), electrolyte concentration (0.04 M β-GP + 0.4 M CA), anodising time (10minutes) and current density (50 and 70 mA.cm{sup −2}) at room temperature. Surfacemore » oxide properties of anodised titanium were characterised by digital single-lens reflex camera (DSLR camera), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). At lower applied voltage (≤150 V), surface of titanium foils were relatively smooth. With increasing applied voltage (≥250 V), the oxide layer became more porous and donut-shaped pores were formed on the surface of titanium foils. The AFM results indicated that the surface roughness of anodised titanium increases with increasing of applied voltage. The porous and rough surface is able to promote the osseointegration and reduce the suffering time of patient.« less

Performance and Surface Integrity of Ti6Al4V After Sinking EDM with Special Graphite Electrodes

NASA Astrophysics Data System (ADS)

Amorim, Fred L.; Stedile, Leandro J.; Torres, Ricardo D.; Soares, Paulo C.; Henning Laurindo, Carlos A.

2014-04-01

Titanium and its alloys have high chemical reactivity with most of the cutting tools. This makes it difficult to work with these alloys using conventional machining processes. Electrical discharge machining (EDM) emerges as an alternative technique to machining these materials. In this work, it is investigated the performance of three special grades of graphite as electrodes when ED-Machining Ti6Al4V samples under three different regimes. The main influences of electrical parameters are discussed for the samples material removal rate, volumetric relative wear and surface roughness. The samples surfaces were evaluated using SEM images, microhardness measurements, and x-ray diffraction. It was found that the best results for samples material removal rate, surface roughness, and volumetric relative wear were obtained for the graphite electrode with 10-μm particle size and negative polarity. For all samples machined by EDM and characterized by x-ray (XRD), it was identified the presence of titanium carbides. For the finish EDM regimes, the recast layer presents an increased amount of titanium carbides compared to semi-finish and rough regimes.

Fabrication of wear-resistant silicon microprobe tips for high-speed surface roughness scanning devices

NASA Astrophysics Data System (ADS)

Wasisto, Hutomo Suryo; Yu, Feng; Doering, Lutz; Völlmeke, Stefan; Brand, Uwe; Bakin, Andrey; Waag, Andreas; Peiner, Erwin

2015-05-01

Silicon microprobe tips are fabricated and integrated with piezoresistive cantilever sensors for high-speed surface roughness scanning systems. The fabrication steps of the high-aspect-ratio silicon microprobe tips were started with photolithography and wet etching of potassium hydroxide (KOH) resulting in crystal-dependent micropyramids. Subsequently, thin conformal wear-resistant layer coating of aluminum oxide (Al2O3) was demonstrated on the backside of the piezoresistive cantilever free end using atomic layer deposition (ALD) method in a binary reaction sequence with a low thermal process and precursors of trimethyl aluminum and water. The deposited Al2O3 layer had a thickness of 14 nm. The captured atomic force microscopy (AFM) image exhibits a root mean square deviation of 0.65 nm confirming the deposited Al2O3 surface quality. Furthermore, vacuum-evaporated 30-nm/200-nm-thick Au/Cr layers were patterned by lift-off and served as an etch mask for Al2O3 wet etching and in ICP cryogenic dry etching. By using SF6/O2 plasma during inductively coupled plasma (ICP) cryogenic dry etching, micropillar tips were obtained. From the preliminary friction and wear data, the developed silicon cantilever sensor has been successfully used in 100 fast measurements of 5- mm-long standard artifact surface with a speed of 15 mm/s and forces of 60-100 μN. Moreover, the results yielded by the fabricated silicon cantilever sensor are in very good agreement with those of calibrated profilometer. These tactile sensors are targeted for use in high-aspect-ratio microform metrology.

Sensitivity of Turbine-Height Wind Speeds to Parameters in Planetary Boundary-Layer and Surface-Layer Schemes in the Weather Research and Forecasting Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Ben; Qian, Yun; Berg, Larry K.

We evaluate the sensitivity of simulated turbine-height winds to 26 parameters applied in a planetary boundary layer (PBL) scheme and a surface layer scheme of the Weather Research and Forecasting (WRF) model over an area of complex terrain during the Columbia Basin Wind Energy Study. An efficient sampling algorithm and a generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of modeled turbine-height winds. The results indicate that most of the variability in the ensemble simulations is contributed by parameters related to the dissipation of the turbulence kinetic energy (TKE), Prandtl number, turbulencemore » length scales, surface roughness, and the von Kármán constant. The relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability. The parameter associated with the TKE dissipation rate is found to be the most important one, and a larger dissipation rate can produce larger hub-height winds. A larger Prandtl number results in weaker nighttime winds. Increasing surface roughness reduces the frequencies of both extremely weak and strong winds, implying a reduction in the variability of the wind speed. All of the above parameters can significantly affect the vertical profiles of wind speed, the altitude of the low-level jet and the magnitude of the wind shear strength. The wind direction is found to be modulated by the same subset of influential parameters. Remainder of abstract is in attachment.« less

3D surface topography study of the biofunctionalized nanocrystalline Ti-6Zr-4Nb/Ca-P

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jakubowicz, J., E-mail: jaroslaw.jakubowicz@put.poznan.pl; Adamek, G.; Jurczyk, M.U.

2012-08-15

In this work surface of the sintered Ti-6Zr-4Nb nanocrystalline alloy was electrochemically biofunctionalized. The porous surface was produced by anodic oxidation in 1 M H{sub 3}PO{sub 4} + 2%HF electrolyte at 10 V for 30 min. Next the calcium-phosphate (Ca-P) layer was deposited, onto the formed porous surface, using cathodic potential - 5 V kept for 60 min in 0.042 M Ca(NO{sub 3}){sub 2} + 0.025 M (NH{sub 4}){sub 2}HPO{sub 4} + 0.1 M HCl electrolyte. The deposited Ca-P layer anchored in the pores. The biofunctionalized surface was studied by XRD, SEM and EDS. In vitro tests culture of normalmore » human osteoblast (NHOst) cells showed very good cells proliferation, colonization and multilayering. Using optical profiler, roughness and hybrid 3D surface topography parameters were estimated. Correlation between surface composition, morphology, roughness and biocompatibility results was done. It has been shown by us that surface with appropriate chemical composition and topography, after combined electrochemical anodic and cathodic surface treatment, supports osteoblast adhesion and proliferation. 3D topography measurements using optical profiler play a key role in the biomaterials surface analysis. - Highlights: Black-Right-Pointing-Pointer Nanocrystalline Ti-6Zr-4Nb/Ca-P material was produced for hard tissue implant applications. Black-Right-Pointing-Pointer Calcium-phosphate results in surface biofunctionalization. Black-Right-Pointing-Pointer The biofunctionalized surface shows good in-vitro behavior.« less

Investigation of Stainless Steel Corrosion in Ultrahigh-Purity Water and Steam Systems by Surface Analytical Techniques

NASA Astrophysics Data System (ADS)

Dong, Xia; Iacocca, Ronald G.; Bustard, Bethany L.; Kemp, Craig A. J.

2010-02-01

Stainless steel pipes with different degrees of rouging and a Teflon®-coated rupture disc with severe corrosion were thoroughly investigated by combining multiple surface analytical techniques. The surface roughness and iron oxide layer thickness increase with increasing rouge severity, and the chromium oxide layer coexists with the iron oxide layer in samples with various degrees of rouging. Unlike the rouging observed for stainless steel pipes, the fast degradation of the rupture disc was caused by a crevice corrosion environment created by perforations in the protective Teflon coating. This failure analysis clearly shows the highly corrosive nature of ultrapure water used in the manufacture of pharmaceutical products, and demonstrates some of the unexpected corrosion mechanisms that can be encountered in these environments.

Surfactant-free carnauba wax dispersion and its use for layer-by-layer assembled protective surface coatings on wood

NASA Astrophysics Data System (ADS)

Lozhechnikova, Alina; Bellanger, Hervé; Michen, Benjamin; Burgert, Ingo; Österberg, Monika

2017-02-01

Protection from liquid water and UV radiation are equally important, and a sophisticated approach is needed when developing surface coatings that preserve the natural and well-appreciated aesthetic appearance of wood. In order to prevent degradation and prolong the service life of timber, a protective coating was assembled using carnauba wax particles and zinc oxide nanoparticles via layer-by-layer deposition in water. For this purpose, a facile sonication route was developed to produce aqueous wax dispersion without any surfactants or stabilizers. The suspension was stable above pH 4 due to the electrostatic repulsion between the negatively charged wax particles. The particle size could be controlled by the initial wax concentration with average particle sizes ranging from 260 to 360 nm for 1 and 10 g/L, respectively. The deposition of wax particles onto the surface of spruce wood introduced additional roughness to the wood surface at micron level, while zinc oxide provided nano roughness and UV-absorbing properties. In addition to making wood superhydrophobic, this novel multilayer coating enhanced the natural moisture buffering capability of spruce. Moreover, wood surfaces prepared in this fashion showed a significant reduction in color change after exposure to UV light. A degradation of the wax through photocatalytic activity of the ZnO particles was measured by FTIR, indicating that further studies are required to achieve long-term stability. Nevertheless, the developed coating showed a unique combination of superhydrophobicity and excellent moisture buffering ability and some UV protection, all achieved using an environmentally friendly coating process, which is beneficial to retain the natural appearance of wood and improve indoor air quality and comfort.

Secondary Instability of Stationary Crossflow Vortices in Mach 6 Boundary Layer Over a Circular Cone

NASA Technical Reports Server (NTRS)

Li, Fei; Choudhari, Meelan M.; Paredes-Gonzalez, Pedro; Duan, Lian

2015-01-01

Hypersonic boundary layer flows over a circular cone at moderate incidence can support strong crossflow instability. Due to more efficient excitation of stationary crossflow vortices by surface roughness, such boundary layer flows may transition to turbulence via rapid amplification of the high-frequency secondary instabilities of finite amplitude stationary crossflow vortices. The amplification characteristics of these secondary instabilities are investigated for crossflow vortices generated by an azimuthally periodic array of roughness elements over a 7-degree half-angle circular cone in a Mach 6 free stream. Depending on the local amplitude of the stationary crossflow mode, the most unstable secondary disturbances either originate from the second (i.e., Mack) mode instabilities of the unperturbed boundary layer or correspond to genuine secondary instabilities that reduce to stable disturbances at sufficiently small amplitudes of the stationary crossflow vortex. The predicted frequencies of dominant secondary disturbances are similar to those measured during wind tunnel experiments at Purdue University and the Technical University of Braunschweig, Germany.

Efficient organic photovoltaic cells on a single layer graphene transparent conductive electrode using MoOx as an interfacial layer.

PubMed

Du, J H; Jin, H; Zhang, Z K; Zhang, D D; Jia, S; Ma, L P; Ren, W C; Cheng, H M; Burn, P L

2017-01-07

The large surface roughness, low work function and high cost of transparent electrodes using multilayer graphene films can limit their application in organic photovoltaic (OPV) cells. Here, we develop single layer graphene (SLG) films as transparent anodes for OPV cells that contain light-absorbing layers comprised of the evaporable molecular organic semiconductor materials, zinc phthalocyanine (ZnPc)/fullerene (C60), as well as a molybdenum oxide (MoO x ) interfacial layer. In addition to an increase in the optical transmittance, the SLG anodes had a significant decrease in surface roughness compared to two and four layer graphene (TLG and FLG) anodes fabricated by multiple transfer and stacking of SLGs. Importantly, the introduction of a MoO x interfacial layer not only reduced the energy barrier between the graphene anode and the active layer, but also decreased the resistance of the SLG by nearly ten times. The OPV cells with the structure of polyethylene terephthalate/SLG/MoO x /CuI/ZnPc/C60/bathocuproine/Al were flexible, and had a power conversion efficiency of up to 0.84%, which was only 17.6% lower than the devices with an equivalent structure but prepared on commercial indium tin oxide anodes. Furthermore, the devices with the SLG anode were 50% and 86.7% higher in efficiency than the cells with the TLG and FLG anodes. These results show the potential of SLG electrodes for flexible and wearable OPV cells as well as other organic optoelectronic devices.

RF plasma based selective modification of hydrophilic regions on super hydrophobic surface

NASA Astrophysics Data System (ADS)

Lee, Jaehyun; Hwang, Sangyeon; Cho, Dae-Hyun; Hong, Jungwoo; Shin, Jennifer H.; Byun, Doyoung

2017-02-01

Selective modification and regional alterations of the surface property have gained a great deal of attention to many engineers. In this paper, we present a simple, a cost-effective, and amendable reforming method for disparate patterns of hydrophilic regions on super-hydrophobic surfaces. Uniform super-hydrophobic layer (Contact angle; CA > 150°, root mean square (RMS) roughness ∼0.28 nm) can be formed using the atmospheric radio frequency (RF) plasma on top of the selective hydrophilic (CA ∼ 70°, RMS roughness ∼0.34 nm) patterns imprinted by electrohydrodynamic (EHD) jet printing technology with polar alcohols (butyl carbitol or ethanol). The wettability of the modified surface was investigated qualitatively utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM), and wavelength scanning interferometer (WSI). Secondary ion mass spectroscopy (SIMS) analysis showed that the alcohol addiction reaction changed the types of radicals on the super-hydrophobic surface. The wettability was found to depend sensitively on chemical radicals on the surface, not on surface morphology (particle size and surface roughness). Furthermore, three different kinds of representative hydrophilic samples (polystyrene nano-particle aqueous solution, Salmonella bacteria medium, and poly(3,4-ethylenediocythiophene) ink) were tested for uniform deposition onto the desired hydrophilic regions. This simple strategy would have broad applications in various research fields that require selective deposition of target materials.

Effect of surface treatment on the corrosion properties of magnesium-based fibre metal laminate

NASA Astrophysics Data System (ADS)

Zhang, X.; Zhang, Y.; Ma, Q. Y.; Dai, Y.; Hu, F. P.; Wei, G. B.; Xu, T. C.; Zeng, Q. W.; Wang, S. Z.; Xie, W. D.

2017-02-01

The surface roughness, weight of phosphating film and wettability of magnesium alloy substrates after abrasion and phosphating treatment were investigated in this work. The interfacial bonding and corrosion properties of a magnesium-based fibre metal laminate (MgFML) were analysed. The results showed that the wettability of the magnesium alloy was greatly influenced by the surface roughness, and the rough surface possessed a larger surface energy and better wettability. The surface energy and wettability of the magnesium alloy were significantly improved by the phosphating treatment. After phosphating for 5 min, a phosphating film with a double-layer structure was formed on the magnesium substrate, and the weight of the phosphating film and the surface energy reached their maximum values. The surface energies of the phosphated substrate after abrasion with #120 and #3000 grit abrasive papers were 84.31 mJ/m2 and 83.65 mJ/m2, respectively. The wettability of the phosphated magnesium was significantly better than the abraded magnesium. The phosphated AZ31B sheet had a better corrosion resistance than the abraded AZ31B sheet within short times. The corrosion resistance of the magnesium alloy was greatly increased by being composited with glass fibre/epoxy prepregs.

NiTi shape-memory alloy oxidized in low-temperature plasma with carbon coating: Characteristic and a potential for cardiovascular applications

NASA Astrophysics Data System (ADS)

Witkowska, Justyna; Sowińska, Agnieszka; Czarnowska, Elżbieta; Płociński, Tomasz; Borowski, Tomasz; Wierzchoń, Tadeusz

2017-11-01

Surface layers currently produced on NiTi alloys do not meet all the requirements for materials intended for use in cardiology. Plasma surface treatments of titanium and its alloys under glow discharge conditions make it possible to produce surface layers, such as TiN or TiO2, which increases corrosion resistance and biocompatibility. The production of layers on NiTi alloys with the same properties, and maintaining their shape memory and superelasticity features, requires the use of low-temperature processes. At the same time, since it is known that the carbon-based layers could prevent excessive adhesion and aggregation of platelets, we examined the composite a-CNH + TiO2 type surface layer produced by means of a hybrid method combining oxidation in low-temperature plasma and Radio Frequency Chemical Vapor Deposition (RFCVD) processes. Investigations have shown that this composite layer increases the corrosion resistance of the material, and both the low degree of roughness and the chemical composition of the surface produced lead to decreased platelet adhesion and aggregation and proper endothelialization, which could extend the range of applications of NiTi shape memory alloys.

Boundary Layer Transition over Blunt Hypersonic Vehicles Including Effects of Ablation-Induced Out-Gassing

NASA Technical Reports Server (NTRS)

Li, Fei; Choudhari, Meelan; Chang, Chau-Lyan; White, Jeffery

2011-01-01

Computations are performed to study the boundary layer instability mechanisms pertaining to hypersonic flow over blunt capsules. For capsules with ablative heat shields, transition may be influenced both by out-gassing associated with surface pyrolysis and the resulting modification of surface geometry including the formation of micro-roughness. To isolate the effects of out-gassing, this paper examines the stability of canonical boundary layer flows over a smooth surface in the presence of gas injection into the boundary layer. For a slender cone, the effects of out-gassing on the predominantly second mode instability are found to be stabilizing. In contrast, for a blunt capsule flow dominated by first mode instability, out-gassing is shown to be destabilizing. Analogous destabilizing effects of outgassing are also noted for both stationary and traveling modes of crossflow instability over a blunt sphere-cone configuration at angle of attack.

Titanium bone implants with superimposed micro/nano-scale porosity and antibacterial capability

NASA Astrophysics Data System (ADS)

Necula, B. S.; Apachitei, I.; Fratila-Apachitei, L. E.; van Langelaan, E. J.; Duszczyk, J.

2013-05-01

This study aimed at producing a multifunctional layer with micro/nano-interconnected porosity and antibacterial capability on a rough macro-porous plasma sprayed titanium surface using the plasma electrolytic oxidation process. The layers were electrochemically formed in electrolytes based on calcium acetate and calcium glycerophosphate salts bearing dispersed Ag nanoparticles. They were characterized with respect to surface morphology and chemical composition using a scanning electron microscope equipped with the energy dispersive spectroscopy and back scattering detectors. Scanning electron microscopy images showed the formation of a micro/nano-scale porous layer, comprised of TiO2 bearing Ca and P species and Ag nanoparticles, following accurately the surface topography of the plasma sprayed titanium coating. The Ca/P atomic ratio was found to be close to that of bone apatite. Ag nanoparticles were incorporated on both on top and inside the porous structure of the TiO2 layer.

Synthesis of Graphene Based Membranes: Effect of Substrate Surface Properties on Monolayer Graphene Transfer.

PubMed

Kafiah, Feras; Khan, Zafarullah; Ibrahim, Ahmed; Atieh, Muataz; Laoui, Tahar

2017-01-21

In this work, we report the transfer of graphene onto eight commercial microfiltration substrates having different pore sizes and surface characteristics. Monolayer graphene grown on copper by the chemical vapor deposition (CVD) process was transferred by the pressing method over the target substrates, followed by wet etching of copper to obtain monolayer graphene/polymer membranes. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle (CA) measurements were carried out to explore the graphene layer transferability. Three factors, namely, the substrate roughness, its pore size, and its surface wetting (degree of hydrophobicity) are found to affect the conformality and coverage of the transferred graphene monolayer on the substrate surface. A good quality graphene transfer is achieved on the substrate with the following characteristics; being hydrophobic (CA > 90°), having small pore size, and low surface roughness, with a CA to RMS (root mean square) ratio higher than 2.7°/nm.

Studying physical properties of CuInS2 absorber layers grown by spin coating method on different kinds of substrates

NASA Astrophysics Data System (ADS)

Amerioun, M. H.; Ghazi, M. E.; Izadifard, M.

2018-03-01

In this work, first the CuInS2 (CIS2) layers are deposited on Aluminum and polyethylene terephthalate (PET) as flexible substrates, and on glass and soda lime glass (SLG) as rigid substrates by the sol-gel method. Then the samples are analyzed by x-ray diffractomery (XRD) and atomic force microscope (AFM) to investigate the crystal structures and surface roughness of the samples. The I-V curve measurements and Seebeck effect setup are used to measure the electrical properties of the samples. The XRD data obtained for the CIS2 layers show that all the prepared samples have a single phase with a preferred orientation that is substrate-dependent. The samples grown on the rigid substrates had higher crystallite sizes. The results obtained for the optical measurements indicate the dependence of the band gap energy on the substrate type. The measured Seebeck coefficient showed that the carriers were of p-type in all the samples. According to the AFM images, the surface roughness also varied in the CIS2 layers with different substrates. In this regard, the type of substrate could be an important parameter for the final performance of the fabricated CIS2 cells.

[Silicate coating of cemented titanium-based shafts in hip prosthetics reduces high aseptic loosening].

PubMed

Marx, R; Faramarzi, R; Jungwirth, F; Kleffner, B V; Mumme, T; Weber, M; Wirtz, D C

2009-01-01

For cemented hip prostheses, all requirements can be fulfilled by using forged Co/Cr/Mo stems. Co/Cr/Mo alloys, however, are contraindicated for allergy sufferers. For these patients, a cemented prosthesis made of titanium (alloy) would be indicated. Cemented stems from titanium (alloy), depending on the geometry of the prosthesis and its specific surface texture, however, may have loosening rates which are clinically not tolerable. In comparison to Co/Cr/Mo alloys, the greater roughness in conjunction with lesser abrasion resistance of titanium-based alloys leads to high loosening rates caused by abrasion. On the other hand, the greater surface roughness permits good mechanical retention of bone cement to the surface. Good mechanical retention enhances migration behaviour and reduces micromotions. However, there is no stable hydrolytic bond between bone cement and metallic surface; intermediate-term debonding between metal and bone cement is predictable. This debonding results in relative movements, consequently in wear particles which have their origin both from the rough metallic surface and from the PMMA cement. The roughness of the metallic surface operates as emery and with that, a rubbing wear from the PMMA. For the above reasons, a low or moderate roughness is essential for easily abradable implants such as shafts made of titanium (alloy) because low roughness provides a fail-safe running function in case of debonding. Thus, one must allow for inappropriate migration behaviour accompanied by greater micromotions due to insufficient mechanical retention in the case of low roughness. This can be accomplished by a silicate layer coating applied to the metal shaft surface via electrochemical "ECD" or physical vapour deposition "PVD". For analysis, specimens (screws for pull-out, cones for push-out tests) were sand-blasted, so that roughnesses between Ra = 0.8 microm (Rz = 4 microm) and Ra = 2.0 microm (Rz = 9 microm) were generated. The bond strengths observed in tensile tests for roughnesses of Ra = 1.7 mm were always well above 25 MPa for all periods of hydrolytic load. Therefore, the investigation shows that surfaces of moderate roughness (Ra = 1.7 microm), however coated, provide a steady retention. Cave-in and micromotions should widely be prevented. The abrasion, which is a consequence of and reason for debonding and loosening at the same time, should be avoidable if the bonding of cement on the metallic shaft is stabilised with the help of a suitable chemical bond system.

Surface studies on superhydrophobic and oleophobic polydimethylsiloxane-silica nanocomposite coating system

NASA Astrophysics Data System (ADS)

Basu, Bharathibai J.; Dinesh Kumar, V.; Anandan, C.

2012-11-01

Superhydrophobic and oleophobic polydimethylsiloxane (PDMS)-silica nanocomposite double layer coating was fabricated by applying a thin layer of low surface energy fluoroalkyl silane (FAS) as topcoat. The coatings exhibited WCA of 158-160° and stable oleophobic property with oil CA of 79°. The surface morphology was characterized by field emission scanning electron microscopy (FESEM) and surface chemical composition was determined by energy dispersive X-ray spectrometery (EDX) and X-ray photoelectron spectroscopy (XPS). FESEM images of the coatings showed micro-nano binary structure. The improved oleophobicity was attributed to the combined effect of low surface energy of FAS and roughness created by the random distribution of silica aggregates. This is a facile, cost-effective method to obtain superhydrophobic and oleophobic surfaces on larger area of various substrates.

Spectroellipsometric detection of silicon substrate damage caused by radiofrequency sputtering of niobium oxide

NASA Astrophysics Data System (ADS)

Lohner, Tivadar; Serényi, Miklós; Szilágyi, Edit; Zolnai, Zsolt; Czigány, Zsolt; Khánh, Nguyen Quoc; Petrik, Péter; Fried, Miklós

2017-11-01

Substrate surface damage induced by deposition of metal atoms by radiofrequency (rf) sputtering or ion beam sputtering onto single-crystalline silicon (c-Si) surface has been characterized earlier by electrical measurements. The question arises whether it is possible to characterize surface damage using spectroscopic ellipsometry (SE). In our experiments niobium oxide layers were deposited by rf sputtering on c-Si substrates in gas mixture of oxygen and argon. Multiple angle of incidence spectroscopic ellipsometry measurements were performed, a four-layer optical model (surface roughness layer, niobium oxide layer, native silicon oxide layer and ion implantation-amorphized silicon [i-a-Si] layer on a c-Si substrate) was created in order to evaluate the spectra. The evaluations yielded thicknesses of several nm for the i-a-Si layer. Better agreement could be achieved between the measured and the generated spectra by inserting a mixed layer (with components of c-Si and i-a-Si applying the effective medium approximation) between the silicon oxide layer and the c-Si substrate. High depth resolution Rutherford backscattering (RBS) measurements were performed to investigate the interface disorder between the deposited niobium oxide layer and the c-Si substrate. Atomic resolution cross-sectional transmission electron microscopy investigation was applied to visualize the details of the damaged subsurface region of the substrate.

Study on influence of Surface roughness of Ni-Al2O3 nano composite coating and evaluation of wear characteristics

NASA Astrophysics Data System (ADS)

Raghavendra, C. R.; Basavarajappa, S.; Sogalad, Irappa

2018-02-01

Electrodeposition is one of the most technologically feasible and economically superior techniques for producing metallic coating. The advancement in the application of nano particles has grabbed the attention in all fields of engineering. In this present study an attempt has been made on the Ni-Al2O3nano particle composite coating on aluminium substrate by electrodeposition process. The aluminium surface requires a specific pre-treatment for better adherence of coating. In light of this a thin zinc layer is coated on the aluminium substrate by electroless process. In addition to this surface roughness is an important parameter for any coating method and material. In this work Ni-Al2O3 composite coating were successfully coated by varying the process parameters such as bath temperature, current density and particle loading. The experimentation was performed using central composite design based 20 trials of experiments. The effect of process parameters and surface roughness before and after coating is analyzed on wear rate and coating thickness. The results shown a better wear resistance of Ni-Al2O3 composite electrodeposited coating compared to Ni coating. The particle loading and interaction effect of current density with temperature has greater significant effect on wear rate. The surface roughness is significantly affected the wear behaviour and thickness of coating.

Roughness Induced Transition in a Supersonic Boundary Layer

NASA Technical Reports Server (NTRS)

Balakumar, Ponnampalam; Kergerise, Michael A.

2013-01-01

Direct numerical simulation is used to investigate the transition induced by threedimensional isolated roughness elements in a supersonic boundary layer at a free stream Mach number of 3.5. Simulations are performed for two different configurations: one is a square planform roughness and the other is a diamond planform roughness. The mean-flow calculations show that the roughness induces counter rotating streamwise vortices downstream of the roughness. These vortices persist for a long distance downstream and lift the low momentum fluid from the near wall region and place it near the outer part of the boundary layer. This forms highly inflectional boundary layer profiles. These observations agree with recent experimental observations. The receptivity calculations showed that the amplitudes of the mass-flux fluctuations near the neutral point for the diamond shape roughness are the same as the amplitude of the acoustic disturbances. They are three times smaller for the square shape roughness.

Inversion of surface parameters using fast learning neural networks

NASA Technical Reports Server (NTRS)

Dawson, M. S.; Olvera, J.; Fung, A. K.; Manry, M. T.

1992-01-01

A neural network approach to the inversion of surface scattering parameters is presented. Simulated data sets based on a surface scattering model are used so that the data may be viewed as taken from a completely known randomly rough surface. The fast learning (FL) neural network and a multilayer perceptron (MLP) trained with backpropagation learning (BP network) are tested on the simulated backscattering data. The RMS error of training the FL network is found to be less than one half the error of the BP network while requiring one to two orders of magnitude less CPU time. When applied to inversion of parameters from a statistically rough surface, the FL method is successful at recovering the surface permittivity, the surface correlation length, and the RMS surface height in less time and with less error than the BP network. Further applications of the FL neural network to the inversion of parameters from backscatter measurements of an inhomogeneous layer above a half space are shown.

Surface changes of biopolymers PHB and PLLA induced by Ar+ plasma treatment and wet etching

NASA Astrophysics Data System (ADS)

Slepičková Kasálková, N.; Slepička, P.; Sajdl, P.; Švorčík, V.

2014-08-01

Polymers, especially group of biopolymers find potential application in a wide range of disciplines due to their biodegradability. In biomedical applications these materials can be used as a scaffold or matrix. In this work, the influence of the Ar+ plasma treatment and subsequent wet etching (acetone/water) on the surface properties of polymers were studied. Two biopolymers - polyhydroxybutyrate with 8% polyhydroxyvalerate (PHB) and poly-L-lactic acid (PLLA) were used in these experiments. Modified surface layers were analyzed by different methods. Surface wettability was characterized by determination of water contact angle. Changes in elemental composition of modified surfaces were performed by X-ray Photoelectron Spectroscopy (XPS). Surface morphology and roughness was examined using Atomic Force Microscopy (AFM). Gravimetry method was used to study the mass loss. It was found that the modification from both with plasma and wet etching leads to dramatic changes of surface properties (surface chemistry, morphology and roughness). Rate of changes of these features strongly depends on the modification parameters.

Disturbances to Air-Layer Skin-Friction Drag Reduction at High Reynolds Numbers

NASA Astrophysics Data System (ADS)

Dowling, David; Elbing, Brian; Makiharju, Simo; Wiggins, Andrew; Perlin, Marc; Ceccio, Steven

2009-11-01

Skin friction drag on a flat surface may be reduced by more than 80% when a layer of air separates the surface from a flowing liquid compared to when such an air layer is absent. Past large-scale experiments utilizing the US Navy's Large Cavitation Channel and a flat-plate test model 3 m wide and 12.9 m long have demonstrated air layer drag reduction (ALDR) on both smooth and rough surfaces at water flow speeds sufficient to reach downstream-distance-based Reynolds numbers exceeding 100 million. For these experiments, the incoming flow conditions, surface orientation, air injection geometry, and buoyancy forces all favored air layer formation. The results presented here extend this prior work to include the effects that vortex generators and free stream flow unsteadiness have on ALDR to assess its robustness for application to ocean-going ships. Measurements include skin friction, static pressure, airflow rate, video of the flow field downstream of the injector, and profiles of the flowing air-water mixture when the injected air forms bubbles, when it is in transition to an air layer, and when the air layer is fully formed. From these, and the prior measurements, ALDR's viability for full-scale applications is assessed.

Stable Stratification Effects on Flow and Pollutant Dispersion in Boundary Layers Entering a Generic Urban Environment

NASA Astrophysics Data System (ADS)

Tomas, J. M.; Pourquie, M. J. B. M.; Jonker, H. J. J.

2016-05-01

Large-eddy simulations (LES) are used to investigate the effect of stable stratification on rural-to-urban roughness transitions. Smooth-wall turbulent boundary layers are subjected to a generic urban roughness consisting of cubes in an in-line arrangement. Two line sources of pollutant are added to investigate the effect on pollutant dispersion. Firstly, the LES method is validated with data from wind-tunnel experiments on fully-developed flow over cubical roughness. Good agreement is found for the vertical profiles of the mean streamwise velocity component and mean Reynolds stress. Subsequently, roughness transition simulations are done for both neutral and stable conditions. Results are compared with fully-developed simulations with conventional double-periodic boundary conditions. In stable conditions, at the end of the domain the streamwise velocity component has not yet reached the fully-developed state even though the surface forces are nearly constant. Moreover, the internal boundary layer is shallower than in the neutral case. Furthermore, an investigation of the turbulence kinetic energy budget shows that the buoyancy destruction term is reduced in the internal boundary layer, above which it is equal to the undisturbed (smooth wall) value. In addition, in stable conditions pollutants emitted above the urban canopy enter the canopy farther downstream due to decreased vertical mixing. Pollutants emitted below the top of the urban canopy are 85 % higher in concentration in stable conditions mostly due to decreased advection. If this is taken into account concentrations remain 17 % greater in stable conditions due to less rapid internal boundary-layer growth. Finally, it is concluded that in the first seven streets the vertical advective pollutant flux is significant, in contrast to the fully-developed case.

Growth evolution of AlN films on silicon (111) substrates by pulsed laser deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Haiyan; Wang, Wenliang; Yang, Weijia

2015-05-14

AlN films with various thicknesses have been grown on Si(111) substrates by pulsed laser deposition (PLD). The surface morphology and structural property of the as-grown AlN films have been investigated carefully to comprehensively explore the epitaxial behavior. The ∼2 nm-thick AlN film initially grown on Si substrate exhibits an atomically flat surface with a root-mean-square surface roughness of 0.23 nm. As the thickness increases, AlN grains gradually grow larger, causing a relatively rough surface. The surface morphology of ∼120 nm-thick AlN film indicates that AlN islands coalesce together and eventually form AlN layers. The decreasing growth rate from 240 to 180 nm/h is amore » direct evidence that the growth mode of AlN films grown on Si substrates by PLD changes from the islands growth to the layer growth. The evolution of AlN films throughout the growth is studied deeply, and its corresponding growth mechanism is hence proposed. These results are instructional for the growth of high-quality nitride films on Si substrates by PLD, and of great interest for the fabrication of AlN-based devices.« less

Novel approach for beacon formation through simulated turbulence: initial lab-test results

NASA Astrophysics Data System (ADS)

Khizhnyak, A.; Markov, V.; Tomov, I.; Wu, F.

2010-02-01

In this paper we report the results of the analysis and experimental modeling of the target-in-the-loop (TIL) approach that is used to form a localized beacon for a laser beam propagating through turbulent atmosphere. The analogy between the TIL system and the laser cavity has been used here to simulate the process shaping the laser beacon on a remote image-resolved target with rough surface. The TIL breadboard was integrated and used for laboratory modeling of the proposed approach. This breadboard allowed to simulate the TIL arrangement with a rough-surface target and laser beam propagation through the turbulent atmospheric layer. Here we present the initial results of the performed studies.

Biocompatibility of modified ultra-high-molecular-weight polyethylene

NASA Astrophysics Data System (ADS)

Novotná, Z.; Lacmanová, V.; Rimpelová, S.; Juřik, P.; Polívková, M.; Å vorčik, V.

2016-09-01

Ultra-high-molecular-weight polyethylene (UHMWPE, PE) is a synthetic polymer used for biomedical applications because of its high impact resistance, ductility and stability in contact with physiological fluids. Therefore this material is being used in human orthopedic implants such as total joint replacements. Surface modification of this material relates to changes of its surface hydrophilicity, energy, microstructure, roughness, and morphology, all influencing its biological response. In our recent work, PE was treated by an Ar+ plasma discharge and then grafted with biologically active polyethylene glycol in order to enhance adhesion and proliferation of mouse fibroblast (L929). The surface properties of pristine PE and its grafted counterparts were studied by goniometry (surface wettability). Furthermore, Atomic Force Microscopy was used to determine the surface morphology and roughness. The biological response of the L929 cell lines seeded on untreated and plasma treated PE matrices was quantified in terms of the cell adhesion, density, and metabolic activity. Plasma treatment leads to the ablation of the polymer surface layers. Plasma treatment and subsequent poly(ethylene glycol) grafting lead to dramatic changes in the polymer surface morphology and roughness. Biological tests, performed in vitro, show increased adhesion and proliferation of cells on modified polymers. Grafting with poly(ethylene glycol) increases cell proliferation compared to plasma treatment.

Surface properties of multilayered, acrylic resin artificial teeth after immersion in staining beverages

PubMed Central

NEPPELENBROEK, Karin Hermana; KUROISHI, Eduardo; HOTTA, Juliana; MARQUES, Vinicius Rizzo; MOFFA, Eduardo Buozi; SOARES, Simone; URBAN, Vanessa Migliorini

2015-01-01

Objective To evaluate the effect of staining beverages (coffee, orange juice, and red wine) on the Vickers hardness and surface roughness of the base (BL) and enamel (EL) layers of improved artificial teeth (Vivodent and Trilux). Material and Methods Specimens (n=8) were stored in distilled water at 37°C for 24 h and then submitted to the tests. Afterwards, specimens were immersed in one of the staining solutions or distilled water (control) at 37°C, and the tests were also performed after 15 and 30 days of immersion. Data were analyzed using 3-way ANOVA and Tukey’s test (α=0.05). Results Vivodent teeth exhibited a continuous decrease (p<0.0005) in hardness of both layers for up to 30 days of immersion in all solutions. For Trilux teeth, similar results were found for the EL (p<0.004), and the BL showed a decrease in hardness after 15 days of immersion (p<0.01). At the end of 30 days, this reduction was not observed for coffee and water (p>0.15), but red wine and orange juice continuously reduced hardness values (p<0.0004). Red wine caused the most significant hardness changes, followed by orange juice, coffee, and water (p<0.006). No significant differences in roughness were observed for both layers of the teeth during the immersion period, despite the beverage (p>0.06). Conclusions Hardness of the two brands of acrylic teeth was reduced by all staining beverages, mainly for red wine. Roughness of both layers of the teeth was not affected by long-term immersion in the beverages. PMID:26398509

Fabrication of silicon-on-diamond substrate with an ultrathin SiO2 bonding layer

NASA Astrophysics Data System (ADS)

Nagata, Masahiro; Shirahama, Ryouya; Duangchan, Sethavut; Baba, Akiyoshi

2018-06-01

We proposed and demonstrated a sputter etching method to prepare both a flat surface (root-mean-square surface roughness of approximately 0.2–0.3 nm) and an ultrathin SiO2 bonding layer at an accuracy of approximately 5 nm in thickness to fabricate a silicon-on-diamond substrate (SOD). We also investigated a plasma activation method on a SiO2 surface using various gases. We found that O2 plasma activation is more suitable for the bonding between SiO2 and Si than N2 or Ar plasma activation. We speculate that the concentration of hydroxyl groups on the SiO2 surface was increased by O2 plasma activation. We fabricated the SOD substrate with an ultrathin (15 nm in thickness) SiO2 bonding layer using the sputter etching and O2 plasma activation methods.

Understanding the barriers to crystal growth: dynamical simulation of the dissolution and growth of urea from aqueous solution.

PubMed

Piana, Stefano; Gale, Julian D

2005-02-16

Both the dissolution and growth of a molecular crystalline material, urea, has been studied using dynamical atomistic simulation. The kinetic steps of dissolution and growth are clearly identified, and the activation energies for each possible step are calculated. Our molecular dynamics simulations indicate that crystal growth on the [001] face is characterized by a nucleation and growth mechanism. Nucleation on the [001] urea crystal face is predicted to occur at a very high rate, followed by rapid propagation of the steps. The rate-limiting step for crystallization is actually found to be the removal of surface defects, rather than the initial formation of the next surface layer. Through kinetic Monte Carlo modeling of the surface growth, it is found that this crystal face evolves via a rough surface topography, rather than a clean layer-by-layer mechanism.

Structure determination of a multilayer with an island-like overlayer using hard x-ray photoelectron spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isomura, N., E-mail: isomura@mosk.tytlabs.co.jp; Kataoka, K.; Horibuchi, K.

We use hard X-ray photoelectron spectroscopy (HAXPES) to obtain the surface structure of a multilayer Au/SiO{sub 2}/Si substrate sample with an island-like overlayer. Photoelectron intensities are measured as a function of incident photon energy (PE) and take-off angle (TOA, measured from the sample surface). The Au layer coverage and Au and SiO{sub 2} layer thicknesses are obtained by the PE dependence, and are used for the following TOA analysis. The Au island lateral width in the cross section is obtained by the TOA dependence, including information about surface roughness, in consideration of the island shadowing at small TOAs. In bothmore » cases, curve-fitting analysis is conducted. The surface structure, which consists of layer thicknesses, overlayer coverage and island width, is determined nondestructively by a combination of PE and TOA dependent HAXPES measurements.« less

High frequency acoustic propagation under variable sea surfaces

NASA Astrophysics Data System (ADS)

Senne, Joseph

This dissertation examines the effects of rough sea surfaces and sub-surface bubbles on high frequency acoustic transmissions. Owing to the strong attenuation of electromagnetic waves in seawater, acoustic waves are used in the underwater realm much in the same way that electromagnetic waves are used in the atmosphere. The transmission and reception of acoustic waves in the underwater environment is important for a variety of fields including navigation, ocean observation, and real-time communications. Rough sea surfaces and sub-surface bubbles alter the acoustic signals that are received not only in the near-surface water column, but also at depth. This dissertation demonstrates that surface roughness and sub-surface bubbles notably affect acoustic transmissions with frequency ranges typical of underwater communications systems (10-50 kHz). The influence of rough surfaces on acoustic transmissions is determined by modeling forward propagation subject to sea surface dynamics that vary with time scales of less than a second to tens of seconds. A time-evolving rough sea surface model is combined with a rough surface formulation of a parabolic equation model for predicting time-varying acoustic fields. Linear surface waves are generated from surface wave spectra, and evolved in time using a Runge-Kutta integration technique. This evolving, range-dependent surface information is combined with other environmental parameters and fed into the acoustic model, giving an approximation of the time-varying acoustic field. The wide-angle parabolic equation model manages the rough sea surfaces by molding them into the boundary conditions for calculations of the near-surface acoustic field. The influence of sub-surface bubbles on acoustic transmissions is determined by modeling the population of bubbles near the surface and using those populations to approximate the effective changes in sound speed and attenuation. Both range-dependent and range-independent bubble models are considered, with the range-dependent model varying over the same time scales as the sea surface model and the range-independent model invariant over time. The bubble-induced sound speed and attenuation fluctuations are read in by the parabolic equation model, which allows for the effects of surface roughness and sub-surface bubbles to be computed separately or together. These merged acoustic models are validated using concurrently-collected acoustic and environmental information, including surface wave spectra. Data to model comparisons demonstrate that the models are able to approximate the ensemble-averaged acoustic intensity at ranges of at least a kilometer for acoustic signals of 10-20 kHz. The rough surface model is shown to capture variations due to surface fluctuations occurring over time scales of less than a second to tens of seconds. The separate bubble models demonstrate the abilities to account for the intermittency of bubble plumes and to determine overall effect of bubbly layers, respectively. The models are shown to capture variations in the acoustic field occurring over time scales of less than a second to tens of seconds. Comparisons against data demonstrate the ability of the model to track acoustic transmissions under evolving sea surfaces. The effects of the evolving bubble field are demonstrated through the use of idealized test cases. For frequency ranges important to communications, surface roughness is shown to have the more dominant effect, with bubbles having an ancillary effect.

Enabling High Performance Instruments for UV Astronomy and Space Exploration with ALD

NASA Technical Reports Server (NTRS)

Greer, F.; Hoenk, M. E.; Jones, T. J.; Jacquot, B. C.; Monacos, S.; Nikzad, S.; Hamden, E.; Schiminovich, D.

2011-01-01

Benefits of Atomic Layer Deposition (ALD) for UV instruments and application are: (1) Ultrathin, highly conformal, and uniform films over arbitrarily large surface area (2) High quality films (density, roughness, conductivity, etc.) (3) Angstrom level control of stoichiometry, interfaces, and surface properties (3a) Multilayer nanolaminates/nanocomposites (3b) Low temperature surface engineering UV flight applications enabled by ALD. (1) Anti -reflective coatings/Mirrors/Filters/Optics for UV/Vis/NIR Detectors (2) Surface Passivation for III -N detectors

Engineered biomimicry: polymeric replication of surface features found on insects

NASA Astrophysics Data System (ADS)

Pulsifer, Drew P.; Lakhtakia, Akhlesh; Martín-Palma, Raúl J.; Pantano, Carlo G.

2011-04-01

By combining the modified conformal-evaporated-film-by-rotation (M-CEFR) technique with nickel electroforming, we have produced master negatives of nonplanar biotemplates. An approximately 250-nm-thick conformal coating of nanocrystaline nickel is deposited on a surface structure of interest found in class Insecta, and the coating is then reinforced with a roughly 60-μm-thick structural layer of nickel by electroforming. This structural layer endows the M-CEFR coating with the mechanical robustness necessary for casting or stamping multiple polymer replicas of the biotemplate. We have made master negatives of blowfly corneas, beetle elytrons, and butterfly wings.

Profilometry of thin films on rough substrates by Raman spectroscopy

PubMed Central

Ledinský, Martin; Paviet-Salomon, Bertrand; Vetushka, Aliaksei; Geissbühler, Jonas; Tomasi, Andrea; Despeisse, Matthieu; De Wolf , Stefaan; Ballif , Christophe; Fejfar, Antonín

2016-01-01

Thin, light-absorbing films attenuate the Raman signal of underlying substrates. In this article, we exploit this phenomenon to develop a contactless thickness profiling method for thin films deposited on rough substrates. We demonstrate this technique by probing profiles of thin amorphous silicon stripes deposited on rough crystalline silicon surfaces, which is a structure exploited in high-efficiency silicon heterojunction solar cells. Our spatially-resolved Raman measurements enable the thickness mapping of amorphous silicon over the whole active area of test solar cells with very high precision; the thickness detection limit is well below 1 nm and the spatial resolution is down to 500 nm, limited only by the optical resolution. We also discuss the wider applicability of this technique for the characterization of thin layers prepared on Raman/photoluminescence-active substrates, as well as its use for single-layer counting in multilayer 2D materials such as graphene, MoS2 and WS2. PMID:27922033

Most-Critical Transient Disturbances in an Incompressible Flat-Plate Boundary Layer

NASA Astrophysics Data System (ADS)

Monschke, Jason; White, Edward

2015-11-01

Transient growth is a linear disturbance growth mechanism that plays a key role in roughness-induced boundary-layer transition. It occurs when superposed stable, non-orthogonal continuous spectrum modes experience algebraic disturbance growth followed by exponential decay. Algebraic disturbance growth can modify the basic state making it susceptible to secondary instabilities rapidly leading to transition. Optimal disturbance theory was developed to model the most-dangerous disturbances. However, evidence suggests roughness-induced transient growth is sub-optimal yet leads to transition earlier than optimal theory suggests. This research computes initial disturbances most unstable to secondary instabilities to further develop the applicability of transient growth theory to surface roughness. The main approach is using nonlinear adjoint optimization with solutions of the parabolized Navier-Stokes and BiGlobal stability equations. Two objective functions were considered: disturbance kinetic energy growth and sinuous instability growth rate. The first objective function was used as validation of the optimization method. Counter-rotating streamwise vortices located low in the boundary layer maximize the sinuous instability growth rate. The authors would like to acknowledge NASA and the AFOSR for funding this work through AFOSR Grant FA9550-09-1-0341.

Laminar-Turbulent Transition Behind Discrete Roughness Elements in a High-Speed Boundary Layer

NASA Technical Reports Server (NTRS)

Choudhari, Meelan M.; Li, Fei; Wu, Minwei; Chang, Chau-Lyan; Edwards, Jack R., Jr.; Kegerise, Michael; King, Rudolph

2010-01-01

Computations are performed to study the flow past an isolated roughness element in a Mach 3.5, laminar, flat plate boundary layer. To determine the effects of the roughness element on the location of laminar-turbulent transition inside the boundary layer, the instability characteristics of the stationary wake behind the roughness element are investigated over a range of roughness heights. The wake flow adjacent to the spanwise plane of symmetry is characterized by a narrow region of increased boundary layer thickness. Beyond the near wake region, the centerline streak is surrounded by a pair of high-speed streaks with reduced boundary layer thickness and a secondary, outer pair of lower-speed streaks. Similar to the spanwise periodic pattern of streaks behind an array of regularly spaced roughness elements, the above wake structure persists over large distances and can sustain strong enough convective instabilities to cause an earlier onset of transition when the roughness height is sufficiently large. Time accurate computations are performed to clarify additional issues such as the role of the nearfield of the roughness element during the generation of streak instabilities, as well as to reveal selected details of their nonlinear evolution. Effects of roughness element shape on the streak amplitudes and the interactions between multiple roughness elements aligned along the flow direction are also investigated.

Plasma-assisted molecular beam epitaxy of ZnO on in-situ grown GaN/4H-SiC buffer layers

NASA Astrophysics Data System (ADS)

Adolph, David; Tingberg, Tobias; Andersson, Thorvald; Ive, Tommy

2015-04-01

Plasma-assisted molecular beam epitaxy (MBE) was used to grow ZnO (0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 440°C-445°C and an O2 flow rate of 2.0-2.5 sccm, we obtained ZnO layers with smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm shown by AFM. The FWHM for X-ray rocking curves recorded across the ZnO(0002) and ZnO(10bar 15) reflections were 200 and 950 arcsec, respectively. These values showed that the mosaicity (tilt and twist) of the ZnO film was comparable to corresponding values of the underlying GaN buffer. It was found that a substrate temperature > 450°C and a high Zn-flux always resulted in a rough ZnO surface morphology. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82.3% and 73.0%, respectively and the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements showed that the layers were intrinsically n-type with an electron concentration of 1019 cm-3 and a Hall mobility of 50 cm2·V-1·s-1.

Development of asymmetric stent for treatment of eccentric plaque.

PubMed

Syaifudin, Achmad; Takeda, Ryo; Sasaki, Katsuhiko

2018-01-01

The selection of stent and balloon type is decisive in the stenting process. In the treatment of an eccentric plaque obstruction, a symmetric expansion from stent dilatation generates nonuniform stress distribution, which may aggravate fibrous cap prone to rupture. This paper developed a new stent design to treat eccentric plaque using structural transient dynamic analysis in ANSYS. A non-symmetric structural geometry of stent is generated to obtain reasonable stress distribution safe for the arterial layer surrounding the stent. To derive the novel structural geometry, a Sinusoidal stent type is modified by varying struts length and width, adding bridges, and varying curvature width of struts. An end ring of stent struts was also modified to eliminate dogboning phenomenon and to reduce the Ectropion angle. Two balloon types were used to deploy the stent, an ordinary cylindrical and offset balloon. Positive modification results were used to construct the final non-symmetric stent design, called an Asymmetric stent. Analyses of the deformation characteristics, changes in surface roughness and induced stresses within intact arterial layer were subsequently examined. Interaction between the stent and vessel wall was implemented by means of changes in surface roughness and stress distribution analyses. The Palmaz and the Sinusoidal stent were used for a comparative study. This study indicated that the Asymmetric stent types reduced the central radial recoiling and the dogboning phenomenon. In terms of changes in surface roughness and induced stresses, the Asymmetric stent has a comparable effect with that of the Sinusoidal stent. In addition, it could enhance the distribution of surface roughening as expanded by an offset balloon.

Boundary-Layer Transition on a Group of Blunt Nose Shapes at a Mach Number of 2.20

NASA Technical Reports Server (NTRS)

Jackson, Mary W.; Czarnecki, K. R.

1961-01-01

An investigation has been made to study boundary-layer transition on six axisymmetrical blunt bodies of revolution. Model shapes were selected with respect to the degree of favorable pressure gradient over the model surface. Tests were conducted at a Mach number of 2.20 and over a range of free-stream Reynolds number per foot of about 1.4 x 10(exp 6) to 6.5 x 10(exp 6). The tests were made at an angle of attack of 0 deg. with zero heat transfer. For the hemisphere, the flow remained essentially laminar over the model surface length for the entire pressure range of the tests. For a strong favorable pressure gradient followed by any weak favorable, neutral, or adverse gradient, the tendency was for transition to occur at or immediately behind the shoulder. A single strip of three-dimensional roughness in the region of strong favorable pressure gradient did not fix transition on the models at the roughness location except at the maximum test pressures, whereas a second roughness strip added in a region of neutral or adverse pressure gradient did fix transition. Experimental pressure coefficients agreed closely with modified Newtonian theory except in the shoulder region.

Experimental- Analitical Procedure Of Definition Of Thermal Fluxes On The Head Fairing Of Launch Vehicles

NASA Astrophysics Data System (ADS)

Yurchenko, I.; Karakotin, I.; Kudinov, A.

2011-05-01

Minimization of head fairing heat protection shield weight during spacecraft injecting in atmosphere dense layers is a complicated task. The identification of heat transfer coefficient on heat protection shield surface during injection can be considered as a primary task to be solved with certain accuracy in order to minimize heat shield weight as well as meet reliability requirements. The height of the roughness around sound point on the head fairing spherical nose tip has a great influence on the heat transfer coefficient calculation. As it has found out during flight tests the height of the roughness makes possible to create boundary layer transition criterion on the head fairing in flight. Therefore the second task is an assessment how height of the roughness influences on the total incoming heat flux to the head fairing. And finally the third task is associated with correct implementation of the first task results, as there are changing boundary conditions during a flight such as bubbles within heat shield surface paint and thermal protection ablation for instance. In the article we have considered results of flight tests carried out using launch vehicles which allowed us to measure heat fluxes in flight and to estimate dispersions of heat transfer coefficient. The experimental-analytical procedure of defining heat fluxes on the LV head fairings has been presented. The procedure includes: - calculation of general-purpose dimensionless heat transfer coefficient - Nusselt number Nueff - based on the proposed effective temperature Teff method. The method allows calculate the Nusselt number values for cylindrical surfaces as well as dispersions of heat transfer coefficient; - universal criterion of turbulent-laminar transition for blunted head fairings - Reynolds number Reek = [ρеUеk/μе]TR = const , which gives the best correlation of all dates of flight experiment carried out per Reda procedure to define turbulent-laminar transition in boundary layer. The criterion allows defining time margins when turbulent flux on space head surfaces exists. It was defined that in conditions when high background disturbances of free stream flux while main LV engines operating join with integrated roughness influence the critical value of Reynolds number is an order-diminished value compared to values obtained in wind tunnels and in free flight. Influence of minimization of height of surface roughness near sound point on head fairing nose has been estimated. It has been found that the criterion of turbulent-laminar transition for smooth head fairings elements - Reynolds number - reaches the limit value which is equal to 200. This value is obtained from momentum thickness Reynolds number when roughness height is close to zero. So the turbulent- laminar flux transition occurs earlier with decreased duration of effect of high turbulent heat fluxes to the heat shield. This will allow decreasing head shield thickness up to 30%

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pecheva, E.; Fingarova, D.; Pramatarova, L.

Polycrystalline silicon (poly-Si) layers were functionalized through the growth of biomimetic hydroxyapatite (HA) on their surface. HA is the mineral component of bones and teeth and thus possesses excellent bioactivity and biocompatibility. MG-63 osteoblast-like cells were cultured on both HA-coated and un-coated poly-Si surfaces for 1, 3, 5 and 7 days and toxicity, proliferation and cell morphology were investigated. The results revealed that the poly-Si layers were bioactive and compatible with the osteoblast-like cells. Nevertheless, the HA coating improved the cell interactions with the poly-Si surfaces based on the cell affinity to the specific chemical composition of the bone-like HAmore » and/or to the higher HA roughness.« less

An investigation of green iridescence on the mollusc Patella granatina

NASA Astrophysics Data System (ADS)

Brink, D. J.; van der Berg, N. G.

2005-01-01

In this paper we investigate the relatively rare phenomenon of iridescence on the outer surface of seashells (not the well known pearly inner surfaces). Using reflection spectroscopy and scanning electron microscopy we show that rows of iridescent green spots on the mollusc Patella granatina are caused by a thin-film stack buried about 100 µm below the rough outer surface of the shell. The high-density layers in the stack seem to be made of crystalline aragonite, but according to Raman spectroscopy and ellipsometry measurements the low-density layers as well as the bulk of the shell wall are a mixture of porous aragonite and organic materials such as carotenoids.

Polycrystalline Silicon: a Biocompatibility Assay

NASA Astrophysics Data System (ADS)

Pecheva, E.; Laquerriere, P.; Bouthors, Sylvie; Fingarova, D.; Pramatarova, L.; Hikov, T.; Dimova-Malinovska, D.; Montgomery, P.

2010-01-01

Polycrystalline silicon (poly-Si) layers were functionalized through the growth of biomimetic hydroxyapatite (HA) on their surface. HA is the mineral component of bones and teeth and thus possesses excellent bioactivity and biocompatibility. MG-63 osteoblast-like cells were cultured on both HA-coated and un-coated poly-Si surfaces for 1, 3, 5 and 7 days and toxicity, proliferation and cell morphology were investigated. The results revealed that the poly-Si layers were bioactive and compatible with the osteoblast-like cells. Nevertheless, the HA coating improved the cell interactions with the poly-Si surfaces based on the cell affinity to the specific chemical composition of the bone-like HA and/or to the higher HA roughness.

Fractional-dimensional Child-Langmuir law for a rough cathode

NASA Astrophysics Data System (ADS)

Zubair, M.; Ang, L. K.

2016-07-01

This work presents a self-consistent model of space charge limited current transport in a gap combined of free-space and fractional-dimensional space (Fα), where α is the fractional dimension in the range 0 < α ≤ 1. In this approach, a closed-form fractional-dimensional generalization of Child-Langmuir (CL) law is derived in classical regime which is then used to model the effect of cathode surface roughness in a vacuum diode by replacing the rough cathode with a smooth cathode placed in a layer of effective fractional-dimensional space. Smooth transition of CL law from the fractional-dimensional to integer-dimensional space is also demonstrated. The model has been validated by comparing results with an experiment.

Comparing Experiment and Computation of Hypersonic Laminar Boundary Layers with Isolated Roughness

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Iyer, Prahladh S.; Mahesh, Krishnan; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Johansen, Craig T.

2014-01-01

Streamwise velocity profile behavior in a hypersonic laminar boundary layer in the presence of an isolated roughness element is presented for an edge Mach number of 8.2. Two different roughness element types are considered: a 2-mm tall, 4-mm diameter cylinder, and a 2-mm radius hemisphere. Measurements of the streamwise velocity behavior using nitric oxide (NO) planar laser-induced fluorescence (PLIF) molecular tagging velocimetry (MTV) have been performed on a 20-degree wedge model. The top surface of this model acts as a flat-plate and is oriented at 5 degrees with respect to the freestream flow. Computations using direct numerical simulation (DNS) of these flows have been performed and are compared to the measured velocity profiles. Particular attention is given to the characteristics of velocity profiles immediately upstream and downstream of the roughness elements. In these regions, the streamwise flow can experience strong deceleration or acceleration. An analysis in which experimentally measured MTV profile displacements are compared with DNS particle displacements is performed to determine if the assumption of constant velocity over the duration of the MTV measurement is valid. This assumption is typically made when reporting MTV-measured velocity profiles, and may result in significant errors when comparing MTV measurements to computations in regions with strong deceleration or acceleration. The DNS computations with the cylindrical roughness element presented in this paper were performed with and without air injection from a rectangular slot upstream of the cylinder. This was done to determine the extent to which gas seeding in the MTV measurements perturbs the boundary layer flowfield.

Heat Transfer Measurements on Surfaces with Natural Ice Castings and Modeled Roughness

NASA Technical Reports Server (NTRS)

Breuer, Kenneth S.; Torres, Benjamin E.; Orr, D. J.; Hansman, R. John

1997-01-01

An experimental method is described to measure and compare the convective heat transfer coefficient of natural and simulated ice accretion roughness and to provide a rational means for determining accretion-related enhanced heat transfer coefficients. The natural ice accretion roughness was a sample casting made from accretions at the NASA Lewis Icing Research Tunnel (IRT). One of these castings was modeled using a Spectral Estimation Technique (SET) to produce three roughness elements patterns that simulate the actual accretion. All four samples were tested in a flat-plate boundary layer at angle of attack in a "dry" wind tunnel test. The convective heat transfer coefficient was measured using infrared thermography. It is shown that, dispite some problems in the current data set, the method does show considerable promise in determining roughness-induced heat transfer coefficients, and that, in addition to the roughness height and spacing in the flow direction, the concentration and spacing of elements in the spanwise direction are important parameters.

Polishability of thin electrolytic and electroless NiP layers

NASA Astrophysics Data System (ADS)

Kinast, Jan; Beier, Matthias; Gebhardt, Andreas; Risse, Stefan; Tünnermann, Andreas

2015-10-01

Ultra-precise metal optics are key components of sophisticated scientific instrumentation in astronomy and space applications, covering a wide spectral range. Especially for applications in the visible or ultra-violet spectral ranges, a low roughness of the optics is required. Therefore, a polishable surface is necessary. State of the art is an amorphous nickel-phosphorus (NiP) layer, which enables several polishing techniques achieving a roughness of <1 nm RMS. Typically, these layers are approximately 30 μm to 60 μm thick. Deposited on Al6061, the bimetallic effect leads to a restricted operational temperature, caused by different coefficients of thermal expansion of Al6061 and NiP. Thinner NiP layers reduce the bimetallic effect. Hence, the possible operating temperature range. A deterministic shape correction via Magnetorheological Finishing of the substrate Al6061 leads to low shape deviations prior to the NiP deposition. This allows for depositing thin NiP-layers, which are polishable via a chemical mechanical polishing technique aiming at ultra-precise metal optics. The present article shows deposition processes and polishability of electroless and electrolytic NiP layers with thicknesses between 1 μm and 10 μm.

Spatial Evolution of Resonant Harmonic Mode Triads in a Blasius Boundary Layer

NASA Technical Reports Server (NTRS)

Davila, Jose B.; King, Rudolph A.

2007-01-01

Blasius boundary layer evolution is studies by means of bicoherence calculations. The layer is acoustically excited at the T-S frequency to provide a controlled transition. Measurements are made using a smooth surface as well as various roughness patterns. The bicoherence calculations are used to determine the extent to which frequency resonant velocity fluctuation waves can participate in energy exchange. The emphasis is on downstream variation of the individual interactions among harmonic modes. A limited picture of the role of quadratic wave interactions is revealed.

Design and performance of the University of Michigan 6.6-inch hypersonic wind tunnel

NASA Technical Reports Server (NTRS)

Amick, J. L.

1975-01-01

The tunnel described has several design features intended to maintain laminar flow in the boundary layer of its nozzle. Measurements show that transition to turbulence in the nozzle wall boundary layer begins at the throat and is sensitive to surface roughness, heat transfer rate, and longitudinal radius of curvature. The observed dependence of transition on heat transfer rate is the reverse of that predicted by stability theory for infinitesimal disturbances. Tests include boundary layer surveys of a contoured nozzle and a conical nozzle with four interchangeable throats.

Some considerations in the evaluation of Seasat-A scatterometer /SASS/ measurements

NASA Technical Reports Server (NTRS)

Halberstam, I.

1980-01-01

A study is presented of the geophysical algorithms relating the Seasat-A scatterometer (SASS) backscatter measurements with a wind parameter. Although these measurements are closely related to surface features, an identification with surface layer parameters such as friction velocity or the roughness length is difficult. It is shown how surface truth in the form of wind speeds and coincident stability can be used to derive friction velocity or the equivalent neutral wind at an arbitrary height; it is also shown that the derived friction velocity values are sensitive to contested formulations relating friction velocity to the roughness length, while the derived values of the equivalent neutral wind are not. Examples of geophysical verification are demonstrated using values obtained from the Gulf of Alaska Seasat Experiment; these results show very little sensitivity to the type of wind parameter employed, suggesting that this insensitivity is mainly due to a large scatter in the SASS and surface truth data.

A semiempirical model for interpreting microwave emission from semiarid land surfaces as seen from space

NASA Technical Reports Server (NTRS)

Kerr, Yann H.; Njoku, Eni G.

1990-01-01

A radiative-transfer model for simulating microwave brightness temperatures over land surfaces is described. The model takes into account sensor viewing conditions (spacecraft altitude, viewing angle, frequency, and polarization) and atmospheric parameters over a soil surface characterized by its moisture, roughness, and temperature and covered with a layer of vegetation characterized by its temperature, water content, single scattering albedo, structure, and percent coverage. In order to reduce the influence of atmospheric and surface temperature effects, the brightness temperatures are expressed as polarization ratios that depend primarily on the soil moisture and roughness, canopy water content, and percentage of cover. The sensitivity of the polarization ratio to these parameters is investigated. Simulation of the temporal evolution of the microwave signal over semiarid areas in the African Sahel is presented and compared to actual satellite data from the SMMR instrument on Nimbus-7.

Effect of Blade Roughness on Transition and Wind Turbine Performance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ehrmann, Robert S.; White, E. B.

The real-world effect of accumulated surface roughness on wind-turbine power production is not well understood. To isolate specific blade roughness features and test their effect, field measurements of turbine-blade roughness were made and simulated on a NACA 633-418 airfoil in a wind tunnel. Insect roughness, paint chips, and erosion were characterized then manufactured. In the tests, these roughness configurations were recreated as distributed roughness, a forward-facing step, and an eroded leading edge. Distributed roughness was tested in three heights and five densities. Chord Reynolds number was varied between 0:8 to 4:8 × 10 6. Measurements included lift, drag, pitching moment,more » and boundary-layer transition location. Results indicate minimal effect from paint-chip roughness. As distributed roughness height and density increase, the lift-curve slope, maximum lift, and lift-to-drag ratio decrease. As Reynolds number increases, natural transition is replaced by bypass transition. The critical roughness Reynolds number varies between 178 to 318, within the historical range. At a chord Reynolds number of 3:2 × 10 6, the maximum lift-to-drag ratio decreases 40% for 140 μm roughness, corresponding to a 2.3% loss in annual energy production. Simulated performance loss compares well to measured performance loss of an in-service wind turbine.« less

Wind resource assessment in heterogeneous terrain

NASA Astrophysics Data System (ADS)

Vanderwel, C.; Placidi, M.; Ganapathisubramani, B.

2017-03-01

High-resolution particle image velocimetry data obtained in rough-wall boundary layer experiments are re-analysed to examine the influence of surface roughness heterogeneities on wind resource. Two different types of heterogeneities are examined: (i) surfaces with repeating roughness units of the order of the boundary layer thickness (Placidi & Ganapathisubramani. 2015 J. Fluid Mech. 782, 541-566. (doi:10.1017/jfm.2015.552)) and (ii) surfaces with streamwise-aligned elevated strips that mimic adjacent hills and valleys (Vanderwel & Ganapathisubramani. 2015 J. Fluid Mech. 774, 1-12. (doi:10.1017/jfm.2015.228)). For the first case, the data show that the power extraction potential is highly dependent on the surface morphology with a variation of up to 20% in the available wind resource across the different surfaces examined. A strong correlation is shown to exist between the frontal and plan solidities of the rough surfaces and the equivalent wind speed, and hence the wind resource potential. These differences are also found in profiles of and (where U is the streamwise velocity), which act as proxies for thrust and power output. For the second case, the secondary flows that cause low- and high-momentum pathways when the spacing between adjacent hills is beyond a critical value result in significant variations in wind resource availability. Contour maps of and show a large difference in thrust and power potential (over 50%) between hills and valleys (at a fixed vertical height). These variations do not seem to be present when adjacent hills are close to each other (i.e. when the spacing is much less than the boundary layer thickness). The variance in thrust and power also appears to be significant in the presence of secondary flows. Finally, there are substantial differences in the dispersive and turbulent stresses across the terrain, which could lead to variable fatigue life depending on the placement of the turbines within such heterogeneous terrain. Overall, these results indicate the importance of accounting for heterogeneous terrain when siting individual turbines and wind farms. This article is part of the themed issue 'Wind energy in complex terrains'.

Feasibilty of a Multi-bit Cell Perpendicular Magnetic Tunnel Junction Device

NASA Astrophysics Data System (ADS)

Kim, Chang Soo

The ultimate objective of this research project was to explore the feasibility of making a multi-bit cell perpendicular magnetic tunnel junction (PMTJ) device to increase the storage density of spin-transfer-torque random access memory (STT-RAM). As a first step toward demonstrating a multi-bit cell device, this dissertation contributed a systematic and detailed study of developing a single cell PMTJ device using L10 FePt films. In the beginning of this research, 13 up-and-coming non-volatile memory (NVM) technologies were investigated and evaluated to see whether one of them might outperform NAND flash memories and even HDDs on a cost-per-TB basis in 2020. This evaluation showed that STT-RAM appears to potentially offer superior power efficiency, among other advantages. It is predicted that STTRAM's density could make it a promising candidate for replacing NAND flash memories and possibly HDDs if STTRAM could be improved to store multiple bits per cell. Ta/Mg0 under-layers were used first in order to develop (001) L1 0 ordering of FePt at a low temperature of below 400 °C. It was found that the tradeoff between surface roughness and (001) L10 ordering of FePt makes it difficult to achieve low surface roughness and good perpendicular magnetic properties simultaneously when Ta/Mg0 under-layers are used. It was, therefore, decided to investigate MgO/CrRu under-layers to simultaneously achieve smooth films with good ordering below 400°C. A well ordered 4 nm L10 FePt film with RMS surface roughness close to 0.4 nm, perpendicular coercivity of about 5 kOe, and perpendicular squareness near 1 was obtained at a deposition temperature of 390 °C on a thermally oxidized Si substrate when MgO/CrRu under-layers are used. A PMTJ device was developed by depositing a thin MgO tunnel barrier layer and a top L10 FePt film and then being postannealed at 450 °C for 30 minutes. It was found that the sputtering power needs to be minimized during the thin MgO tunnel barrier deposition because the high sputtering power can degrade perpendicular magnetic anisotropy of the bottom L1 0 FePt film and also increase RMS film surface roughness of the MgO tunnel barrier layer. From a lithographically unpatterned PMTJ sample, MR ratio and RA were measured at room temperature by the CIPT method and found to be 138% and 6.4 kOmicrom2, respectively. A completed PMTJ test pattern with a junction size of 80x40 microm2 was fabricated and showed a measured MR ratio and RA product of 108% and 4~6 kOmicrom 2, respectively. These values agree relatively well with the corresponding values of 138% and 6.4 kOmicrom2 obtained from the unpatterned PMTJ sample measured by a current-in-plane tunneling (CIPT) method.

Control of Stationary Cross-Flow Modes in a Mach 3.5 Boundary Layer Using Patterned Passive and Active Roughness

NASA Technical Reports Server (NTRS)

Schuele, Chan Yong

2011-01-01

Spanwise-periodic roughness designed to excite selected wavelengths of stationary cross- ow modes was investigated in a 3-D boundary layer at Mach 3.5. The test model was a sharp-tipped 14deg right-circular cone. The model and integrated sensor traversing system were placed in the Mach 3.5 Supersonic Low Disturbance Tunnel (SLDT) equipped with a "quiet design" nozzle at the NASA Langley Research Center. The model was oriented at a 4:2deg angle of attack to produce a mean cross-fl ow velocity component in the boundary layer over the cone. Five removable cone tips have been investigated. One has a smooth surface that is used to document the baseline ("natural") conditions. Two had minute (20 - 40 micron) "dimples" that are equally spaced around the circumference, at a streamwise location that is just upstream of the linear stability neutral growth branch for cross- ow modes. The azimuthal mode numbers of the dimpled tips were selected to either enhance the most amplified wave numbers, or to suppress the growth of the most amplified wave numbers. Two of the cone tips had an array of plasma streamwise vortex generators that were designed to simulate the disturbances produced by the passive patterned roughness. The results indicate that the stationary cross-fl ow modes were highly receptive to the patterned roughness of both passive and active types. The patterned passive roughness that was designed to suppress the growth of the most amplified modes had an azimuthal wavelength that was 66% smaller that that of the most amplified stationary cross- ow mode. This had the effect to increase the transition Reynolds number from 25% to 50% depending on the measurement technique. The application of the research is on turbulent transition control on swept wings of supersonic aircraft. The plasma-based roughness has the advantage over the passive roughness of being able to be adaptable to different conditions that would occur during a flight mission.

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

PubMed Central

Brennan, Joseph C; Geraldi, Nicasio R; Morris, Robert H; Fairhurst, David J; McHale, Glen; Newton, Michael I

2015-01-01

In recent years extensive work has been focused onto using superhydrophobic surfaces for drag reduction applications. Superhydrophobic surfaces retain a gas layer, called a plastron, when submerged underwater in the Cassie-Baxter state with water in contact with the tops of surface roughness features. In this state the plastron allows slip to occur across the surface which results in a drag reduction. In this work we report flexible and relatively large area superhydrophobic surfaces produced using two different methods: Large roughness features were created by electrodeposition on copper meshes; Small roughness features were created by embedding carbon nanoparticles (soot) into Polydimethylsiloxane (PDMS). Both samples were made into cylinders with a diameter under 12 mm. To characterize the samples, scanning electron microscope (SEM) images and confocal microscope images were taken. The confocal microscope images were taken with each sample submerged in water to show the extent of the plastron. The hydrophobized electrodeposited copper mesh cylinders showed drag reductions of up to 32% when comparing the superhydrophobic state with a wetted out state. The soot covered cylinders achieved a 30% drag reduction when comparing the superhydrophobic state to a plain cylinder. These results were obtained for turbulent flows with Reynolds numbers 10,000 to 32,500. PMID:25975704

Plume Dispersion over Idealized Urban-liked Roughness with Height Variation: an LES Approach

NASA Astrophysics Data System (ADS)

Wong, Colman Ching Chi; Liu, Chun-Ho

2013-04-01

Human activities (e.g. vehicular emission) are the primary pollutant sources affecting the health and living quality of stakeholders in modern compact cities. Gaussian plume dispersion model is commonly used for pollutant distribution estimate that works well over rural areas with flat terrain. However, its major parameters, dispersion coefficients, exclude the effect of surface roughness that unavoidably prone to error handling the pollutant transport in the urban boundary layer (UBL) over building roughness. Our recent large-eddy simulation (LES) has shown that urban surfaces affect significantly the pollutant dispersion over idealized, identical two-dimensional (2D) street canyons of uniform height. As an extension to our on-going effort, this study is conceived to investigate how rough urban surfaces, which are constructed by 2D street canyons of non-uniform height, modify the UBL pollutant dispersion . A series of LESs with idealized roughness elements of non-uniform heights were performed in neutral stratification. Building models with two different heights were placed alternatively in the computational domain to construct 2D street canyons in cross flows. The plume dispersion from a ground-level passive pollutant source over more realistic urban areas was then examined. Along with the existing building-height-to-street-width (aspect) ratio (AR), a new parameter, building-height variability (BHV), is used to measure the building height unevenness. Four ARs (1, 0.5, 0.25 and 0.125) and three BHVs (20%, 40% and 60%) were considered in this study. Preliminary results show that BHV greatly increases the aerodynamic roughness of the hypothetical urban surfaces for narrow street canyons. Analogous to our previous findings, the air exchange rate (ACH) of street canyons increases with increasing friction factor, implying that street-level ventilation could be improved by increasing building roughness via BHV. In addition, the parameters used in dispersion coefficient estimates are related to the friction factor in the way similar to that of uniform street canyons, i.e. they are linear functions of friction factor when the roughness is small and become insensitive to friction factor thereafter over very rough surfaces. It is thus suggested that aerodynamic resistance is the key factor affecting the air quality in urban areas. Moreover, the friction factor could be used to parameterize the dispersion coefficients over different roughness elements.

Surface morphology and structure of Ge layer on Si(111) after solid phase epitaxy

NASA Astrophysics Data System (ADS)

Yoshida, Ryoma; Tosaka, Aki; Shigeta, Yukichi

2018-05-01

The surface morphology change of a Ge layer on a Si(111) surface formed by solid phase epitaxy has been investigated with a scanning tunneling microscope (STM). The Ge film was deposited at room temperature and annealed at 400 °C or 600 °C. The STM images of the sample surface after annealing at 400 °C show a flat wetting layer (WL) with small three-dimensional islands on the WL. After annealing at 600 °C, the STM images show a surface roughening with large islands. From the relation between the average height of the roughness and the deposited layer thickness, it is confirmed that the diffusion of Ge atoms becomes very active at 600 °C. The Si crystal at the interface is reconstructed and the intermixing occurs over 600 °C. However, the intermixing is fairly restricted in the solid phase epitaxy growth at 400 °C. The surface morphology changes with the crystallization at 400 °C are discussed by the shape of the islands formed on the WL surface. It is shown that the diffusion of the Ge atoms in the amorphous phase is active even at 400 °C.

Influence of shot peening on surface quality of austenitic and duplex stainless steel

NASA Astrophysics Data System (ADS)

Vinoth Jebaraj, A.; Sampath Kumar, T.; Ajay Kumar, L.; Deepak, C. R.

2017-11-01

In the present investigation, an attempt has been made to enhance the surface quality of austenitic stainless steel 316L and duplex stainless steel 2205 through shot peening process. The study mainly focuses the surface morphology, microstructural changes, surface roughness and microhardness of the peened layers. Metallography analysis was carried out and compared with the unpeened surface characteristics. As result of peening process, surface recrystallization was achieved on the layers of the peened samples. It was found that shot peening plays significant role in enhancing the surface properties of 316L and 2205. Particularly it has greater influence on the work hardening of austenitic stainless steel than the duplex stainless steel due to its more ductility nature under the investigated shot peening parameters. The findings of the present study will be useful with regard to the enhancement of surface texture achieved through peening.