Non-homogeneous Surface Research Articles

Detection and Quantification of Slip Along Non-Uniform Frictional Discontinuities Using Digital Image Correlation

A deformation measurement system based on the principles of digital image correlation (DIC) has been developed to evaluate the process of slip along frictional discontinuities. A biaxial compression apparatus is used to impose shear failure on perfectly mated gypsum specimens with nonhomogeneous contact surfaces. The contact surfaces are made by casting gypsum against flat surfaces with different frictional characteristics and consisted of a smooth surface with low frictional strength on the upper half and a rough surface with high frictional strength on the lower half. Design, implementation, and verification of the DIC measurement system are presented in this paper. DIC successfully identified slip as a jump in the displacement field across the discontinuity. Slip is observed to initiate from the smooth surface with minimum frictional resistance and as the shear load is increased, propagates to the rough surface that has higher frictional resistance. DIC clearly exhibits a reduction in fracture’s shear stiffness based on an increase in the rate of relative vertical displacement across the discontinuity, which initiates from the smooth surface and propagates to the rough surface.

Experimental consideration of the Hansen solubility parameters of as-produced multi-walled carbon nanotubes by inverse gas chromatography.

The Hansen solubility parameters (HSPs) of as-produced multi-walled carbon nanotubes (APMWCNTs) were determined by means of the inverse gas chromatography (IGC) technique. Due to non-homogeneous surfaces of the APMWCNTs arising from defects and impurities, it was necessary to establish adequate working conditions for determining the HSPs of the CNTs. We then obtained the HSPs of the APMWCNTs and compared these results with earlier reports as determined by using sedimentation and molecular dynamics simulation methods. It was found that the determination of the HSPs of the CNTs by IGC can give an enhanced determination range based on the adsorption thermodynamic parameters, compared to the HSPs determined using sedimentation methods. And the HSPs of the APMWCNTs, determined here, provided good guidelines for the selection of feasible solvents that can improve the dispersion of the APMWCNTs.

Multi-Modal Monitoring of Slip Along Frictional Discontinuities

Seismic wave transmission and digital image correlation (DIC) are employed to study slip processes along frictional discontinuities. A series of biaxial compression experiments are performed on gypsum specimens with non-homogeneous contact surfaces. The specimens are composed of two blocks with perfectly mated contact surfaces with a smooth surface with low frictional strength on the upper half and a rough surface with high frictional strength on the lower half. Compressional, P, and shear, S, wave pulses were transmitted through the discontinuity while digital images of the specimen surface were acquired during the test. A distinct peak in the amplitude of transmitted wave occurs prior to the peak shear strength and is considered a “precursor” to the failure. Precursors indicate that slip initiates from the smooth surface and extends to the rough surface as the shear load is increased. From the DIC data, slip is identified as a jump in the displacement field along the fracture that initiates from the smooth surface and propagates to the rough surface. Precursors are associated with an increase in the rate of slip across the discontinuity and are a measure of the reduction in the fracture shear stiffness.

A new estimate of the China temperature anomaly series and uncertainty assessment in 1900–2006

AbstractWhile global warming during the last century has been well recognized, the magnitude of the climate warming in regions such as China over the past 100 years still has some uncertainty due to limited observations during the early years. Several series of temperature anomalies for the 20th century in China have been independently developed by different groups. The uncertainty arises mainly from the sparse observations before 1950, where statistics are sensitive to the small and potentially biased sample. In this study, BSHADE‐MSN (Biased Sentinel Hospitals Areal Disease Estimation and Means of Stratified Nonhomogeneous Surface), a combination of two novel distinct statistical methods that are applicable with different sample situations to a spatial heterogeneous surface, is applied to estimate annual mean temperature anomalies for China. This method takes into account prior knowledge of geographical spatial autocorrelation and nonhomogeneity of target domains, remedies the biased sample, and maximizes an objective function for the best linear unbiased estimation (BLUE) of the regional mean quantity. For the period 1900–1999, the overall trend estimated by BSHADE‐MSN is 0.80°C with a 95% confidential interval between 0.41°C and 1.18°C. This is significantly lower than that calculated by Climate Anomaly Method (CAM) and Block Kriging. The new temperature anomaly series for China exhibits slightly warmer conditions for the period before 1950 than existing studies. All the methods applied so far agree well with each other for the period after 1950, when there are sufficient stations across the country for the estimation of temperature anomaly series. Cross validation shows that the new regional mean temperature anomaly series has smaller estimation error variance and higher accuracy than those based on the other methods assessed in this study.

Evaluation of edible films and coatings formulated with cassava starch, glycerol, carnauba wax and stearic acid

This study aimed at characterizing four formulations of cassava starch, glycerol, carnauba wax and stearic acid-based edible coatings/films, evaluating their water vapor resistance, the respiration rate of coated apple slices, surface solid density, solubility, mechanical properties, thermal properties and microstructure. Among the formulations evaluated, only the formulation with higher wax content did not promote an effective barrier to oxygen and water vapor and resulted in more rigid films. Formulations with higher glycerol content promoted lower respiration rate of apple slices, good water vapor resistance and flexible films, but the microstructure analysis showed a non-homogenous surface of the films with higher wax content. The glycerol added in formulations increased the solubility and reduced the melting temperature of the films. Formulation with 0.2% carnauba wax showed intermediate values of analyzed properties and promoted films with a more regular surface. Formulation containing 3% (w/w) cassava starch, 1.5% (w/w) glycerol, 0.2% (w/w) carnauba wax and 0.8% (w/w) stearic acid, presented films with a cohesive matrix, resulting in better mechanical properties, barrier to moisture and gas exchange.

A review of block copolymer‐based biomaterials that control protein and cell interactions

Block copolymers posses the ability to phase separate into micro and nanoscale patterns resulting in nonhomogeneous surfaces and solids. This nonhomogeneity has been harnessed to improve mechanical properties, control degradation, and add functionality to biomaterials. The ability of block copolymers to generate a wide variety of surface chemistries and morphologies can also be harnessed to control protein adsorption, protein conformation, and cell adhesion. Proteins and cells will respond to periodically structured surfaces, so block copolymers have a great deal of potential as biomaterials. This review will explore the ability of block copolymers to control specific biological responses such as cell adhesion, protein adsorption and conformation, parameters that govern the overall host response to a material. In addition, some of the specific applications of block copolymer, antithrombogenic materials and their ability to pattern proteins, will be discussed.

Tribology, friction and traction: understanding shoe-surface interaction

Friction has been studied since the early investigations of Leonardo da Vinci, Amontons, Coulomb, and Euler, and many experimental investigations have been used to measure the friction force between contact surfaces. However, in the case of non-homogenous and different surfaces commonly experienced in sports, all of the laws of friction are violated. The area of tribology provides an opportunity to describe the relationship between footwear and the surface in engineering terms and explain how traction is generated on sports surfaces. The paper firstly examines the mechanisms used to explain dry friction, and uses these to explain the complex mechanisms associated with field footwear-surface interaction.

Modeling pollutant transport in overland flow over non-planar and non-homogenous infiltrating surfaces

Pollutant transport in overland flow over surfaces with spatially varying microtopography, roughness, and infiltration was investigated using the diffusion wave equation and transport rate-based equation. The finite volume method in space and an implicit backward difference scheme in time were employed in the numerical solution of the 2D governing equations. The developed model was first tested against an analytical solution and an experimental study involving overland flow and the associated pollutant transport, subsequently a series of numerical tests were carried out. Non-point source pollution was investigated under spatially varying microtopography, roughness, and infiltration. The simulation results showed that microtopography and roughness were the dominant factors causing significant spatial variations in solute concentration. When the spatially varying microtopography was replaced by a smooth surface, the result was an overestimation of the solute rate at the outlet of the upland. On the other hand, when the spatially varying roughness was replaced by the average roughness and spatially varying infiltration rate by the average infiltration rate, the pollutant discharge at the outlet of the upland was not significantly affected. The numerical results further showed that one cannot ignore the spatial variations of slope and roughness when investigating the local pollutant concentration distribution.

Surface enhanced bacterial fluorescence and enumeration of bacterial adhesion

The use of flow displacement systems for studying initial bacterial adhesion to surfaces is mostly confined to transparent substrata. The objective of this study was to investigate a method based on macroscopic fluorescence imaging to enumerate adhering fluorescent bacteria on non-transparent substrata, real-time and under flow. To this end, a stepwise protocol is described to quantify adhesion of green-fluorescent-protein producing Staphylococcus aureus on polished and non-polished metal and polymer surfaces accounting for surface-enhanced-fluorescence on metal surfaces, quantified by the ratio of the single cell fluorescence observed for adhering and planktonic bacteria. Enumeration of adhering fluorescent staphylococci by the proposed method is consistent with results obtained using metallurgical microscopy. An advantage however, is that the non-homogeneous surface coverage and surface roughness do not limit the applicability of the method. Moreover, the accurate quantification of surface-enhanced-fluorescence arising from adhering bacteria offers a new pathway for evaluating bacterial cell surface deformation during adhesion.

Quantitative Aspects of Ohmic Microscopy

The potential difference between two microreference electrodes, Δφ(sol), immersed in an aqueous sulfuric acid solution was monitored while performing conventional cyclic voltammetric experiments with a Pt disk electrode embedded in an insulating surface in an axisymmetric cell configuration. The resulting Δφ(sol) vs E curves, where E is the potential applied to the Pt disk electrode were remarkably similar to the voltammograms regardless of the position of the microreference probes. Most importantly, the actual values of Δφ(sol) were in very good agreement with those predicted by the primary current distribution using Newman's formalism (Newman, J. J. Electrochem. Soc. 1966, 113, 501-502). These findings afford a solid basis for the development of ohmic microscopy as a quantitative tool for obtaining spatially resolved images of electrodes displaying nonhomogenous surfaces.

The use of quantitative cytology in identifying high-risk oral lesions in community practice

This study evaluated whether quantitative cytology (QC) can disclose abnormal DNA content (aneuploidy) and abnormal nuclear morphology of high-risk potentially malignant disorders (PMDs) of the oral mucosa found in the community in reference to clinicohistopathologic features. A total of 171 patients at community-based clinic with suspicious oral lesions were evaluated with concurrent but independent histopathologic and QC assessments. QC-positive results were associated with oral lesions with higher clinical risk factors: large size, nonhomogeneous surface texture, and located at high-risk anatomic sites. Only 3% of benign/reactive and 5% of low-risk PMDs were QC positive, while 92% of high-risk PMDs and 88% of squamous cell carcinomas (SCCs) were QC positive. The sensitivity and specificity of QC for detection of high-grade dysplasia/SCC were 89% and 97%. QC could serve as an adjunctive tool for the detection of high-risk PMD/SCC requiring immediate clinical care.

Band gap coupling in photocatalytic activity in ZnO–TiO2 thin films

Zinc oxide and titanium dioxide composite thin films were prepared on Corning 7059 glass substrates by co-sputtering. The reactive gas-surroundings used was ultrahigh purity oxygen. To analyze the structural, optical and photocatalytic properties of the ZnO–TiO2 samples, X-ray diffraction (XRD), atomic force microscopy (AFM), optical absorption, Raman spectroscopy and methylene blue bleaching were carried out at room temperature. XRD patterns indicate the presence of TiO2 (anatase and rutile phases), ZnO, ZnTiO3, and Zn2TiO4 crystalline structures. AFM images allow the observation of non-homogeneous surface in the ZnO–TiO2 system, suggesting the separation of different crystalline phases in the composite. Raman studies exhibit different spectra in the films depending on the area analyzed, which can be interpreted as a result of the existence of well separated crystalline regions as seen in AFM images. The photocatalytic activity (PA) of TiO2–ZnO–ZnTiO3–Zn2TiO4 composite, as expected for adequate coupling semiconductors, is larger than PA of ZnO and TiO2 oxides, used as references. A simple proposal about the probable alignment of the conduction band, the valence band, and the Fermi level is included.

Modeling and control of an anti-lock brake and steering system for cooperative control on split-mu surfaces

The brake and steering systems in vehicles are the most effective actuators that directly affect the vehicle dynamics. In general, the brake system affects the longitudinal dynamics and the steering system affects the lateral dynamics; however, their effects are coupled when the vehicle is braking on a non-homogenous surface, such as a split-mu road. The yaw moment compensation of the steering control on a split-mu road is one of the basic functions of integrated or coordinated chassis control systems and has been demonstrated by several chassis suppliers. However, the disturbance yaw moment is generally compensated for using the yaw rate feedback or using wheel brake pressure measurement. Access to the wheel brake pressure through physical sensors is not cost effective; therefore, we modeled the hydraulic brake system to avoid using physical sensors and to estimate the brake pressure. The steering angle controller was designed to mitigate the non-symmetric braking force effect and to stabilize the yaw rate dynamics of the vehicle. An H-infinity design synthesis was used to take the system model and the estimation errors into account, and the designed controller was evaluated using vehicle tests.

Control of Epitaxial Graphene Thickness on 4H-SiC(0001) and Buffer Layer Removal through Hydrogen Intercalation

We report graphene thickness, uniformity and surface morphology dependence on the growth temperature and local variations in the off-cut of Si-face 4H-SiC on-axis substrates. The transformation of the buffer layer through hydrogen intercalation and the subsequent influence on the charge carrier mobility are also studied. A hot-wall CVD reactor was used for in-situ etching, graphene growth in vacuum and the hydrogen intercalation process. The number of graphene layers is found to be dependent on the growth temperature while the surface morphology also depends on the local off-cut in the substrate and results in a non-homogeneous surface. Additionally, the influence of dislocations on surface morphology and graphene thickness uniformity is also presented.

Stacking of adjacent graphene layers grown on C-face SiC

Graphene was grown on the C-face of nominally on-axis SiC substrates using high-temperature sublimation with Ar as the buffer inert gas. The results of studies of the morphology, thickness, and electronic structure of these samples using low-energy electron microscopy (LEEM), x-ray photoelectron emission microscopy, photoelectron spectroscopy, angle-resolved photoelectron spectroscopy (ARPES), and low-energy electron diffraction (LEED) are presented. The graphene thickness is determined to vary from 1 or 2 to 6 or 7 monolayers (MLs), depending on the specific growth conditions utilized. The formation of fairly large grains (i.e., crystallographic domains) of graphene exhibiting sharp 1\ifmmode\times\else\texttimes\fi{}1 spots in micro-LEED is revealed. Adjacent grains are found to show different azimuthal orientations. Macro-LEED patterns recorded mimic previously published, strongly modulated, diffraction ring LEED patterns, indicating contribution from several grains of different azimuthal orientations. We collected selected area constant initial energy photoelectron angular distribution patterns that show the same results. When utilizing a small aperture size, one Dirac cone centered on each of the six K-points in the Brillouin zone is clearly resolved. When using a larger aperture, several Dirac cones from differently oriented grains are detected. Our findings thus clearly show the existence of distinct graphene grains with different azimuthal orientations; they do not show adjacent graphene layers are rotationally disordered, as previously reported for C-face graphene. The graphene grain size is shown to be different on the different samples. In some cases, a probing area of 400 nm is needed to detect the grains. On one sample, a probing area of 5 \ensuremath{\mu}m can be used to collect a 1\ifmmode\times\else\texttimes\fi{}1 LEED pattern from a multilayer graphene grain. ARPES is used to determine the position of the Dirac point relative to the Fermi level on two samples that LEEM shows have dominant coverage of 2 and 3 MLs of graphene, respectively. The Dirac point is found to be located within 75 meV of the Fermi level on both samples, which indicates that the electron carrier concentration induced in the second and third graphene layers on the C-face is less than \ensuremath{\sim}4\ifmmode\times\else\texttimes\fi{}10${}^{11}$ cm${}^{\ensuremath{-}2}$. Formation of patches of silicate is revealed on some samples, but the graphene formed on such nonhomogenous surfaces can contain fairly large ordered multilayer graphene grains.

Cell adhesion and focal contact formation on linear RGD molecular gradients: study of non-linear concentration dependence effects

Cell adhesion onto bioengineered surfaces is affected by a number of variables, including the former substrate derivatization process. In this investigation, we studied the correlation between cell adhesion and cell–adhesive ligand surface concentration and organization due to substrate modification. For this purpose, Arg-Gly-Asp (RGD) gradient surfaces were created on poly(methyl methacrylate) substrates by continuous hydrolysis and were then grafted with biotin-PEG-RGD molecules. Cell culture showed that adhesion behavior changes in a nonlinear way in the narrow range of RGD surface densities assayed (2.8 to 4.4 pmol/cm2), with a threshold value of 4.0 pmol/cm2 for successful cell attachment and spreading. This nonlinear dependence may be explained by nonhomogeneous RGD surface distribution at the nanometre scale, conditioned by the stochastic nature of the hydrolysis process. Atomic force microscopy analysis of the gradient surface showed an evolution of surface morphology compatible with this hypothesis. From the Clinical EditorThe authors observed by AFM nonlinear dependence of cell adhesion on RGD gradient surfaces with different surface densities. The nonlinear characteristics may be explained by non-homogeneous RGD surface distribution at the nanometer scale, conditioned by the stochastic nature of the hydrolysis process.

Ultrafast laser melting of Au nanoparticles: atomistic simulations

In spite of the technological importance of laser modification and processing of nanoparticles, the interaction of laser energy with nanoparticles is not well understood. In this work, integrated molecular dynamics (MD) and two-temperature (TTM) computational models have been developed to study ultrafast laser interaction with free Au nanoparticles with sizes 2.44–6.14 nm. At low intensity, when surface premelting and solid–liquid phase transition dominate, a nonhomogeneous surface premelting mechanism was identified. The appearance of a contiguous surface liquid layer (complete surface premelting) is size dependent and is not related to surface premelting history. The effects of temporary superheating and stable supercooling of nanoparticles were found and examined.

Quantitative analysis of phospholipids using nanostructured laser desorption ionization targets.

Since its introduction as an ionization technique in mass spectrometry, matrix-assisted laser desorption ionization (MALDI) has been applied to a wide range of applications. Quantitative small molecule analysis by MALDI, however, is limited due to the presence of intense signals from the matrix coupled with non-homogeneous surfaces. The surface used in nano-structured laser desorption ionization (NALDI) eliminates the need for a matrix and the resulting interferences, and allows for quantitative analysis of small molecules. This study was designed to analyze and quantitate phospholipid components of liposomes. Here we have developed an assay to quantitate the DPPC and DC(8,9)PC in liposomes by NALDI following various treatments. To test our method we chose to analyze a liposome system composed of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DC(8,9)PC (1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine), as DC(8,9)PC is known to undergo cross-linking upon treatment with UV (254 nm) and this reaction converts the monomer into a polymer. First, calibration curves for pure lipids (DPPC and DC(8,9)PC) were created using DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) as an internal standard. The calibration curve for both DPPC and DC(8,9)PC showed an R(2) of 0.992, obtained using the intensity ratio of analyte and internal standard. Next, DPPC:DC(8,9)PC liposomes were treated with UV radiation (254 nm). Following this treatment, lipids were extracted from the liposomes and analyzed. The analysis of the lipids before and after UV exposure confirmed a decrease in the signal of DC(8,9)PC of about 90%. In contrast, there was no reduction in DPPC signal.

Surface temperature measurement in the medium and long wavelength infrared range on MAST

Experiments and theoretical investigations of surface temperature measurement in the medium and long wavelength infrared range carried out on MAST show that a nonhomogenous surface temperature distribution due to the surface state (micro-metric hot-spots and/or surface roughness) can lead to a significant difference (up to ∼40%) between both wavelengths. The over-estimation of the bulk temperature decreases with wavelength and the discrepancy observed on MAST can be reproduced using a hot-spot simulation model, by varying the dust size and the dust coverage such that a coverage of 0.2‰ with 1μm dust size which is consistent with the observations. The over-estimation of the bulk temperature is assessed at medium and long wavelength as a function of dust contribution (coverage/size). The effect is also assessed in different conditions (temperature of the bulk as well as the incident power flux).

On Hyperspectral Image Simulation of a Complex Woodland Area

Hyperspectral imaging (HSI) systems can acquire both spectral and spatial information of ground surface simultaneously and have been used in a variety of applications such as object detection, material identification, land cover classification, etc. Through simulation of a HSI process, it is in favor of finding key contributors to optimize system performance and sensor design. Although it is difficult to be expressed accurately, a hyperspectral image simulator could be built on the premise of some simplifications. In this paper, a complex scenario that includes a woodland area with low shrubbery and a woodland area surrounded by high building walls is simulated. The simulated scene model is built, in which a bidirectional reflectance distribution function (BRDF) is introduced and reflectance functions for ground materials are represented using a combination of canopy BRDF and a subpixel fraction model. To improve our previous work, we introduce in the model the secondary illumination based on geometric analysis methods to simulate the effects of reflected solar radiance from other buildings, which improves atmospheric modeling on the basis of nonhomogeneous and non-Lambertian surface. Experiments and analysis show that reasonable results could be achieved.