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Sample records for contact surfaces evaluated

  1. Analysis of different approaches for evaluation of surface energy of microbial cells by contact angle goniometry.

    PubMed

    Sharma, P K; Rao, K Hanumantha

    2002-08-01

    Microbial adhesion on solid substrate is important in various fields of science. Mineral-microbe interactions alter the surface chemistry of the minerals and the adhesion of the bacterial cells to mineral surface is a prerequisite in several biobeneficiation processes. Apart from the surface charge and hydrophobic or hydrophilic character of the bacterial cells, the surface energy is a very important parameter influencing their adhesion on solid surfaces. There were many thermodynamic approaches in the literature to evaluate the cells surface energy. Although contact angle measurements with different liquids with known surface tension forms the basis in the calculation of the value of surface energy of solids, the results are different depending on the approach followed. In the present study, the surface energy of 140 bacterial and seven yeast cell surfaces has been studied following Fowkes, Equation of state, Geometric mean and Lifshitz-van der Waals acid-base (LW-AB) approaches. Two independent issues were addressed separately in our analysis. At first, the surface energy and the different components of the surface energy for microbial cells surface are examined. Secondly, the different approaches are evaluated for their internal consistency, similarities and dissimilarities. The Lifshitz-van der Waals component of surface energy for most of the microbial cells is realised to be approximately 40 mJ/m2 +/-10%. Equation of state and Geometric mean approaches do not possess any internal consistency and yield different results. The internal consistency of the LW-AB approach could be checked only by varying the apolar liquid and it evaluates coherent surface energy parameters by doing so. The electron-donor surface energy component remains exactly the same with the change of apolar liquid. This parameter could differentiate between the Gram-positive and Gram-negative bacterial cells. Gram-negative bacterial cells having higher electron-donor parameter had lower

  2. Evaluation of Salmonella biofilm cell transfer from contact surfaces to beef products

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Introduction: Meat contamination by Salmonella enterica is a serious food safety concern. One common transmission route that leads to cross contamination in meat plants is bacteria transfer from biofilms on contact surfaces to meat products via direct contact. Many factors could affect biofilm tra...

  3. Handheld non-contact evaluation of fastener flushness and countersink surface profiles using optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Wang, James H.; Wang, Michael R.

    2016-07-01

    We report the use of spectral domain optical coherence tomography (SD-OCT) for non-contact optical evaluation of fastener flushness and countersink surface profile. Using a handheld galvanometer scanner of only 0.5 lb in weight the SD-OCT can perform line scan surface profile measurement of fastener and countersink without demanding accurate scan center alignment. It demonstrates fast measurement of fastener flushness, radius, slant angle, as well as countersink edge radius and surface angle within 90 ms suitable for handheld operation. With the use of a broadband light source at 840 nm center wavelength and 45 nm spectral bandwidth and a lens of 60 mm focal length, the low coherence interferometry based SD-OCT measurement offers axial depth resolution of 8.5 μm, lateral resolution of 19 μm, and measurement depth of 3.65 mm in the air. Multi-line scans can yield 3D surface profiles of fastener and countersink.

  4. Waterless Coupling of Ultrasound from Planar Contact Transducers to Curved and Irregular Surfaces during Non-destructive Ultrasonic Evaluations

    SciTech Connect

    Denslow, Kayte M.; Diaz, Aaron A.; Jones, Anthony M.; Meyer, Ryan M.; Cinson, Anthony D.; Wells, Mondell D.

    2012-04-30

    The Applied Physics group at the Pacific The Applied Physics group at the Pacific Northwest National Laboratory (PNNL) in Richland, WA has evaluated a method for waterless/liquidless coupling of ultrasonic energy from planar ultrasonic contact transducers to irregular test surfaces for ultrasonic non-destructive evaluation applications. Dry couplant material placed between a planar transducer face and a curved or uneven steel or plastic surface allows for effective sound energy coupling and preserves the integrity of the planar transducer sound field by serving as an acoustic impedance matching layer, providing good surface area contact between geometrically dissimilar surfaces and conforming to rough and unsmooth surfaces. Sound fields radiating from planar ultrasonic contact transducers coupled to curved and uneven surfaces using the dry coupling method were scanned and mapped using a Pinducer receiver connected to a raster scanner. Transducer sound field coverage at several ultrasonic frequencies and several distances from the transducer contact locations were found to be in good agreement with theoretical beam divergence and sound field coverage predictions for planar transducers coupled to simple, planar surfaces. This method is valuable for applications that do not allow for the use of traditional liquid-based ultrasonic couplants due to the sensitivity of the test materials to liquids and for applications that might otherwise require curved transducers or custom coupling wedges. The selection of dry coupling material is reported along with the results of theoretical sound field predictions, the laboratory testing apparatus and the empirical sound field data.

  5. Microbiological evaluation of foodservice contact surfaces in Iowa assisted-living facilities.

    PubMed

    Sneed, Jeannie; Strohbehn, Catherine; Gilmore, Shirley A; Mendonca, Aubrey

    2004-11-01

    A study of 40 assisted-living facilities in Iowa was conducted to assess the microbiological quality of food-contact surfaces (work tables/counters, cooking equipment such as mixing bowls, and cutting boards) and a surface that could cross-contaminate food (refrigerator or freezer handles) to determine the effectiveness of cleaning and sanitation. Standards were set for foodservice for aerobic plate count, Enterobacteriaceae, and Staphylococcus aureus . Two facilities met standards for all five surfaces for each of the three tests. Fewer facilities met the standard for aerobic plate count than for the other two tests, and nearly three fourths of the facilities failed to meet the aerobic plate count for cutting boards. Critically, cross-contamination from these surfaces could result in contamination of food; thus, attention needs to be given to training and supervision to ensure proper hand washing and appropriate cleaning and sanitation procedures to reduce or eliminate cross-contamination. PMID:15499361

  6. Evaluation of Three Swabbing Devices for Detection of Listeria monocytogenes on Different Types of Food Contact Surfaces

    PubMed Central

    Lahou, Evy; Uyttendaele, Mieke

    2014-01-01

    Listeria monocytogenes can adhere to different types of food contact surfaces within a food processing environment. Therefore, environmental sampling devices should be capable of detecting unacceptable contamination. In this study, a sponge-stick, foam spatula and an environmental swab were evaluated on their ability to detect low concentrations of L. monocytogenes on different types of food contact surfaces. A cocktail of four L. monocytogenes serotypes was inoculated with a concentration of 100 CFU/250 cm2 onto stainless steel (SS), high density polyethylene (HDPE) and rubber surfaces in a 250 cm2 area. Immediately after inoculation and after 1 h exposure, the surfaces were swabbed with the different swabbing devices. The results of the study show only minor differences in the ability of the swabbing devices to detect L. monocytogenes. All devices were capable to detect the contamination immediately after inoculation. However, when the surfaces were allowed to air-dry for 1 h, L. monocytogenes was undetected in 11.1% of the samples (n = 27) with the sponge stick, in 7.4% of the samples (n = 27) with the foam spatula and in 3.7% of the samples (n = 27) with the environmental swab, especially on SS surfaces. The detection ability of the different devices for L. monocytogenes can be concluded to be rather high on different types of food contact surfaces. PMID:24406663

  7. Evaluation of three swabbing devices for detection of Listeria monocytogenes on different types of food contact surfaces.

    PubMed

    Lahou, Evy; Uyttendaele, Mieke

    2014-01-01

    Listeria monocytogenes can adhere to different types of food contact surfaces within a food processing environment. Therefore, environmental sampling devices should be capable of detecting unacceptable contamination. In this study, a sponge-stick, foam spatula and an environmental swab were evaluated on their ability to detect low concentrations of L. monocytogenes on different types of food contact surfaces. A cocktail of four L. monocytogenes serotypes was inoculated with a concentration of 100 CFU/250 cm2 onto stainless steel (SS), high density polyethylene (HDPE) and rubber surfaces in a 250 cm2 area. Immediately after inoculation and after 1 h exposure, the surfaces were swabbed with the different swabbing devices. The results of the study show only minor differences in the ability of the swabbing devices to detect L. monocytogenes. All devices were capable to detect the contamination immediately after inoculation. However, when the surfaces were allowed to air-dry for 1 h, L. monocytogenes was undetected in 11.1% of the samples (n = 27) with the sponge stick, in 7.4% of the samples (n = 27) with the foam spatula and in 3.7% of the samples (n = 27) with the environmental swab, especially on SS surfaces. The detection ability of the different devices for L. monocytogenes can be concluded to be rather high on different types of food contact surfaces. PMID:24406663

  8. Method for lubricating contacting surfaces

    DOEpatents

    Dugger, Michael T.; Ohlhausen, James A.; Asay, David B.; Kim, Seong H.

    2011-12-06

    A method is provided for tribological lubrication of sliding contact surfaces, where two surfaces are in contact and in motion relative to each other, operating in a vapor-phase environment containing at least one alcohol compound at a concentration sufficiently high to provide one monolayer of coverage on at least one of the surfaces, where the alcohol compound continuously reacts at the surface to provide lubrication.

  9. Evaluation of the surface properties of PTFE foam coating filter media using XPS and contact angle measurements

    NASA Astrophysics Data System (ADS)

    Park, Byung Hyun; Lee, Myong-Hwa; Kim, Sang Bum; Jo, Young Min

    2011-02-01

    A newly developed PTFE foam coating filter was developed which can be used for hot gas cleaning at temperatures up to 250 °C. The emulsion-type PTFE was coated onto a woven glass fiber using a foam coating method. The filter surface was closely examined using X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The XPS results were used to determine the binding force between the carbon and fluorine of PTFE, which imparts coating stability to the filter medium. More than 95% of the bonds of the PTFE foam coating filter were between carbon and fluorine, and this filter demonstrated excellent hydrophobic and good oleophobic properties at the same time. The contact angles of liquid droplets on the filter surface were used to predict the potential wetability of the filter against water or oil. In addition, the very low surface free energy of the filter medium, which was evaluated using the Owens-Wendt method, demonstrates a very stable surface and a high de-dusting quality.

  10. A method to evaluate the effect of contact with excipients on the surface crystallization of amorphous drugs.

    PubMed

    Zhang, Si-Wei; Yu, Lian; Huang, Jun; Hussain, Munir A; Derdour, Lotfi; Qian, Feng; de Villiers, Melgardt M

    2014-12-01

    Amorphous drugs are used to improve the solubility, dissolution, and bioavailability of drugs. However, these metastable forms of drugs can transform into more stable, less soluble, crystalline counterparts. This study reports a method for evaluating the effect of commonly used excipients on the surface crystallization of amorphous drugs and its application to two model amorphous compounds, nifedipine and indomethacin. In this method, amorphous samples of the drugs were covered by excipients and stored in controlled environments. An inverted light microscope was used to measure in real time the rates of surface crystal nucleation and growth. For nifedipine, vacuum-dried microcrystalline cellulose and lactose monohydrate increased the nucleation rate of the β polymorph from two to five times when samples were stored in a desiccator, while D-mannitol and magnesium stearate increased the nucleation rate 50 times. At 50% relative humidity, the nucleation rates were further increased, suggesting that moisture played an important role in the crystallization caused by the excipients. The effect of excipients on the crystal growth rate was not significant, suggesting that contact with excipients influences the physical stability of amorphous nifedipine mainly through the effect on crystal nucleation. This effect seems to be drug specific because for two polymorphs of indomethacin, no significant change in the nucleation rate was observed under the excipients. PMID:25037732

  11. Evaluation of surface water characteristics of novel daily disposable contact lens materials, using refractive index shifts after wear

    PubMed Central

    Schafer, Jeffery; Steffen, Robert; Reindel, William; Chinn, Joseph

    2015-01-01

    Purpose Contact lens wearers today spend much time using digital display devices. Contact lens manufacturers are challenged to develop products that account for longer periods of time where blink rate is reduced and tear-film evaporation rate is increased, affecting both visual acuity and comfort. Two manufacturers recently introduced novel daily disposable contact lenses with high surface water content. The objective of the present study was to compare surface water characteristics before and after initial wear of recently introduced nesofilcon A and delefilcon A high surface water lenses with those of etafilcon A lenses. Patients and methods Twenty healthy subjects wore each of the three lens types studied in a randomly determined order for 15 minutes. After each wearing, lenses were removed and the surface refractive index (RI) of each lens was immediately measured. Results The mean RI of the unworn delefilcon A lens was 1.34, consistent with water content in excess of 80%. After 15 minutes of wear, the surface RI shifted to 1.43, consistent with its reported 33% bulk water content. In contrast, the mean surface RI of the nesofilcon A lens was 1.38, both initially and after 15 minutes of wear, and that of the etafilcon A lens was 1.41 initially and 1.42 after 15 minutes of wear. Conclusion The surface of the delefilcon A lens behaves like a high water hydrogel upon insertion but quickly dehydrates to behave like its low-water silicone-hydrogel bulk material with respect to surface water content during wear, while both nesofilcon A and etafilcon A lenses maintain their water content during initial wear. The nesofilcon A lens appears unique among high water lenses in maintaining high surface and bulk water content during wear. This is important because changes in surface RI due to dehydration are reported to lead to visual aberration affecting user experience. PMID:26543349

  12. Computationally efficient magnetic resonance imaging based surface contact modeling as a tool to evaluate joint injuries and outcomes of surgical interventions compared to finite element modeling.

    PubMed

    Johnson, Joshua E; Lee, Phil; McIff, Terence E; Toby, E Bruce; Fischer, Kenneth J

    2014-04-01

    Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. This may be partially achieved by monitoring changes in joint mechanics that are a direct consequence of injury. Techniques such as image-based finite element modeling can provide in vivo joint mechanics data but can also be laborious and computationally expensive. Alternate modeling techniques that can provide similar results in a computationally efficient manner are an attractive prospect. It is likely possible to estimate risk of OA due to injury from surface contact mechanics data alone. The objective of this study was to compare joint contact mechanics from image-based surface contact modeling (SCM) and finite element modeling (FEM) in normal, injured (scapholunate ligament tear), and surgically repaired radiocarpal joints. Since FEM is accepted as the gold standard to evaluate joint contact stresses, our assumption was that results obtained using this method would accurately represent the true value. Magnetic resonance images (MRI) of the normal, injured, and postoperative wrists of three subjects were acquired when relaxed and during functional grasp. Surface and volumetric models of the radiolunate and radioscaphoid articulations were constructed from the relaxed images for SCM and FEM analyses, respectively. Kinematic boundary conditions were acquired from image registration between the relaxed and grasp images. For the SCM technique, a linear contact relationship was used to estimate contact outcomes based on interactions of the rigid articular surfaces in contact. For FEM, a pressure-overclosure relationship was used to estimate outcomes based on deformable body contact interactions. The SCM

  13. Evaluation of a bioluminescence method, contact angle measurements and topography for testing the cleanability of plastic surfaces under laboratory conditions

    NASA Astrophysics Data System (ADS)

    Redsven, I.; Kymäläinen, H.-R.; Pesonen-Leinonen, E.; Kuisma, R.; Ojala-Paloposki, T.; Hautala, M.; Sjöberg, A.-M.

    2007-04-01

    Detection of adenosine triphosphate (ATP) by bioluminescence is used, for instance, in the food industry and in hospitals to assess the hygiene status of surfaces. The aim of this laboratory study was to investigate the feasibility of the ATP method for estimating the cleanability of resilient floor coverings from biological soil. The surfaces were worn using a Soiling and Wearing Drum Tester, and soiled and cleaned with an Erichsen Washability and Scrubbing Resistance Tester. In the laboratory test carried out with the bioluminescence method, most of the new and worn floor coverings that were biologically soiled were cleaned efficiently. According to this study, the semiquantitative ATP screening method can be used for hygiene monitoring of flooring materials. No correlation was found between cleanability and contact angles or surface topography measured using a profilometer. However, by revealing local irregularities and damage on surfaces, scanning electron micrographs appeared useful in explaining differences in cleanability.

  14. Surface Contact Model for Comets and Asteroids

    NASA Technical Reports Server (NTRS)

    Blackmore, Lars James C.; Trease, Brian P.; Acikmese, Behcet; Mandic, Milan; Carson, John M.

    2011-01-01

    A contact force model was developed for use in touch and go (TAG) surface sampling simulations on small celestial bodies such as comets and asteroids. In TAG scenarios, a spacecraft descending toward the surface of a small body comes into contact with the surface for a short duration of time, collects material samples with a sampler device, and then ascends to leave the surface. The surface contact required 6-DOF (degrees of freedom) dynamics models due to coupling of the attitude and translation dynamics during the contact. The model described here is for contact scenarios that utilize a rotating brush wheel sampler (BWS) to collect surface material. The model includes stiffness and damping of the surface material during BWS vertical motion, lateral friction from the BWS dragging across the surface, and lateral shear from the rotating BWS scooping the surface material. This model is useful for any mission to asteroids or comets that incorporates surface sampling operations.

  15. Wireless Measurement of Contact and Motion Between Contact Surfaces

    NASA Technical Reports Server (NTRS)

    Woodard, Stanley E.; Taylor, Bryant D.

    2007-01-01

    This method uses a magnetic-field- response contact sensor that is designed to identify surface contact and motion between contact locations. The sensor has three components: (1) a capacitor-inductor circuit with two sets of electrical contact pads, (2) a capacitor with a set of electrical contact pads, and (3) an inductor with a set of electrical contact pads. A unique feature of this sensor is that it is inherently multifunctional. Information can be derived from analyzing such sensor response attributes as amplitude, frequency, and bandwidth. A change in one attribute can be due to a change in a physical property of a system. A change in another attribute can be due to another physical property, which has no relationship to the first one.

  16. Evaluation of changes induced by temperature, contact time, and surface in the efficacies of disinfectants against avian influenza virus.

    PubMed

    Jang, Yangho; Lee, Joongbok; So, Byungjae; Lee, Kwangjick; Yun, Seonjong; Lee, Myoungheon; Choe, Nonghoon

    2014-01-01

    Avian influenza viruses (AIV) are highly susceptible to all disinfectants because they are enveloped viruses. Disinfectants effective against AIV have optimum efficacies at temperatures above 20°C. Very few studies on effective disinfectants at low temperatures have been done. Disinfectants were investigated at 4 different temperatures (25, 4, 0, and -10°C) and 2 contact times (1 and 5 min) with suspension tests. Virucidal activity of the disinfectants was evaluated by carrier tests (wood and stainless steel) at 25 and -10°C. The concentration of each disinfectant for efficient disinfection within a short time (<1 min) at 25 and -10°C was also reestablished. The results from the suspension test indicated that low temperatures inhibited the virucidal efficacy of citric acid (CA) and CA + quaternary ammonium compounds (CA+ QAC) for 1 and 5 min, whereas the remaining disinfectants were effective, regardless of the short contact times and low temperatures. The carrier test results suggested that dried virus on wood was more difficult to inactivate compared with that on stainless steel. However, sodium dichloroisocyanurate and glutaraldehyde could inactivate AIV on both wood and stainless steel at -10°C. Citric acid-based agents could not sufficiently inactivate AIV at -10°C; however, the limitation due to low temperatures was overcome by adjusting disinfectant concentration. For a successful disinfection during winter, the disinfectants that could have short contact times with optimum efficacy against the target organism should be selected. PMID:24570425

  17. Advancing contact angles on large structured surfaces

    NASA Astrophysics Data System (ADS)

    Yoshitake, Yumiko; Itakura, Yoshinori; Gobo, Junichi; Takahashi, Tsutomu

    2014-11-01

    To understand wetting phenomena on complex surfaces, simple modeling experiments in two-dimension system would be one of the most efficient approaches. We develop a new experimental method for wetting dynamics using a large pseudo two- dimensional droplet. This method is useful to examine theoretical studies developed in two dimensional systems. In this study, we examine a pinning and depinning phenomena on millimeter-size structured surface to explain the origin of contact angle hysteresis. Contact lines of the droplet are pinned and deppined at the edge of surface texture. The contact lines can move when the contact angle is equal to the Young's contact angle which are determined by the balance of the surface and interfacial tension immediate vicinity of the contact lines, which is different from the Wenzel's low. Our approach enables to realize a macroscopic modelling experiment of wetting on complex surfaces, which opens a path to design functional surfaces with chemical and physical structure.

  18. Thermal contact conductance of nominaly flat surfaces

    NASA Astrophysics Data System (ADS)

    Yüncü, H.

    2006-11-01

    The variation of thermal conductance of contact has been investigated as a function of apparent contact pressure experimentally. Experimental data has been obtained for steel, brass, copper and aluminum test pieces having different surface roughness over a wide range of contact pressures. Experimental results are compared with the theoretical predictions of an existing theory. Comparison revealed good agreement of trend with the experimental data, however, numerical values vary widely. Theory can predict the experimental results within an over-all error of less than 35%.

  19. Thermal contact conductance of packed beds in contact with a flat surface

    SciTech Connect

    Peterson, G.P.; Fletcher, L.S. )

    1988-02-01

    An experimental investigation was conducted to determine the thermal contact conductance of packed beds of spherical particles in contact with flat surfaces. Beds comprised of four materials, Aluminum 2017-T4, Yellow Brass, Stainless Steel 304, and Chromium Alloy AISI 52100, all in contact with flat Stainless Steel 304, surfaces were evaluated in a vacuum environment, at a mean interface temperature of 66C. In addition to the experimental program, an analytical expression was developed by combining previous work performed by other investigators. The results of the experimental investigation are compared with the analytical expression and indicate that an accurate method of predicting the thermal contact conductance at the interface between beds of spherical particles and nominally flat surfaces has been identified.

  20. Dynamic contact angle cycling homogenizes heterogeneous surfaces.

    PubMed

    Belibel, R; Barbaud, C; Mora, L

    2016-12-01

    In order to reduce restenosis, the necessity to develop the appropriate coating material of metallic stent is a challenge for biomedicine and scientific research over the past decade. Therefore, biodegradable copolymers of poly((R,S)-3,3 dimethylmalic acid) (PDMMLA) were prepared in order to develop a new coating exhibiting different custom groups in its side chain and being able to carry a drug. This material will be in direct contact with cells and blood. It consists of carboxylic acid and hexylic groups used for hydrophilic and hydrophobic character, respectively. The study of this material wettability and dynamic surface properties is of importance due to the influence of the chemistry and the potential motility of these chemical groups on cell adhesion and polymer kinetic hydrolysis. Cassie theory was used for the theoretical correction of contact angles of these chemical heterogeneous surfaces coatings. Dynamic Surface Analysis was used as practical homogenizer of chemical heterogeneous surfaces by cycling during many cycles in water. In this work, we confirmed that, unlike receding contact angle, advancing contact angle is influenced by the difference of only 10% of acidic groups (%A) in side-chain of polymers. It linearly decreases with increasing acidity percentage. Hysteresis (H) is also a sensitive parameter which is discussed in this paper. Finally, we conclude that cycling provides real information, thus avoiding theoretical Cassie correction. H(10)is the most sensible parameter to %A. PMID:27612817

  1. The contact mechanics of fractal surfaces

    NASA Astrophysics Data System (ADS)

    Buzio, Renato; Boragno, Corrado; Biscarini, Fabio; Buatier de Mongeot, Francesco; Valbusa, Ugo

    2003-04-01

    The role of surface roughness in contact mechanics is relevant to processes ranging from adhesion to friction, wear and lubrication. It also promises to have a deep impact on applied science, including coatings technology and design of microelectromechanical systems. Despite the considerable results achieved by indentation experiments, particularly in the measurement of bulk hardness on nanometre scales, the contact behaviour of realistic surfaces, showing random multiscale roughness, remains largely unknown. Here we report experimental results concerning the mechanical response of self-affine thin films indented by a micrometric flat probe. The specimens, made of cluster-assembled carbon or of sexithienyl, an organic molecular material, were chosen as prototype systems for the broad class of self-affine fractal interfaces, today including surfaces grown under non-equilibrium conditions, fractures, manufactured metal surfaces and solidified liquid fronts. We observe that a regime exists in which roughness drives the contact mechanics: in this range surface stiffness varies by a few orders of magnitude on small but significant changes of fractal parameters. As a consequence, we demonstrate that soft solid interfaces can be appreciably strengthened by reducing both fractal dimension and surface roughness. This indicates a general route for tailoring the mechanical properties of solid bodies.

  2. Thermal contact conductance of pressurized surfaces

    NASA Technical Reports Server (NTRS)

    Voss, Fred E.

    1988-01-01

    Thermal vacuum testing has demonstrated the feasibility of the concept of pressurizing contact surfaces for the transfer of waste heat on the Space Station. Data show a thin inflatable bladder design to provide a greater contact conductance than an expandable bellows approach, with substantially less interface volume to transfer the same amount of heat. Extended vacuum testing of the Radiator-to-Thermal Bus assembly indicated a continual increase of conductance as the interface was maintained at 150 psi for a 100-hour period.

  3. Surface roughness effects in elastohydrodynamic contacts

    NASA Technical Reports Server (NTRS)

    Tripp, J. H.; Hamrock, B. J.

    1985-01-01

    Surface roughness effects in full-film EHL contacts were studied. A flow factor modification to the Reynolds equation was applied to piezoviscous-elastic line contacts. Results for ensemble-averaged film shape, pressure distribution, and other mechanical quantities were obtained. Asperities elongated in the flow direction by a factor exceeding two decreased both film shape and pressure extrema at constant load; isotropic or transverse asperities increased these extrema. The largest effects are displayed by traction, which increased by over 5% for isotropic or transverse asperities and by slightly less for longitudinal roughness.

  4. 78 FR 14549 - National Contact Center; Information Collection; National Contact Center Customer Evaluation Survey

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-06

    ... ADMINISTRATION National Contact Center; Information Collection; National Contact Center Customer Evaluation Survey AGENCY: Contact Center Services, Federal Citizen Information Center, Office of Citizen Services... requirement regarding the National Contact Center customer evaluation surveys. In this request, the...

  5. Imaging surface contacts: Power law contact distributions and contact stresses in quartz, calcite, glass and acrylic plastic

    USGS Publications Warehouse

    Dieterich, J.H.; Kilgore, B.D.

    1996-01-01

    A procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials, while the surfaces are subjected to static loads or undergoing frictional slip. Static loading experiments with quartz, calcite, soda-lime glass and acrylic plastic at normal stresses to 30 MPa yield power law distributions of contact areas from the smallest contacts that can be resolved (3.5 ??m2) up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces. In each material, increasing normal stress results in a roughly linear increase of the real area of contact. Mechanisms of contact area increase are by growth of existing contacts, coalescence of contacts and appearance of new contacts. Mean contacts stresses are consistent with the indentation strength of each material. Contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self-similar. The contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies. The contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap. Synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography.

  6. Assessment of surface contamination with contact mechanics

    SciTech Connect

    EMERSON,JOHN A.; MILLER,GREGORY V.; SORENSEN,CHRISTOPHER R.; PEARSON,RAYMOND A.

    2000-02-21

    The authors are particularly interested in the work of adhesion measurements as a means to facilitate the understanding of the adhesive failure mechanisms for systems containing encapsulated and bonded components. Of the several issues under investigation, one is the effect of organic contamination on the adhesive strength for several types of polymer/metal interface combinations. The specific question that the authors are trying to address is at what level of contamination does adhesive strength decrease. The use of contact mechanics, the JKR method, is a good approach for studying this question. Another approach being studied is the use of interracial fracture mechanics. The model contaminant is hexadecane--non-polar, medium molecular weight hydrocarbon fluid. They choose hexadecane because it replicates typical machining fluids, is nonreactive with Al surfaces, and should not dissolve readily into the adhesive systems of interest. The application of a uniform, controllable and reproducible hexadecane layer on Al surfaces has proven to be difficult. A primary concern is whether studies of model systems can be extended to systems of technological interest. The JKR theory is a continuum mechanics model of contact between two solid spheres that was developed by Johnson, Kendall and Roberts. The JKR theory is an extension of Hertzian contact theory and attributes the additional increase in the contact area between a soft elastomeric hemisphere to adhesive forces between the two surfaces. The JKR theory allows a direct estimate of the surface free energy of interface as well as the work of adhesion (Wa) between solids. Early studies performed in this laboratory involved the determination of Wa between silicone (PDMS) and Al surfaces in order to establish the potential adhesive failure mechanisms. However, the JKR studies using commercial based PDMS [poly(dimethylsiloxane)] was fraught with difficulty that were attributed to the additives used in commercial PDMS

  7. Development of Titanium Dioxide (TiO2 ) Nanocoatings on Food Contact Surfaces and Method to Evaluate Their Durability and Photocatalytic Bactericidal Property.

    PubMed

    Yemmireddy, Veerachandra K; Farrell, Glenn D; Hung, Yen-Con

    2015-08-01

    Titanium dioxide (TiO2 ) is a well-known photocatalyst for its excellent bactericidal property under UVA light. The purpose of this study was to develop physically stable TiO2 coatings on food contact surfaces using different binding agents and develop methods to evaluate their durability and microbicidal property. Several types of organic and inorganic binders such as polyvinyl alcohol, polyethylene glycol, polyurethane, polycrylic, sodium and potassium silicates, shellac resin, and other commercial binders were used at 1:1 to 1:16 nanoparticle to binder weight ratios to develop a formulation for TiO2 coating on stainless steel surfaces. Among the tested binders, polyurethane, polycrylic, and shellac resin were found to be physically more stable when used in TiO2 coating at 1:4 to 1:16 weight ratio. The physical stability of TiO2 coatings was determined using adhesion strength and scratch hardness tests by following standard ASTM procedures. Further, wear resistance of the coatings was evaluated based on a simulated cleaning procedure used in food processing environments. TiO2 coating with polyurethane at a 1:8 nanoparticle to binder weight ratio showed the highest scratch hardness (1.08 GPa) followed by coating with polycrylic (0.68 GPa) and shellac (0.14 GPa) binders. Three different techniques, namely direct spreading, glass cover-slip, and indented coupon were compared to determine the photocatalytic bactericidal property of TiO2 coatings against Escherichia coli 0157:H7 at 2 mW/cm(2) UVA light intensity. Under the tested conditions, the indented coupon technique was found to be the most appropriate method to determine the bactericidal property of TiO2 coatings and showed a reduction of 3.5 log CFU/cm(2) in 2 h. PMID:26189653

  8. Contact of nonflat crack surfaces during fatigue

    SciTech Connect

    Sehitoglu, H.; Garcia, A.M.

    1999-07-01

    A model has been developed to predict crack opening and closure behavior for propagating fatigue cracks which are nonflat and undergo significant sliding displacements. Crack surfaces were characterized by a random distribution of asperity heights, density of asperities, and asperity radii. The propagating crack was subdivided into ligaments and each ligament was treated as a contact problem between two randomly rough surfaces. The far-field tensile stresses were varied in a cyclic manner for R = 0.1 and {minus}1 loading conditions. The contact stresses at the minimal load were determined by analyzing the local crushing of the asperities. Then, upon loading the crack opening, stresses were computed when the contact stresses were overcome. The results of crack opening stresses were correlated with CTOD/{sigma}{sub 0} where CTOD is the crack-tip opening displacement and {sigma}{sub 0} is the average asperity height. The asperity effects on closure were compared with plasticity-induced closure results from the literature for identification of conditions when one mechanism dominates the other.

  9. Influence of surface tension on fractal contact model

    NASA Astrophysics Data System (ADS)

    Long, J. M.; Wang, G. F.; Feng, X. Q.; Yu, S. W.

    2014-03-01

    Almost all solid surfaces have roughness on different length scales, from macro, micro to nano. In the conventional fractal contact model, the macroscopic Hertzian contact theory is employed to predict the contact load-area relation for all sizes of contact spots. However, when the contact radius of an asperity shrinks to nanometers, surface tension may greatly alter the contact behavior. In the present paper, we address surface effects on the contact between a rigid sphere and an elastic half space, and we demonstrate that the contact load-area relation is size-dependent, especially for nanosized asperities. Then, the refined contact relation is incorporated into the Majumdar-Bhushan fractal contact model. It is found that the presence of surface tension requires higher load than the conventional fractal contact model to generate the same real contact area.

  10. Evaluating the Impact of Institutional Contacts.

    ERIC Educational Resources Information Center

    Pagano, Marian F.; Terkla, Dawn Geronimo

    1991-01-01

    Evaluation of the impact of prospective students' contacts with the institution is an objective of the admissions research agenda at Tufts University (Massachusetts). An annual survey gathers information on individuals who make inquiries but do not submit an application and on the parents of matriculating students. (MSE)

  11. The Frictional Force with Respect to the Actual Contact Surface

    NASA Technical Reports Server (NTRS)

    Holm, Ragnar

    1944-01-01

    Hardy's statement that the frictional force is largely adhesion, and to a lesser extent, deformation energy is proved by a simple experiment. The actual contact surface of sliding contacts and hence the friction per unit of contact surface was determined in several cases. It was found for contacts in normal atmosphere to be about one-third t-one-half as high as the macroscopic tearing strength of the softest contact link, while contacts annealed in vacuum and then tested, disclosed frictional forces which are greater than the macroscopic strength.

  12. Fractal prediction model of thermal contact conductance of rough surfaces

    NASA Astrophysics Data System (ADS)

    Ji, Cuicui; Zhu, Hua; Jiang, Wei

    2013-01-01

    The thermal contact conductance problem is an important issue in studying the heat transfer of engineering surfaces, which has been widely studied since last few decades, and for predicting which many theoretical models have been established. However, the models which have been existed are lack of objectivity due to that they are mostly studied based on the statistical methodology characterization for rough surfaces and simple partition for the deformation formats of contact asperity. In this paper, a fractal prediction model is developed for the thermal contact conductance between two rough surfaces based on the rough surface being described by three-dimensional Weierstrass and Mandelbrot fractal function and assuming that there are three kinds of asperity deformation modes: elastic, elastoplastic and fully plastic. Influences of contact load and contact area as well as fractal parameters and material properties on the thermal contact conductance are investigated by using the presented model. The investigation results show that the thermal contact conductance increases with the increasing of the contact load and contact area. The larger the fractal dimension, or the smaller the fractal roughness, the larger the thermal contact conductance is. The thermal contact conductance increases with decreasing the ratio of Young's elastic modulus to the microhardness. The results obtained indicate that the proposed model can effectively predict the thermal contact conductance at the interface, which provide certain reference to the further study on the issue of heat transfer between contact surfaces.

  13. Non-contact friction for ion-surface interactions

    NASA Astrophysics Data System (ADS)

    Jentschura, Ulrich D.; Lach, Grzegorz

    2015-05-01

    Non-contact friction forces are exerted on physical systems through dissipative processes, when the two systems are not in physical contact with each other, or, in quantum mechanical terms, when the overlap of their wave functions is negligible. Non-contact friction is mediated by the exchange of virtual quanta, with the additional requirement that the scattering process needs to have an inelastic component. For finite-temperature ion-surface interactions, the friction is essentially caused by Ohmic resistance due to the motion of the image charge moving in a dielectric material. A conceivable experiment is difficult because the friction force needs to be isolated from the interaction with the image charge, which significantly distorts the ion's flight path. We propose an experimental setup which is designed to minimize the influence of the image charge interaction though a compensation mechanism, and evaluate the energy loss due to non-contact friction for helium ions (He+) interacting with gold, vanadium, titanium and graphite surfaces. Interactions with the infinite series of mirror charges in the plates are summed in terms of the logarithmic derivatives of the Gamma function, and of the Hurwitz zeta function.

  14. Contact heat transfer and thermal contact conductance between nonconforming surfaces in an abrupt contact

    SciTech Connect

    Kumar, R.K.; Kroeger, V.D.

    1996-08-01

    An understanding of the thermal contact conductance behavior when a fuel pin contacts the pressure tube is important in the safety analyses of CANDU reactors. Experiments were therefore performed in a small-scale apparatus with fuel element and pressure tube specimens coming into contact in an argon/oxygen atmosphere, which kinetically simulated steam. The contact was initiated when the fuel-element and pressure-tube specimens were at {approximately} 1,000 C and {approximately} 400 C respectively. The experiments were analyzed using a finite-element code. Heat transfer rates through the contact and thermal contact conductances were determined for contact loads ranging from 20 to 80 N. For most contact loads, the contact conductance increased with time during the transient heat-up of the fuel element specimen. It was found that the calculated thermal contact conductances were in the range of 1 to 30 kW/(m{sup 2} K) based on a reference contact width of 2.5 mm. The variation of contact conductance with contact load was nearly linear.

  15. Using Chemoattractants to Lure Bacteria to Contact-Killing Surfaces.

    PubMed

    Jain, Rishabh; Faith, Nancy G; Milkowski, Andrew; Nelson, Kevin; Busche, David; Lynn, David M; Czuprynski, Charles J; Abbott, Nicholas L

    2016-05-01

    Antimicrobial surfaces with covalently attached biocidal functionalities only kill microbes that come into direct contact with the surfaces (contact-killing surfaces). Herein, the activity of contact-killing surfaces is shown to be enhanced by using gradients in the concentration of soluble chemoattractants (CAs) to attract bacteria to the surfaces. Two natural and nonbiocidal CAs (aspartate and glucose) were used to attract bacteria to model surfaces decorated with quaternary ammonium groups (known to kill bacteria that come into contact with them). These results demonstrate the killing of Escherichia coli and Salmonella typhimurium, two common pathogens, at levels 10- to 20-times greater than that of the native surfaces alone. This approach is general and provides new strategies for the design of active or dynamic contact-killing surfaces with enhanced antimicrobial activities. PMID:27059788

  16. Allergic contact dermatitis: Patient diagnosis and evaluation.

    PubMed

    Mowad, Christen M; Anderson, Bryan; Scheinman, Pamela; Pootongkam, Suwimon; Nedorost, Susan; Brod, Bruce

    2016-06-01

    Allergic contact dermatitis resulting from exposure to a chemical or chemicals is a common diagnosis in the dermatologist's office. We are exposed to hundreds of potential allergens daily. Patch testing is the criterion standard for diagnosing the causative allergens responsible for allergic contact dermatitis. Patch testing beyond standard trays is often needed to fully diagnose patients, but not all dermatology practices have access to this testing procedure or these allergens. In order to adequately evaluate patients, physicians must understand the pathophysiology of the disease process and be well versed in the proper evaluation of patients, indications for patch testing, proper testing procedure, and other diagnostic tools available and be aware of new and emerging allergens. PMID:27185421

  17. Superhydrophobic surfaces: A model approach to predict contact angle and surface energy of soil particles

    NASA Astrophysics Data System (ADS)

    Shirtcliffe, Neil; Hamlett, Christopher; McHale, Glen; Newton, Michael; Bachmann, Joerg; Woche, S.

    2010-05-01

    C. Hamlett(a), G. McHALE(a), N. Shirtcliffe(a), M. Newton(a), S.K. Woche(b), and J. BACHMANN(b) aSchool of Science & Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK and bInstitute of Soil Science, Leibniz University Hannover, Herrenhaeuser Str.2, 30419, Hannover, Germany. Summary Wettability of soil affects a wide variety of processes including infiltration, preferential flow and surface runoff. The problem of determining contact angles and surface energy of powders, such as soil particles, remains unsolved. So far, several theories and approaches have been proposed, but formulation of surface and interfacial free energy, as regards its components, is still a very debatable issue. In the present study, the general problem of the interpretation of contact angles and surface free energy on chemically heterogeneous and rough soil particle surfaces are evaluated by a reformulation of the Cassie-Baxter equation assuming that the particles are attached on to a plane and rigid surface. Compared with common approaches, our model considers a roughness factor which depends on the Young's Law contact angle determined by the surface chemistry. Results of the model are discussed and compared with independent contact angle measurements using the Sessile Drop and the Wilhelmy Plate methods. Based on contact angle data, the critical surface tension of the grains were determined by the method proposed by Zisman. Experiments were made with glass beads and three soil materials ranging from sand to clay. Soil particles were coated with different loadings of dichlorodimethylsilane (DCDMS) to vary the wettability. Varying the solid surface tension using DCDMS treatments provided pure water wetting behaviours ranging from wettable to extremely hydrophobic with contact angles >150°. Results showed that the critical surface energy measured on grains with the highest DCDMS loadings was similar to the surface energy measured independently on ideal DCDMS

  18. Contact angles of drops on curved superhydrophobic surfaces.

    PubMed

    Viswanadam, Goutham; Chase, George G

    2012-02-01

    Superhydrophobic surfaces have contact angles that exceed 150 degrees and are known to reduce surface fouling, protect surfaces, and improve liquid-liquid separations. Electrospun sub-micron fiber mats can perform as superhydrophobic surfaces. Superhydrophobic behavior is typically measured on planar surfaces, whereas applications may require curved surfaces. This paper discuses the measurement of water contact angles of fiber mats formed on cylindrical surfaces to create superhydrophobic behavior on curved surfaces. Equations are derived that relate the radius of curvature of spherical and cylindrical surfaces and drop size to the observed contact angle on the curved surfaces. Calculations from the equations agree well with experimental observations on spherical surfaces reported in literature and on cylindrical surfaces created in our lab. PMID:22129634

  19. The estimation of dynamic contact angle of ultra-hydrophobic surfaces using inclined surface and impinging droplet methods

    NASA Astrophysics Data System (ADS)

    Jasikova, Darina; Kotek, Michal

    2014-03-01

    The development of industrial technology also brings with optimized surface quality, particularly where there is contact with food. Application ultra-hydrophobic surface significantly reduces the growth of bacteria and facilitates cleaning processes. Testing and evaluation of surface quality are used two methods: impinging droplet and inclined surface method optimized with high speed shadowgraphy, which give information about dynamic contact angle. This article presents the results of research into new methods of measuring ultra-hydrophobic patented technology.

  20. Contact between traps and surfaces during contact sampling of explosives in security settings.

    PubMed

    Chaffee-Cipich, Michelle N; Hoss, Darby J; Sweat, Melissa L; Beaudoin, Stephen P

    2016-03-01

    Realistic descriptions of interfacial contact between rough, deformable surfaces under load are difficult to obtain; however, this contact is of great import in a wide range of applications. Here, we detail, through experiment and computational simulation, the interfacial contact between four common traps and five commonly investigated surfaces encountered in explosives detection applications associated with airport security. The Young's modulus and hardness of four traps and seven substrates were measured using nanoindentation. These properties determine how deformation occurs when traps are applied for contact sampling of explosives. The nanoindentation data were analyzed using the Oliver-Pharr method, and an indenter area function was created using silicon and gold as the reference materials. The Young's moduli of the traps ranged from 0.2 to 8GPa, while those of the surfaces ranged from 0.5 to 4GPa. The hardness values of the traps ranged from 0.005 to 0.22GPa, while those of the surfaces ranged from 0.02 to 0.2GPa. For each of 20 scenarios (4 traps, 5 surfaces), six contact simulations were performed. In these contact simulations, the Greenwood-Willliamson microcontact model was used to represent the behavior of the asperities on the traps, while the Timoshenko Beam model was used to describe the macroscopic behavior of the bulk trap materials spanning the space between asperities. This combination of feature- and trap-scale modeling provides a more realistic description of the interfacial contact than either model applied individually. The calculated distributions of separation distances between the traps and surfaces when the traps were contacted with the surfaces under a normal load were compared to estimate the relative effectiveness of the traps at interrogating the topography of the surfaces. This method is proposed as a tool to guide the development of trap materials for surface sampling and surface cleaning applications. PMID:26836243

  1. Two dimensional nanoscale reciprocating sliding contacts of textured surfaces

    NASA Astrophysics Data System (ADS)

    Tong, Ruiting; Liu, Geng; Liu, Tianxiang

    2016-05-01

    Detailed behaviors of nanoscale textured surfaces during the reciprocating sliding contacts are still unknown although they are widely used in mechanical components to improve tribological characteristics. The current research of sliding contacts of textured surfaces mainly focuses on the experimental studies, while the cost is too high. Molecular dynamics(MD) simulation is widely used in the studies of nanoscale single-pass sliding contacts, but the CPU cost of MD simulation is also too high to simulate the reciprocating sliding contacts. In this paper, employing multiscale method which couples molecular dynamics simulation and finite element method, two dimensional nanoscale reciprocating sliding contacts of textured surfaces are investigated. Four textured surfaces with different texture shapes are designed, and a rigid cylindrical tip is used to slide on these textured surfaces. For different textured surfaces, average potential energies and average friction forces of the corresponding sliding processes are analyzed. The analyzing results show that "running-in" stages are different for each texture, and steady friction processes are discovered for textured surfaces II, III and IV. Texture shape and sliding direction play important roles in reciprocating sliding contacts, which influence average friction forces greatly. This research can help to design textured surfaces to improve tribological behaviors in nanoscale reciprocating sliding contacts.

  2. Two dimensional nanoscale reciprocating sliding contacts of textured surfaces

    NASA Astrophysics Data System (ADS)

    Tong, Ruiting; Liu, Geng; Liu, Tianxiang

    2016-04-01

    Detailed behaviors of nanoscale textured surfaces during the reciprocating sliding contacts are still unknown although they are widely used in mechanical components to improve tribological characteristics. The current research of sliding contacts of textured surfaces mainly focuses on the experimental studies, while the cost is too high. Molecular dynamics(MD) simulation is widely used in the studies of nanoscale single-pass sliding contacts, but the CPU cost of MD simulation is also too high to simulate the reciprocating sliding contacts. In this paper, employing multiscale method which couples molecular dynamics simulation and finite element method, two dimensional nanoscale reciprocating sliding contacts of textured surfaces are investigated. Four textured surfaces with different texture shapes are designed, and a rigid cylindrical tip is used to slide on these textured surfaces. For different textured surfaces, average potential energies and average friction forces of the corresponding sliding processes are analyzed. The analyzing results show that "running-in" stages are different for each texture, and steady friction processes are discovered for textured surfaces II, III and IV. Texture shape and sliding direction play important roles in reciprocating sliding contacts, which influence average friction forces greatly. This research can help to design textured surfaces to improve tribological behaviors in nanoscale reciprocating sliding contacts.

  3. Non-Contact Laser Based Ultrasound Evaluation of Canned Foods

    NASA Astrophysics Data System (ADS)

    Shelton, David

    2005-03-01

    Laser-Based Ultrasound detection was used to measure the velocity of compression waves transmitted through canned foods. Condensed broth, canned pasta, and non-condensed soup were evaluated in these experiments. Homodyne adaptive optics resulted in measurements that were more accurate than the traditional heterodyne method, as well as yielding a 10 dB gain in signal to noise. A-Scans measured the velocity of ultrasound sent through the center of the can and were able to distinguish the quantity of food stuff in its path, as well as distinguish between meat and potato. B-Scans investigated the heterogeneity of the sample’s contents. The evaluation of canned foods was completely non-contact and would be suitable for continuous monitoring in production. These results were verified by conducting the same experiments with a contact piezo transducer. Although the contact method yields a higher signal to noise ratio than the non-contact method, Laser-Based Ultrasound was able to detect surface waves the contact transducer could not.

  4. Microbial biofilm detection on food contact surfaces by macro-scale fluorescence imaging

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Hyperspectral fluorescence imaging methods were utilized to evaluate the potential of multispectral fluorescence methods for detection of pathogenic biofilm formations on four types of food contact surface materials: stainless steel, high density polyethylene (HDPE) commonly used for cutting boards,...

  5. Early contacts between T lymphocytes and activating surfaces

    NASA Astrophysics Data System (ADS)

    Cretel, E.; Touchard, D.; Benoliel, A. M.; Bongrand, P.; Pierres, A.

    2010-05-01

    Cells continually probe their environment to adapt their behaviour. A current challenge is to determine how they analyse nearby surfaces and how they process information to take decisions. We addressed this problem by monitoring human T lymphocyte attachment to surfaces coated with activating anti-CD3 or control anti-HLA antibodies. Interference reflection microscopy allowed us to monitor cell-to-surface apposition with a few nanometre vertical resolution during the first minutes following contact. We found that (i) when a cell fell on a surface, contact extension was preceded by a lag of several tens of seconds. (ii) During this lag, vertical membrane undulations seemed to generate transient contacts with underlying surfaces. (iii) After the lag period, the contact area started increasing linearly with a rate of about 1.5 µm2 s - 1 on activating surfaces and about 0.2 µm2 s - 1 on control surfaces. (iv) Concomitantly with lateral surface extension, the apparent distance between cell membranes and surfaces steadily decreased. These results are consistent with the hypothesis that the cell decision to spread rapidly on activating surfaces resulted from the integration of information yielded by transient contacts with these surfaces generated by membrane undulations during a period of about 1 min.

  6. Surface roughness, asperity contact and gold RF MEMS switch behavior

    NASA Astrophysics Data System (ADS)

    Rezvanian, O.; Zikry, M. A.; Brown, C.; Krim, J.

    2007-10-01

    Modeling predictions and experimental measurements were obtained to characterize the electro-mechanical response of radio frequency (RF) microelectromechanical (MEM) switches due to variations in surface roughness and finite asperity deformations. Three-dimensional surface roughness profiles were generated, based on a Weierstrass-Mandelbrot fractal representation, to match the measured roughness characteristics of contact bumps of manufactured RF MEMS switches. Contact asperity deformations due to applied contact pressures were then obtained by a creep constitutive formulation. The contact pressure is derived from the interrelated effects of roughness characteristics, material hardening and softening, temperature increases due to Joule heating and contact forces. This modeling framework was used to understand how contact resistance evolves due to changes in the real contact area, the number of asperities in contact, and the temperature and resistivity profiles at the contact points. The numerical predictions were qualitatively consistent with the experimental measurements and observations of how contact resistance evolves as a function of deformation time history. This study provides a framework that is based on integrated modeling and experimental measurements, which can be used in the design of reliable RF MEMS devices with extended life cycles.

  7. 78 FR 30303 - National Contact Center; Submission for OMB Review; National Contact Center Customer Evaluation...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-22

    ... in the Federal Register at 78 FR 14549, on March 6, 2013. No comments were received. DATES: Submit... ADMINISTRATION National Contact Center; Submission for OMB Review; National Contact Center Customer Evaluation Survey AGENCY: Contact Center Services, Federal Citizen Information Center, Office of Citizen...

  8. 75 FR 6032 - National Contact Center; Submission for OMB Review; National Contact Center Customer Evaluation...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-02-05

    ... renewal of a previously approved information collection requirement regarding the National Contact Center customer evaluation survey. A request for public comments was published in the Federal Register at 74 FR... ADMINISTRATION National Contact Center; Submission for OMB Review; National Contact Center Customer...

  9. Low-coherence interferometer for contact lens surface metrology

    NASA Astrophysics Data System (ADS)

    Heideman, Kyle C.; Greivenkamp, John E.

    2016-03-01

    Contact lens performance depends on a number of lens properties. Many metrology systems have been developed to measure different aspects of a contact lens, but none test the surface figure in reflection to subwavelength accuracy. Interferometric surface metrology of immersed contact lenses is complicated by the close proximity of the surfaces, low surface reflectivity, and instability of the lens. An interferometer to address these issues was developed and is described here. The accuracy of the system is verified by comparison of glass reference sample measurements against a calibrated commercial interferometer. The described interferometer can accurately reconstruct large surface departures from spherical with reverse raytracing. The system is shown to have residual errors better than 0.05% of the measured surface departure for high slope regions. Measurements made near null are accurate to λ/20. Spherical, toric, and bifocal soft contact lenses have been measured by this system and show characteristics of contact lenses not seen in transmission testing. The measurements were used to simulate a transmission map that matches an actual transmission test of the contact lens to λ/18.

  10. Rough surface electrical contact resistance considering scale dependent properties and quantum effects

    SciTech Connect

    Jackson, Robert L.; Crandall, Erika R.; Bozack, Michael J.

    2015-05-21

    The objective of this work is to evaluate the effect of scale dependent mechanical and electrical properties on electrical contact resistance (ECR) between rough surfaces. This work attempts to build on existing ECR models that neglect potentially important quantum- and size-dependent contact and electrical conduction mechanisms present due to the asperity sizes on typical surfaces. The electrical conductance at small scales can quantize or show a stepping trend as the contact area is varied in the range of the free electron Fermi wavelength squared. This work then evaluates if these effects remain important for the interface between rough surfaces, which may include many small scale contacts of varying sizes. The results suggest that these effects may be significant in some cases, while insignificant for others. It depends on the load and the multiscale structure of the surface roughness.

  11. Dynamic contact angle and three-phase contact line of water drop on copper surface

    NASA Astrophysics Data System (ADS)

    Orlova, E. G.; Feoktistov, D. V.; Batishcheva, K. A.

    2015-10-01

    Nowadays there is a lack of experimental data describing the physical process of drop spreading on a solid metal surface for developing wetting and spreading theory. The experimental data obtained by using the high speed video-recording will allow to identify unknown previously spreading modes as well as the change of the dynamic contact angle and the three-phase contact line. The purpose of the work is to determine the effect of the drop growth rate and the copper substrate surface roughness on the dynamic contact angle and the three-phase contact line speed at distilled water drop spreading. Shadow and Schlieren methods are used to obtain experimental data. Three drop spreading modes on the rough surfaces were identified. Time dependences of the dynamic contact angle and contact line speed were obtained. Experimental results can be used for assessing the validity of the developed mathematical models of wetting and spreading processes in the field of micro- and nanoelectronics, ink jet printing, thin-film coatings, spray cooling, and optoelectronics.

  12. Evaluation of the electrical contact area in contact-mode scanning probe microscopy

    SciTech Connect

    Celano, Umberto E-mail: u.celano@gmail.com; Chintala, Ravi Chandra; Vandervorst, Wilfried; Hantschel, Thomas; Giammaria, Guido; Conard, Thierry; Bender, Hugo

    2015-06-07

    The tunneling current through an atomic force microscopy (AFM) tip is used to evaluate the effective electrical contact area, which exists between tip and sample in contact-AFM electrical measurements. A simple procedure for the evaluation of the effective electrical contact area is described using conductive atomic force microscopy (C-AFM) in combination with a thin dielectric. We characterize the electrical contact area for coated metal and doped-diamond tips operated at low force (<200 nN) in contact mode. In both cases, we observe that only a small fraction (<10 nm{sup 2}) of the physical contact (∼100 nm{sup 2}) is effectively contributing to the transport phenomena. Assuming this reduced area is confined to the central area of the physical contact, these results explain the sub-10 nm electrical resolution observed in C-AFM measurements.

  13. Evaluation of the electrical contact area in contact-mode scanning probe microscopy

    NASA Astrophysics Data System (ADS)

    Celano, Umberto; Hantschel, Thomas; Giammaria, Guido; Chintala, Ravi Chandra; Conard, Thierry; Bender, Hugo; Vandervorst, Wilfried

    2015-06-01

    The tunneling current through an atomic force microscopy (AFM) tip is used to evaluate the effective electrical contact area, which exists between tip and sample in contact-AFM electrical measurements. A simple procedure for the evaluation of the effective electrical contact area is described using conductive atomic force microscopy (C-AFM) in combination with a thin dielectric. We characterize the electrical contact area for coated metal and doped-diamond tips operated at low force (<200 nN) in contact mode. In both cases, we observe that only a small fraction (<10 nm2) of the physical contact (˜100 nm2) is effectively contributing to the transport phenomena. Assuming this reduced area is confined to the central area of the physical contact, these results explain the sub-10 nm electrical resolution observed in C-AFM measurements.

  14. High contact angle hysteresis of superhydrophobic surfaces: Hydrophobic defects

    NASA Astrophysics Data System (ADS)

    Chang, Feng-Ming; Hong, Siang-Jie; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2009-08-01

    A typical superhydrophobic surface is essentially nonadhesive and exhibits very low water contact angle (CA) hysteresis, so-called Lotus effect. However, leaves of some plants such as scallion and garlic with an advancing angle exceeding 150° show very serious CA hysteresis. Although surface roughness and epicuticular wax can explain the very high advancing CA, our analysis indicates that the unusual hydrophobic defect, diallyl disulfide, is the key element responsible for contact line pinning on allium leaves. After smearing diallyl disulfide on an extended polytetrafluoroethylene (PTFE) film, which is originally absent of CA hysteresis, the surface remains superhydrophobic but becomes highly adhesive.

  15. Drop shape visualization and contact angle measurement on curved surfaces.

    PubMed

    Guilizzoni, Manfredo

    2011-12-01

    The shape and contact angles of drops on curved surfaces is experimentally investigated. Image processing, spline fitting and numerical integration are used to extract the drop contour in a number of cross-sections. The three-dimensional surfaces which describe the surface-air and drop-air interfaces can be visualized and a simple procedure to determine the equilibrium contact angle starting from measurements on curved surfaces is proposed. Contact angles on flat surfaces serve as a reference term and a procedure to measure them is proposed. Such procedure is not as accurate as the axisymmetric drop shape analysis algorithms, but it has the advantage of requiring only a side view of the drop-surface couple and no further information. It can therefore be used also for fluids with unknown surface tension and there is no need to measure the drop volume. Examples of application of the proposed techniques for distilled water drops on gemstones confirm that they can be useful for drop shape analysis and contact angle measurement on three-dimensional sculptured surfaces. PMID:21889152

  16. DEVELOPMENT OF EVALUATION OF A QUANTITATIVE VIDEO-FLUORESCENCE IMAGING SYSTEM AND FLUORESCENT TRACER FOR MEASURING TRANSFER OF PESTICIDE RESIDUES FROM SURFACES TO HANDS WITH REPEATED CONTACTS

    EPA Science Inventory

    A video imaging system and the associated quantification methods have been developed for measurement of the transfers of a fluorescent tracer from surfaces to hands. The highly fluorescent compound riboflavin (Vitamin B2), which is also water soluble and non-toxic, was chosen as...

  17. Contact Potentials, Fermi Level Equilibration, and Surface Charging.

    PubMed

    Peljo, Pekka; Manzanares, José A; Girault, Hubert H

    2016-06-14

    This article focuses on contact electrification from thermodynamic equilibration of the electrochemical potential of the electrons of two conductors upon contact. The contact potential difference generated in bimetallic macro- and nanosystems, the Fermi level after the contact, and the amount and location of the charge transferred from one metal to the other are discussed. The three geometries considered are spheres in contact, Janus particles, and core-shell particles. In addition, the force between the two spheres in contact with each other is calculated and is found to be attractive. A simple electrostatic model for calculating charge distribution and potential profiles in both vacuum and an aqueous electrolyte solution is described. Immersion of these bimetallic systems into an electrolyte solution leads to the formation of an electric double layer at the metal-electrolyte interface. This Fermi level equilibration and the associated charge transfer can at least partly explain experimentally observed different electrocatalytic, catalytic, and optical properties of multimetallic nanosystems in comparison to systems composed of pure metals. For example, the shifts in the surface plasmon resonance peaks in bimetallic core-shell particles seem to result at least partly from contact charging. PMID:27176729

  18. Surface-Energy Dependent Contact Activation of Blood Factor XII

    PubMed Central

    Golas, Avantika; Parhi, Purnendu; Dimachkie, Ziad O.; Siedlecki, Christopher A.; Vogler, Erwin A.

    2009-01-01

    Contact activation of blood factor XII (FXII, Hageman factor) in neat-buffer solution exhibits a parabolic profile when scaled as a function of silanized-glass-particle activator surface energy (measured as advancing water adhesion tension τao=γlvocosθ in dyne/cm, where γlvo is water interfacial tension in dyne/cm and θ is the advancing contact angle). Nearly equal activation is observed at the extremes of activator water-wetting properties −36<τao<72 dyne/cm (0° ≤ θ < 120°), falling sharply through a broad minimum within the 20<τao<40 dyne/cm (55° < θ < 75°) range over which activation yield (putatively FXIIa) rises just above detection limits. Activation is very rapid upon contact with all activators tested and did not significantly vary over 30 minutes of continuous FXII-procoagulant contact. Results suggest that materials falling within the 20<τao<40 dyne/cm surface-energy range should exhibit minimal activation of blood-plasma coagulation through the intrinsic pathway. Surface chemistries falling within this range are, however, a perplexingly difficult target for surface engineering because of the critical balance that must be struck between hydrophobicity and hydrophilicity. Results are interpreted within the context of blood plasma coagulation and the role of water and proteins at procoagulant surfaces. PMID:19892397

  19. Surface energy tailoring of glass by contact printed PDMS

    NASA Astrophysics Data System (ADS)

    Lamberti, A.; Quaglio, M.; Sacco, A.; Cocuzza, M.; Pirri, C. F.

    2012-09-01

    A simple contact printing method to modulate the surface wettability of glass employing poly(dimethyl)siloxane (PDMS) mold was investigated. PDMS is a well known material in microfluidics and soft lithography for biomedical applications, being easy to process, low cost, biocompatible and transparent. Moreover its wettability can be tuned, by the exposure to oxygen plasma, UV-ozone or chemical oxidant solutions, or by surface functionalization. Unfortunately the effects of these treatments are not so stable in time. In this work a method to modify the surface energy (SE) of PDMS by changing its composition is proposed. Different mixing ratios (polymer base/curing agent) are analyzed evidencing that SE decreases while increasing the content of the polymer base, permanently modifying the surface behavior. As a thin layer of PDMS can be transferred to glass surfaces by contact printing, it is possible to locally change the wettability of glass simply patterning PDMS. In this work a SE patterning technique for glass surfaces by PDMS transfer is proposed. The technological process is based on the fabrication of PDMS molds by lift-off technique using Laser Direct Writing (LDW) lithography to process commercial photoresist. The transferring process for structures having a width of 10 μm was studied for a chosen PDMS composition, analyzing the surface energy of the patterned thin film by contact angle (CA) measurements.

  20. Contact angle and film pressure: study of a talc surface.

    PubMed

    Douillard, J M; Zajac, J; Malandrini, H; Clauss, F

    2002-11-15

    Talc samples in both sheet and powder form are studied by adsorption calorimetry and adsorption isotherm techniques. A model is used to determine the solid surface energy, the solid surface tension and the dispersive, acidic, and basic components of these terms. These results are introduced in an approximate equation relating adsorption to contact angle data. Experimental contact angles are in correct agreement with this approach. The Neumann equation of state is used to fit the data and discussed. It appears as a numerical form of the general equation taking into account gas adsorption and film pressure. Behaviors of talc in contact with liquids do not appear very different whether the solid is in sheet or powder form. PMID:12505082

  1. Minimal adhesion surface area in tangentially loaded digital contacts.

    PubMed

    Terekhov, Alexander V; Hayward, Vincent

    2011-09-01

    The stick-to-slip transition of a fingertip in contact with a planar surface does not occur instantaneously. As the tangential load increases, portions of the skin adhere while others slip, giving rise to an evolution of the contact state, termed partial slip. We develop a quasi-static model that predicts that if the coefficient of kinetic friction is larger than the coefficient of static friction, then the stuck surface area diminishes as the tangential load increases until reaching a 'minimal adhesion surface area' where it vanishes abruptly. This phenomenon was observed in recently measured finger-slip image data (André et al., 2011) that were processed by an optic flow detection algorithm. We examined the results of 10 trials. Four of them exhibited the minimal adhesion surface area phenomenon, four of them did not, and two were inconclusive. PMID:21774936

  2. Contact Interface Verification for DYNA3D Scenario 2: Multi-Surface Contact

    SciTech Connect

    McMichael, L D

    2006-05-10

    A suite of test problems has been developed to examine contact behavior within the nonlinear, three-dimensional, explicit finite element analysis (FEA) code DYNA3D (Lin, 2005). The test problems use multiple interfaces and a combination of enforcement methods to assess the basic functionality of the contact algorithms. The results from the DYNA3D analyses are compared to closed form solutions to verify the contact behavior. This work was performed as part of the Verification and Validation efforts of LLNL W Program within the NNSA's Advanced Simulation and Computing (ASC) Program. DYNA3D models the transient dynamic response of solids and structures including the interactions between disjoint bodies (parts). A wide variety of contact surfaces are available to represent the diverse interactions possible during an analysis, including relative motion (sliding), separation and gap closure (voids), and fixed relative position (tied). The problem geometry may be defined using a combination of element formulations, including one-dimensional beam and truss elements, two-dimensional shell elements, and three-dimensional solid elements. Consequently, it is necessary to consider various element interactions during contact. This report and associated test problems examine the scenario where multiple bodies interact with each other via multiple interfaces. The test problems focus on whether any ordering issues exist in the contact logic by using a combination of interface types, contact enforcement options (i.e., penalty, Lagrange, and kinematic), and element interactions within each problem. The influence of rigid materials on interface behavior is also examined. The companion report (McMichael, 2006) and associated test problems address the basic contact scenario where one contact surface exists between two disjoint bodies. The test problems are analyzed using version 5.2 (compiled on 12/22/2005) of DYNA3D. The analytical results are used to form baseline solutions for

  3. Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis.

    PubMed

    Hozumi, Atsushi; McCarthy, Thomas J

    2010-02-16

    Ultralyophobic oxidized aluminum surfaces exhibiting negligible contact angle hysteresis for probe liquids were prepared by chemical vapor deposition (CVD) of bis((tridecafluoro-1,1,2,2,-tetrahydrooctyl)-dimethylsiloxy)methylsilane (CF(3)(CF(2))(5)CH(2)CH(2)Si(CH(3))(2)O)(2)SiCH(3)H, (R(F)Si(Me)(2)O)(2)SiMeH). Oxidized aluminum surfaces were prepared by photooxidation/cleaning of sputter-coated aluminum on silicon wafers (Si/Al(Al(2)(O(3)))) using oxygen plasma. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) confirmed that this facile CVD method produces a monolayer with a thickness of 1.1 nm on the Si/Al(Al(2)(O(3))) surface without a discernible change in surface morphology. After monolayer deposition, the hydrophilic Si/Al(Al(2)(O(3))) surface became both hydrophobic and oleophobic and exhibited essentially no contact angle hysteresis for water and n-hexadecane (advancing/receding contact angles (theta(A)/theta(R)) = 110 degrees/109 degrees and 52 degrees/50 degrees, respectively). Droplets move very easily on this surface and roll off of slightly tilted surfaces, independently of the contact angle (which is a practical definition of ultralyophobic). A conventional fluoroalkylsilane monolayer was also prepared from 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (CF(3)(CF(2))(7)CH(2)CH(2)Si(OCH(3))(3), R(F)Si(OMe)(3)) for comparison. The theta(A)/theta(R) values for water and n-hexadecane are 121 degrees/106 degrees and 76 degrees/71 degrees, respectively. The larger hysteresis values indicate the "pinning" of probe liquids, even though advancing contact angles are larger than those of the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers. The (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers have excellent hydrolytic stability in water. We propose that the (R(F)Si(Me)(2)O)(2)SiMeH-derived monolayers are flexible and liquidlike and that drops in contact with these surfaces experience very low energy barriers between metastable states, leading to the

  4. Early cell response to contact with biomaterial's surface.

    PubMed

    Komorowski, Piotr; Walkowiak-Przybyło, Magdalena; Walkowiak, Bogdan

    2016-07-01

    Most biomaterials at present have sufficient mechanical properties; however compliance with standards for biocompatibility is often not sufficient in clinical practice. This may be due to the complexity of biological systems in general and the diversity of individual responses to these materials by implant recipients. Significant improvement of biocompatibility must involve surface modification of implants, which in the future will make it possible to introduce individually selected types of surface modification for individual recipients. The key to this technology seems to be understanding the processes occurring at the site of contact of the implant with the tissue. Processes resulting from the stress generated by the contact of the biomaterial surfaces were observed with endothelial cells line EA.hy926, and it was demonstrated that differently modified surfaces of medical steel (polished medical steel and medical steel coated with Parylene C and nanocrystalline diamond) cause diverse cellular response in cells grown on these surfaces, on both the cellular (cell morphology and cell survival) and molecular (transcriptome and proteome profiles) levels. The herein presented observations are a good starting point not only for further research and the development of far-reaching personalization of medical implants, but also to study the potential use of cells as a specific sensor capable of recognizing different surfaces with which these cells come into contact. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 880-893, 2016. PMID:25951795

  5. Contact Angles and Surface Tension of Germanium-Silicon Melts

    NASA Technical Reports Server (NTRS)

    Croell, A.; Kaiser, N.; Cobb, S.; Szofran, F. R.; Volz, M.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Precise knowledge of material parameters is more and more important for improving crystal growth processes. Two important parameters are the contact (wetting) angle and the surface tension, determining meniscus shapes and surface-tension driven flows in a variety of methods (Czochralski, EFG, floating-zone, detached Bridgman growth). The sessile drop technique allows the measurement of both parameters simultaneously and has been used to measure the contact angles and the surface tension of Ge(1-x)Si(x) (0 less than or equal to x less than or equal to 1.3) alloys on various substrate materials. Fused quartz, Sapphire, glassy carbon, graphite, SiC, carbon-based aerogel, pyrolytic boron nitride (pBN), AIN, Si3N4, and polycrystalline CVD diamond were used as substrate materials. In addition, the effect of different cleaning procedures and surface treatments on the wetting behavior were investigated. Measurements were performed both under dynamic vacuum and gas atmospheres (argon or forming gas), with temperatures up to 1100 C. In some experiments, the sample was processed for longer times, up to a week, to investigate any changes of the contact angle and/or surface tension due to slow reactions with the substrate. For pure Ge, stable contact angles were found for carbon-based substrates and for pBN, for Ge(1-x)Si(x) only for pBN. The highest wetting angles were found for pBN substrates with angles around 170deg. For the surface tension of Ge, the most reliable values resulted in gamma(T) = (591- 0.077 (T-T(sub m)) 10(exp -3)N/m. The temperature dependence of the surface tension showed similar values for Ge(1-x)Si(x), around -0.08 x 10(exp -3)N/m K, and a compositional dependence of 2.2 x 10(exp -3)N/m at%Si.

  6. Understanding contact angle hysteresis on an ambient solid surface.

    PubMed

    Wang, Yong Jian; Guo, Shuo; Chen, Hsuan-Yi; Tong, Penger

    2016-05-01

    We report a systematic study of contact angle hysteresis (CAH) with direct measurement of the capillary force acting on a contact line formed on the surface of a long glass fiber intersecting a liquid-air interface. The glass fiber of diameter 1-2μm and length 100-200μm is glued onto the front end of a rectangular cantilever beam, which is used for atomic force microscopy. From the measured hysteresis loop of the capillary force for 28 different liquids with varying surface tensions and contact angles, we find a universal behavior of the unbalanced capillary force in the advancing and receding directions and the spring constant of a stretched meniscus by the glass fiber. Measurements of the capillary force and its fluctuations suggest that CAH on an ambient solid surface is caused primarily by two types of coexisting and spatially intertwined defects with opposite natures. The contact line is primarily pinned by the relatively nonwetting (repulsive) defects in the advancing direction and by the relatively wetting (attractive) defects in the receding direction. Based on the experimental observations, we propose a "composite model" of CAH and relevant scaling laws, which explain the basic features of the measured hysteresis force loops. PMID:27300959

  7. Understanding contact angle hysteresis on an ambient solid surface

    NASA Astrophysics Data System (ADS)

    Wang, Yong Jian; Guo, Shuo; Chen, Hsuan-Yi; Tong, Penger

    2016-05-01

    We report a systematic study of contact angle hysteresis (CAH) with direct measurement of the capillary force acting on a contact line formed on the surface of a long glass fiber intersecting a liquid-air interface. The glass fiber of diameter 1 -2 μ m and length 100 -200 μ m is glued onto the front end of a rectangular cantilever beam, which is used for atomic force microscopy. From the measured hysteresis loop of the capillary force for 28 different liquids with varying surface tensions and contact angles, we find a universal behavior of the unbalanced capillary force in the advancing and receding directions and the spring constant of a stretched meniscus by the glass fiber. Measurements of the capillary force and its fluctuations suggest that CAH on an ambient solid surface is caused primarily by two types of coexisting and spatially intertwined defects with opposite natures. The contact line is primarily pinned by the relatively nonwetting (repulsive) defects in the advancing direction and by the relatively wetting (attractive) defects in the receding direction. Based on the experimental observations, we propose a "composite model" of CAH and relevant scaling laws, which explain the basic features of the measured hysteresis force loops.

  8. Surface morphology of contact lenses probed with microscopy techniques.

    PubMed

    Guryca, Vilém; Hobzová, Radka; Prádný, Martin; Sirc, Jakub; Michálek, Jirí

    2007-09-01

    The present study is bringing a comparison of surface morphology for various types of contact lenses. A novel method--scanning electron microscopy under aqueous conditions (cryo-SEM)--was tested for visualization of lenses at magnifications up to 2000x. For imaging lens surface on nanometre scale, we employed atomic force microscopy (AFM) in aqueous media. Various materials of lenses, based on silicone hydrogels or conventional hydrogels, were investigated. Total, 10 types of contact lenses from five manufacturers were selected and probed. We found that different methods of lens manufacture (lathe-cutting, cast-moulding, and spin casting) led to different values of surface roughness. In the swollen state, roughness values of lens surfaces lie between 4 and 140 nm. Lenses manufactured by lathe-cutting exhibit notable higher values, so that they could be easily distinguished from others. In cast-moulded lenses, the surface roughness decreased with increasing water content. Moreover, additional treatments of lenses introduced unique structural motifs onto surface. For instance, porous structure was found on lens surface finalized with plasma oxidation. PMID:17507281

  9. Contact shape controls adhesion of bioinspired fibrillar surfaces.

    PubMed

    del Campo, Aránzazu; Greiner, Christian; Arzt, Eduard

    2007-09-25

    Following a recent bioinspired paradigm, patterned surfaces can exhibit better adhesion than flat contacts. Previous studies have verified that finer contact structures give rise to higher adhesion forces. In this study, we report on the effect of the tip shape, which was varied systematically in fibrillar PDMS surfaces, produced by lithographic and soft-molding methods. For fiber radii between 2.5 and 25 microm, it is found that shape exerts a stronger effect on adhesion than size. The highest adhesion is measured for mushroom-like and spatular terminals, which attain adhesion values 30 times in excess of the flat controls and similar to a gecko toe. These results explain the shapes commonly found in biological systems, and help in the exploration of the parameter space for artificial attachment systems. PMID:17722937

  10. Extended Aging of Ag/W Circuit Breaker Contacts: Influence on Surface Structure, Electrical Properties, and UL Testing Performance

    NASA Astrophysics Data System (ADS)

    Yu, Haibo; Kesim, M. Tumerkan; Sun, Yu; Harmon, Jason; Potter, Jonathan; Alpay, S. Pamir; Aindow, Mark

    2016-01-01

    Samples of 120 V, 30 A commercial circuit breakers were subjected to various aging treatments and the resulting microstructures at the surfaces of the Ag/W contacts were studied using a combination of x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy techniques. Breakers aged naturally in a hot, humid climate were compared to those subjected to accelerated aging in dry and humid environments. The most extensive oxidation was observed for contacts from breakers subjected to accelerated humid aging; these contacts exhibited thick surface layers consisting of Ag2O, Ag2WO4, Cu(OH)2•H2O, and WO3 phases. Far less surface degradation was observed for dry-aged contacts. Naturally aged contacts showed variations in degradation with more oxidation at the surface regions outside the physical contact area on the contact face. A correlation was found between the contact resistances measured from these samples following ASTM standard B 667-97 and the observed surface microstructures. To evaluate the effects of the surface oxides on breaker performance, humid-aged breakers were subjected to standardized UL overload/temperature-rise, endurance, and short-circuit testing following UL489. The contacts in these breakers exhibit similar microstructural and property changes to those observed previously for as-manufactured contacts after UL testing. These data illustrate the robust performance of this contact technology even after being subjected to aggressive artificial aging.

  11. Nucleation at the Contact Line Observed on Nanotextured Surfaces

    NASA Astrophysics Data System (ADS)

    Kostinski, A. B.; Gurganus, C.; Charnawskas, J. C.; Shaw, R. A.

    2015-12-01

    Surface nucleation, and contact nucleation in particular, are important for many physical processes, including pharmaceutical drug synthesis, metallurgy, and heterogeneous ice nucleation. It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). It is found that nano-scale texture causes a shift in the nucleation of ice in super-cooled water to the three-phase contact line, while micro-scale texture does not. The reduction in the Gibbs barrier for nucleation at the droplet triple line suggests that a line tension, inversely proportional to the surface feature length scale, may be the relevant physical mechanism. A survey of line tension values in literature supports this hypothesis. This work suggests that the physical morphology of a particle, and not just its chemical composition, is important for characterizing a nucleation catalyst.

  12. 3D stochastic geophysical inversion for contact surface geometry

    NASA Astrophysics Data System (ADS)

    Lelièvre, Peter; Farquharson, Colin; Bijani, Rodrigo

    2015-04-01

    Geologists' interpretations about the Earth typically involve distinct rock units with contacts (interfaces) between them. As such, 3D geological Earth models typically comprise wireframe contact surfaces of tessellated triangles or other polygonal planar facets. In contrast, standard minimum-structure geophysical inversions are performed on meshes of space-filling cells (typically prisms or tetrahedra) and recover smoothly varying physical property distributions that are inconsistent with typical geological interpretations. There are several approaches through which mesh-based geophysical inversion can help recover models with some of the desired characteristics. However, a more effective strategy is to consider a fundamentally different type of inversion that works directly with models that comprise surfaces representing contacts between rock units. We are researching such an approach, our goal being to perform geophysical forward and inverse modelling directly with 3D geological models of any complexity. Geological and geophysical models should be specified using the same parameterization such that they are, in essence, the same Earth model. We parameterize the wireframe contact surfaces in a 3D model as the coordinates of the nodes (facet vertices). The physical properties of each rock unit in a model remain fixed while the geophysical inversion controls the position of the contact surfaces via the control nodes, perturbing the surfaces as required to fit the geophysical data responses. This is essentially a "geometry inversion", which can be used to recover the unknown geometry of a target body or to investigate the viability of a proposed Earth model. We apply global optimization strategies to solve the inverse problem, including stochastic sampling to obtain statistical information regarding the likelihood of particular features in the model, helping to assess the viability of a proposed model. Jointly inverting multiple types of geophysical data is simple

  13. Surface charging, discharging and chemical modification at a sliding contact

    SciTech Connect

    Singh, S. V.; Kusano, Y.; Morgen, P.; Michelsen, P. K.

    2012-04-15

    Electrostatic charging, discharging, and consequent surface modification induced by sliding dissimilar surfaces have been studied. The surface-charge related phenomena were monitored by using a home-built capacitive, non-contact electrical probe, and the surface chemistry was studied by X-ray photoelectron spectroscopy (XPS). The experiments were performed on the disk surface of a ball-on-rotating-disk apparatus; using a glass disk and a Teflon (polytetrafluoroethylene) ball arrangement, and a polyester disks and a diamondlike carbon (DLC) coated steel ball arrangement. The capacitive probe is designed to perform highly resolved measurements, which is sensitive to relative change in charge density on the probed surface. For glass and Teflon arrangement, electrical measurements show that the ball track acquires non-uniform charging. Here not only the increase in charge density, but interestingly, increase in number of highly charged regions on the ball track was resolved. Threefold increase in the number of such highly charged regions per cycle was detected immediately before the gas breakdown-like incidences compared to that of other charge/discharge incidences at a fixed disk rotation speed. We are also able to comment on the behavior and the charge decay time in the ambient air-like condition, once the sliding contact is discontinued. XPS analysis showed a marginal deoxidation effect on the polyester disks due to the charging and discharging of the surfaces. Moreover, these XPS results clearly indicate that the wear and friction (sliding without charging) on the surface can be discarded from inducing such a deoxidation effect.

  14. Surface charging, discharging and chemical modification at a sliding contact

    NASA Astrophysics Data System (ADS)

    Singh, S. V.; Kusano, Y.; Morgen, P.; Michelsen, P. K.

    2012-04-01

    Electrostatic charging, discharging, and consequent surface modification induced by sliding dissimilar surfaces have been studied. The surface-charge related phenomena were monitored by using a home-built capacitive, non-contact electrical probe, and the surface chemistry was studied by X-ray photoelectron spectroscopy (XPS). The experiments were performed on the disk surface of a ball-on-rotating-disk apparatus; using a glass disk and a Teflon (polytetrafluoroethylene) ball arrangement, and a polyester disks and a diamondlike carbon (DLC) coated steel ball arrangement. The capacitive probe is designed to perform highly resolved measurements, which is sensitive to relative change in charge density on the probed surface. For glass and Teflon arrangement, electrical measurements show that the ball track acquires non-uniform charging. Here not only the increase in charge density, but interestingly, increase in number of highly charged regions on the ball track was resolved. Threefold increase in the number of such highly charged regions per cycle was detected immediately before the gas breakdown-like incidences compared to that of other charge/discharge incidences at a fixed disk rotation speed. We are also able to comment on the behavior and the charge decay time in the ambient air-like condition, once the sliding contact is discontinued. XPS analysis showed a marginal deoxidation effect on the polyester disks due to the charging and discharging of the surfaces. Moreover, these XPS results clearly indicate that the wear and friction (sliding without charging) on the surface can be discarded from inducing such a deoxidation effect.

  15. Inverse heat transfer problem of thermal contact conductance estimation in periodically contacting surfaces

    NASA Astrophysics Data System (ADS)

    Shojaeefard, M. H.; Goudarzi, K.; Mazidi, M. Sh.

    2009-06-01

    The problems involving periodic contacting surfaces have different practical applications. An inverse heat conduction problem for estimating the periodic Thermal Contact Conductance (TCC) between one-dimensional, constant property contacting solids has been investigated with conjugate gradient method (CGM) of function estimation. This method converges very rapidly and is not so sensitive to the measurement errors. The advantage of the present method is that no a priori information is needed on the variation of the unknown quantities, since the solution automatically determines the functional form over the specified domain. A simple, straight forward technique is utilized to solve the direct, sensitivity and adjoint problems, in order to overcome the difficulties associated with numerical methods. Two general classes of results, the results obtained by applying inexact simulated measured data and the results obtained by using data taken from an actual experiment are presented. In addition, extrapolation method is applied to obtain actual results. Generally, the present method effectively improves the exact TCC when exact and inexact simulated measurements input to the analysis. Furthermore, the results obtained with CGM and the extrapolation results are in agreement and the little deviations can be negligible.

  16. Studies on contact activation: effects of surface and inhibitors.

    PubMed

    Cameron, C L; Fisslthaler, B; Sherman, A; Reddigari, S; Silverberg, M

    1989-01-01

    Contact activation is initiated when the plasma proteins, Hageman factor (factor XII), prekallikrein and high molecular weight kininogen interact with negatively charged materials. The activation of the intrinsic pathway of blood coagulation and the production of bradykinin are among the sequelae of contact activation. The kinetics of the activation of the contact system are modified by plasma inhibitors, C1 inhibitor being quantitatively the most important. We propose that the activation of the system requires that the stimulus provided by the surface must be greater than a threshold value to overcome the effects of the inhibitors. We show in this paper that the amount of surface required for activation is much reduced in the absence of C1 inhibitor (Hereditary Angioedema) or in the cold where the inhibitor loses much of its effectiveness. Antithrombin III inhibition of activated Hageman factor is augmented by heparin which is also an activator of Hageman factor. The rate constants for inhibition remain much lower than for C1 inhibitor, however. PMID:2530427

  17. Recreational Water Contact and Fish Consumption Assessment to Inform Risk Estimates and Evaluate Ecosystem Services

    EPA Science Inventory

    Background: Surface waters provide invaluable ecosystem services, including drinking water, food, waste water disposal, and recreation. The nature and frequency of recreational contact with surface waters is a critical consideration in evaluating benefits to human well-being (e.g...

  18. Influence of surface roughness and contact load on friction coefficient and scratch behavior of thermoplastic olefins

    NASA Astrophysics Data System (ADS)

    Jiang, Han; Browning, Robert; Fincher, Jason; Gasbarro, Anthony; Jones, Scooter; Sue, Hung-Jue

    2008-05-01

    To study the effects of surface roughness and contact load on the friction behavior and scratch resistance of polymers, a set of model thermoplastic olefins (TPO) systems with various surface roughness ( Ra) levels were prepared and evaluated. It is found that a higher Ra corresponds to a lower surface friction coefficient ( μs). At each level of Ra, μs gets larger as contact load increases, with a greater increase in μs as Ra level increases. It is also observed that with increasing contact load and increasing Ra, the μs tend to level off. In evaluating TPO scratch resistance, a lower μs would delay the onset of ductile drawing-induced fish-scale surface deformation feature, thereby raising the load required to cause scratch visibility. However, as the contact load is further increased, the μs evolves to become scratch coefficient of friction (SCOF) as significant sub-surface deformation and tip penetration occur and material displacement begins, i.e., ploughing. No dependence of Ra and μs on the critical load for the onset of ploughing is observed. In this work, the distinction between μs and SCOF will be illustrated. Approaches for improving scratch resistance of polymers via control of Ra are also discussed.

  19. Mass transport of deposited particles by surface-to-surface contact.

    PubMed

    McDonagh, A; Sextro, R G; Byrne, M A

    2012-08-15

    The spread of particle-borne contamination by surface-to-surface contact and its implications for exposures within the indoor environment have been observed - largely qualitatively. The present study was conducted with the aim of quantifying the mass transfer efficiency (TE) of deposited aerosol particles when selected soft and hard surfaces come in contact. The surfaces used were 100% cotton, synthetic fleece, plastic laminate and brass. Contact transfer efficiencies ranging from 2 to 45% were observed; these are very significant numbers in terms of hazardous aerosol transport in the environment. Other observations include an increase in the mass transferred with increased surface roughness. An increase in the applied pressure between the two surfaces in contact leads to a step change in transfer efficiency, so that two pressure regimes can be identified, with a transition pressure between them that depends on surface type. Time of contact appears to have little to no effect on the mass transfer efficiency for the surfaces studied, while contaminant loading has some effect that is not systematic. PMID:22683108

  20. Changes in contact angle providing evidence for surface alteration in multi-component solid foods

    NASA Astrophysics Data System (ADS)

    Reinke, Svenja K.; Hauf, Katharina; Vieira, Josélio; Heinrich, Stefan; Palzer, Stefan

    2015-11-01

    Chocolate blooming, one of the major problems in the confectionery industry, is the formation of visible white spots or a greyish haze on the surface of chocolate products due to large sugar or fat crystals on the surface. This leads to aesthetic changes and deterioration of taste and thus large sales losses for the confectionery industry due to consumer complaints. Chocolate blooming is often related to migration of lipids or sugar molecules to the chocolate surface, where they recrystallize with an associated polymorphic change of crystal structure on the surface. The wetting behaviour from contact angle measurements gives further insight into surface properties and is needed to determine surface energies and to evaluate possible migration mechanisms and preferred pathways. Therefore, an equilibrium contact angle is needed which is not directly accessible and is influenced by surface texture and interaction between solid and test liquid. In this study, the surface of cocoa butter and conventional chocolates was characterized by measuring the contact angle with the sessile drop protocol. The influence of roughness, test liquid and pre-crystallization of the samples as well as the storage temperature were investigated. In case of no pre-crystallization, a change in surface properties due to storage at 20 °C was detected, whereas samples stored at 30 °C showed the same wetting behaviour as fresh samples. This is associated with polymorphic transformation from thermodynamically less stable crystals to more stable configurations.

  1. Surface Coating of Tungsten Carbide by Electric Exploding of Contact

    SciTech Connect

    Grigoryev, Evgeny G.

    2011-01-17

    Electric exploding of a tungsten carbide--cobalt material near-by high-speed steel surface forms on it a hardening coating. The essential structure properties of the formed coatings are determined by parameters of contact exploding electrode at the pulse current amplitude from above 106 A/cm2 and duration less than 10-4 s. The metallographic investigations of coating structures were done by microscope 'Neophot-24'. They have shown that the contact electric exploding caused the transfer of tungsten carbide and cobalt on the surface of high-speed steel. The breakdown of tungsten carbide--cobalt material took place during electrical exploding. The hardening layers of tungsten carbide and pure nanocrystalline tungsten have been formed upon the surface of high-speed steel as a result of electric exploding. Crystalline grains of tungsten have an almost spherical form and their characteristic size less than 400 nanometers. Micro hardness of the coating layers and high-speed steel structures was measured.

  2. Creation of Principally New Generation of Switching Technique Elements (Reed Switches) with Nanostructured Contact Surfaces

    NASA Astrophysics Data System (ADS)

    Karabanov, S. M.; Zeltser, I. A.; Maizels, R. M.; Moos, E. N.; Arushanov, K. A.

    2011-04-01

    The cycle of activities of the creation of principally new generation of reed switches with nanostructured contact surfaces was implemented. Experimental justification of the opportunity of reed switches creation with modified contact surface was given (instead of precious metals-based galvanic coating). Principally new technological process of modification of magnetically operated contacts contacting surfaces was developed, based on the usage of the ion-plasma methods of nanolayers and nanostructures forming having specified contact features.

  3. An Experimental-Numerical Evaluation of Thermal Contact Conductance in Fin-Tube Heat Exchangers

    NASA Astrophysics Data System (ADS)

    Kim, Chang Nyung; Jeong, Jin; Youn, Baek; Kil, Seong Ho

    The contact between fin collar and tube surface of a fin-tube heat exchanger is secured through mechanical expansion of tubes. However, the characteristics of heat transfer through the interfaces between the tubes and fins have not been clearly understood because the interfaces consist partially of metal-to-metal contact and partially of air. The objective of the present study is to develop a new method utilizing an experimental-numerical method for the estimation of the thermal contact resistance between the fin collar and tube surface and to evaluate the factors affecting the thermal contact resistance in a fin-tube heat exchanger. In this study, heat transfer characteristics of actual heat exchanger assemblies have been tested in a vacuum chamber using water as an internal fluid, and a finite difference numerical scheme has been employed to reduce the experimental data for the evaluation of the thermal contact conductance. The present study has been conducted for fin-tube heat exchangers of tube diameter of 7mm with different tube expansion ratios, fin spacings, and fin types. The results show, with an appropriate error analysis, that these parameters as well as hydrophilic fin coating affect notably the thermal contact conductance. It has been found out that the thermal contact resistance takes fairly large portion of the total thermal resistance in a fin-tube heat exchanger and it turns out that careful consideration is needed in a manufacturing process of heat exchangers to reduce the thermal contact resistance.

  4. Removal and Transfer of Viruses on Food Contact Surfaces by Cleaning Cloths

    PubMed Central

    Crandall, Philip G.; Ricke, Steven C.

    2012-01-01

    Contamination of food contact surfaces with pathogens is considered an important vehicle for the indirect transmission of food-borne diseases. Five different cleaning cloths were assessed for the ability to remove viruses from food contact surfaces (stainless steel surface and nonporous solid surface) and to transfer viruses back to these surfaces. Cleaning cloths evaluated include two different cellulose/cotton cloths, one microfiber cloth, one nonwoven cloth, and one cotton terry bar towel. Four viral surrogates (murine norovirus [MNV], feline calicivirus [FCV], bacteriophages PRD1 and MS2) were included. Removal of FCV from stainless steel was significantly greater (P ≤ 0.05) than that from nonporous solid surface, and overall removal of MNV from both surfaces was significantly less (P ≤ 0.05) than that of FCV and PRD1. Additionally, the terry towel removed significantly fewer total viruses (P ≤ 0.05) than the microfiber and one of the cotton/cellulose cloths. The cleaning cloth experiments were repeated with human norovirus. For transfer of viruses from cloth to surface, both cellulose/cotton cloths and microfiber transferred an average of 3.4 and 8.5 total PFU, respectively, to both surfaces, and the amounts transferred were significantly different (P ≤ 0.05) from those for the nonwoven cloth and terry towel (309 and 331 total PFU, respectively). There was no statistically significant difference (P > 0.05) in the amount of virus transfer between surfaces. These data indicate that while the cleaning cloths assessed here can remove viruses from surfaces, some cloths may also transfer a significant amount of viruses back to food contact surfaces. PMID:22327573

  5. Improvement and evaluation of thermal, electrical, sealing and mechanical contacts, and their interface materials

    NASA Astrophysics Data System (ADS)

    Luo, Xiangcheng

    Material contacts, including thermal, electrical, seating (fluid sealing and electromagnetic sealing) and mechanical (pressure) contacts, together with their interface materials, were, evaluated, and in some cases, improved beyond the state of the art. The evaluation involved the use of thermal, electrical and mechanical methods. For thermal contacts, this work evaluated and improved the heat transfer efficiency between two contacting components by developing various thermal interface pastes. Sodium silicate based thermal pastes (with boron nitride particles as the thermally conductive filler) as well as polyethylene glycol (PEG) based thermal pastes were developed and evaluated. The optimum volume fractions of BN in sodium silicate based pastes and PEG based pastes were 16% and 18% respectively. The contribution of Li+ ions to the thermal contact conductance in the PEG-based paste was confirmed. For electrical contacts, the relationship between the mechanical reliability and electrical reliability of solder/copper and silver-epoxy/copper joints was addressed. Mechanical pull-out testing was conducted on solder/copper and silver-epoxy/copper joints, while the contact electrical resistivity was measured. Cleansing of the copper surface was more effective for the reliability of silver-epoxy/copper joint than that of solder/copper joint. For sealing contacts, this work evaluated flexible graphite as an electromagnetic shielding gasket material. Flexible graphite was found to be at least comparable to conductive filled silicone (the state of the art) in terms of the shielding effectiveness. The conformability of flexible graphite with its mating metal surface under repeated compression was characterized by monitoring the contact electrical resistance, as the conformability is important to both electromagnetic scaling and fluid waling using flexible graphite. For mechanical contacts, this work focused on the correlation of the interface structure (such as elastic

  6. Noncontact charge measurement of moving microparticles contacting dielectric surfaces

    NASA Astrophysics Data System (ADS)

    Nesterov, Alexander; Löffler, Felix; König, Kai; Trunk, Ulrich; Leibe, Klaus; Felgenhauer, Thomas; Stadler, Volker; Bischoff, Ralf; Breitling, Frank; Lindenstruth, Volker; Hausmann, Michael

    2007-07-01

    In this study examples for a noncontact procedure that allow the description of instant electric charging of moving microparticles that contact dielectric surfaces, for instance, of a flow hose are presented. The described principle is based on the measurement of induced currents in grounded metal wire probes, as moving particles pass close to the probe. The feasibility of the approach was tested with laser printer toner particles of a given size for different basic particle flow and charging conditions. An analytic description for the induced currents was developed and compared to observed effects in order to interpret the results qualitatively. The implementation of the presented procedure can be applied to transparent and nontransparent particle containers and flow lines of complex geometry which can be composed from the presented basic flow stream configurations.

  7. Post-procedural evaluation of catheter contact force characteristics

    NASA Astrophysics Data System (ADS)

    Koch, Martin; Brost, Alexander; Kiraly, Atilla; Strobel, Norbert; Hornegger, Joachim

    2012-03-01

    Minimally invasive catheter ablation of electric foci, performed in electrophysiology labs, is an attractive treatment option for atrial fibrillation (AF) - in particular if drug therapy is no longer effective or tolerated. There are different strategies to eliminate the electric foci inducing the arrhythmia. Independent of the particular strategy, it is essential to place transmural lesions. The impact of catheter contact force on the generated lesion quality has been investigated recently, and first results are promising. There are different approaches to measure catheter-tissue contact. Besides traditional haptic feedback, there are new technologies either relying on catheter tip-to-tissue contact force or on local impedance measurements at the tip of the catheter. In this paper, we present a novel tool for post-procedural ablation point evaluation and visualization of contact force characteristics. Our method is based on localizing ablation points set during AF ablation procedures. The 3-D point positions are stored together with lesion specific catheter contact force (CF) values recorded during the ablation. The force records are mapped to the spatial 3-D positions, where the energy has been applied. The tracked positions of the ablation points can be further used to generate a 3-D mesh model of the left atrium (LA). Since our approach facilitates visualization of different force characteristics for post-procedural evaluation and verification, it has the potential to improve outcome by highlighting areas where lesion quality may be less than desired.

  8. From hygrophilic to superhygrophobic: theoretical conditions for making high-contact-angle surfaces from low-contact-angle materials.

    PubMed

    Marmur, Abraham

    2008-07-15

    The possibility of making high-contact-angle, rough surfaces from low-contact-angle materials has recently been suggested and demonstrated. A thermodynamic analysis of this possibility in terms of feasibility and stability is presented. It turns out that only roughness topographies that conform to a feasibility condition which is developed in the present paper can support this phenomenon. Even under conditions that support the phenomenon, the high-contact-angle state may not be stable, and transition from the heterogeneous (Cassie-Baxter) wetting regime to the homogeneous (Wenzel) regime with a lower contact angle may occur. In addition, it is suggested to use the general terms hygrophilic and hygrophobic (based on the Greek prefix hygro- that means liquid) to describe low- and high-contact-angle surfaces, respectively. PMID:18543997

  9. Statistical contact angle analyses; "slow moving" drops on a horizontal silicon-oxide surface.

    PubMed

    Schmitt, M; Grub, J; Heib, F

    2015-06-01

    Sessile drop experiments on horizontal surfaces are commonly used to characterise surface properties in science and in industry. The advancing angle and the receding angle are measurable on every solid. Specially on horizontal surfaces even the notions themselves are critically questioned by some authors. Building a standard, reproducible and valid method of measuring and defining specific (advancing/receding) contact angles is an important challenge of surface science. Recently we have developed two/three approaches, by sigmoid fitting, by independent and by dependent statistical analyses, which are practicable for the determination of specific angles/slopes if inclining the sample surface. These approaches lead to contact angle data which are independent on "user-skills" and subjectivity of the operator which is also of urgent need to evaluate dynamic measurements of contact angles. We will show in this contribution that the slightly modified procedures are also applicable to find specific angles for experiments on horizontal surfaces. As an example droplets on a flat freshly cleaned silicon-oxide surface (wafer) are dynamically measured by sessile drop technique while the volume of the liquid is increased/decreased. The triple points, the time, the contact angles during the advancing and the receding of the drop obtained by high-precision drop shape analysis are statistically analysed. As stated in the previous contribution the procedure is called "slow movement" analysis due to the small covered distance and the dominance of data points with low velocity. Even smallest variations in velocity such as the minimal advancing motion during the withdrawing of the liquid are identifiable which confirms the flatness and the chemical homogeneity of the sample surface and the high sensitivity of the presented approaches. PMID:25524007

  10. Effect of metallic coatings on the thermal contact conductance of turned surfaces

    NASA Astrophysics Data System (ADS)

    Kang, T. K.; Peterson, G. P.; Fletcher, L. S.

    1990-11-01

    An experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhanced through the use of vapor-deposited metallic coatings. Three different coating materials (lead, tin, and indium) were evaluated using four different thicknesses for each coating material. The results verified the existence of an optimum coating thickness, shown to be in the range of 2.0 to 3.0 microns for indium, 1.5 to 2.5 microns for lead, and 0.2 to 0.5 microns for tin. The enhancement factors for thermal contact conductance were found to be on the order of 700, 400, and 50 percent, respectively. Based upon the experimental data, the hardness of the coating materials appears to be the most significant parameter in ranking the substrate and coating material combinations; however, additional experimental data are needed to substantiate this hypothesis. Finally, it was apparent that the thermal contact conductance enhancement effect was greatest at low contact pressures and decreased significantly with increases in the contact pressure.

  11. Effect of metallic coatings on the thermal contact conductance of turned surfaces

    SciTech Connect

    Kang, T.K.; Peterson, G.P.; Fletcher, L.S. )

    1990-11-01

    An experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhanced through the use of vapor-deposited metallic coating. Three different coating materials (lead, tin, and indium) were evaluated using four different thicknesses for each coating material. The results verified the existence of an optimum coating thickness, shown to be in the range of 2.0 to 3.0 {mu}m for indium, 1.5 to 2.5 {mu}m for lead, and 0.2 to 0.5 {mu}m for tin. The enhancement factors for thermal contact condcutance were found to be on the order of 700, 400, and 50%, respectively. Based upon the experimental data, the hardness of the coating materials appears to be the most significant parameter in ranking the substrate and coating material combinations; however, addition experimental data are needed to substantiate this hypothesis. Finally, it was apparent that the thermal contact conductance enhancement effect was greatest at low contact pressures and decreased significantly with increases in the contact pressure.

  12. Effect of metallic coatings on the thermal contact conductance of turned surfaces

    NASA Technical Reports Server (NTRS)

    Kang, T. K.; Peterson, G. P.; Fletcher, L. S.

    1990-01-01

    An experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhanced through the use of vapor-deposited metallic coatings. Three different coating materials (lead, tin, and indium) were evaluated using four different thicknesses for each coating material. The results verified the existence of an optimum coating thickness, shown to be in the range of 2.0 to 3.0 microns for indium, 1.5 to 2.5 microns for lead, and 0.2 to 0.5 microns for tin. The enhancement factors for thermal contact conductance were found to be on the order of 700, 400, and 50 percent, respectively. Based upon the experimental data, the hardness of the coating materials appears to be the most significant parameter in ranking the substrate and coating material combinations; however, additional experimental data are needed to substantiate this hypothesis. Finally, it was apparent that the thermal contact conductance enhancement effect was greatest at low contact pressures and decreased significantly with increases in the contact pressure.

  13. The influence of surface roughness on the contact stiffness and the contact filter effect in nonlinear wheel-track interaction

    NASA Astrophysics Data System (ADS)

    Lundberg, Oskar E.; Nordborg, Anders; Lopez Arteaga, Ines

    2016-03-01

    A state-dependent contact model including nonlinear contact stiffness and nonlinear contact filtering is used to calculate contact forces and rail vibrations with a time-domain wheel-track interaction model. In the proposed method, the full three-dimensional contact geometry is reduced to a point contact in order to lower the computational cost and to reduce the amount of required input roughness-data. Green's functions including the linear dynamics of the wheel and the track are coupled with a point contact model, leading to a numerically efficient model for the wheel-track interaction. Nonlinear effects due to the shape and roughness of the wheel and the rail surfaces are included in the point contact model by pre-calculation of functions for the contact stiffness and contact filters. Numerical results are compared to field measurements of rail vibrations for passenger trains running at 200 kph on a ballast track. Moreover, the influence of vehicle pre-load and different degrees of roughness excitation on the resulting wheel-track interaction is studied by means of numerical predictions.

  14. Design and evaluation of high contact ratio gearing

    NASA Technical Reports Server (NTRS)

    Frint, Harold K.

    1986-01-01

    Scoring test and surface fatigue tests were conducted on spur gears of a standard design and spur gears of a high contact ratio design. All testing was conducted in the Sikorsky 6-inch dynamic test facility at a speed of 8000 rpm using 23699 oil. Bulk gear temperatures were also recorded. The surface fatigue tests were run at Hertz stresses of 165 x 10 to the 7th power N/sq m and 145 x 10 to the 7th power N/sq m (240,000 and 210,000 psi), respectively.

  15. The Effect of Surface Contamination on Adhesive Forces as Measured by Contact Mechanics

    SciTech Connect

    EMERSON,JOHN A.; GIUNTA,RACHEL K.; MILLER,GREGORY V.; SORENSEN,CHRISTOPHER R.; PEARSON,RAYMOND A.

    2000-12-18

    The contact adhesive forces between two surfaces, one being a soft hemisphere and the other being a hard plate, can readily be determined by applying an external compressive load to mate the two surfaces and subsequently applying a tensile load to peel the surfaces apart. The contact region is assumed the superposition of elastic Hertzian pressure and of the attractive surface forces that act only over the contact area. What are the effects of the degree of surface contamination on adhesive forces? Clean aluminum surfaces were coated with hexadecane as a controlled contaminant. The force required to pull an elastomeric hemisphere from a surface was determined by contact mechanics, via the JKR model, using a model siloxane network for the elastomeric contact sphere. Due to the dispersive nature of the elastomer surface, larger forces were required to pull the sphere from a contaminated surface than a clean aluminum oxide surface.

  16. Influence of Thickness and Contact Surface Geometry of Condylar Stem of TMJ Implant on Its Stability

    NASA Astrophysics Data System (ADS)

    Arabshahi, Zohreh; Kashani, Jamal; Kadir, Mohammed Rafiq Abdul; Azari, Abbas

    The aim of this study is to examine the effect thickness and contact surface geometry of condylar stem of TMJ implant on its stability in total reconstruction system and evaluate the micro strain resulted in bone at fixation screw holes in jaw bone embedded with eight different designs of temporomandibular joint implants. A three dimensional model of a lower mandible of an adult were developed from a Computed Tomography scan images. Eight different TMJ implant designs and fixation screws were modeled. Three dimensional finite element models of eight implanted mandibles were analyzed. The forces assigned to the masticatory muscles for incisal clenching were applied consisting of nine important muscular loads. In chosen loading condition, The results indicated that the anatomical curvature contact surface design of TMJ implant can moderately improve the stability and the strain resulted in fixation screw holes in thinner TMJ implant was diminished in comparison with other thicknesses.

  17. Assessing a novel contact heater as a new method of recovering explosives traces from porous surfaces.

    PubMed

    Yu, Holly A; Lewis, Simon W; Beardah, Matthew S; NicDaeid, Niamh

    2016-02-01

    It can be very challenging to recover explosives traces from porous surfaces, such as clothing and car seats, compared to non-porous surfaces. The contact heater has been developed as a novel instrument designed to recover explosives traces from porous surfaces. Samples are taken by heating and drawing air across a surface, with the air flowing through a sampling cartridge containing adsorbent polymer beads, which act to trap any recovered explosive material. Any collected explosive can then be eluted from this cartridge using a solvent, prior to analysis. This paper outlines work performed to evaluate the usefulness of the contact heater with regards to the recovery of explosives traces from porous materials. Ethylene glycol dinitrate (EGDN) and triacetone triperoxide (TATP) were chosen as two representative explosives for this study. Quantification was performed using GC-MS for EGDN and LC-MS/MS for TATP. Different sampling temperatures, sampling times and elution solvents were investigated. Recovery was trialled from leather, carpet and denim. Recoveries of up to 71% were obtained following optimisation. It was also possible to recover TATP from fabrics exposed to TATP vapour in a vapour-laden jar up to two hours after exposure. The contact heater therefore appears to be a very useful tool for the recovery of explosives traces from porous materials. PMID:26653508

  18. Evaluating a new segmented germanium detector contact technology

    NASA Astrophysics Data System (ADS)

    Jackson, E. G.; Lister, C. J.; Chowdhury, P.; Hull, E.; Pehl, R.

    2012-10-01

    New technologies for making gamma ray detectors position sensitive have many applications in space science, medical imaging, homeland security, and in nuclear structure research. One promising approach uses high-purity germanium wafers with the planar surfaces segmented into orthogonal strip patterns forming a Double-Sided Strip Detector (DSSD). The combination of data from adjoining strips, or pixels, is physics-rich for Compton image formation and polarization studies. However, sensitivity to charge loss and various kinds of cross-talk [1] have limited the usefulness of first generation devices. We are investigating new contact technologies, developed by PhDs Co [2], based on amorphous-germanium and yttrium contacts RF sputter deposited to a thickness of ˜ 1000 å. New techniques allow both physical and photolithographic segmentation of the contacts with inter-strip gap widths of 0.25 mm. These modifications should improve all aspects of charge collection. The new detector technology employs the same material and fabrication technique for both the n- and p- contacts, thus removing artificial asymmetry in the data. Results from tests of cross-talk, charge collection, and scattering asymmetry will be presented and compared with older technologies. This mechanically cooled counter, NP-7, seems to represent a breakthrough.[4pt] [1] S. Gros et al., Nucl. Inst. Meth. A 602, 467 (2009).[0pt] [2] E. Hull et al Nucl Inst Meth A 626, 39 (2011)

  19. Locally contacted rear surface passivated solar cells by inkjet printing

    NASA Astrophysics Data System (ADS)

    Phiwpha, N.; Fangsuwannarak, T.; Sopitpan, S.

    2014-06-01

    Inkjet printing of photoresist material may provide a new route for low-cost fabrication of patterned oxide passivation layer of solar cells that require fine patterning and simple process. However, printing by liquid-based, environmentally friendly ink and printing device required development efforts aimed at achieving a fine patterning and long used inkjet nozzles under corrosive influence. This work was demonstrated a concept for grooved silicon oxide patterning for rear localized contact of p-n junction solar cells by chemical etching after photoresist patterning obtained. This article reviews the silicon dioxide fabrication on p-Si substrate from sol-gel technique for oxide passivation layer of solar cells. The aluminium was deposited on the patterned oxide layer and then heated at its Al-Si eutectic temperature. Finally, an aluminium-induced solid-phase epitaxial growth of p+ forming into the openings of the oxide passivation layer was presented. The sheet resistance of n-emitter layer, carrier life-time and surface recombination velocity values are investigated. Photoconductive measurements were performed on the prepared samples after each thermal process to measure the effective lifetime of the minority carriers. Carrier lifetime up to 60 microseconds has been measured on c-Si wafer passivated by the opened SiO2 layer. It was shown that the patterned SiO2 passivation has obtained high passivation quality making by the proposed inkjet printing method.

  20. Temporal Modulations of Contact Force during Haptic Surface Exploration

    PubMed Central

    Martin, Sven; Schwarz, Michael

    2016-01-01

    Individuals constantly modulate their exploratory movements and adapt their internal hypotheses to incoming sensory information to achieve a thorough and realistic percept. Perception depends on the exploratory movements as well as influencing them. While this seems to be common sense, scientifically we know very little about the temporal dynamics during haptic exploration. To address this, we investigated the exploratory force modulations of two groups of healthy young adults during the exploration of grated surfaces with differing detection difficulty during successive (n = 20) and random stimulus presentation (n = 20). Results showed that exploratory force depended on stimulus properties and increased with increasing detection difficulty. Both experiments yielded the same direction of results with slightly smaller effects in the random stimulus presentation group. Across exploration time average fingertip force also increased. The biggest increase occurred systematically at the beginning (within the first 40 percent) of exploration time per stimulus indicating that most critical information is received during the initial contact phase and is directly transformed into the exploration procedure and force application. Furthermore, video-analyses and comparisons to our high temporal resolution data revealed strong dynamic changes in pressure application during test stimulus exploration with differences in the force dynamics and exploration strategies of simple and difficult stimuli. PMID:27073843

  1. Effect of progressive wear on the contact mechanics of hip replacements--does the realistic surface profile matter?

    PubMed

    Wang, Ling; Yang, Wenjian; Peng, Xifeng; Li, Dichen; Dong, Shuangpeng; Zhang, Shu; Zhu, Jinyu; Jin, Zhongmin

    2015-04-13

    The contact mechanics of artificial metal-on-polyethylene hip joints are believed to affect the lubrication, wear and friction of the articulating surfaces and may lead to the joint loosening. Finite element analysis has been widely used for contact mechanics studies and good agreements have been achieved with current experimental data; however, most studies were carried out with idealist spherical geometries of the hip prostheses rather than the realistic worn surfaces, either for simplification reason or lacking of worn surface profile. In this study, the worn surfaces of the samples from various stages of hip simulator testing (0 to 5 million cycles) were reconstructed as solid models and were applied in the contact mechanics study. The simulator testing results suggested that the center of the head has various departure value from that of the cup and the value of the departure varies with progressively increased wear. This finding was adopted into the finite element study for better evaluation accuracy. Results indicated that the realistic model provided different evaluation from that of the ideal spherical model. Moreover, with the progressively increased wear, large increase of the contact pressure (from 12 to 31 MPa) was predicted on the articulating surface, and the predicted maximum von Mises stress was increased from 7.47 to 13.26 MPa, indicating the marked effect of the worn surface profiles on the contact mechanics of the joint. This study seeks to emphasize the importance of realistic worn surface profile of the acetabular cup especially following large wear volume. PMID:25680298

  2. High-speed cinematographic evaluation of claw-ground contact pattern of lactating cows.

    PubMed

    Schmid, Tanja; Weishaupt, Michael A; Meyer, Sven W; Waldern, Nina; Peinen, Katja von; Nuss, Karl

    2009-08-01

    To evaluate the manner in which a cow's claws make contact with the ground at the walk, the gait, and in particular the claw-ground contact pattern, were studied in 12 healthy, lactating dairy cows, using high-speed cinematography (500frames/s) while the animals were walking on a treadmill. The results showed that the limbs were advanced around the contralateral limbs in a sigmoid curve. The feet contacted the ground with the foot axis and the tips of the claws rotated slightly outwards. In all cows the lateral claws contacted the ground before the medial claws in the hindlimbs, and in 10/12 cows in the forelimbs. The heel of the lateral claws was the region of initial contact with the ground in the hindlimbs of all cows and in the forelimbs in 9/12 cows. Lateral 'heel first' contact in the fore and hindlimbs appeared to be the normal gait pattern in these animals. Compared with a previous study of heifers, lactating cows had a larger step width in the hindlimbs and a smaller step width in the forelimbs. These ground contact patterns offer an explanation for the predisposition to claw disorders of the lateral claw of the hindlimb. The results of this study reinforce the suggestion that soft floor surfaces should be provided for cattle to prevent mechanical injury to the claws. PMID:18424198

  3. Bio-activated titanium surface utilizable for mimetic bone implantation in dentistry—Part III: Surface characteristics and bone implant contact formation

    NASA Astrophysics Data System (ADS)

    Strnad, Jakub; Strnad, Zdeněk; Šesták, Jaroslav; Urban, Karel; Povýšil, Ctibor

    2007-05-01

    This study was carried out to quantify the effect of an alkali-modified surface on the bone implant interface formation during healing using an animal model. A total of 24 screw-shaped, self-tapping, (c.p.) titanium dental implants, divided into test group B—implants with alkali-modified surface (Bio surface) and control group M—implants with turned, machined surface, were inserted without pre-tapping in the tibiae of three beagle dogs. The animals were sacrificed after 2, 5 and 12 weeks and the bone implant contact (BIC%) was evaluated histometrically. The surface characteristics that differed between the implant surfaces, i.e. specific surface area, contact angle, may represent factors that influence the rate of osseointegration and the secondary implant stability. The alkali-treated surface enhances the BIC formation during the first 2 5 weeks of healing compared to the turned, machined surface.

  4. On the physically based modeling of surface tension and moving contact lines with dynamic contact angles on the continuum scale

    NASA Astrophysics Data System (ADS)

    Huber, M.; Keller, F.; Säckel, W.; Hirschler, M.; Kunz, P.; Hassanizadeh, S. M.; Nieken, U.

    2016-04-01

    The description of wetting phenomena is a challenging problem on every considerable length-scale. The behavior of interfaces and contact lines on the continuum scale is caused by intermolecular interactions like the Van der Waals forces. Therefore, to describe surface tension and the resulting dynamics of interfaces and contact lines on the continuum scale, appropriate formulations must be developed. While the Continuum Surface Force (CSF) model is well-engineered for the description of interfaces, there is still a lack of treatment of contact lines, which are defined by the intersection of an ending fluid interface and a solid boundary surface. In our approach we use a balance equation for the contact line and extend the Navier-Stokes equations in analogy to the extension of a two-phase interface in the CSF model. Since this model depicts a physically motivated approach on the continuum scale, no fitting parameters are introduced and the deterministic description leads to a dynamical evolution of the system. As verification of our theory, we show a Smoothed Particle Hydrodynamics (SPH) model and simulate the evolution of droplet shapes and their corresponding contact angles.

  5. Contact Lenses Wettability In Vitro: Effect of Surface-Active Ingredients

    PubMed Central

    Lin, Meng C.; Svitova, Tatyana F.

    2010-01-01

    Purpose To investigate the release of surface-active agents (surfactants) from unworn soft contact lenses and their influence on the lens surface wettability in vitro. Methods Surface tension (ST) of blister pack solutions was measured by pendant-drop technique. STs at the air-aqueous interface and contact angles (CAs) of four conventional and seven silicone hydrogel (SiH) soft contact lenses (SCLs) were evaluated in a dynamic-cycling regime using a modified captive-bubble tensiometer-goniometer. Measurements were performed immediately after removal from blister packs, and after soaking in a glass vial filled with a surfactant-free solution, which was replaced daily for one week. Lens surface wettability was expressed as adhesion energy (AE) according to Young’s equation. Results STs of all blister pack solutions were lower than the reference ST of pure water (72.5 mN/m), indicating the presence of surfactants. When lenses were depleted of surfactants by soaking, the STs of all studied lenses and advancing CAs of selected lenses increased (p < 0.001). Receding CAs of all studied lenses were 12° ± 5° and were not affected by the presence of surfactants. For most of the conventional lenses, the surface wettability was largely dependent on surfactants, and reduced significantly after surfactant depletion. In contrast, most SiH lenses exhibited stable and self-sustained surface wettability in vitro. Conclusions The manufacturer-added surfactants affected wetting properties of all studied SCLs, although to different degrees. PMID:20400924

  6. Evaluation of Contact Separation Force Testing as a Screening Methodology for Electrical Socket Contacts

    NASA Technical Reports Server (NTRS)

    Green, Chris; Greenwell, Chris; Brusse, jay; Krus, Dennis; Leidecker, Henning

    2009-01-01

    During system level testing intermittent and permanent open circuit failures of mated, crimp removable, electrical contact pairs were experienced. The root cause of the failures was determined to be low (but not zero) contact forces applied by the socket contact tines against the engaging pin. The low contact force reduces the effectiveness of the wiping action of the socket tines against the pin. The observed failure mode may be produced when insufficient wiping during mate, demate and small relative movement in use allows for the accumulation of debris or insulating films that electrically separate the contact pair. The investigation identified at least three manufacturing process control problems associated with the socket contacts that enabled shipment of contacts susceptible to developing low contact forces: (1) Improper heat treatment of the socket tines resulting in plastic rather than elastic behavior; (2) Overly thinned socket tines at their base resulting in reduced pin retention forces; (3) insufficient screening tests to identify parts susceptible to the aforementioned failure mechanisms. The results from an extensive screening program of socket contacts utilizing the industry standard contact separation force test procedures are described herein. The investigation shows this method to be capable of identifying initially weak sockets. However, sockets whose contact retention forces may degrade during use may not be screened out by pin retention testing alone. Further investigations are required to correlate low contact retention forces with increased electrical contact resistance in the presence of insulating films that may accumulate in the use environment.

  7. Lens surface roughening for tears invariant contact lens performance

    NASA Astrophysics Data System (ADS)

    Zalevsky, Zeev; Azogui, Jonathan; Limon, Ofer; Rudnitsky, Arkady

    2014-03-01

    In many extended depth of focus diffractive or interferometry based ophthalmic contact lenses the time varied tears layers affect the ophthalmic functionality of the lens. In this paper we present a new approach involving nano pillars realized inside the grooves of a contact lens aiming to implement any type of extended depth of focus or diffractive optical element for ophthalmic applications in order to solve the micro fluidics layer uncertainty within the micro sag features.

  8. Bulk, surface, and blood-contacting properties of polyetherurethanes modified with polyethylene oxide.

    PubMed

    Okkema, A Z; Grasel, T G; Zdrahala, R J; Solomon, D D; Cooper, S L

    1989-01-01

    The bulk, surface, and blood-contacting properties of a series of polyether polyurethanes based on polyethylene oxide (PEO) (MW = 1450), polytetramethylene oxide (PTMO) (MW = 1000), and mixed PEO/PTMO soft segments were evaluated. The effect of varying the weight percentage of PEO, and thus the overall polarity of the mixed soft segment phase, was investigated. Two polymer blends prepared from a PTMO-based and a PEO-based polyurethane were also studied. Differential scanning calorimetry (DSC) and dynamic mechanical analysis indicated that the polyurethanes based on either the PEO or the PTMO soft segments are relatively phase mixed. The degree of phase mixing in the polymers increased with increasing weight fraction of PEO. As expected, water absorption and the hydrophilicity of the polymer increased with increasing PEO soft segment content. In vacuum, the PEO-rich polymers have a lower concentration of soft segment at the surface, possibly due to the migration of the polar PEO segments away from the polymer/vacuum interface. The blood-contacting results indicated that the higher PEO-containing polymers were more thrombogenic than the pure PTMO-based polyurethane. A threshold concentration of PEO in the polyurethane appeared to be required before the blood-contacting properties were significantly affected. PMID:2488846

  9. Mathematical modelling of contact of ruled surfaces: theory and practical application

    NASA Astrophysics Data System (ADS)

    Panchuk, K. L.; Niteyskiy, A. S.

    2016-04-01

    In the theory of ruled surfaces there are well known researches of contact of ruled surfaces along their common generator line (Klein image is often used [1]). In this paper we propose a study of contact of non developable ruled surfaces via the dual vector calculus. The advantages of this method have been demonstrated by E. Study, W. Blaschke and D. N. Zeiliger in differential geometry studies of ruled surfaces in space R3 over the algebra of dual numbers. A practical use of contact is demonstrated by the example modeling of the working surface of the progressive tool for tillage.

  10. Bioluminescence ATP monitoring for the routine assessment of food contact surface cleanliness in a university canteen.

    PubMed

    Osimani, Andrea; Garofalo, Cristiana; Clementi, Francesca; Tavoletti, Stefano; Aquilanti, Lucia

    2014-01-01

    ATP bioluminescence monitoring and traditional microbiological analyses (viable counting of total mesophilic aerobes, coliforms and Escherichia coli) were used to evaluate the effectiveness of Sanitation Standard Operating Procedures (SSOP) at a university canteen which uses a HACCP-based approach. To that end, 10 cleaning control points (CPs), including food contact surfaces at risk of contamination from product residues or microbial growth, were analysed during an 8-month monitoring period. Arbitrary acceptability limits were set for both microbial loads and ATP bioluminescence readings. A highly significant correlation (r = 0.99) between the means of ATP bioluminescence readings and the viable counts of total mesophilic aerobes was seen, thus revealing a strong association of these parameters with the level of surface contamination. Among CPs, the raw meat and multi-purpose chopping boards showed the highest criticalities. Although ATP bioluminescence technology cannot substitute traditional microbiological analyses for the determination of microbial load on food contact surfaces, it has proved to be a powerful tool for the real time monitoring of surface cleanliness at mass catering plants, for verify the correct application of SSOP, and hence for their implementation/revision in the case of poor hygiene. PMID:25329534

  11. Bioluminescence ATP Monitoring for the Routine Assessment of Food Contact Surface Cleanliness in a University Canteen

    PubMed Central

    Osimani, Andrea; Garofalo, Cristiana; Clementi, Francesca; Tavoletti, Stefano; Aquilanti, Lucia

    2014-01-01

    ATP bioluminescence monitoring and traditional microbiological analyses (viable counting of total mesophilic aerobes, coliforms and Escherichia coli) were used to evaluate the effectiveness of Sanitation Standard Operating Procedures (SSOP) at a university canteen which uses a HACCP-based approach. To that end, 10 cleaning control points (CPs), including food contact surfaces at risk of contamination from product residues or microbial growth, were analysed during an 8-month monitoring period. Arbitrary acceptability limits were set for both microbial loads and ATP bioluminescence readings. A highly significant correlation (r = 0.99) between the means of ATP bioluminescence readings and the viable counts of total mesophilic aerobes was seen, thus revealing a strong association of these parameters with the level of surface contamination. Among CPs, the raw meat and multi-purpose chopping boards showed the highest criticalities. Although ATP bioluminescence technology cannot substitute traditional microbiological analyses for the determination of microbial load on food contact surfaces, it has proved to be a powerful tool for the real time monitoring of surface cleanliness at mass catering plants, for verify the correct application of SSOP, and hence for their implementation/revision in the case of poor hygiene. PMID:25329534

  12. Eradication of high viable loads of Listeria monocytogenes contaminating food-contact surfaces

    PubMed Central

    de Candia, Silvia; Morea, Maria; Baruzzi, Federico

    2015-01-01

    This study demonstrates the efficacy of cold gaseous ozone treatments at low concentrations in the eradication of high Listeria monocytogenes viable cell loads from glass, polypropylene, stainless steel, and expanded polystyrene food-contact surfaces. Using a step by step approach, involving the selection of the most resistant strain-surface combinations, 11 Listeria sp. strains resulted inactivated by a continuous ozone flow at 1.07 mg m-3 after 24 or 48 h of cold incubation, depending on both strain and surface evaluated. Increasing the inoculum level to 9 log CFU coupon-1, the best inactivation rate was obtained after 48 h of treatment at 3.21 mg m-3 ozone concentration when cells were deposited onto stainless steel and expanded polystyrene coupons, resulted the most resistant food-contact surfaces in the previous assays. The addition of naturally contaminated meat extract to a high load of L. monocytogenes LMG 23775 cells, the most resistant strain out of the 11 assayed Listeria sp. strains, led to its complete inactivation after 4 days of treatment. To the best of our knowledge, this is the first report describing the survival of L. monocytogenes and the effect of ozone treatment under cold storage conditions on expanded polystyrene, a commonly used material in food packaging. The results of this study could be useful for reducing pathogen cross-contamination phenomena during cold food storage. PMID:26236306

  13. An in-situ sensor to measure contact area and surface stresses between real tribological bodies

    SciTech Connect

    Bryant, M.D.; Fernandez, B.

    1996-11-01

    Many machine components such as rollers (bearings and gears) and sliders (brushes and brakes) have elements with surfaces in contact. Failure is often by fatigue from contact stresses. Measurement of these stresses could reduce maintenance costs and avoid catastrophic failures. Common manufacturing techniques such as extruding, pressing and punching employ dies with surface contact. Direct and real time measurement of contact stresses within the dies could lead to improved process control through real time control feedback. Presented will be the concept of an in-situ sensor to visualize and measure real contact areas and surface stresses at all points within a contact interface. The sensor generates photoelastic fringes (fields of light intensity values) which it converts into surface stresses. First presented will be photoelastic principles and sensor operation; photographs of fringes taken under various contact conditions; measurements of real contact area extracted from these photographs; and calculations that relate the fringes to the contact stresses. These forward calculations map fields of contact stresses (input data) to fields of photoelastic light intensity values (output data). To extract surface stresses from light intensity measurements, Artificial Neural Networks generate an inverse map. Network architectures will be presented and training procedures discussed.

  14. White light optical profiling to unworn contact lenses surface topography analysis

    NASA Astrophysics Data System (ADS)

    Giraldez, M. J.; Garcia-Resua, C.; Real Oliveira, M. E.; Sánchez-Sellero, C.; Yebra-Pimentel, E.

    2011-05-01

    Purpose: White light optical profiling (WLOP), no usually applied to contact lenses (CL), is a well-established technique for non-contact measurement of surface topography over large areas at moderate lateral and high vertical resolution (sub-nanometer). The aim of this study is to analyze surface properties of five hydrogel CL evaluating representative roughness parameters as Roughness Average (Ra) and Root-Mean-Square Roughness (Rq), that depend on the sampling length, obtained by WLOP. Methods: Lenses used in this study were two highly biocompatible CL and three silicone-hydrogel CL. Unworn CL surface roughness and topography were studied with WLOP (Wyco NT1100) in VSI mode (Vertical Scanning Interferometry). 50X and 20X objectives were used. Height roughness parameters Ra and Rq were calculated for 625, 2500, 10829 and 67646 μm2 areas using the WycoVision®32 analytical software package. Results: High quality 3D topographic images were recorded at randomly different surface locations. Surface topography and Ra and Rq show different values depending on the contact lens and the measurement areas, with the highest roughness scores in biocompatible CL (Ra/Rq for 625, 2500, 10829 and 67646 μm2 areas were: Hioxifilcon 31,04/40,07 - 32,88/44,94 - 42,26/61,54 and 47,88/63,24; omafilcon A 17,61/22,41 - 22,18/28,20 - 49,84/65,98 and 67,12/89,37; senofilcon A 14.47/18,65 - 14,79/18,84 - 12,62/16,09 and 35,93/46,61; comfilcon A: 9,58/11,93 - 14,70/18,42 - 12,17/16,21 and 38,81/51,13; balafilcon A: 7,60/9,69 - 16,30/20,84/ - 9,77/12,83 and 24,19/32,09). Higher roughness parameters were obtained for larger areas in all lenses. Conclusions: Highly biocompatible CL presented the highest roughness surface. WLOP provides useful information about contact lens surface measuring larger areas than other techniques used before.

  15. Observations of a shock and a recombination layer at the contact surface of Comet Halley

    NASA Technical Reports Server (NTRS)

    Goldstein, B. E.; Altwegg, K.; Balsiger, H.; Fuselier, S. A.; Ip, W.-H.

    1989-01-01

    Results are presented on observations in the vicinity of the contact surface of the Comet Halley, obtained by the Giotto ion mass spectrometer, with emphasis placed on two specific events observed in this region on the inbound pass. One was a burst of energized ions (about 20 eV) of 2-sec duration observed two seconds before the contact surface was encountered, which coincided with a pulse in magnetic field strength interpreted by Neubauer (1988) as a fast-mode shock traveling away from the contact surface. The second was a sharp spike in ion densities observed at the contact surface by the mass analyzer, centered approximately at the inner edge of the contact surface. This ion-density spike is interpreted as a boundary layer into which the radial ionospheric flow enters and piles up; the density increase is limited by recombination.

  16. Instability of Contact Resistance in MEMS and NEMS DC Switches under Low Force: the Role of Alien Films on the Contact Surface

    PubMed Central

    Qiu, Haodong; Wang, Hong; Ke, Feixiang

    2013-01-01

    The metal contact is one of the most crucial parts in ohmic-contact microelectromechanical (MEMS) switches, as it determines the device performance and reliability. It has been observed that there is contact instability when the contact force is below a threshold value (minimum contact force). However, there has been very limited knowledge so far about the unstable electrical contact behavior under low contact force. In this work, the instability of Au-Au micro/nano-contact behavior during the initial stage of contact formation is comprehensively investigated for the first time. It has been found that the alien film on the contact surface plays a critical role in determining the contact behavior at the initial contact stage under low contact force. A strong correlation between contact resistance fluctuation at the initial contact stage and the presence of a hydrocarbon alien film on the contact surface is revealed. The enhancement of contact instability due to the alien film can be explained within a framework of trap-assisted tunneling.

  17. Silicone hydrogel contact lens surface analysis by atomic force microscopy: shape parameters

    NASA Astrophysics Data System (ADS)

    Giraldez, M. J.; Garcia-Resua, C.; Lira, M.; Sánchez-Sellero, C.; Yebra-Pimentel, E.

    2011-05-01

    Purpose: Average roughness (Ra) is generally used to quantify roughness; however it makes no distinction between spikes and troughs. Shape parameters as kurtosis (Rku) and skewness (Rsk) serve to distinguish between two profiles with the same Ra. They have been reported in many biomedical fields, but they were no applied to contact lenses before. The aim of this study is to analyze surface properties of four silicone hydrogel contact lenses (CL) by Atomic Force Microscopy (AFM) evaluating Ra, Rku and Rsk. Methods: CL used in this study were disposable silicone hydrogel senofilcon A, comfilcon A, balafilcon A and lotrafilcon B. Unworn CL surfaces roughness and topography were measured by AFM (Veeco, multimode-nanoscope V) in tapping modeTM. Ra, Rku and Rsk for 25 and 196 μm2 areas were determined. Results: Surface topography and parameters showed different characteristics depending on the own nature of the contact lens (Ra/Rku/Rsk for 25 and 196 μm2 areas were: senofilcon A 3,33/3,74/0,74 and 3,76/18,16/1,75; comfilcon A: 1,56/31,09/2,93 and 2,76/45,82/3,60; balafilcon A: 2,01/33,62/-2,14 and 2,54/23,36/-1,96; lotrafilcon B: 26,97/4,11/-0,34 and 29,25/2,82/-0,23). In lotrafilcon B, with the highest Ra, Rku showed a lower degree of peakedness of its distribution. Negative Rsk value obtained for balafilcon A showed a clear predominance of valleys in this lens. Conclusions: Kku and Rsk are two statistical parameters useful to analyse CL surfaces, which complete information from Ra. Differences in values distribution and symmetry were observed between CL.

  18. Sub-discretized surface model with application to contact mechanics in multi-body simulation

    SciTech Connect

    Johnson, S; Williams, J

    2008-02-28

    The mechanics of contact between rough and imperfectly spherical adhesive powder grains are often complicated by a variety of factors, including several which vary over sub-grain length scales. These include several traction factors that vary spatially over the surface of the individual grains, including high energy electron and acceptor sites (electrostatic), hydrophobic and hydrophilic sites (electrostatic and capillary), surface energy (general adhesion), geometry (van der Waals and mechanical), and elasto-plastic deformation (mechanical). For mechanical deformation and reaction, coupled motions, such as twisting with bending and sliding, as well as surface roughness add an asymmetry to the contact force which invalidates assumptions for popular models of contact, such as the Hertzian and its derivatives, for the non-adhesive case, and the JKR and DMT models for adhesive contacts. Though several contact laws have been offered to ameliorate these drawbacks, they are often constrained to particular loading paths (most often normal loading) and are relatively complicated for computational implementation. This paper offers a simple and general computational method for augmenting contact law predictions in multi-body simulations through characterization of the contact surfaces using a hierarchically-defined surface sub-discretization. For the case of adhesive contact between powder grains in low stress regimes, this technique can allow a variety of existing contact laws to be resolved across scales, allowing for moments and torques about the contact area as well as normal and tangential tractions to be resolved. This is especially useful for multi-body simulation applications where the modeler desires statistical distributions and calibration for parameters in contact laws commonly used for resolving near-surface contact mechanics. The approach is verified against analytical results for the case of rough, elastic spheres.

  19. Surface tension and contact angles: Molecular origins and associated microstructure

    NASA Technical Reports Server (NTRS)

    Davis, H. T.

    1982-01-01

    Gradient theory converts the molecular theory of inhomogeneous fluid into nonlinear boundary value problems for density and stress distributions in fluid interfaces, contact line regions, nuclei and microdroplets, and other fluid microstructures. The relationship between the basic patterns of fluid phase behavior and the occurrence and stability of fluid microstructures was clearly established by the theory. All the inputs of the theory have molecular expressions which are computable from simple models. On another level, the theory becomes a phenomenological framework in which the equation of state of homogeneous fluid and sets of influence parameters of inhomogeneous fluids are the inputs and the structures, stress tensions and contact angles of menisci are the outputs. These outputs, which find applications in the science and technology of drops and bubbles, are discussed.

  20. Non-contact large-scale separated surfaces flatness measurement by using laser beam and laser distance sensor

    NASA Astrophysics Data System (ADS)

    Li, Xudong; Fan, Bo; Jiang, Hongzhi; Zhao, Huijie

    2015-07-01

    Large-scale separated surface is very common in modern manufacturing industry. The measurement of the flatness of such surfaces is one of the most important procedures when evaluating the manufacturing quality. Usually, the measurement needs to be accomplished in an in-situ and non-contact way. Although there are many conventional approaches such as autocollimator, capacitance displacement sensor and even CMM, they can not meet the needs from the separated surfaces measurement either because of their contact-nature or inapplicable to separated surfaces. A non-contact large-scale separated surfaces flatness measurement device utilizing laser beam and laser distance sensor (LDS) is proposed. The laser beam is rotated to form an optical reference plane. The LDS is used to measure the distance between the surface and the sensor accurately. A Position Sensitive Detector (PSD) is mounted with the LDS firmly to determine the distance between the LDS and the reference plane and then the distance between the surface and the reference plane can be obtained by subtracting the two distances. The device can be easily mounted on a machine-tool spindle and is moved to measure all the separated surfaces. Then all the data collected are used to evaluate the flatness of these separated surfaces. The accuracy analysis, the corresponding flatness evaluation algorithm, the prototype construction and experiments are also discussed. The proposed approach and device feature as high accuracy, in-situ usage and the higher degree of automatic measurement, and can be used in the areas that call for non-contact and separated surfaces measurement.

  1. Liquid-bridge stability and breakup on surfaces with contact-angle hysteresis.

    PubMed

    Akbari, Amir; Hill, Reghan J

    2016-08-10

    We study the stability and breakup of liquid bridges with a free contact line on surfaces with contact-angle hysteresis (CAH) under zero-gravity conditions. Non-ideal surfaces exhibit CAH because of surface imperfections, by which the constraints on three-phase contact lines are influenced. Given that interfacial instabilities are constraint-sensitive, understanding how CAH affects the stability and breakup of liquid bridges is crucial for predicting the drop size in contact-drop dispensing. Unlike ideal surfaces on which contact lines are always free irrespective of surface wettability, contact lines may undergo transitions from pinned to free and vice versa during drop deposition on non-ideal surfaces. Here, we experimentally and theoretically examine how stability and breakup are affected by CAH, highlighting cases where stability is lost during a transition from a pinned-pinned (more constrained) to pinned-free (less constrained) interface-rather than a critical state. This provides a practical means of expediting or delaying stability loss. We also demonstrate how the dynamic contact angle can control the contact-line radius following stability loss. PMID:27443494

  2. Surface cationized cellulose nanofibrils for the production of contact active antimicrobial surfaces.

    PubMed

    Saini, Seema; Yücel Falco, Çiğdem; Belgacem, Mohamed Naceur; Bras, Julien

    2016-01-01

    In the last decade, a new fiber pretreatment has been proposed to make easy cellulose fibrillation into microfibrils. In this context, different surface cationized MFC was prepared by optimizing the experimental parameters for cellulose fibers pretreatment before fibrillation. All MFCs were characterized by conductometric titration to establish degree of substitution, field emission gun scanning electron microscopy (FEG-SEM), atomic force microscopy (AFM) and optical microscopy assessed the effect of pretreatment on the morphology of the ensuing MFCs. Antibacterial activities of neat and cationized MFC samples were investigated against Gram positive bacteria (Bacillus subtilis, Staphylococcus aureus) and Gram negative bacteria (Escherichia coli). The CATMFC sample at DS greater than 0.18 displayed promising results with antibacterial properties without any leaching of quaternary ammonium into the environment. This work proved the potential of cationic MFCs with specific DS for contact active antimicrobial surface applications in active food packaging, medical packaging or in health and cosmetic field. PMID:26453874

  3. Preacclimation alters Salmonella Enteritidis surface properties and its initial attachment to food contact surfaces.

    PubMed

    Yang, Yishan; Kumar, Amit; Zheng, Qianwang; Yuk, Hyun-Gyun

    2015-04-01

    Exposure of Salmonella to environmental stress, prior to its adherence to a food contact surface, may change the cell surface properties and consequently affect its initial attachment and biofilm formation. This study investigated the influence of temperature and pH preacclimation on the initial attachment of Salmonella Enteritidis to acrylic and stainless steel. Besides, changes in physicochemical properties of cells were examined; and their surface attachment was modeled by xDLVO theory. Results showed that control cells pre-grown at 37°C had significantly (P<0.05) higher initial attachment, followed by those pre-grown at 25, 42, and 10°C. The initial attachment of cells pre-grown at pH 5.3 or 6.3 was not significantly (P>0.05) different from control cells pre-grown at pH 7.3, but they were significantly higher compared to cells pre-grown at pH 8.3 and 9.0. No significant difference was observed between cell attachment to acrylic and stainless steel, although they had different physicochemical properties. The xDLVO theory successfully explained higher attachment for cells pre-grown at optimal condition on both contact surfaces. However, the xDLVO theory could not explain the similar attachment of cells to acrylic and stainless steel. This study elucidates that commonly used intervention technologies including cold storage, thermal treatment, and alkaline antimicrobial agents might alter the physicochemical properties of S. Enteritidis cells and result in varied initial attachment levels. PMID:25800356

  4. Modeling of contact mechanics and friction limit surfaces for soft fingers in robotics, with experimental results

    SciTech Connect

    Xydas, N.; Kao, I.

    1999-09-01

    A new theory in contact mechanics for modeling of soft fingers is proposed to define the relationship between the normal force and the radius of contact for soft fingers by considering general soft-finger materials, including linearly and nonlinearly elastic materials. The results show that the radius of contact is proportional to the normal force raised to the power of {gamma}, which ranges from 0 to 1/3. This new theory subsumes the Hertzian contact model for linear elastic materials, where {gamma} = 1/3. Experiments are conducted to validate the theory using artificial soft fingers made of various materials such as rubber and silicone. Results for human fingers are also compared. This theory provides a basis for numerically constructing friction limit surfaces. The numerical friction limit surface can be approximated by an ellipse, with the major and minor axes as the maximum friction force and the maximum moment with respect to the normal axis of contact, respectively. Combining the results of the contact-mechanics model with the contact-pressure distribution, the normalized friction limit surface can be derived for anthropomorphic soft fingers. The results of the contact-mechanics model and the pressure distribution for soft fingers facilitate the construction of numerical friction limit surfaces, and will enable us to analyze and simulate contact behaviors of grasping and manipulation in robotics.

  5. A thermodynamic approach to predict apparent contact angles on microstructures using surface polygonal maps.

    PubMed

    Calvimontes, A

    2014-11-01

    The thermodynamic model of wetting developed and tested in this work allows the understanding and prediction of apparent contact angles on topographic maps of real and digitally-generated microstructures. The model considers the solid component as a set of finite areal elements in the form of a polygonal map. Liquid and gas components are instead evaluated as continuous and incompressible volumes. In this study, the concept of the wetting topographic spectrum (WTS) is proposed to simulate the changes in the liquid-solid contact areas and of the interfacial energies while wetting the microstructure from the top to the bottom of the topographic map, passing through various states of metastable equilibrium, to find a stable configuration. The model was successfully applied to predict the wetting apparent contact angles on randomly micro-structured polypropylene (PP) surfaces and on a superhydrophobic and superoleophobic transparent polydimethylsiloxane (PDMS) microstructure previously presented as a communication in this journal by other authors. The method presented in this study can be used to design and predict the geometry of microstructures with special wetting characteristics. PMID:25192555

  6. Gas bearings. [fluid lubrication theory of sliding contact surfaces

    NASA Technical Reports Server (NTRS)

    Pan, C. H. T.

    1980-01-01

    The present work deals with the fundamentals of gas lubrication theory, which forms the foundation of all analytical design tools for gas bearings. Most of the hard lessons learned in the past are outlined with reference to dry contact, debris ingestion, sliding speed, and chemical stability of lubricant. The mathematical theory of gas lubrication is described for scaling rules in thin-film viscous flow, momentum conservation, mass conservation, energy conservation, isothermal gas bearing theory, coupling effects, and global bearing characteristics. Particular attention is given to the governing differential equations for common bearing configurations. Also discussed are representative solutions of self-acting gas bearings, externally pressurized bearings, and time-dependent effects.

  7. Wettability Control of Gold Surfaces Modified with Benzenethiol Derivatives: Water Contact Angle and Thermal Stability.

    PubMed

    Tatara, Shingo; Kuzumoto, Yasutaka; Kitamura, Masatoshi

    2016-04-01

    The water wettability of Au surfaces has been controlled using various benzenethiol derivatives including 4-methylbenzenethiol, pentafluorobenzenethiol, 4-flubrobenzenethiol, 4-methoxy-benzenethiol, 4-nitrobenzenethiol, and 4-hydroxybenzenethiol. The water contact angle of the Au surface modified with the benzenethiol derivative was found to vary in the wide range of 30.9° to 88.3°. The contact angle of the modified Au films annealed was also measured in order to investigate their thermal stability. The change in the contact angle indicated that the modified surface is stable at temperatures below about 400 K. Meanwhile, the activation energy of desorption from the modified surface was estimated from the change in the contact angle. The modified Au surface was also examined using X-ray photoelectron spectroscopy. PMID:27451620

  8. Surface modification of fluorosilicone acrylate RGP contact lens via low-temperature argon plasma

    NASA Astrophysics Data System (ADS)

    Yin, Shiheng; Wang, Yingjun; Ren, Li; Zhao, Lianna; Kuang, Tongchun; Chen, Hao; Qu, Jia

    2008-11-01

    A fluorosilicone acrylate rigid gas permeable (RGP) contact lens was modified via argon plasma to improve surface hydrophilicity and resistance to protein deposition. The influence of plasma treatment on surface chemical structure, hydrophilicity and morphology of RGP lens was investigated by X-ray photoelectron spectrometer (XPS), contact angle measurements and scanning electron microscope (SEM), respectively. The contact angle results showed that the hydrophilicity of the contact lens was improved after plasma treatment. XPS results indicated that the incorporation of oxygen-containing groups on surface and the transformation of silicone into hydrophilic silicate after plasma treatment are the main reasons for the surface hydrophilicity improvement. SEM results showed that argon plasma with higher power could lead to surface etching.

  9. Numerical investigation of relationship between water contact angle and drag reduction ratio of superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Yin, Liang; Zhang, Hai-Feng; Shi, Shu-Yuan; Lu, Yao; Wang, Yang; Liu, Xiao-Wei

    2016-06-01

    This paper proposes a novel bubble model to analyze drag reduction. The relationship between the slip length and air bubble height is discussed. The numerical relationship between the surface contact angle and slip length is obtained using the solid-liquid contact ratio in the Cassie equation. The surface drag reduction ratio increases by 40% at low velocities when the solid liquid contact ratio decreases from 90% to 10%. An experimental setup to study liquid/solid friction drag is reported. The drag reduction ratio for the superhydrophobic surface tested experimentally is 30%-35% at low velocities. These results are similar to the simulation results obtained at low velocities.

  10. Boundary lubrication of heterogeneous surfaces and the onset of cavitation in frictional contacts

    PubMed Central

    Savio, Daniele; Pastewka, Lars; Gumbsch, Peter

    2016-01-01

    Surfaces can be slippery or sticky depending on surface chemistry and roughness. We demonstrate in atomistic simulations that regular and random slip patterns on a surface lead to pressure excursions within a lubricated contact that increase quadratically with decreasing contact separation. This is captured well by a simple hydrodynamic model including wall slip. We predict with this model that pressure changes for larger length scales and realistic frictional conditions can easily reach cavitation thresholds and significantly change the load-bearing capacity of a contact. Cavitation may therefore be the norm, not the exception, under boundary lubrication conditions. PMID:27051871

  11. Boundary lubrication of heterogeneous surfaces and the onset of cavitation in frictional contacts.

    PubMed

    Savio, Daniele; Pastewka, Lars; Gumbsch, Peter

    2016-03-01

    Surfaces can be slippery or sticky depending on surface chemistry and roughness. We demonstrate in atomistic simulations that regular and random slip patterns on a surface lead to pressure excursions within a lubricated contact that increase quadratically with decreasing contact separation. This is captured well by a simple hydrodynamic model including wall slip. We predict with this model that pressure changes for larger length scales and realistic frictional conditions can easily reach cavitation thresholds and significantly change the load-bearing capacity of a contact. Cavitation may therefore be the norm, not the exception, under boundary lubrication conditions. PMID:27051871

  12. Ternary free-energy lattice Boltzmann model with tunable surface tensions and contact angles

    NASA Astrophysics Data System (ADS)

    Semprebon, Ciro; Krüger, Timm; Kusumaatmaja, Halim

    2016-03-01

    We present a ternary free-energy lattice Boltzmann model. The distinguishing feature of our model is that we are able to analytically derive and independently vary all fluid-fluid surface tensions and the solid surface contact angles. We carry out a number of benchmark tests: (i) double emulsions and liquid lenses to validate the surface tensions, (ii) ternary fluids in contact with a square well to compare the contact angles against analytical predictions, and (iii) ternary phase separation to verify that the multicomponent fluid dynamics is accurately captured. Additionally we also describe how the model presented here can be extended to include an arbitrary number of fluid components.

  13. The influence of surface dents and grooves on traction in sliding EHD point contacts

    NASA Technical Reports Server (NTRS)

    Cusano, C.; Wedeven, L. D.

    1982-01-01

    Changes in traction, caused by dents and grooves on a highly polished ball,are investigated as these defects approach and go through sliding elastohydrodynamic point contacts. The contacts are formed with the ball loading against a transparent disk. The ball and thus the topographical features are held stationary at various locations in the vicinity and within the contact while the disk is rotating. These topographical features can cause substantial changes in the traction when compared to traction obtained with smooth surfaces.

  14. Apparent-contact-angle model at partial wetting and evaporation: impact of surface forces.

    PubMed

    Janeček, V; Nikolayev, V S

    2013-01-01

    This theoretical and numerical study deals with evaporation of a fluid wedge in contact with its pure vapor. The model describes a regime where the continuous wetting film is absent and the actual line of the triple gas-liquid-solid contact appears. A constant temperature higher than the saturation temperature is imposed at the solid substrate. The fluid flow is solved in the lubrication approximation. The introduction of the surface forces in the case of the partial wetting is discussed. The apparent contact angle (the gas-liquid interface slope far from the contact line) is studied numerically as a function of the substrate superheating, contact line velocity, and parameters related to the solid-fluid interaction (Young and microscopic contact angles, Hamaker constant, etc.). The dependence of the apparent contact angle on the substrate temperature is in agreement with existing approaches. For water, the apparent contact angle may be 20° larger than the Young contact angle for 1 K superheating. The effect of the surface forces on the apparent contact angle is found to be weak. PMID:23410341

  15. Apparent-contact-angle model at partial wetting and evaporation: Impact of surface forces

    NASA Astrophysics Data System (ADS)

    Janeček, V.; Nikolayev, V. S.

    2013-01-01

    This theoretical and numerical study deals with evaporation of a fluid wedge in contact with its pure vapor. The model describes a regime where the continuous wetting film is absent and the actual line of the triple gas-liquid-solid contact appears. A constant temperature higher than the saturation temperature is imposed at the solid substrate. The fluid flow is solved in the lubrication approximation. The introduction of the surface forces in the case of the partial wetting is discussed. The apparent contact angle (the gas-liquid interface slope far from the contact line) is studied numerically as a function of the substrate superheating, contact line velocity, and parameters related to the solid-fluid interaction (Young and microscopic contact angles, Hamaker constant, etc.). The dependence of the apparent contact angle on the substrate temperature is in agreement with existing approaches. For water, the apparent contact angle may be 20∘ larger than the Young contact angle for 1 K superheating. The effect of the surface forces on the apparent contact angle is found to be weak.

  16. Dynamics of the contact between a ruthenium surface with a single nanoasperity and a flat ruthenium surface: Molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    de Oliveira, Alan Barros; Fortini, Andrea; Buldyrev, Sergey V.; Srolovitz, David

    2011-04-01

    We study the dynamics of the contact between a pair of surfaces (with properties designed to mimic ruthenium) via molecular dynamics simulations. In particular, we study the contact between a ruthenium surface with a single nanoasperity and a flat ruthenium surface. The results of such simulations suggest that contact behavior is highly variable. The goal of this study is to investigate the source and degree of this variability. We find that during compression, the behavior of the contact force displacement curves is reproducible, while during contact separation, the behavior is highly variable. Examination of the contact surfaces suggests that two separation mechanisms are in operation and give rise to this variability. One mechanism corresponds to the formation of a bridge between the two surfaces that plastically stretches as the surfaces are drawn apart and eventually separate in shear. This leads to a morphology after separation in which there are opposing asperities on the two surfaces. This plastic separation/bridge formation mechanism leads to a large work of separation. The other mechanism is a more brittle-like mode in which a crack propagates across the base of the asperity (slightly below the asperity/substrate junction) leading to most of the asperity on one surface or the other after separation and a slight depression facing this asperity on the opposing surface. This failure mode corresponds to a smaller work of separation. This failure mode corresponds to a smaller work of separation. Furthermore, contacts made from materials that exhibit predominantly brittle-like behavior will tend to require lower work of separation than those made from ductile-like contact materials.

  17. Microalgae Scatter off Solid Surfaces by Hydrodynamic and Contact Forces.

    PubMed

    Contino, Matteo; Lushi, Enkeleida; Tuval, Idan; Kantsler, Vasily; Polin, Marco

    2015-12-18

    Interactions between microorganisms and solid boundaries play an important role in biological processes, such as egg fertilization, biofilm formation, and soil colonization, where microswimmers move within a structured environment. Despite recent efforts to understand their origin, it is not clear whether these interactions can be understood as being fundamentally of hydrodynamic origin or hinging on the swimmer's direct contact with the obstacle. Using a combination of experiments and simulations, here we study in detail the interaction of the biflagellate green alga Chlamydomonas reinhardtii, widely used as a model puller microorganism, with convex obstacles, a geometry ideally suited to highlight the different roles of steric and hydrodynamic effects. Our results reveal that both kinds of forces are crucial for the correct description of the interaction of this class of flagellated microorganisms with boundaries. PMID:26722946

  18. Microalgae Scatter off Solid Surfaces by Hydrodynamic and Contact Forces

    NASA Astrophysics Data System (ADS)

    Contino, Matteo; Lushi, Enkeleida; Tuval, Idan; Kantsler, Vasily; Polin, Marco

    2015-12-01

    Interactions between microorganisms and solid boundaries play an important role in biological processes, such as egg fertilization, biofilm formation, and soil colonization, where microswimmers move within a structured environment. Despite recent efforts to understand their origin, it is not clear whether these interactions can be understood as being fundamentally of hydrodynamic origin or hinging on the swimmer's direct contact with the obstacle. Using a combination of experiments and simulations, here we study in detail the interaction of the biflagellate green alga Chlamydomonas reinhardtii, widely used as a model puller microorganism, with convex obstacles, a geometry ideally suited to highlight the different roles of steric and hydrodynamic effects. Our results reveal that both kinds of forces are crucial for the correct description of the interaction of this class of flagellated microorganisms with boundaries.

  19. Cold plasma rapid decontamination of food contact surfaces contaminated with Salmonella biofilms

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cross-contamination of fresh produce and other foods from persistent pathogen reservoirs is a known risk factor in processing environments. Industry requires a rapid, waterless, zero-contact, chemical-free method for removing pathogens from food-contact surfaces. Cold plasma was tested for its abili...

  20. Cell surface energy, contact angles and phase partition. II. Bacterial cells in biphasic aqueous mixtures.

    PubMed

    Gerson, D F; Akit, J

    1980-11-01

    Partition coefficients in biphasic mixtures of poly(ethylene glycol) and Dextran are compared to cell surface energies obtained from contact angles of each liquid phase on cell layers. Linear relationships are observed between these two independent measurements for a variety of bacterial cells. The results demonstrate the importance of interfacial phenomena and contact angles in the phase-partition process. PMID:6159003

  1. Phase-field simulations of contact-line dynamics on rough surfaces

    NASA Astrophysics Data System (ADS)

    Yang, Fengchao; Yue, Pengtao; Chen, Xiaopeng

    2015-11-01

    Wetting of solid surfaces is ubiquitous in nature, and in most cases the surfaces are not smooth. In this work, we will investigate how surface roughness influences contact-line dynamics by simulating the forced wetting in a capillary tube with microposts or microgrooves on its wall. A phase-field method is used to capture fluid interfaces as well as moving contact lines. The governing equations are solved by an implicit finite-element method on an adaptive triangular mesh, which conforms to the topological patterns on the tube wall and also refines at the fluid interface. With our computational setup, we can capture the advancing and receding contact angles. As the contact line moves, it jumps from one pillar to the next; consequently, the apparent contact angle exhibits a periodic behavior. By comparing with the result on a smooth surface, we will explain how surface roughness affects contact-line dynamics by modifying the effective contact angle and slip length. Numerical results on different arrangements and shapes of microposts will be presented.

  2. Evaluating soft contact lens quality: a manufacturer's perspective.

    PubMed

    Seibel, E J; Trilsch, W R; Lee, D

    1988-04-01

    This study was designed to compare quality control between six aphakic contact lens brands. The methodology eliminates the sampling and experimental variables of previous studies. The lenses were all purchased new at +13.00 D power, with the same number of lenses and distribution of manufacturing batch/lots per brand. We measured or assessed 120 study lenses (20 per brand) for diameter, front sagittal height, power and image quality, center thickness, surface and edge quality, and edge design. The base curve radius was calculated accurately using lens cross-sectioning techniques. The reproducibility of measured lens parameters (precision) and conformance to label claims (accuracy) were tabulated separately and the lens brands were ranked and grouped statistically. The tabulated results are represented graphically in one spread sheet where selected American National Standards Institute (ANSI) tolerances were used as a standard to which all lens brands were compared. Lens brands coded as Brand A and Brand B rated the highest using our criterion for ranking overall quality control. PMID:3377065

  3. Generation of spiral bevel gears with conjugate tooth surfaces and tooth contact analysis

    NASA Technical Reports Server (NTRS)

    Litvin, Faydor L.; Tsung, Wei-Jiung; Lee, Hong-Tao

    1987-01-01

    A new method for generation of spiral bevel gears is proposed. The main features of this method are as follows: (1) the gear tooth surfaces are conjugated and can transform rotation with zero transmission errors; (2) the tooth bearing contact is localized; (3) the center of the instantaneous contact ellipse moves in a plane that has a fixed orientation; (4) the contact normal performs in the process of meshing a parallel motion; (5) the motion of the contact ellipse provides improved conditions of lubrication; and (6) the gears can be manufactured by use of Gleason's equipment.

  4. Comprehensive analytical model for locally contacted rear surface passivated solar cells

    NASA Astrophysics Data System (ADS)

    Wolf, Andreas; Biro, Daniel; Nekarda, Jan; Stumpp, Stefan; Kimmerle, Achim; Mack, Sebastian; Preu, Ralf

    2010-12-01

    For optimum performance of solar cells featuring a locally contacted rear surface, the metallization fraction as well as the size and distribution of the local contacts are crucial, since Ohmic and recombination losses have to be balanced. In this work we present a set of equations which enable to calculate this trade off without the need of numerical simulations. Our model combines established analytical and empirical equations to predict the energy conversion efficiency of a locally contacted device. For experimental verification, we fabricate devices from float zone silicon wafers of different resistivity using the laser fired contact technology for forming the local rear contacts. The detailed characterization of test structures enables the determination of important physical parameters, such as the surface recombination velocity at the contacted area and the spreading resistance of the contacts. Our analytical model reproduces the experimental results very well and correctly predicts the optimum contact spacing without the use of free fitting parameters. We use our model to estimate the optimum bulk resistivity for locally contacted devices fabricated from conventional Czochralski-grown silicon material. These calculations use literature values for the stable minority carrier lifetime to account for the bulk recombination caused by the formation of boron-oxygen complexes under carrier injection.

  5. Contact-angle hysteresis on periodic microtextured surfaces: Strongly corrugated liquid interfaces

    NASA Astrophysics Data System (ADS)

    Iliev, Stanimir; Pesheva, Nina

    2016-06-01

    We study numerically the shapes of a liquid meniscus in contact with ultrahydrophobic pillar surfaces in Cassie's wetting regime, when the surface is covered with identical and periodically distributed micropillars. Using the full capillary model we obtain the advancing and the receding equilibrium meniscus shapes when the cross-sections of the pillars are both of square and circular shapes, for a broad interval of pillar concentrations. The bending of the liquid interface in the area between the pillars is studied in the framework of the full capillary model and compared to the results of the heterogeneous approximation model. The contact angle hysteresis is obtained when the three-phase contact line is located on one row (block case) or several rows (kink case) of pillars. It is found that the contact angle hysteresis is proportional to the line fraction of the contact line on pillars tops in the block case and to the surface fraction for pillar concentrations 0.1 -0.5 in the kink case. The contact angle hysteresis does not depend on the shape (circular or square) of the pillars cross-section. The expression for the proportionality of the receding contact angle to the line fraction [Raj et al., Langmuir 28, 15777 (2012), 10.1021/la303070s] in the case of block depinning is theoretically substantiated through the capillary force, acting on the solid plate at the meniscus contact line.

  6. Fabricating Ohmic contact on Nb-doped SrTiO3 surface in nanoscale

    NASA Astrophysics Data System (ADS)

    Wang, Yuhang; Shi, Xiaolan; Lai, Xubo; Gao, Zhipeng; Liu, Lixin; Wang, Yuan; Zhu, Wenjun; Meng, Chuanmin; Zhang, Liuwan

    2016-05-01

    Fabricating reliable nano-Ohmic contact on wide gap semiconductors is an important yet difficult step in oxide nanoelectronics. We fabricated Ohmic contact on the n-type wide gap oxide Nb-doped SrTiO3 in nanoscale by mechanically scratching the surface using an atomic force microscopy tip. Although contacted to high work function metal, the scratched area exhibits nearly linear IV behavior with low contact resistance, which maintains for hours in vacuum. In contrast, the unscratched area shows Fowler-Nordheim tunneling dominated Schottky rectifying behavior with high contact resistance. It was found that the Ohmic conductivity in the scratched area was drastically suppressed by oxygen gas indicating the oxygen vacancy origin of the Ohmic behavior. The surface oxygen vacancy induced barrier width reduction was proposed to explain the phenomena. The nanoscale approach is also applicable to macroscopic devices and has potential application in all-oxide devices.

  7. Streptococcal Surface Proteins Activate the Contact System and Control Its Antibacterial Activity*

    PubMed Central

    Wollein Waldetoft, Kristofer; Svensson, Lisbeth; Mörgelin, Matthias; Olin, Anders I.; Nitsche-Schmitz, D. Patric; Björck, Lars; Frick, Inga-Maria

    2012-01-01

    Group G streptococci (GGS) are important bacterial pathogens in humans. Here, we investigated the interactions between GGS and the contact system, a procoagulant and proinflammatory proteolytic cascade that, upon activation, also generates antibacterial peptides. Two surface proteins of GGS, protein FOG and protein G (PG), were found to bind contact system proteins. Experiments utilizing contact protein-deficient human plasma and isogenic GGS mutant strains lacking FOG or PG showed that FOG and PG both activate the procoagulant branch of the contact system. In contrast, only FOG induced cleavage of high molecular weight kininogen, generating the proinflammatory bradykinin peptide and additional high molecular weight kininogen fragments containing the antimicrobial peptide NAT-26. On the other hand, PG protected the bacteria against the antibacterial effect of NAT-26. These findings underline the significance of the contact system in innate immunity and demonstrate that GGS have evolved surface proteins to exploit and modulate its effects. PMID:22648411

  8. MRI-based modeling for evaluation of in vivo contact mechanics in the human wrist during active light grasp.

    PubMed

    Pillai, Ravi R; Thoomukuntla, Bhaskar; Ateshian, Gerard A; Fischer, Kenneth J

    2007-01-01

    Investigations of in vivo joint mechanics are important for understanding the joint function under functional loading and the mechanisms of pathology. In this study we used magnetic resonance imaging (MRI) based joint contact modeling to evaluate in vivo joint contact mechanics in the human wrist. MRI scans were performed on the wrists of four subjects while they maintained light grasp of a cylinder, and with the same wrist relaxed. 3D models of the radius, scaphoid and lunate, including cartilage surface data, were constructed from the relaxed image data. These models were transformed into the loaded configuration, as determined from the grasp image data, and contact mechanics were evaluated. The resulting contact pressures, areas and forces were then analyzed for each articulation and for each subject. Contact areas were measured directly from grasp MRI images for comparison to the model predictions. The first-ever estimates for in vivo radioscaphoid and radiolunate contact pressure agreed reasonably well with previous cadaveric studies. This investigation also produced novel in vivo scapholunate contact results that were similar to radiolunate data. The specimen-specific contact area comparison generally showed substantial variability between the models and the direct measurements from MRI. On average, the models were within about 10% of the direct MRI measurements for radioscaphoid and scapholunate contact areas, but radiolunate contact areas from the model were only within 55% of the direct measurements. Overall, the results of the study suggest that MRI-based modeling has substantial potential for evaluation of in vivo joint contact mechanics, especially as technology and methodology improve. PMID:17391678

  9. Controlling the hydrophilicity and contact resistance of fuel cell bipolar plate surfaces using layered nanoparticle assembly

    NASA Astrophysics Data System (ADS)

    Wang, Feng

    Hybrid nanostructured coatings exhibiting the combined properties of electrical conductivity and surface hydrophilicity were obtained by using Layer-by-Layer (LBL) assembly of cationic polymer, silica nanospheres, and carbon nanoplatelets. This work demonstrates that by controlling the nanoparticle zeta (zeta) potential through the suspension parameters (pH, organic solvent type and amount, and ionic content) as well as the assembly sequence, the nanostructure and composition of the coatings may be adjusted to optimize the desired properties. Two types of silica nanospheres were evaluated as the hydrophilic component: X-TecRTM 3408 from Nano-X Corporation, with a diameter of about 20 nm, and polishing silica from Electron Microscopy Supply, with diameter of about 65 nm. Graphite nanoplatelets with a thickness of 5~10nm (Aquadag RTM E from Acheson Industries) were used as electrically conductive filler. A cationic copolymer of acrylamide and a quaternary ammonium salt (SuperflocRTM C442 from Cytec Corporation) was used as the binder for the negatively charged nanoparticles. Coatings were applied to gold-coated stainless steel substrates presently used a bipolar plate material for proton exchange membrane (PEM) fuel cells. Coating thickness was found to vary nearly linearly with the number of polymer-nanoparticle layers deposited while a monotonic increase in coating contact resistance was observed for all heterogeneous and pure silica coatings. Thickness increased if the difference in the oppositely charged zeta potentials of the adsorbing components was enhanced through alcohol addition. Interestingly, an opposite effect was observed if the zeta potential difference was increased through pH variation. This previously undocumented difference in adsorption behavior is herein related to changes to the surface chemical heterogeneity of the nanoparticles. Coating contact resistance and surface wettability were found to have a more subtle dependence on the assembly

  10. Method for formation of high quality back contact with screen-printed local back surface field

    DOEpatents

    Rohatgi, Ajeet; Meemongkolkiat, Vichai

    2010-11-30

    A thin silicon solar cell having a back dielectric passivation and rear contact with local back surface field is described. Specifically, the solar cell may be fabricated from a crystalline silicon wafer having a thickness from 50 to 500 micrometers. A barrier layer and a dielectric layer are applied at least to the back surface of the silicon wafer to protect the silicon wafer from deformation when the rear contact is formed. At least one opening is made to the dielectric layer. An aluminum contact that provides a back surface field is formed in the opening and on the dielectric layer. The aluminum contact may be applied by screen printing an aluminum paste having from one to 12 atomic percent silicon and then applying a heat treatment at 750 degrees Celsius.

  11. Experimental Investigation of Thermal Contact Conductance: Variations of Surface Microhardness and Roughness

    NASA Astrophysics Data System (ADS)

    Li, Y. Z.; Madhusudana, C. V.; Leonardi, E.

    1998-11-01

    Surface roughness parameters were measured using nine different sampling intervals. The results showed that the roughness of profile was nearly a constant at all sampling intervals; the slope, peak curvature and density of the profile decreased with increasing sampling interval; and the distribution of the peak height was different from the profile height distribution and was not Gaussian. It was found that the surface microhardness value, under small loads, varied with the indentation size and the surface preparation procedure. A model was developed which used a discretization method to obtain the contact radius and area in each section of the surface summit height distribution curve. This model eliminated some of the assumptions made by previous models and can be used to predict the thermal contact conductance without assuming the asperity deformation mode and surface summit height distribution. The predicted thermal contact conductance values were in good agreement with experimental results.

  12. Stabilized numerical solution for transient dynamic contact of inelastic solids on rough surfaces

    NASA Astrophysics Data System (ADS)

    Suwannachit, A.; Nackenhorst, U.; Chiarello, R.

    2012-06-01

    A simulation technique to deal with transient dynamic contact of tire rubber compounds on rough road surfaces is presented. The segment-to-surface approach is used for modeling the contact between tire tread rubber and road track. While the rubber components are deformable and described by a sophisticated viscoelastic damage constitutive model, the road surface is assumed to be rigid and characterized by an analytical function. A spectral approach based on an inverse computation of the 2D-Fast Fourier transform has been suggested for the reconstruction of rough surface profiles. The Newmark time-stepping method is used for the integration of transient dynamic equations. With the so-called contact-stabilized Newmark method the spurious oscillation at contact boundary has been removed. The detailed investigation on the dynamic contact of inelastic rubber block with rough road surfaces has been made. The robustness of the contact-stabilized Newmark method within a finite deformation framework is underlined by numerical studies, in which it is compared with several dissipation-based stabilization techniques selected from literature.

  13. Surface evolution of perfluoropolyether film at high speed quasi-contact conditions

    NASA Astrophysics Data System (ADS)

    Chen, Yung-Kan; Peng, Jih-Ping; Bogy, David B.

    2016-05-01

    Nanoscale analysis characterized by microscopy with atomic resolution demand that the targeted surface remains nearly static. Therefore, the interaction between two fast moving surfaces requires a unique methodology to capture its dynamics when contacts are of nominal area on the order of 100 μm2 but only a few angstroms in depth. We present a contact study of the head-disk interface in hard disk drives, which consists of a disk surface coated with a molecularly thin perfluoropolyether lubricant and a slider surface moving slightly separated from it with a relative velocity of 20 m/s and with 10 nm spacing. By investigating the slider dynamics and lubricant topography in-situ, we disclose that high-speed contact initiates when the slider shears the top surface of the lubricant. Such contact can pile up molecules a few angstroms high as "moguls" or annihilate existing ones through a 5-10 Å interference. The transitional spacing regime of mogul evolution is defined as "quasi-contact," and it is the initial contact in the fast sliding interface.

  14. Water Contact Angle Dependence with Hydroxyl Functional Groups on Silica Surfaces under CO2 Sequestration Conditions.

    PubMed

    Chen, Cong; Zhang, Ning; Li, Weizhong; Song, Yongchen

    2015-12-15

    Functional groups on silica surfaces under CO2 sequestration conditions are complex due to reactions among supercritical CO2, brine and silica. Molecular dynamics simulations have been performed to investigate the effects of hydroxyl functional groups on wettability. It has been found that wettability shows a strong dependence on functional groups on silica surfaces: silanol number density, space distribution, and deprotonation/protonation degree. For neutral silica surfaces with crystalline structure (Q(3), Q(3)/Q(4), Q(4)), as silanol number density decreases, contact angle increases from 33.5° to 146.7° at 10.5 MPa and 318 K. When Q(3) surface changes to an amorphous structure, water contact angle increases 20°. Water contact angle decreases about 12° when 9% of silanol groups on Q(3) surface are deprotonated. When the deprotonation degree increases to 50%, water contact angle decreases to 0. The dependence of wettability on silica surface functional groups was used to analyze contact angle measurement ambiguity in literature. The composition of silica surfaces is complicated under CO2 sequestration conditions, the results found in this study may help to better understand wettability of CO2/brine/silica system. PMID:26509282

  15. Dynamics of contact line motion during the wetting of rough surfaces and correlation with topographical surface parameters.

    PubMed

    Kubiak, K J; Wilson, M C T; Mathia, T G; Carras, S

    2011-01-01

    Dynamics of contact line motion and wettability is essential in many industrial applications such as liquid coating, lubrication, printing, painting, condensation, etc. However, the wettability of surfaces depends not only on liquid-solid chemical properties but also can be strongly affected by surface roughness. As a practical application of controlled wettability, we can mention the self-cleaning surfaces, protective clothing, microfluidics devices, electro wetting, etc. In this article, we experimentally investigate the spreading of droplets deposited onto rough surfaces. Anisotropic surfaces were prepared by abrasive polishing on the following materials: aluminium alloy AA7064, titanium alloy Ti-6Al-4V, steel AISI 8630, copper alloy UNS C17000, machinable glass ceramic, and poly-methylmethacrylate. Topographical 2D parameters were calculated according to the following standards, defining Geometrical Product Specifications (GPS): ISO 4287, ISO 12085, ISO 13565, ISO 12780, and ISO 12181. The influence of topographical parameters on wettability and spreading phenomenon has been evaluated by statistical covariance analysis. The following parameters have strong influence on fluid spreading on rough surfaces: R(mr) is the relative material ratio of the roughness profile, T(rc) is the microgeometric material ratio, P(mr) is the relative material ratio of the raw profile, K(r) is the mean slope of the roughness motifs, RON(t) is the peak to valley roundness deviation, and P(sk) is the Skewness of the raw profile. The physical meaning of selected parameters is discussed, and K(r) (the mean slope of the roughness motifs) is selected as the most important and physically meaningful parameter. It has been found that for all tested materials, fluid spreading shows increasing tendency when mean slope of the roughness motifs (K(r) ) increases. PMID:21938731

  16. Evaluation of safety and efficacy of a new multipurpose disinfecting solution on silicone hydrogel contact lenses☆

    PubMed Central

    Pinto-Fraga, José; Blázquez Arauzo, Francisco; Urbano Rodríguez, Rubén; González-García, María J.

    2014-01-01

    Purpose To evaluate the safety and efficacy of a new multipurpose disinfecting solution (MPDS) with a formulation that includes aloe vera on its composition. Methods This is a prospective, randomized, double-masked clinical trial with a crossover design that included seven examinations. Two different MPDSs, Avizor Alvera® (study solution) and All Clean Soft® (control solution), each were used for 1 month. Comfilcon A silicone hydrogel contact lenses were used during the trial. The main outcome variables were corneal staining and deposits on the surfaces of the contact lenses. Other parameters including ocular surface response, contact lens wettability, user satisfaction, and adverse events, were analyzed according to the International Organization for Standardization (ISO) 11980:2010 guidance for clinical investigation. Results Twenty subjects (10 women, 10 men) (mean age, 27.7 ± 5.6 years; range, 20–41) were included. No differences between both MPDSs were found in the percentage of subjects with corneal staining >0 at day 30 (study: 35%, control: 50%; p = 0.46); neither in the percentage of subjects with deposits on the surface of the contact lens >0 at day 30 (study: 26.32%, control: 52.63%; p = 0.18). The study MPDS received higher rates in comfort (study: 8.14 ± 1.09, control: 7.94 ± 0.92; p = 0.56) and satisfaction at day 30 (study: 8.63 ± 0.91, control: 8.29 ± 0.80; p = 0.19), however the scores were not significantly different with the control MPDS. Conclusions The clinical trial showed that the study MPDS is safe, efficient, and has acceptable physiologic tolerance, according to the ISO 11980:2010 guidance for clinical investigation. PMID:25649640

  17. Monitoring the Contact Stress Distribution of Gecko-Inspired Adhesives Using Mechano-Sensitive Surface Coatings.

    PubMed

    Neubauer, Jens W; Xue, Longjian; Erath, Johann; Drotlef, Dirk-M; Campo, Aránzazu Del; Fery, Andreas

    2016-07-20

    The contact geometry of microstructured adhesive surfaces is of high relevance for adhesion enhancement. Theoretical considerations indicate that the stress distribution in the contact zone is crucial for the detachment mechanism, but direct experimental evidence is missing so far. In this work, we propose a method that allows, for the first time, the detection of local stresses at the contact area of biomimetic adhesive microstructures during contact formation, compression and detachment. We use a mechano-sensitive polymeric layer, which turns mechanical stresses into changes of fluorescence intensity. The biomimetic surface is brought into contact with this layer in a well-defined fashion using a microcontact printer, while the contact area is monitored with fluorescence microscopy in situ. Thus, changes in stress distribution across the contact area during compression and pull-off can be visualized with a lateral resolution of 1 μm. We apply this method to study the enhanced adhesive performance of T-shaped micropillars, compared to flat punch microstructures. We find significant differences in the stress distribution of the both differing contact geometries during pull-off. In particular, we find direct evidence for the suppression of crack nucleation at the edge of T-shaped pillars, which confirms theoretical models for the superior adhesive properties of these structures. PMID:27327111

  18. Effect of surface modification on interfacial nanobubble morphology and contact line tension.

    PubMed

    Rangharajan, Kaushik K; Kwak, Kwang J; Conlisk, A T; Wu, Yan; Prakash, Shaurya

    2015-07-14

    Past research has confirmed the existence of surface nanobubbles on various hydrophobic substrates (static contact angle >90°) when imaged in air-equilibrated water. Additionally, the use of solvent exchange techniques (based on the difference in saturation levels of air in various solvents) also introduced surface nanobubbles on hydrophilic substrates (static contact angle <90°). In this work, tapping mode atomic force microscopy was used to image interfacial nanobubbles formed on bulk polycarbonate (static contact angle of 81.1°), bromo-terminated silica (BTS; static contact angle of 85.5°), and fluoro-terminated silica (FTS; static contact angle of 105.3°) surfaces when immersed in air-equilibrated water without solvent exchange. Nanobubbles formed on the above three substrates were characterized on the basis of Laplace pressure, bubble density, and contact line tension. Results reported here show that (1) the Laplace pressures of all nanobubbles formed on both BTS and polycarbonate were an order of magnitude higher than those of FTS, (2) the nanobubble number density per unit area decreased with an increase in substrate contact angle, and (3) the contact line tension of the nanobubbles was calculated to be positive for both BTS and polycarbonate (lateral radius, Rs < 50 nm for all nanobubbles), and negative for FTS (Rs > 50 nm for all nanobubbles). The nanobubble morphology and distribution before and after using the solvent exchange method (ethanol-water), on the bulk polycarbonate substrate was also characterized. Analysis for these polycarbonate surface nanobubbles showed that both the Laplace pressure and nanobubble density reduced by ≈98% after ethanol-water exchange, accompanied by a flip in the magnitude of contact line tension from positive (0.19 nN) to negative (-0.11 nN). PMID:26041331

  19. Receding dynamics of contact lines and size-dependent adhesion on microstructured hydrophobic surfaces.

    PubMed

    Li, Dandan; Xue, Yahui; Lv, Pengyu; Huang, Shenglin; Lin, Hao; Duan, Huiling

    2016-05-14

    The microstructure size on textured surfaces of a given solid fraction exhibits an important effect on their properties. To understand the size effect on surface adhesion, we study the receding dynamics of the microscopic three-phase contact lines, the adhesive properties, and the relation between them on microstructured surfaces. Two types of surfaces are used, which are micropillar and micropore, respectively. First, the receding process of the contact line is directly observed by laser scanning confocal microscopy (LSCM), which shows distinct characteristics on the two types of surfaces. The micro contact line experiences pinnning, sliding, and rupture on micropillar-patterned surfaces while no rupture occurs on micropore-patterned surfaces. The three-dimensional morphology of the micromeniscus on the micropillared surfaces and the two-dimensional scanning of the cross-sections of the micromeniscus along the diagonal direction are imaged. Based on the images, the local contact angles around the micropillar at the receding front, and the curvatures of the micro-meniscus are obtained. Then, the adhesive force on these surfaces is measured, which surprisingly shows an increasing trend with the size of the microstructure for micropillared surfaces but no obvious size dependence for micropored surfaces. Wetting hysteresis is also measured to testify the similar trend with the size for the two types of surfaces. Further investigation shows that the monotonic increase of the adhesive force with the increasing size of micropillars is due to the growing difficulty of the detachment of the contact lines. The underlying mechanism responsible for the size dependence of the adhesive force is the enhancement of the local reduced pressure exerted on the top of the micropillar with increasing size, resulting from the concave profile of the outer micromeniscus. PMID:27072295

  20. Triclocarban: evaluation of contact dermatitis potential in man.

    PubMed

    Maibach, H; Bandmann, H J; Calnan, C D; Cronin, E; Fregert, S; Hjorth, N; Magnusson, B; Malten, K E; Meneghini, C L; Pirilä, V; Wilkinson, D S; Johannsen, F R

    1978-10-01

    Triclocarban was subjected to a profiling of its dermatitis producing potential including irritancy (21-day cumulative irritancy potential and application to 213 normal controls), phototoxicity (method of Marzulli), predictive contact sensitization (modified Draize method), predictive phototesting and battery screening in 2200 dermatitis patients, in an effort to define its relative dermatitis potential. The allergic contact dermatitis potential of triclocarban following bar soap use appears minimal. PMID:743875

  1. Delta-comb potential in modeling three-phase contact line (TPCL) on periodically patterned surfaces.

    PubMed

    Tsekov, Roumen; Grozev, Nikolay A; Delcheva, Iliyana V; Ivanov, Ivan T; Balashev, Konstantin; Karakashev, Stoyan I

    2012-11-01

    This work is a study of wetting of small water droplets on smooth glass surfaces with periodic patterns in the form of imprinted net with hydrophilic cells and hydrophobic bars. Microcover slides consisted of soda lime glass were used. The imprinted images of the net were with cell sizes in the range 40-200 μm, which corresponds to a quite narrow scope of hydrophilic surface fractions f(1)(30-36%) due to the relative increase in the size of the hydrophobic bars. The receding contact angles θ(R) of small water droplets, positioned on the patterned surfaces, were measured. The experiment showed significantly lower receding contact angles as compared to the theoretical expectations by the Cassie formula, which accounts for the contribution to the contact angle of the surface fraction of the imprinted hydrophobic/hydrophilic net. For this reason, we developed new theory accounting for the periodicity of the surface and the contribution of the three-phase contact line on the contact angle. This new theory considered delta-comb potential energy Δ(x,y) of the surface, effective line tension κ, and the lattice parameter a. The restriction of theory was discussed as well. It was pointed out that the theory is not valid for very small and very large lattice parameters. PMID:23078081

  2. Detection of fresh-cut produce processing residues on food contact surface materials using hyperspectral imaging

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To reduce the risk of foodborne-illness, produce processors currently clean and sanitize food contact surfaces daily before production starts. Current methods to verify the efficacy of cleaning procedures include visual inspection and direct surface sampling using ATP bioluminescence assays and cul...

  3. Tyre contact length on dry and wet road surfaces measured by three-axial accelerometer

    NASA Astrophysics Data System (ADS)

    Matilainen, Mika; Tuononen, Ari

    2015-02-01

    We determined the tyre contact length on dry and wet roads by measuring the accelerations of the inner liner with a three-axial accelerometer. The influence of the tyre pressure, driving velocity, and tread depth on the contact length was studied in both types of road surface conditions. On dry asphalt the contact length was almost constant, regardless of the driving velocity. On wet asphalt the presence of water could be detected even at low driving velocities (e.g. 20 km/h for a worn tyre) as the contact length began to decrease from that found in the dry asphalt situation. In addition to improving the performance of active safety systems and driver warning systems, the contact length information could be beneficial for classifying and studying the aquaplaning behaviour of tyres.

  4. Investigation of surface porosity measurements and compaction pressure as means to ensure consistent contact angle determinations.

    PubMed

    Holm, René; Borkenfelt, Simon; Allesø, Morten; Andersen, Jens Enevold Thaulov; Beato, Stefania; Holm, Per

    2016-02-10

    Compounds wettability is critical for a number of central processes including disintegration, dispersion, solubilisation and dissolution. It is therefore an important optimisation parameter both in drug discovery but also as guidance for formulation selection and optimisation. Wettability for a compound is determined by its contact angle to a liquid, which in the present study was measured using the sessile drop method applied to a disc compact of the compound. Precise determination of the contact angle is important should it be used to either rank compounds or selected excipients to e.g. increase the wetting from a solid dosage form. Since surface roughness of the compact has been suggested to influence the measurement this study investigated if the surface quality, in terms of surface porosity, had an influence on the measured contact angle. A correlation to surface porosity was observed, however for six out of seven compounds similar results were obtained by applying a standard pressure (866 MPa) to the discs in their preparation. The data presented in the present work therefore suggest that a constant high pressure should be sufficient for most compounds when determining the contact angle. Only for special cases where compounds have poor compressibility would there be a need for a surface-quality-control step before the contact angle determination. PMID:26688037

  5. Tyre-road contact using a particle-envelope surface model

    NASA Astrophysics Data System (ADS)

    Pinnington, Roger J.

    2013-12-01

    Determination of the contact forces is the central problem in all aspects of road-tyre interaction: i.e. noise, energy loss and friction. A procedure to find the contact forces under a rolling tyre is presented in four stages. First, the contact stiffness of a uniform peak array from indentations in the rubber tread, and also tyre carcass deflection, is described by some new simplified expressions. Second, a routine divides a single surface profile into equal search intervals, in which the highest peaks are identified. These are used to obtain the parameters for the interval, i.e. the mean envelope and the mean interval. The process is repeated at geometrically decreasing search intervals until the level of the data resolution, thereby describing the profile by a set of envelopes. The ‘strip profile’ ultimately used to describe the surface, is obtained by selecting the highest points across the profiles of one stone's width. The third stage is to combine the strip profile envelopes with the contact stiffness expressions, yielding the nonlinear stiffness-displacement, and force-displacement relationships for the chosen road-tyre combination. Finally the contact pressure distribution from a steady-state rolling tyre model is applied to the strip profile, via the force-displacement relationship, giving the local tyre displacements on the road texture. This displacement pattern is shown to be proportional to the time and space varying contact pressure, which then is incorporated into a wave equation for rolling contact.

  6. The influence of surface dents and grooves on traction in sliding EHD point contacts

    NASA Technical Reports Server (NTRS)

    Cusano, C.; Wedeven, L. D.

    1983-01-01

    Changes in traction, caused by dents and grooves on a highly polished ball, are investigated as these defects approach and go through sliding elastohydrodynamic point contacts. The contacts are formed with the ball loading against a transparent disk. The ball and thus the topographical features are held stationary at various locations in the vicinity and within the contact while the disk is rotating. These topographical features can cause substantial changes in the traction when compared to traction obtained with smooth surfaces. Previously announced in STAR as N82-32734

  7. Measurement of diffusion length and surface recombination velocity in Interdigitated Back Contact (IBC) and Front Surface Field (FSF) solar cells

    NASA Astrophysics Data System (ADS)

    Verlinden, Pierre; Van de Wiele, Fernand

    1985-03-01

    A method is proposed for measuring the diffusion length and surface recombination velocity of Interdigitated Back Contact (IBC) solar cells by means of a simple linear regression on experimental quantum efficiency values versus the inverse of the absorption coefficient. This method is extended to the case of Front Surface Field (FSF) solar cells. Under certain conditions, the real or the effective surface recombination velocity may be measured.

  8. A generalized continuum theory with internal corner and surface contact interactions

    NASA Astrophysics Data System (ADS)

    Fosdick, Roger

    2016-03-01

    We consider a classical derivation of a continuum theory, based on the fundamental balance laws of mass and momenta, for a body with internal corner and surface contact interactions. The balances of mass and linear and angular momentum are applied to the arbitrary parts of a continuum which supports non-classical internal corner and surface contact interactions. The form of the specific corner contact interaction force measured per unit length of the corner is derived. A generalized form of Cauchy's stress theorem is obtained, which shows that the surface traction on an oriented surface depends in a specific way on both the oriented unit normal as well as the curvature of the surface. An explicit form of the surface-couple traction which acts on every oriented surface is obtained. Two fields in the continuum, which are denoted as stress and hyperstress fields, are shown to exist, and their role in representing the surface traction and the surface-couple traction is identified. Finally, the field equations for this theory are determined, and a fundamental power theorem is derived. In the absence of internal corner and surface-couple traction interactions, the equations of classical continuum mechanics are recovered. There is no appeal to any `principle of virtual power' in this work.

  9. The first contact of a droplet impacting a dry solid surface

    NASA Astrophysics Data System (ADS)

    Thoroddsen, S. T.; Li, E. Q.; Vakarelski, I. U.

    2015-11-01

    The first contact of a drop hitting a dry solid surface, does not occur at a point but along a ring, owing to viscous lubrication pressure in the intervening air layer. This always leads to the entrapment of a small bubble under the center of the drop. The nature of the actual first contact is affected by the roughness of the solid. We use ultra-high-speed imaging, with 200 ns time resolution, to observe the structure of this first contact between the liquid and a smooth solid surface. For a water drop impacting onto regular micro-scope glass slide we observe a ring of micro-bubbles as observed by Thoroddsen et al. which conveniently marks the original diameter of the air-disc. This ring of bubbles arises owing to multiple initial contacts just before the formation of the fully wetted outer section. These contacts are spaced by a few microns and quickly grow in size until they meet each other, entrapping the bubbles. We thereby conclude that the localized contacts are due to nanometric roughness of the glass surface and the presence of the micro-bubbles can therefore distinguish between glass with 10 nm roughness from perfectly smooth glass.

  10. A unified mechanism for the stability of surface nanobubbles: contact line pinning and supersaturation.

    PubMed

    Liu, Yawei; Zhang, Xianren

    2014-10-01

    In this paper, we apply the molecular dynamics simulation method to study the stability of surface nanobubbles in both pure fluids and gas-liquid mixtures. First, we demonstrate with molecular simulations, for the first time, that surface nanobubbles can be stabilized in superheated or gas supersaturated liquid by the contact line pinning caused by the surface heterogeneity. Then, a unified mechanism for nanobubble stability is put forward here that stabilizing nanobubbles require both the contact line pinning and supersaturation. In the mechanism, the supersaturation refers to superheating for pure fluids and gas supersaturation or superheating for the gas-liquid mixtures, both of which exert the same effect on nanobubble stability. As the level of supersaturation increases, we found a Wenzel or Cassie wetting state for undersaturated and saturated fluids, stable nanobubbles at moderate supersaturation with decreasing curvature radius and contact angle, and finally the liquid-to-vapor phase transition at high supersaturation. PMID:25296823

  11. A unified mechanism for the stability of surface nanobubbles: Contact line pinning and supersaturation

    NASA Astrophysics Data System (ADS)

    Liu, Yawei; Zhang, Xianren

    2014-10-01

    In this paper, we apply the molecular dynamics simulation method to study the stability of surface nanobubbles in both pure fluids and gas-liquid mixtures. First, we demonstrate with molecular simulations, for the first time, that surface nanobubbles can be stabilized in superheated or gas supersaturated liquid by the contact line pinning caused by the surface heterogeneity. Then, a unified mechanism for nanobubble stability is put forward here that stabilizing nanobubbles require both the contact line pinning and supersaturation. In the mechanism, the supersaturation refers to superheating for pure fluids and gas supersaturation or superheating for the gas-liquid mixtures, both of which exert the same effect on nanobubble stability. As the level of supersaturation increases, we found a Wenzel or Cassie wetting state for undersaturated and saturated fluids, stable nanobubbles at moderate supersaturation with decreasing curvature radius and contact angle, and finally the liquid-to-vapor phase transition at high supersaturation.

  12. Two-dimensional random surface model for asperity-contact in elastohydrodynamic lubrication

    NASA Technical Reports Server (NTRS)

    Coy, J. J.; Sidik, S. M.

    1979-01-01

    Relations for the asperity-contact time function during elastohydrodynamic lubrication of a ball bearing are presented. The analysis is based on a two-dimensional random surface model, and actual profile traces of the bearing surfaces are used as statistical sample records. The results of the analysis show that transition from 90 percent contact to 1 percent contact occurs within a dimensionless film thickness range of approximately four to five. This thickness ratio is several times large than reported in the literature where one-dimensional random surface models were used. It is shown that low pass filtering of the statistical records will bring agreement between the present results and those in the literature.

  13. Correlation between contact surface and friction during the optical glass polishing

    NASA Astrophysics Data System (ADS)

    Belkhir, N.; Aliouane, T.; Bouzid, D.

    2014-01-01

    This study aims to determine the correlation between the contact surface, the polishing pressure and the friction coefficient during the optical glass polishing. For this purpose, BK7 optical glass samples were polished and the mentioned parameters were measured to find a correlation between them. Several methods of characterization have been used; the mechanical profilometer, the AFM, and in addition setups for measuring forces and the contact surface have been developed and adapted to the polishing machine. The found results have shown the existence of a close relationship between the three parameters and the influence of each other. This have allowed to deduce that during the polishing process it is very important to control the contact pressure and the polisher form according to the pressure distribution in order to guarantee a very high quality of the polished surface.

  14. Estimation of Thermal Contact Conductance between Blank and Tool Surface in Hot Stamping Process

    NASA Astrophysics Data System (ADS)

    Taha, Zahari; Hanafiah Shaharudin, M. A.

    2016-02-01

    In hot stamping, the determination of the thermal contact conductance values between the blank and tool surface during the process is crucial for the purpose of simulating the blank rapid cooling inside the tool using finite element analysis (FEA). The thermal contact conductance value represents the coefficient of the heat transfer at the surface of two solid bodies in contact and is known to be influenced greatly by the applied pressure. In order to estimate the value and its dependency on applied pressure, the process of hot stamping was replicated and simplified into a process of compression of heated flat blank in between the tool at different applied pressure. The temperature of the blank and tool surface were measured by means of thermocouples installed inside the tool. Based on the measured temperature, the thermal contact conductance between the surfaces was calculated using Newton's cooling law equation. The calculated value was then used to simulate the blank cooling inside the tool using FEA commercial software. This paper describes an experimental approach to estimate the thermal contact conductance between a blank made of Boron Steel (USIBOR 1500) and tool made of Tool Steel (STAVAX). Its dependency on applied pressure is also studied and the experimental results were then compared with FEA simulations.

  15. Surface Degradation of Ag/W Circuit Breaker Contacts During Standardized UL Testing

    NASA Astrophysics Data System (ADS)

    Yu, Haibo; Sun, Yu; Kesim, M. Tumerkan; Harmon, Jason; Potter, Jonathan; Alpay, S. Pamir; Aindow, Mark

    2015-09-01

    The near-surface microstructure of Ag/W contacts from 120 V, 30 A commercial circuit breakers in the as-manufactured condition and after standardized UL overload/temperature-rise, endurance, and short-circuit testing have been investigated using a combination of x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, focused ion beam milling, and transmission electron microscopy. The as-manufactured contacts comprised three constituents: sintered Ag/W composite particles with fine-grained Ag and coarse-grained W, coarse-grained pockets of Ag infiltrate, and a nano-crystalline surface Ag layer. There are also WO3 and Ag2O phases at the surface. After UL overload/temperature-rise testing, there is Ag loss giving a porous W-rich layer at the contact surface. In addition to binary oxides, we observe the formation of Ag2WO4. After UL endurance testing, material is swept across the surface by the breaker action giving a W-rich eroded porous surface on one side and a build-up of mixed oxides on the other. After UL short-circuit testing, a W crust forms due to melting and re-solidification of W and vaporization of Ag, and mid-plane cracks form due to the severe thermal gradients. There is a strong correlation between the observed microstructural features and the contact resistance measurements obtained from these samples.

  16. A contact mechanics model for ankle implants with inclusion of surface roughness effects

    NASA Astrophysics Data System (ADS)

    Hodaei, M.; Farhang, K.; Maani, N.

    2014-02-01

    Total ankle replacement is recognized as one of the best procedures to treat painful arthritic ankles. Even though this method can relieve patients from pain and reproduce the physiological functions of the ankle, an improper design can cause an excessive amount of metal debris due to wear, causing toxicity in implant recipient. This paper develops a contact model to treat the interaction of tibia and talus implants in an ankle joint. The contact model describes the interaction of implant rough surfaces including both elastic and plastic deformations. In the model, the tibia and the talus surfaces are viewed as macroscopically conforming cylinders or conforming multi-cylinders containing micrometre-scale roughness. The derived equations relate contact force on the implant and the minimum mean surface separation of the rough surfaces. The force is expressed as a statistical integral function of asperity heights over the possible region of interaction of the roughness of the tibia and the talus implant surfaces. A closed-form approximate equation relating contact force and minimum separation is used to obtain energy loss per cycle in a load-unload sequence applied to the implant. In this way implant surface statistics are related to energy loss in the implant that is responsible for internal void formation and subsequent wear and its harmful toxicity to the implant recipient.

  17. Contact angles and wettability of ionic liquids on polar and non-polar surfaces.

    PubMed

    Pereira, Matheus M; Kurnia, Kiki A; Sousa, Filipa L; Silva, Nuno J O; Lopes-da-Silva, José A; Coutinho, João A P; Freire, Mara G

    2015-12-21

    Many applications involving ionic liquids (ILs) require the knowledge of their interfacial behaviour, such as wettability and adhesion. In this context, herein, two approaches were combined aiming at understanding the impact of the IL chemical structures on their wettability on both polar and non-polar surfaces, namely: (i) the experimental determination of the contact angles of a broad range of ILs (covering a wide number of anions of variable polarity, cations, and cation alkyl side chain lengths) on polar and non-polar solid substrates (glass, Al-plate, and poly-(tetrafluoroethylene) (PTFE)); and (ii) the correlation of the experimental contact angles with the cation-anion pair interaction energies generated by the Conductor-like Screening Model for Real Solvents (COSMO-RS). The combined results reveal that the hydrogen-bond basicity of ILs, and thus the IL anion, plays a major role through their wettability on both polar and non-polar surfaces. The increase of the IL hydrogen-bond accepting ability leads to an improved wettability of more polar surfaces (lower contact angles) while the opposite trend is observed on non-polar surfaces. The cation nature and alkyl side chain lengths have however a smaller impact on the wetting ability of ILs. Linear correlations were found between the experimental contact angles and the cation-anion hydrogen-bonding and cation ring energies, estimated using COSMO-RS, suggesting that these features primarily control the wetting ability of ILs. Furthermore, two-descriptor correlations are proposed here to predict the contact angles of a wide variety of ILs on glass, Al-plate, and PTFE surfaces. A new extended list is provided for the contact angles of ILs on three surfaces, which can be used as a priori information to choose appropriate ILs before a given application. PMID:26554705

  18. Laser excitation and fully non-contact sensing ultrasonic propagation imaging system for damage evaluation

    NASA Astrophysics Data System (ADS)

    Dhital, Dipesh; Lee, Jung Ryul; Park, Chan Yik; Flynn, Eric

    2012-04-01

    Various types of damages occur in aerospace, mechanical and many other engineering structures, and a reliable nondestructive evaluation technique is essential to detect any possible damage at the initiation phase. Ultrasound has been widely used but the conventional contact ultrasonic inspection techniques are not suitable for mass and couplant sensitive structures and are relatively slow. This study presents a fully non-contact hybrid laser ultrasonic generation and piezoelectric air-coupled transducer (ACT)/laser Doppler vibrometer (LDV) sensing technique combined with ultrasonic wave propagation imaging (UWPI), ultrasonic spectral imaging (USI) and wavelet-transformed ultrasonic propagation imaging (WUPI) algorithms to extract defect-sensitive features aimed at performing a thorough diagnosis of damage. Optimization enables improved performance efficiency of ACT and LDV to be used as receivers for non-contact hybrid laser ultrasonic propagation imaging (UPI) system as shown from the experimental results in this study. Real fatigue closed surface micro crack on metal structure was detected using hybrid laser ultrasonic generation/ACT sensing system, with size detection accuracy as high as 96%. Impact damages on carbon fiber reinforced plastic composite wing-box specimen were detected and localized using hybrid laser ultrasonic generation/LDV sensing system.

  19. Simple modeling of the ratio of fields at a tip and at contacting surface

    NASA Astrophysics Data System (ADS)

    Bortchagovsky, E. G.

    2016-06-01

    The proposed concept of Raman probe for nearfield optical microscopy raises the question about the similarity of fields acting on specimens deposited at the tip apex and contacting surface. The signal generated at these two close but different points is defined by local fields, so it is the ratio of the fields at these points, that is the quantity of interest here. This work is concerned with the application of a simple dipole model for the analysis of the ratio of fields at the tip apex and at contacting surface as a function of their separation.

  20. Utilizing dynamic tensiometry to quantify contact angle hysteresis and wetting state transitions on nonwetting surfaces.

    PubMed

    Kleingartner, Justin A; Srinivasan, Siddarth; Mabry, Joseph M; Cohen, Robert E; McKinley, Gareth H

    2013-11-01

    Goniometric techniques traditionally quantify two parameters, the advancing and receding contact angles, that are useful for characterizing the wetting properties of a solid surface; however, dynamic tensiometry, which measures changes in the net force on a surface during the repeated immersion and emersion of a solid into a probe liquid, can provide further insight into the wetting properties of a surface. We detail a framework for analyzing tensiometric results that allows for the determination of wetting hysteresis, wetting state transitions, and characteristic topographical length scales on textured, nonwetting surfaces, in addition to the more traditional measurement of apparent advancing and receding contact angles. Fluorodecyl POSS, a low-surface-energy material, was blended with commercially available poly(methyl methacrylate) (PMMA) and then dip- or spray-coated onto glass substrates. These surfaces were probed with a variety of liquids to illustrate the effects of probe liquid surface tension, solid surface chemistry, and surface texture on the apparent contact angles and wetting hysteresis of nonwetting surfaces. Woven meshes were then used as model structured substrates to add a second, larger length scale for the surface texture. When immersed into a probe liquid, these spray-coated mesh surfaces can form a metastable, solid-liquid-air interface on the largest length scale of surface texture. The increasing hydrostatic pressure associated with progressively greater immersion depths disrupts this metastable, composite interface and forces penetration of the probe liquid into the mesh structure. This transition is marked by a sudden change in the wetting hysteresis, which can be systematically probed using spray-coated, woven meshes of varying wire radius and spacing. We also show that dynamic tensiometry can accurately and quantitatively characterize topographical length scales that are present on microtextured surfaces. PMID:24070378

  1. Non-contact monitoring of electrical characteristics of silicon surface and near-surface region

    NASA Astrophysics Data System (ADS)

    Roman, P.; Brubaker, M.; Staffa, J.; Kamieniecki, E.; Ruzyllo, J.

    1998-11-01

    The SPV-based method of Surface Charge Profiling (SCP) is discussed, and its applications in silicon surface monitoring in IC manufacturing are reviewed. The SCP method shows high sensitivity to changes in the condition of the Si surface (e.g. surface cleaning operations) and a very thin near-surface region (e.g. variations of active dopant concentration near the surface).

  2. The effect of contact angle hysteresis on droplet motion and collisions on superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Nilsson, Michael; Rothstein, Jonathan

    2010-11-01

    The effect of varying the contact angle hysteresis of a superhydrophobic surface on the characteristics and dynamics of water droplet motion and their subsequent collision are investigated using a high-speed camera. The surfaces are created by imparting random roughness to Teflon through sanding. With this technique, it is possible to create surfaces with similar advancing contact angles near 150 degrees, but with varying contact angle hysteresis. This talk will focus on a number of interesting experimental observations pertaining to drop dynamics along a surface with uniform hysteresis, drop motion along surfaces with transition zones from one hysteresis to another, and the collision of droplets on surfaces of uniform hysteresis. For single drop studies, gravity is used as the driving force, while the collision studies use pressurized air to propel one drop into the other. For the case of droplet collision, the effect of hysteresis, Weber number, and impact number on the maximum deformation of the drops, and the post-collision dynamics will be discussed. For the single droplet measurements, the resistance to motion will be characterized as well as the transition from rolling to sliding as a function of drop size, inclination angle, and hysteresis. Additionally, we will quantify the effect of surface transitions on the resulting motion, mixing, and deflection of the drops.

  3. Automated fabrication of back surface field silicon solar cells with screen printed wraparound contacts

    NASA Technical Reports Server (NTRS)

    Thornhill, J. W.

    1977-01-01

    The development of a process for fabricating 2 x 4 cm back surface field silicon solar cells having screen printed wraparound contacts is described. This process was specifically designed to be amenable for incorporation into the automated nonvacuum production line. Techniques were developed to permit the use of screen printing for producing improved back surface field structures, wraparound dielectric layers, and wraparound contacts. The optimized process sequence was then used to produce 1852 finished cells. Tests indicated an average conversion efficiency of 11% at AMO and 28 C, with an average degradation of maximum power output of 1.5% after boiling water immersion or thermal shock cycling. Contact adherence was satisfactory after these tests, as well as long term storage at high temperature and high humidity.

  4. Tuning thermal contact conductance at graphene-copper interface via surface nanoengineering

    NASA Astrophysics Data System (ADS)

    Hong, Yang; Li, Lei; Zeng, Xiao Cheng; Zhang, Jingchao

    2015-03-01

    Due to rapidly increasing power densities in nanoelectronics, efficient heat removal has become one of the most critical issues in thermal management and nanocircuit design. In this study, we report a surface nanoengineering design that can reduce the interfacial thermal resistance between graphene and copper substrate by 17%. Contrary to the conventional view that a rough surface tends to give higher thermal contact resistances, we find that by engraving the copper substrate with nanopillared patterns, an optimized hybrid structure can effectively facilitate the thermal transport across the graphene-copper interface. This counterintuitive behavior is due to the enhanced phonon interactions with the optimal nanopillared pattern. For pliable 2D materials like graphene, the structures can be easily bent to fit the surface formations of the substrate. The suspended areas of graphene are pulled towards the substrate via an attractive interatomic force, causing high local pressures (~2.9 MPa) on the top region of nanopillars. The high local pressures can greatly enhance the thermal energy coupling between graphene and copper, thereby lowering the thermal contact resistances. Our study provides a practical way to manipulate the thermal contact resistance between graphene and copper for the improvement of nano-device performance through engineering optimal nanoscale contact.Due to rapidly increasing power densities in nanoelectronics, efficient heat removal has become one of the most critical issues in thermal management and nanocircuit design. In this study, we report a surface nanoengineering design that can reduce the interfacial thermal resistance between graphene and copper substrate by 17%. Contrary to the conventional view that a rough surface tends to give higher thermal contact resistances, we find that by engraving the copper substrate with nanopillared patterns, an optimized hybrid structure can effectively facilitate the thermal transport across the graphene

  5. Intelligent tires for identifying coefficient of friction of tire/road contact surfaces

    NASA Astrophysics Data System (ADS)

    Matsuzaki, Ryosuke; Kamai, Kazuto; Seki, Ryosuke

    2015-03-01

    Intelligent tires equipped with sensors as well as the monitoring of the tire/road contact conditions are in demand for improving vehicle control and safety. With the aim of identifying the coefficient of friction of tire/road contact surfaces during driving, including during cornering, we develop an identification scheme for the coefficient of friction that involves estimation of the slip angle and applied force by using a single lightweight three-axis accelerometer attached on the inner surface of the tire. To validate the developed scheme, we conduct tire-rolling tests using an accelerometer-equipped tire with various slip angles on various types of road surfaces, including dry and wet surfaces. The results of these tests confirm that the estimated slip angle and applied force are reasonable. Furthermore, the identified coefficient of friction by the developed scheme agreed with that measured by standardized tests.

  6. Wetting behaviour and contact angles anisotropy of nematic nanodroplets on flat surfaces.

    PubMed

    Vanzo, Davide; Ricci, Matteo; Berardi, Roberto; Zannoni, Claudio

    2016-02-01

    We have studied the wetting behaviour of liquid crystal nanodroplets deposited on a planar surface, modelling the mesogens with Gay-Berne ellipsoids and the support surface with a slab of Lennard-Jones (LJ) spherical particles whose mesogen-surface affinity can be tuned. A crystalline and an amorphous planar surface, both showing planar anchoring, have been investigated: the first is the (001) facet of a LJ fcc crystal, the second is obtained from a disordered LJ glass. In both cases we find that the deposited nanodroplet is, in general, elongated and that the contact angle changes around its contour. Simulations for the crystalline substrate show that the angle of contact turns reversibly from anisotropic to isotropic when crossing the clearing transition. As far as we know this is a novel, not yet explored effect for thermotropic liquid crystals, that we hope will stimulate experimental investigations. PMID:26670582

  7. Surface acid-base characteristics of fiber materials by contact angle measurements

    SciTech Connect

    Mao Youan . Dept. of Materials Science and Applied Chemistry)

    1993-11-05

    Contact angle measurements were used to study the surface acid-base characteristics of treated and untreated carbon fibers, and of treated and untreated silicon carbide fibers. It has been shown that, when untreated the surfaces of these two fibers exhibits amphoteric, but the base character is dominant. After oxidization in a liquid phase, the surface acid character of the carbon fibers changes little, whereas the base character becomes much stronger. The treatment, with boiling-concentrated HNO[sub 3] for three hours and the sintering treatment in air at 500 C. for eight hours, has little effect on the surface acid-base characteristics of the silicon carbide fibers.

  8. Effect of leaflet-to-chordae contact interaction on computational mitral valve evaluation

    PubMed Central

    2014-01-01

    Background Computational simulation using numerical analysis methods can help to assess the complex biomechanical and functional characteristics of the mitral valve (MV) apparatus. It is important to correctly determine physical contact interaction between the MV apparatus components during computational MV evaluation. We hypothesize that leaflet-to-chordae contact interaction plays an important role in computational MV evaluation, specifically in quantitating the degree of leaflet coaptation directly related to the severity of mitral regurgitation (MR). In this study, we have performed dynamic finite element simulations of MV function with and without leaflet-to-chordae contact interaction, and determined the effect of leaflet-to-chordae contact interaction on the computational MV evaluation. Methods Computational virtual MV models were created using the MV geometric data in a patient with normal MV without MR and another with pathologic MV with MR obtained from 3D echocardiography. Computational MV simulation with full contact interaction was specified to incorporate entire physically available contact interactions between the leaflets and chordae tendineae. Computational MV simulation without leaflet-to-chordae contact interaction was specified by defining the anterior and posterior leaflets as the only contact inclusion. Results Without leaflet-to-chordae contact interaction, the computational MV simulations demonstrated physically unrealistic contact interactions between the leaflets and chordae. With leaflet-to-chordae contact interaction, the anterior marginal chordae retained the proper contact with the posterior leaflet during the entire systole. The size of the non-contact region in the simulation with leaflet-to-chordae contact interaction was much larger than for the simulation with only leaflet-to-leaflet contact. Conclusions We have successfully demonstrated the effect of leaflet-to-chordae contact interaction on determining leaflet coaptation in

  9. ICAM-1 mediates surface contact between neutrophils and keratocytes following corneal epithelial abrasion in the mouse

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Corneal epithelial abrasion elicits an inflammatory response involving neutrophil (PMN) recruitment from the limbal vessels into the corneal stroma. These migrating PMNs make surface contact with collagen and stromal keratocytes. Using mice deficient in PMN integrin CD18, we previously showed that P...

  10. Persistence and elimination of human norovirus in food and on food contact surfaces: a critical review

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This critical review addresses the persistence of human norovirus (NoV) in water, shellfish, processed meats, soils and organic wastes; on berries, herbs, vegetables, fruits and salads; and on food contact surfaces. The review focuses on studies using NoV; information from studies involving only su...

  11. Process for Non-Contact Removal of Organic Coatings from the Surface of Paintings

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Rutledge, Sharon K. (Inventor)

    1996-01-01

    The present invention discloses a method of removing organic protective coatings from a painting. In the present invention degraded protective coatings such as lacquers, acrylics, natural resins, carbons, soot, and polyurethane are safely removed from the surface of a painting without contact to the surface of the painting. This method can be used for restoration of paintings when they have been damaged, through age, fire, etc.

  12. Optimization of the heating surface shape in the contact melting problem

    NASA Technical Reports Server (NTRS)

    Fomin, Sergei A.; Cheng, Shangmo

    1991-01-01

    The theoretical analysis of contact melting by the migrating heat source with an arbitrary shaped isothermal heating surface is presented. After the substantiated simplification, the governing equations are transformed to the convenient equations for engineering calculations relationships. Analytical solutions are used for numerical prediction of optimal shape of the heating surface. The problem is investigated for the constant and for temperature dependent physical properties of the melt.

  13. Process for non-contact removal of organic coatings from the surface of paintings

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Rutledge, Sharon K. (Inventor)

    1995-01-01

    The present invention discloses a method of removing organic protective coatings from a painting. In the present invention degraded protective coatings such as lacquers, acrylics, natural resins, carbons, soot, and polyurethane are safely removed from the surface of a painting without contact to the surface of the painting. This method can be used for restoration of paintings when they have been damaged, through age, fire, etc.

  14. Numerical study of drop motion on a surface with stepwise wettability gradient and contact angle hysteresis

    NASA Astrophysics Data System (ADS)

    Huang, Jun-Jie; Huang, Haibo; Wang, Xinzhu

    2014-06-01

    In this work, the motion of a two-dimensional drop on a surface with stepwise wettability gradient (WG) is studied numerically by a hybrid lattice-Boltzmann finite-difference method. We incorporate the geometric wetting boundary condition that allows accurate implementation of a contact angle hysteresis (CAH) model. The method is first validated through a series of tests that check different constituents of the numerical model. Then, simulations of a drop on a wall with given stepwise WG are performed under different conditions. The effects of the Reynolds number, the viscosity ratio, the WG, as well as the CAH on the drop motion are investigated in detail. It was discovered that the shape of the drop in steady motion may be fitted by two arcs that give two apparent contact angles, which are related to the respective contact line velocities and the relevant contact angles (that specify the WG and CAH) through the relation derived by Cox ["The dynamics of the spreading of liquids on a solid surface. Part 1. viscous flow," J. Fluid Mech. 168, 169-194 (1986)] if the slip length in simulation is defined according to Yue et al. ["Sharp-interface limit of the Cahn-Hilliard model for moving contact lines," J. Fluid Mech. 645, 279-294 (2010)]. It was also found that the steady capillary number of the drop is significantly affected by the viscosity ratio, the magnitudes of the WG, and the CAH, whereas it almost shows no dependence on the Reynolds number.

  15. Visualizing the shape of soft solid and fluid contacts between two surfaces

    NASA Astrophysics Data System (ADS)

    Pham, Jonathan; Schellenberger, Frank; Kappl, Michael; Vollmer, Doris; Butt, Hans-Jürgen

    The soft contact between two surfaces is fundamentally interesting for soft materials and fluid mechanics and relevant for friction and wear. The deformation of soft solid interfaces has received much interest because it interestingly reveals similarities to fluid wetting. We present an experimental route towards visualizing the three-dimensional contact geometry of either liquid-solid (i.e., oil and glass) or solid-solid (i.e., elastomer and glass) interfaces using a home-built combination of confocal microscopy and atomic force microscopy. We monitor the shape of a fluid capillary bridge and the depth of indentation in 3D while simultaneously measuring the force. In agreement with theoretical predictions, the height of the capillary bridge depends on the interfacial tensions. By using a slowly evaporating solvent, we quantify the temporal evolution of the capillary bridge and visualized the influence of pinning points on its shape. The position dependence of the advancing and receding contact angle along the three-phase contact line, particle-liquid-air, is resolved. Extending our system, we explore the contact deformation of soft solids where elasticity, in addition to surface tension, becomes an important factor.

  16. Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves.

    PubMed

    Hiraiwa, M; Abi Ghanem, M; Wallen, S P; Khanolkar, A; Maznev, A A; Boechler, N

    2016-05-13

    Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks. PMID:27232047

  17. Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Hiraiwa, M.; Abi Ghanem, M.; Wallen, S. P.; Khanolkar, A.; Maznev, A. A.; Boechler, N.

    2016-05-01

    Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks.

  18. Surface effects on elastic properties of silver nanowires: Contact atomic-force microscopy

    NASA Astrophysics Data System (ADS)

    Jing, G. Y.; Duan, H. L.; Sun, X. M.; Zhang, Z. S.; Xu, J.; Li, Y. D.; Wang, J. X.; Yu, D. P.

    2006-06-01

    Silver nanowires with different diameters were synthesized by a hydrothermal chemical method. The elastic properties of the nanowires with outer diameters ranging from 20 to 140nm were measured using contact atomic force microscopy. The apparent Young modulus of the nanowires is found to decrease with the increase of the diameter. When the diameter of the silver nanowires is larger than 100nm , the Young modulus approaches a constant value. The size dependence of the apparent Young modulus of the silver nanowires is attributed to the surface effect, which includes the effects of the surface stress, the oxidation layer, and the surface roughness. Thus, a theoretical analysis is presented to explain the size dependence. This analysis is different from the previous models in that both the surface stress and the surface moduli are included in it. We also show that the apparent surface modulus and the surface stress of the silver nanowires can be experimentally determined.

  19. Probability distributions of whisker-surface contact: quantifying elements of the rat vibrissotactile natural scene.

    PubMed

    Hobbs, Jennifer A; Towal, R Blythe; Hartmann, Mitra J Z

    2015-08-01

    Analysis of natural scene statistics has been a powerful approach for understanding neural coding in the auditory and visual systems. In the field of somatosensation, it has been more challenging to quantify the natural tactile scene, in part because somatosensory signals are so tightly linked to the animal's movements. The present work takes a step towards quantifying the natural tactile scene for the rat vibrissal system by simulating rat whisking motions to systematically investigate the probabilities of whisker-object contact in naturalistic environments. The simulations permit an exhaustive search through the complete space of possible contact patterns, thereby allowing for the characterization of the patterns that would most likely occur during long sequences of natural exploratory behavior. We specifically quantified the probabilities of 'concomitant contact', that is, given that a particular whisker makes contact with a surface during a whisk, what is the probability that each of the other whiskers will also make contact with the surface during that whisk? Probabilities of concomitant contact were quantified in simulations that assumed increasingly naturalistic conditions: first, the space of all possible head poses; second, the space of behaviorally preferred head poses as measured experimentally; and third, common head poses in environments such as cages and burrows. As environments became more naturalistic, the probability distributions shifted from exhibiting a 'row-wise' structure to a more diagonal structure. Results also reveal that the rat appears to use motor strategies (e.g. head pitches) that generate contact patterns that are particularly well suited to extract information in the presence of uncertainty. PMID:26290591

  20. Identifying Differences and Similarities in Static and Dynamic Contact Angles between Nanoscale and Microscale Textured Surfaces Using Molecular Dynamics Simulations.

    PubMed

    Slovin, Mitchell R; Shirts, Michael R

    2015-07-28

    We quantify some of the effects of patterned nanoscale surface texture on static contact angles, dynamic contact angles, and dynamic contact angle hysteresis using molecular dynamics simulations of a moving Lennard-Jones droplet in contact with a solid surface. We observe static contact angles that change with the introduction of surface texture in a manner consistent with theoretical and experimental expectations. However, we find that the introduction of nanoscale surface texture at the length scale of 5-10 times the fluid particle size does not affect dynamic contact angle hysteresis even though it changes both the advancing and receding contact angles significantly. This result differs significantly from microscale experimental results where dynamic contact angle hysteresis decreases with the addition of surface texture due to an increase in the receding contact angle. Instead, we find that molecular-kinetic theory, previously applied only to nonpatterned surfaces, accurately describes dynamic contact angle and dynamic contact angle hysteresis behavior as a function of terminal fluid velocity. Therefore, at length scales of tens of nanometers, the kinetic phenomena such as contact line pinning observed at larger scales become insignificant in comparison to the effects of molecular fluctuations for moving droplets, even though the static properties are essentially scale-invariant. These findings may have implications for the design of highly hierarchical structures with particular wetting properties. We also find that quantitatively determining the trends observed in this article requires the careful selection of system and analysis parameters in order to achieve sufficient accuracy and precision in calculated contact angles. Therefore, we provide a detailed description of our two-surface, circular-fit approach to calculating static and dynamic contact angles on surfaces with nanoscale texturing. PMID:26110823

  1. Ultrathin coating of plasma polymer of methane applied on the surface of silicone contact lenses.

    PubMed

    Ho, C P; Yasuda, H

    1988-10-01

    Silicone rubber has great advantages as a contact lens material because of its very high oxygen permeability, softness, and excellent mechanical strength and durability. Practical application is hampered by inherent characteristics of elastomers, i.e., high tackiness and highly hydrophobic surface properties. By applying a thin layer, e.g., 5 nm, of plasma polymer of methane, it was found that all these disadvantages can be eliminated without sacrificing high oxygen permeation rate, e.g., less than 15% reduction. Optimization of operational parameters to achieve this task has been investigated. It was also found that under optimum conditions the coating withstood severe and repeated flexing of the contact lens. PMID:3220842

  2. Contact Angle of Drops Measured on Nontransparent Surfaces and Capillary Flow Visualized

    NASA Technical Reports Server (NTRS)

    Chao, David F.; Zhang, Nengli

    2003-01-01

    The spreading of a liquid on a solid surface is important for various practical processes, and contact-angle measurements provide an elegant method to characterize the interfacial properties of the liquid with the solid substrates. The complex physical processes occurring when a liquid contacts a solid play an important role in determining the performance of chemical processes and materials. Applications for these processes are in printing, coating, gluing, textile dyeing, and adhesives and in the pharmaceutical industry, biomedical research, adhesives, flat panel display manufacturing, surfactant chemistry, and thermal engineering.

  3. Protein adsorption on surfaces: dynamic contact-angle (DCA) and quartz-crystal microbalance (QCM) measurements.

    PubMed

    Stadler, H; Mondon, M; Ziegler, C

    2003-01-01

    Adsorption of the protein bovine serum albumin (BSA) on gold has been tested at various concentrations in aqueous solution by dynamic contact-angle analysis (DCA) and quartz-crystal microbalance (QCM) measurements. With the Wilhelmy plate technique advancing and receding contact angles and the corresponding hysteresis were measured and correlated with the hydrophilicity and the homogeneity of the surface. With electrical admittance measurements of a gold-coated piezoelectrical quartz crystal, layer mass and viscoelastic contributions to the resonator's frequency shift during adsorption could be separated. A correlation was found between the adsorbed mass and the homogeneity and hydrophilicity of the adsorbed film. PMID:12520439

  4. Tuning thermal contact conductance at graphene-copper interface via surface nanoengineering.

    PubMed

    Hong, Yang; Li, Lei; Zeng, Xiao Cheng; Zhang, Jingchao

    2015-04-14

    Due to rapidly increasing power densities in nanoelectronics, efficient heat removal has become one of the most critical issues in thermal management and nanocircuit design. In this study, we report a surface nanoengineering design that can reduce the interfacial thermal resistance between graphene and copper substrate by 17%. Contrary to the conventional view that a rough surface tends to give higher thermal contact resistances, we find that by engraving the copper substrate with nanopillared patterns, an optimized hybrid structure can effectively facilitate the thermal transport across the graphene-copper interface. This counterintuitive behavior is due to the enhanced phonon interactions with the optimal nanopillared pattern. For pliable 2D materials like graphene, the structures can be easily bent to fit the surface formations of the substrate. The suspended areas of graphene are pulled towards the substrate via an attractive interatomic force, causing high local pressures (∼2.9 MPa) on the top region of nanopillars. The high local pressures can greatly enhance the thermal energy coupling between graphene and copper, thereby lowering the thermal contact resistances. Our study provides a practical way to manipulate the thermal contact resistance between graphene and copper for the improvement of nano-device performance through engineering optimal nanoscale contact. PMID:25784494

  5. Bearing surface design changes affect contact patterns in total knee arthroplasty.

    PubMed

    Cottrell, Jocelyn M; Townsend, Elizabeth; Lipman, Joseph; Sculco, Thomas P; Wright, Timothy M

    2007-11-01

    The impact of design changes intended to improve wear of knee replacements can be assessed from analysis of retrieved implants. We hypothesized changes in bearing surface conformity from the Insall-Burstein II knee to a successor, the Optetrak, intended to improve contact stresses would be apparent in wear patterns observed on retrieved tibial inserts. From 151 Insall-Burstein II and 54 Optetrak retrieved components, 35 pairs (Insall-Burstein II and Optetrak) were matched on length of implantation, body mass index, and age. Digital images of the bearing surfaces were used to identify and measure wear modes, which were then converted to a percentage of the total possible contact area. Burnishing was the most prevalent mode for both designs followed by scratching and then pitting. The percentage of involved area was greater for the Optetrak for 23 pairs. Interestingly, for the nine matched pairs with length of implantation longer than 2 years, six of the Insall-Burstein II inserts had considerably greater scratching and pitting and five exhibited abrasion and creep absent from Optetrak implants. Bearing surface design is a major factor that can affect kinematics and contact patterns. Our observations confirm the considerable impact of small changes in conformity and suggest models predicting contact stresses adequately reflect in vivo performance. PMID:18062045

  6. Non-Contact, No Wafer Preparation Deep Level Transient Spectroscopy Based on Surface Photovoltage

    NASA Astrophysics Data System (ADS)

    Lagowski, Jacek; Morawski, Andrzej; Edelman, Piotr

    1992-08-01

    We discuss a novel approach to Deep Level Transient Spectroscopy (DLTS) in which the emission of trapped minority carriers is analyzed employing the surface photovoltage (SPV) transient as measured in a non-contact manner on the native depletion barrier on semiconductor surfaces. Optical excitation is used as the trap-filling pulse. Experiments done on n-type GaAs demonstrate that the SPV-DLTS is suitable for wafer-scale, non-contact determination of deep level defects on semiconductor surfaces. The SPV approach can monitor emission rates up to 106 s-1 which is 102 to 103 above the limit of standard capacitance DLTS. The sensitivity of the method is comparable to that of the oplical capacitance DLTS.

  7. Effective Darcy-Scale Contact Angles in Porous Media Imbibing Solutions of Various Surface Tensions

    SciTech Connect

    Weisbrod, Noam; McGinnis, Thomas; Rockhold, Mark L.; Niemet, Mike; Selker, John S.

    2009-10-17

    Surface tensions of high-salinity solutions are significantly different from those of pure water. Our objective was to develop and test a methodology to determine whether these surface-tension effects predictably alter imbibition into dry and moist porous media. Static and dynamic experiments were performed using four grades of quartz sand to determine the effects of solution salinity on imbibition. Results were quantified as apparent contact angles between the sand and three solutions (pure water, 5 molal NaNO3, n-hexane). Contact angles determined using a static method in initially air-dried sand ranged from 23° to 31°, with the same values found for both water and the NaNO3 solution. Effective contact angles determined for the air-dried sand using a dynamic method based on a modified version of the Green and Ampt model were about twice those found using the static method, averaging 45° and 62° for water and the NaNO3 solution, respectively. In pre-wetted sands, the dynamic imbibition data yielded apparent contact angles of 2° and 21° for water and the NaNO3 solution, respectively, with the latter value comparing well to a predicted value of 25° for the NaNO3 solution based solely on surface-tension contrast. The results of this study indicate that on the Darcy-scale, saline solutions appear to follow the relationship of non-zero contact angles with other miscible fluids of different surface tensions used to pre-wet the sand grains, in agreement with the macro-scale infiltration results of Weisbrod et al. [2004].

  8. Rolling-contact fatigue and wear of CVD-SiC with residual surface compression

    SciTech Connect

    Chao, L.Y.; Lakshminarayanan, R.; Shetty, D.K.; Cutler, R.A.

    1995-09-01

    The rolling-contact fatigue life and wear of CVD-SiC coatings with surface compression were studied using a three-ball-on-rod rolling-contact fatigue (RCF) tester. Two levels of surface compression in the coatings, approximately 190 {micro}m thick, were introduced by using substrates of a liquid-phase sintered SiC and a SiC-30 vol% TiC to obtain desired thermal-expansion mismatches with the CVD-SiC. Residual surface compressions of 250 and 680 MPa were measured in the CVD-SiC coatings on SiC and SiC-30 vol% TiC substrates, respectively, by a strain-gage technique. In the RCF test, the fatigue life of the CVD-SiC coating with the moderate surface compression was limited by severe wear by a brittle fracture mechanism at a Hertzian contact stress of 5.5 GPa. The CVD-SiC coating on the SiC-30 vol% TiC composite, on the other hand, did not show measurable wear. A majority of the tests (11 out of 16) were suspended at 100 h or stopped due to failure of the steel balls. Five tests stopped due to spalling of the CVD-SiC coating at weak interfaces 10 to 15 {micro}m below the contact surface. Examination of the microstructure of the CVD-SiC coating in cross sections revealed that the weak interfaces that led to the spalling were related to discontinuous growth of the CVD-SiC in the form of nodules or growth regions. Elimination of these defective structures is likely to enhance the tribological performance of surface-toughened CVD-SiC.

  9. Excluding Contact Electrification in Surface Potential Measurement Using Kelvin Probe Force Microscopy.

    PubMed

    Li, Shengming; Zhou, Yusheng; Zi, Yunlong; Zhang, Gong; Wang, Zhong Lin

    2016-02-23

    Kelvin probe force microscopy (KPFM), a characterization method that could image surface potentials of materials at the nanoscale, has extensive applications in characterizing the electric and electronic properties of metal, semiconductor, and insulator materials. However, it requires deep understanding of the physics of the measuring process and being able to rule out factors that may cause artifacts to obtain accurate results. In the most commonly used dual-pass KPFM, the probe works in tapping mode to obtain surface topography information in a first pass before lifting to a certain height to measure the surface potential. In this paper, we have demonstrated that the tapping-mode topography scan pass during the typical dual-pass KPFM measurement may trigger contact electrification between the probe and the sample, which leads to a charged sample surface and thus can introduce a significant error to the surface potential measurement. Contact electrification will happen when the probe enters into the repulsive force regime of a tip-sample interaction, and this can be detected by the phase shift of the probe vibration. In addition, the influences of scanning parameters, sample properties, and the probe's attributes have also been examined, in which lower free cantilever vibration amplitude, larger adhesion between the probe tip and the sample, and lower cantilever spring constant of the probe are less likely to trigger contact electrification. Finally, we have put forward a guideline to rationally decouple contact electrification from the surface potential measurement. They are decreasing the free amplitude, increasing the set-point amplitude, and using probes with a lower spring constant. PMID:26824304

  10. Detailed statistical contact angle analyses; "slow moving" drops on inclining silicon-oxide surfaces.

    PubMed

    Schmitt, M; Groß, K; Grub, J; Heib, F

    2015-06-01

    Contact angle determination by sessile drop technique is essential to characterise surface properties in science and in industry. Different specific angles can be observed on every solid which are correlated with the advancing or the receding of the triple line. Different procedures and definitions for the determination of specific angles exist which are often not comprehensible or reproducible. Therefore one of the most important things in this area is to build standard, reproducible and valid methods for determining advancing/receding contact angles. This contribution introduces novel techniques to analyse dynamic contact angle measurements (sessile drop) in detail which are applicable for axisymmetric and non-axisymmetric drops. Not only the recently presented fit solution by sigmoid function and the independent analysis of the different parameters (inclination, contact angle, velocity of the triple point) but also the dependent analysis will be firstly explained in detail. These approaches lead to contact angle data and different access on specific contact angles which are independent from "user-skills" and subjectivity of the operator. As example the motion behaviour of droplets on flat silicon-oxide surfaces after different surface treatments is dynamically measured by sessile drop technique when inclining the sample plate. The triple points, the inclination angles, the downhill (advancing motion) and the uphill angles (receding motion) obtained by high-precision drop shape analysis are independently and dependently statistically analysed. Due to the small covered distance for the dependent analysis (<0.4mm) and the dominance of counted events with small velocity the measurements are less influenced by motion dynamics and the procedure can be called "slow moving" analysis. The presented procedures as performed are especially sensitive to the range which reaches from the static to the "slow moving" dynamic contact angle determination. They are characterised by

  11. Survival and persistence of Campylobacter and Salmonella species under various organic loads on food contact surfaces.

    PubMed

    De Cesare, Alessandra; Sheldon, Brian W; Smith, Katie S; Jaykus, Lee-Ann

    2003-09-01

    Although many cases of Campylobacter and Salmonella enteritis have been attributed to the undercooking of poultry and other foods, cross-contamination between raw and cooked foods via food contact surfaces and worker contact has also been identified as a significant risk factor. Cross-contamination may be particularly important in relation to the high prevalence of contamination in raw poultry products and other foods and the low infectious doses that have been reported for Campylobacter species. Lag phase and decimal reduction times (D-values at 27 degrees C [81 degrees F] and 60 to 62% relative humidity) were determined for Campylobacter jejuni and Salmonella species (five-strain pools) suspended in either a phosphate-buffered saline (PBS) solution or Trypticase soy broth (TSB) and then inoculated (0.1-ml drop per surface) on 5-cm2 samples of Formica laminate (F), glazed ceramic tile (CT), 304 polished stainless steel (SS), and 100% cotton dishcloth (D). Triplicate samples were collected from each contact surface periodically, and the populations of surviving organisms were enumerated on Campy Cefex and brain heart infusion agars for C. jejuni and Salmonella species, respectively. Lag time and rate of inactivation were influenced by organism type, contact surface, and suspending medium. Initial mean lag times ranging from 60 to 190 min were followed by log-linear (r2 > 0.94) decreases in cell populations that varied across contact surfaces. D-values of 12.5, 19.1, 24.1, and 29.7 min and of 23.7, 10.5, 12.7, and 13.9 min were calculated for C. jejuni suspended in PBS and TSB and then spotted on D, F, SS, and CT surfaces, respectively. The times required to produce a 3-log reduction in population with PBS and TSB ranged from 102 (D) to 247 (F) min and from 112 (CT) to 167 (F) min, respectively. C. jejuni cells suspended in the nutritionally enriched medium (TSB) and spotted on the hard surfaces were inactivated about 1.4 times as fast as cells suspended in PBS. For

  12. Motion of a three-phase contact line on a moistened surface

    NASA Astrophysics Data System (ADS)

    Shikhmurzaev, Yu. D.

    1992-12-01

    The motion of the line of contact in gas-liquid-solid systems is investigated theoretically for low values of the capillary and Reynolds numbers. The analysis allows for the possible presence on the solid substrate of a microscopic residual film formed by adsorbed liquid molecules. A comparison is made of the spreading characteristics of the liquid for dry and moistened solid substrates. Based on the experimental data and the model used, the motion of the liquid during wetting is characterized as a rolling motion. The increase in the dynamic contact angle during the wetting of a moistened surface is found to be slower than in the case of a dry substrate. The maximum dynamic contact angle in the case of a moistened substrate is significantly less than 180 deg.

  13. EVALUATION AND PERFORMANCE ASSESSMENT OF INNOVATIVE LOW-VOC CONTACT ADHESIVES IN WOOD LAMINATING OPERATIONS

    EPA Science Inventory

    The report gives results of an evaluation and assessment of the perfor-mance, economics, and emission reduction potential upon application of low-volatile organic compound (VOC) waterborne contact adhesive formulations specifically ina manual laminating operation for assembling s...

  14. Sensor Prototype to Evaluate the Contact Force in Measuring with Coordinate Measuring Arms

    PubMed Central

    Cuesta, Eduardo; Telenti, Alejandro; Patiño, Hector; González-Madruga, Daniel; Martínez-Pellitero, Susana

    2015-01-01

    This paper describes the design, development and evaluation tests of an integrated force sensor prototype for portable Coordinate Measuring Arms (CMAs or AACMMs). The development is based on the use of strain gauges located on the surface of the CMAs’ hard probe. The strain gauges as well as their cables and connectors have been protected with a custom case, made by Additive Manufacturing techniques (Polyjet 3D). The same method has been selected to manufacture an ergonomic handle that includes trigger mechanics and the electronic components required for synchronizing the trigger signal when probing occurs. The paper also describes the monitoring software that reads the signals in real time, the calibration procedure of the prototype and the validation tests oriented towards increasing knowledge of the forces employed in manual probing. Several experiments read and record the force in real time comparing different ways of probing (discontinuous and continuous contact) and measuring different types of geometric features, from single planes to exterior cylinders, cones, or spheres, through interior features. The probing force is separated into two components allowing the influence of these strategies in probe deformation to be known. The final goal of this research is to improve the probing technique, for example by using an operator training programme, allowing extra-force peaks and bad contacts to be minimized or just to avoid bad measurements. PMID:26057038

  15. Sensor Prototype to Evaluate the Contact Force in Measuring with Coordinate Measuring Arms.

    PubMed

    Cuesta, Eduardo; Telenti, Alejandro; Patiño, Hector; González-Madruga, Daniel; Martínez-Pellitero, Susana

    2015-01-01

    This paper describes the design, development and evaluation tests of an integrated force sensor prototype for portable Coordinate Measuring Arms (CMAs or AACMMs). The development is based on the use of strain gauges located on the surface of the CMAs' hard probe. The strain gauges as well as their cables and connectors have been protected with a custom case, made by Additive Manufacturing techniques (Polyjet 3D). The same method has been selected to manufacture an ergonomic handle that includes trigger mechanics and the electronic components required for synchronizing the trigger signal when probing occurs. The paper also describes the monitoring software that reads the signals in real time, the calibration procedure of the prototype and the validation tests oriented towards increasing knowledge of the forces employed in manual probing. Several experiments read and record the force in real time comparing different ways of probing (discontinuous and continuous contact) and measuring different types of geometric features, from single planes to exterior cylinders, cones, or spheres, through interior features. The probing force is separated into two components allowing the influence of these strategies in probe deformation to be known. The final goal of this research is to improve the probing technique, for example by using an operator training programme, allowing extra-force peaks and bad contacts to be minimized or just to avoid bad measurements. PMID:26057038

  16. In situ measurement of contact angles and surface tensions of interfacial nanobubbles in ethanol aqueous solutions.

    PubMed

    Zhao, Binyu; Wang, Xingya; Wang, Shuo; Tai, Renzhong; Zhang, Lijuan; Hu, Jun

    2016-04-14

    The astonishing long lifetime and large contact angles of interfacial nanobubbles are still in hot debate despite numerous experimental and theoretical studies. One hypothesis to reconcile the two abnormalities of interfacial nanobubbles is that they have low surface tensions. However, few studies have been reported to measure the surface tensions of nanobubbles due to the lack of effective measurements. Herein, we investigate the in situ contact angles and surface tensions of individual interfacial nanobubbles immersed in different ethanol aqueous solutions using quantitative nanomechanical atomic force microscopy (AFM). The results showed that the contact angles of nanobubbles in the studied ethanol solutions were also much larger than the corresponding macroscopic counterparts on the same substrate, and they decreased with increasing ethanol concentrations. More significantly, the surface tensions calculated were much lower than those of the gas-liquid interfaces of the solutions at the macroscopic scale but have similar tendencies with increasing ethanol concentrations. Those results are expected to be helpful in further understanding the stability of interfacial nanobubbles in complex solutions. PMID:26954468

  17. Controlling adhesion between multi-asperity contacting surfaces in MEMS devices by local heating

    NASA Astrophysics Data System (ADS)

    Gkouzou, A.; Kokorian, J.; Janssen, G. C. A. M.; van Spengen, W. M.

    2016-09-01

    In this work, we have incorporated heaters in a MEMS device, which allow the in situ local heating of its contacting surfaces. This design offers a promising solution for MEMS devices with contacting components by preventing capillary-induced adhesion. The force of adhesion was assessed by optically measuring in-plane snap-off displacements. We were able to decrease adhesion from 500 nN to 200 nN with just one heated surface of which the temperature was set above 300 °C. The temperature should not be set too high: we observed increased adhesion due to a direct bonding process once the temperature was increased above 750 °C. Remarkably, adhesion increased by heating from room temperature to 75 °C, which is attributed to more water being transferred to the contact area due to faster kinetics. We observed the same effect in the cases where both surfaces were heated, although at slightly different temperatures. We demonstrated that heating only one surface to between 300 °C and 750 °C is sufficient to significantly lower adhesion, due to the removal of capillary menisci. The required heater is typically most easily implemented in a stationary part of the device.

  18. Pseudomonas aeruginosa Survival at Posterior Contact Lens Surfaces after Daily Wear

    PubMed Central

    Wu, Yvonne T.; Zhu, Lucia S.; Tam, K. P. Connie; Evans, David J.; Fleiszig, Suzanne M. J.

    2015-01-01

    Purpose Pseudomonas aeruginosa keratitis is a sight-threatening complication of contact lens wear, yet mechanisms by which lenses predispose to infection remain unclear. Here, we tested the hypothesis that tear fluid at the posterior contact lens surface can lose antimicrobial activity over time during lens wear. Methods Daily disposable lenses were worn for 1, 2, 4, 6 or 8 h immediately after removal from their packaging, or after presoaking in sterile saline for 2 days to remove packaging solution. Unworn lenses were also tested, some coated in tears “aged” in vitro for 1 or 8 h. Lenses were placed anterior surface down into tryptic soy agar cradles containing gentamicin (100µg/ml) to kill bacteria already on the lens, and posterior surfaces inoculated with gentamicin-resistant P. aeruginosa for 3 h. Surviving bacteria were enumerated by viable counts of lens homogenates. Results Posterior surfaces of lenses worn by patients for 8 h supported more P. aeruginosa growth than lenses worn for only 1 h, if lenses were presoaked prior to wear (~ 2.4-fold, p = 0.01). This increase was offset if lenses were not presoaked to remove packaging solution (p = 0.04 at 2 h and 4 h). Irrespective of presoaking, lenses worn for 8 h showed more growth on their posterior surface than unworn lenses coated with tear fluid that was “aged” for 8 h vitro (~8.6-fold, presoaked, p = 0.003: ~ 5.4-fold from packaging solution, p = 0.004). Indeed, in vitro incubation did not impact tear antimicrobial activity. Conclusions This study shows that post lens tear fluid can lose antimicrobial activity over time during contact lens wear, supporting the idea that efficient tear exchange under a lens is critical for homeostasis. Additional studies are needed to determine applicability to other lens types, wearing modalities, and relevance to contact lens-related infections. PMID:25955639

  19. Surface Strength of Silicon Nitride in Relation to Rolling Contact Performance

    SciTech Connect

    Wang, Wei; Hadfield, M.; Wereszczak, Andrew A

    2009-01-01

    Silicon nitride material has been traditionally used as bearing material due to its superior performance against bearing steel. Its successful application as a bearing element has led to the development of rolling contact applications in turbomachinery and automotive industries. In the case of latter, this is especially true for the engine manufacturing industry where its excellent rolling contact performance can make significant savings on warranty cost for engine manufactures. In spite of these advantages, the remaining limitation for their broader application is the high component machining cost. Further understanding of rolling contact performance of silicon nitride in relation to its surface integrity will enable engine manufacturers to produce components that meet the design requirements while at the same time reduce the machining cost. In the present study, the relationship between the C-sphere strength of a silicon nitride and its rolling contact fatigue life is investigated. The C-sphere test is used here to compare the strengths of three batches of sintered reaction-bonded silicon nitride (SRBSN) specimens with different subsurface quality induced by variation of machining parameters. In parallel, the rolling contact fatigue (RCF) performance of those machining conditions is studied on a modified four-ball tester. The results show that the most aggressively machined specimens have the weakest C-sphere strength and the shortest RCF life. This positive relationship can give component manufacturers a valuable reference when they make selections of candidate material and finishing standards.

  20. Is a Knowledge of Surface Topology and Contact Angles Enough to Define the Drop Impact Outcome?

    PubMed

    Malavasi, Ileana; Veronesi, Federico; Caldarelli, Aurora; Zani, Maurizio; Raimondo, Mariarosa; Marengo, Marco

    2016-06-28

    It is well known that a superhydrophobic surface may not be able to repel impacting droplets because of the so-called Cassie-to-Wenzel transition. It has been proven that a critical value of the receding contact angle (θR) exists for the complete rebound of water, recently experimentally measured to be 100° for a large range of impact velocities. On the contrary, in the present work, no rebound was observed when low-surface-tension liquids such as hexadecane (σ = 27.5 mN/m at 25 °C) are concerned, even for very low impact velocities and very high values of θR and low contact angle hysteresis. Therefore, the critical threshold of θR ≈ 100° does not sound acceptable for all liquids and for all hydrophobic surfaces. For the same Weber numbers, a Cassie-to-Wenzel state transition occurs after the impact as a result of the easier penetration of low-surface-tension fluids in the surface structure. Hence, a criterion for the drop rebound of low-surface-tension liquids must consider not only the contact angle values with surfaces but also their surface tension and viscosity. This suggests that, even if it is possible to produce surfaces with enhanced static repellence against oils and organics, generally the realization of synthetic materials with self-cleaning and antisticking abilities in dynamic phenomena, such as spray impact, remains an unsolved task. Moreover, it is demonstrated that the chemistry of the surface, the physicochemical interactions with the liquid drops, and the possible wettability gradient of the surface asperity also play important roles in determining the critical Weber number above which impalement occurs. Therefore, the classical numerical simulations of drop impact on dry surfaces are definitively not able to capture the final outcomes of the impact for all possible fluids if the surface topology and chemistry and/or the wettability gradient in the surface structure are not properly reflected. PMID:27228028

  1. Materials selection and evaluation of Copper-Tungsten particulate composites for extreme electrical contacts

    NASA Astrophysics Data System (ADS)

    Watkins, Bobby Gene, II

    2011-12-01

    Materials for extreme electrical contacts need to have high electrical conductivity coupled with good structural properties. Potential applications include motor contacts, high power switches, and the components of electromagnetic launch (EML) systems. The lack of durability experienced with these contact materials limits service life. Due to extreme current densities coupled with the local sliding, electrical contact surfaces can degrade due to a one or more wear mechanisms, including adhesive wear and thermally-assisted wear associated with extreme local Joule heating. A systematic materials selection procedure was developed to identify and compare candidate materials that would be more durable for these types of applications. The most promising materials identified on the Pareto frontier are tungsten alloys. Moreover, several possible candidate monolithic materials as well as hybrid materials that could potentially be even better, filling the "white spaces" on the material property charts, were identified. A couple of these potential candidate materials were obtained and evaluated. These included copper-tungsten W-Cu, "self-lubricating" graphite-impregnated Cu, and Gr-W-Cu composites with different volume fractions of the constituents. The structure-property relations were determined through mechanical and electrical resistivity testing. A unique test protocol for exposing mechanical test specimens to extreme current densities up to 1.2 GA/m2 was developed and used to evaluate these candidate materials. The design of materials including optimizing the microstructure attributes for these applications can potentially be accelerated by using micromechanics modeling and other materials design tools coupled with systematic mechanical and tribological experiments. In this study, physics- and micromechanics-based models were used to correlate properties to the volume fraction of the tungsten. These properties included elastic modulus, hardness, tensile strength, and

  2. AFM-based tribological study of nanopatterned surfaces: the influence of contact area instabilities

    NASA Astrophysics Data System (ADS)

    Rota, A.; Serpini, E.; Gazzadi, G. C.; Valeri, S.

    2016-04-01

    Although the importance of morphology on the tribological properties of surfaces has long been proved, an exhaustive understanding of nanopatterning effects is still lacking due to the difficulty in both fabricating ‘really nano-’ structures and detecting their tribological properties. In the present work we show how the probe-surface contact area can be a critical parameter due to its remarkable local variability, making a correct interpretation of the data very difficult in the case of extremely small nanofeatures. Regular arrays of parallel 1D straight nanoprotrusions were fabricated by means of a low-dose focused ion beam, taking advantage of the amorphization-related swelling effect. The tribological properties of the patterns were detected in the presence of air and in vacuum (dry ambient) by atomic force microscopy. We have introduced a novel procedure and data analysis to reduce the uncertainties related to contact instabilities. The real time estimation of the radius of curvature of the contacting asperity enables us to study the dependence of the tribological properties of the patterns from their geometrical characteristics. The effect of the patterns on both adhesion and the coefficient of friction strongly depends on the contact area, which is linked to the local radius of curvature of the probe. However, a detectable hydrophobic character induced on the hydrophilic native SiO2 has been observed as well. The results suggest a scenario for capillary formation on the patterns.

  3. An adhesive contact mechanics formulation based on atomistically induced surface traction

    NASA Astrophysics Data System (ADS)

    Fan, Houfu; Ren, Bo; Li, Shaofan

    2015-12-01

    In this work, we have developed a novel multiscale computational contact formulation based on the generalized Derjuguin approximation for continua that are characterized by atomistically enriched constitutive relations in order to study macroscopic interaction between arbitrarily shaped deformable continua. The proposed adhesive contact formulation makes use of the microscopic interaction forces between individual particles in the interacting bodies. In particular, the double-layer volume integral describing the contact interaction (energy, force vector, matrix) is converted into a double-layer surface integral through a mathematically consistent approach that employs the divergence theorem and a special partitioning technique. The proposed contact model is formulated in the nonlinear continuum mechanics framework and implemented using the standard finite element method. With no large penalty constant, the stiffness matrix of the system will in general be well-conditioned, which is of great significance for quasi-static analysis. Three numerical examples are presented to illustrate the capability of the proposed method. Results indicate that with the same mesh configuration, the finite element computation based on the surface integral approach is faster and more accurate than the volume integral based approach. In addition, the proposed approach is energy preserving even in a very long dynamic simulation.

  4. AFM-based tribological study of nanopatterned surfaces: the influence of contact area instabilities.

    PubMed

    Rota, A; Serpini, E; Gazzadi, G C; Valeri, S

    2016-04-01

    Although the importance of morphology on the tribological properties of surfaces has long been proved, an exhaustive understanding of nanopatterning effects is still lacking due to the difficulty in both fabricating 'really nano-' structures and detecting their tribological properties. In the present work we show how the probe-surface contact area can be a critical parameter due to its remarkable local variability, making a correct interpretation of the data very difficult in the case of extremely small nanofeatures. Regular arrays of parallel 1D straight nanoprotrusions were fabricated by means of a low-dose focused ion beam, taking advantage of the amorphization-related swelling effect. The tribological properties of the patterns were detected in the presence of air and in vacuum (dry ambient) by atomic force microscopy. We have introduced a novel procedure and data analysis to reduce the uncertainties related to contact instabilities. The real time estimation of the radius of curvature of the contacting asperity enables us to study the dependence of the tribological properties of the patterns from their geometrical characteristics. The effect of the patterns on both adhesion and the coefficient of friction strongly depends on the contact area, which is linked to the local radius of curvature of the probe. However, a detectable hydrophobic character induced on the hydrophilic native SiO2 has been observed as well. The results suggest a scenario for capillary formation on the patterns. PMID:26934217

  5. Investigation of Contact Angle Behavior and Stability of Drops to Airflow Forcing on Rough Surfaces

    NASA Astrophysics Data System (ADS)

    Schmucker, Jason; White, Edward

    2011-11-01

    A method for measuring full-field, instantaneous drop interface profiles on rough surfaces has been implemented to study contact angles and stability to wind forcing on metallic surfaces with micron-scale roughness. Wind tunnel experiments are conducted to produce criteria for runback of drops and set these thresholds for measured water drops spanning a range of Bond numbers from Bo = 0 . 5 to 5 on roughness in the range of RA = 0 . 8 to 4 . 9 with drop based Reynolds numbers spanning an order of magnitude. More importantly, these stability limits are tested with particular care taken to observe their relation to the behavior of both the contact line and contact angle distribution as the drop adjusts its configuration to find a stable condition until it is no longer able to do so and is blown downstream. Results such as critical shear rates and contact angles are discussed and compared with previous numerical studies in the literature such as Dimitrakopoulos [J.Fluid.Mech. 580, 2007] and Ding and Spelt [J.Coll.Sci. 599, 2008] along with experimental results such as Milne [Langmuir 25:24, 2009].

  6. Slow tool servo diamond turning of optical freeform surface for astigmatic contact lens

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Chieh; Cheng, Yuan-Chieh; Hsu, Wei-Yao; Chou, Hsiao-Yu; Wang, Pei-Jen; Tsai, Din Ping

    2011-09-01

    Three ultra-precision machining processes namely fast tool servo, slow tool servo and diamond milling, are frequently used to produce optical freeform surface. Slow tool servo machining has the advantages of no extra attachment and fast setting-up, however the three dimensional tool shape compensation and tool-path generation must be conducted carefully for getting high form accuracy and fine surface finish. This research aimed to develop a model of three dimensional tool shape compensation for generating 3D tool path in slow tool servo diamond turning of asymmetrically toric surface for astigmatic contact lens. The form accuracy of freeform surface was measured by ultra-high accuracy 3D profilometer (UA3P) with user define function. After correction, the form error is less than 0.5μm both in X- and Y-direction and the surface roughness is less than 5nm.

  7. Microscopic Receding Contact Line Dynamics on Pillar and Irregular Superhydrophobic Surfaces

    PubMed Central

    Yeong, Yong Han; Milionis, Athanasios; Loth, Eric; Bayer, Ilker S.

    2015-01-01

    Receding angles have been shown to have great significance when designing a superhydrophobic surface for applications involving self-cleaning. Although apparent receding angles under dynamic conditions have been well studied, the microscopic receding contact line dynamics are not well understood. Therefore, experiments were performed to measure these dynamics on textured square pillar and irregular superhydrophobic surfaces at micron length scales and at micro-second temporal scales. Results revealed a consistent “slide-snap” motion of the microscopic receding line as compared to the “stick-slip” dynamics reported in previous studies. Interface angles between 40–60° were measured for the pre-snap receding lines on all pillar surfaces. Similar “slide-snap” dynamics were also observed on an irregular nanocomposite surface. However, the sharper features of the surface asperities resulted in a higher pre-snap receding line interface angle (~90°). PMID:25670630

  8. Thermal Diffusion Processes in Metal-Tip-Surface Interactions: Contact Formation and Adatom Mobility

    NASA Astrophysics Data System (ADS)

    Sørensen, Mads R.; Jacobsen, Karsten W.; Jónsson, Hannes

    1996-12-01

    We have carried out computer simulations to identify and characterize various thermally activated atomic scale processes that can play an important role in room temperature experiments where a metal tip is brought close to a metal surface. We find that contact formation between the tip and the surface can occur by a sequence of atomic hop and exchange processes which become active on a millisecond time scale when the tip is about 3-5 Å from the surface. Adatoms on the surface are stabilized by the presence of the tip and energy barriers for diffusion processes in the region under the tip are reduced. This can cause adatoms to follow the tip as it is moved over the surface.

  9. Fractal properties of worn surface of Fe-based alloy coatings during rolling contact process

    NASA Astrophysics Data System (ADS)

    Chen, Shu-ying; Wang, Hai-dou; Ma, Guo-zheng; Kang, Jia-jie; Xu, Bin-shi

    2016-02-01

    The rolling contact fatigue (RCF) failure procedure of Fe-based alloy coating, fabricated by high efficient plasma spray (PS) technology, was investigated by a double-roller test machine with oil lubrication under pure rolling contact condition. The fractal dimension (FD) was utilized to quantitatively characterize the profile of the worn surface at different experiment stage and the failure mechanism of the coating was discussed. The results indicated that the nonlinear morphologies of the worn surface of Fe-Cr alloy coating possessed excellent fractal properties. The failure procedure could be divided into four stages according to the value and change rule of FD, i.e. (1) running-in stage, (2) stable abrade stage, (3) accelerated damage stage, (4) unstable removal stage.

  10. Method for growing a back surface contact on an imaging detector used in conjunction with back illumination

    NASA Technical Reports Server (NTRS)

    Blacksberg, Jordana (Inventor); Hoenk, Michael Eugene (Inventor); Nikzad, Shouleh (Inventor)

    2010-01-01

    A method is provided for growing a back surface contact on an imaging detector used in conjunction with back illumination. In operation, an imaging detector is provided. Additionally, a back surface contact (e.g. a delta-doped layer, etc.) is grown on the imaging detector utilizing a process that is performed at a temperature less than 450 degrees Celsius.

  11. A clinical evaluation of the non-contact tonometer.

    PubMed

    Wittenberg, S

    1977-02-01

    Paired non-contact tonometer readings were taken on patients at the Boston City Hospital Eye Clinic before and after routine vision care that included Goldmann tonometry. The variability of NCT readings was determined and comparisons made between readings obtained with the NCT and Goldmann instruments. The regression equation relating the pre-Goldmann NCT findings (N1), to the Goldmann (G), was N1 = 1.01G + 1.97; and the equation relating the post-Goldmann NCT findings (N2), to the Goldman was N2 = .94G + 1.70. The N1 mean was 2.06 mm. higher than the mean G, while the N2 mean was .58 mm. higher than the mean G. The correlation coefficients and standard deviation of the differences for the two comparisons were, .88, 3.91, and .93, 3.07, respectively. The Goldmann findings therefore were seen to agree more closely with the NCT findings taken after them. The linear regression and correlation coefficients between the NCT and the Goldmann were generally in good agreement with those of prior studies, although the standard deviations of the differences between findings were larger in this study. This result is not surprising since no attempt was made to train Goldmann operators to criterion or to limit variability induced by differing observer criteria or by the use of only one Goldmann operator. The operators of the Goldmann tonometer had varying degrees of training as residents in ophthalmology. Interestingly, the agreement between pre-Goldmann NCT and post-Goldmann NCT findings was not good. This suggested that the taking of the Goldmann findings themselves may have had a significant effect on the tonometric readings and that the considerable time that frequently took place between the two sets of NCT readings could have affected the value. The standard deviation of the differences between pre- and post-Goldmann readings on the same patient was 3.27 as compared to that for paired readings which was 2.28. The data also showed a much better agreement between the NCT and

  12. Bearing material. [composite material with low friction surface for rolling or sliding contact

    NASA Technical Reports Server (NTRS)

    Sliney, H. E. (Inventor)

    1976-01-01

    A composite material is described which will provide low friction surfaces for materials in rolling or sliding contact and is self-lubricating and oxidation resistant up to and in excess of about 930 C. The composite is comprised of a metal component which lends strength and elasticity to the structure, a fluoride salt component which provides lubrication and, lastly, a glass component which not only provides oxidation protection to the metal but may also enhance the lubrication qualities of the composite.

  13. Determination of the surface isoelectric point of oxide films on metals by contact angle titration

    SciTech Connect

    McCafferty, E.; Wightman, J.P.

    1997-10-15

    The surface isoelectric point for the native air-formed oxide films on aluminum, chromium, and tantalum has been determined by measurement of contact angles at the hexadecane/aqueous solution interface as a function of pH of the aqueous phase. Application of Young`s equation, the Gibbs equation, and surface equilibria conditions for hydroxylated oxide films leads to a mathematical expression which shows that the contact angle goes through a maximum at the isoelectric point of the oxide. The experimentally determined isoelectric point of oxide-covered chromium is 5.2 to 5.3, of oxide-covered aluminum is 9.5, and of oxide-covered tantalum is approximately {minus}0.7. These values for the oxide films are within one to three pH units of the reported isoelectric points for the corresponding bulk oxide powders. The oxide-covered metal surfaces were cleaned by argon plasma treatment prior to measurement of contact angles, in that XPS measurements showed this treatment to be effective in reducing the thickness of the carbon contamination layer. In addition, interfacial tensions were measured at the hexadecane/aqueous solution interface and were observed to have only a slight dependence on the pH of the aqueous phase.

  14. Formation of Surface Nanobubbles and the Universality of Their Contact Angles: A Molecular Dynamics Approach

    NASA Astrophysics Data System (ADS)

    Weijs, Joost H.; Snoeijer, Jacco H.; Lohse, Detlef

    2012-03-01

    We study surface nanobubbles using molecular dynamics simulation of ternary (gas, liquid, solid) systems of Lennard-Jones fluids. They form for a sufficiently low gas solubility in the liquid, i.e., for a large relative gas concentration. For a strong enough gas-solid attraction, the surface nanobubble is sitting on a gas layer, which forms in between the liquid and the solid. This gas layer is the reason for the universality of the contact angle, which we calculate from the microscopic parameters. Under the present equilibrium conditions the nanobubbles dissolve within less of a microsecond, consistent with the view that the experimentally found nanobubbles are stabilized by a nonequilibrium mechanism.

  15. The numerical calculation of the viscous incompressible fluid transfer between contacting surfaces

    NASA Astrophysics Data System (ADS)

    Varepo, L. G.; Panichkin, A. V.; Trapeznikova, O. V.

    2016-04-01

    The movement of the thin layer of the viscous incompressible fluid (VTF) between two cylinders is analysed. The numerical calculations results of VTF transfer from the engaged zone of two cylinders to porous substrates are presented. The VTF (ink) is moved along the rubberized top blanket of the first cylinder. The surface of the second cylinder contacts the substrate with some part of the VTF layer transferred from the first cylinder. The fluid is double bounded by the free surface. Images of cylinders boundary deformation and VTF flow areas are shown.

  16. Normal contact and friction of rubber with model randomly rough surfaces.

    PubMed

    Yashima, S; Romero, V; Wandersman, E; Frétigny, C; Chaudhury, M K; Chateauminois, A; Prevost, A M

    2015-02-01

    We report on normal contact and friction measurements of model multicontact interfaces formed between smooth surfaces and substrates textured with a statistical distribution of spherical micro-asperities. Contacts are either formed between a rigid textured lens and a smooth rubber, or a flat textured rubber and a smooth rigid lens. Measurements of the real area of contact A versus normal load P are performed by imaging the light transmitted at the microcontacts. For both interfaces, A(P) is found to be sub-linear with a power law behavior. Comparison with two multi-asperity contact models, which extend the Greenwood-Williamson (J. Greenwood and J. Williamson, Proc. Royal Soc. London Ser. A, 295, 300 (1966)) model by taking into account the elastic interaction between asperities at different length scales, is performed, and allows their validation for the first time. We find that long range elastic interactions arising from the curvature of the nominal surfaces are the main source of the non-linearity of A(P). At a shorter range, and except for very low pressures, the pressure dependence of both density and area of microcontacts remains well described by Greenwood-Williamson's model, which neglects any interaction between asperities. In addition, in steady sliding, friction measurements reveal that the mean shear stress at the scale of the asperities is systematically larger than that found for a macroscopic contact between a smooth lens and a rubber. This suggests that frictional stresses measured at macroscopic length scales may not be simply transposed to microscopic multicontact interfaces. PMID:25514137

  17. Surface-controlled contact printing for nanowire device fabrication on a large scale.

    PubMed

    Roßkopf, D; Strehle, S

    2016-05-01

    Assembly strategies for functional nanowire devices that merge bottom-up and top-down technologies have been debated for over a decade. Although several breakthroughs have been reported, nanowire device fabrication techniques remain generally incompatible with large-scale and high-yield top-down microelectronics manufacturing. Strategies enabling the controlled transfer of nanowires from the growth substrate to pre-defined locations on a target surface would help to address this challenge. Based on the promising concept of mechanical nanowire transfer, we developed the technique of surface-controlled contact printing, which is based purely on dry friction between a nanowire and a target surface. Surface features, so-called catchers, alter the local frictional force or deposition probability and allow the positioning of single nanowires. Surface-controlled contact printing extends the current scope of nanowire alignment strategies with the intention to facilitate efficient nanowire device fabrication. This is demonstrated by the simultaneous assembly of 36 nanowire resistors within a chip area of greater than 2 cm(2) aided only by mask-assisted photolithography. PMID:27007944

  18. Surface-controlled contact printing for nanowire device fabrication on a large scale

    NASA Astrophysics Data System (ADS)

    Roßkopf, D.; Strehle, S.

    2016-05-01

    Assembly strategies for functional nanowire devices that merge bottom-up and top-down technologies have been debated for over a decade. Although several breakthroughs have been reported, nanowire device fabrication techniques remain generally incompatible with large-scale and high-yield top-down microelectronics manufacturing. Strategies enabling the controlled transfer of nanowires from the growth substrate to pre-defined locations on a target surface would help to address this challenge. Based on the promising concept of mechanical nanowire transfer, we developed the technique of surface-controlled contact printing, which is based purely on dry friction between a nanowire and a target surface. Surface features, so-called catchers, alter the local frictional force or deposition probability and allow the positioning of single nanowires. Surface-controlled contact printing extends the current scope of nanowire alignment strategies with the intention to facilitate efficient nanowire device fabrication. This is demonstrated by the simultaneous assembly of 36 nanowire resistors within a chip area of greater than 2 cm2 aided only by mask-assisted photolithography.

  19. Atomic Oxygen Treatment for Non-Contact Removal of Organic Protective Coatings from Painting Surfaces

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Cales, Michael

    1994-01-01

    Current techniques for removal of varnish (lacquer) and other organic protective coatings from paintings involve contact with the surface. This contact can remove pigment, or alter the shape and location of paint on the canvas surface. A thermal energy atomic oxygen plasma, developed to simulate the space environment in low Earth orbit, easily removes these organic materials. Uniform removal of organic protective coatings from the surfaces of paintings is accomplished through chemical reaction. Atomic oxygen will not react with oxides so that most paint pigments will not be affected by the reaction. For paintings containing organic pigments, the exposure can be carefully timed so that the removal stops just short of the pigment. Color samples of Alizarin Crimson, Sap Green, and Zinc White coated with Damar lacquer were exposed to atomic oxygen. The lacquer was easily removed from all of the samples. Additionally, no noticeable change in appearance was observed after the lacquer was reapplied. The same observations were made on a painted canvas test sample obtained from the Cleveland Museum of Art. Scanning electron microscope photographs showed a slight microscopic texturing of the vehicle after exposure. However, there was no removal or disturbance of the paint pigment on the surface. It appears that noncontact cleaning using atomic oxygen may provide a viable alternative to other cleaning techniques. It is especially attractive in cases where the organic protective surface cannot be acceptably or safely removed by conventional techniques.

  20. Contact angle and surface tension measurements of a five-ring polyphenyl ether

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1985-01-01

    Contact angle measurements were performed for a five-ring polyphenyl ether isomeric mixture on M-50 steel in a dry nitrogen atmosphere. Two different techniques were used: (1) a tilting plate apparatus, and (2) a sessile drop apparatus. Measurements were made for the temperature range 25 to 190 C. Surface tension was measured by a differential maximum bubble pressure technique over the range 23 to 220C in room air. The critical surface energy of spreading (gamma (sub c)) was determined for the polyphenyl ether by plotting the cosine of the contact angle (theta) versus the surface tension (gamma (sub LV)). The straight line intercept at cosine theta = 1 is defined as gamma (sub c). Gamma (sub c) was found to be 30.1 dyn/cm for the tilting plate technique and 31.3 dyn/cm for the sessile drop technique. These results indicate that the polyphenyl ether is inherently autophobic (i.e., it will not spread on its own surface film until its surface tension is less than gamma (sub c). This phenomenon is discussed in light of the wettability and wear problems encountered with this fluid.

  1. Tribological behavior of micro/nano-patterned surfaces in contact with AFM colloidal probe

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoliang; Wang, Xiu; Kong, Wen; Yi, Gewen; Jia, Junhong

    2011-10-01

    In effort to investigate the influence of the micro/nano-patterning or surface texturing on the nanotribological properties of patterned surfaces, the patterned polydimethylsiloxane (PDMS) surfaces with pillars were fabricated by replica molding technique. The surface morphologies of patterned PDMS surfaces with varying pillar sizes and spacing between pillars were characterized by atomic force microscope (AFM) and scanning electron microscope (SEM). The AFM/FFM was used to acquire the friction force images of micro/nano-patterned surfaces using a colloidal probe. A difference in friction force produced a contrast on the friction force images when the colloidal probe slid over different regions of the patterned polymer surfaces. The average friction force of patterned surface was related to the spacing between the pillars and their size. It decreased with the decreasing of spacing between the pillars and the increasing of pillar size. A reduction in friction force was attributed to the reduced area of contact between patterned surface and colloidal probe. Additionally, the average friction force increased with increasing applied load and sliding velocity.

  2. Adhesion of Pathogenic Bacteria to Food Contact Surfaces: Influence of pH of Culture

    PubMed Central

    Mafu, Akier Assanta; Plumety, Corinne; Deschênes, Louise; Goulet, Jacques

    2011-01-01

    The adhesion of Aeromonas hydrophila, Escherichia coli O157:H7, Salmonella Enteritidis, and Staphylococcus aureus to hydrophobic and hydrophilic surfaces in cultures with different pHs (6, 7, and 8) was studied. The results indicated that the type of material had no effect on the attachment capacity of microorganisms, while environmental pH influenced the adhesion of A. hydrophila, E. coli, and S. aureus to both solid substrates. The attachment of S. Enteritidis (P > .05) was not affected by the type of substrate or the culture pH, whereas E. coli displayed the weakest affinity for both polystyrene and glass surfaces. No correlation was established between the physicochemical properties of the materials, or the bacterial and the rate of bacterial adhesion, except for S. aureus. Photomicrographs have shown that surfaces were contaminated by small clusters of S. Enteritidis while S. aureus invaded the food contact surfaces in the form of small chains or cell aggregates. PMID:20981289

  3. Surface properties and wear performances of siloxane-hydrogel contact lenses.

    PubMed

    Bettuelli, Michela; Trabattoni, Silvia; Fagnola, Matteo; Tavazzi, Silvia; Introzzi, Laura; Farris, Stefano

    2013-11-01

    The low surface roughness of disposable contact lenses made of a new siloxane-hydrogel loaded with hyaluronic acid is reported, as studied by atomic force microscopy (AFM). Before the wear, the surface is characterized by out-of-plane and sharp structures, with maximum height of about 10 nm. After a wear of 8 h, evidence of two typical morphologies is provided and discussed. One morphology (sharp type) has a similar aspect as the unworn lenses with a slight increase in both the height and the number of the sharp peaks. The other morphology (smooth type) is characterized by troughs and bumpy structures. Wettability and clinical performances are also discussed, the latter deduced by the ocular-surface-disease index (OSDI). The main finding arising from this work is the indication of correlation between the change of the OSDI before and after wear and the lens surface characteristics obtained by AFM. PMID:23559566

  4. Finger cooling by contact with cold aluminium surfaces--effects of pressure, mass and whole body thermal balance.

    PubMed

    Chen, F; Nilsson, H; Holmér, I

    1994-01-01

    Finger skin temperature change during contact with a cold aluminium surface was studied in 20 subjects (10 men and 10 women). Contact pressure (0.1 N, 5.9 N and 9.8 N), contact material mass (large one, mass 3559 g, small one, mass 108 g), surface temperatures (-7 degrees C, 0 degree C, +7 degrees C) and whole body thermal balance were controlled as independent factors. The contact experiments were performed in a small chamber and only the first section of the index finger of the left hand was in contact with the aluminium surface. The results indicated that all the factors studied had significant effects on the contact skin temperature change with time. The study confirmed that a modified Newtonian model with two components can accurately describe the contact skin temperature change with time. The study resulted in three predictive models for critical skin temperature when in contact with cold aluminium. The results indicated that metal surfaces in contact with bare hands should not be below 4 degrees C surface temperature. Lower temperatures require insulating material or the wearing of protective gloves. PMID:7957157

  5. Understanding the Acute Skin Injury Mechanism Caused by Player-Surface Contact During Soccer

    PubMed Central

    van den Eijnde, Wilbert A.J.; Peppelman, Malou; Lamers, Edwin A.D.; van de Kerkhof, Peter C.M.; van Erp, Piet E.J.

    2014-01-01

    Background: Superficial skin injuries are considered minor, and their incidence is probably underestimated. Insight into the incidence and mechanism of acute skin injury can be helpful in developing suitable preventive measures and safer playing surfaces for soccer and other field sports. Purpose: To gain insight into the incidence and severity of skin injuries related to soccer and to describe the skin injury mechanism due to player-surface contact. Study Design: Systematic review; Level of evidence, 4. Methods: The prevention model by van Mechelen et al (1992) combined with the injury causation model of Bahr and Krosshaug (2005) were used as a framework for the survey to describe the skin injury incidence and mechanism caused by player-surface contact. Results: The reviewed literature showed that common injury reporting methods are mainly based on time lost from participation or the need for medical attention. Because skin abrasions seldom lead to absence or medical attention, they are often not reported. When reported, the incidence of abrasion/laceration injuries varies from 0.8 to 6.1 injuries per 1000 player-hours. Wound assessment techniques such as the Skin Damage Area and Severity Index can be a valuable tool to obtain a more accurate estimation of the incidence and severity of acute skin injuries. Conclusion: The use of protective equipment, a skin lubricant, or wet surface conditions has a positive effect on preventing abrasion-type injuries from artificial turf surfaces. The literature also shows that essential biomechanical information of the sliding event is lacking, such as how energy is transferred to the area of contact. From a clinical and histological perspective, there are strong indications that a sliding-induced skin lesion is caused by mechanical rather than thermal injury to the skin. PMID:26535330

  6. Piercing the water surface with a blade: Singularities of the contact line

    NASA Astrophysics Data System (ADS)

    Alimov, Mars M.; Kornev, Konstantin G.

    2016-01-01

    An external meniscus on a narrow blade with a slit-like cross section is studied using the hodograph formulation of the Laplace nonlinear equation of capillarity. On narrow blades, the menisci are mostly shaped by the wetting and capillary forces; gravity plays a secondary role. To describe a meniscus in this asymptotic case, the model of Alimov and Kornev ["Meniscus on a shaped fibre: Singularities and hodograph formulation," Proc. R. Soc. A 470, 20140113 (2014)] has been employed. It is shown that at the sharp edges of the blade, the contact line makes a jump. In the wetting case, the contact line sitting at each side of the blade is lifted above the points where the meniscus first meets the blade edges. In the non-wetting case, the contact line is lowered below these points. The contours of the constant height emanating from the blade edges generate unusual singularities with infinite curvatures at some points at the blade edges. The meniscus forms a unique surface made of two mirror-symmetric sheets fused together. Each sheet is supported by the contact line sitting at each side of the blade.

  7. Evaluation of transition metal oxide as carrier-selective contacts for silicon heterojunction solar cells

    SciTech Connect

    Ding, L.; Boccard, Matthieu; Holman, Zachary; Bertoni, M.

    2015-04-06

    passivation. In complement, we construct full device structures incorporating in some cases surface passivation schemes, with measured initial conversion efficiency over 15% and evaluate the carrier transport properties using temperature-dependent current-voltage and capacitance-voltage measurements. With this detailed characterization study, we aim at providing the framework to assess the potential of a material as a carrier selective contact and the understanding of how each of the aforementioned parameters on the metal oxide films influence the full solar cell operating performances.

  8. Contact and artificial soil tests using earthworms to evaluate the impact of wastes in soil

    SciTech Connect

    Neuhauser, E.F.; Loehr, R.C.; Malecki, M.R.

    1986-01-01

    The study was designed to evaluate two methods using earthworms that can be used to estimate the biological impact of organic and inorganic compounds that may be in wastes applied to land for treatment and disposal. The two methods were the contact test and the artificial soil test. The contact test is 48-h test using an adult worm, a small glass vial, and filter paper to which the test chemical or waste is applied. The test is designed to provide close contact between the worm and a chemical, similar to the situation in soils. The method provides a rapid estimate of the relative toxicity of chemicals and industrial wastes.

  9. Relationship between the surface chemical composition of implants and contact with the substrate.

    PubMed

    Lima da Costa Valente, Mariana; Shimano, Antonio Carlos; Marcantonio Junior, Elcio; Reis, Andréa Candido Dos

    2015-02-01

    The purpose of the study was to use scanning electron microscopy and energy dispersive x-ray spectrometry to assess possible morphologic and chemical changes after performing double-insertion and pullout tests of implants of different shapes and surface treatments. Four different types of implants were used-cylindrical machined-surface implants, cylindrical double-surface-treated porous implants, cylindrical surface-treated porous implants, and tapered surface-treated porous implants-representing a total of 32 screws. The implants were inserted into synthetic bone femurs, totaling 8 samples, before performing each insertion with standardized torque. After each pullout the implants were analyzed by scanning electron microscopy and energy dispersive x-ray spectrometry using a universal testing machine and magnified 35 times. No structural changes were detected on morphological surface characterization, only substrate accumulation. As for composition, there were concentration differences in the titanium, oxygen, and carbon elements. Implants with surface acid treatment undergo greater superficial changes in chemical composition than machined implants, that is, the greater the contact area of the implant with the substrate, the greater the oxide layer change. In addition, prior manipulation can alter the chemical composition of implants, typically to a greater degree in surface-treated implants. PMID:23339297

  10. Contact effects and quantum interference in engineered dangling bond loops on silicon surfaces.

    PubMed

    Kleshchonok, Andrii; Gutierrez, Rafael; Cuniberti, Gianaurelio

    2015-09-01

    Dangling bond structures created on H-passivated silicon surfaces offer a novel platform for engineering planar nanoscale circuits, compatible with conventional semiconductor technologies. In this investigation we focus on the electronic structure and quantum transport signatures of dangling bond loops built on H-passivated Si(100) surfaces contacted by carbon nanoribbons, thus leading to a two-terminal planar, nanoscale setup. The computational studies were carried out to rationalize the influence of the local atomic-scale contacts of the dangling bond system to the mesoscopic electrodes as well as the possibility of revealing quantum interference effects in the dangling bond loops. Our results reveal a strong sensitivity of the low-energy quantum transmission to the loop topology and to the atomistic details of the electrode-loop contact. Varying the length of the loop or the spatial position of at least one of the electrodes has a drastic impact on the quantum interference pattern; depending on whether constructive or destructive interference within the loop takes place, the conductance of the system can be tuned over several orders of magnitude, thus suggesting the possibility of exploiting such quantum mechanical effects in the design of two-dimensional, atomic-scale electronic devices such as logic gates. PMID:26228007