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Sample records for contact surfaces evaluated

  1. A noise-resistant ADSA-PH algorithm for superhydrophobic surface's static contact angle evaluation

    NASA Astrophysics Data System (ADS)

    Xu, Z. N.

    2017-03-01

    The blur around the contact points significantly decreases the evaluated static contact angle for superhydrophobic surface which is clearly presented in the paper. To improve the accuracy in the evaluated static contact angle for superhydrophobic surface, an accurate static contact angle algorithm, namely ADSA-PH (axisymmetric drop shape analysis-profile and height), is proposed. It discards the extracted drop edge points close to the contact points and makes use of the residual points and the drop height to determine the static contact angle. The contact angle errors caused by the blur close to the contact points are significantly reduced. The classical ADSA-P algorithm, the modified selected-plane method and the proposed algorithm are used to evaluate static contact angle. The results validate the proposed algorithm. The accuracy in the evaluated contact angle increases with increasing image resolution. To reduce the error caused by a limitation of image resolution, the minimum allowable image resolutions are presented.

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

    USDA-ARS?s Scientific Manuscript database

    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. Waterless coupling of ultrasound from planar contact transducers to curved and irregular surfaces during non-destructive ultrasonic evaluations

    NASA Astrophysics Data System (ADS)

    Denslow, Kayte; Diaz, Aaron; Jones, Mark; Meyer, Ryan; Cinson, Anthony; Wells, Mondell

    2012-04-01

    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.

  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. Method for lubricating contacting surfaces

    DOEpatents

    Dugger, Michael T [Tijeras, NM; Ohlhausen, James A [Albuquerque, NM; Asay, David B [Boalsburg, PA; Kim, Seong H [State College, PA

    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.

  8. Antibacterial surface design - Contact kill

    NASA Astrophysics Data System (ADS)

    Kaur, Rajbir; Liu, Song

    2016-08-01

    Designing antibacterial surfaces has become extremely important to minimize Healthcare Associated Infections which are a major cause of mortality worldwide. A previous biocide-releasing approach is based on leaching of encapsulated biocides such as silver and triclosan which exerts negative impacts on the environment and potentially contributes to the development of bacterial resistance. This drawback of leachable compounds led to the shift of interest towards a more sustainable and environmentally friendly approach: contact-killing surfaces. Biocides that can be bound onto surfaces to give the substrates contact-active antibacterial activity include quaternary ammonium compounds (QACs), quaternary phosphoniums (QPs), carbon nanotubes, antibacterial peptides, and N-chloramines. Among the above, QACs and N-chloramines are the most researched contact-active biocides. We review the engineering of contact-active surfaces using QACs or N-chloramines, the modes of actions as well as the test methods. The charge-density threshold of cationic surfaces for desired antibacterial efficacy and attempts to combine various biocides for the generation of new contact-active surfaces are discussed in detail. Surface positive charge density is identified as a key parameter to define antibacterial efficacy. We expect that this research field will continue to attract more research interest in view of the potential impact of self-disinfective surfaces on healthcare-associated infections, food safety and corrosion/fouling resistance required on industrial surfaces such as oil pipes and ship hulls.

  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. Stress evaluations under rolling/sliding contacts

    NASA Technical Reports Server (NTRS)

    Kannel, J. W.; Tevaarwerk, J. L.

    1981-01-01

    The state of stress beneath traction drive type of contacts were analyzed. Computing stresses and stress reversals on various planes for points beneath the surface were examined. The effect of tangential and axial friction under gross slip conditions is evaluated with the models. Evaluations were performed on an RC (rolling contact) tester configuration and it is indicated that the classical fatigue stresses are not altered by friction forces typical of lubricated contact. Higher values of friction can result in surface shear reversal that exceeds the stresses at the depth of maximum shear reversal under rolling contact.

  11. Interfacial closure of contacting surfaces

    NASA Astrophysics Data System (ADS)

    Rieutord, F.; Rauer, C.; Moriceau, H.

    2014-08-01

    Understanding the contact between solid surfaces is a long-standing problem which has a strong impact on the physics of many processes such as adhesion, friction, lubrication and wear. Experimentally, the investigation of solid/solid interfaces remains challenging today, due to the lack of experimental techniques able to provide sub-nanometer scale information on interfaces buried between millimeters of materials. Yet, a strong interest exists improving the modeling of contact mechanics of materials in order to adjust their interface properties (e.g., thermal transport, friction). We show here that the essential features of the residual gap between contacting surfaces can be measured using high energy X-ray synchrotron reflectivity. The presence of this nano-gap is general to the contact of solids. In some special case however, it can be removed when attractive forces take over repulsive contributions, depending on both height and wavelength of asperity distributions (roughness). A criterion for this instability is established in the standard case of van der Waals attractive forces and elastic asperity compression repulsive forces (Hertz model). This collapse instability is confirmed experimentally in the case of silicon direct bonding, using high-energy X-ray synchrotron reflectivity and adhesion energy measurements. The possibility to achieve fully closed interfaces at room temperature opens interesting perspectives to build stronger assemblies with smaller thermal budgets.

  12. 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.

  13. [Study of the surface tear tension and evaluation of its importance for the retinal physiology and pathology in contact correction and in adaptation to soft contact lenses].

    PubMed

    Cherepnin, A I; Smoliakova, G P; Sorokin, E L

    2003-01-01

    The surface lachrymal-fluid (LF) tension was investigated by teardrop dissection in 115 patients with myopia before they were prescribed soft contact lenses (SCL). Such tension was found to be of clinical importance for the development of SCL adaptation disorders. A longer adaptation period in patients with myopia was associated with a low surface LF tension. A high surface LF tension concurrent with the teardrop dissection mode of the destruction type was typical of the pathological nature of SCL adaptation (12.1% of patients). The obtained data are needed to detect timely the risk of dysadaptation disorders and corneal complications before SCL prescription for the purpose of undertaking the pathogenetically substantiated medication to prevent such complications.

  14. 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

  15. 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

  16. Resin bonding to a feldspar ceramic after different ceramic surface conditioning methods: evaluation of contact angle, surface pH, and microtensile bond strength durability.

    PubMed

    Amaral, Regina; Ozcan, Mutlu; Bottino, Marco Antonio; Valandro, Luiz Felipe

    2011-12-01

    To evaluate the surface pH, contact angle and microtensile bond strength (MTBS) of a resin-cement to feldspathic ceramic after various surface conditioning methods (SC). For pH measurements, 96 glass-ceramic disks were assigned into 12 groups (n = 8): SC1-pH: No ceramic surface conditioning (control); SC2-pH: hydrofluoric-acid (HF) 9% 1 min; SC3-pH: SC2-pH+wash/dry; SC4-pH: SC3-pH+silane; SC5-pH: HF 4% 1 min; SC6-pH: SC5-pH+wash/dry; SC7-pH: SC6 -pH +silane; SC8-pH: HF 5% 1 min; SC9-pH: SC8-pH+wash/dry; SC10-pH: SC9-pH+silane; SC11-pH: SC9-pH +neutralizer+wash/dry+sonic-cleaning; SC12-pH: SC11-pH+silane. For contact angle analysis, 40 disks were divided into 5 groups (n = 8): SC1-ca: no conditioning; SC2-ca: HF 9%+wash/dry; SC3-ca: HF 4%+wash/dry; SC4 -ca: HF 5%+wash/dry; SC5-ca: HF 5%+neutralizer+wash/dry+ultrasonic-cleaning. To evaluate the MTBS, 40 blocks were distributed into 4 groups SC (N = 10): SC1-bond: HF 9% 1 min+silane; SC2-bond: HF 4% 1 min+silane; SC3-bond: HF 5% 1 min+silane; SC4-bond: HF 5% 1 min+neutralizer+wash/dry+ultrasonic cleaning+silane. The resin cement was applied on the treated surfaces and bar specimens were produced that were submitted to 2 conditions: dry: immediate MTBS; TC: storage for 150 days and thermocycling 5000x. Fifty bar specimens were produced per group (n = 50). Contact angle and pH results were submitted to one-way ANOVA and Tukey's test (α = 0.05). Microtensile data were submitted to two-way ANOVA and Tukey's test (a = 0.05). pH values were significantly higher for SC6-ph (11.5 ± 2.6) when compared to those of SC5-pH (2.7 ± 0.4), SC8-pH (2.7 ± 0.2) and SC2-pH (2.2 ± 0.2) (p < 0.00, ANOVA). SC1-ca had the largest contact angle (48 ± 16 degrees) and SC3-ca the smallest (9.4 ± 7.7 degrees). The results of the MTBS test were as follows: independent of the storage condition, SC2-bond = SC1-bond > SC3-bond = SC4-bond. SC4-bond had the lowest MTBS value after TC (10.6 ± 2.6 MPa). The acid neutralization step appears to be

  17. 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.

  18. Dynamic contact angle measurements on superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Hyun; Kavehpour, H. Pirouz; Rothstein, Jonathan P.

    2015-03-01

    In this paper, the dynamic advancing and receding contact angles of a series of aqueous solutions were measured on a number of hydrophobic and superhydrophobic surfaces using a modified Wilhelmy plate technique. Superhydrophobic surfaces are hydrophobic surfaces with micron or nanometer sized surface roughness. These surfaces have very large static advancing contact angles and little static contact angle hysteresis. In this study, the dynamic advancing and dynamic receding contact angles on superhydrophobic surfaces were measured as a function of plate velocity and capillary number. The dynamic contact angles measured on a smooth hydrophobic Teflon surface were found to obey the scaling with capillary number predicted by the Cox-Voinov-Tanner law, θD3 ∝ Ca. The response of the dynamic contact angle on the superhydrophobic surfaces, however, did not follow the same scaling law. The advancing contact angle was found to remain constant at θA = 160∘, independent of capillary number. The dynamic receding contact angle measurements on superhydrophobic surfaces were found to decrease with increasing capillary number; however, the presence of slip on the superhydrophobic surface was found to result in a shift in the onset of dynamic contact angle variation to larger capillary numbers. In addition, a much weaker dependence of the dynamic contact angle on capillary number was observed for some of the superhydrophobic surfaces tested.

  19. 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.

  20. 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.

  1. Micro- and nano-force evaluation of bioengineered muscle cells: a non-contact two-dimensional biosensing using surface acoustic wave devices

    NASA Astrophysics Data System (ADS)

    Wong, Yoke-Rung

    2015-08-01

    A high degree of cell-generated force measurement is required to evaluate the biomechanical performance of bioengineered muscle tissues. However, the conventional cantilever types of direct force measurement methods have limitations in developing a non-contact two-dimensional force sensing device for a single muscle cell. In this paper, a method is proposed and discussed by using focused surface acoustic wave and magneto-optic Kerr measurements. To depict the capability of the proposed method, a conceptual design of such a sensory device is demonstrated for non-contact two-dimensional force measurement of a single muscle cell.

  2. 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.

  3. Contact angle measurement on rough surfaces.

    PubMed

    Meiron, Tammar S; Marmur, Abraham; Saguy, I Sam

    2004-06-15

    A new method for the measurement of apparent contact angles at the global energy minimum on real surfaces has been developed. The method consists of vibrating the surface, taking top-view pictures of the drop, monitoring the drop roundness, and calculating the contact angle from the drop diameter and weight. The use of the new method has been demonstrated for various rough surfaces, all having the same surface chemistry. In order to establish the optimal vibration conditions, the proper ranges for the system parameters (i.e., drop volume, vibration time, frequency of vibration, and amplitude of vibration) were determined. The reliability of the method has been demonstrated by the fact that the ideal contact angles of all surfaces, as calculated from the Wenzel equation using the measured apparent contact angles, came out to be practically identical. This ideal contact angle has been compared with three methods of calculation from values of advancing and receding contact angles.

  4. Evaluation of Electrolytically-Generated Hypochlorous Acid ('Electrolyzed Water') for Sanitation of Meat and Meat-Contact Surfaces.

    PubMed

    Veasey, Shawnna; Muriana, Peter M

    2016-06-13

    'Electrolyzed water' generators are readily available in the food industry as a renewable source of hypochlorous acid that eliminates the need for workers to handle hazardous hypochlorite concentrates. We applied electrolyzed water (EW) directly to multi-strain cocktails of Listeria monocytogenes, E. coli O157:H7, and Salmonella sp. at 250 ppm free available chlorine (FAC) and achieved greater than 6-log reductions in 2 min. Lower EW values were examined as antimicrobial interventions for fresh meat (beef carcasses), processed meats (frankfurters), and food contact surfaces (slicing blades). Little or no reduction relative to controls was observed when generic E. coli-inoculated beef carcasses or L. monocytogenes-inoculated frankfurters were showered with EW. Spray application of EW (25 and 250-ppm FAC) onto L. monocytogenes-inoculated slicing blades showed that greater reductions were obtained with 'clean' (3.6 and 5.7-log reduction) vs. 'dirty' (0.6 and 3.3-log reduction) slicing blades, respectively. Trials with L. monocytogenes-inoculated protein-EW solutions demonstrated that protein content as low as 0.1% is capable of eliminating FAC, reducing antimicrobial activity against L. monocytogenes. EW appears better positioned as a surface sanitizer with minimal organic material that can otherwise act as an effective reducing agent to the oxidizing solution rendering it ineffective.

  5. Evaluation of Electrolytically-Generated Hypochlorous Acid (‘Electrolyzed Water’) for Sanitation of Meat and Meat-Contact Surfaces

    PubMed Central

    Veasey, Shawnna; Muriana, Peter M.

    2016-01-01

    ‘Electrolyzed water’ generators are readily available in the food industry as a renewable source of hypochlorous acid that eliminates the need for workers to handle hazardous hypochlorite concentrates. We applied electrolyzed water (EW) directly to multi-strain cocktails of Listeria monocytogenes, E. coli O157:H7, and Salmonella sp. at 250 ppm free available chlorine (FAC) and achieved greater than 6-log reductions in 2 min. Lower EW values were examined as antimicrobial interventions for fresh meat (beef carcasses), processed meats (frankfurters), and food contact surfaces (slicing blades). Little or no reduction relative to controls was observed when generic E. coli-inoculated beef carcasses or L. monocytogenes-inoculated frankfurters were showered with EW. Spray application of EW (25 and 250-ppm FAC) onto L. monocytogenes-inoculated slicing blades showed that greater reductions were obtained with ‘clean’ (3.6 and 5.7-log reduction) vs. ‘dirty’ (0.6 and 3.3-log reduction) slicing blades, respectively. Trials with L. monocytogenes-inoculated protein-EW solutions demonstrated that protein content as low as 0.1% is capable of eliminating FAC, reducing antimicrobial activity against L. monocytogenes. EW appears better positioned as a surface sanitizer with minimal organic material that can otherwise act as an effective reducing agent to the oxidizing solution rendering it ineffective. PMID:28231137

  6. Evaluation of peak-free electromechanical piezo-impedance and electromagnetic contact sensing using metamaterial surface plasmons for load monitoring

    NASA Astrophysics Data System (ADS)

    Gopal Madhav Annamdas, Venu; Kiong Soh, Chee

    2017-01-01

    Continuous structural health monitoring (SHM) and delayed SHM techniques can be contact/ contactless, surface bonded/embedded, wired/wireless and active/passive actuator-sensor systems which transfer the recorded condition of the structure to the base station almost instantaneously or with time delay respectively. The time between fatal crack initiation and its propagation leading to the collapse of key infrastructures such as aerospace, nuclear facilities, oil and gas is mostly short. Timely discovery of structural problem depends heavily on the scanning period in well-established techniques like piezoelectric (PZT) based electromechanical impedance (EMI) technique. This often takes much scanning time due to the acquisition of resonant structural peaks at all frequencies in the considered bandwidth; thus poses a challenge for its implementation in practice. On the other hand, recently developed strain sensors based on metamaterials and their breeds such as nested split-ring resonators, localized surface plasmons (LSP), etc, employ measurement of reflected or transmitted signal, with super-fast scanning in the order of at most 1/100th of the time taken by the EMI technique. This paper articulates faster measurements by reducing unnecessary resonant structural peaks and focusing on rapid monitoring using PZT and metamaterial plasmons. Our research adopted wired PZT and wireless LSP communications with impedance analyser and vector network analyser respectively. We present integrated and complementary nature of these techniques, which can be processed rapidly for key infrastructures with great effectiveness. This integration can result in both continuous and delayed SHM techniques based on time or frequency or both domains.

  7. In vitro evaluation of modified surface microhardness measurement, focus variation 3D microscopy and contact stylus profilometry to assess enamel surface loss after erosive–abrasive challenges

    PubMed Central

    Baumann, Tommy; Carvalho, Thiago Saads; Assunção, Cristiane Meira; Lussi, Adrian

    2017-01-01

    The aim of the study was to compare surface loss values after erosion—abrasion cycles obtained with modified surface microhardness measurement (mSMH), focus variation 3D microscopy (FVM) and contact stylus profilometry (CSP). We cut human molars into buccal and lingual halves, embedded them in resin and ground 200 μm of enamel away. The resulting surfaces were polished. To maintain a reference area, we applied Block-Out resin to partly cover the enamel surface. The samples were incubated in artificial saliva (37°C; 1 h), then rinsed in deionized water (10 s) and dried with oil-free air (5 s). We immersed the specimens individually in 30 mL citric acid (1%, pH 3.6) for 2 min (25°C, 70 rpm dynamic conditions) before brushing them (50 strokes, 200 g) in an automatic brushing machine with toothpaste-slurry. We calculated the surface loss as per mSMH, by re-measuring the length of the same six indentations made before the abrasive challenge. The experiment consisted of five experimental groups that received between 2 and 10 erosion—abrasion cycles. Each group contained 15 specimens and samples in groups 1, 2, 3, 4 and 5 underwent a total of 2, 4, 6, 8 and 10 cycles, respectively. The resin was removed from the reference area in one piece under 10× magnification and the FVM and CSP were performed. Agreement between the methods was calculated with the intraclass correlation coefficient (ICC) and depicted in Bland-Altman plots. All methods presented a linear pattern of surface loss measurements throughout the experiment, leading overall to a strong, statistically significant correlation between the methods (ICC = 0.85; p<0.001). So, despite the different surface loss values, all methods presented consistent results for surface loss measurement. PMID:28380015

  8. In vitro evaluation of modified surface microhardness measurement, focus variation 3D microscopy and contact stylus profilometry to assess enamel surface loss after erosive-abrasive challenges.

    PubMed

    Gyurkovics, Milán; Baumann, Tommy; Carvalho, Thiago Saads; Assunção, Cristiane Meira; Lussi, Adrian

    2017-01-01

    The aim of the study was to compare surface loss values after erosion-abrasion cycles obtained with modified surface microhardness measurement (mSMH), focus variation 3D microscopy (FVM) and contact stylus profilometry (CSP). We cut human molars into buccal and lingual halves, embedded them in resin and ground 200 μm of enamel away. The resulting surfaces were polished. To maintain a reference area, we applied Block-Out resin to partly cover the enamel surface. The samples were incubated in artificial saliva (37°C; 1 h), then rinsed in deionized water (10 s) and dried with oil-free air (5 s). We immersed the specimens individually in 30 mL citric acid (1%, pH 3.6) for 2 min (25°C, 70 rpm dynamic conditions) before brushing them (50 strokes, 200 g) in an automatic brushing machine with toothpaste-slurry. We calculated the surface loss as per mSMH, by re-measuring the length of the same six indentations made before the abrasive challenge. The experiment consisted of five experimental groups that received between 2 and 10 erosion-abrasion cycles. Each group contained 15 specimens and samples in groups 1, 2, 3, 4 and 5 underwent a total of 2, 4, 6, 8 and 10 cycles, respectively. The resin was removed from the reference area in one piece under 10× magnification and the FVM and CSP were performed. Agreement between the methods was calculated with the intraclass correlation coefficient (ICC) and depicted in Bland-Altman plots. All methods presented a linear pattern of surface loss measurements throughout the experiment, leading overall to a strong, statistically significant correlation between the methods (ICC = 0.85; p<0.001). So, despite the different surface loss values, all methods presented consistent results for surface loss measurement.

  9. Contact angle hysteresis on fluoropolymer surfaces.

    PubMed

    Tavana, H; Jehnichen, D; Grundke, K; Hair, M L; Neumann, A W

    2007-10-31

    Contact angle hysteresis of liquids with different molecular and geometrical properties on high quality films of four fluoropolymers was studied. A number of different causes are identified for hysteresis. With n-alkanes as probe liquids, contact angle hysteresis is found to be strongly related to the configuration of polymer chains. The largest hysteresis is obtained with amorphous polymers whereas the smallest hysteresis occurs for polymers with ordered molecular chains. This is explained in terms of sorption of liquid by the solid and penetration of liquid into the polymer film. Correlation of contact angle hysteresis with the size of n-alkane molecules supports this conclusion. On the films of two amorphous fluoropolymers with different molecular configurations, contact angle hysteresis of one and the same liquid with "bulky" molecules is shown to be quite different. On the surfaces of Teflon AF 1600, with stiff molecular chains, the receding angles of the probe liquids are independent of contact time between solid and liquid and similar hysteresis is obtained for all the liquids. Retention of liquid molecules on the solid surface is proposed as the most likely cause of hysteresis in these systems. On the other hand, with EGC-1700 films that consist of flexible chains, the receding angles are strongly time-dependent and the hysteresis is large. Contact angle hysteresis increases even further when liquids with strong dipolar intermolecular forces are used. In this case, major reorganization of EGC-1700 chains due to contact with the test liquids is suggested as the cause. The effect of rate of motion of the three-phase line on the advancing and receding contact angles, and therefore contact angle hysteresis, is investigated. For low viscous liquids, contact angles are independent of the drop front velocity up to approximately 10 mm/min. This agrees with the results of an earlier study that showed that the rate-dependence of the contact angles is an issue only

  10. Ocular Surface Displacement with and without Contact Lenses during Non-Contact Tonometry

    PubMed Central

    Rimayanti, Ulfah; Kiuchi, Yoshiaki; Uemura, Shohei; Takenaka, Joji; Mochizuki, Hideki; Kaneko, Makoto

    2014-01-01

    Purpose To evaluate the displacement of the central ocular surface during non-contact tonometry with and without soft contact lenses and determine the factors associated with the displacement of the central ocular surface and intraocular pressure (IOP) reading changes caused by wearing soft contact lenses (CLs). Methods One eye each in 21 subjects was studied. The cornea was photographed using a high-speed camera at 5,000 frames/sec during non-contact tonometry without contact lenses (NCL), with -5.0 diopters (D), -0.5 D and +5.0 D CL. The displacement of the ocular surface and the factors affecting displacement at the IOP reading and maximum displacement time were investigated. Results The IOP readings while wearing +5 D CL were significantly higher than those obtained while wearing -5 D CL. The ocular surface displacement between +5 D CL and other groups were significantly different. A significant positive correlation was found between the ocular surface displacement of subjects at the IOP reading time and the IOP obtained with the non-contact tonometer. A significant negative correlation was found between the ocular surface curvature and the IOP obtained using the non-contact tonometer. The radius of curvature of the ocular surface affected the displacement during the IOP reading and maximum displacement time. Conclusions Our results indicate that soft contact lens use changes the ocular surface behavior and IOP readings during non-contact tonometry. The radius of curvature of the eye affects the ocular surface displacement and IOP readings in this situation. PMID:24781212

  11. Interfacial contact stiffness of fractal rough surfaces.

    PubMed

    Zhang, Dayi; Xia, Ying; Scarpa, Fabrizio; Hong, Jie; Ma, Yanhong

    2017-10-09

    In this work we describe a theoretical model that predicts the interfacial contact stiffness of fractal rough surfaces by considering the effects of elastic and plastic deformations of the fractal asperities. We also develop an original test rig that simulates dovetail joints for turbo machinery blades, which can fine tune the normal contact load existing between the contacting surfaces of the blade root. The interfacial contact stiffness is obtained through an inverse identification method in which finite element simulations are fitted to the experimental results. Excellent agreement is observed between the contact stiffness predicted by the theoretical model and by the analogous experimental results. We demonstrate that the contact stiffness is a power law function of the normal contact load with an exponent α within the whole range of fractal dimension D(1 < D < 2). We also show that for 1 < D < 1.5 the Pohrt-Popov behavior (α = 1/(3 - D)) is valid, however for 1.5 < D < 2, the exponent α is different and equal to 2(D - 1)/D. The diversity between the model developed in the work and the Pohrt-Popov one is explained in detail.

  12. 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.

  13. Adhesive contact of randomly rough surfaces

    NASA Astrophysics Data System (ADS)

    Pastewka, Lars; Robbins, Mark

    2012-02-01

    The contact area, stiffness and adhesion between rigid, randomly rough surfaces and elastic substrates is studied using molecular statics and continuum simulations. The surfaces are self-affine with Hurst exponent 0.3 to 0.8 and different short λs and long λL wavelength cutoffs. The rms surface slope and the range and strength of the adhesive potential are also varied. For parameters typical of most solids, the effect of adhesion decreases as the ratio λL/λs increases. In particular, the pull-off force decreases to zero and the area of contact Ac becomes linear in the applied load L. A simple scaling argument is developed that describes the increase in the ratio Ac/L with increasing adhesion and a corresponding increase in the contact stiffness [1]. The argument also predicts a crossover to finite contact area at zero load when surfaces are exceptionally smooth or the ratio of surface tension to bulk modulus is unusually large, as for elastomers. Results that test this prediction will be presented and related to the Maugis-Dugdale [2] theories for individual asperities and the more recent scaling theory of Persson [3]. [1] Akarapu, Sharp, Robbins, Phys. Rev. Lett. 106, 204301 (2011) [2] Maugis, J. Colloid Interface Sci. 150, 243 (1992) [3] Persson, Phys. Rev. Lett. 74, 75420 (2006)

  14. 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.

  15. The contact mechanics of fractal surfaces.

    PubMed

    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.

  16. Clinical findings correlated with contact angles on rigid gas permeable contact lens surfaces in vivo.

    PubMed

    Bourassa, S; Benjamin, W J

    1989-08-01

    Functional wettability of daily wear rigid gas permeable (RGP) contact lenses worn by 16 human subjects was monitored over a 4-month period during which wettability was also assessed with an equilibrium sessile-drop contact angle method in vivo. In all, 2,128 lens surface break-up time (LBUT) and in vivo contact angle data points were accumulated. Six hundred thirty-one associated graded evaluations of lens surface deposition and patient discomfort were also recorded. The four factors (LBUT, contact angle, deposition, and discomfort) were found to be correlated to each other, their paired values having statistically significant correlation coefficients. Contact angles were of predictive value for extremes of functional wettability, based on criterion of 20 degrees equivalent to an LBUT of 5 seconds. We confirm that surface deposition and subject discomfort are related to RGP lens wettability on the eye. In addition, the in vivo contact angle is perhaps the first contact angle measurement to be correlated with functional RGP wettability.

  17. 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.

  18. Dynamic contact interactions of fractal surfaces

    NASA Astrophysics Data System (ADS)

    Jana, Tamonash; Mitra, Anirban; Sahoo, Prasanta

    2017-01-01

    Roughness parameters and material properties have significant influence on the static and dynamic properties of a rough surface. In the present paper, fractal surface is generated using the modified two-variable Weierstrass-Mandelbrot function in MATLAB and the same is imported to ANSYS to construct the finite element model of the rough surface. The force-deflection relationship between the deformable rough fractal surface and a contacting rigid flat is studied by finite element analysis. For the dynamic analysis, the contacting system is represented by a single degree of freedom spring mass-damper-system. The static force-normal displacement relationship obtained from FE analysis is used to determine the dynamic characteristics of the rough surface for free, as well as for forced damped vibration using numerical methods. The influence of fractal surface parameters and the material properties on the dynamics of the rough surface is also analyzed. The system exhibits softening property for linear elastic surface and the softening nature increases with rougher topography. The softening nature of the system increases with increase in tangent modulus value. Above a certain value of yield strength the nature of the frequency response curve is observed to change its nature from softening to hardening.

  19. Gas flow between immobile contact-surfaces

    NASA Astrophysics Data System (ADS)

    Lemberskii, V. B.

    1982-04-01

    Consideration is given to the problem of leakage through imperfectly connected detachable joints. A method is developed to analyze the rate of gas flow through such joints, with allowance for the displacement of the contact surfaces under the influence of the pressure of the gas flowing through the joint. It is shown that in the case of sufficiently large surface displacements the dependence of gas flow rate on the square of gas pressure inside the joint differs significantly fom a linear dependence, which occurs when the displacement effect is absent.

  20. 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

  1. 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.

  2. 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 previously...

  3. 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

    ... 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 Services... requirement regarding the National Contact Center customer evaluation surveys. In this request, the previously...

  4. 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.

  5. Contact Analysis of Nominally Flat Surfaces

    DTIC Science & Technology

    2008-06-01

    researchers, Abdo and Farhang [7]. The work began with a literature survey which discussed the work of Greenwood and Williamson and the downfalls of Hertz...Electrical Conductivity γ N or m al iz ed E le ct ric al C on du ct iv ity 1.3 1.4 1.5 1.7 1.9 0.9 1 1.1 1.2 Temperature γ N or m al iz ed T em pe...40 (21 July 2007), pp. 4245-4252. [7] J. Abdo and K. Farhang, “Elastic-Plastic Contact Model for Rough Surfaces Based on Plastic Asperity

  6. Comparison of methods to evaluate bacterial contact-killing materials.

    PubMed

    van de Lagemaat, Marieke; Grotenhuis, Arjen; van de Belt-Gritter, Betsy; Roest, Steven; Loontjens, Ton J A; Busscher, Henk J; van der Mei, Henny C; Ren, Yijin

    2017-09-01

    Cationic surfaces with alkylated quaternary-ammonium groups kill adhering bacteria upon contact by membrane disruption and are considered increasingly promising as a non-antibiotic based way to eradicate bacteria adhering to surfaces. However, reliable in vitro evaluation methods for bacterial contact-killing surfaces do not yet exist. More importantly, results of different evaluation methods are often conflicting. Therefore, we compared five methods to evaluate contact-killing surfaces. To this end, we have copolymerized quaternary-ammonium groups into diurethane dimethacrylate/glycerol dimethacrylate (UDMA/GDMA) and determined contact-killing efficacies against five different Gram-positive and Gram-negative strains. Spray-coating bacteria from an aerosol onto contact-killing surfaces followed by air-drying as well as ASTM E2149-13a (American Society for Testing and Materials) were found unsuitable, while the Petrifilm® system and JIS Z 2801 (Japanese Industrial Standards) were found to be excellent methods to evaluate bacterial contact-killing surfaces. It is recommended however, that these methods be used in combination with a zone of inhibition on agar assay to exclude that leakage of antimicrobials from the material interferes with the contact-killing ability of the surface. Bacterial adhesion to surfaces of biomaterials implants can be life-threatening. Antimicrobials to treat biomaterial-associated infections often fail due to the bacterial biofilm-mode-of-growth or are ineffective due to antibiotic-resistance of causative organisms. Positively-charged, quaternized surfaces can kill bacteria upon contact and are promising as a non-antibiotic-based treatment of biomaterial-associated infections. Reliable methods to determine efficacies of contact-killing surfaces are lacking, however. Here, we show that three out of five methods compared, including an established ASTM, are unsuitable. Methods found suitable should be used in combination with a zone

  7. Designing surfaces that kill bacteria on contact

    PubMed Central

    Tiller, Joerg C.; Liao, Chun-Jen; Lewis, Kim; Klibanov, Alexander M.

    2001-01-01

    Poly(4-vinyl-N-alkylpyridinium bromide) was covalently attached to glass slides to create a surface that kills airborne bacteria on contact. The antibacterial properties were assessed by spraying aqueous suspensions of bacterial cells on the surface, followed by air drying and counting the number of cells remaining viable (i.e., capable of growing colonies). Amino glass slides were acylated with acryloyl chloride, copolymerized with 4-vinylpyridine, and N-alkylated with different alkyl bromides (from propyl to hexadecyl). The resultant surfaces, depending on the alkyl group, were able to kill up to 94 ± 4% of Staphylococcus aureus cells sprayed on them. A surface alternatively created by attaching poly(4-vinylpyridine) to a glass slide and alkylating it with hexyl bromide killed 94 ± 3% of the deposited S. aureus cells. On surfaces modified with N-hexylated poly(4-vinylpyridine), the numbers of viable cells of another Gram-positive bacterium, Staphylococcus epidermidis, as well as of the Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, dropped more than 100-fold compared with the original amino glass. In contrast, the number of viable bacterial cells did not decline significantly after spraying on such common materials as ceramics, plastics, metals, and wood. PMID:11353851

  8. Designing surfaces that kill bacteria on contact.

    PubMed

    Tiller, J C; Liao, C J; Lewis, K; Klibanov, A M

    2001-05-22

    Poly(4-vinyl-N-alkylpyridinium bromide) was covalently attached to glass slides to create a surface that kills airborne bacteria on contact. The antibacterial properties were assessed by spraying aqueous suspensions of bacterial cells on the surface, followed by air drying and counting the number of cells remaining viable (i.e., capable of growing colonies). Amino glass slides were acylated with acryloyl chloride, copolymerized with 4-vinylpyridine, and N-alkylated with different alkyl bromides (from propyl to hexadecyl). The resultant surfaces, depending on the alkyl group, were able to kill up to 94 +/- 4% of Staphylococcus aureus cells sprayed on them. A surface alternatively created by attaching poly(4-vinylpyridine) to a glass slide and alkylating it with hexyl bromide killed 94 +/- 3% of the deposited S. aureus cells. On surfaces modified with N-hexylated poly(4-vinylpyridine), the numbers of viable cells of another Gram-positive bacterium, Staphylococcus epidermidis, as well as of the Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, dropped more than 100-fold compared with the original amino glass. In contrast, the number of viable bacterial cells did not decline significantly after spraying on such common materials as ceramics, plastics, metals, and wood.

  9. Designing surfaces that kill bacteria on contact

    NASA Astrophysics Data System (ADS)

    Tiller, Joerg C.; Liao, Chun-Jen; Lewis, Kim; Klibanov, Alexander M.

    2001-05-01

    Poly(4-vinyl-N-alkylpyridinium bromide) was covalently attached to glass slides to create a surface that kills airborne bacteria on contact. The antibacterial properties were assessed by spraying aqueous suspensions of bacterial cells on the surface, followed by air drying and counting the number of cells remaining viable (i.e., capable of growing colonies). Amino glass slides were acylated with acryloyl chloride, copolymerized with 4-vinylpyridine, and N-alkylated with different alkyl bromides (from propyl to hexadecyl). The resultant surfaces, depending on the alkyl group, were able to kill up to 94 ± 4% of Staphylococcus aureus cells sprayed on them. A surface alternatively created by attaching poly(4-vinylpyridine) to a glass slide and alkylating it with hexyl bromide killed 94 ± 3% of the deposited S. aureus cells. On surfaces modified with N-hexylated poly(4-vinylpyridine), the numbers of viable cells of another Gram-positive bacterium, Staphylococcus epidermidis, as well as of the Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, dropped more than 100-fold compared with the original amino glass. In contrast, the number of viable bacterial cells did not decline significantly after spraying on such common materials as ceramics, plastics, metals, and wood.

  10. Surface free energy of a solid from contact angle hysteresis.

    PubMed

    Chibowski, Emil

    2003-04-25

    Nature of contact angle hysteresis is discussed basing on the literature data (Colloids Surf. A 189 (2001) 265) of dynamic advancing and receding contact angles of n-alkanes and n-alcohols on a very smooth surface of 1,1,2,-trichloro-1,2,2,-trifluoroethane (FC-732) film deposited on a silicon plate. The authors considered the liquid absorption and/or retention (swelling) processes responsible for the observed hysteresis. In this paper hysteresis is considered to be due to the liquid film left behind the drop during retreating of its contact line. Using the contact angle hysteresis an approach is suggested for evaluation of the solid surface free energy. Molecular spacing and the film structure are discussed to explain the difference in n-alkanes and n-alcohols behaviour as well as to explain the difference between dispersion free energy gamma(s)(d) and total surface free energy gamma(s)(tot) of FC-732, as determined from the advancing contact angles and the hysteresis, respectively.

  11. Evaluation of pigment location in tinted soft contact lenses.

    PubMed

    Jung, Ji Won; Han, Sun Hyup; Kim, Sang Ah; Kim, Eung Kweon; Seo, Kyoung Yul; Kim, Tae-Im

    2016-06-01

    The purpose of this study was to investigate efficient methods to evaluate the pigment layer location of tinted soft contact lenses and to assess various lens products on the market using those methods. Two types of tinted soft contact lenses with known pigment location embedded or back surface were manufactured and examined. Light microscopy (LM), focused ion beam milling and scanning electron microscopy (FIB-SEM), and Fourier-domain optical coherence tomography (FD-OCT) were used to examine the pigment layer. Lens surface roughness was also measured using atomic force microscopy. In the second part of the experiment, pigment location and surface roughness of a clear lens (Lens A) and eight commercially-available tinted soft contact lenses (Lens B-I) were evaluated using FIB-SEM and FD-OCT. Pigment location could be reliably determined with FIB-SEM and FD-OCT. With LM, 40% of the lens sections were broken or deformed during slide preparation. The pigment particles in Lens B were buried below the front surface and there were no significant differences of roughness between the front and back surfaces. However, all tinted lenses with surface pigment had significant difference of roughness between front and back surfaces at the pigmented area. The FIB-SEM and FD-OCT could reliably locate the pigment layer of tinted soft contact lenses. In addition, lens surface roughness was influenced by pigment layer location. Copyright © 2016 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

  12. Apparent contact angle and contact angle hysteresis on liquid infused surfaces

    NASA Astrophysics Data System (ADS)

    Semprebon, Ciro; McHale, Glen; Kusumaatmaja, Halim

    We theoretically investigate the apparent contact angle and contact angle hysteresis of a droplet placed on a liquid infused surface. We show that the apparent contact angle is not uniquely defined by material parameters, but also has a strong dependence on the relative size between the droplet and its surrounding wetting ridge formed by the infusing liquid. We derive a closed form expression for the contact angle in the limit of vanishing wetting ridge, and compute the correction for small but finite ridge, which corresponds to an effective line tension term. We also predict contact angle hysteresis on liquid infused surfaces generated by the pinning of the contact lines by the surface corrugations. Our analytical expressions for both the apparent contact angle and contact angle hysteresis can be interpreted as `weighted sums' between the contact angles of the infusing liquid relative to the droplet and surrounding gas phases, where the weighting coefficients are given by ratios of the fluid surface tensions.

  13. Apparent contact angle and contact angle hysteresis on liquid infused surfaces.

    PubMed

    Semprebon, Ciro; McHale, Glen; Kusumaatmaja, Halim

    2016-12-21

    We theoretically investigate the apparent contact angle and contact angle hysteresis of a droplet placed on a liquid infused surface. We show that the apparent contact angle is not uniquely defined by material parameters, but also has a dependence on the relative size between the droplet and its surrounding wetting ridge formed by the infusing liquid. We derive a closed form expression for the contact angle in the limit of vanishing wetting ridge, and compute the correction for small but finite ridge, which corresponds to an effective line tension term. We also predict contact angle hysteresis on liquid infused surfaces generated by the pinning of the contact lines by the surface corrugations. Our analytical expressions for both the apparent contact angle and contact angle hysteresis can be interpreted as 'weighted sums' between the contact angles of the infusing liquid relative to the droplet and surrounding gas phases, where the weighting coefficients are given by ratios of the fluid surface tensions.

  14. Contact-angle hysteresis on super-hydrophobic surfaces.

    PubMed

    McHale, G; Shirtcliffe, N J; Newton, M I

    2004-11-09

    The relationship between perturbations to contact angles on a rough or textured surface and the super-hydrophobic enhancement of the equilibrium contact angle is discussed theoretically. Two models are considered. In the first (Wenzel) case, the super-hydrophobic surface has a very high contact angle and the droplet completely contacts the surface upon which it rests. In the second (Cassie-Baxter) case, the super-hydrophobic surface has a very high contact angle, but the droplet bridges across surface protrusions. The theoretical treatment emphasizes the concept of contact-angle amplification or attenuation and distinguishes between the increases in contact angles due to roughening or texturing surfaces and perturbations to the resulting contact angles. The theory is applied to predicting contact-angle hysteresis on rough surfaces from the hysteresis observable on smooth surfaces and is therefore relevant to predicting roll-off angles for droplets on tilted surfaces. The theory quantitatively predicts a "sticky" surface for Wenzel-type surfaces and a "slippy" surface for Cassie-Baxter-type surfaces.

  15. Comparison of surface roughness and bacterial adhesion between cosmetic contact lenses and conventional contact lenses.

    PubMed

    Ji, Yong Woo; Cho, Young Joo; Lee, Chul Hee; Hong, Soon Ho; Chung, Dong Yong; Kim, Eung Kweon; Lee, Hyung Keun

    2015-01-01

    To compare physical characteristics of cosmetic contact lenses (Cos-CLs) and conventional contact lenses (Con-CLs) that might affect susceptibility to bacterial adhesion on the contact lens (CL) surface. Surface characteristics of Cos-CLs and Con-CLs made from the same material by the same manufacturer were measured by atomic force microscopy (AFM) and scanning electron microscopy. To determine the extent and rate of bacterial adhesion, Cos-CL and Con-CL were immersed in serum-free Roswell Park Memorial Institute media containing Staphylococcus aureus or Pseudomonas aeruginosa. Additionally, the rate of removal of adherent bacteria was evaluated using hand rubbing or immersion in multipurpose disinfecting solutions (MPDS). The mean surface roughness (root mean square and peak-to-valley value) measured by AFM was significantly higher for Cos-CL than for Con-CL. At each time point, significantly more S. aureus and P. aeruginosa adhered to Cos-CL than to Con-CL, which correlated with the surface roughness of CL. In Cos-CL, bacteria were mainly found on the tinted surface rather than on the noncolored or convex areas. Pseudomonas aeruginosa attached earlier than S. aureus to all types of CL. However, P. aeruginosa was more easily removed from the surface of CL than S. aureus by hand rubbing or MPDS soaking. Increased surface roughness is an important physical factor for bacterial adhesion in Cos-CL, which may explain why rates of bacterial keratitis rates are higher in Cos-CL users in CL physical characteristics.

  16. 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.

  17. 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.

  18. 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

    2016-05-04

    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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Investigation of drop dynamic contact angle on copper surface

    NASA Astrophysics Data System (ADS)

    Orlova, Evgenija; Feoktistov, Dmitriy; Kuznetsov, Geniy

    2015-01-01

    This paper presents experimental results of the studying the effect of surface roughness, microstructure and flow rate on the dynamic contact angle at spreading of distilled non deaerate water drop on a solid horizontal substrates. Copper substrates with different roughness have been investigated. For each substrate static contact angles depending on volume flow rate have been obtained using shadow system. Increasing the volume flow rate resulted in an increase of the static contact angle. It was found that with increasing surface roughness dynamic contact angle arises. Also difference in formation of the equilibrium contact angle at low and high rates of drop growth has been detected.

  20. 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

    ... ADMINISTRATION National Contact Center; Submission for OMB Review; National Contact Center Customer Evaluation... renewal of a previously approved information collection requirement regarding the National Contact Center... 20405. Please cite OMB Control No. 3090-0278, National Contact Center Customer Evaluation Survey, in all...

  1. Fabrication of zero contact angle ultra-super hydrophilic surfaces.

    PubMed

    Jothi Prakash, C G; Clement Raj, C; Prasanth, R

    2017-06-15

    Zero contact angle surfaces have been created with the combined effect of nanostructure and UV illumination. The contact angle of titanium surface has been optimized to 3.25°±1°. with nanotubular structures through electrochemical surface modification. The porosity and surface energy of tubular TiO2 layer play critical role over the surface wettability and the hydrophilicity of the surface. The surface free energy has been enhanced from 23.72mJ/m(2) (bare titanium surface) to 87.11mJ/m(2) (nanotubular surface). Similar surface with TiO2 nanoparticles coating shows superhydrophilicity with contact angle up to 5.63°±0.95°. This implies liquid imbibition and surface curvature play a crucial role in surface hydrophilicity. The contact angle has been further reduced to 0°±0.86° by illuminating the surface with UV radiation. Results shows that by tuning the nanotube morphology, highly porous surfaces can be fabricated to reduce contact angle and enhance wettability. This study provides an insight into the inter-relationship between surface structural factors and ultra-superhydrophilic surfaces which can help to optimize thermal hydraulic and self cleaning surfaces.

  2. Modeling contact angle hysteresis on chemically patterned and superhydrophobic surfaces.

    PubMed

    Kusumaatmaja, H; Yeomans, J M

    2007-05-22

    We investigate contact angle hysteresis on chemically patterned and superhydrophobic surfaces, as the drop volume is quasistatically increased and decreased. We consider both two (cylindrical drops) and three (spherical drops) dimensions using analytical and numerical approaches to minimize the free energy of the drop. In two dimensions, we find, in agreement with other authors, a slip, jump, stick motion of the contact line. In three dimensions, this behavior persists, but the position and magnitude of the contact line jumps are sensitive to the details of the surface patterning. In two dimensions, we identify analytically the advancing and receding contact angles on the different surfaces, and we use numerical insights to argue that these provide bounds for the three-dimensional cases. We present explicit simulations to show that a simple average over the disorder is not sufficient to predict the details of the contact angle hysteresis and to support an explanation for the low contact angle hysteresis of suspended drops on superhydrophobic surfaces.

  3. Alternative methods to model frictional contact surfaces using NASTRAN

    NASA Technical Reports Server (NTRS)

    Hoang, Joseph

    1992-01-01

    Elongated (slotted) holes have been used extensively for the integration of equipment into Spacelab racks. In the past, this type of interface has been modeled assuming that there is not slippage between contact surfaces, or that there is no load transfer in the direction of the slot. Since the contact surfaces are bolted together, the contact friction provides a load path determined by the normal applied force (bolt preload) and the coefficient of friction. Three alternate methods that utilize spring elements, externally applied couples, and stress dependent elements are examined to model the contacted surfaces. Results of these methods are compared with results obtained from methods that use GAP elements and rigid elements.

  4. Wettability and Contact Time on a Biomimetic Superhydrophobic Surface.

    PubMed

    Liang, Yunhong; Peng, Jian; Li, Xiujuan; Huang, Jubin; Qiu, Rongxian; Zhang, Zhihui; Ren, Luquan

    2017-03-02

    Inspired by the array microstructure of natural superhydrophobic surfaces (lotus leaf and cicada wing), an array microstructure was successfully constructed by high speed wire electrical discharge machining (HS-WEDM) on the surfaces of a 7075 aluminum alloy without any chemical treatment. The artificial surfaces had a high apparent contact angle of 153° ± 1° with a contact angle hysteresis less than 5° and showed a good superhydrophobic property. Wettability, contact time, and the corresponding superhydrophobic mechanism of artificial superhydrophobic surface were investigated. The results indicated that the micro-scale array microstructure was an important factor for the superhydrophobic surface, while different array microstructures exhibited different effects on the wettability and contact time of the artificial superhydrophobic surface. The length (L), interval (S), and height (H) of the array microstructure are the main influential factors on the wettability and contact time. The order of importance of these factors is H > S > L for increasing the apparent contact angle and reducing the contact time. The method, using HS-WEDM to fabricate superhydrophobic surface, is simple, low-cost, and environmentally friendly and can easily control the wettability and contact time on the artificial surfaces by changing the array microstructure.

  5. Wettability and Contact Time on a Biomimetic Superhydrophobic Surface

    PubMed Central

    Liang, Yunhong; Peng, Jian; Li, Xiujuan; Huang, Jubin; Qiu, Rongxian; Zhang, Zhihui; Ren, Luquan

    2017-01-01

    Inspired by the array microstructure of natural superhydrophobic surfaces (lotus leaf and cicada wing), an array microstructure was successfully constructed by high speed wire electrical discharge machining (HS-WEDM) on the surfaces of a 7075 aluminum alloy without any chemical treatment. The artificial surfaces had a high apparent contact angle of 153° ± 1° with a contact angle hysteresis less than 5° and showed a good superhydrophobic property. Wettability, contact time, and the corresponding superhydrophobic mechanism of artificial superhydrophobic surface were investigated. The results indicated that the micro-scale array microstructure was an important factor for the superhydrophobic surface, while different array microstructures exhibited different effects on the wettability and contact time of the artificial superhydrophobic surface. The length (L), interval (S), and height (H) of the array microstructure are the main influential factors on the wettability and contact time. The order of importance of these factors is H > S > L for increasing the apparent contact angle and reducing the contact time. The method, using HS-WEDM to fabricate superhydrophobic surface, is simple, low-cost, and environmentally friendly and can easily control the wettability and contact time on the artificial surfaces by changing the array microstructure. PMID:28772613

  6. Shape of red blood cells in contact with artificial surfaces.

    PubMed

    Grzhibovskis, Richards; Krämer, Elisabeth; Bernhardt, Ingolf; Kemper, Björn; Zanden, Carl; Repin, Nikolay V; Tkachuk, Bogdan V; Voinova, Marina V

    2017-03-01

    The phenomenon of physical contact between red blood cells and artificial surfaces is considered. A fully three-dimensional mathematical model of a bilayer membrane in contact with an artificial surface is presented. Numerical results for the different geometries and adhesion intensities are found to be in agreement with experimentally observed geometries obtained by means of digital holographic microscopy.

  7. 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 8 GPa, while those of the surfaces ranged from 0.5 to 4 GPa. The hardness values of the traps ranged from 0.005 to 0.22 GPa, while those of the surfaces ranged from 0.02 to 0.2 GPa. 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.

  8. Thermodynamic modeling of contact angles on rough, heterogeneous surfaces.

    PubMed

    Long, J; Hyder, M N; Huang, R Y M; Chen, P

    2005-12-30

    Theoretical modelling for contact angle hysteresis carried out to date has been mostly limited to several idealized surface configurations, either rough or heterogeneous surfaces. This paper presents a preliminary study on the thermodynamics of contact angles on rough and heterogeneous surfaces by employing the principle of minimum free energy and the concept of liquid front. Based on a two-dimensional regular model surface, a set of relations were obtained, which correlate advancing, receding and system equilibrium contact angles to surface topography, roughness and heterogeneity. It was found that system equilibrium contact angles (theta(ES)) can be expressed as a function of surface roughness factor (delta) and the Cassie contact angle (theta(C)): costheta(ES) = deltacostheta(C). This expression can be reduced to the classical Wenzel equation.: theta(ES) = theta(W) for rough but homogeneous surfaces, and the classical Cassie equation theta(ES) = theta(C) for heterogeneous but smooth surfaces. A non-dimensional parameter called surface feature factor (omega) was proposed to classify surfaces into three categories (types): roughness-dominated, heterogeneity-dominated and mixed-rough-heterogeneous. The prediction of advancing and receding contact angles of a surface is dependent on which category the surface belongs to. The thermodynamic analysis of contact angle hysteresis was further extended from the regular model surface to irregular surfaces; consistent results were obtained. The current model not only agrees well with the models previously studied by other researchers for idealized surfaces, but also explores more possibilities to explain the reported experimental results/observations that most existing theories could not explain.

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

    USDA-ARS?s Scientific Manuscript database

    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,...

  10. Is there a link between blastomere contact surfaces of day 3 embryos and live birth rate?

    PubMed Central

    2012-01-01

    Background Cell-cell communication and adhesion are essential for the compaction process of early stage embryos. The aim of this study was to develop a non-invasive objective calculation system of embryo compaction in order to test the hypothesis that embryos with a larger mean contact surface result in a higher live birth rate compared to embryos with a lower mean contact surface. Methods Multilevel images of 474 embryos transferred on day 3 were evaluated by the Cellify software. This software calculates the contact surfaces between the blastomeres. The primary outcome of this study was live birth. An ideal range of contact surface was determined and the positive and negative predictive value, the sensitivity, the specificity and the area under the curve for this new characteristic were calculated. Results In total, 115 (24%) transferred embryos resulted in a live birth. Selection of an embryo for transfer on its mean contact surface could predict live birth with a high sensitivity (80%) and high negative predicting value (83%) but with a low positive predictive value (27%), a low specificity (31%) and low area under the ROC curve (0.56). The mean contact surface of embryos cultured in a single medium was significantly higher compared to the mean contact surface of embryos cultured in a sequential medium (p = 0.0003). Conclusions Neither the mean contact surface nor the number of contact surfaces of a day 3 embryo had an additional value in the prediction of live birth. The type of culture medium, however, had an impact on the contact surface of an embryo. Embryos cultured in a single medium had a significant larger contact surface compared to embryos cultured in the sequential medium. PMID:22963278

  11. Modeling liquid bridge between surfaces with contact angle hysteresis.

    PubMed

    Chen, H; Amirfazli, A; Tang, T

    2013-03-12

    This paper presents the behaviors of a liquid bridge when being compressed and stretched in a quasi-static fashion between two solid surfaces that have contact angle hysteresis (CAH). A theoretical model is developed to obtain the profiles of the liquid bridge given a specific separation between the surfaces. Different from previous models, both contact lines in the upper and lower surfaces were allowed to move when the contact angles reach their advancing or receding values. When the contact angles are between their advancing and receding values, the contact lines are pinned while the contact angles adjust to accommodate the changes in separation. Effects of CAH on both asymmetric and symmetric liquid bridges were analyzed. The model was shown to be able to correctly predict the behavior of the liquid bridge during a quasi-static compression/stretching loading cycle in experiments. Because of CAH, the liquid bridge can have two different profiles at the same separation during one loading and unloading cycle, and more profiles can be obtained during multiple cycles. The maximum adhesion force generated by the liquid bridge is found to be influenced by the CAH of surfaces. CAH also leads to energy cost during a loading cycle of the liquid bridge. In addition, the minimum separation between the two solid surfaces is shown to affect how the contact radii and angles change on the two surfaces as the liquid bridge is stretched.

  12. Variations in the corneal surface temperature with contact lens wear.

    PubMed

    Ooi, E H; Ng, E Y K; Purslow, C; Acharya, R

    2007-05-01

    This paper presents the two-dimensional simulation of heat propagation in the human eye model during contact lens wear with finite element analysis. Three types of contact lens are studied: Lotrafilcon A, Balafilcon A, and Etafilcon A. The models are solved for both steady and transient solutions. The corneal surface temperature during contact lens wear is found to decrease (average, 0.52 +/- 0.05 degrees C compared with a bare cornea for all lens types). A contact lens with a higher water content has a lower steady state temperature than a contact lens with a lower water content does. Various initial temperatures for the contact lens are found to affect the first 400 s of the temperature variation. When the initial temperature is lower than the corneal temperature, a reduction in temperature is observed during contact lens insertion while the opposite is observed when the initial temperature is higher than the corneal temperature. The increase in evaporation rate when a contact lens is worn increases the cooling effect on the ocular surface. This is suggested to be the cause of lower corneal surface temperature when wearing a contact lens.

  13. Hierarchically structured superoleophobic surfaces with ultralow contact angle hysteresis.

    PubMed

    Kota, Arun K; Li, Yongxin; Mabry, Joseph M; Tuteja, Anish

    2012-11-14

    Hierarchically structured, superoleophobic surfaces are demonstrated that display one of the lowest contact angle hysteresis values ever reported - even with extremely low-surface-tension liquids such as n-heptane. Consequently, these surfaces allow, for the first time, even ≈2 μL n-heptane droplets to bounce and roll-off at tilt angles. ≤ 2°.

  14. Copper Reduction and Contact Killing of Bacteria by Iron Surfaces.

    PubMed

    Mathews, Salima; Kumar, Ranjeet; Solioz, Marc

    2015-09-01

    The well-established killing of bacteria by copper surfaces, also called contact killing, is currently believed to be a combined effect of bacterial contact with the copper surface and the dissolution of copper, resulting in lethal bacterial damage. Iron can similarly be released in ionic form from iron surfaces and would thus be expected to also exhibit contact killing, although essentially no contact killing is observed by iron surfaces. However, we show here that the exposure of bacteria to iron surfaces in the presence of copper ions results in efficient contact killing. The process involves reduction of Cu(2+) to Cu(+) by iron; Cu(+) has been shown to be considerably more toxic to cells than Cu(2+). The specific Cu(+) chelator, bicinchoninic acid, suppresses contact killing by chelating the Cu(+) ions. These findings underline the importance of Cu(+) ions in the contact killing process and infer that iron-based alloys containing copper could provide novel antimicrobial materials. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

  15. Water contact angles and hysteresis of polyamide surfaces.

    PubMed

    Extrand, C W

    2002-04-01

    The wetting behavior of a series of aliphatic polyamides (PAs) has been examined. PAs with varying amide content and polyethylene (PE) were molded against glass to produce surfaces with similar roughness. After cleaning, chemical composition of the surfaces was verified with X-ray photoelectron spectroscopy. Advancing and receding contact angles were measured from small sessile water drops. Contact angles decreased with amide content while hysteresis increased. Hysteresis arose primarily from molecular interactions between the contact liquid and the solid substrates, rather than moisture absorption, variations in crystallinity, surface deformation, roughness, reorientation of amide groups, or surface contamination. Free energies of hysteresis were calculated from contact angles. For PE, which is composed entirely of nonpolar methylene groups, free energies were equivalent to the strength of dispersive van der Waals bonds. For PAs, free energies corresponded to fractional contributions from the dispersive methylene groups and polar amide groups.

  16. Contact mechanics for layered materials with randomly rough surfaces.

    PubMed

    Persson, B N J

    2012-03-07

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

  17. Multipoint contact modeling of nanoparticle manipulation on rough surface

    NASA Astrophysics Data System (ADS)

    Zakeri, M.; Faraji, J.; Kharazmi, M.

    2016-12-01

    In this paper, the atomic force microscopy (AFM)-based 2-D pushing of nano/microparticles investigated on rough substrate by assuming a multipoint contact model. First, a new contact model was extracted and presented based on the geometrical profiles of Rumpf, Rabinovich and George models and the contact mechanics theories of JKR and Schwartz, to model the adhesion forces and the deformations in the multipoint contact of rough surfaces. The geometry of a rough surface was defined by two main parameters of asperity height (size of roughness) and asperity wavelength (compactness of asperities distribution). Then, the dynamic behaviors of nano/microparticles with radiuses in range of 50-500 nm studied during their pushing on rough substrate with a hexagonal or square arrangement of asperities. Dynamic behavior of particles were simulated and compared by assuming multipoint and single-point contact schemes. The simulation results show that the assumption of multipoint contact has a considerable influence on determining the critical manipulation force. Additionally, the assumption of smooth surfaces or single-point contact leads to large error in the obtained results. According to the results of previous research, it anticipated that a particles with the radius less than about 550 nm start to slide on smooth substrate; but by using multipoint contact model, the predicted behavior changed, and particles with radii of smaller than 400 nm begin to slide on rough substrate for different height of asperities, at first.

  18. Bacterial adhesion capacity on food service contact surfaces.

    PubMed

    Fink, Rok; Okanovič, Denis; Dražič, Goran; Abram, Anže; Oder, Martina; Jevšnik, Mojca; Bohinc, Klemen

    2017-03-28

    The aim of this study was to analyse the adhesion of E. coli, P. aeruginosa and S. aureus on food contact materials, such as polyethylene terephthalate, silicone, aluminium, Teflon and glass. Surface roughness, streaming potential and contact angle were measured. Bacterial properties by contact angle and specific charge density were characterised. The bacterial adhesion analysis using staining method and scanning electron microscopy showed the lowest adhesion on smooth aluminium and hydrophobic Teflon for most of the bacteria. However, our study indicates that hydrophobic bacteria with high specific charge density attach to those surfaces more intensively. In food services, safety could be increased by selecting material with low adhesion to prevent cross contamination.

  19. Role of Surface Roughness in Hysteresis during Adhesive Elastic Contact.

    PubMed

    Kesari, Haneesh; Doll, Joseph C; Pruitt, Beth L; Cai, Wei; Lew, Adrian J

    2010-12-01

    In experiments that involve contact with adhesion between two surfaces, as found in atomic force microscopy or nanoindentation, two distinct contact force (P) vs. indentation-depth (h) curves are often measured depending on whether the indenter moves towards or away from the sample. The origin of this hysteresis is not well understood and is often attributed to moisture, plasticity or viscoelasticity. Here we report experiments that show that hysteresis can exist in the absence of these effects, and that its magnitude depends on surface roughness. We develop a theoretical model in which the hysteresis appears as the result of a series of surface instabilities, in which the contact area grows or recedes by a finite amount. The model can be used to estimate material properties from contact experiments even when the measured P-h curves are not unique.

  20. Modeling of moving contact lines on electrically charged heated surfaces

    NASA Astrophysics Data System (ADS)

    Ajaev, Vladimir

    2011-11-01

    Local fluid flow and heat transfer near moving contact lines on heated surfaces is usually described by mathematical models incorporating the effects of evaporation, surface tension, thermocapillarity, and disjoining pressure due to London-van der Waals forces. However, this description is not accurate for the cases when electric charges in the liquid and on the heated surface are present, which is usually the case in applications involving water and liquid metals. We develop a model which incorporates the electrostatic effects into the standard lubrication-type model of a contact line on a heated surface. The gas phase above the liquid is assumed to be pure vapor and the macroscopically dry region of the solid is covered with an adsorbed film. The local liquid-vapor interface shapes and the apparent contact angle are described as functions of the temperature and the charge density at the solid surface.

  1. Contact angle hysteresis on regular pillar-like hydrophobic surfaces.

    PubMed

    Yeh, Kuan-Yu; Chen, Li-Jen; Chang, Jeng-Yang

    2008-01-01

    A series of pillar-like patterned silicon wafers with different pillar sizes and spacing are fabricated by photolithography and further modified by a self-assembled fluorosilanated monolayer. The dynamic contact angles of water on these surfaces are carefully measured and found to be consistent with the theoretical predictions of the Cassie model and the Wenzel model. When a water drop is at the Wenzel state, its contact angle hysteresis increases along with an increase in the surface roughness. While the surface roughness is further raised beyond its transition roughness (from the Wenzel state to the Cassie state), the contact angle hysteresis (or receding contact angle) discontinuously drops (or jumps) to a lower (or higher) value. When a water drop is at the Cassie state, its contact angle hysteresis strongly depends on the solid fraction and has nothing to do with the surface roughness. Even for a superhydrophobic surface, the contact angle hysteresis may still exhibit a value as high as 41 degrees for the solid fraction of 0.563.

  2. 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.

  3. 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.

  4. Cylindrical roller bearings with profiled contacting surfaces

    NASA Astrophysics Data System (ADS)

    Creţu, S. S.

    2017-02-01

    An initial loading of cylindrical roller bearings in the elastic-plastic domain was performed to induce elastic shakedown phenomena able to change the basic profiles of both, rollers and raceways, which endorses a different value for the basic reference rating life. Fatigue life tests carried out on four lots of NJ206 cylindrical roller bearings revealed much higher values of L10 and Lm criteria for the bearings lots which experienced a suitable initial loading operation in the elastic-plastic domain. The reference rating lives, evaluated by using the lamina technique, confirmed the superiority of bearings lots which undergone an appropriate primary loading in the elastic-plastic domain.

  5. Mechanical contact between rough surfaces at low load

    NASA Astrophysics Data System (ADS)

    Lu, Pin; O'Shea, S. J.

    2012-11-01

    A model is developed to describe the initial contact between rough surfaces. The Greenwood-Williamson statistical approach is used with exponential or Weibull asperity height distributions, and modified with the relative displacement between the surfaces referenced to the initial contact of the highest asperity (within a given area) at zero load. This form provides a framework for investigating contact at low loads or contact over small area e.g. as found in microfabricated structures. The approach gives the expected number of asperities touching, the real area of contact and the normal force in terms of the indentation. The model results show that for hard surface materials (e.g. Silicon), very few asperities may be in contact at low loads (˜1 µN) even over large nominal surface areas (˜20 × 20 µm2), in accordance with observations drawn from microfabrication experiments. This suggests an analytical means to bridge nanoscale concepts and approaches (e.g. superlubricity, friction at a single asperity) to microscale structures.

  6. Drop impact on soft surfaces: beyond the static contact angles.

    PubMed

    Rioboo, Romain; Voué, Michel; Adão, Helena; Conti, Joséphine; Vaillant, Alexandre; Seveno, David; De Coninck, Joël

    2010-04-06

    The wettability of cross-linked poly(dimethylsiloxane) elastomer films and of octadecyltrichlorosilane self-assembled monolayers with water has been measured and compared using various methods. Contact angle hysteresis values were compared with values reported in the literature. A new method to characterize advancing, receding contact angles, and hysteresis using drop impact have been tested and compared with usual methods. It has been found that for the rigid surfaces the drop impact method is comparable with other methods but that for elastomer surfaces the hysteresis is function of the drop impact velocity which influences the extent of the deformation of the soft surface at the triple line.

  7. 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.

  8. 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. Copyright © 2011 Elsevier Inc. All rights reserved.

  9. Contact angle of a nanodrop on a nanorough solid surface.

    PubMed

    Berim, Gersh O; Ruckenstein, Eli

    2015-02-21

    The contact angle of a cylindrical nanodrop on a nanorough solid surface is calculated, for both hydrophobic and hydrophilic surfaces, using the density functional theory. The emphasis of the paper is on the dependence of the contact angle on roughness. The roughness is modeled by rectangular pillars of infinite length located on the smooth surface of a substrate, with fluid-pillar interactions different in strength from the fluid-substrate ones. It is shown that for hydrophobic substrates the trend of the contact angle to increase with increasing roughness, which was noted in all previous studies, is not universally valid, but depends on the fluid-pillar interactions, pillar height, interpillar distance, as well as on the size of the drop. For hydrophilic substrate, an unusual kink-like dependence of the contact angle on the nanodrop size is found which is caused by the change in the location of the leading edges of the nanodrop on the surface. It is also shown that the Wenzel and Cassie-Baxter equations can not explain all the peculiarities of the contact angle of a nanodrop on a nanorough surface.

  10. Contact angle hysteresis on textured surfaces with nanowire clusters.

    PubMed

    Liao, Ying-Chih; Chiang, Cheng-Kun; Lu, Yen-Wen

    2013-04-01

    Nanowire arrays with various agglomeration patterns were synthesized by adjusting the solvent evaporation rates. Nanowires with 200 nm diameter and 2-25 microm in length were fabricated from an anodic aluminum oxide (AAO) porous template. Various drying treatments were applied to develop nanostructured surfaces with topological differences. Due to surface tension forces, copper nanowires after thermal and evaporative drying treatments agglomerated into clusters, while supercritical drying technique provided excellent bundled-free and vertically-standing nanowire arrays. Although all dried surfaces exhibited hydrophobic nature, the contact angle hysteresis, or the difference between advancing and receding angles, was found to be larger on those surfaces with bundled nanowire clusters. To explain the difference, the wetted solid fraction on each surface was calculated using the Cassie-Baxter model to show that the hysteresis was contributed by liquid/solid contact area on the textured surfaces.

  11. Contact angle hysteresis on randomly rough surfaces: a computational study.

    PubMed

    David, Robert; Neumann, A Wilhelm

    2013-04-09

    Wetting is important in many applications, and the solid surfaces being wet invariably feature some amount of surface roughness. A free energy-based computational simulation is used to study the effect of roughness on wetting and especially contact angle hysteresis. On randomly rough, self-affine surfaces, it is found that hysteresis depends primarily on the value of the Wenzel roughness parameter r, increasing in proportion with r - 1. Micrometer-level roughness causes hysteresis of a few degrees.

  12. 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.

  13. 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.

  14. Determination of near-surface plastic deformation in sliding contacts

    NASA Technical Reports Server (NTRS)

    Kennedy, F. E., Jr.; Grotelueschen, L. P.

    1984-01-01

    It is pointed out that substantial plastic deformation occurs on and near the contact surfaces, when two solid bodies slide against each other without lubrication. It has been found that this deformation plays an important role in the tribological behavior of the sliding contact. The present investigation has the objective to develop an analytical model to predict the near-surface plastic deformation resulting from a single pass of one metallic surface over another. A finite element viscoplasticity program was written relating velocities to forces in a two-dimensional domain. The program was employed in the study of plastic deformation during a single pass of a hardened tool steel slider over a copper rub specimen. It was found that essentially the only material set in motion by the slider was directly under the contact zone. The agreement between values obtained in the analysis and experimental data is reasonably good.

  15. Evaluation of metal-nanowire electrical contacts by measuring contact end resistance

    NASA Astrophysics Data System (ADS)

    Park, Hongsik; Beresford, Roderic; Ha, Ryong; Choi, Heon-Jin; Shin, Hyunjung; Xu, Jimmy

    2012-06-01

    It is known, but often unappreciated, that the performance of nanowire (NW)-based electrical devices can be significantly affected by electrical contacts between electrodes and NWs, sometimes to the extent that it is really the contacts that determine the performance. To correctly understand and design NW device operation, it is thus important to carefully measure the contact resistance and evaluate the contact parameters, specific contact resistance and transfer length. A four-terminal pattern or a transmission line model (TLM) pattern has been widely used to measure contact resistance of NW devices and the TLM has been typically used to extract contact parameters of NW devices. However, the conventional method assumes that the electrical properties of semiconducting NW regions covered by a metal are not changed after electrode formation. In this study, we report that the conventional methods for contact evaluation can give rise to considerable errors because of an altered property of the NW under the electrodes. We demonstrate that more correct contact resistance can be measured from the TLM pattern rather than the four-terminal pattern and correct contact parameters including the effects of changed NW properties under electrodes can be evaluated by using the contact end resistance measurement method.

  16. Comparison of contact and non-contact asphere surface metrology devices

    NASA Astrophysics Data System (ADS)

    DeFisher, Scott; Fess, Edward M.

    2013-09-01

    Metrology of asphere surfaces is critical in the precision optics industry. Surface metrology serves as feedback into deterministic grinding and polishing platforms. Many different techniques and devices are used to qualify an asphere surface during fabrication. A contact profilometer is one of the most common measurement technologies used in asphere manufacturing. A profilometer uses a fine stylus to drag a diamond or ruby tip over the surface, resulting in a high resolution curved profile. Coordinate measuring machines (CMM) apply a similar concept by touching the optic with a ruby or silicon carbine sphere. A CMM is able to move in three dimensions while collecting data points along the asphere surface. Optical interferometers use a helium-neon laser with transmission spheres to compare a reflected wavefront from an asphere surface to a reference spherical wavefront. Large departure aspheres can be measured when a computer generated hologram (CGH) is introduced between the interferometer and the optic. OptiPro Systems has developed a non-contact CMM called UltraSurf. It utilizes a single point non-contact sensor, and high accuracy air bearings. Several different commercial non-contact sensors have been integrated, allowing for the flexibility to measure a variety of surfaces and materials. Metrology of a sphere and an asphere using a profilometer, CMM, Interferometer with a CGH, and the UltraSurf will be presented. Cross-correlation of the measured surface error magnitude and shape will be demonstrated. Comparisons between the techniques and devices will be also presented with attention to accuracy, repeatability, and overall measurement time.

  17. Surface structure influences contact killing of bacteria by copper

    PubMed Central

    Zeiger, Marco; Solioz, Marc; Edongué, Hervais; Arzt, Eduard; Schneider, Andreas S

    2014-01-01

    Copper kills bacteria rapidly by a mechanism that is not yet fully resolved. The antibacterial property of copper has raised interest in its use in hospitals, in place of plastic or stainless steel. On the latter surfaces, bacteria can survive for days or even weeks. Copper surfaces could thus provide a powerful accessory measure to curb nosocomial infections. We here investigated the effect of the copper surface structure on the efficiency of contact killing of Escherichia coli, an aspect which so far has received very little attention. It was shown that electroplated copper surfaces killed bacteria more rapidly than either polished copper or native rolled copper. The release of ionic copper was also more rapid from electroplated copper compared to the other materials. Scanning electron microscopy revealed that the bacteria nudged into the grooves between the copper grains of deposited copper. The findings suggest that, in terms of contact killing, more efficient copper surfaces can be engineered. PMID:24740976

  18. Surface structure influences contact killing of bacteria by copper.

    PubMed

    Zeiger, Marco; Solioz, Marc; Edongué, Hervais; Arzt, Eduard; Schneider, Andreas S

    2014-06-01

    Copper kills bacteria rapidly by a mechanism that is not yet fully resolved. The antibacterial property of copper has raised interest in its use in hospitals, in place of plastic or stainless steel. On the latter surfaces, bacteria can survive for days or even weeks. Copper surfaces could thus provide a powerful accessory measure to curb nosocomial infections. We here investigated the effect of the copper surface structure on the efficiency of contact killing of Escherichia coli, an aspect which so far has received very little attention. It was shown that electroplated copper surfaces killed bacteria more rapidly than either polished copper or native rolled copper. The release of ionic copper was also more rapid from electroplated copper compared to the other materials. Scanning electron microscopy revealed that the bacteria nudged into the grooves between the copper grains of deposited copper. The findings suggest that, in terms of contact killing, more efficient copper surfaces can be engineered.

  19. Capillary surfaces in a wedge: Differing contact angles

    NASA Technical Reports Server (NTRS)

    Concus, Paul; Finn, Robert

    1994-01-01

    The possible zero-gravity equilibrium configurations of capillary surfaces u(x, y) in cylindrical containers whose sections are (wedge) domains with corners are investigated mathematically, for the case in which the contact angles on the two sides of the wedge may differ. In such a situation the behavior can depart in significant qualitative ways from that for which the contact angles on the two sides are the same. Conditions are described under which such qualitative changes must occur. Numerically computed surfaces are depicted to indicate the behavior.

  20. Effective macroscopic adhesive contact behavior induced by small surface roughness

    NASA Astrophysics Data System (ADS)

    Kesari, Haneesh; Lew, Adrian J.

    2011-12-01

    In this paper we study a model contact problem involving adhesive elastic frictionless contact between rough surfaces. The problem's most notable feature is that it captures the phenomenon of depth-dependent-hysteresis (DDH) (e.g., see Kesari et al., 2010), which refers to the observation of different contact forces during the loading and unloading stages of a contact experiment. We specifically study contact between a rigid axi-symmetric punch and an elastic half-space. The roughness is represented as arbitrary periodic undulations in the punch's radial profile. These undulations induce multiple equilibrium contact regions between the bodies at each indentation-depth. Assuming that the system evolves so as to minimize its potential energy, we show that different equilibrium contact regions are selected during the loading and unloading stages at each indentation-depth, giving rise to DDH. When the period and amplitude of our model's roughness is reduced, we show that the evolution of the contact force and radius with the indentation-depth can be approximated with simpler curves, the effective macroscopic behavior, which we compute. Remarkably, the effective behavior depends solely on the amplitude and period of the model's roughness. The effective behavior is useful for estimating material properties from contact experiments displaying DDH. We show one such example here. Using the effective behavior for a particular roughness model (sinusoidal) we analyze the energy loss during a loading/unloading cycle, finding that roughness can toughen the interface. We also estimate the energy barriers between the different equilibrium contact regions at a fixed indentation-depth, which can be used to assess the importance of ambient energy fluctuations on DDH.

  1. Contact lens surface deposits increase the adhesion of Pseudomonas aeruginosa.

    PubMed

    Butrus, S I; Klotz, S A

    1990-08-01

    Soft contact lenses are bathed with tear components during wear and surface deposits accumulate. This report shows that Pseudomonas aeruginosa adheres to the surface of worn extended wear contact lenses in direct proportion to the amount of lens surface deposits as determined by the Rudko method (P less than .05). More hydrophobic bacteria adhered 10 times greater than bacteria which were relatively hydrophilic (P less than .005). The effect upon bacterial adhesion of enzyme and surfactant cleaning of worn extended wear contact lenses was investigated by two independent methods: one involving a high inoculum and the other a low inoculum of Pseudomonas. Treatment of worn lenses with commercially available enzymes such as papain and pork pancreatin as well as treatment with neuraminidase, mannosidase, glucosidase and alkylcarboxylic acid for as long as 48 hours failed to reduce subsequent bacterial adhesion in both the high and low inoculum experiments. We conclude that soft contact lens surface deposits are a major determinant in the adhesion of Pseudomonas aeruginosa to the worn lens surface and that enzyme cleaning of worn lenses does not significantly reduce bacterial adhesion.

  2. Contact angle measurements at the colemanite and realgar surfaces

    NASA Astrophysics Data System (ADS)

    Koca, Sabiha; Savas, Mehmet

    2004-03-01

    Colemanite is one of the most important boron minerals and covers an important part of Turkey's boron mineral deposits. The friable nature of the colemanite tends to produce a large amount of fines. Flotation appears to be a promising technique to recover colemanite from such fines. During flotation process, selectivity problem arises between colemanite and associated gangue minerals such as realgar. There is a close relationship between floatability of minerals and contact angle. Therefore, surface hydrophobicity of colemanite and realgar minerals were investigated by receding contact angle measurements in the absence and presence of flotation reagents. The water contact angle values at the colemanite surface remained almost unchanged at 32-35° in the solutions of potassium amyl xanthate (KAX), potassium ethyl xanthate (KEX) and petroleum sulphanate (R825) while another petroleum sulphanate (R840), sodium oleate and tallow amine (Armac-T) affected hydrophobicity of colemanite, and the contact angle values increased up to 47°. The contact angle values of 62, 63, 45, 46, 39, and 43° at the realgar surface were obtained in the solutions of KAX, KEX, sodium oleate, R825, R840 and Armac-T, respectively.

  3. 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...

  4. 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...

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

    PubMed Central

    Gagen, Debjani; Laubinger, Sara; Li, Zhijie; Petrescu, Matei S.; Brown, Evelyn S.; Smith, C. Wayne; Burns, Alan R.

    2010-01-01

    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 PMN contact with stromal keratocytes is CD18-dependent, while contact with collagen is CD18-independent. In the present study, we wished to extend these observations and determine if ICAM-1, a known ligand for CD18, mediates PMN contact with keratocytes during corneal wound healing. Uninjured and injured right corneas from C57Bl/6 wild type (WT) mice and ICAM-1−/− mice were processed for transmission electron microscopy and imaged for morphometric analysis. PMN migration, stromal thickness, and ICAM-1 staining were evaluated using light microscopy. Twelve hours after epithelial abrasion, PMN surface contact with paralimbal keratocytes in ICAM-1−/− corneas was reduced to ~50% of that observed in WT corneas; PMN surface contact with collagen was not affected. Stromal thickness (edema), keratocyte network surface area and keratocyte shape were similar in ICAM-1−/− and WT corneas. WT keratocyte ICAM-1 expression was detected at baseline and ICAM-1 staining intensity increased following injury. Since ICAM-1 is readily detected on mouse keratocytes and PMN-keratocyte surface contact in ICAM-1−/− mice is markedly reduced, the data suggest PMN adhesive interactions with keratocyte stromal networks is in part regulated by keratocyte ICAM-1 expression. PMID:20713042

  6. Clinical evaluation of Acuvue contact lenses with UV blocking characteristics.

    PubMed

    Hickson-Curran, S B; Nason, R J; Becherer, P D; Davis, R A; Pfeifer, J; Stiegemeier, M J

    1997-08-01

    In response to increasing scientific evidence which indicates that ultraviolet radiation (UVR) is a potential threat to ocular health, Acuvue contact lenses (Vistakon, Johnson & Johnson Vision Products Inc., Jacksonville, Florida) have been developed which incorporate an ultraviolet (UV) blocker within the lens polymer. Data are presented for the first clinical evaluation of Acuvue lenses with UV blocking characteristics. A double-masked, multicenter, prospective clinical trial involving 94 subjects was conducted. The study followed a randomized, parallel group design and consisted of 3 months of daily wear with two-weekly lens replacement. Two thirds of the subjects (61) wore the test lenses (Acuvue with UV blocker) and the remaining subjects (33) wore conventional Acuvue lenses (without UV blocker). Biomicroscopic evaluations indicated that the performance of the test and control lenses was clinically similar. No clinically relevant differences between the test and control lenses were noted in the subjective assessments of vision, comfort, or handling. In addition, no differences were shown for surface deposition, lens durability, visual acuity, and subjective symptoms. The study findings indicate that the addition of a UV blocker to Acuvue contact lenses has been achieved without affecting daily wear clinical performance. Because there is increasing evidence to suggest that the ocular tissues may be damaged by UVR, it is prudent for eye care practitioners to prescribe contact lenses that offer the benefits of both regular replacement and UV protection.

  7. Rapid microbial quantification of disinfected contact lens surfaces.

    PubMed

    Powers, Linda S; Snyder, Robert W; Wardell, Lois J

    2012-09-01

    The efficacy of disinfection of contact lenses is difficult to determine. We have monitored microbial contamination on surfaces and in fluids by intrinsic fluorescence of microbes and distinguished their metabolic states (viable cells, nonviable cells, and endospores). This approach is sensitive (10 cells), requires no added reagents or sample contact, and measurements can be made in near real time. The disinfection performance of AMO Easy Rub™ and Alcon No Rub™ contact lens solutions was compared with CVS-brand saline for contact lenses on contact lenses contaminated with Pseudomonas aeruginosa (ATCC 10145). Our aim is to show that intrinsic fluorescence measurements can yield real-time, critical information about the efficacy of contact lens decontamination products and protocols. Intrinsic fluorescence of Acuvue™ contact lenses (samples and controls) was measured before and after incubation with P. aeruginosa. Inoculated lenses were then cleaned and disinfected, according to directions for AMO Easy Rub™ and Alcon No Rub™, rubbed and rinsed with saline for contact lenses (the brand made a difference in the experiment), followed by measurement of the effectiveness of the disinfection procedure with the intrinsic fluorescence instrument. Both the sample lenses after disinfection and the control lenses were immediately placed in LB broth for outgrowth and measured by standard cell-counting methods. The experiments were performed in triplicate. The concentration of P. aeruginosa formed on the lenses by the above methods varied from 10(6)-10(13) cells/mL. All lenses that were cultured following cleaning yielded no colonies. However, 10(5)-10(9) cells/mL of the bacteria on the treated lenses remained viable when analyzed by intrinsic fluorescence methodology. These results indicate that a medically significant amount of bacteria remained on the contact lenses after disinfection and/or cleaning, which were viable but nonculturable and are likely to go

  8. Survival of norovirus surrogate on various food-contact surfaces.

    PubMed

    Kim, An-Na; Park, Shin Young; Bae, San-Cheong; Oh, Mi-Hwa; Ha, Sang-Do

    2014-09-01

    Norovirus (NoV) is an environmental threat to humans, which spreads easily from one infected person to another, causing foodborne and waterborne diseases. Therefore, precautions against NoV infection are important in the preparation of food. The aim of this study was to investigate the survival of murine norovirus (MNV), as a NoV surrogate, on six different food-contact surfaces: ceramic, wood, rubber, glass, stainless steel, and plastic. We inoculated 10(5) PFU of MNV onto the six different surface coupons that were then kept at room temperature for 28 days. On the food-contact surfaces, the greatest reduction in MNV was 2.28 log10 PFU/coupon, observed on stainless steel, while the lowest MNV reduction was 1.29 log10 PFU/coupon, observed on wood. The rank order of MNV reduction, from highest to lowest, was stainless steel, plastic, rubber, glass, ceramic, and wood. The values of d R (time required to reduce the virus by 90%) on survival plots of MNV determined by a modified Weibull model were 277.60 h (R(2) = 0.99) on ceramic, 492.59 h (R(2) = 0.98) on wood, 173.56 h on rubber (R(2) = 0.98), 97.18 h (R(2) = 0.94) on glass, 91.76 h (R(2) = 0.97) on stainless steel, and 137.74 h (R(2) = 0.97) on plastic. The infectivity of MNV on all food-contact surfaces remained after 28 days. These results show that MNV persists in an infective state on various food-contact surfaces for long periods. This study may provide valuable information for the control of NoV on various food-contact surfaces, in order to prevent foodborne disease.

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

    PubMed

    Terekhov, Alexander V; Hayward, Vincent

    2011-09-02

    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.

  10. RBS analysis of front contacts for surface-barrier detectors

    NASA Astrophysics Data System (ADS)

    Stojanović, M. S.; MilosavljeviĆ, M.; Subotić, K. M.; Boreli, F.; Wilson, I. H.; Novković, D.

    1990-04-01

    Surface-barrier detector structures based on Au, WTi and Au/WTi contacts on (111) n-Si were analysed. The metal layers were deposited by evaporation or sputtering to 40-100 nm thicknesses. The aim was to improve the thermal stability of the surface-barrier structures and retain the favourable detector properties of the Au/Si system. Contact structures which contain WTi layers have shown a much better thermal stability compared to the Au/Si system, but the properties of the detectors were poorer. The probable reasons are the reactivity of W and Ti with the thin oxide layer on the silicon surface and perhaps the higher energy of adatoms during sputter-deposition. Both effects can influence the degradation of the surface-barrier properties.

  11. Eccentricity effect of micropatterned surface on contact angle.

    PubMed

    Kashaninejad, Navid; Chan, Weng Kong; Nguyen, Nam-Trung

    2012-03-13

    This article experimentally shows that the wetting property of a micropatterned surface is a function of the center-to-center offset distance between successive pillars in a column, referred to here as eccentricity. Studies were conducted on square micropatterns which were fabricated on a silicon wafer with pillar eccentricity ranging from 0 to 6 μm for two different pillar diameters and spacing. Measurement results of the static as well as the dynamic contact angles on these surfaces revealed that the contact angle decreases with increasing eccentricity and increasing relative spacing between the pillars. Furthermore, quantification of the contact angle hysteresis (CAH) shows that, for the case of lower pillar spacing, CAH could increase up to 41%, whereas for the case of higher pillar spacing, this increment was up to 35%, both corresponding to the maximum eccentricity of 6 μm. In general, the maximum obtainable hydrophobicity corresponds to micropillars with zero eccentricity. As the pillar relative spacing decreases, the effect of eccentricity on hydrophobicity becomes more pronounced. The dependence of the wettability conditions of the micropatterned surface on the pillar eccentricity is attributed to the contact line deformation resulting from the changed orientation of the pillars. This finding provides additional insights in design and fabrication of efficient micropatterned surfaces with controlled wetting properties.

  12. Can foot anthropometric measurements predict dynamic plantar surface contact area?

    PubMed

    McPoil, Thomas G; Vicenzino, Bill; Cornwall, Mark W; Collins, Natalie

    2009-10-28

    Previous studies have suggested that increased plantar surface area, associated with pes planus, is a risk factor for the development of lower extremity overuse injuries. The intent of this study was to determine if a single or combination of foot anthropometric measures could be used to predict plantar surface area. Six foot measurements were collected on 155 subjects (97 females, 58 males, mean age 24.5 +/- 3.5 years). The measurements as well as one ratio were entered into a stepwise regression analysis to determine the optimal set of measurements associated with total plantar contact area either including or excluding the toe region. The predicted values were used to calculate plantar surface area and were compared to the actual values obtained dynamically using a pressure sensor platform. A three variable model was found to describe the relationship between the foot measures/ratio and total plantar contact area (R2 = 0.77, p < 0.0001)). A three variable model was also found to describe the relationship between the foot measures/ratio and plantar contact area minus the toe region (R2 = 0.76, p < 0.0001). The results of this study indicate that the clinician can use a combination of simple, reliable, and time efficient foot anthropometric measurements to explain over 75% of the plantar surface contact area, either including or excluding the toe region.

  13. 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

  14. A novel modelling and simulation method of hip joint surface contact stress.

    PubMed

    Wang, Monan; Wang, Lei; Li, Pengcheng; Fu, Yili

    2017-01-02

    Understanding the hip joint surface contact stress distribution characteristics is helpful to determine hip joint biomechanical features and abnormal pathological behavior. Firstly, a 3-dimensional static hip joint biomechanical model is built using analytical method of model in order to study biomechanical properties including bearing area, stress distribution and the peak value of the contact stress of the femoral head, which reveals the relationship between the biomechanical properties and its geometric parameters. Secondly, based on the finite element analysis of the hip joint model, the contact stress distribution on the surface of femoral head is acquired under the condition of the different joint force and the acetabulum coverage rate. Finally, according to the evaluation of the femoral head surface stress and contact stress peak under different load distribution, accuracy and universality of the biomechanical model is verified.

  15. 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

  16. Possible influence of surfactants and proteins on the efficiency of contact agar microbiological surface sampling.

    PubMed

    Deckers, Sylvie M; Sindic, Marianne; Anceau, Christine; Brostaux, Yves; Detry, Jean G

    2010-11-01

    Agar contact microbiological sampling techniques, based on a transfer of the microorganisms present on a surface to a culture medium, are widely used to assess and control surface cleanliness and to evaluate microbial contamination levels. The effectiveness of these techniques depends on many environmental parameters that influence the strength of attachment of the bacteria to the surface. In the present study, stainless steel and high density polyethylene surfaces were inoculated with known concentrations of Staphylococcus epidermidis. Following an experimental design, the surfaces were sampled with different types of replicate organism direct agar contact plates and Petrifilm; results indicated that recovery rates were influenced by the presence of egg white albumin or Tween 80 in the inoculum solutions or by the introduction of surfactants into the contact agar of the microbiological sampling techniques. The techniques yielded significantly different results, depending on sampling conditions, underlining the need for a standardization of laboratory experiments to allow relevant comparisons of such techniques.

  17. Contact angles of surfactant solutions on heterogeneous surfaces.

    PubMed

    Milne, A J B; Elliott, J A W; Amirfazli, A

    2015-02-28

    Using Gibbs' adsorption equation and a literature isotherm, a new general model to predict the contact angle of surfactant solutions on (smooth or rough) chemically heterogeneous surfaces is constructed based on the Cassie equation. The model allows for adsorption at the liquid-vapor, solid-liquid, and solid-vapor interfaces. Solid-vapor adsorption is allowed in order to model the autophobic effect on hydrophilic surfaces. Using representative values for the coefficients which describe adsorption at each interface, model predictions for contact angles as a function of f parameters (area fractions) and surfactant concentration are made for heterogeneous surfaces made up of different materials. On smooth surfaces, the f parameters serve as weighting factors determining how to combine the effects of surfactant adsorption on each material to predict the behavior on the heterogeneous surface. Due to the non-linear nature of the model, the inclusion of a small amount of hydrophobic material has a greater effect on a predominantly hydrophilic material than vice versa, explaining the result seen in literature that a small amount of hydrophobic contamination (such as oil) significantly increases contact angle on a hydrophilic surface. The fact that even a small amount of heterogeneity can greatly change experimental results could lead to incorrect experimental conclusions about surfactant adsorption if a surface were wrongly assumed to be homogeneous. Model predictions rapidly become more complex as the number of differently wettable materials present on the surface increases. Also, an approximately equal weighting of different materials generally leads to more complex behaviors compared to heterogeneous surfaces composed largely of a single material. Rough heterogeneous surfaces follow previous results for surfactant wetting of rough homogeneous surfaces, leading to an amplification/attenuation of surfactant effects for penetrated/unpenetrated wetting, and further

  18. 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.

  19. 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.

  20. Microbiological analysis of food contact surfaces in child care centers.

    PubMed

    Cosby, Catherine M; Costello, C A; Morris, W C; Haughton, B; Devereaux, M J; Harte, F; Davidson, P M

    2008-11-01

    A study of six child care centers was conducted to assess the microbiological quality of three food contact surfaces (one food serving surface and two food preparation surfaces) and one non-food contact surface (diaper changing surface) to determine the effectiveness of cleaning and sanitization procedures within the facilities. Aerobic plate counts (APCs) and Escherichia coli/coliform counts of 50-cm(2) areas on all surfaces were determined using standard microbiological swabbing methods. Samples were taken three times a day (preopening, lunchtime, and following final cleanup) twice per month for 8 months in each child care center (n = 288 sampling times). Mean log APCs over the survey period were 1.32, 1.71, 1.34, 1.96, 1.50, and 1.81 log CFU/50 cm(2) for the six centers. Mean log coliform counts were 0.15, 0.40, 0.33, 1.41, 0.28, and 1.12 CFU/50 cm(2) for the same centers. Coliforms were detected in 283 of 1,149 (24.7%) samples, with counts ranging from 1 to 2,000 CFU/50 cm(2), while E. coli was detected in 18 of 1,149 (1.6%) samples, with counts ranging from 1 to 35 CFU/50 cm(2). The findings of this study demonstrated that the extent of bacterial contamination was dependent on the center, time of day, and the area sampled. While no direct correlation between contamination and illness can be made, given the high risk of food-borne illness associated with children, microbial contamination of food contact or non-food contact surfaces is an aspect of food safety that requires more attention. Emphasis on training and the development of modified standard sanitation operating procedures for child care centers are needed to reduce potential hazards.

  1. Cultured human ocular surface epithelium on therapeutic contact lenses

    PubMed Central

    Girolamo, Nick Di; Chui, Jeanie; Wakefield, Denis; Coroneo, Minas T

    2007-01-01

    Background This study was initiated after observation of some intriguing epithelial growth properties of contact lenses used as a bandage for patients after pterygium surgery. Aim To determine the efficacy of culturing human ocular surface epithelial cells on therapeutic contact lenses in autologous serum with a view of using this system to transfer epithelial cells to patients with persistent corneal or limbal defects. Methods Excess graft tissue resected from patients undergoing pterygium surgery (n = 3) consisting of limbal epithelium was placed on siloxane–hydrogel contact lenses (lotrafilcon A and balafilcon A). Limbal explants were cultured in media with 10% autologous serum. Morphology, proliferative capacity and cytokeratin profile were determined by phase contrast, light and electron microscopy, and immunohistochemical analysis. Results Lotrafilcon A contact lenses sustained proliferation and migration from limbal tissue. Cells became confluent after 10–14 days and consisted of 2–3 layers with a corneal phenotype (CK3+/CK12+/CK19−) and a propensity to proliferate (p63+). Electron microscopy showed microvilli on the apical surface with adhesive projections, indicating that these cells were stable and likely to survive for a long term. Growth was not observed from limbal explants cultured on balafilcon A contact lenses. Conclusion A method for culturing human ocular surface epithelium on contact lenses that may facilitate expansion and transfer of autologous limbal epithelial cells while avoiding the risks associated with transplanting allogeneic tissue has been developed. This technique may be potentially useful for the treatment of patients with limbal stem cell deficiency. PMID:16987897

  2. Plasma surface modification of rigid contact lenses decreases bacterial adhesion.

    PubMed

    Wang, Yingming; Qian, Xuefeng; Zhang, Xiaofeng; Xia, Wei; Zhong, Lei; Sun, Zhengtai; Xia, Jing

    2013-11-01

    Contact lens safety is an important topic in clinical studies. Corneal infections usually occur because of the use of bacteria-carrying contact lenses. The current study investigated the impact of plasma surface modification on bacterial adherence to rigid contact lenses made of fluorosilicone acrylate materials. Boston XO and XO2 contact lenses were modified using plasma technology (XO-P and XO2-P groups). Untreated lenses were used as controls. Plasma-treated and control lenses were incubated in solutions containing Staphylococcus aureus or Pseudomonas aeruginosa. MTT colorimetry, colony-forming unit counting method, and scanning electron microscopy were used to measure bacterial adhesion. MTT colorimetry measurements showed that the optical density (OD) values of XO-P and XO2-P were significantly lower than those of XO and XO2, respectively, after incubation with S. aureus (P < 0.01). The OD value of XO-P was also much lower than that of XO after incubation with P. aeruginosa (P < 0.01). Colony-forming unit counting revealed that a significantly lower number of bacterial colonies attached to the XO-P versus XO lenses and to the XO2-P versus XO2 lenses incubated with S. aureus (P < 0.01). Fewer bacterial colonies attached to the XO-P versus XO lenses incubated with P. aeruginosa (P < 0.01). Further, scanning electron microscopy suggested different bacterial adhesion morphology on plasma-treated versus control lenses. Plasma surface modification can significantly decrease bacterial adhesion to fluorosilicone acrylate contact lenses. This study provides important evidence of a unique benefit of plasma technology in contact lens surface modification.

  3. Comparing contact angle measurements and surface tension assessments of solid surfaces.

    PubMed

    Cwikel, Dory; Zhao, Qi; Liu, Chen; Su, Xueju; Marmur, Abraham

    2010-10-05

    Four types of contact angles (receding, most stable, advancing, and "static") were measured by two independent laboratories for a large number of solid surfaces, spanning a large range of surface tensions. It is shown that the most stable contact angle, which is theoretically required for calculating the Young contact angle, is a practical, useful tool for wettability characterization of solid surfaces. In addition, it is shown that the experimentally measured most stable contact angle may not always be approximated by an average angle calculated from the advancing and receding contact angles. The "static" CA is shown in many cases to be very different from the most stable one. The measured contact angles were used for calculating the surface tensions of the solid samples by five methods. Meaningful differences exist among the surface tensions calculated using four previously known methods (Owens-Wendt, Wu, acid-base, and equation of state). A recently developed, Gibbsian-based correlation between interfacial tensions and individual surface tensions was used to calculate the surface tensions of the solid surfaces from the most stable contact angle of water. This calculation yielded in most cases higher values than calculated with the other four methods. On the basis of some low surface energy samples, the higher values appear to be justified.

  4. Tear film evaluation and management in soft contact lens wear: a systematic approach.

    PubMed

    Downie, Laura E; Craig, Jennifer P

    2017-09-01

    The human tear film is a highly ordered structure consisting of a thin layer of lipid on the surface and a thicker aqueous-mucin phase, which increases in mucin concentration toward the corneal epithelial cell layer. The health of the tear film and ocular surface influences the likelihood of being able to achieve successful contact lens wear. Contact lens discomfort and dryness are the most frequent reasons why contact lens wearers experience reduced wearing times, which can eventually lead to contact lens discontinuation. Comprehensive clinical assessment of tear film integrity and ocular surface health is therefore essential prior to commencing contact lens wear, to enable the ocular surface environment to be optimised to support lens wear. These parameters should also be evaluated over the course of contact lens wear, in order to identify any aspects requiring clinical management and ensure maintenance of optimal lens-wearing conditions. This review summarises current knowledge relating to the effects of soft contact lens wear on the tear film and ocular surface. It also provides a systematic approach to evaluating tear film and ocular surface integrity, in order to guide the clinical management of tear film anomalies with respect to contact lens wear. © 2017 Optometry Australia.

  5. 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.

  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.

  7. Contact between rough surfaces and a criterion for macroscopic adhesion

    PubMed Central

    Pastewka, Lars; Robbins, Mark O.

    2014-01-01

    At the molecular scale, there are strong attractive interactions between surfaces, yet few macroscopic surfaces are sticky. Extensive simulations of contact by adhesive surfaces with roughness on nanometer to micrometer scales are used to determine how roughness reduces the area where atoms contact and thus weakens adhesion. The material properties, adhesive strength, and roughness parameters are varied by orders of magnitude. In all cases, the area of atomic contact is initially proportional to the load. The prefactor rises linearly with adhesive strength for weak attractions. Above a threshold adhesive strength, the prefactor changes sign, the surfaces become sticky, and a finite force is required to separate them. A parameter-free analytic theory is presented that describes changes in these numerical results over up to five orders of magnitude in load. It relates the threshold adhesive strength to roughness and material properties, explaining why most macroscopic surfaces do not stick. The numerical results are qualitatively and quantitatively inconsistent with classical theories based on the Greenwood−Williamson approach that neglect the range of adhesion and do not include asperity interactions. PMID:24550489

  8. Magnetically induced decrease in droplet contact angle on nanostructured surfaces.

    PubMed

    Zhou, Qian; Ristenpart, William D; Stroeve, Pieter

    2011-10-04

    We report a magnetic technique for altering the apparent contact angle of aqueous droplets deposited on a nanostructured surface. Polymeric tubes with embedded superparamagnetic magnetite (Fe(3)O(4)) nanoparticles were prepared via layer-by-layer deposition in the 800 nm diameter pores of polycarbonate track-etched (PCTE) membranes. Etching away the original membrane yields a superparamagnetic film composed of mostly vertical tubes attached to a rigid substrate. We demonstrate that the apparent contact angle of pure water droplets deposited on the nanostructured film is highly sensitive to the ante situm strength of an applied magnetic field, decreasing linearly from 117 ± 1.3° at no applied field to 105 ± 0.4° at an applied field of approximately 500 G. Importantly, this decrease in contact angle did not require an inordinately strong magnetic field: a 15° decrease in contact angle was observed even with a standard alnico bar magnet. We interpret the observed contact angle behavior in terms of magnetically induced conformation changes in the film nanostructure, and we discuss the implications for reversibly switching substrates from hydrophilic to hydrophobic via externally tunable magnetic fields.

  9. Surface tension and contact with soft elastic solids

    NASA Astrophysics Data System (ADS)

    Style, Robert W.; Hyland, Callen; Boltyanskiy, Rostislav; Wettlaufer, John S.; Dufresne, Eric R.

    2013-11-01

    The Johnson-Kendall-Roberts theory is the basis of modern contact mechanics. It describes how two deformable objects adhere together, driven by adhesion energy and opposed by elasticity. Here we characterize the indentation of glass particles into soft, silicone substrates using confocal microscopy. We show that, whereas the Johnson-Kendall-Roberts theory holds for particles larger than a critical, elastocapillary lengthscale, it fails for smaller particles. Instead, adhesion of small particles mimics the adsorption of particles at a fluid interface, with a size-independent contact angle between the undeformed surface and the particle given by a generalized version of the Young's law. A simple theory quantitatively captures this behaviour and explains how solid surface tension dominates elasticity for small-scale indentation of soft materials.

  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. Differential MS2 Interaction with Food Contact Surfaces Determined by Atomic Force Microscopy and Virus Recovery.

    PubMed

    Shim, J; Stewart, D S; Nikolov, A D; Wasan, D T; Wang, R; Yan, R; Shieh, Y C

    2017-10-06

    Enteric viruses are recognized as a major etiology for U.S. foodborne infections. These viruses are easily transmitted via food contact surfaces. Understanding virus interactions with surfaces may facilitate developing improved means for their removal thus reducing transmission. Using MS2 coliphage as a virus surrogate, the strength of virus adhesion onto common food processing and preparation surfaces of polyvinyl chloride (PVC) and glass were assessed by atomic force microscopy (AFM) and virus recovery assays. The interaction forces of MS2 to various surfaces were measured from adhesion peaks in force-distance curves registered using a spherical bead probe pre-conjugated with MS2 particles. MS2 in PBS demonstrated approximately 5 times less adhesion force to glass [0.54 nano Newton (nN)] than to PVC (2.87 nN), P < 0.0001. This is consistent with the virus recovery assay, which shows 1.4-fold fewer virus plaque-forming units (PFU) recovered from PVC than from glass after identical inoculation and 24 hr-cold storage. The difference in adhesion was ascribed to both the intrinsic chemical characteristics and the substrate surface porosity, smooth glass vs. porous PVC. Incorporating a surfactant micellar solution of sodium dodecyl sulfate (SDS) into the PBS medium reduced the adhesion force of PVC (∼ 0 nN), and consistently increased virus recovery by 19%. With direct and indirect evidence of virus adhesion, this study illustrated a two-way assessment of virus adhesion for the initial evaluation of a potential means in mitigating virus adhesion to food contact surfaces.IMPORTANCE Spread of foodborne viruses is likely associated with their adhesive nature. Virus attachment on food contact surfaces has been evaluated by quantitating their recoveries from inoculated surfaces. This study aims to evaluate the microenvironment where nano-sized viruses interact with food contact surfaces, and to compare the virus adhesion differences using atomic force microscopy (AFM

  13. Evaluation of residue-residue contact prediction in CASP10

    PubMed Central

    Monastyrskyy, Bohdan; D’Andrea, Daniel; Fidelis, Krzysztof; Tramontano, Anna; Kryshtafovych, Andriy

    2013-01-01

    We present the results of the assessment of the intra-molecular residue-residue contact predictions from 26 prediction groups participating in the 10th round of the CASP experiment. The most recently developed direct coupling analysis methods did not take part in the experiment likely because they require a very deep sequence alignment not available for any of the 114 CASP10 targets. The performance of contact prediction methods was evaluated with the measures used in previous CASPs (i.e., prediction accuracy and the difference between the distribution of the predicted contacts and that of all pairs of residues in the target protein), as well as new measures, such as the Matthews correlation coefficient, the area under the precision-recall curve and the ranks of the first correctly and incorrectly predicted contact. We also evaluated the ability to detect inter-domain contacts and tested whether the difficulty of predicting contacts depends upon the protein length and the depth of the family sequence alignment. The analyses were carried out on the target domains for which structural homologs did not exist or were difficult to identify. The evaluation was performed for all types of contacts (short, medium, and long-range), with emphasis placed on long-range contacts, i.e. those involving residues separated by at least 24 residues along the sequence. The assessment suggests that the best CASP10 contact prediction methods perform at approximately the same level, and comparably to those participating in CASP9. PMID:23760879

  14. Continuous wear contact lens surface chemistry and wearability.

    PubMed

    Nicolson, Paul C

    2003-01-01

    Continuous wear (CW) contact lenses are defined as lenses composed of hydrogel polymers containing elements other than carbon, hydrogen, oxygen, and nitrogen that enhance oxygen permeability to an extent greater than water alone. Those elements are silicon and fluorine. Silicon is incorporated as siloxanes, and fluorine is used as fluoroalkyl. Despite the water present in CW lenses, they are not wearable without surface modification because of the tendency of siloxanes and fluoroakyls to move in the soft polymers, orient, and become enriched at the surface. Various methods of surface modification are discussed, with emphasis on the plasma technologies used by the two commercial CW lens products, Focus Night & Day and PureVision. Speculation about future directions in surface chemistry are also presented.

  15. 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.

  16. Investigation of Contact Fatigue of High Strength Steel Gears Subjected to Surface Treatment

    NASA Astrophysics Data System (ADS)

    Dimitrov, L.; Michalopoulos, D.; Apostolopoulos, Ch. Alk.; Neshkov, T. D.

    2009-10-01

    In this paper the contact fatigue resistance of gearwheel teeth, subjected to shot-peening treatment, was investigated experimentally and analytically. The main objective was the evaluation and prediction of fatigue crack initiation, propagation, direction, and rate. A specially designed experimental rig was used to test a number of spur gears with the following characteristics: (a) unhardened, thermally untreated unpeened surfaces, (b) thermally treated unpeened surfaces, (c) unhardened peened surfaces, and (d) thermally treated peened surfaces. The theoretical model assumed initiation and propagation of surface cracks of gears operating in the elastohydrodynamic lubrication regime while loading was due to simultaneous rolling and sliding. Finite element modeling was used for the calculation of the stress field at the gear teeth. Comparison of the experimental and analytical results showed considerable improvement in the contact fatigue strength of thermally treated gear teeth and especially those that underwent shot peening, which increased surface durability. The residual stresses induced by shot peening are mainly effective in stopping microcrack propagation. When shot peening is applied on thermally untreated gear teeth surface, it increases the contact fatigue life of the material by 17% at 7 × 105 loading cycles. If shot peening is applied on carburized gear teeth surfaces, it increases the surface fatigue life by approximately 8% at 106 cycles. Contact fatigue and eventual pitting are treated as a normal consequence of the operation of machine elements. To study this failure process different types of testing machines have been designed. The purpose of this paper is the presentation and evaluation of a new design experimental rig for studying contact fatigue damage of gear teeth subjected to different load patterns.

  17. Effect of contact lens surface properties on comfort, tear stability and ocular physiology.

    PubMed

    Vidal-Rohr, Maria; Wolffsohn, James S; Davies, Leon N; Cerviño, Alejandro

    2017-09-15

    Retrospective analysis of different contact lens wearing groups suggests lens surface lubricity is the main factor influencing contact lens comfort. However, the examined commercially available contact lenses differ in material and design as well as surface properties. Hence this study isolates the contribution of lens surface properties using an ultra-thin coating technology. Nineteen habitual contact lens wearers (21.6±1.7years) wore formofilcon B soft monthly disposable contact lenses with and without coating technology modified surface properties for a month each in a randomised double-masked cross-over study. OBJECTIVE NON-INVASIVE: breakup time (NIKBUT), NIKBUT average and ocular redness (Jenvis grading scale) were evaluated (Keratograph 5M) after 1 week and 1 month of wear. Symptoms were assessed using the Contact Lens Dry Eye Questionnaire (CLDEQ-8); perceived vision quality and subjective lens comfort at insertion, mid-day and end of the day were rated with four Visual Analog Scales. Perceived visual quality (F=5.049,p=0.037), contact lens dry eye symptoms (F=14.408,p=0.001) and subjective lens comfort (F=28.447,p<0.001) were better for coated compared to uncoated lenses. The surface coating postponed the lens dewetting (F=8.518,p=0.009) and increased the pre-lens tear film stability (F=5.626,p=0.029), but bulbar (F=0.340,p=0.567) and limbal (F=0.110,p=0.744) redness were similar for both contact lenses. No parameter changed significantly between a weeks' and months' wear (p>0.05). Lens surface wettability and ocular redness were not correlated to changes in symptoms (p>0.05). As previously hypothesised, enhancing the physical surface properties of a soft contact lens improves subjectively rated wearer comfort, which, in turn, should result in reduced contact lens discontinuation. Copyright © 2017 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

  18. [Evaluation of children with tuberculosis contact].

    PubMed

    Gutiérrez C, Daniela; Moreno M, Claudia; Araya D, Andrea; González L, Marcela

    2010-10-01

    Tuberculosis (TB) is a worldwide infectious disease, caused by Mycobacterium tuberculosis (Koch bacilli), that has re-emerged since the decade of the 80's in relation to the pandemic of HIV infection. Chile has one of the lowest TB prevalence rates in Latin America. In children, TB exhibits some differences from adult disease in terms of pathogenesis, clinical manifestations and probability of progression from the infected state to disease, making it more difficult to diagnose and increasing the likelihood of developing the disease once the infection is acquired. There is a National Program for the Prevention and Control of TB that allows us to develop prevention and chemoprophylaxis strategies. This article summarizes these strategies to guide the study and management of children in contact with TB patients.

  19. Tactile contact and evaluation of the toucher.

    PubMed

    Erceau, Damien; Guéguen, Nicolas

    2007-08-01

    The authors investigated the effect of touch on a person's evaluation of the toucher in a field setting. In the context of selling a 2nd-hand car, the authors instructed a male seller to slightly touch (or not touch) a man who was interested in the car. After the participant left the seller, a female confederate solicited him, asking him to evaluate the car seller on various dimensions. The results showed that for each dimension that the participants evaluated, the touch condition was associated with statistically higher positive evaluations of the toucher than the no-touch control condition.

  20. Non-Contact Ultrasonic Characterization of Angled Surface Defects

    NASA Astrophysics Data System (ADS)

    Edwards, R. S.; Dutton, B.; Rosli, M. H.; Clough, A. R.

    2011-06-01

    Surface ultrasonic waves have been shown to have many uses in non-destructive testing, in particular for gauging the depth of surface defects. Much of the previous work has assumed that these defects are oriented normal to the surface. However, this is not always the case; for example, rolling contact fatigue in rails propagates at an angle of around 25° to the surface, and this angle may affect the characterisation. We present results using non-contact ultrasonic methods to generate and detect ultrasound on samples with a range of defect angles, and compare these with finite element method (FEM) models. We use both electromagnetic acoustic transducers (EMATs) and laser ultrasound. The depth calibration when measuring ultrasound transmission is considered, and what affect the angle of a defect has. Several other methods of characterising crack depth and angle are also discussed, including the arrival times of reflected and mode-converted waves, the delay in the transmission of the high-frequency Rayleigh wave, and the enhancement of the signal at the defect in both the in-plane and out-of-plane components.

  1. 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.

  2. Effectiveness of domestic antibacterial products in decontaminating food contact surfaces.

    PubMed

    DeVere, Elizabeth; Purchase, Diane

    2007-06-01

    Four commercially available antibacterial products (two wipes and two sprays) were tested under laboratory conditions on a range of food contact surfaces (wood, glass, plastic, Microban incorporated plastic). The products' effectiveness at preventing cross-contamination of Escherichia coli and Staphylococcus aureus and the influence of surface type and drying time were assessed. Survival of the bacterial culture (approximately 400 colonies per 8 cm(2)) on the above preparation surfaces was determined using an in situ nitroblue tetrazolium (NBT) method. In the absence of any antibacterial products, both bacteria survived up to 120 min on all test surfaces with glass and plastic showing no reduction in bacterial number. The order of survival is: glass>plastic>Microban incorporated plastic>wood (<8%). The length of drying time did not affect the survival of either bacterium on glass and plastic surfaces. On wood and Microban incorporated plastic, E. coli appeared to be more sensitive to drying time than S. aureus. Only plastic appeared to affect the effectiveness of the antibacterial products, where the reduction in bacterial number was significantly lower than the other test surfaces (p<0.05). The overall results suggest the antibacterial products are effective in disinfecting food preparing surfaces, provided products instructions are carefully followed.

  3. Cleanability evaluation of ceramic glazes with nanometer far-infrared materials using contact angle measurement.

    PubMed

    Wang, Lijuan; Liang, Jinsheng; Di, Xingfu; Tang, Qingguo

    2014-05-01

    The cleanability of easy-to-clean ceramic glazes doped with nanometer far-infrared materials was compared with that of some high-quality household ceramic glazes from the market. The cleanability was evaluated by the contact angle measurement using a sessile drop method with a Dataphysics OCA-30 contact angle analyzer. The results showed that the difference of contact angles of water on the glazes before soiling and after cleaning could be used as a parameter for evaluating the cleanability of the glazes. The relationship between cleanability and surface properties, such as surface free energy and surface topography, was investigated. The surface free energy of the samples and their components were calculated using van Oss acid-base approach. By measuring advancing and receding contact angles, the contact angle hysteresis of the ceramic glazes due to the surface topography was investigated. It was shown that the cleanability of ceramic glazes containing nanometer far-infrared materials (NFIM) is better than that of household ceramic glazes from market, due to a higher ratio of electron-acceptor parameter to electron-donor parameter, which led to the effect of water hydration as well as better hydrophilic property and increased smoothness. The contact angle measurement not only accurately evaluates the cleanability of the ceramic glazes, but also has a contribution to the study of cleanability theory. Moreover, this method is simple, convenient and less sample-consumption.

  4. 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.

  5. A Mathematical Method to Calculate Tumor Contact Surface Area: An Effective Parameter to Predict Renal Function after Partial Nephrectomy.

    PubMed

    Hsieh, Po-Fan; Wang, Yu-De; Huang, Chi-Ping; Wu, Hsi-Chin; Yang, Che-Rei; Chen, Guang-Heng; Chang, Chao-Hsiang

    2016-07-01

    We proposed a mathematical formula to calculate contact surface area between a tumor and renal parenchyma. We examined the applicability of using contact surface area to predict renal function after partial nephrectomy. We performed this retrospective study in patients who underwent partial nephrectomy between January 2012 and December 2014. Based on abdominopelvic computerized tomography or magnetic resonance imaging, we calculated the contact surface area using the formula (2*π*radius*depth) developed by integral calculus. We then evaluated the correlation between contact surface area and perioperative parameters, and compared contact surface area and R.E.N.A.L. (Radius/Exophytic/endophytic/Nearness to collecting system/Anterior/Location) score in predicting a reduction in renal function. Overall 35, 26 and 45 patients underwent partial nephrectomy with open, laparoscopic and robotic approaches, respectively. Mean ± SD contact surface area was 30.7±26.1 cm(2) and median (IQR) R.E.N.A.L. score was 7 (2.25). Spearman correlation analysis showed that contact surface area was significantly associated with estimated blood loss (p=0.04), operative time (p=0.04) and percent change in estimated glomerular filtration rate (p <0.001). On multivariate analysis contact surface area and R.E.N.A.L. score independently affected percent change in estimated glomerular filtration rate (p <0.001 and p=0.03, respectively). On ROC curve analysis contact surface area was a better independent predictor of a greater than 10% change in estimated glomerular filtration rate compared to R.E.N.A.L. score (AUC 0.86 vs 0.69). Using this simple mathematical method, contact surface area was associated with surgical outcomes. Compared to R.E.N.A.L. score, contact surface area was a better predictor of functional change after partial nephrectomy. Copyright © 2016 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

  6. 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.

  7. 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...

  8. 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...

  9. Contact inhibition of phagocytosis in epithelial sheets: alterations of cell surface properties induced by cell-cell contacts.

    PubMed

    Vasiliev, J M; Gelfand, I M; Domnina, L V; Zacharova, O S; Ljubimov, A V

    1975-02-01

    Contact inhibition of phagocytosis was found to be characteristic for epithelial sheets formed in cultures by several cell types: normal and transformed mouse kidney cells, and differentiated mouse hepatoma cells. In these sheets most central cells surrounded by other cells had very low phagocytic activity. In contrast, marginal cells having a free edge were able to perform an active phagocytosis. Contact inhibition of phagocytosis was absent in dense cultures of mouse embryo fibroblasts and in cultures of anaplastic mouse hepatoma 22a. The upper surface of epithelial sheets was nonadhesive for prelabeled epithelial cells and fibroblasts. In contrast, the upper surface of dense cultures of mouse fibroblasts was adhesive for these cells. These and other data strengthen the suggestion that contact inhibition of phagocytosis is a result of different adhesiveness of the upper cell surface and of the surfaces near the free edge. Agents inhibiting cell surface movements at the free edges of marginal epithelial cells (cytochalasin, azide, sorbitol, low temperature) prevented adhesion of particles to these edges. Possibly, the surface of actively moving cytoplasmic processes is the only cell part that has adhesive properties necessary for the formation of attachments with other cellular and noncellular surfaces. In epithelial sheets, in contrast to fibroblast cultures, Colcemid did not activate movements of immobile contacting cell edges. These results indicate that mechanisms of contact immobilization of cell surface may be different in epithelium and fibroblasts. Firm contacts formed between epithelial cells are sufficient for stable immobilization of the surface; additional stabilization of the surface by microtubules is not essential. Fibroblasts do not form firm contacts and the Colcemid-sensitive stabilization process is essential for maintenance of the immobile state of their surfaces. Differences in the stability of cell surface immobilization produced by cell

  10. Surface conductance of graphene from non-contact resonant cavity

    PubMed Central

    Obrzut, Jan; Emiroglu, Caglar; Kirillov, Oleg; Yang, Yanfei; Elmquist, Randolph E.

    2016-01-01

    A method is established to reliably determine surface conductance of single-layer or multi-layer atomically thin nano-carbon graphene structures. The measurements are made in an air filled standard R100 rectangular waveguide configuration at one of the resonant frequency modes, typically at TE103 mode of 7.4543 GHz. Surface conductance measurement involves monitoring a change in the quality factor of the cavity as the specimen is progressively inserted into the cavity in quantitative correlation with the specimen surface area. The specimen consists of a nano-carbon-layer supported on a low loss dielectric substrate. The thickness of the conducting nano-carbon layer does not need to be explicitly known, but it is assumed that the lateral dimension is uniform over the specimen area. The non-contact surface conductance measurements are illustrated for a typical graphene grown by chemical vapor deposition process, and for a high quality monolayer epitaxial graphene grown on silicon carbide wafers for which we performed non-gated quantum Hall resistance measurements. The sequence of quantized transverse Hall resistance at the Landau filling factors ν = ±6 and ±2, and the absence of the Hall plateau at ν = 4 indicate that the epitaxially grown graphene is a high quality mono-layer. The resonant microwave cavity measurement is sensitive to the surface and bulk conductivity, and since no additional processing is required, it preserves the integrity of the conductive graphene layer. It allows characterization with high speed, precision and efficiency, compared to transport measurements where sample contacts must be defined and applied in multiple processing steps. PMID:27499569

  11. A nonmonotonic dependence of the contact angles on the surface polarity for a model solid surface.

    PubMed

    Qi, Chonghai; Zhou, Bo; Wang, Chunlei; Zheng, Yujun; Fang, Haiping

    2017-03-01

    Based on molecular dynamics simulations, we found a nonmonotonic relationship between the contact angle of water droplets and the surface polarity on a solid surface with specific hexagonal charge patterns at room temperature. The contact angle firstly decreases and then increases as polarity (denoted as charge q) increases from 0 e to 1.0 e with a vertex value of q = 0.5 e. We observed a different wetting behavior for a water droplet on a conventional nonwetted solid surface when q ≤ 0.5 e, and a water droplet on an ordered water monolayer adsorbed on a highly polar solid surface when q > 0.5 e. The solid-water interaction, density of water, hydrogen bonds, and water structures were analyzed. Remarkably, there was up to six times difference in the solid-water interactions despite the same value of the apparent contact angle values.

  12. Surface-contacting vibrometers for seismic landmine detection

    NASA Astrophysics Data System (ADS)

    Martin, James S.; Larson, Gregg D.; Scott, Waymond R., Jr.

    2005-06-01

    A technique has been developed that exploits remote seismic sources and local measurement of the surface displacement of the ground for the detection of buried landmines. Most of the previously reported investigation of this technique has focused on non-contact displacement sensors in order to ensure the safety of the operators of both handheld and vehicle-based systems. This is not inherently a constraint that requires a non-contact sensor, but rather one requiring a sensor that is non-intrusive (i.e. its presence does not alter the measured quantity). Current research is directed toward the development of autonomous and semi-autonomous robotic systems based on this technique. Here both unit cost and power consumption are issues of comparable importance to the survival of the sensor platform. Non-intrusive surface-contacting vibrometers are therefore a reasonable alternative. Several configurations have been studied for suitable vibrometers. The configuration that has shown the most promise is based on a commercial accelerometer coupled to the ground with a small normal force and isolated from the backing structure that is used to reposition it between measurements. It is a relatively simple matter to detect seismic motion with an accelerometer. The major issue in an effective implementation of the technique is to combine reproducibility with fidelity in the measurement. These are competing goals in that reproducibility is easily achieved with large normal forces, but fidelity requires that these be small. Sufficient reproducibility for imaging purposes has been achieved with normal forces that pose no danger of landmine detonation. Unlike reproducibility, fidelity is linked to both the nature of the imposed force and to its magnitude through the nonlinearity of the soil"s elasticity. Both continuous and incremental motions of the sensor platform have been studied, although incremental movement shows the most promise for the intended application.

  13. Estimating Surface Temperature of a Calibration Apparatus for Contact Surface Thermometers from Its Internal Temperature Profile

    NASA Astrophysics Data System (ADS)

    Saito, I.; Nakano, T.; Tamba, J.

    2017-10-01

    A calibration apparatus for contact surface thermometers was developed. Temperature of the upper surface of a copper cube of the calibration apparatus was used as reference surface temperature, which was estimated at around 50 {°}C, 100 {°}C, and 150 {°}C by not only two conventional industrial platinum resistance thermometers (IPRTs) but also five small-sized platinum resistance thermometers (SSPRTs) calibrated based on the International Temperature Scale of 1990 (ITS-90). These thermometers were inserted horizontally into the copper cube and aligned along the center axis of the copper cube. In the case of a no-load state without anything on the upper surface, the temperature profile inside the copper cube linearly decreased from the lower part to the upper surface, which suggests that the heat conduction inside the copper cube can be regarded as a one-dimensional steady state. On the other hand, in the case of a transient state just after the contact surface thermometer was applied to the upper surface, the temperature profile became a round shape. We obtained good agreement between the curvature of the temperature profiles and the results estimated by using an error function used for a one-dimensional transient heat conduction problem. The temperature difference between the estimated temperature by linear extrapolation using two IPRTs and that by extrapolation using the error function was within 0.2 {°}C in the transient state at around 150 {°}C. Over 10 min after the contact surface thermometer was applied, the temperature profile showed a linear shape again, which indicated that linear extrapolation using two IPRTs was well for the estimation of the reference surface temperature because the heat conduction state inside the copper cube came back to the one-dimensional steady state. Difference between the surface temperature and temperature detected by the contact surface thermometer was also observed after the contact surface thermometer touched on the

  14. Restoration of rolling-contact-fatigued surfaces via nanoskin technology.

    PubMed

    Pyun, Young Sik; Kim, Jun Hyong; Kayumov, Ravil; He, Yinsheng; Shin, Kee Sam

    2013-09-01

    Rolling contact fatigue (RCF) is known as the dominant factor determining the service life of bearing materials. In this work, the fatigue life of the typical bearing alloy was significantly improved by introducing a nanoskin layer on the surfaces of the test specimens. The nanoskin layer structure was obtained by means of the ultrasonic nanocrystal surface modification (UNSM) technology. The microstructure of the nanoskin was analyzed via scanning electron microscope (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscope (TEM). SUJ2 and SUJ3 bearings at different states of fatigue were subjected to UNSM treatment. For SUJ2 a rotary-bending fatigue (RBF) life average for three untreated specimens was chosen as 100% life, and then several untreated specimens were fatigued to 25%, 50% and 75% of life with subsequent UNSM treatment. This way used bearing conditions were simulated. The rotary-bending fatigue (RBF) tests of fatigue+UNSM SUJ2 specimens have shown 377-430% improvement of fatigue life, comparing to untreated specimens. For SUJ3 a RCF life untreated specimen was chosen as 100% life, and then several specimens were fatigued to approximately 100% of surface damage with subsequent UNSM treatment. Thus damaged surface conditions were simulated. The RCF tests of fatigue+UNSM SUJ3 specimens have shown 218% improvement of fatigue life, comparing to untreated specimens. This indicates the possibility of the restoration of the RCF life of bearing alloys by means of nanoskin treatment via UNSM technology.

  15. Modified Contact Line Dynamics about a Surface-Piercing Hydrofoil

    NASA Astrophysics Data System (ADS)

    Grivel, Morgane; Jeon, David; Gharib, Morteza

    2016-11-01

    The contact line around a surface-piercing hydrofoil is modified by introducing alternating hydrophobic and hydrophilic bands along one side of the body. These bands are either aligned perpendicular or parallel to the flow direction. The other side of the hydrofoil is un-patterned and retains its original, uniformly hydrophilic properties. The hydrofoil is mounted onto air bearings, such that it can freely move side-to-side in the water tunnel. A force sensor is attached to the setup via a universal joint in order to measure the forces acting on the body for several Reynolds numbers (ranging from 104 to 105) and angles of attack (ranging from -10o to 10o) . Cameras are also used to record the resulting flow structures and free surface elevation. The generation of wave trains and an altered free-surface elevation (also associated with the generation of surface waves) are observed over a wide range flow conditions. Force measurements elucidate how introducing these flow features impacts the forces acting on the hydrofoil, specifically with regards to the generation of lateral forces due to the asymmetric wetting conditions on either side of the hydrofoil. Work is funded by ONR Grant N00014-11-1-0031 and NSF GRFP Grant DGE-1144469.

  16. Ciliary contact interactions dominate surface scattering of swimming eukaryotes

    PubMed Central

    Kantsler, Vasily; Dunkel, Jörn; Polin, Marco; Goldstein, Raymond E.

    2013-01-01

    Interactions between swimming cells and surfaces are essential to many microbiological processes, from bacterial biofilm formation to human fertilization. However, despite their fundamental importance, relatively little is known about the physical mechanisms that govern the scattering of flagellated or ciliated cells from solid surfaces. A more detailed understanding of these interactions promises not only new biological insights into structure and dynamics of flagella and cilia but may also lead to new microfluidic techniques for controlling cell motility and microbial locomotion, with potential applications ranging from diagnostic tools to therapeutic protein synthesis and photosynthetic biofuel production. Due to fundamental differences in physiology and swimming strategies, it is an open question of whether microfluidic transport and rectification schemes that have recently been demonstrated for pusher-type microswimmers such as bacteria and sperm cells, can be transferred to puller-type algae and other motile eukaryotes, because it is not known whether long-range hydrodynamic or short-range mechanical forces dominate the surface interactions of these microorganisms. Here, using high-speed microscopic imaging, we present direct experimental evidence that the surface scattering of both mammalian sperm cells and unicellular green algae is primarily governed by direct ciliary contact interactions. Building on this insight, we predict and experimentally verify the existence of optimal microfluidic ratchets that maximize rectification of initially uniform Chlamydomonas reinhardtii suspensions. Because mechano-elastic properties of cilia are conserved across eukaryotic species, we expect that our results apply to a wide range of swimming microorganisms. PMID:23297240

  17. Automation of contact lens fitting evaluation by digital image processing

    NASA Astrophysics Data System (ADS)

    Costa, Manuel F. M.; Barros, Rui; Franco, Sandra B.

    1997-08-01

    Contact lens' fitting evaluation is of critical importance in the contact lens' prescription process. For the correction of eye's refraction problems the use of contact lens' is very appealing to the user. However its prescription is far more demanding than the one of eye glasses. The fitting of a contact lens to a particular cornea must be carefully assessed in order to reduce possible user's physical miscomfort or even medical situations.The traditional way of easily checking the fitting of a contact lens is to perform a fluorescein test. The simple visual evaluation of the 'smoothness' of the color/brightness distribution of the fluorescence at the contact lens' location gives the optometrist an idea of the fitting's quality. We suggested the automation of the process simply by the substitution of the optometrist's eye by a CCD camera, and the use of appropriated simple image processing techniques. The setup and the digitalization and processing routines will be described in this communication. The processed images may then be directly analyzed by the optometrist in a faster, easier and more efficient way. However, it is also possible to perform an automated fitting evaluation by working out the information given by the image's intensity histograms for the green and blue RGB' channels.

  18. Automation of contact lens' fitting evaluation by digital image processing

    NASA Astrophysics Data System (ADS)

    da Cunha Martins Costa, M.; Barros, Rui; Franco, Sandra B.

    1997-10-01

    Contact lens' fitting evaluation is of critical importance in the contact lens' prescription process. For the correction of eye's refraction problems the use of contact lens' is very appealing to the user. However its prescription is far more demanding than the one of eye glasses. The fitting of a contact lens to a particular cornea must be carefully assessed in order to reduce possible user's physical miscomfort or even medical situations.The traditional way of easily checking the fitting of a contact lens is to perform a fluorescein test. The simple visual evaluation of the 'smoothness' of the color/brightness distribution of the fluorescence at the contact lens' location gives the optometrist an idea of the fitting's quality. We suggested the automation of the process simply by the substitution of the optometrist's eye by a CCD camera, and the use of appropriated simple image processing techniques. The setup and the digitalization and processing routines will be described in this communication. The processed images may then be directly analyzed by the optometrist in a faster, easier and more efficient way. However, it is also possible to perform an automated fitting evaluation by working out the information given by the image's intensity histograms for the green and blue RGB' channels.

  19. New method for evaluation of hard contact lens materials with regard to cell injury by dynamic contact.

    PubMed

    Iguchi, I; Kamiyama, K; Ohashi, T; Wang, X; Imanishi, J

    1996-11-01

    To establish a new method for evaluation of contact lens materials, we studied the porcine endothelial cell injury caused by dynamic contact (rotatory rubbing) with three kinds of hard contact lenses (HCL). The HCLs used were 1) PMMA HCL, 2) oxygen-permeable HCL composed of a graft copolymer of dextran derivative and methylmethacrylate (MMA) (Suncon Mild II, 12 Dk), and 3) oxygen-permeable-HCL composed of a copolymer of a monomer containing silicone, a monomer containing fluorine, and MMA (RGPL-A, 216 Dk). Cell injury rates were significantly different among these HCLs (Suncon Mild II < PMMA < RGPL-A) although there were no differences in rotatory rubbing forces. The smoothness of HCL surface, the qualities of injured cell layers observed by scanning electron microscopy, and the water wettability of HCLs were not correlated with cell injury rate. These results suggest that physicochemical properties of materials other than rotatory rubbing force, smoothness, and water wettability were involved in the cell injury. Our evaluation method for biomaterials that injure the corneal endothelial cells by dynamic contact should be very useful for the development of biomaterials or medical devices, including HCLs and intracardiac and urethral catheters.

  20. Removal and transfer of viruses on food contact surfaces by cleaning cloths.

    PubMed

    Gibson, Kristen E; Crandall, Philip G; Ricke, Steven C

    2012-05-01

    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.

  1. 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

  2. Effects of Surface Roughness and Surface Force on the Thin Film Elastohydrodynamic Lubrication of Circular Contacts

    NASA Astrophysics Data System (ADS)

    Chu, Li-Ming; Lin, Jaw-Ren; Chen, Jiann-Lin

    2012-07-01

    The effects of surface roughness and surface force on thin film elastohydrodynamic lubrication (TFEHL) circular contact problems are analyzed and discussed under constant load condition. The multi-level multi-integration (MLMI) algorithm and the Gauss-Seidel iterative method are used to simultaneously solve the average Reynolds type equation, surface force equations, the load balance equation, the rheology equations, and the elastic deformation equation. The simulation results reveal that the difference between the TFEHL model and the traditional EHL model increase with decreasing film thickness. The effects of surface forces become significant as the film thickness becomes thinner. The surface forces have obvious effects in the Hertzian contact region. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Objective Assessment of Ocular Surface Response to Contact Lens Wear in Presbyopic Contact Lens Wearers of Asian Descent.

    PubMed

    Guillon, Michel; Dumbleton, Kathy; Theodoratos, Panagiotis; Patel, Trisha; Karkkainen, Tom; Moody, Kurt

    2016-10-13

    Contact lens wearers of Asian descent may be predisposed to experience microtrauma of the ocular surface as a result a thinner post-lens tear film and higher eyelid tension, and these effects would be anticipated to be most marked in an older population. The objective of this study was to quantify the mechanical effects of the study contact lenses on the ocular surface in a population of presbyopic contact lens wearers of Asian descent. Twenty established presbyopic contact lens wearers (hydrogel n=5, none habitual wearers of etafilcon A lenses; silicone hydrogel n=15) of Asian descent were refitted with etafilcon A multifocal daily disposable contact lenses (1-DAY ACUVUE MOIST MULTIFOCAL) for a period of 1 month of daily lens wear. The habitual modalities of wear were 45% daily disposable and 55% planned replacement. Digital photographs of the upper lid margins, nasal and temporal conjunctiva, and superior cornea were taken after 6 hr of wear of the participants' habitual contact lenses, after 1 day without contact lens wear, and after 6 hr of wear of the study contact lenses at the end of the 1-month period. The photographs were masked according to study visit and the staining extent measured using proprietary software. Lid margin staining was significantly lower with the study contact lenses (2.0±1.0 mm) than with the participants' own contact lenses (3.2±3.0 mm) after 6 hr of wear, representing a mean staining decrease of 38% (P=0.010). Lid margin staining after 6 hr of wear of the study contact lenses was not different from that measured after 1 day without contact lenses (P=0.507). Limbal staining was also significantly less with the study contact lenses than with the participants' own contact lenses after 6 hr of wear (P=0.009). There was minimal upper corneal staining, and the degree was similar with the study and habitual lenses. Etafilcon A material, worn under a daily disposable modality, was shown to reduce upper lid margin and limbal staining in

  8. Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food

    PubMed Central

    Miranda, Robyn C.

    2016-01-01

    ABSTRACT Bacterial cross-contamination from surfaces to food can contribute to foodborne disease. The cross-contamination rate of Enterobacter aerogenes on household surfaces was evaluated by using scenarios that differed by surface type, food type, contact time (<1, 5, 30, and 300 s), and inoculum matrix (tryptic soy broth or peptone buffer). The surfaces used were stainless steel, tile, wood, and carpet. The food types were watermelon, bread, bread with butter, and gummy candy. Surfaces (25 cm2) were spot inoculated with 1 ml of inoculum and allowed to dry for 5 h, yielding an approximate concentration of 107 CFU/surface. Foods (with a 16-cm2 contact area) were dropped onto the surfaces from a height of 12.5 cm and left to rest as appropriate. Posttransfer, surfaces and foods were placed in sterile filter bags and homogenized or massaged, diluted, and plated on tryptic soy agar. The transfer rate was quantified as the log percent transfer from the surface to the food. Contact time, food, and surface type all had highly significant effects (P < 0.000001) on the log percent transfer of bacteria. The inoculum matrix (tryptic soy broth or peptone buffer) also had a significant effect on transfer (P = 0.013), and most interaction terms were significant. More bacteria transferred to watermelon (∼0.2 to 97%) than to any other food, while the least bacteria transferred to gummy candy (∼0.1 to 62%). Transfer of bacteria to bread (∼0.02 to 94%) was similar to transfer of bacteria to bread with butter (∼0.02 to 82%), and these transfer rates under a given set of conditions were more variable than with watermelon and gummy candy. IMPORTANCE The popular notion of the “five-second rule” is that food dropped on the floor and left there for <5 s is “safe” because bacteria need time to transfer. The rule has been explored by a single study in the published literature and on at least two television shows. Results from two academic laboratories have been shared

  9. 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

  10. Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food.

    PubMed

    Miranda, Robyn C; Schaffner, Donald W

    2016-11-01

    Bacterial cross-contamination from surfaces to food can contribute to foodborne disease. The cross-contamination rate of Enterobacter aerogenes on household surfaces was evaluated by using scenarios that differed by surface type, food type, contact time (<1, 5, 30, and 300 s), and inoculum matrix (tryptic soy broth or peptone buffer). The surfaces used were stainless steel, tile, wood, and carpet. The food types were watermelon, bread, bread with butter, and gummy candy. Surfaces (25 cm(2)) were spot inoculated with 1 ml of inoculum and allowed to dry for 5 h, yielding an approximate concentration of 10(7) CFU/surface. Foods (with a 16-cm(2) contact area) were dropped onto the surfaces from a height of 12.5 cm and left to rest as appropriate. Posttransfer, surfaces and foods were placed in sterile filter bags and homogenized or massaged, diluted, and plated on tryptic soy agar. The transfer rate was quantified as the log percent transfer from the surface to the food. Contact time, food, and surface type all had highly significant effects (P < 0.000001) on the log percent transfer of bacteria. The inoculum matrix (tryptic soy broth or peptone buffer) also had a significant effect on transfer (P = 0.013), and most interaction terms were significant. More bacteria transferred to watermelon (∼0.2 to 97%) than to any other food, while the least bacteria transferred to gummy candy (∼0.1 to 62%). Transfer of bacteria to bread (∼0.02 to 94%) was similar to transfer of bacteria to bread with butter (∼0.02 to 82%), and these transfer rates under a given set of conditions were more variable than with watermelon and gummy candy.

  11. Analytical and experimental evaluation of biaxial contact stress

    NASA Technical Reports Server (NTRS)

    Richerson, D. W.; Finger, D. G.; Wimmer, J. M.

    1981-01-01

    Contact stress analysis was conducted for ceramic-metal and ceramic-ceramic interfaces using a finite element model. Ceramics investigated included NC-132 hot-pressed silicon nitride, NC-350 reaction-bonded silicon nitride, Hexaloy SA SiC, and RBN104 reaction-bonded silicon nitride. The results are shown to be well correlated with closed-form solution both for normal and normal-tangential loading. The latter load condition is found to be especially critical for ceramic materials due to the presence of a high tensile stress at the trailing edge of the ceramic surface contact zone. It is shown that during sliding contact or biaxial loading, the magnitude of this tensile stress increases with the coefficient of friction.

  12. 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.

  13. Surface coupling effects on contact mechanics: contact area and interfacial separation between an elastic solid and a hard substrate with randomly rough, self-affine fractal surfaces

    NASA Astrophysics Data System (ADS)

    Feshanjerdi, M.; Masoudi, A. A.; Khorrami, M.

    2016-12-01

    The objective of this study is to investigate both the contact area and the interfacial separation between two surfaces. Both surfaces are considered to be rough, one of them being elastic and the other one hard. The work is based on an extended version of Persson's model of contact mechanics to study the behavior of the contact area, the interfacial separation and the pressure distribution. The results are compared with the case merely the hard substrate is rough. It is seen that introducing a roughness in the elastic surface decreases the real contact, if the surfaces are uncorrelated. A positive (negative) correlation increases (decreases) the real contact. A reverse pattern occurs for the width of the pressure distribution, as well as the interfacial separation (at equal pressures).

  14. Investigating How Contact Angle Effects the Interaction between Water and a Hydrophobic Surface

    NASA Astrophysics Data System (ADS)

    Poynor, Adele; Neidig, Caitlyn

    2012-02-01

    By definition hydrophobic substances hate water. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low-density region forms near the surface. Contact angle is a measure of how hydrophobic a surface is. We have employed an automated home-built Surface Plasmon Resonance (SPR) apparatus to investigate the effect of varying the contact angle on the depletion layer

  15. A highly accurate dynamic contact angle algorithm for drops on inclined surface based on ellipse-fitting.

    PubMed

    Xu, Z N; Wang, S Y

    2015-02-01

    To improve the accuracy in the calculation of dynamic contact angle for drops on the inclined surface, a significant number of numerical drop profiles on the inclined surface with different inclination angles, drop volumes, and contact angles are generated based on the finite difference method, a least-squares ellipse-fitting algorithm is used to calculate the dynamic contact angle. The influences of the above three factors are systematically investigated. The results reveal that the dynamic contact angle errors, including the errors of the left and right contact angles, evaluated by the ellipse-fitting algorithm tend to increase with inclination angle/drop volume/contact angle. If the drop volume and the solid substrate are fixed, the errors of the left and right contact angles increase with inclination angle. After performing a tremendous amount of computation, the critical dimensionless drop volumes corresponding to the critical contact angle error are obtained. Based on the values of the critical volumes, a highly accurate dynamic contact angle algorithm is proposed and fully validated. Within nearly the whole hydrophobicity range, it can decrease the dynamic contact angle error in the inclined plane method to less than a certain value even for different types of liquids.

  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. Copyright © 2015 Elsevier B.V. All rights reserved.

  18. Static and dynamic contact angles of water droplet on a solid surface using molecular dynamics simulation.

    PubMed

    Hong, Seung Do; Ha, Man Yeong; Balachandar, S

    2009-11-01

    The present study investigates the variation of static contact angle of a water droplet in equilibrium with a solid surface in the absence of a body force and the dynamic contact angles of water droplet moving on a solid surface for different characteristic energies using the molecular dynamics simulation. With increasing characteristic energy, the static contact angle in equilibrium with a solid surface in the absence of a body force decreases because the hydrophobic surface changes its characteristics to the hydrophilic surface. In order to consider the effect of moving water droplet on the dynamic contact angles, we apply the constant acceleration to an individual oxygen and hydrogen atom. In the presence of a body force, the water droplet changes its shape with larger advancing contact angle than the receding angle. The dynamic contact angles are compared with the static contact angle in order to see the effect of the presence of a body force.

  19. Evaluation of Contact Heat Transfer Coefficient and Phase Transformation during Hot Stamping of a Hat-Type Part

    PubMed Central

    Kim, Heung-Kyu; Lee, Seong Hyeon; Choi, Hyunjoo

    2015-01-01

    Using an inverse analysis technique, the heat transfer coefficient on the die-workpiece contact surface of a hot stamping process was evaluated as a power law function of contact pressure. This evaluation was to determine whether the heat transfer coefficient on the contact surface could be used for finite element analysis of the entire hot stamping process. By comparing results of the finite element analysis and experimental measurements of the phase transformation, an evaluation was performed to determine whether the obtained heat transfer coefficient function could provide reasonable finite element prediction for workpiece properties affected by the hot stamping process. PMID:28788046

  20. 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.

  1. 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

  2. Geometry, contact, surface, and optical developments for photoconductive power switches

    SciTech Connect

    Nunnally, W.C.; Hammond, R.B.; Wagner, R.S.

    1984-01-01

    Photoconductive Power Switches (PCPSs) have the advantages of precise control, extremely fast closure times, extremely low inductances and scalability to very high voltages and currents. PCPSs have these advantages because the size or power of the switch is not related to its closure time. The closure time is determined by the external optical source that uniformly illuminates the PCPS between the electrodes. Because carriers are generated uniformly between the electrodes at the desired density, current can flow through the switch immediately without waiting for carrier transient delays. The operating voltage is determined by the switch length l, and the operating current is determined by the switch width w. The electrodes can be made as wide as desired so that the inductance can be extremely low, or the area available for heat removal can be increased and the entire switch brough into conduction at the same instant if the same optical pulse and path length are used. This paper describes recent research at Los Alamos that has improved PCPS contact fabrication technology, has developed a simple optical control illumination system using fiber optics and rectangular optics, and has improved photoconductor surface fabrication methods and processes for high electric field operation.

  3. Effect of the residual near-surface stresses of the working surface on the contact resistance of rolls

    NASA Astrophysics Data System (ADS)

    Rusakov, A. D.

    2010-05-01

    The results of contact resistance tests of roll steel samples with various levels of near-surface residual compressive stresses are analyzed. A relation between these stresses and the contact resistance is found. Recommendations are made for the formation of rational near-surface residual stresses in the active surfaces of rolls in order to increase their resistance.

  4. 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.

  5. The role of whole blood in thrombin generation in contact with various titanium surfaces.

    PubMed

    Thor, Andreas; Rasmusson, Lars; Wennerberg, Ann; Thomsen, Peter; Hirsch, Jan-Michael; Nilsson, Bo; Hong, Jaan

    2007-02-01

    Understanding of the thrombotic response (activation of the intrinsic coagulation system followed by platelet activation) from blood components upon contact with a titanium dental implant is important and not fully understood. The aims of this study were to evaluate: (1) the thrombogenic response of whole blood, platelet-rich plasma (PRP) and platelet-poor plasma (PPP) in contact with a highly thrombogenic surface as titanium, (2) the thrombogenic response of clinically used surfaces as hydroxyapatite (HA), machined titanium (mTi), TiO2 grit-blasted titanium (TiOB) and fluoride ion-modified grit-blasted titanium (TiOB-F). An in vitro slide chamber model, furnished with heparin, was used in which whole blood, PRP or PPP came in contact with slides of the test surfaces. After incubation (60 min rotation at 22 rpm in a 37 degrees C water bath), blood/plasma was mixed with EDTA or citrate, further centrifuged at +4 degrees C (2200 g at 10 min). Finally, plasma was collected pending analysis. Whole blood in contact with Ti alloy resulted in the binding of platelets to the material surface and in the generation of thrombin-antithrombin (TAT) complexes. With whole blood TAT levels increased 1000-fold compared with PRP and PPP, in which both almost no increase of TAT could be detected. In addition, the platelet activation showed a similar pattern with a 15-fold higher release of beta-TG in whole blood. In the in vitro chamber model with the clinically relevant materials, the fluoride-modified surface (TiOB-F) showed pronounced TAT generation compared with TiOB, mTi and HA. Similar results were achieved for platelet consumption and activation markers of the intrinsic coagulation system. Taken together these results implicate first that whole blood is necessary for sufficient thrombin generation and platelet activation during placement of implants. Second, a fluoride ion modification seems to augment the thrombogenic properties of titanium.

  6. Contact ratio of rough surfaces with multiple asperities in mixed lubrication at high pressures

    NASA Astrophysics Data System (ADS)

    Xiao, Huaping; Guo, Dan; Liu, Shuhai; Pan, Guoshun; Lu, Xinchun

    2012-02-01

    Relative optical intensity interference was used to measure the lubrication film thickness when four kinds of polyalphaolefin (PAO) were used as lubricants confined between a smooth sapphire disc surface and a rough steel ball surface. Maximum Hertz contact pressure up to 3 GPa was applied in the central part of the contact region in mixed lubrication. It was found that the contact ratio (the ratio of real contact region to the whole nominal contact region) is related to the film thickness, the applied pressure, the surface roughness and the rolling speed, and so on. Contact ratio evidently reduces as lubrication film thickness or rolling speed increases. Quantitative relationship between the contact ratio and the influence factors was summarized based on the nonlinear fitting of experimental measurements. A formula was put forward to calculate the contact ratio at high pressure conditions according to the current experimental results.

  7. Low surface energy polymeric release coating for improved contact print lithography

    NASA Astrophysics Data System (ADS)

    Mancini, David P.; Resnick, Douglas J.; Gehoski, Kathleen A.; Popovich, Laura L.; Chang, Daniel

    2002-03-01

    Contact printing has been used for decades in many various lithography applications in the microelectronic industry. While vacuum contact printing processes offer sub-micron resolution and high throughput, they often suffer from some important drawbacks. One of the most common problems is degradation in both resolution and defect density which occurs when the same mask si used for multiple exposures without frequent mask cleans. This is largely due to the relatively high surface energy of both quartz and chrome and the tendency of most photoresists to adhere to these surfaces. As a result, when a mask and wafer are pressed into intimate contact, resist will tend to stick to the mask creating a defect on the wafer, effectively propagating defects to subsequent wafers. In this study, DuPont Teflon AF 1601S is used as a photomask coating and evaluated for its ability to act as a release agent and reduce defects while maintaining resolution for multiple exposures. Teflon AF is an amorphous, transparent, low surface energy, polymeric material that can be spin coated into a thin conformal film. Tests have shown that when using an uncoated mask in vacuum contact, resolution of 0.75 micrometers dense lines is severely degraded after less than 10 consecutive exposures. However, when the mask is coated, 0.75 micrometers dense lines were successfully resolved using vacuum contact for over 200 exposures without cleaning. In addition, it has been demonstrated that Teflon AF coatings impart to a mask a self-cleaning capability, since particles tend to stick to the photoresist rather than the mask. A coated mask, which was purposefully contaminated with particulates, resolved 0.75 micrometers dense lines on all but the first wafer of a series of 25 consecutive exposures. The patented mask releases layer process has successfully been demonstrated with a positive novolak resist. Additional data which describes the system chemistry, dilution and coating process, and film morphology

  8. Estimation of the Surface Properties of Styrene-Acrylonitrile Random Copolymers from Contact Angle Measurements.

    PubMed

    Adão; Saramago; Fernandes

    1999-09-01

    The surface free energy per unit area of a solid, gamma(S), is a fundamental property of materials and determines their surface and interfacial behavior in processes like wetting and adhesion. In this study the gamma(S) of a series of styrene-acrylonitrile random copolymers is evaluated. Three different approaches are used to determine the components in which the surface free energy can be decomposed. Using the geometric and the harmonic mean approach, the dispersive, gamma(d), and polar, gamma(p), components of the solid surface free energy were determined and compared to the Lifshitz-van der Waals, gamma(LW), and acid-base, gamma(AB), components using the approach developed by C. J. van Oss et al. (1987, Adv. Colloid Interface Sci. 28, 35). The acid-base approach was also used to evaluate the work of adhesion of the test liquids: water, glycerol, and thiodiglycol. It was found that the contact angles of these liquids follow closely the predictions of Cassie equation. The evaluation of the surface free energy components on one hand and the relative magnitude of the work of adhesion components on the other hand, suggest that below 50% of acrylonitrile the polystyrene repeating units are preferentially at the surface. Above 50% of acrylonitrile the segregation of the low-energy homopolymer at the surface decreases. Copyright 1999 Academic Press.

  9. 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)

  10. Optical properties and surface morphology studies of palladium contacts on mercuric iodide single crystals

    NASA Astrophysics Data System (ADS)

    George, M. A.; Azoulay, M.; Burger, A.; Biao, Y.; Silberman, E.; Nason, D.

    1993-04-01

    Palladium is chemically suitable for electric contacts on mercuric iodide detectors for photon and nuclear radiation detection, so the understanding of palladium contacts is important for fundamental and practical scientific purposes. A study has been conducted on the surface morphology of evaporated contacts using atomic force microscopy (AFM) and optical transmission and reflection. Evaporated palladium coatings are typically nonuniform and may deposit selectively on mercuric iodide surface defects. Reflection measurements show that coating thickness and surface treatment affect intensity, position, and shape of a reflected peak characteristic of the mercuric iodide structure. Results indicate that the band gap energy in the surface of the mercuric iodide is lowered by palladium contacts.

  11. Indirect methods to measure wetting and contact angles on spherical convex and concave surfaces.

    PubMed

    Extrand, C W; Moon, Sung In

    2012-05-22

    In this work, a method was developed for indirectly estimating contact angles of sessile liquid drops on convex and concave surfaces. Assuming that drops were sufficiently small that no gravitational distortion occurred, equations were derived to compute intrinsic contact angles from the radius of curvature of the solid surface, the volume of the liquid drop, and its contact diameter. These expressions were tested against experimental data for various liquids on polytetrafluoroethylene (PTFE) and polycarbonate (PC) in the form of flat surfaces, spheres, and concave cavities. Intrinsic contact angles estimated indirectly using dimensions and volumes generally agreed with the values measured directly from flat surfaces using the traditional tangent method.

  12. Corneal contact times of ophthalmic vehicles. Evaluation by microscintigraphy.

    PubMed

    Trueblood, J H; Rossomondo, R M; Wilson, L A; Carlton, W H

    1975-02-01

    Lacrimal microscintigraphy, in conjunction with a recently developed computer system, was used to evaluate the corneal contact time of three ophthalmic vehicles in 18 humans. The percentage of a radioactively labeled vehicle remaining over the cornea after 90 seconds was 2.9% plus and minus 2.2% for saline, 4.3% plus and minus 2.4% for polyvinyl alcohol, and 8.8% plus and minus 4.1% for hydroxypropyl methylcellulose.

  13. Elastoplastic contact mechanics model of rough surface based on fractal theory

    NASA Astrophysics Data System (ADS)

    Yuan, Yuan; Gan, Li; Liu, Kai; Yang, Xiaohui

    2017-01-01

    Because the result of the MB fractal model contradicts with the classical contact mechanics, a revised elastoplastic contact model of a single asperity is developed based on fractal theory. The critical areas of a single asperity are scale dependent, with an increase in the contact load and contact area, a transition from elastic, elastoplastic to full plastic deformation takes place in this order. In considering the size distribution function, analytic expression between the total contact load and the real contact area on the contact surface is obtained. The elastic, elastoplastic and full plastic contact load are obtained by the critical elastic contact area of the biggest asperity and maximun contact area of a single asperity. The results show that a rough surface is firstly in elastic deformation. As the load increases, elastoplastic or full plastic deformation takes place. For constant characteristic length scale G, the slope of load-area relation is proportional to fractal dimension D. For constant fractal dimension D, the slope of load-area relation is inversely proportional to G. For constant D and G, the slope of load-area relation is inversely proportional to property of the material ϕ, namely with the same load, the material of rough surface is softer, and the total contact area is larger. The contact mechanics model provides a foundation for study of the friction, wear and seal performance of rough surfaces.

  14. 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

  15. Receding Contact Line Motion on Nano- and Micro-patterned Polymer Surfaces.

    PubMed

    Gao, Nan; Chiu, Ming; Neto, Chiara

    2017-10-10

    Surface properties such as topography and chemistry affect the motion of the three-phase contact line (solid/liquid/air), which in turn affects the contact angle of a liquid moving on a solid surface. In this work, the motion of the receding water contact line was studied on chemically and topographically patterned surfaces obtained from the dewetting of thin polymer films. The patterned surfaces consisted of hydrophilic poly(4-vinylpyridine) (P4VP) bumps, which were either micro-sized and sparse or nano-sized and dense, on top of a hydrophobic polystyrene (PS) background layer. These patterns are designed for atmospheric water capture, for which the easy roll-off of water droplets is crucial to their efficient performance. The dynamic receding contact angle and contact line height of the patterned surfaces were measured by withdrawing vertically the surfaces from a water bath and compared to those of a flat P4VP substrate. For both the micro-patterned and nano-patterned surfaces, the height of the dynamic contact lines normalised by the capillary length were characterised by the equilibrium limit that was predicted from static states. The nano-patterned surface had faster increase in the normalised height as the capillary number increased. The dynamic receding contact angles on all surfaces studied decreased with increasing withdrawing velocity. Surprisingly, even for these patterned surfaces with high hysteresis, the dynamic receding contact angle followed the Cox-Voinov relation, at capillary numbers between 1 - 5 ∙10-5.

  16. Beyond Cassie equation: Local structure of heterogeneous surfaces determines the contact angles of microdroplets

    PubMed Central

    Zhang, Bo; Wang, Jianjun; Liu, Zhiping; Zhang, Xianren

    2014-01-01

    The application of Cassie equation to microscopic droplets is recently under intense debate because the microdroplet dimension is often of the same order of magnitude as the characteristic size of substrate heterogeneities, and the mechanism to describe the contact angle of microdroplets is not clear. By representing real surfaces statistically as an ensemble of patterned surfaces with randomly or regularly distributed heterogeneities (patches), lattice Boltzmann simulations here show that the contact angle of microdroplets has a wide distribution, either continuous or discrete, depending on the patch size. The origin of multiple contact angles observed is ascribed to the contact line pinning effect induced by substrate heterogeneities. We demonstrate that the local feature of substrate structure near the contact line determines the range of contact angles that can be stabilized, while the certain contact angle observed is closely related to the contact line width. PMID:25059292

  17. Multipole rf switch contact resistance interference, an industrial application of surface analysis

    SciTech Connect

    Hmiel, A.F.; Bauer, Y.; Leikus, V.; Rodriguez, H.; Halada, G.P.; Clayton, C.R.

    1995-12-31

    Low contact resistance is vital in communication and switching systems where the insertion loss and the rf/microwave performances of multi-contact switches are pushed to maximum performance. Increased resistance in the switch contact interface is a concern for optimal operation upon first turn-on of the switch. The study of high contact resistance invited the application of the surface analysis tools XPS, SEM and EDX. Environmentally compatible cleaning of the contact parts must retain acceptable compliance with the operational requirements. Hence, the effects of various cleaning agents became a concern. Gold plated beryllium copper contact surfaces function well with the application of a synthetic oil for corrosion protection. The surface contaminants` spectra from a high resistance contact in comparison with control samples demonstrated the utility of these analytical tools. The knowledge of the relative amounts of the contaminants and the circumstances of their arrival assist in revising manufacturing processes to insure long term low resistance operation of the switch.

  18. 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.

  19. In vitro and in vivo evaluation of ketotifen fumarate-loaded silicone hydrogel contact lenses for ocular drug delivery.

    PubMed

    Xu, Jinku; Li, Xinsong; Sun, Fuqian

    2011-02-01

    The purpose of this work was to evaluate the usefulness of silicone hydrogel contact lenses loaded with ketotifen fumarate for ocular drug delivery. First, silicone contact lenses were prepared by photopolymerization of bitelechelic methacrylated polydimethylsiloxanes macromonomer, 3-methacryloxypropyltris(trimethylsiloxy)silane, and N,N-dimethylacrylamide using ethylene glycol dimethacrylate as a cross-linker and Darocur 1173 as an initiator followed by surface plasma treatment. Then, the silicone hydrogel matrices of the contact lenses were characterized by equilibrium swelling ratio (ESR), tensile tests, ion permeability, and surface contact angle. Finally, the contact lenses were loaded with ketotifen fumarate by pre-soaking in drug solution to evaluate drug loading capacity, in vitro and in vivo release behavior of the silicone contact lenses. The results showed that ESR and ion permeability increase, and the surface contact angle and tensile strength decreased with the increase of DMA component in the silicone hydrogel. The drug loading and in vitro releases were dependent on the hydrogel composition of hydrophilic/hydrophobic phase of the contact lenses. In rabbit eyes, the pre-soaked contact lenses sustained ketotifen fumarate release for more than 24 h, which leads to a more stable drug concentration and a longer mean retention time in tear fluid than that of eye drops of 0.05%.

  20. Modeling and experimental validation of a linear ultrasonic motor considering rough surface contact

    NASA Astrophysics Data System (ADS)

    Lv, Qibao; Yao, Zhiyuan; Li, Xiang

    2017-04-01

    Linear ultrasonic motor is driven by the interface friction between the stator and the slider. The performance of the motor is significantly affected by the contact state between the stator and slider which depends considerably on the morphology of the contact interface. A novel fiction model is developed to evaluate the output characteristics of a linear ultrasonic motor. The proposed model, where the roughness and plastic deformation of contact surfaces are considered, differs from the previous spring model. Based on the developed model, the effects of surface roughness parameters on motor performance are investigated. The behavior of the force transmission between the stator and the slider is studied to understand the driving mechanism. Furthermore, a comparison between the proposed model and the spring model is made. An experiment is designed to verify the feasibility and effectiveness of this proposed model by comparing the simulation results with the measured one. The results show that the proposed model is more accurate than the spring model. These discussions will be very useful for the improvement of control and the optimal design of linear ultrasonic motor.

  1. Effects of surface material, ventilation, and human behavior on indirect contact transmission risk of respiratory infection.

    PubMed

    Sze-To, Gin Nam; Yang, Yang; Kwan, Joseph K C; Yu, Samuel C T; Chao, Christopher Y H

    2014-05-01

    Infectious particles can be deposited on surfaces. Susceptible persons who contacted these contaminated surfaces may transfer the pathogens to their mucous membranes via hands, leading to a risk of respiratory infection. The exposure and infection risk contributed by this transmission route depend on indoor surface material, ventilation, and human behavior. In this study, quantitative infection risk assessments were used to compare the significances of these factors. The risks of three pathogens, influenza A virus, respiratory syncytial virus (RSV), and rhinovirus, in an aircraft cabin and in a hospital ward were assessed. Results showed that reducing the contact rate is relatively more effective than increasing the ventilation rate to lower the infection risk. Nonfabric surface materials were found to be much more favorable in the indirect contact transmission for RSV and rhinovirus than fabric surface materials. In the cases considered in this study, halving the ventilation rate and doubling the hand contact rate to surfaces and the hand contact rate to mucous membranes would increase the risk by 3.7-16.2%, 34.4-94.2%, and 24.1-117.7%, respectively. Contacting contaminated nonfabric surfaces may pose an indirect contact risk up to three orders of magnitude higher than that of contacting contaminated fabric surfaces. These findings provide more consideration for infection control and building environmental design.

  2. 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.

  3. 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

    2014-10-17

    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.

  4. 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

  5. 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

  6. Application of time-dependent sessile drop contact angles on compacts to characterise the surface energetics of sulfathiazole crystals.

    PubMed

    Muster, Tim H; Prestidge, Clive A

    2002-03-02

    The time-dependent wetting of sulfathiazole compacts with sessile water drops was evaluated using video microscopy. The influence of sulfathiazole crystalline form, particle size, pre-saturation with water, humidity and compaction pressure on the droplet spreading kinetics and contact angles are reported. The rate and extent of droplet spreading decreased for compact surfaces of high microscopic roughness; this was determined by atomic force microscopy (AFM). Pre-saturation of powder compacts with water (pre-saturated with sulfathiazole) enhanced droplet spreading and enabled pseudo-equilibrium contact angles to be determined for up to 10 min. Sessile-drop contact angles on both sulfathiazole powder compacts and single crystals are compared with particle contact angles determined by liquid penetration. This study has led to an improved understanding of the influence of physical heterogeneities and the face-specific surface chemistry of individual crystals on the wetting characteristics of pharmaceutical compacts.

  7. Finite element based contact analysis of radio frequency MEMs switch membrane surfaces

    NASA Astrophysics Data System (ADS)

    Liu, Jin-Ya; Chalivendra, Vijaya; Huang, Wenzhen

    2017-10-01

    Finite element simulations were performed to determine the contact behavior of radio frequency (RF) micro-electro-mechanical (MEM) switch contact surfaces under monotonic and cyclic loading conditions. Atomic force microscopy (AFM) was used to capture the topography of RF-MEM switch membranes and later they were analyzed for multi-scale regular as well as fractal structures. Frictionless, non-adhesive contact 3D finite element analysis was carried out at different length scales to investigate the contact behavior of the regular-fractal surface using an elasto-plastic material model. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly cluster around the regular pattern. The contribution from the fractal structure is not significant. Under cyclic loading conditions, plastic deformation in the 1st loading/unloading cycle smooth the surface. The subsequent repetitive loading/unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces. The work is expected to shed light on the quality of the switch surface contact as well as the optimum design of RF MEM switch surfaces.

  8. Unified model for contact angle hysteresis on heterogeneous and superhydrophobic surfaces.

    PubMed

    Raj, Rishi; Enright, Ryan; Zhu, Yangying; Adera, Solomon; Wang, Evelyn N

    2012-11-13

    Understanding the complexities associated with contact line dynamics on chemically heterogeneous and superhydrophobic surfaces is important for a wide variety of engineering problems. Despite significant efforts to capture the behavior of a droplet on these surfaces over the past few decades, modeling of the complex dynamics at the three-phase contact line is needed. In this work, we demonstrate that contact line distortion on heterogeneous and superhydrophobic surfaces is the key aspect that needs to be accounted for in the dynamic droplet models. Contact line distortions were visualized and modeled using a thermodynamic approach to develop a unified model for contact angle hysteresis on chemically heterogeneous and superhydrophobic surfaces. On a surface comprised of discrete wetting defects on an interconnected less wetting area, the advancing contact angle was determined to be independent of the defects, while the relative fraction of the distorted contact line with respect to the baseline surface was shown to govern the receding contact angle. This behavior reversed when the relative wettability of the discrete defects and interconnected area was inverted. The developed model showed good agreement with the experimental advancing and receding contact angles, both at low and high solid fractions. The thermodynamic model was further extended to demonstrate its capability to capture droplet shape evolution during liquid addition and removal in our experiments and those in literature. This study offers new insight extending the fundamental understanding of solid-liquid interactions required for design of advanced functional coatings for microfluidics, biological, manufacturing, and heat transfer applications.

  9. Control of Surface Attack by Gallium Alloys in Electrical Contacts.

    DTIC Science & Technology

    1986-03-28

    and atmospheric control but does not allow visual observation of the contact brushes. This machine is a small homopolar motor built from mild steel...collectors,gallium, homopolar devices,liquid metals,~- is. ABSTRACT ICNI.. .. w 41N"w -~dv.mp.d Wrllt by Itabata" * Electrical contact between a copp’er...32 5 Test rig with felt metal brushes 32 6 Homopolar test apparatus 33 7 Rewetting of alloy track 33 8 Alloy track after running with finger 34 brushes

  10. Surface Physics and Chemistry of Electrical Contact Phenomena.

    DTIC Science & Technology

    1981-09-01

    multiprogrammer. Typical \\ Auger traces covering a 50-1300- eV range were directly digi- tized with an energy increment of 0.65 eV . Computerized VL, -vL- 2...covering a 50 to 1300 eV range were directly digitized. Computerized values of peak to peak heights and concentrations of the various elements were... Rabinowicz and P. Chan, Electrical Contacts 1979 (I.I.T. Chicago), 123 (1979). 11. J.L. Johnson and O.S. Taylor, Electrical Contacts 1979 (I.I.T. Chicago

  11. 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.

  12. 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.

  13. Biogeochemical analysis of the calcification patterns of cold-water corals Madrepora oculata and Lophelia pertusa along contact surfaces with calcified tubes of the symbiotic polychaete Eunice norvegica: Evaluation of a 'mucus' calcification hypothesis

    NASA Astrophysics Data System (ADS)

    Oppelt, Alexandra; López Correa, Matthias; Rocha, Carlos

    2017-09-01

    The scleractinian cold-water corals (CWCs), including the species Madrepora oculata and especially Lophelia pertusa, have been studied extensively in an attempt to decipher environmental signals recorded during biomineralisation in order to extract environmental chronologies. However, understanding the mechanisms of carbonate precipitation is a prerequisite to interpret variations in geochemical signatures locked into the skeleton during coral growth; to date results are still inconclusive. Here a novel approach, comparing the calcification patterns within the coral microstructure of species L. pertusa and M. oculata and the geochemistry along the contact surfaces with calcified polychaete tubes is undertaken to provide additional information on the mechanisms of biomineralisation in colonial corals. The fact that no significant difference in microstructures, variations in growth rate, or geochemical composition between the corallite theca and the calcified polychaete tube was detectable leads to the conclusion that both have been deposited by the coral tissue in L. pertusa and M. oculata. Based on prior knowledge on the symbiotic relationship between CWCs and the polychaete Eunice norvegica, an involvement of mucus in the calcification of the parchment tubes had been suspected. However, we found only evidence for aragonite precipitated by coral tissue, without evidence for an involvement of mucus in the calcification.

  14. Friction of viscoelastic elastomers with rough surfaces under torsional contact conditions

    NASA Astrophysics Data System (ADS)

    Trejo, Miguel; Fretigny, Christian; Chateauminois, Antoine

    2013-11-01

    Frictional properties of contacts between a smooth viscoelastic rubber and rigid surfaces are investigated using a torsional contact configuration where a glass lens is continuously rotated on the rubber surface. From the inversion of the displacement field measured at the surface of the rubber, spatially resolved values of the steady state frictional shear stress are determined within the nonhomogeneous pressure and velocity fields of the contact. For contacts with a smooth lens, a velocity-dependent but pressure-independent local shear stress is retrieved from the inversion. On the other hand, the local shear stress is found to depend on both velocity and applied contact pressure when a randomly rough (sand-blasted) glass lens is rubbed against the rubber surface. As a result of changes in the density of microasperity contacts, the amount of light transmitted by the transparent multicontact interface is observed to vary locally as a function of both contact pressure and sliding velocity. Under the assumption that the intensity of light transmitted by the rough interface is proportional to the proportion of area into contact, it is found that the local frictional stress can be expressed experimentally as the product of a purely velocity-dependent term, k(v), by a term representing the pressure and velocity dependence of the actual contact area, A/A0. A comparison between k(v) and the frictional shear stress of smooth contacts suggests that nanometer scale dissipative processes occurring at the interface predominate over viscoelastic dissipation at microasperity scale.

  15. 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.

  16. 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.

  17. 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.

  18. Dynamics of inhomogeneous condensates in contact with a surface

    SciTech Connect

    Bludov, Yu. V.; Yan Zhenya; Konotop, V. V.

    2010-06-15

    We show that interplay of linear attractive (repulsive) boundary with inhomogeneous repulsive (attractive) interatomic interactions results in nonlinear localized surface modes (surface solitons), some of which are stable. We consider several example systems describing interaction of inhomogeneous Bose-Einstein condensates with rigid surfaces and allowing for exact solutions. The stability of the obtained modes is analyzed analytically and numerically. Stable localized surface modes are found and dynamics of the unstable modes is described.

  19. 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.

  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. Effect of initial contact surface condition on the friction and wear properties of bearing steel in cyclic reciprocating sliding contact

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Endo, M.; Moriyama, S.

    2017-05-01

    Delamination failure is one of the most important engineering problems. This failure can frequently be detrimental to rolling contact machine elements such as bearings, gear wheels, etc. This phenomenon, called rolling contact fatigue, has a close relationship not only with opening-mode but also with shear-mode fatigue crack growth. The crack face interference is known to significantly affect the shear-mode fatigue crack propagation and its threshold behavior. Quantitative investigation on friction and wear at fatigue crack faces in the material is essentially impossible. Previously, thus, a novel ring-on-ring test by making use of fatigue testing machine was proposed to simulate a cyclic reciprocating sliding contact of crack surfaces. However, this test procedure had some problems. For instance, in order to achieve the uniform contact at the start of test, the rubbing of specimens must be conducted in advance. By this treatment, the specimen surfaces were already damaged before the test. In this study, an improvement of experimental method was made to perform the test using the damage-free specimens. The friction and wear properties for heat-treated high carbon-chromium bearing steel were investigated with this new method and the results were compared to the results obtained by using the initially damaged specimens.

  2. Relationship between Wetting Hysteresis and Contact Time of a Bouncing Droplet on Hydrophobic Surfaces.

    PubMed

    Shen, Yizhou; Tao, Jie; Tao, Haijun; Chen, Shanlong; Pan, Lei; Wang, Tao

    2015-09-23

    The contact time of impacting water droplets on superhydrophobic surfaces directly reflects the extent of thermal and energy conversions between the water droplet and the surface, which is also considered to be crucial to the practical applications. The purpose of this study was to reveal the relationship between the contact time and the wetting hysteresis. We designed and fabricated six classes of surfaces with different extent of hydrophobicity through modifying the microscale/nanoscale hierarchical textured titanium surfaces with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, and we filmed the contact process of the water droplet impacting on these surfaces using a high-speed camera. It can be concluded that wetting hysteresis played a significant role in determining how long the impacting water droplet can bounce off the surface, based on the interfacial wetting mechanism and the work done against the resistance force generated by contact angle hysteresis during the dynamic process.

  3. Evaluation of Contact Loss and Wear Considering the Friction Under Electric Current for Sliding Contact in Electric Railway

    NASA Astrophysics Data System (ADS)

    Kimura, Yoshio; Mishina, Hiroshi

    At the contact point of current collector of railway, it is difficult to investigate the relation between the wear and the electric current because of many influence factors and the sliding conditions. Therefore we need to show this relation by means of smaller current conditions than railway to see the effects of electric current on friction and wear. Experimental device is pin-on-wire type, which we improve pin-on-disk type sliding system into. It is set in a direct-current circuit and the pin rubs wires under an electric current. At this point, there is not only the mechanical phenomenon by adhesive wear, but also the electric phenomena including fusion caused by the heat from constriction resistance and the arc discharge caused by the contact loss during sliding test. To examine the effects on the wear of contact materials by them, we investigate the details classifying contact loss, which has a great influence on the wear of contact materials, to two kinds of contact loss, arc contact loss and complete contact loss. As a result of it, we can show the relations between the power supply voltage and the outbreak number, the outbreak ratio of two types of contact loss, and relations between the wear and the power supply voltage, materials by means of the former two relations. And we can see the effects of fusion and arc discharge on the sliding surface by optical microscope.

  4. 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.

  5. Mechanism of copper surface toxicity in vancomycin-resistant enterococci following wet or dry surface contact.

    PubMed

    Warnes, S L; Keevil, C W

    2011-09-01

    Contaminated touch surfaces have been implicated in the spread of hospital-acquired infections, and the use of biocidal surfaces could help to reduce this cross-contamination. In a previous study we reported the death of aqueous inocula of pathogenic Enterococcus faecalis or Enterococcus faecium isolates, simulating fomite surface contamination, in 1 h on copper alloys, compared to survival for months on stainless steel. In our current study we observed an even faster kill of over a 6-log reduction of viable enterococci in less than 10 min on copper alloys with a "dry" inoculum equivalent to touch contamination. We investigated the effect of copper(I) and copper(II) chelation and the quenching of reactive oxygen species on cell viability assessed by culture and their effects on genomic DNA, membrane potential, and respiration in situ on metal surfaces. We propose that copper surface toxicity for enterococci involves the direct or indirect action of released copper ionic species and the generation of superoxide, resulting in arrested respiration and DNA breakdown as the first stages of cell death. The generation of hydroxyl radicals by the Fenton reaction does not appear to be the dominant instrument of DNA damage. The bacterial membrane potential is unaffected in the early stages of wet and dry surface contact, suggesting that the membrane is not compromised until after cell death. These results also highlight the importance of correct surface cleaning protocols to perpetuate copper ion release and prevent the chelation of ions by contaminants, which could reduce the efficacy of the surface.

  6. 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.

  7. Calculation of the surface potential and surface charge density by measurement of the three-phase contact angle.

    PubMed

    Horiuchi, H; Nikolov, A; Wasan, D T

    2012-11-01

    The silica/silicon wafer is widely used in the semiconductor industry in the manufacture of electronic devices, so it is essential to understand its physical chemistry and determine the surface potential at the silica wafer/water interface. However, it is difficult to measure the surface potential of a silica/silicon wafer directly due to its high electric resistance. In the present study, the three-phase contact angle (TPCA) on silica is measured as a function of the pH. The surface potential and surface charge density at the silica/water surface are calculated by a model based on the Young-Lippmann equation in conjunction with the Gouy-Chapman model for the electric double layer. In measurements of the TPCA on silica, two distinct regions were identified with a boundary at pH 9.5-showing a dominance of the surface ionization of silanol groups below pH 9.5 and a dominance of the dissolution of silica into the aqueous solution above pH 9.5. Since the surface chemistry changes above pH 9.5, the model is applied to solutions below pH 9.5 (ionization dominant) for the calculation of the surface potential and surface charge density at the silica/aqueous interface. In order to evaluate the model, a galvanic mica cell was made of a mica sheet and the surface potential was measured directly at the mica/water interface. The model results are also validated by experimental data from the literature, as well as the results obtained by the potentiometric titration method and the electro-kinetic measurements.

  8. Nanoparticle-Wetted Relays: Reconfigurable Surfaces for Energy Transmission Contacts

    DTIC Science & Technology

    2007-01-01

    Turkevich , J ., Stevenson , P . C . & Hillier , J . A study of the nucleation and growth processes in the...capacitive microelectromechanical systems radio frequency switch contacts. Journal of Applied Physics 99, 94910- 1 -94910-11 (2006). 5. Dickrell, D. J ...Microelectromechanical Systems 14, 954-960 (2005). 10 9. Patton, S. T., Eapen, K. C ., Zabinski, J . S., Sanders, J . H. & Voevodin, A. A. Lubrication

  9. 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.

  10. METHOD FOR PRODUCING WETTABLE SURFACES ON CONTACT LENSES BY CHEMICAL FORMATION OF INORGANIC FILMS

    DTIC Science & Technology

    Wettable surfaces of a permanent nature can be produced on contact lenses by means of the technic of chemical deposition of an inorganic film on the...immersion resistance. Stepwise instructions are given for the preparation of hydrophilic surfaces on contact lenses . The equipment developed for this work is relatively simple and inexpensive. (Author)...lens surface. The process is simpler, both in apparatus and procedure, than the vacuum deposition technic designed earlier for producing wettable

  11. Universal deformation of soft substrates near contact line reveals solid surface stresses

    NASA Astrophysics Data System (ADS)

    Style, Robert; Wettlaufer, John; Wilen, Larry; Dufresne, Eric

    2012-11-01

    We study how sessile droplets behave on soft substrates. Using confocal microscopy, we investigate how droplet surface tension (and Laplace pressure) deforms the substrate. We show that the near-tip shape of the wetting ridge is entirely determined by the surface tensions of the three contacting phases. In particular we can use this observation to (i) directly measure solid-vapour and solid-liquid surface tensions, (ii) resolve how out-of-plane force balance is ensured at the contact line.

  12. A novel quantitative approach for evaluating contact mechanics of meniscal replacements.

    PubMed

    Linder-Ganz, E; Elsner, J J; Danino, A; Guilak, F; Shterling, A

    2010-02-01

    One of the functions of the meniscus is to distribute contact forces over the articular surfaces by increasing the joint contact areas. It is widely accepted that total/partial loss of the meniscus increases the risk of joint degeneration. A short-term method for evaluating whether degenerative arthritis can be prevented or not would be to determine if the peak pressure and contact area coverage of the tibial plateau (TP) in the knee are restored at the time of implantation. Although several published studies already utilized TP contact pressure measurements as an indicator for biomechanical performance of allograft menisci, there is a paucity of a quantitative method for evaluation of these parameters in situ with a single effective parameter. In the present study, we developed such a method and used it to assess the load distribution ability of various meniscal implant configurations in human cadaveric knees (n=3). Contact pressures under the intact meniscus were measured under compression (1200 N, 0 deg flexion). Next, total meniscectomy was performed and the protocol was repeated with meniscal implants. Resultant pressure maps were evaluated for the peak pressure value, total contact area, and its distribution pattern, all with respect to the natural meniscus output. Two other measures--implant-dislocation and implant-impingement on the ligaments--were also considered. If any of these occurred, the score was zeroed. The total implant score was based on an adjusted calculation of the aforementioned measures, where the natural meniscus score was always 100. Laboratory experiments demonstrated a good correlation between qualitative and quantitative evaluations of the same pressure map outputs, especially in cases where there were contradicting indications between different parameters. Overall, the proposed approach provides a novel, validated method for quantitative assessment of the biomechanical performance of meniscal implants, which can be used in various

  13. Assessment of ultraviolet B–blocking effects of weekly disposable contact lenses on corneal surface in a mouse model

    PubMed Central

    Lin, David Pei-Cheng; Chang, Han-Hsin; Yang, Li-Chien; Huang, Tzu-Ping; Liu, Hsiang-Jui; Chang, Lin-Song; Lin, Chien-Hsun

    2013-01-01

    Purpose Weekly disposable soft contact lenses have been widely used recently, but their shield effects against ultraviolet (UV) irradiation remain to be evaluated. This study investigated the bioprotective effects of several weekly soft contact lenses against UVB irradiation on the corneal surface in a mouse model. Methods Fifty ICR mice were randomly divided into five groups: (1) blank control, (2) exposed to UVB without contact lens protection, (3) exposed to UVB and protected with Vifilcon A contact lenses, (4) exposed to UVB and protected with Etafilcon A contact lenses, and (5) exposed to UVB and protected with HEMA+MA contact lenses. The exposure to UVB irradiation was performed at 0.72 J/cm2/day after anesthesia for a 7-day period, followed by cornea surface assessment for smoothness, opacity, and grading of lissamine green staining. Tissue sections were prepared for hematoxylin and eosin staining and immunohistochemical detection by using antibodies against myeloperoxidase, cytokeratin-5, P63, Ki-67, nuclear factor-kappa B (p65), cyclooxygenase-2, Fas L, and Fas. Results The results showed impaired corneal surface with myeloperoxidase+ polymorphonuclear leukocyte infiltration into the stroma after UVB exposure, in contrast to the intact status of the blank controls. The corneas with Etafilcon A and HEMA+MA contact lenses maintained more cells positive for cytokeratin-5, P63, and Ki-67 compared to those with Vifilcon A or without contact lens protection. Furthermore, less proinflammatory factors, including nuclear factor-kappa (p65), cyclooxygenase-2, Fas L, and Fas, were induced in the corneas protected by Etafilcon A and HEMA+MA. Conclusions This study demonstrated various protective effects of weekly disposable contact lenses against UVB irradiation. The mouse model used in the present study may be used extensively for in vivo assessment of UV shield efficacy. PMID:23734085

  14. Contact angle hysteresis of cylindrical drops on chemically heterogeneous striped surfaces.

    PubMed

    Iwamatsu, Masao

    2006-05-15

    Contact angle hysteresis of a macroscopic droplet on a heterogeneous but flat substrate is studied using the interface displacement model. First, the apparent contact angle of a droplet on a heterogeneous surface under the condition of constant volume is considered. By assuming a cylindrical liquid-vapor surface (meniscus) and minimizing the total free energy, we derive an equation for the apparent contact angle, which is similar but different from the well-known Cassie's law. Next, using this modified Cassie's law as a guide to predict the behavior of a droplet on a heterogeneous striped surface, we examine several scenarios of contact angle hysteresis using a periodically striped surface model. By changing the volume of the droplet, we predict a sudden jump of the droplet edge, and a continuous change of the apparent contact angle at the edge of two stripes. Our results suggest that as drop volume is increased (advancing contact lines), the predominant drop configuration observed is the one whose contact angle is large; whereas, decreasing drop volume from a large value (receding contact lines) yields drop configuration that predominantly exhibit the smaller contact angle.

  15. 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.

  16. Thermal sensing and imaging of the dry-sliding contact surface using IR thermomicroscope

    NASA Astrophysics Data System (ADS)

    Sakagami, Takahide; Ogura, Keiji; Shoda, Masahiro

    1995-03-01

    A new experimental technique using an infrared (IR) thermography combined with IR transmitting materials is proposed for the visualization of the contact surface temperature of two solids. A dry sliding contact between a pin and a disk is investigated. IR transmitting solids such as sapphire, alumina ceramics and silicon are employed for the disk material. The temperature distribution on the contact surface is measured by the IR thermography through the IR transmitting disk. It is found that the temperature rise on the contact surface as well as the contact area is accurately analyzed from the obtained thermal images. The influence of contact pressure and sliding velocity on the contact surface temperature is discussed. Further, the dynamic process of wear of bearing steel against sapphire is investigated under dry sliding contact by the new type IRCCD thermography. Transient temperature distribution around the frictional heat spot was computed by the FEM analyses in order to estimate the magnitude of flush temperature from the experimental result in the dry sliding contact. All the results show that the proposed technique is useful for examining the successive process of the tribological phenomena.

  17. Investigating the Interface of Superhydrophobic Surfaces in Contact With Water

    DTIC Science & Technology

    2005-06-11

    pressure technique was used to prepare a rough, highly porous organosilica aerogel -like film. UV/ozone treatments were used to control the surface coverage...a rough, highly porous organosilica aerogel -like film. UV/ozone treatments were used to control the surface coverage of hydrophobic organic ligands on...earlier work on low-temperature/ low-pressure aerogel coatings.42 In this process, surface derivatization of silica sols with fluroalkyl groups28

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. Lubricant pressure rippling in dynamic Hertzian contacts induced by surface roughness

    NASA Technical Reports Server (NTRS)

    Tallian, T. E.; Mccool, J. I.

    1974-01-01

    A numerical analysis of the pressure distribution of a lubricant in contact with a rough surface was conducted. The magnitude of the pressures was determined by their root mean square value for the contact of two dimensional cylinders. The pressure was found to vary in the following manner: (1) the location in the contact, (2) the spectrum or frequency content of the surface roughness, (3) the mean plateau film thickness, and (4) the root mean square value of the surface roughness. Mathematical models are developed to show the relationships of the parameters.

  4. 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.

  5. Model and experimental studies for contact angles of surfactant solutions on rough and smooth hydrophobic surfaces.

    PubMed

    Milne, A J B; Elliott, J A W; Zabeti, Parham; Zhou, Jiyan; Amirfazli, A

    2011-09-28

    Despite the practical need, no models exist to predict contact angles or wetting mode of surfactant solutions on rough hydrophobic or superhydrophobic surfaces. Using Gibbs' adsorption equation and a literature isotherm, a new model is constructed based on the Wenzel and Cassie equations. Experimental data for aqueous solutions of sodium dodecyl sulfate (SDS) contact angles on smooth Teflon surfaces are fit to estimate values for the adsorption coefficients in the model. Using these coefficients, model predictions for contact angles as a function of topological f (Cassie) and r (Wenzel) factors and SDS concentration are made for different intrinsic contact angles. The model is also used to design/tune surface responses. It is found that: (1) predictions compare favorably to data for SDS solutions on five superhydrophobic surfaces. Further, the model predictions can determine which wetting mode (Wenzel or Cassie) occurred in each experiment. The unpenetrated or partially penetrated Cassie mode was the most common, suggesting that surfactants inhibit the penetration of liquids into rough hydrophobic surfaces. (2) The Wenzel roughness factor, r, amplifies the effect of surfactant adsorption, leading to larger changes in contact angles and promoting total wetting. (3) The Cassie solid area fraction, f, attenuates the lowering of contact angles on rough surfaces. (4) The amplification/attenuation is understood to be due to increased/decreased solid-liquid contact-area.

  6. 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.

  7. 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.

  8. 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. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. Two-dimensional Gaussian processes applied to the determination of contact between lubricated rolling surfaces

    NASA Technical Reports Server (NTRS)

    Sidik, S. M.

    1974-01-01

    The effectiveness of a lubricant film preventing metallic contact between two rolling surfaces (such as in ball bearings) as a function of surface roughness parameters was investigated. The parameters considered are the spectral moments of the two-dimensional surface obtained by superposition of the two rolling surfaces. The peak height distribution, estimation of one-dimensional profile spectral moments, and the estimation of two-dimensional surface moments from several profile measurements were considered. Also given is an asymptotic relation between the mean film thickness and contact occurrences.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  11. The role of the roughness spectral breadth in elastic contact of rough surfaces

    NASA Astrophysics Data System (ADS)

    Yastrebov, Vladislav A.; Anciaux, Guillaume; Molinari, Jean-François

    2017-10-01

    We study frictionless and non-adhesive contact between elastic half-spaces with self-affine surfaces. Using a recently suggested corrective technique, we ensure an unprecedented accuracy in computation of the true contact area evolution under increasing pressure. This accuracy enables us to draw conclusions on the role of the surface's spectrum breadth (Nayak parameter) in the contact area evolution. We show that for a given normalized pressure, the contact area decreases logarithmically with the Nayak parameter. By linking the Nayak parameter with the Hurst exponent (or fractal dimension), we show the effect of the latter on the true contact area. This effect, undetectable for surfaces with poor spectral content, is quite strong for surfaces with rich spectra. Numerical results are compared with analytical models and other available numerical results. A phenomenological equation for the contact area growth is suggested with coefficients depending on the Nayak parameter. Using this equation, the pressure-dependent friction coefficient is deduced based on the adhesive theory of friction. Some observations on Persson's model of rough contact, whose prediction does not depend on Nayak parameter, are reported. Overall, the paper provides a unifying picture of rough elastic contact and clarifies discrepancies between preceding results.

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

    PubMed

    Gerson, D F; Akit, J

    1980-11-04

    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.

  13. Investigation of transient temperature's influence on damage of high-speed sliding electrical contact rail surface

    NASA Astrophysics Data System (ADS)

    Zhang, Yuyan; Sun, Shasha; Guo, Quanli; Yang, Degong; Sun, Dongtao

    2016-11-01

    In the high speed sliding electrical contact with large current, the temperature of contact area rises quickly under the coupling action of the friction heating, the Joule heating and electric arc heating. The rising temperature seriously affects the conductivity of the components and the yield strength of materials, as well affects the contact state and lead to damage, so as to shorten the service life of the contact elements. Therefore, there is vital significance to measure the temperature accurately and investigate the temperature effect on damage of rail surface. Aiming at the problem of components damage in high speed sliding electrical contact, the transient heat effect on the contact surface was explored and its influence and regularity on the sliding components damage was obtained. A kind of real-time temperature measurement method on rail surface of high speed sliding electrical contact is proposed. Under the condition of 2.5 kA current load, based on the principle of infrared radiation non-contact temperature sensor was used to measure the rail temperature. The dynamic distribution of temperature field was obtained through the simulation analysis, further, the connection between temperature changes and the rail surface damage morphology, the damage volume was analyzed and established. Finally, the method to reduce rail damage and improve the life of components by changing the temperature field was discussed.

  14. Surface Physics and Chemistry of Electrical Contact Phenomena.

    DTIC Science & Technology

    1980-06-01

    terms of a simple outgassing model that involves bulk diffusion of sulfur to the surface and its precipitation there. Clearly locally high...on diffusion controlled " outgassing " in which the sulfur segregated to the surface instead of vaporizing. The activation energies for this process for...increased slightly with temperature. tially identical to that involved in the outgassing of materials However, only for the Ag/Cu alloy, above 500’C the

  15. 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.

  16. Impact of contact lens material and design on the ocular surface.

    PubMed

    Ruiz-Alcocer, Javier; Monsálvez-Romín, Daniel; García-Lázaro, Santiago; Albarrán-Diego, César; Hernández-Verdejo, José Luis; Madrid-Costa, David

    2017-10-11

    To evaluate the impact on the ocular surface of a daily disposable hydrogel contact lens with high water content compared with two silicone hydrogel daily disposable lenses of lower water content. The hydrogel lens assessed was made from nesofilcon A and the silicone hydrogel lenses were made of delefilcon A and stenfilcon A. Contact lens thickness was measured to assess material stability during daily wear, and ocular surface parameters such as tear film osmolarity, tear meniscus area and central corneal thickness were also assessed. Optical quality was analysed for all cases by means of wavefront aberrometry. The nesofilcon A was shown to be the thinnest lens (p < 0.001), while no differences in lens thickness were found between the two silicone hydrogel lenses (p = 0.495). No significant differences were found in tear film osmolarity, tear meniscus area, central corneal thickness or corneal aberrations, either as a function of the lens measured or time of use (p > 0.05). In spite of having the thinnest lens and the highest water content, the hydrogel does not significantly impact on tear film and corneal swelling after one day of use in first-time wearers. © 2017 Optometry Australia.

  17. The Emitter Having Microcrystalline Surface in Silicon Heterojunction Interdigitated Back Contact Solar Cells

    NASA Astrophysics Data System (ADS)

    Ji, Kwang-sun; Syn, Hojung; Choi, Junghoon; Lee, Heon-Min; Kim, Donghwan

    2012-10-01

    In producing the Si heterojunction interdigitated backcontact solar cells, we investigated the feasibility of applying amorphous Si emitter having considerable crystalline Si phase at the facing to transparent conducting oxide (TCO) layer. Prior to evaluating electrical property, we characterized material nature of hydrogenated microcrystalline p-type silicon (µc-p-Si:H) as crystallized fraction, surface morphology, bonding kinds in thin films and then surface passivation quality finally. The diode and interface contact characteristics were induced by the simple test device and then current-voltage (I-V) curve showed more linearity in µc/hydrogenated amorphous silicon (a-Si:H) emitter case. We fabricated heterojunction back contact (HBC) solar cells using p/n interdigitated structure and acquired the 23.4% efficiency in cell size with performance parameters as open-circuit voltage (Voc) 723 mV, short-circuit current density (Jsc) 41.8 mA/cm2, fill factor (FF) 0.774, in the cell size (at 2×2 cm2).

  18. Contact angle hysteresis: a different view and a trivial recipe for low hysteresis hydrophobic surfaces.

    PubMed

    Krumpfer, Joseph W; McCarthy, Thomas J

    2010-01-01

    Contact angle hysteresis is addressed from two perspectives. The first is an analysis of the events that occur during motion of droplets on superhydrophobic surfaces. Hysteresis is discussed in terms of receding contact line pinning and the tensile failure of capillary bridges. The sign of the curvature of the solid surface is implicated as playing a key role. The second is the report of a new method to prepare smooth low hysteresis surfaces. The thermal treatment of oxygen plasma-cleaned silicon wafers with trimethylsilyl-terminated linear poly(dimethylsiloxane) (PDMS - commercial silicone oils) in disposable glass vessels is described. This treatment renders silicon/silica surfaces that contain covalently attached PDMS chains. The grafted layers of nanometre scale thickness are liquid-like (rotationally dynamic at room temperature), decrease activation barriers for contact line motion and minimize water contact angle hysteresis. This simple method requires neither sophisticated techniques nor substantial laboratory skills to perform.

  19. Contact Angle Hysteresis on Graphene Surfaces and Hysteresis-free Behavior on Oil-infused Graphite Surfaces

    NASA Astrophysics Data System (ADS)

    Wu, Cyuan-Jhang; Li, Yueh-Feng; Woon, Wei-Yen; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2016-11-01

    Contact angle hysteresis (CAH) on graphitic surfaces, including chemical vapor deposition (CVD) graphene, reduced electrophoretic deposition (EPD) graphene, highly oriented pyrolytic graphite (HOPG), and polished graphite sheet, has been investigated. The hysteresis loops of water drops on the first three samples are similar but the receding contact angle is particularly small for the polished graphite sheet.The significant CAH observed on CVD graphene and HOPG associated with atom-scale roughness has to be attributed mainly to adhesion hysteresis (surface relaxation), instead of roughness or defects.The difference of the wetting behavior among those four graphitic samples has been further demonstrated by hexadecane drops. On the surface of HOPG or CVD graphene,the contact line expands continuously with time, indicating total wetting for which the contact angle does not exist and contact line pinning disappears. In contrast, on the surface of reduced EPD graphene, spontaneous spreading is halted by spikes on it and partial wetting with small contact angle (θ≈4°) is obtained. On the surface of polished graphite sheet, the superlipophilicity and porous structure are demonstrated by imbibition and capillary rise of hexadecane. Consequently, an oil-infused graphite surface can be fabricated and the ultralow CAH of water (∆θ≈2°) is achieved.

  20. Mitigation of Alicyclobacillus spp. spores on food contact surfaces with aqueous chlorine dioxide and hypochlorite.

    PubMed

    Friedrich, Loretta M; Goodrich-Schneider, Renee; Parish, Mickey E; Danyluk, Michelle D

    2009-12-01

    The prevalence of Alicyclobacillus spp. and other spore-forming spoilage organisms in food handling and processing environments presents a sanitation challenge to manufacturers of products such as juices and beverages. The objectives of this study were to determine the efficacy of chlorine dioxide and sodium hypochlorite in killing Alicyclobacillus spores in situ and to evaluate the efficacy of various chlorine dioxide and hypochlorite sanitizing regimes on Alicyclobacillus spp. spores on stainless steel, wood, and rubber conveyor material. Five or two log CFU/ml spore concentrations were left in aqueous solution or inoculated onto stainless steel, rubber, or wood coupons and challenged with sanitizer for varied time intervals. After treatment, the coupons were placed in sterile sample bags, massaged with neutralizing buffer, and enumerated on Ali agar. Surfaces were also examined before and after treatment by scanning electron microscopy to confirm destruction or removal of the spores. For both five and two log CFU/ml spore concentrations, treatments of 50 and 100 ppm of chlorine dioxide and 1000 and 2000 ppm of hypochlorite, respectively, were the most effective. Of the range of chlorine dioxide concentrations and contact time regimes evaluated for all surfaces, the most effective concentration/time regime applied was 100 ppm for 10 min. Reductions ranged from 0 to 4.5 log CFU/coupon. Chlorine dioxide was least effective when applied to wood. Hypochlorite was not efficient at eliminating Alicyclobacillus spores from any of the food contact surfaces at any time and concentration combinations tested. Chlorine dioxide is an alternative treatment to kill spores of Alicyclobacillus spp. in the processing environment.

  1. 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.

  2. Impact of Cosmetics on the Surface Properties of Silicone Hydrogel Contact Lenses.

    PubMed

    Srinivasan, Sruthi; Otchere, Heinz; Yu, Mili; Yang, Jeffery; Luensmann, Doerte; Jones, Lyndon

    2015-07-01

    This study evaluated the impact of various cosmetics on the surface properties of silicone hydrogel (SiHy) contact lens materials. In this in vitro experiment, 7 SiHy contact lens materials were coated with 1 of 9 cosmetics, including common hand creams (3), eye makeup removers (3), and mascaras (3). Dark-field microscopy images were taken to determine pixel brightness (PB) after cosmetic exposure, which describes the visible surface deposition (n=6 for each lens type), with a higher PB indicating increased deposition. The sessile drop technique was used to determine the advancing contact angle (CA). Measurements were repeated for both methods after a single peroxide-based cleaning cycle. Pixel brightness was significantly higher for mascara-coated lenses compared with the other cosmetic products (P<0.01). The peroxide-based lens care solution removed most deposits from the nonwaterproof mascara for 4 lens types, whereas deposits remained relatively unchanged for 1 waterproof mascara (P>0.05). Hand creams and makeup remover had minimal impact on PB. Changes in CA measurements after cosmetic application were highly lens dependent. Hand creams caused primarily a decrease in CA for 5 of the 7 lens types, whereas 1 of the waterproof mascaras caused a significant increase of 30 to 50° for 3 lens types. Some mascara-lens combinations resulted in increased CA and PB, which could have an impact on in vivo lens performance. Nonwaterproof mascara was mostly removed after a cleaning cycle. Further research is needed to understand the clinical implications for SiHy lens wearers using cosmetics.

  3. 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.

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

    PubMed

    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)LANGD50743-746310.1021/la303070s] in the case of block depinning is theoretically substantiated through the capillary force, acting on the solid plate at the meniscus contact line.

  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. Fabricating Ohmic contact on Nb-doped SrTiO{sub 3} surface in nanoscale

    SciTech Connect

    Wang, Yuhang; Shi, Xiaolan; Zhang, Liuwan E-mail: lwzhang@mail.tsinghua.edu.cn; Lai, Xubo; Gao, Zhipeng; Liu, Lixin; Wang, Yuan; Zhu, Wenjun; Meng, Chuanmin E-mail: lwzhang@mail.tsinghua.edu.cn

    2016-05-09

    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 SrTiO{sub 3} 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.

  8. Surface wettability and hydrophilicity of soft contact lens materials, before and after wear.

    PubMed

    Shirafkan, A; Woodward, E G; Port, M J; Hull, C C

    1995-09-01

    Surface wettability and hydrophilicity of pHEMA soft contact lenses were investigated utilising adherent liquid/laser method (ALLM) and adherent liquid/balance method (ALBM). The measurements were carried out before and after periods of 15 min to 2 h contact lens wear. Following the lens removal, the wetting angle of the contact lens of the left eyes and hydrophilicity (maximum force) of the contact lens of the right eyes of the five subjects were immediately measured, respectively, without cleaning (one value for pre-lens wear and eight values for post-lens wear). The wettability of soft contact lenses significantly increased after 15 min of wearing and stabilised at a maximum level after 30 min in vivo. Contact lens hydrophilicity was found to decrease as the lens was worn. The reduction continued for up to 1.5 h of wearing, for male cases, and for the female cases, the reduction continued until the end of the experiment.

  9. The effect of drop volume and micropillar shape on the apparent contact angle of ordered microstructured surfaces.

    PubMed

    Afferrante, Luciano; Carbone, Giuseppe

    2014-06-14

    In the present paper, we propose a new theoretical approach to evaluate the shape and apparent contact angle (ACA) of a drop gently deposited on microstructured superhydrophobic surfaces. We exploit the very large separation of scales between the drop size and the features of the micromorphology of the interface to propose a numerical methodology to calculate the apparent contact area and apparent contact angle. In agreement with very recent experiments, calculations show that, in the case of surfaces made of conical micropillars, the ACA may take values very close to 180° not depending on the size of the liquid drop. At large drop volumes, the shape of the drop deviates from the spherical one as a result of the gravity effects, but it is noteworthy that the apparent contact angle does not change at all. Our calculations shows that this holds true also for different pillar shapes, showing that, for any given Young contact angle of the solid constituting the pillars, the ACA is an intrinsic property of the surface microgeometry.

  10. Normal adhesive contact on rough surfaces: efficient algorithm for FFT-based BEM resolution

    NASA Astrophysics Data System (ADS)

    Rey, Valentine; Anciaux, Guillaume; Molinari, Jean-François

    2017-07-01

    We introduce a numerical methodology to compute the solution of an adhesive normal contact problem on rough surfaces with the Boundary Element Method. Based on the Fast Fourier Transform and the Westergaard's fundamental solution, the proposed algorithm enables to solve efficiently the constrained minimization problem: the numerical solution strictly verifies contact orthogonality and the algorithm takes advantage of the constraints to speed up the minimization. Comparisons with the analytical solution of the Hertz case prove the quality of the numerical computation. The method is also used to compute normal adhesive contact between rough surfaces made of multiple asperities.

  11. Normal adhesive contact on rough surfaces: efficient algorithm for FFT-based BEM resolution

    NASA Astrophysics Data System (ADS)

    Rey, Valentine; Anciaux, Guillaume; Molinari, Jean-François

    2017-03-01

    We introduce a numerical methodology to compute the solution of an adhesive normal contact problem on rough surfaces with the Boundary Element Method. Based on the Fast Fourier Transform and the Westergaard's fundamental solution, the proposed algorithm enables to solve efficiently the constrained minimization problem: the numerical solution strictly verifies contact orthogonality and the algorithm takes advantage of the constraints to speed up the minimization. Comparisons with the analytical solution of the Hertz case prove the quality of the numerical computation. The method is also used to compute normal adhesive contact between rough surfaces made of multiple asperities.

  12. A thermodynamic approach for determining the contact angle hysteresis for superhydrophobic surfaces.

    PubMed

    Li, W; Amirfazli, A

    2005-12-01

    Contact angle hysteresis (CAH) is critical to superhydrophobicity of a surface. This study proposes a free energy thermodynamic analysis (of a 2-D model surface) that significantly simplifies calculations of free energy barrier associated with CAH phenomena. A microtextured surface with pillar structure, typical of one used in experimental studies, is used as an example. We demonstrate that the predicted CAH and equilibrium contact angles are consistent with experimental observations and predictions of Wenzel's and Cassie's equations, respectively. We also establish a criterion for transition between noncomposite and composite wetting states. The results and methodology presented can potentially be used for designing superhydrophobic surfaces.

  13. Drop evaporation on superhydrophobic PTFE surfaces driven by contact line dynamics.

    PubMed

    Ramos, S M M; Dias, J F; Canut, B

    2015-02-15

    In the present study, we experimentally study the evaporation modes and kinetics of sessile drops of water on highly hydrophobic surfaces (contact angle ∼160°), heated to temperatures ranging between 40° and 70 °C. These surfaces were initially constructed by means of controlled tailoring of polytetrafluoroethylene (PTFE) substrates. The evaporation of droplets was observed to occur in three distinct phases, which were the same for the different substrate temperatures. The drops started to evaporate in the constant contact radius (CCR) mode, then switched to a more complex mode characterized by a set of stick-slip events accompanied by a decrease in contact angle, and finally shifted to a mixed mode in which the contact radius and contact angle decreased simultaneously until the drops had completely evaporated. It is shown that in the case of superhydrophobic surfaces, the energy barriers (per unit length) associated with the stick-slip motion of a drop ranges in the nJ m(-1) scale. Furthermore, analysis of the evaporation rates, determined from experimental data show that, even in the CCR mode, a linear relationship between V(2/3) and the evaporation time is verified. The values of the evaporation rate constants are found to be higher in the pinned contact line regime (the CCR mode) than in the moving contact line regime. This behavior is attributed to the drop's higher surface to volume ratio in the CCR mode. Copyright © 2014 Elsevier Inc. All rights reserved.

  14. Multi-centre evaluation of two daily disposable contact lenses.

    PubMed

    Walker, Jon; Young, Graeme; Hunt, Chris; Henderson, Terri

    2007-05-01

    To evaluate the clinical performance of two daily disposable contact lenses: 1-DAY ACUVUE (1DA) (etafilcon A, Johnson & Johnson Vision Care) and FOCUS DAILIES with AquaComfort (FD) (nelfilcon A, CIBA Vision, Inc.), which contains a quickly released moisture enhancing agent, polyvinyl alcohol (PVA). This was a 1-week, daily wear, subject-masked, bilateral, parallel group study with subjects randomly assigned to one of two daily disposable soft contact lenses. Subjects were existing soft contact lens wearers in the age range 18-39 years with a spherical refraction between -0.50 and -6.00 D. Subjects were assessed at baseline and after 1 week. Assessments included both subjective (symptoms, wearing time, vision) and objective (lens fit and ocular health) outcomes. Twenty clinical sites enrolled 282 subjects (74% female) of whom 276 (98%) successfully completed the study. Significantly more 1DA wearers reported higher mean comfort scores than with FD (3.95 versus 3.41, respectively, P<0.0001). End-of-day comfort means were also significantly higher with the 1DA group compared to the FD group (3.3 versus 3.0, P=0.03). The 1DA group reported significantly longer mean overall wearing time (1DA was worn on average 0.66+/-0.30 h longer than FD, P=0.03) and longer mean comfortable wearing time (1DA was worn on average 1.73+/-0.35 h longer than FD, P<0.0001). The 1DA lens generally showed significantly better on-eye fitting in terms of movement in primary (P<0.0001) and upgaze (P<0.0001) and ease of removal from the eye (92% versus 63%, P<0.0001) compared to FD. There was significantly less corneal staining observed with the 1DA wearing eyes compared with the FD wearing eyes (23% versus 45%, respectively, P<0.0001). Finally, there was a weak correlation between corneal staining and comfort for FD (r=0.27, P=0.002, n=136), but not for 1DA (r=-0.11, P=0.18, n=140). Subjective and objective clinical performance differences between two commonly used daily disposable lenses

  15. 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

  16. Optimum contact conditions for miniaturized surface acoustic wave linear motor

    PubMed

    Takasaki; Kurosawa; Higuchi

    2000-03-01

    This paper reports the successful operation of a 70 MHz driving surface acoustic wave (SAW) linear motor with a miniaturized stator transducer. This paper also deals with an investigation into an optimized slider design for the miniaturized SAW linear motor. The performance of three silicon type sliders, with different projection size, was compared. Output forces of the three sliders were measured with change of pre-load. It was found that the slider with smaller projection tended to produce greater output force.

  17. Surface modification of model hydrogel contact lenses with hyaluronic acid via thiol-ene "click" chemistry for enhancing surface characteristics.

    PubMed

    Korogiannaki, Myrto; Zhang, Jianfeng; Sheardown, Heather

    2017-10-01

    Discontinuation of contact lens wear as a result of ocular dryness and discomfort is extremely common; as many as 26% of contact lens wearers discontinue use within the first year. While patients are generally satisfied with conventional hydrogel lenses, improving on-eye comfort continues to remain a goal. Surface modification with a biomimetic, ocular friendly hydrophilic layer of a wetting agent is hypothesized to improve the interfacial interactions of the contact lens with the ocular surface. In this work, the synthesis and characterization of poly(2-hydroxyethyl methacrylate) surfaces grafted with a hydrophilic layer of hyaluronic acid are described. The immobilization reaction involved the covalent attachment of thiolated hyaluronic acid (20 kDa) on acrylated poly(2-hydroxyethyl methacrylate) via nucleophile-initiated Michael addition thiol-ene "click" chemistry. The surface chemistry of the modified surfaces was analyzed by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray photoelectron spectroscopy. The appearance of N (1s) and S (2p) peaks on the low resolution X-ray photoelectron spectroscopy spectra confirmed successful immobilization of hyaluronic acid. Grafting hyaluronic acid to the poly(2-hydroxyethyl methacrylate) surfaces decreased the contact angle, the dehydration rate, and the amount of nonspecific sorption of lysozyme and albumin in comparison to pristine hydrogel materials, suggesting the development of more wettable surfaces with improved water-retentive and antifouling properties, while maintaining optical transparency (>92%). In vitro testing also showed excellent viability of human corneal epithelial cells with the hyaluronic acid-grafted poly(2-hydroxyethyl methacrylate) surfaces. Hence, surface modification with hyaluronic acid via thiol-ene "click" chemistry could be useful in improving contact lens surface properties, potentially alleviating symptoms of contact lens related dryness and discomfort during

  18. Structures of simple liquids in contact with nanosculptured surfaces.

    PubMed

    Singh, Swarn Lata; Schimmele, Lothar; Dietrich, S

    2015-03-01

    We present a density functional study of Lennard-Jones liquids in contact with a nanocorrugated wall. The corresponding substrate potential is taken to exhibit a repulsive hard core and a Van der Waals attraction. The corrugation is modeled by a periodic array of square nanopits. We have used the modified Rosenfeld density functional in order to study the interfacial structure of these liquids which with respect to their thermodynamic bulk state are considered to be deep inside their liquid phase. We find that already considerably below the packing fraction of bulk freezing of these liquids, inside the nanopits a three-dimensional-like density localization sets in. If the sizes of the pits are commensurate with the packing requirements, we observe high-density spots separated from each other in all spatial directions by liquid of comparatively very low density. The number, shape, size, and density of these high-density spots depend sensitively on the depth and width of the pits. Outside the pits, only layering is observed; above the pit openings these layers are distorted with the distortion reaching up to a few molecular diameters. We discuss quantitatively how this density localization is affected by the geometrical features of the pits and how it evolves upon increasing the bulk packing fraction. Our results are transferable to colloidal systems and pit dimensions corresponding to several diameters of the colloidal particles. For such systems the predicted unfolding of these structural changes can be studied experimentally on much larger length scales and more directly (e.g., optically) than for molecular fluids which typically call for sophisticated x-ray scattering.

  19. 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.

  20. Modulating contact angle hysteresis to direct fluid droplets along a homogenous surface.

    PubMed

    Luo, Mingxiang; Gupta, Rohini; Frechette, Joelle

    2012-02-01

    The shape and motion of drops on surfaces is governed by the balance between the driving and the pinning forces. Here we demonstrate control over the motion of droplets on an inclined surface by exerting control over the contact angle hysteresis. The external modulation of contact angle hysteresis is achieved through a voltage-induced local molecular reorganization within the surface film at the solid-liquid interface. We show that tuning contact angle hysteresis alone is sufficient to direct and deform drops when subjected to a constant external driving force, here gravity, in the absence of a pre-defined surface energy gradient or pattern. We also show that the observed stretching and contraction of the drops mimic the motion of an inchworm. Such reversible manipulation of the pinning forces could be an attractive means to direct drops, especially with the dominance of surface forces at micro-/nanoscale.

  1. 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.

  2. Determination of the Surface Tension of Microporous Membranes Using Contact Angle Measurements

    PubMed

    Tröger; Lunkwitz; Bürger

    1997-10-15

    In this paper, a new method of determining the surface tension of the solid material that a microporous membrane is made from is introduced. The method is based on the well known determination of the so-called contact angle that is formed on the solid/liquid/gaseous three phase line. A nonideal state of the solid phase leads to a deviation of the contact angle that can be observed experimentally from the equilibrium angle that arises from the thermodynamically state of lowest energy, as it must be used to calculate the solid surface tension via the Young equation. The deviation caused from the porous structure of the solid material will be taken into account in this work. Doing so, we derived an equation that connects the surface porosity, the measured contact angle, and the equilibrium contact angle. Using this equation, the measured and therefore deviated contact angles can be corrected for the porosity of the solid material, yielding the contact angle observable on a surface made from the same but nonporous material. The equation derived was tested on different microporous membranes made from expanded poly(tetrafluoroethylene). The surface porosity needed was determined using scanning electron microscopy followed by computerized image analysis. Copyright 1997 Academic Press. Copyright 1997Academic Press

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

    SciTech Connect

    Chen, Yung-Kan E-mail: ykchen@berkeley.edu; Bogy, David B.; Peng, Jih-Ping

    2016-05-30

    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 μm{sup 2} 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.

  4. 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. Copyright © 2011 Wiley Periodicals, Inc.

  5. Wetting and scanning force microscopy on rough polymer surfaces: Wenzel's roughness factor and the thermodynamic contact angle

    NASA Astrophysics Data System (ADS)

    Kamusewitz, H.; Possart, W.

    The influence of the surface roughness of polypropylene on the contact angle hysteresis is investigated by means of ethylene glycol drops in order to estimate the true Young's equilibrium contact angle. A new relationship between the contact angle hysteresis and Wenzel's contact angle is derived. In addition, the determination of Wenzel's roughness factor by means of scanning force microscopy opens an alternative way to obtaining Young's equilibrium contact angle without any surface manipulation. The experimental results presented verify this new approach.

  6. Imaging surfaces of hydrophilic contact lenses with the atomic force microscope.

    PubMed

    Baguet, J; Sommer, F; Duc, T M

    1993-01-01

    Soft contact lens (SCL) surfaces were imaged with atomic force microscopy (AFM). High-resolution images of unworn SCL were obtained under nearly physiological medium. We present images of surfaces of collagen bandage lens under dry or aqueous conditions and of SCL of different water content and fabrication processes. Roughness parameters were determined. AFM studies of surfaces of SCL are expected to provide useful information on the hydrogel surfaces.

  7. Self-assembling surfaces of blood-contacting materials.

    PubMed

    Major, Roman

    2013-03-01

    The optimal scaffold should have the self-organising property of activating the appropriate tissues surrounding the re-population. The anti-bacterial property of the coating was obtained through surface pre-treatment with coatings a few nanometres in thickness deposited using vapour-based methods. The coating's anti-thrombogenic properties were obtained by the selective mobilisation of cellular functions, which was controlled by the structure of porous coatings deposited on bulk substrates and by the small biological agent-L-arginyl-glycyl-L-aspartic acid (tripeptide Arg-Gly-Asp-RGD) protein domains. Two tests simulating arterial flow conditions were performed: Impact-R, for examining platelet function under near physiological conditions, and radial flow chamber, a cell detachment test that gives an overview of cell behaviour and shear stresses that could appear between the cell and the biomaterial. Cell structures were analysed using laser scanning confocal microscopy and flow cytometry. The performed in vitro dynamic test for the haemo-compatibility revealed the most promising surface functionalization was based on porous extracellular-like structure covered with endothelium cells simultaneously. The antibacterial function was achieved by the appropriate phase composition of the coating used for the pre-treatment stage. The coating for the pre-treatment was selected on the basis of the blood-material and bacteria-material interaction.

  8. 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.

  9. Fabrication of surfaces with extremely high contact angle hysteresis from polyelectrolyte multilayer.

    PubMed

    Wang, Liming; Wei, Jingjing; Su, Zhaohui

    2011-12-20

    High contact angle hysteresis on polyelectrolyte multilayers (PEMs) ion-paired with hydrophobic perfluorooctanoate anions is reported. Both the bilayer number of PEMs and the ionic strength of deposition solutions have significant influence on contact angle hysteresis: higher ionic strength and greater bilayer number cause increased contact angle hysteresis values. The hysteresis values of ~100° were observed on smooth PEMs and pinning of the receding contact line on hydrophilic defects is implicated as the cause of hysteresis. Surface roughness can be used to further tune the contact angle hysteresis on the PEMs. A surface with extremely high contact angle hysteresis of 156° was fabricated when a PEM was deposited on a rough substrate coated with submicrometer scale silica spheres. It was demonstrated that this extremely high value of contact angle hysteresis resulted from the penetration of water into the rough asperities on the substrate. The same substrate hydrophobized by chemical vapor deposition of 1H,1H,2H,2H-perfluorooctyltriethoxysilane exhibits high advancing contact angle and low hysteresis.

  10. Adhesive contact of rough surfaces: comparison between numerical calculations and analytical theories.

    PubMed

    Carbone, G; Scaraggi, M; Tartaglino, U

    2009-09-01

    The authors have employed a numerical procedure to analyse the adhesive contact between a soft elastic layer and a rough rigid substrate. The solution to the problem, which belongs to the class of the free boundary problems, is obtained by calculating Green's function which links the pressure distribution to the normal displacements at the interface. The problem is then formulated in the form of a Fredholm integral equation of the first kind with a logarithmic kernel. The boundaries of the contact area are calculated by requiring the energy of the system to be stationary. This methodology has been employed to study the adhesive contact between an elastic semi-infinite solid and a randomly rough rigid profile with a self-affine fractal geometry. We show that, even in the presence of adhesion, the true contact area still linearly depends on the applied load. The numerical results are then critically compared with the predictions of an extended version of Persson's contact mechanics theory, which is able to handle anisotropic surfaces, as 1D interfaces. It is shown that, for any given load, Persson's theory underestimates the contact area by about 50% in comparison with our numerical calculations. We find that this discrepancy is larger than for 2D rough surfaces in the case of adhesionless contact. We argue that this increased difference might be explained, at least partially, by considering that Persson's theory is a mean-field theory in spirit, so it should work better for 2D rough surfaces rather than for 1D rough surfaces. We also observe that the predicted value of separation is in agreement with our numerical results as well as the exponents of the power spectral density of the contact pressure distribution and of the elastic displacement of the solid. Therefore, we conclude that Persson's theory captures almost exactly the main qualitative behaviour of the rough contact phenomena.

  11. 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).

  12. Adhesive contact of rough surfaces: Comparison between numerical calculations and analytical theories

    NASA Astrophysics Data System (ADS)

    Carbone, G.; Scaraggi, M.; Tartaglino, U.

    2009-09-01

    The authors have employed a numerical procedure to analyse the adhesive contact between a soft elastic layer and a rough rigid substrate. The solution to the problem, which belongs to the class of the free boundary problems, is obtained by calculating Green’s function which links the pressure distribution to the normal displacements at the interface. The problem is then formulated in the form of a Fredholm integral equation of the first kind with a logarithmic kernel. The boundaries of the contact area are calculated by requiring the energy of the system to be stationary. This methodology has been employed to study the adhesive contact between an elastic semi-infinite solid and a randomly rough rigid profile with a self-affine fractal geometry. We show that, even in the presence of adhesion, the true contact area still linearly depends on the applied load. The numerical results are then critically compared with the predictions of an extended version of Persson’s contact mechanics theory, which is able to handle anisotropic surfaces, as 1D interfaces. It is shown that, for any given load, Persson’s theory underestimates the contact area by about 50% in comparison with our numerical calculations. We find that this discrepancy is larger than for 2D rough surfaces in the case of adhesionless contact. We argue that this increased difference might be explained, at least partially, by considering that Persson’s theory is a mean-field theory in spirit, so it should work better for 2D rough surfaces rather than for 1D rough surfaces. We also observe that the predicted value of separation is in agreement with our numerical results as well as the exponents of the power spectral density of the contact pressure distribution and of the elastic displacement of the solid. Therefore, we conclude that Persson’s theory captures almost exactly the main qualitative behaviour of the rough contact phenomena. in here

  13. Assessing the accuracy of contact angle measurements for sessile drops on liquid-repellent surfaces.

    PubMed

    Srinivasan, Siddarth; McKinley, Gareth H; Cohen, Robert E

    2011-11-15

    Gravity-induced sagging can amplify variations in goniometric measurements of the contact angles of sessile drops on super-liquid-repellent surfaces. The very large value of the effective contact angle leads to increased optical noise in the drop profile near the solid-liquid free surface and the progressive failure of simple geometric approximations. We demonstrate a systematic approach to determining the effective contact angle of drops on super-repellent surfaces. We use a perturbation solution of the Bashforth-Adams equation to estimate the contact angles of sessile drops of water, ethylene glycol, and diiodomethane on an omniphobic surface using direct measurements of the maximum drop width and height. The results and analysis can be represented in terms of a dimensionless Bond number that depends on the maximum drop width and the capillary length of the liquid to quantify the extent of gravity-induced sagging. Finally, we illustrate the inherent sensitivity of goniometric contact angle measurement techniques to drop dimensions as the apparent contact angle approaches 180°.

  14. Evaluation of the occlusal contact of crowns fabricated with the bite impression method.

    PubMed

    Makino, Sachi; Okada, Daizo; Shin, Chiharu; Ogura, Reiko; Ikeda, Masaomi; Miura, Hiroyuki

    2013-09-30

    In prosthodontic treatment, reconstruction of a proper occlusal contact relationship is very important as well as reconstruction of a proper interproximal relationship and marginal fitness. Unfortunately, occlusal relationships are sometimes lost in the process of occlusal adjustment of crowns. The purpose of this study was to compare the occlusal contacts of single crown fabricated by two different types of impression techniques. Nine subjects, whose molars required treatment with crown restoration, were enrolled in this study. Full cast crowns were fabricated using two types of impression techniques: the conventional impression method (CIM) and the bite impression method (BIM). The occlusal contacts of crowns were precisely evaluated at the following stages: after occlusal adjustment on the articulator (Step 0), before occlusal adjustment in the mouth (Step 1), after occlusal adjustment at the intercuspal position (Step 2), and after occlusal adjustment during lateral and protrusive excursions (Step 3). The number of occlusal contacts of the crowns on the functional cusps fabricated with BIM was significantly greater than that with CIM after occlusal adjustment. For this reason, the crowns fabricated with BIM might have a more functionally desirable occlusal surface compared to the crowns fabricated with CIM.

  15. Effect of Surface Roughness on Contact Angle Measurement of Nanofluid on Surface of Stainless Steel 304 by Sessile Drop Method

    NASA Astrophysics Data System (ADS)

    Prajitno, D. H.; Maulana, A.; Syarif, D. G.

    2016-08-01

    Contact angles play an important role in the mass and heat transfer. Stainless steel 304 has been used for nuclear power plan structure material until now. An experiment to measure contact angle of demineralized aqua and nanofluid containing nano particle of zirconia on metal surface of stainless steel 304 with sessile drop method was conducted. The measurement to measure the static contact angle and drop of nano fluid containing nano particle zirconia on stainless steel with different surface roughness was carried out. It was observed that stainless steel 304 was good hydrophylic properties with decreasing surface roughness of stainless steel during drop of aqua demineralized and nano fluid respectively. As a result the contact angle of demineralized aqua is decreased from 97.39 to 78.42 and contact angle of nano fluid from 94.3 to 67.50, respectively with decreasing surface roughness of stainless stee 304. Wettability of nanofluid on surface stainless steel 304 is better than aqua demineralized.

  16. Contact mechanics and rubber friction for randomly rough surfaces with anisotropic statistical properties

    NASA Astrophysics Data System (ADS)

    Carbone, G.; Lorenz, B.; Persson, B. N. J.; Wohlers, A.

    2009-07-01

    In this paper we extend the theory of contact mechanics and rubber friction developed by one of us (B.N.J. Persson, J. Chem. Phys. 115, 3840 (2001)) to the case of surfaces with anisotropic surface roughness. As an application we calculate the viscoelastic contribution to the rubber friction. We show that the friction coefficient may depend significantly on the sliding direction, while the area of contact depends weakly on the sliding direction. We have carried out experiments for rubber blocks sliding on unidirectionally polished steel surfaces. The experimental data are in a good qualitative agreement with the theory.

  17. Contact angle determination procedure and detection of an invisible surface film

    NASA Technical Reports Server (NTRS)

    Meyer, G.; Grat, R.

    1990-01-01

    The contact angle value, i.e., the tangent angle of liquid resting on a planar solid surface, is a basic parameter which can be applied to a wide range of applications. The goal is to provide a basic understanding of the contact angle measurement technique and to present a simple illustration that can be applied as a quality control method; namely, detection of a surface contaminant which exists on a surface that appears clean to the unaided eye. The equipment and experimental procedures are detailed.

  18. Surface chemical structure for soft contact lenses as a function of polymer processing.

    PubMed

    Grobe, G L; Valint, P L; Ammon, D M

    1996-09-01

    The surface chemistry and topography of cast-molded Etafilcon-A and doubled-sided lathed Etafilcon-A soft contact lenses were determined to be significantly different. The variations in surface chemical and morphologic structure between the two lenses were the result of contact lens manufacturing methods. The surface of the cast-molded Etafilcon-A had a consistently less rough surface compared to the doubled sided lathed Etafilcon-A as determined by atomic force microscopy. The surface of the doubled sided lathed Etafilcon-A contained primarily silicone and wax contamination in addition to minute amounts of HEMA. The cast-molded Etafilcon-A had an elemental and chemical content which was consistent with the polymer stoichiometry. Contact angle wettability profiles revealed inherent wettability differences between the two lenses types. The cast-molded Etafilcon-A had an inherently greater water wettability, polarity, and critical surface tension. This means that these two lenses cannot be compared as similar or identical lens materials in terms of surface composition. The manufacturing method used to produce a soft contact lens directly determines the surface elemental and chemical structure as well as the morphology of the finished lens material. These results suggest possible differences in the clinical comfort, spoilage, and lubricity felt during patient wear.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  20. Contact-Angle Hysteresis Caused by a Random Distribution of Weak Heterogeneities on a Solid Surface.

    PubMed

    Öpik

    2000-03-15

    A model according to which contact-angle hysteresis arises as the result of a random distribution of irregularities on the solid surface is investigated on the basis of probability theory. An estimate is obtained of the mathematical expectation of the number of stable equilibria when the effective angle between the liquid-gas surface and the solid surface with which the liquid is in contact deviates from the value, say theta(0), which would obtain if the solid surface were uniform, i.e., free from irregularities. It is found that when the effective contact angle deviates from theta(0) by less than a critical value, then the expected number of stable equilibria increases exponentially with the length of the contact line; therefore such a contact angle can occur under static conditions. But if the deviation of the contact angle from theta(0) exceeds the critical value, then the expected number of stable equilibria decreases exponentially with the length of the contact line, so a stable equilibrium is not possible for a macroscopic length of the contact line. The method is applicable only if the random deviations of the spreading power (defined as the solid-gas surface tension minus the sum of the liquid-gas and liquid-solid surface tensions) from its average are sufficiently small. It is found that the critical deviation of the contact angle from theta(0) is, apart from a slowly varying logarithmic factor, proportional to H(2)rho(s), where H is a measure of the amplitude of the surface irregularities and rho(s) is the surface density (i.e., number per unit area) of the irregularities. This qualitative feature agrees with the results previously obtained by several other authors, and, moreover, there is a surprisingly close agreement of the proportionality factor with the results of some earlier work in which the method of statistical analysis was much less elaborate than here. The effect of the logarithmic factor is to make the critical deviation of the contact angle

  1. [Deformation of the central corneal surface following use of hard and soft contact lenses].

    PubMed

    Roth, H W

    1989-01-01

    Use of a computer connected with a slit-lamp-video-camera detected changes in the cornea topography after wearing contact lenses on a daily basis. Also subtle surface changes were observed within the upper portion of the areas measured. These appeared to be spiral-shaped or cloudlike patterns as a result of wearing hard or soft contact lenses respectively. The changes observed appeared to have resulted from movement of the contact lens. However, this device has also been used to determine changes that are similar in early keratokonus. The computer can store data from 1600 sites on the surface; there sites are distributed over a 4-mm diameter area in the central cornea. On command the computer can display an image of the corneal surface. Images from hour 0 and 6 weeks later were compared to determine the topographic differences. The surface patterns observed after 6 weeks of wearing lenses appeared to be involve numerous small depressions.

  2. 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.

  3. Self-aligned Cu electroplating of the front surface contact on silicon solar cells

    NASA Astrophysics Data System (ADS)

    Nurain, S. N. Sharifah; Zaidi, Saleem H.; Sulaiman, M. Y.; Sopian, Kamaruzzaman

    2012-11-01

    Industrially-manufactured crystalline silicon (Si) solar cell contacts are based on screen printing of metal pastes silver (Ag) on the front and aluminum (Al) on the back surface, respectively. Screen printed contacts are inherently inefficient and requires high processing temperatures. Alternate metal contacts for silicon solar cells based on electroplating have been investigated. Metallization schemes based on electroless nickel (Ni) and copper (Cu) electroplating offers a simple, costeffective, low processing temperature and reduced contact resistivity option for silicon solar cells. An ohmic contact to ndoped emitter is formed with an electroless Ni deposition process using self-aligned approach. This allows Cu electroplating only on the Ni seed layer, which eliminates the need of additional processing for protecting active device regions. This metallization scheme exhibited higher performance with higher fill factors and open-circuit voltages in contrast with screen-printed solar cells.

  4. 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

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

    PubMed

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

    2015-01-01

    To evaluate the safety and efficacy of a new multipurpose disinfecting solution (MPDS) with a formulation that includes aloe vera on its composition. 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. 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. 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. Copyright © 2014 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.

  6. Modeling contact angle hysteresis of a liquid droplet sitting on a cosine wave-like pattern surface.

    PubMed

    Promraksa, Arwut; Chen, Li-Jen

    2012-10-15

    A liquid droplet sitting on a hydrophobic surface with a cosine wave-like square-array pattern in the Wenzel state is simulated by using the Surface Evolver to determine the contact angle. For a fixed drop volume, multiple metastable states are obtained at two different surface roughnesses. Unusual and non-circular shape of the three-phase contact line of a liquid droplet sitting on the model surface is observed due to corrugation and distortion of the contact line by structure of the roughness. The contact angle varies along the contact line for each metastable state. The maximum and minimum contact angles among the multiple metastable states at a fixed viewing angle correspond to the advancing and the receding contact angles, respectively. It is interesting to observe that the advancing/receding contact angles (and contact angle hysteresis) are a function of viewing angle. In addition, the receding (or advancing) contact angles at different viewing angles are determined at different metastable states. The contact angle of minimum energy among the multiple metastable states is defined as the most stable (equilibrium) contact angle. The Wenzel model is not able to describe the contact angle along the three-phase contact line. The contact angle hysteresis at different drop volumes is determined. The number of the metastable states increases with increasing drop volume. Drop volume effect on the contact angles is also discussed.

  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. Droplet compression and relaxation by a superhydrophobic surface: contact angle hysteresis.

    PubMed

    Hong, Siang-Jie; Chou, Tung-He; Chan, Seong Heng; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2012-04-03

    In this article, the contact angle hysteresis (CAH) of acrylic glass is experimentally and theoretically studied through the compression-relaxation process of droplets by using a superhydrophobic surface with negligible CAH effect. In contrast to the existing technique in which the volume of the droplet changes during the measurement of CAH, this procedure is carried out at a constant volume of the droplet. By observing the base diameter (BD) and the contact angle (CA) of the droplet during the compression-relaxation process, the wetting behavior of the droplet can be divided into two regimes, the contact line withdrawal and the contact line pinning regimes, depending on the gap thickness (H) at the end of the compression process. During the compression process, both regimes possess similar droplet behavior; the contact line will move outward and the BD will expand while the CA remains at the advancing angle. During the relaxation process, the two regimes are significantly different. In the contact line withdrawal regime, the contact line will withdraw with the CA remaining at the receding angle. In the contact line pinning regime, however, the contact line will be pinned at the final position and the CA will decline to a certain value higher than the receding angle. Furthermore, the advancing pinning behavior can also be realized through a successive compression-relaxation process. On the basis of the liquid-induced defects model, Surface Evolver simulations are performed to reproduce the behavior of the droplet during the compression-relaxation process; both contact line withdrawal and pinning regimes can also be identified. The results of the experiment and simulation agree with each other very well.

  9. 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.

  10. Evaluation of the contact angle and frost resistance of hydrophobised heat-insulating mortars with polystyrene

    NASA Astrophysics Data System (ADS)

    Barnat-Hunek, Danuta; Łagód, Grzegorz; Klimek, Beata

    2017-07-01

    The aim of the research presented in the paper was to evaluate the feasibility of using hydrophobic preparation based on organosilicon compounds for surface protection on the heat-insulating mortars modified with polystyrene. The work discusses issues related to wettability, absorptivity and frost resistance of the surface layer of mortars. The experimental part pertains to the physical and mechanical properties of polystyrene-modified mortars and the influence of hydrophobic preparation on the contact angle and frost resistance. The frost resistance of mortars was examined following 25 cycles of freezing and thawing. The contact angle of light mortars (θw) was determined before and after the tests of frost resistance, in the function of time using a single measurement liquid. This provided a basis for calculating the surface free energy with Neumann method, characterizing the wettability and adhesion of mortars under normal conditions and with damages resulting from frost weathering. The structure of mortars and the adhesion of lightweight aggregate to cement paste were presented by means of scanning electron microscopy. The studies enabled to determine the hydrophobisation efficiency of heat-insulating mortars with polystyrene. The obtained results confirmed the possibility of producing heat-insulating mortars modified with polystyrene along with proper surface protection against moisture and frost.

  11. Surface cleaning of CCD imagers using an electrostatic dissipative formulation of First Contact polymer

    NASA Astrophysics Data System (ADS)

    Derylo, G.; Estrada, J.; Flaugher, B.; Hamilton, J.; Kubik, D.; Kuk, K.; Scarpine, V.

    2008-07-01

    We describe the results obtained cleaning the surface of DECam CCD detectors with a new electrostatic dissipative formulation of First ContactTM polymer from Photonic Cleaning Technologies. We demonstrate that cleaning with this new product is possible without ESD damage to the sensors and without degradation of the antireflective coating used to optimize the optical performance of the detector. We show that First ContactTM is more effective for cleaning a CCD than the commonly used acetone swab.

  12. Effect of surface texturing on superoleophobicity, contact angle hysteresis, and "robustness".

    PubMed

    Zhao, Hong; Park, Kyoo-Chul; Law, Kock-Yee

    2012-10-23

    Previously, we reported the creation of a fluorosilane (FOTS) modified pillar array silicon surface comprising ~3-μm-diameter pillars (6 μm pitch with ~7 μm height) that is both superhydrophobic and superoleophobic, with water and hexadecane contact angles exceeding 150° and sliding angles at ~10° owing to the surface fluorination and the re-entrant structure in the side wall of the pillar. In this work, the effects of surface texturing (pillar size, spacing, and height) on wettability, contact angle hysteresis, and "robustness" are investigated. We study the static, advancing, and receding contact angles, as well as the sliding angles as a function of the solid area fraction. The results reveal that pillar size and pillar spacing have very little effect on the static and advancing contact angles, as they are found to be insensitive to the solid area fraction from 0.04 to ~0.4 as the pillar diameter varies from 1 to 5 μm and the center-to-center spacing varies from 4.5 to 12 μm. On the other hand, sliding angle, receding contact angle, and contact angle hysteresis are found to be dependent on the solid area fraction. Specifically, receding contact angle decreases and sliding angle and hysteresis increase as the solid area fraction increases. This effect can be attributable to the increase in pinning as the solid area fraction increases. Surface Evolver modeling shows that water wets and pins the pillar surface whereas hexadecane wets the pillar surface and then penetrates into the side wall of the pillar with the contact line pinning underneath the re-entrant structure. Due to the penetration of the hexadecane drop into the pillar structure, the effect on the receding contact angle and hysteresis is larger relative to that of water. This interpretation is supported by studying a series of FOTS pillar array surfaces with varying overhang thickness. With the water drop, the contact line is pinned on the pillar surface and very little overhang thickness effect

  13. Interdigitated back contact silicon heterojunction solar cell and the effect of front surface passivation

    NASA Astrophysics Data System (ADS)

    Lu, Meijun; Bowden, Stuart; Das, Ujjwal; Birkmire, Robert

    2007-08-01

    This letter reports interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells which combine the performance benefits of both back contact and heterojunction technologies while reducing their limitations. Low temperature (<200°C) deposited p- and n-type amorphous silicon used to form interdigitated heteroemitter and contacts in the rear preserves substrate lifetime while minimizes optical losses in the front. The IBC-SHJ structure is ideal for diagnosing surface passivation quality, which is analyzed and measured by internal quantum efficiency and minority carrier lifetime measurements. Initial cells have independently confirmed efficiency of 11.8% under AM1.5 illumination. Simulations indicate efficiencies greater than 20% after optimization.

  14. Human enamel nanohardness, elastic modulus and surface integrity after beverage contact.

    PubMed

    Machado, Camilo; Lacefield, William; Catledge, Aaron

    2008-01-01

    This study evaluated nanohardness, elastic modulus and surface roughness of human enamel after contact with citric beverages. Human enamel samples were assigned to 3 groups according to the type of beverage used: carbonated drink, orange juice and tap water (control). Surface roughness was assessed using a profilometer, and nanohardness and elastic modulus were recorded using a nanoindenter. The pH of the beverages was measured before and after citric contact during 5 weeks. Means(SD) were as follows: Carbonated drink: elastic modulus decreased from 111.6(14.5) to 62.3(10.3) GPa, nanohardness decreased from 4.62(0.67) to 1.28(0.46) GPa, roughness increased from 5.30(2.39) to 6.86(2.56) microm, and the pH changed from 2.69(0.35) to 2.29(0.24); Orange juice: elastic modulus changed from 115.15(12.94) to 92.11 GPa (13.83), nanohardness from 5.54(1.48) to 3.18 GPa (0.64), roughness from 5.26(2.27) to 6.73(2.25) microm, and pH from 3.46(0.20) to 3.03(0.14); Tap water (control): elastic modulus changed from 117.87(22.3) to 107.91(20.05) GPa, nanohardness from 4.35(1.66) to 4.28(0.93) GPa, roughness from 5.76(3.11) to 6.11(2.65) microm, and pH from 7.97(0.28) to 8.11(0.21). In conclusion, soft drink exposure caused a significant decrease in nanohardness and elastic modulus. The pH of the soft drink was more acidic from 5 degrees C to 37 degrees C. Orange juice showed a similar trend but, surprisingly, it had less effect on hardness, elastic modulus and roughness of enamel than the carbonated drink.

  15. Improvement of metal-semiconductor contact on silicon microstructured surface by electroless nickel technique

    NASA Astrophysics Data System (ADS)

    Long, Fei; Guo, Anran; Huang, Lieyun; Yu, Feng; Li, Wei

    2016-11-01

    Si micro-structures served as anti-reflection layer are widely employed in Si-based solar cells and detectors to enhance light harvesting. However, performance of these devices is suffered from the poor contact between the metal electrode and micro-structured surface. Conventional vacuum deposited metal electrode makes only superficial contact with the top of micro-structured surface and unable to fill the holes in the micro-structures. In this paper, instead, electroless nickel technique is applied to form low resistance ohmic contact. The surface micro-structures were fabricated by electrochemistry etching while the metal electrodes were deposited by sputtering and electroless pasting. Results show that only electroless nickel layer could fully fill the holes and achieve better ohmic contact than the sputtering ones before rapid annealing. Furthermore, a higher temperature rapid annealing process could improve the contact of all samples prepared by different ways. The specific contact resistance achieved by high alkalinity (pH=12) electroless nickel is 1.34×10-1Ω·cm2.

  16. 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.

  17. 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.

  18. General contact mechanics theory for randomly rough surfaces with application to rubber friction.

    PubMed

    Scaraggi, M; Persson, B N J

    2015-12-14

    We generalize the Persson contact mechanics and rubber friction theory to the case where both surfaces have surface roughness. The solids can be rigid, elastic, or viscoelastic and can be homogeneous or layered. We calculate the contact area, the viscoelastic contribution to the friction force, and the average interface separation as a function of the sliding speed and the nominal contact pressure. We illustrate the theory with numerical results for the classical case of a rubber block sliding on a road surface. We find that with increasing sliding speed, the influence of the roughness on the rubber block decreases to the extent that only the roughness of the stiff counter face needs to be considered.

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

    PubMed

    Liu, Yawei; Zhang, Xianren

    2014-10-07

    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.

  20. Slip-stick wetting and large contact angle hysteresis on wrinkled surfaces.

    PubMed

    Bukowsky, Colton; Torres, Jessica M; Vogt, Bryan D

    2011-02-15

    Wetting on a corrugated surface that is formed via wrinkling of a hard skin layer formed by UV oxidation (UVO) of a poly(dimethylsiloxane) (PDMS) slab is studied using advancing and receding water contact angle measurements. The amplitude of the wrinkled pattern can be tuned through the pre-strain of the PDMS prior to surface oxidation. These valleys and peaks in the surface topography lead to anisotropic wetting by water droplets. As the droplet advances, the fluid is free to move along the direction parallel to the wrinkles, but the droplet moving orthogonal to the wrinkles encounters energy barriers due to the topography and slip-stick behavior is observed. As the wrinkle amplitude increases, anisotropy in the sessile droplet increases between parallel and perpendicular directions. For the drops receding perpendicular to the wrinkles formed at high strains, the contact angle tends to decrease steadily towards zero as the drop volume decreases, which can result in apparent hysteresis in the contact angle of over 100°. The wrinkled surfaces can exhibit high sessile and advancing contact angles (>115°), but the receding angle in these cases is generally vanishing as the drop is removed. This effect results in micrometer sized drops remaining in the grooves for these highly wrinkled surfaces, while the flat analogous UVO-treated PDMS shows complete removal of all macroscopic water drops under similar conditions. These wetting characteristics should be considered if these wrinkled surfaces are to be utilized in or as microfluidic devices.

  1. 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.

  2. 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.

  3. Physicochemical factors influencing bacterial transfer from contact lenses to surfaces with different roughness and wettability.

    PubMed

    Vermeltfoort, Pit B J; van der Mei, Henny C; Busscher, Henk J; Hooymans, Johanna M M; Bruinsma, Gerda M

    2004-11-15

    The aim of this study was to determine the transfer of Pseudomonas aeruginosa No. 3 and Staphylococcus aureus 835 from contact lenses to surfaces with different hydrophobicity and roughness. Bacteria were allowed to adhere to contact lenses (Surevue, PureVision, or Focus Night & Day) by incubating the lenses in a bacterial suspension for 30 min. The contaminated lenses were put on a glass, poly(methylmethacrylate), or silicone rubber substratum, shaped to mimic the eye. After 2 and 16 h, lenses were separated from the substrata and bacteria were swabbed off from the respective surfaces and resuspended in saline. Appropriate serial dilutions of these suspensions were made, from which aliquots were plated on agar for enumeration. Bacterial transfer varied between 4 and 60%, depending on the combination of strain, contact time, contact lens, and substratum surface. For P. aeruginosa No. 3, transfer was significantly higher after 16 h than after 2 h, whereas less increase with time was seen for S. aureus 835. Bacterial transfer from all tested contact lenses was least to silicone rubber, the most hydrophobic and roughest substratum surface included.

  4. The enrichment ratio of atomic contacts in crystals, an indicator derived from the Hirshfeld surface analysis.

    PubMed

    Jelsch, Christian; Ejsmont, Krzysztof; Huder, Loïc

    2014-03-01

    The partitioning of space with Hirshfeld surfaces enables the analysis of fingerprint molecular interactions in crystalline environments. This study uses the decomposition of the crystal contact surface between pairs of interacting chemical species to derive an enrichment ratio. This quantity enables the analysis of the propensity of chemical species to form intermolecular interactions with themselves and other species. The enrichment ratio is obtained by comparing the actual contacts in the crystal with those computed as if all types of contacts had the same probability to form. The enrichments and contact tendencies were analyzed in several families of compounds, based on chemical composition and aromatic character. As expected, the polar contacts of the type H⋯N, H⋯O and H⋯S, which are generally hydrogen bonds, show enrichment values larger than unity. O⋯O and N⋯N contacts are impoverished while H⋯H interactions display enrichment ratios which are generally close to unity or slightly lower. In aromatic compounds, C⋯C contacts can display large enrichment ratios due to extensive π⋯π stacking in the crystal packings of heterocyclic compounds. C⋯C contacts are, however, less enriched in pure (C,H) hydrocarbons as π⋯π stacking is not so favourable from the electrostatic point of view compared with heterocycles. C⋯H contacts are favoured in (C,H) aromatics, but these interactions occur less in compounds containing O, N or S as some H atoms are then involved in hydrogen bonds. The study also highlights the fact that hydrogen is a prefered interaction partner for fluorine.

  5. 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.

  6. Effects of load, speed, and surface roughness on sliding EHD contact temperatures

    NASA Technical Reports Server (NTRS)

    Nagaraj, H. S.; Sanborn, D. M.; Winer, W. O.

    1976-01-01

    An infrared technique has been used to determine the effects of load, speed and surface roughness on temperature in a sliding elastohydrodynamic (EHD) point contact. Ball surface temperatures are reported for sliding speeds of 0.35 to 5.08 m/s at 0.52 to 2.03 GN/per sq m maximum pressure with surface roughness in the range 0.01 to 0.38 micron c.l.a. The relationship between asperity interaction, as measured by relocation surface profilimetry and high frequency temperature measurements, and the ratio of film thickness to surface roughness has also been studied.

  7. Filamentary superhydrophobic Teflon surfaces: Moderate apparent contact angle but superior air-retaining properties.

    PubMed

    Di Mundo, Rosa; Bottiglione, Francesco; Palumbo, Fabio; Notarnicola, Michele; Carbone, Giuseppe

    2016-11-15

    Micro-scale textured Teflon surfaces, resulting from plasma etching modification, show extremely high water contact angle values and fairly good resistance to water penetration when hit by water drops at medium-high speed. This behavior is more pronounced when these surfaces present denser and smaller micrometric reliefs. Tailoring the top of these reliefs with a structure which further stabilizes the air may further increase resistance to wetting (water penetration) under static and dynamic conditions. Conditions of the oxygen fed plasma were tuned in order to explore the possibility of obtaining differently topped structures on the surface of the polymer. Scanning Electron Microscopy (SEM) was used to explore topography and X-ray Photoelectron Spectroscopy (XPS) to assess chemical similarity of the modified surfaces. Beside the usual advancing and receding water contact angle (WCA) measurements, surfaces were subjected to high speed impacting drops and immersion in water. At milder, i.e. shorter time and lower input power, plasma conditions formation of peculiar filaments is observed on the top of the sculpted reliefs. Filamentary topped surfaces result in a lower WCA than the spherical ones, appearing in this sense less superhydrophobic. However, these surfaces give rise to the formation of a more pronounced air layer when placed underwater. Further, when hit by water drops falling at medium/high speed, they show a higher resistance to water penetration and a sensitively lower surface-liquid contact time. The contact time is as low as previously observed only on heated solids. This behavior may be ascribed to the cavities formed beneath the filaments which, similarly with the salvinia leaf structures, require a surplus of pressure to be filled by water. Also, it suggests a different concept of superhydrophobicity, which cannot be expected on the basis of the conventional water contact angle characterization. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. Two Novel Genes Induced by Hard-Surface Contact of Colletotrichum gloeosporioides Conidia

    PubMed Central

    Kim, Yeon-Ki; Liu, Zhi-Mei; Li, Daoxin; Kolattukudy, Pappachan E.

    2000-01-01

    Germinating conidia of many phytopathogenic fungi must differentiate into an infection structure called the appressorium in order to penetrate into their hosts. This differentiation is known to require contact with a hard surface. However, the molecular basis for this requirement is not known. Induction of this differentiation in the avocado pathogen, Colletotrichum gloeosporioides, by chemical signals such as the host's surface wax or the fruit-ripening hormone, ethylene, requires contact of the conidia with a hard surface for about 2 h. To study molecular events triggered by hard-surface contact, we isolated several genes expressed during the early stage of hard-surface treatment by a differential-display method. The genes that encode Colletotrichum hard-surface induced proteins are designated chip genes. In this study, we report the characterization of CHIP2 and CHIP3 genes that would encode proteins with molecular masses of 65 and 64 kDa, respectively, that have no homology to any known proteins. The CHIP2 product would contain a putative nuclear localization signal, a leucine zipper motif, and a heptad repeat region which might dimerize into coiled-coil structure. The CHIP3 product would be a nine-transmembrane-domain-containing protein. RNA blots showed that CHIP2 and CHIP3 are induced by a 2-h hard-surface contact. However, disruption of these genes did not affect the appressorium-forming ability and did not cause a significant decrease in virulence on avocado or tomato fruits suggesting that C. gloeosporioides might have genes functionally redundant to CHIP2 and CHIP3 or that these genes induced by hard-surface contact control processes not directly involved in pathogenesis. PMID:10940006

  9. Rigid gas permeable contact lenses surface roughness examined by interferential shifting phase and scanning electron microscopies.

    PubMed

    Merindano, M D; Canals, M; Saona, C; Costa, J

    1998-01-01

    The anterior surface roughness of seven factory new rigid gas permeable (RGP) contact lenses has been studied by interferential shifting phase microscopy (ISPM) and scanning electron microscopy (SEM). Five lenses were fluorsilicone acrylate and two lenses were silicone acrylate. Their material Dk ranged from 14 to 210. ISPM is shown to be a reliable and non-destructive method to observe and measure the relief of the contact lens surface. Moreover, profile and contour data are easily stored for further quantitative studies. ISPM contour patterns of the studied lenses are qualitatively compared with those obtained by SEM for the same lenses. Results point out that ISPM gives similar accuracy but it is non-destructive and cheaper than SEM. Moreover, the quantitative study of surface roughness suggests that there is a relationship between surface roughness and Dk of the lens material: surface roughness increases with Dk and allows to distinguish between lenses with low, medium and high Dk.

  10. 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.

  11. 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

    2013-11-05

    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.

  12. Statistical model of rough surface contact accounting for size-dependent plasticity and asperity interaction

    NASA Astrophysics Data System (ADS)

    Song, H.; Vakis, A. I.; Liu, X.; Van der Giessen, E.

    2017-09-01

    The work by Greenwood and Williamson (GW) has initiated a simple but effective method of contact mechanics: statistical modeling based on the mechanical response of a single asperity. Two main assumptions of the original GW model are that the asperity response is purely elastic and that there is no interaction between asperities. However, as asperities lie on a continuous substrate, the deformation of one asperity will change the height of all other asperities through deformation of the substrate and will thus influence subsequent contact evolution. Moreover, a high asperity contact pressure will result in plasticity, which below tens of microns is size dependent, with smaller being harder. In this paper, the asperity interaction effect is taken into account through substrate deformation, while a size-dependent plasticity model is adopted for individual asperities. The intrinsic length in the strain gradient plasticity (SGP) theory is obtained by fitting to two-dimensional discrete dislocation plasticity simulations of the flattening of a single asperity. By utilizing the single asperity response in three dimensions and taking asperity interaction into account, a statistical calculation of rough surface contact is performed. The effectiveness of the statistical model is addressed by comparison with full-detail finite element simulations of rough surface contact using SGP. Throughout the paper, our focus is on the difference of contact predictions based on size-dependent plasticity as compared to conventional size-independent plasticity.

  13. Investigation of regularities of formation and propagation of elastic vortices in surface layers of materials under dynamic contact loading

    NASA Astrophysics Data System (ADS)

    Astafurov, S. V.; Shilko, E. V.; Psakhie, S. G.

    2016-11-01

    On the base of computer-aided simulation by movable cellular automaton method regularities of formation of vortices in surface layers of materials under dynamic contact loading were investigated. It was shown that the dynamic contact loading leads to the formation of an elastic vortex in the area of contact interaction and its subsequent propagation in the volume of material. Direction of vortex movement essentially depends on the velocity of contact loading and value of the contact pressure, which are determined features of the interaction of the material surface and the counterbody (e.g. stress state of contact area).

  14. Droplet spreading on rough surfaces: Tackling the contact line boundary condition

    NASA Astrophysics Data System (ADS)

    Chamakos, Nikolaos T.; Kavousanakis, Michail E.; Boudouvis, Andreas G.; Papathanasiou, Athanasios G.

    2016-02-01

    The complicated dynamics of the contact line of a moving droplet on a solid substrate often hamper the efficient modeling of microfluidic systems. In particular, the selection of the effective boundary conditions, specifying the contact line motion, is a controversial issue since the microscopic physics that gives rise to this displacement is still unknown. Here, a sharp interface, continuum-level, novel modeling approach, accounting for liquid/solid micro-scale interactions assembled in a disjoining pressure term, is presented. By following a unified conception (the model applies both to the liquid/solid and the liquid/ambient interfaces), the friction forces at the contact line, as well as the dynamic contact angle are derived implicitly as a result of the disjoining pressure and viscous effects interplay in the vicinity of the substrate's intrinsic roughness. Previous hydrodynamic model limitations, of imposing the contact line boundary condition to an unknown number and reconfigurable contact lines, when modeling the spreading dynamics on textured substrates, are now overcome. The validity of our approach is tested against experimental data of a droplet impacting on a horizontal solid surface. The study of the early spreading stage on hierarchically structured and chemically patterned solid substrates reveal an inertial regime where the contact radius grows according to a universal power law, perfectly agreeing with recently published experimental findings.

  15. Liquid transfer between two solid surfaces with the effect of contact angle hysteresis

    NASA Astrophysics Data System (ADS)

    Chen, Huanchen; Tang, Tian; Amirfazli, Alidad

    2013-11-01

    Drop transfer from one solid surface to another (e.g. due to the approach of a surface from top to a sessile drop resting on a lower surface) is widely observed in many industrial areas, e.g. offset printing. This process is governed by many factors such as the contact angle (CA) and contact angle hysteresis (CAH) of surfaces, viscosity of the liquid and the rate at which the donor and acceptor surfaces are separated. In this work, an experimental apparatus is developed to study the transfer of liquid drop between surfaces, with the particular focus on addressing the effect of the surfaces' CAH when the loading speed is low (transfer is quasi-static). In the experiment, a liquid bridge between the two surfaces is first formed by compression; then stretched to the point of breakage. By using surfaces that have similar CA but dissimilar CAH, the liquid transfer ratio (the amount of liquid transferred to the acceptor surface over the total amount of liquid) is found to be significantly influenced by CAH. In addition, as a result of CAH, the maximum compression of the liquid bridge is found to play an important role in determining the transfer ratio. These findings can be very helpful for the design of surfaces and loading conditions to achieve desired transfer ratios in practice.

  16. Theory of wetting-induced fluid entrainment by advancing contact lines on dry surfaces.

    PubMed

    Ledesma-Aguilar, R; Hernández-Machado, A; Pagonabarraga, I

    2013-06-28

    We report on the onset of fluid entrainment when a contact line is forced to advance over a dry solid of arbitrary wettability. We show that entrainment occurs at a critical advancing speed beyond which the balance between capillary, viscous, and contact-line forces sustaining the shape of the interface is no longer satisfied. Wetting couples to the hydrodynamics by setting both the morphology of the interface at small scales and the viscous friction of the front. We find that the critical deformation that the interface can sustain is controlled by the friction at the contact line and the viscosity contrast between the displacing and displaced fluids, leading to a rich variety of wetting-entrainment regimes. We discuss the potential use of our theory to measure contact-line forces using atomic force microscopy and to study entrainment under microfluidic conditions exploiting colloid-polymer fluids of ultralow surface tension.

  17. Touchscreen surface based on interaction of ultrasonic guided waves with a contact impedance

    NASA Astrophysics Data System (ADS)

    Quaegebeur, Nicolas; Masson, Patrice; Beaudet, Nicolas; Sarret, Philippe

    2017-04-01

    In the present paper, a touchscreen device is proposed, based on guided wave reflection and transmission induced by the presence of an object. The principle uses the advantages of other acoustic waves devices in terms of simplicity and applicability to any thin surface but is not subject to classical drawbacks (single-touch, sensitivity to scratches or contaminant, impossibility to follow motion of contact point). The theoretical interaction of guided waves with a contact impedance are first derived in order to define the requirements of the sensor in terms of frequency range, mode, sensor type and location, and embedded electronics. Design criteria and experimental validation on a small prototype (300 x 300 mm) are proposed to demonstrate the potential of the approach for simple, robust and reliable contact detection and contact pressure estimation of point-like or extended objects for consumer electronics or biomedical applications.

  18. Theory of Wetting-Induced Fluid Entrainment by Advancing Contact Lines on Dry Surfaces

    NASA Astrophysics Data System (ADS)

    Ledesma-Aguilar, R.; Hernández-Machado, A.; Pagonabarraga, I.

    2013-06-01

    We report on the onset of fluid entrainment when a contact line is forced to advance over a dry solid of arbitrary wettability. We show that entrainment occurs at a critical advancing speed beyond which the balance between capillary, viscous, and contact-line forces sustaining the shape of the interface is no longer satisfied. Wetting couples to the hydrodynamics by setting both the morphology of the interface at small scales and the viscous friction of the front. We find that the critical deformation that the interface can sustain is controlled by the friction at the contact line and the viscosity contrast between the displacing and displaced fluids, leading to a rich variety of wetting-entrainment regimes. We discuss the potential use of our theory to measure contact-line forces using atomic force microscopy and to study entrainment under microfluidic conditions exploiting colloid-polymer fluids of ultralow surface tension.

  19. 'Soft' Au, Pt and Cu contacts for molecular junctions through surface-diffusion-mediated deposition.

    PubMed

    Bonifas, Andrew P; McCreery, Richard L

    2010-08-01

    Virtually all types of molecular electronic devices depend on electronically addressing a molecule or molecular layer through the formation of a metallic contact. The introduction of molecular devices into integrated circuits will probably depend on the formation of contacts using a vapour deposition technique, but this approach frequently results in the metal atoms penetrating or damaging the molecular layer. Here, we report a method of forming 'soft' metallic contacts on molecular layers through surface-diffusion-mediated deposition, in which the metal atoms are deposited remotely and then diffuse onto the molecular layer, thus eliminating the problems of penetration and damage. Molecular junctions fabricated by this method exhibit excellent yield (typically >90%) and reproducibility, and allow examination of the effects of molecular-layer structure, thickness and contact work function.

  20. Quantitative sub-surface and non-contact imaging using scanning microwave microscopy

    NASA Astrophysics Data System (ADS)

    Gramse, Georg; Brinciotti, Enrico; Lucibello, Andrea; Patil, Samadhan B.; Kasper, Manuel; Rankl, Christian; Giridharagopal, Rajiv; Hinterdorfer, Peter; Marcelli, Romolo; Kienberger, Ferry

    2015-03-01

    The capability of scanning microwave microscopy for calibrated sub-surface and non-contact capacitance imaging of silicon (Si) samples is quantitatively studied at broadband frequencies ranging from 1 to 20 GHz. Calibrated capacitance images of flat Si test samples with varying dopant density (1015-1019 atoms cm-3) and covered with dielectric thin films of SiO2 (100-400 nm thickness) are measured to demonstrate the sensitivity of scanning microwave microscopy (SMM) for sub-surface imaging. Using standard SMM imaging conditions the dopant areas could still be sensed under a 400 nm thick oxide layer. Non-contact SMM imaging in lift-mode and constant height mode is quantitatively demonstrated on a 50 nm thick SiO2 test pad. The differences between non-contact and contact mode capacitances are studied with respect to the main parameters influencing the imaging contrast, namely the probe tip diameter and the tip-sample distance. Finite element modelling was used to further analyse the influence of the tip radius and the tip-sample distance on the SMM sensitivity. The understanding of how the two key parameters determine the SMM sensitivity and quantitative capacitances represents an important step towards its routine application for non-contact and sub-surface imaging.

  1. Contact angle hysteresis and meniscus corrugation on randomly heterogeneous surfaces with mesa-type defects.

    PubMed

    Iliev, Dimitar; Pesheva, Nina; Iliev, Stanimir

    2013-05-14

    The results of a numerical study of the various characteristics of the static contact of a liquid meniscus with a flat but heterogeneous surface, consisting of two types of homogeneous materials, forming regularly and randomly distributed microscopic defects are presented. The solutions for the meniscus shape are obtained numerically using the full expression of the system free energy functional. The goal is to establish how the magnitude and the limits of the hysteresis interval of the equilibrium contact angle, the Cassie's angle, and the contact line (CL) roughness exponent are related to the parameters, characterizing the heterogeneous surface-the equilibrium contact angles on the two materials and their fractions. We compare the results of different ways of determining the averaged contact angle on heterogeneous surfaces. We study the spread of the CL corrugation along the liquid meniscus. We compare our results with the numerical results, obtained using linearized energy functional, and also with experimental results for the CL roughness exponent. The obtained results support the conclusion that some characteristics depends on the type (regular or random) of the heterogeneity pattern.

  2. Surface topography and contact mechanics of dry and wet human skin.

    PubMed

    Kovalev, Alexander E; Dening, Kirstin; Persson, Bo N J; Gorb, Stanislav N

    2014-01-01

    The surface topography of the human wrist skin is studied by using optical and atomic force microscopy (AFM) methods. By using these techniques the surface roughness power spectrum is obtained. The Persson contact mechanics theory is used to calculate the contact area for different magnifications, for the dry and wet skin. The measured friction coefficient between a glass ball and dry and wet skin can be explained assuming that a frictional shear stress σf ≈ 13 MPa and σf ≈ 5 MPa, respectively, act in the area of real contact during sliding. These frictional shear stresses are typical for sliding on surfaces of elastic bodies. The big increase in friction, which has been observed for glass sliding on wet skin as the skin dries up, can be explained as result of the increase in the contact area arising from the attraction of capillary bridges. Finally, we demonstrated that the real contact area can be properly defined only when a combination of both AFM and optical methods is used for power spectrum calculation.

  3. Surface contact stimulates the just-in-time deployment of bacterial adhesins

    PubMed Central

    Li, Guanglai; Brown, Pamela J.B.; Tang, Jay X.; Xu, Jing; Quardokus, Ellen M.; Fuqua, Clay; Brun, Yves V.

    2011-01-01

    Summary The attachment of bacteria to surfaces provides advantages such as increasing nutrient access and resistance to environmental stress. Attachment begins with a reversible phase, often mediated by surface structures such as flagella and pili, followed by a transition to irreversible attachment, typically mediated by polysaccharides. Here we show that the interplay between pili and flagellum rotation stimulates the rapid transition between reversible and polysaccharide-mediated irreversible attachment. We found that reversible attachment of Caulobacter crescentus cells is mediated by motile cells bearing pili and that their contact with a surface results in the rapid pili-dependent arrest of flagellum rotation and concurrent stimulation of polar holdfast adhesive polysaccharide. Similar stimulation of polar adhesin production by surface contact occurs in Asticcacaulis biprosthecum and Agrobacterium tumefaciens. Therefore, single bacterial cells respond to their initial contact with surfaces by triggering just-in-time adhesin production. This mechanism restricts stable attachment to intimate surface interactions, thereby maximizing surface attachment, discouraging non-productive self-adherence, and preventing curing of the adhesive. PMID:22053824

  4. Surface contact stimulates the just-in-time deployment of bacterial adhesins.

    PubMed

    Li, Guanglai; Brown, Pamela J B; Tang, Jay X; Xu, Jing; Quardokus, Ellen M; Fuqua, Clay; Brun, Yves V

    2012-01-01

    The attachment of bacteria to surfaces provides advantages such as increasing nutrient access and resistance to environmental stress. Attachment begins with a reversible phase, often mediated by surface structures such as flagella and pili, followed by a transition to irreversible attachment, typically mediated by polysaccharides. Here we show that the interplay between pili and flagellum rotation stimulates the rapid transition between reversible and polysaccharide-mediated irreversible attachment. We found that reversible attachment of Caulobacter crescentus cells is mediated by motile cells bearing pili and that their contact with a surface results in the rapid pili-dependent arrest of flagellum rotation and concurrent stimulation of polar holdfast adhesive polysaccharide. Similar stimulation of polar adhesin production by surface contact occurs in Asticcacaulis biprosthecum and Agrobacterium tumefaciens. Therefore, single bacterial cells respond to their initial contact with surfaces by triggering just-in-time adhesin production. This mechanism restricts stable attachment to intimate surface interactions, thereby maximizing surface attachment, discouraging non-productive self-adherence, and preventing curing of the adhesive.

  5. 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.

  6. Elastic contact conditions to optimize friction drive of surface acoustic wave motor.

    PubMed

    Kuribayashi Kurosawa, M; Takahashi, M; Higuchi, T

    1998-01-01

    The optimum pressing force, namely the preload, for a slider to obtain superior operation conditions in a surface acoustic wave motor have been examined. We used steel balls as sliders. The preload was controlled using a permanent magnet. The steel balls were 0.5, 1, and 2 mm diameter, with the differences in diameter making it possible to change contact conditions, such as the contact pressure, contact area, and deformation of the stator and the slider. The stator transducer was lithium niobate, 128 degrees rotated, y-cut x-propagation substrate. The driving frequency of the Rayleigh wave was about 10 MHz. Hence, the particle vibration amplitude at the surface is as small as 10 nm. For superior friction drive conditions, a high contact pressure was required. For example, in the case of the 1 mm diameter steel ball at the sinusoidal driving voltage of 180 V(peak), the slider speed was 43 cm/sec, the thrust output force was 1 mN, and the acceleration was 23 times as large as the gravitational acceleration at a contact pressure of 390 MPa. From the Hertz theory of contact stress, the contact area radius was only 3 microm. The estimation of the friction drive performance was carried out from the transient traveling distance of the slider in a 3 msec burst drive. As a result, the deformation of the stator and the slider by the preload should be half of the vibration amplitude. This condition was independent of the ball diameter and the vibration amplitude. The output thrust per square millimeter was 50 N, and the maximum speed was 0.7 m/sec. From these results, we conclude that it is possible for the surface acoustic wave motor to have a large output force, high speed, quick response, long traveling distance, and a thin micro linear actuator.

  7. 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.

  8. Numerical models for the evaluation of the contact angle from axisymmetric drop profiles: a statistical comparison.

    PubMed

    Bortolotti, Mauro; Brugnara, Marco; Della Volpe, Claudio; Siboni, Stefano

    2009-08-01

    Axisymmetric drop shape analysis (ADSA) is a well-established methodology for estimating the contact angle value and the surface tension of liquids starting from sessile drops images. It consists of an iterative procedure in which a best fit between a theoretical axisymmetric Laplacian curve and an experimental drop profile is performed. When only an evaluation of the geometric contact angle value is needed, a similar numerical approach can be adopted by using simpler algebraic models in place of a Laplace profile, thus allowing more straightforward implementations and shorter computation times. In this work the relative merits of the different methodologies are compared. Beside the standard ADSA procedure, four different mathematical models are examined, namely the circular and elliptical models, the first-order perturbative solution of the Laplace equation, and a cubic spline model. Their relative statistical performances are tested on both calculated and experimental drop profiles. For simulated drops, the actual capability of the models to predict the correct contact angle is also investigated.

  9. Mechanical guidance through cell-cell and cell-surface contact during multicellular streaming

    NASA Astrophysics Data System (ADS)

    Wang, Chenlu; Driscoll, Meghan; Gupta, Satyandra K.; Parent, Carole; Losert, Wolfgang

    2014-03-01

    During collective cell migration, mechanical forces arise from the extracellular matrix (ECM) through cell-surface contact and from other cells through cell-cell contact. These forces regulate the motion of migrating cell groups. To determine how these mechanical interactions balance during cell migration, we measured the shape dynamics of Dictyostelium discoideum cells at the multicellular streaming stage. We found that cells can coordinate their motion by synchronizing protrusion waves that travel along their membranes when they form proper cell-cell adhesion and cell-surface adhesion. In addition, our experiments on live actin labeled cells show that intracellular actin polymerization actively responds to the change of cell-cell/surface adhesion and helps to stabilize multicellular migration streams. Our finding suggests that the coordination of motion between neighboring cells in collective migration requires a balance between cell-cell adhesion and cell-surface adhesion, and that the cell cytoskeleton plays an important role in this balance.

  10. ZnO nanowire photodetectors based on Schottky contact with surface passivation

    NASA Astrophysics Data System (ADS)

    Zhang, Dakuan; Sheng, Yun; Wang, Jianyu; Gao, Fan; Yan, Shancheng; Wang, Junzhuan; Pan, Lijia; Wan, Qing; Shi, Yi

    2017-07-01

    Performance characteristics, such as dark current and response time, of ZnO nanowire (NW) photodetectors are usually degraded by H2O/O2 adsorption on the NW surfaces. In this work, ZnO NW photodetectors based on Au Schottky contact through passivating surface states were investigated. ZnO NW photodetectors were fabricated with a lateral electrode structure, in which Au served as Au/ZnO Schottky contact and semi-transparent top electrode. Specifically, passivation of the surface states of ZnO NWs by using highly intensive UV irradiation effectively improved the photoresponse. A physical model based on surface band theory was developed to understand the origin of the performance improvement of the photodetector. The present device architecture prevents ZnO NWs photodetector from H2O/O2 adsorption in air and efficiently extracts photogenerated carriers across a diametrical direction.

  11. Detection of rolling contact sub-surface fatigue cracks using acoustic emission technique

    SciTech Connect

    Yoshioka, T. )

    1993-04-01

    A method of locating the position of acoustic emission sources has been developed to analyze the mechanism of rolling contact fatigue. Using this method, sub-surface fatigue cracks were found at positions corresponding to the actual source positions of acoustic emissions. When fatigue tests were run under maximum stresses of 5.75 GPa and lubricant film parameters of 0.19, the cracks propagated parallel to the surface, had a maximum length of approximately 200 microns in the rolling direction of balls, and were distributed between 50 microns and 200 microns below the surface. Although the lubricant film parameter was small, no cracks from the surface were found. 12 refs.

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

    USDA-ARS?s Scientific Manuscript database

    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...

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

    USDA-ARS?s Scientific Manuscript database

    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...

  14. Liquid transfer mechanism between two surfaces and the role of contact angles.

    PubMed

    Chen, H; Tang, T; Amirfazli, A

    2014-04-21

    The transfer ratio of quasi-static liquid transfer was found to strongly depend on the difference between the receding contact angles of the two surfaces. In contrast to traditional thinking, the transfer ratio was quite insensitive to the adhesion force between the solid and the liquid when the liquid bridge broke.

  15. Assessment of Cold Welding Between Separable Contact Surfaces Due to Impact and Fretting under Vacuum

    NASA Astrophysics Data System (ADS)

    Merstallinger, A.; Sales, M.; Semerad, E.; Dunn, B. D.

    2009-11-01

    A common failure mode seen during the testing and operation of spacecraft is termed "cold welding". European laboratories refer to this as "adhesion", "sticking" or "stiction". This publication is intended to provide the space community with the most recent understanding of the phenomenon of "cold welding" in relation to spacecraft mechanisms with separable contact surfaces. It presents some basic theory and describes a test method and the required equipment. Cold welding between two contacting surfaces can occur under conditions of impact or fretting. These surfaces may be bare metals, or inorganically or organically coated metals and their alloys. Standard procedures for quantifying the propensity of material surface pairs to cold weld to each other are proposed. Of particular interest will be the contact data of different materials, which are presented in numerical form and as tables summarising contacts between materials that can be either recommended or considered unsuitable for use under vacuum. The data have been compiled in a database that can be accessed online.

  16. 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.

  17. 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.

  18. 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.

  19. Plastic Deformations of Measured Object Surface in Contact with Undeformable Surface of Measuring Tool

    NASA Astrophysics Data System (ADS)

    Kowalik, Marek; Rucki, Mirosław; Paszta, Piotr; Gołębski, Rafał

    2016-10-01

    Measuring errors caused by deformation (flattening) of a measured object appear under the influence of pressure force and weight of the measured object. Plastic strain, arising at the contact of a measured object and an undeformable contact tip of a measuring device, can be calculated by applying the Hertz plastic solution and the hypothesis of plastic strain. In a small area of contact between two bodies pressing against one another with force F, there appears the so-called contact stress. It can sometime reach very high values, exceeding the yield point, even when the contact pressure is relatively small. In the present work, the authors describe a theoretical solution to the problem of plastic strain between two bodies. The derived relationships enable to calculate force F during measurements of a deformable object by means of an instrument with an undeformable, spherical measuring tip. By applying the τmax hypothesis, a solution was obtained for the force F in an inexplicit form. The theoretical solution was verified with the digital simulation and experimental measurement. With the FEM method, the limit length gage was modeled in interaction with the measured shaft of a diameter d larger than the nominal one of Δl value.

  20. Interpreting contact angle results under air, water and oil for the same surfaces

    NASA Astrophysics Data System (ADS)

    Ozkan, Orkun; Yildirim Erbil, H.

    2017-06-01

    Under-water and under-oil superhydropobicity and superhydrophilicity have gained significant attention over the last few years. In this study, contact angles on five flat surfaces (polypropylene, poly(methyl methacrylate), polycarbonate, TEFLON-FEP and glass slide) were measured in water drop-in-air, air bubble-under-water, oil drop-in-air, air bubble-under-oil, oil drop-under-water and water drop-under-oil conditions. Heptane, octane, nonane, decane, dodecane, and hexadecane hydrocarbons were used as oils. Immiscible water/oil pairs were previously mutually saturated to provide thermodynamical equilibrium conditions and their surface and interfacial tensions were determined experimentally. These pairs were used in the two-liquid contact angle measurements. Surface free energies of the solid surfaces in air were determined independently by using the van Oss-Good method, using the contact angle results of pure water, ethylene glycol, formamide, methylene iodide and α-bromonaphalene. In addition, Zisman’s ‘critical surface tension’ values were also determined for comparison. In theory, the summation of contact angle results in a complementary case would give a total of 180° for ideal surfaces. However, it was determined that there are large deviations from this rule in practical cases and these deviations depend on surface free energies of solids. Three complementary cases of (water-in-air with air bubble-under-water); (oil-in-air with air bubble-under-oil); and (oil-under-water with water-under-oil) were investigated in particular to determine the deviations from ideality. A novel approach, named ‘complementary hysteresis’ [γ WA(cosθ 1  -  cosθ 2) and γ OW(cosθ 6  -  cosθ 5)] was developed where γ WA and γ OW represent the interfacial tensions of water/air and oil/water, and θ 1, θ 2, θ 5, and θ 6 were the contact angles of water/air, air bubble/water, oil/water and water/oil respectively. It was experimentally determined that

  1. Effect of electric fields on contact angle and surface tension of drops.

    PubMed

    Bateni, A; Laughton, S; Tavana, H; Susnar, S S; Amirfazli, A; Neumann, A W

    2005-03-01

    Contact angles of sessile drops were experimentally investigated in the electric field. The experimental setup was designed such that the electric field was applied to all three interfaces. The advanced Automated Polynomial Fitting (APF) methodology was employed to measure contact angles with high accuracy. The significance of the observations and trends was examined by conducting statistical tests of hypothesis. It was found that contact angles of polar liquids such as alcohols increase in the electric field. However, no significant trend was observed for nonpolar liquids such as alkanes. The change in the contact angle was found to be stronger for liquids with longer molecules. It was shown that the polarity of the electric field is not an underlying factor in the observed trends. Using the equation of state for interfacial tensions, the observed shift in contact angles was translated into a corresponding change in surface tension of the liquids. The results suggest that the surface tension of alcohols increases by one to two percent (depending on the size of molecules) when an electric field of the order of magnitude of 10(6) V/m is applied.

  2. 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.

  3. Microbiological Analysis of Food Contact Surfaces in Child Care Centers ▿

    PubMed Central

    Cosby, Catherine M.; Costello, C. A.; Morris, W. C.; Haughton, B.; Devereaux, M. J.; Harte, F.; Davidson, P. M.

    2008-01-01

    A study of six child care centers was conducted to assess the microbiological quality of three food contact surfaces (one food serving surface and two food preparation surfaces) and one non-food contact surface (diaper changing surface) to determine the effectiveness of cleaning and sanitization procedures within the facilities. Aerobic plate counts (APCs) and Escherichia coli/coliform counts of 50-cm2 areas on all surfaces were determined using standard microbiological swabbing methods. Samples were taken three times a day (preopening, lunchtime, and following final cleanup) twice per month for 8 months in each child care center (n = 288 sampling times). Mean log APCs over the survey period were 1.32, 1.71, 1.34, 1.96, 1.50, and 1.81 log CFU/50 cm2 for the six centers. Mean log coliform counts were 0.15, 0.40, 0.33, 1.41, 0.28, and 1.12 CFU/50 cm2 for the same centers. Coliforms were detected in 283 of 1,149 (24.7%) samples, with counts ranging from 1 to 2,000 CFU/50 cm2, while E. coli was detected in 18 of 1,149 (1.6%) samples, with counts ranging from 1 to 35 CFU/50 cm2. The findings of this study demonstrated that the extent of bacterial contamination was dependent on the center, time of day, and the area sampled. While no direct correlation between contamination and illness can be made, given the high risk of food-borne illness associated with children, microbial contamination of food contact or non-food contact surfaces is an aspect of food safety that requires more attention. Emphasis on training and the development of modified standard sanitation operating procedures for child care centers are needed to reduce potential hazards. PMID:18820060

  4. 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.

  5. 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. © 2015. Published by The Company of Biologists Ltd.

  6. Dental floss selection and its impact on evaluation of interproximal contacts in licensure exams.

    PubMed

    Teich, Sorin T; Joseph, Jay; Sartori, Neimar; Heima, Masahiro; Duarte, Sillas

    2014-06-01

    Ideal interproximal contacts between adjacent natural teeth or dental restorations are a critical factor for the health of the dental-alveolar complex. Interproximal contact tightness is a physiological entity affected by many patient-related and restorative parameters. This variation poses a challenge in defining the "clinically acceptable" contact area tightness (CAT) and therefore how students and clinicians should be trained to evaluate this parameter. The most widely used method to evaluate interproximal contacts is to pass dental floss between contact areas. Candidates for licensure exams are instructed to check contact areas with dental floss and are advised that this will be one of the crucial parameters to be evaluated in the overall restoration quality. The purpose of this study was to evaluate a standardized interproximal contact with six brands of dental floss. Thirty faculty members and thirty dental students at one U.S. dental school evaluated the tightness of a single interproximal contact on a typodont. The results showed that no difference was found between CAT evaluations by faculty and students, whereas significant differences were found between different floss brands. In light of the results, it is suggested that licensure boards should standardize the recommendation for which floss brand should be used in order to avoid inconsistencies in students' preparation.

  7. 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.

  8. Comparison of contact angle hysteresis of different probe liquids on the same solid surface.

    PubMed

    Chibowski, Emil; Jurak, Malgorzata

    2013-02-01

    Advancing and receding contact angles of water, formamide and diiodomethane were measured on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) layers deposited on three different solid supports-glass, mica and poly(methyl methacrylate). Up to five statistical monolayers were deposited on the surfaces by spreading DPPC solution. It was found that even on five statistical DPPC monolayers, the hysteresis of a given liquid depends on the kind of solid support. Also on the same solid support the contact angle hysteresis is different for each probe liquid used. The AFM images show that the heights of roughness of the DPPC films cannot be the primary cause of the observed hysteresis because the heights are too small to cause the observed hystereses. It is believed that the hysteresis is due to the liquid film present right behind the three-phase solid surface/liquid drop/gas (vapour) contact line and the presence of Derjaguin pressure. The value of contact angle hysteresis depends on both the solid surface and liquid properties as well as on intermolecular interactions between them.

  9. Surface modification of corneal contact lens with phosphoryl choline by glow discharge.

    PubMed

    Sunny, M C; Sharma, C P

    1991-01-01

    Polymers like poly(methylmethacrylate) (PMMA) and poly(2-hydroxyethylmethacrylate) (PHEMA) are widely used in the development of hard and soft contact lenses. Cell adhesion and deposition of chemicals such as calcium, lipoproteins and mucin on the lens surface cause visual acuity which is the main problem in extended uses of contact ocular lenses. In order to minimise the cell adhesion and other type of depositions, a method of surface modification of lens involving the use of phosphoryl choline, a phospholipid and the glow discharge technique has been described. The power variation of the lenses after modification has been checked using Topcon lensometer. The possible power changes of the modified samples due to the exposure to the normal light in the laboratory, darkness, ultraviolet (U.V.) light or saline have been investigated by taking the visible and ultra violet spectra using Beckman spectrophotometer. Surface energy variations after modifications of the samples have been checked by sessile drop water contact angle measurements. Glow discharge treatment increases the hydrophilicity of the samples. It seems, the modifications do not affect the power of hard contact lens significantly. It is also observed that the exposure of samples to the normal light in the laboratory, darkness, U.V. light or saline make no significant change in the visible and ultraviolet spectra of the samples before and after modification.

  10. 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.

  11. Dissipative particle dynamics simulation of contact angle hysteresis on a patterned solid/air composite surface.

    PubMed

    Kong, Bin; Yang, Xiaozhen

    2006-02-28

    We have studied two types of topological substrates--the continuous solid substrates (CSS) and the discontinuous solid substrates (DSS)--by using the dissipative particle dynamics (DPD) method for a better understanding of the contact angle hysteresis on two such substrates. After the validation of DPD in the system, we found that DSS has a different distribution of the metastable states from that of CSS and that DSS has relatively larger contact angle hysteresis at lower temperature. Obtained results also show that CSS is more suitable for making an ultrahydrophobic or ultralyophobic surface than DSS from the point of view of dynamic wettability.

  12. 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.

  13. Fabrication of reflection gratings by contact copying of amplitude holographic gratings on a metal surface

    NASA Astrophysics Data System (ADS)

    Madjidi-Zolbanine, Habib; Hodjat-Zadeh, A.

    1995-04-01

    This paper describes the contact copying of amplitude transmission holographic gratings. Master gratings (MG) are written in silver halide sensitized gelatine. A smooth and flat sheet is coated with a layer of negative photoresist constituted from a combination of polyvinyl alcohol, ammonium dichromate and Arabic gum, then the MG is put in contact with the metal surface and exposed by a mercury lamp. After processing with deionized water at (35 degree(s)C), a reflection grating is obtained. For a MG with 117 l/mm of spatial frequency and 10% of diffraction efficiency (DE), we have obtained a DE of 12%.

  14. Contact models of repaired articular surfaces: influence of loading conditions and the superficial tangential zone.

    PubMed

    Owen, John R; Wayne, Jennifer S

    2011-07-01

    The superficial tangential zone (STZ) plays a significant role in normal articular cartilage's ability to support loads and retain fluids. To date, tissue engineering efforts have not replicated normal STZ function in cartilage repairs. This finite element study examined the STZ's role in normal and repaired articular surfaces under different contact conditions. Contact area and pressure distributions were allowed to change with time, tension-compression nonlinearity modeled collagen behavior in the STZ, and nonlinear geometry was incorporated to accommodate finite deformation. Responses to loading via impermeable and permeable rigid surfaces were compared to loading via normal cartilage, a more physiologic condition, anticipating the two rigid loading surfaces would bracket that of normal. For models loaded by normal cartilage, an STZ placed over the inferior repair region reduced the short-term axial compression of the articular surface by 15%, when compared to a repair without an STZ. Covering the repair with a normal STZ shifted the flow patterns and strain levels back toward that of normal cartilage. Additionally, reductions in von Mises stress (21%) and an increase in fluid pressure (13%) occurred in repair tissue under the STZ. This continues to show that STZ properties of sufficient quality are likely critical for the survival of transplanted constructs in vivo. However, response to loading via normal cartilage did not always fall within ranges predicted by the rigid surfaces. Use of more physiologic contact models is recommended for more accurate investigations into properties critical to the success of repair tissues.

  15. Surface esterification of cellulose fibers: characterization by DRIFT and contact angle measurements.

    PubMed

    Pasquini, Daniel; Belgacem, Mohamed Naceur; Gandini, Alessandro; Curvelo, Antonio Aprigio da Silva

    2006-03-01

    The surface chemical modification of microcrystalline cellulose and cellulose fibers obtained from different sugar cane bagasse pulping processes, viz. Kraft, organosolv ethanol/water and organosolv/supercritical carbon dioxide, were studied in heterogeneous conditions using modest amounts of octadecanoyl and dodecanoyl chloride. The ensuing surfaces acquired a non-polar character, suitable for incorporating these fibers as reinforcing agents in composite materials based on polymeric matrices. The success of these chemical modifications was assessed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, elemental analysis, scanning electron microscopy (SEM) and contact angle measurements. In particular, the dynamic and equilibrium contact angle measurements, before and after the treatments, revealed that the value of the polar component (gamma(s)p) of the surface energy had decreased very considerably following the modification.

  16. Investigation of contact-induced charging kinetics on variably modified glass surfaces

    NASA Astrophysics Data System (ADS)

    Agnello, G.; Hamilton, J.; Manley, R.; Streltsova, E.; LaCourse, W.; Cormack, A.

    2015-11-01

    The accumulation and dissipation of electrical charge on glass surfaces is of considerable academic and industrial interest. The purpose of the present article, is to report on the differences in charging kinetics of several flat alumina-borosilicate (low alkali content) glass surfaces via a rolling sphere test (RST) [1] that have been physically and/or chemically modified by different approaches and exposed to variable environmental conditions (i.e. relative humidity). Methods used for surface modification include chemical etching (HF based chemistries of variable molarity) and plasma processing/thin film deposition (CH4 via Reactive Ion Etch (RIE) and/or Atmospheric Pressure Plasma Chemical Vapor Deposition (APPCVD)). Trends in glass surface charge rates, along with corresponding surface resistivity, energy and zeta potential measurements indicate that glass surface, and perhaps bulk, chemistry (specifically a surface' reactivity/affinity with/to water) play critical roles in charge dynamics. Based on the results, we propose an ion-based transfer model facilitated by surface-water molecular interactions as the primary mechanism responsible for contact electrification in glass-metal contact systems.

  17. Zeta potential, contact angles, and AFM imaging of protein conformation adsorbed on hybrid nanocomposite surfaces.

    PubMed

    Pinho, Ana C; Piedade, Ana P

    2013-08-28

    The sputtering deposition of gold (Au) and poly(tetrafluoroethylene) (PTFE) was used to prepare a nanocomposite hybrid thin film suitable for protein adsorption while maintaining the native conformation of the biological material. The monolithic PTFE and the nanocomposite PTFE/Au thin films, with Au content up to 1 at %, were co-deposited by r.f. magnetron sputtering using argon as a discharge gas and deposited onto 316L stainless steel substrates, the most commonly used steel in biomaterials. The deposited thin films, before and after bovine serum albumin (BSA) adsorption, were thoroughly characterized with special emphasis on the surface properties/characteristics by atomic force microscopy (AFM), zeta potential, and static and dynamic contact angle measurements, in order to assess the relationship between structure and conformational changes. The influence of a pre-adsorbed peptide (RGD) was also evaluated. The nanotopographic and chemical changes induced by the presence of gold in the nanocomposite thin films enable RGD bonding, which is critical for the maintenance of the BSA native conformation after adsorption.

  18. 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].

  19. Attention to Eye Contact in the West and East: Autonomic Responses and Evaluative Ratings

    PubMed Central

    Akechi, Hironori; Senju, Atsushi; Uibo, Helen; Kikuchi, Yukiko; Hasegawa, Toshikazu; Hietanen, Jari K.

    2013-01-01

    Eye contact has a fundamental role in human social interaction. The special appearance of the human eye (i.e., white sclera contrasted with a coloured iris) implies the importance of detecting another person's face through eye contact. Empirical studies have demonstrated that faces making eye contact are detected quickly and processed preferentially (i.e., the eye contact effect). Such sensitivity to eye contact seems to be innate and universal among humans; however, several studies suggest that cultural norms affect eye contact behaviours. For example, Japanese individuals exhibit less eye contact than do individuals from Western European or North American cultures. However, how culture modulates eye contact behaviour is unclear. The present study investigated cultural differences in autonomic correlates of attentional orienting (i.e., heart rate) and looking time. Additionally, we examined evaluative ratings of eye contact with another real person, displaying an emotionally neutral expression, between participants from Western European (Finnish) and East Asian (Japanese) cultures. Our results showed that eye contact elicited stronger heart rate deceleration responses (i.e., attentional orienting), shorter looking times, and higher ratings of subjective feelings of arousal as compared to averted gaze in both cultures. Instead, cultural differences in the eye contact effect were observed in various evaluative responses regarding the stimulus faces (e.g., facial emotion, approachability etc.). The rating results suggest that individuals from an East Asian culture perceive another's face as being angrier, unapproachable, and unpleasant when making eye contact as compared to individuals from a Western European culture. The rating results also revealed that gaze direction (direct vs. averted) could influence perceptions about another person's facial affect and disposition. These results suggest that cultural differences in eye contact behaviour emerge from differential

  20. 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

  1. 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

  2. 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.

  3. Hydrophobic/superhydrophobic oxidized metal surfaces showing negligible contact angle hysteresis.

    PubMed

    Hozumi, Atsushi; Cheng, Dalton F; Yagihashi, Makoto

    2011-01-15

    Dynamic wettability of oxidized metal (aluminum and titanium) surfaces could be tuned by chemical vapor deposition (CVD) of 1,3,5,7-tetramethylcyclotetrasiloxane (D(4)(H)). This facile CVD method produces not only monomeric layers but also particulate films by changing the CVD temperature, resulting in a marked difference in the final wetting properties. In the samples prepared at 80°C for ~3 days, D(4)(H) layers with thicknesses of ~0.5 nm were formed on the surfaces without discernible change in surface morphology, as evidenced by X-ray photoelectron spectroscopy and atomic force microscopy. After this D(4)(H) monomeric layer formation, the hydrophilic oxidized aluminum and titanium surfaces became hydrophobic (advancing/receding water contact angles (θ(A)/θ(R))=102-104°/99-102°) showing essentially negligible contact angle hysteresis. Performing CVD of D(4)(H) at 180°C for ~1 day produced opaque film with particulate morphologies with diameters in the range of 500 nm to 4 μm observed on the surfaces. This geometric morphology enhanced the surface hydrophobicity (θ(A)/θ(R)=163°/160-161°). Droplets on these negligible-hysteresis surfaces moved very easily without "pinning".

  4. Silver deposition on stainless steel container surfaces in contact with disinfectant silver aqueous solutions

    NASA Astrophysics Data System (ADS)

    Petala, M.; Tsiridis, V.; Mintsouli, I.; Pliatsikas, N.; Spanos, Th.; Rebeyre, P.; Darakas, E.; Patsalas, P.; Vourlias, G.; Kostoglou, M.; Sotiropoulos, S.; Karapantsios, Th.

    2017-02-01

    Silver is the preservative used on the Russian segment of the International Space Station (ISS) to prevent microbial proliferation within potable water supplies. Yet, in the frame of the European Automated Transfer Vehicle (ATV) missions to ISS, silver depletion from water has been detected during ground transportation of this water to launch site, thereby indicating a degradation of water quality. This study investigates the silver loss from water when in contact with stainless steel surfaces. Experiments are conducted with several types of stainless steel surfaces being exposed to water containing 10 or 0.5 mg/L silver ions. Results show that silver deposits on stainless steel surfaces even when a passivation layer protects the metallic surface. The highest protection to silver deposition is offered by acid passivated and electropolished SS 316L. SEM and XPS experiments were carried out at several locations of the sample area that was in contact with the Ag solution and found similar morphological (SEM) and compositional (sputter-etch XPS) results. The results reveal that silver deposits uniformly across the wetted surface to a thickness larger than 3 nm. Moreover, evidence is provided that silver deposits in its metallic form on all stainless steel surfaces, in line with a galvanic deposition mechanism. Combination of ICP-MS and XPS results suggests a mechanism for Ag deposition/reduction with simultaneous substrate oxidation resulting in oxide growth at the exposed stainless steel surface.

  5. Analysis of the influence of bone fragment displacement in long bone fractures on interfragmentary contact surface.

    PubMed

    Szczęsny, Grzegorz

    2012-12-18

    The aim of the study was to validate the impact of angular and lateral displacements of bone fragments on the interfragmentary contact surface. Mathematical analysis was performed in a model of transverse fracture of long bone shaft treated as a tubular structure with a diameter of 42 mm. We performed our calculations for cortical thickness of 4, 6 and 8 mm. Displacements to the side were analyzed within a range from 0 to a half of bone diameter (21 mm), and angular displacements within a 0-18 degree range. Acquired results were related to the contact area of a non-displaced fracture. Lateral displacement of bone fragments equal to the width of bone's cortical layer (4, 6 and 8 mm) leads to a decrease in interfragmentary contact area to 48.6%, 51.3% and 54.6%, while displacement equal to a half of bone's diameter--to 7.9%, 20.1% and 28.4% of the contact area in an anatomically reduced fracture for cortical thickness values of 4, 6 and 8 mm respectively. Interfragmentary contact area equal to 80% of anatomically reduced fracture is achieved for displacements of 1.5 mm, 2.4 mm and 3.5 mm, corresponding to 3.6%, 5.7% and 8.3% of bone diameter, and to 37.5%, 40% and 42.5% of its cortical thickness (4, 6 and 8 mm, respectively). Angular displacement of less than 2.5 degrees did not affect the interfragmentary contact area, decreasing rapidly to reach values of 66.1%, 76.1% and 81.1% of anatomically reduced fractures at 3.3-degree angulation (values given for cortical thickness of 4, 6 and 8 mm, respectively). Obtained results indicate pronounced loss of contact surface between bone fragments during their displacement to the side and for angular displacements greater than 2.5 degrees. Moreover, bone fragments contact surface decreases with reduction of cortical thickness. In conclusion, it is necessary to reduce a fracture as precisely as possible, particularly in case of bone atrophy.

  6. 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.

  7. Effects of synthesizing parameters on surface roughness and contact angles of ZnO nanowire films.

    PubMed

    Jing, Weixuan; Wang, Bing; Niu, Lingling; Jiang, Zhuangde; Qi, Han; Chen, Lujia; Zhou, Fan

    2014-06-01

    Effects of the synthesizing parameters on the surface roughness and the contact angles of ZnO nanowire films were studied in this paper. ZnO nanowire films were synthesized with the hydrothermal method on glass substrates, and the synthesizing parameters include the concentrations of the growth solution and the seed layer solution, the growth time span as well as the temperature. Atomic force microscopy and scanning electron microscopy were employed respectively to characterize the surface and the profile roughness of ZnO nanowire films. The measurement results by atomic force microscopy were in agreement with that by scanning electron microscopy, hence the former was used for the investigation of aforementioned effects. Relationships between the synthesizing parameters, the surface roughness and the contact angles of ZnO nanowire films were established, revealing that the synthesizing parameters affected significantly not only the surface roughness but also the contact angles of ZnO nanowire films. The results can be used for batch fabrication of ZnO nanowire-based structures and these structures-based sensors in a wide variety of applications.

  8. Surface free energy and wettability of silyl layers on silicon determined from contact angle hysteresis.

    PubMed

    Chibowski, Emil J

    2005-05-30

    Using the literature data of the advancing and receding contact angles for water, diiodomethane and hexadecane measured on various hydrophobic silyl layers (mostly monolayers) produced on silicon wafers the apparent surface free energies gamma(s)(tot) were calculated by applying new model of the contact angle hysteresis interpretation. It was found that, for the same silyl layer, the calculated gamma(s)(tot) values to some degree depended on the probe liquid used. Therefore, thus calculated the surface free energies should be considered as apparent ones. Moreover, also the values of the dispersion component gamma(s)(d) of these layers depend on the probe liquid used, but to a less degree. This must be due to the strength of the force field originating from the probe liquid and the spacing between the interacting molecules. The relationships between gamma(s)(tot) and gamma(s)(d) are discussed on the basis of the equations derived. It may be postulated that applying proposed model of the contact angle hysteresis and calculating the apparent total surface free energies and the dispersion contributions better insight into wetting properties of the silyled silicon surface can be achieved.

  9. Contact angle and droplet heat transfer during evaporation on structured and smooth surfaces of heated wall

    NASA Astrophysics Data System (ADS)

    Misyura, S. Y.

    2017-08-01

    Water evaporation in a wide range of droplet diameters and wall temperatures on the structured and smooth surfaces were studied experimentally. Linear dependence of evaporation rate (dV/dt) on a droplet radius varies when the volume is greater than 40-60 μl. The static contact angles on the structured surface vary with a droplet diameter for high wall superheating. Dependence of the contact angle on diameter for the corrugated surface is defined by a change in both potential energy barrier U and three-phase contact line tension τcl. This energy barrier for the structured wall changes with an increase in the initial droplet diameter and becomes constant for the large droplets. For high wall superheating, the power in the law of evaporation increases from 1 to 1.45 with an increase in the initial droplet diameter. Depending on the droplet radius, number of droplets and heater length, four different characters of evaporation are realized. Complete droplet evaporation time on structured surface is less than smooth wall. Heat transfer coefficient is greater for structured wall than smooth one. When simulating droplet evaporation and heat transfer, it is necessary to take into account free convection of air and vapor.

  10. On the interfacial behavior of ionic liquids: surface tensions and contact angles.

    PubMed

    Restolho, José; Mata, José L; Saramago, Benilde

    2009-12-01

    In this work the liquid/vapour and the solid/liquid interfaces of a series of ionic liquids: 1-ethyl-3-methylpyridinium ethyl sulfate, [EMPy][EtSO4], 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM][EtSO4], 1-ethanol-3-methylimidazolium tetrafluoroborate, [C2OHMIM][BF4], 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIM][BF4], were investigated. The surface tension was measured in a wide temperature range, (298-453) K. The contact angles were determined on substrates of different polarities. Both on the polar (glass) and the non-polar substrates ((poly-(tetrafluoroethylene) and poly-(ethylene)), the liquids with maximum and minimum surface tensions lead, respectively, to the highest and the lowest contact angles. The dispersive, gamma(L)(d), and non-dispersive, gamma(L)(nd), components of the liquid surface tension, gamma(L), were calculated from the contact angles on the non-polar substrates using the Fowkes approach. The polarity fraction, gamma(L)(nd)/gamma(L), was compared with the polarity parameter, k, obtained from the fitting of the surface tension vs. temperature data to the Eötvös equation. Good agreement was found for the extreme cases: [OMIM][BF4] exhibits the lowest polarity and [BMIM][BF4], the highest. When compared with the polarity fractions of standard liquids considered as "polar" liquids, the ionic liquids studied may be considered as moderately polar.

  11. 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

  12. Contact-dependent killing by Caulobacter crescentus via cell surface-associated, glycine zipper proteins

    PubMed Central

    García-Bayona, Leonor; Guo, Monica S; Laub, Michael T

    2017-01-01

    Most bacteria are in fierce competition with other species for limited nutrients. Some bacteria can kill nearby cells by secreting bacteriocins, a diverse group of proteinaceous antimicrobials. However, bacteriocins are typically freely diffusible, and so of little value to planktonic cells in aqueous environments. Here, we identify an atypical two-protein bacteriocin in the α-proteobacterium Caulobacter crescentus that is retained on the surface of producer cells where it mediates cell contact-dependent killing. The bacteriocin-like proteins CdzC and CdzD harbor glycine-zipper motifs, often found in amyloids, and CdzC forms large, insoluble aggregates on the surface of producer cells. These aggregates can drive contact-dependent killing of other organisms, or Caulobacter cells not producing the CdzI immunity protein. The Cdz system uses a type I secretion system and is unrelated to previously described contact-dependent inhibition systems. However, Cdz-like systems are found in many bacteria, suggesting that this form of contact-dependent inhibition is common. DOI: http://dx.doi.org/10.7554/eLife.24869.001 PMID:28323618

  13. Methods of determining the contact between a probe and a surface under scanning electron microscopy

    SciTech Connect

    Nien, C.-H.; Tsai, C. H.; Shin, K. Y.; Jian, W. B.

    2006-10-15

    Based on the charging effect common to various kinds of electron microscopy, we have developed novel methods of determining 'when' and 'where' a probe starts to contact an electrically isolated surface. The touchdown of an electrically grounded probe leads to an acute change in the imaging contrast of the contacted surface, which also causes a rapid jump (ranging from a few to tens of picoamperes) of the grounding current. Thus, the detection of contact can be carried out in both qualitative and quantitative manners, providing a basis for establishing relevant standard procedures. In addition, we have achieved the spatial mapping of the contact point(s) using a specially designed lithographical pattern with two mutually vertical sets of parallel conductive lines. The precision of this mapping technique is simply determined by the pitch of parallel lines, which can be as small as the capability achievable in e-beam lithography. A possible 'one-probe' version of the electrical characterization is also discussed with the same underlying principle, which may turn out to be indispensable for various studies and applications of nanostructures. Further development along this track is promising to realize an instrumentally simple version of 'scanning electron spectroscopy' with various modes.

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

    SciTech Connect

    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.

  15. 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].

  16. Contact-dependent killing by Caulobacter crescentus via cell surface-associated, glycine zipper proteins.

    PubMed

    García-Bayona, Leonor; Guo, Monica S; Laub, Michael T

    2017-03-21

    Most bacteria are in fierce competition with other species for limited nutrients. Some bacteria can kill nearby cells by secreting bacteriocins, a diverse group of proteinaceous antimicrobials. However, bacteriocins are typically freely diffusible, and so of little value to planktonic cells in aqueous environments. Here, we identify an atypical two-protein bacteriocin in the α-proteobacterium Caulobacter crescentus that is retained on the surface of producer cells where it mediates cell contact-dependent killing. The bacteriocin-like proteins CdzC and CdzD harbor glycine-zipper motifs, often found in amyloids, and CdzC forms large, insoluble aggregates on the surface of producer cells. These aggregates can drive contact-dependent killing of other organisms, or Caulobacter cells not producing the CdzI immunity protein. The Cdz system uses a type I secretion system and is unrelated to previously described contact-dependent inhibition systems. However, Cdz-like systems are found in many bacteria, suggesting that this form of contact-dependent inhibition is common.

  17. 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.

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

    PubMed

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

    2016-04-06

    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.

  19. 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

  20. Fluid dynamics at the interface between contacting elastic solids with randomly rough surfaces.

    PubMed

    Persson, B N J

    2010-07-07

    We study fluid dynamics at the interface between elastic solids with randomly rough surfaces. The contact mechanics model of Persson is used to take into account the elastic interaction between the solid walls, and the Bruggeman effective medium theory to account for the influence of the disorder on the fluid flow. We calculated the flow tensor which determines the pressure flow factor and, for example, the leak rate of static seals. It is shown how the perturbation treatment of Tripp can be extended to arbitrary order in the ratio between the root-mean-square roughness amplitude and the average interfacial surface separation. We introduce a matrix D(ζ), determined by the surface roughness power spectrum, which can be used to describe the anisotropy of the surface at any magnification ζ. Results are presented for the asymmetry factor γ(ζ) (generalized Peklenik number) for grinded steel and sandblasted PMMA surfaces. © 2010 IOP Publishing Ltd

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

    PubMed

    Niemira, Brendan A; Boyd, Glenn; Sites, Joseph

    2014-05-01

    Cross-contamination of 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 ability to inactivate Salmonella biofilms. A 3-strain Salmonella culture was grown to form adherent biofilms for 24, 48, or 72 h on a test surface (glass slides). These were placed on a conveyor belt and passed at various line speeds to provide exposure times of 5, 10, or 15 s. The test plate was either 5 or 7.5 cm under a plasma jet emitter operating at 1 atm using filtered air as the feed gas. The frequency of high-voltage electricity was varied from 23 to 48 kHz. At the closer spacing (5 cm), cold plasma reduced Salmonella biofilms by up to 1.57 log CFU/mL (5 s), 1.82 log CFU/mL (10 s), and 2.13 log CFU/mL (15 s). Increasing the distance to 7.5 cm generally reduced the efficacy of the 15 s treatment, but had variable effects on the 5 and 10 s treatments. Variation of the high-voltage electricity had a greater effect on 10 and 15 s treatments, particularly at the 7.5 cm spacing. For each combination of time, distance, and frequency, Salmonella biofilms of 24, 48, and 72 h growth responded consistently with each other. The results show that short treatments with cold plasma yielded up to a 2.13 log reduction of a durable form of Salmonella contamination on a model food contact surface. This technology shows promise as a possible tool for rapid disinfection of materials associated with food processing. Pathogens such as Salmonella can form chemical-resistant biofilms, making them difficult to remove from food contact surfaces. A 15 s treatment with cold plasma reduced mature Salmonella biofilms by up to 2.13 log CFU/mL (99.3%). This contact-free, waterless method uses no chemical sanitizers. Cold plasma may therefore have a practical application for conveyor belts, equipment, and other food contact

  2. 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.

  3. 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.

  4. Free surface profile of evaporative liquids at the vicinity of the contact line

    NASA Astrophysics Data System (ADS)

    Houssainy, Sammy; Kavehpour, Pirouz

    2014-11-01

    Interfacial phenomenon, specifically those associated with evaporation from thin liquid films near the contact line of a liquid drop, play a major role in many current engineering applications which require high local heat fluxes, as evident in heat pipes, grooved evaporators, fuel cells and suction nucleate boiling devices. This study will prove useful in the improvement of such applications. Fluoresces microscopy was used as our main technique of investigating the free surface profiles of evaporative liquids, as it delivers sufficient range and resolution to address the challenge of capturing the microscopic and macroscopic aspects of this phenomenon. Subsequent to our experimental findings, the results are compared with non-volatile liquids for both contact angle and free surface structures.

  5. Cytoplasmic calcium levels and membrane fluidity of platelets in contact with polyether-polyamide multiblock-copolymer surfaces.

    PubMed

    Yui, N; Okano, T; Sakurai, Y; Kora, S; Ishikawa, K; Hiranuma, T; Yamashita, S

    1996-02-01

    Cytoplasmic calcium levels and the membrane fluidity of rabbit platelets stored in mini blood bags of crystalline-amorphous microstructured polymers (polyether-polyamide multiblock-copolymers) were studied. Fluorescent dye (Fura 2 or 1,6-diphenyl-1,3,5-hexatriene)-loaded platelet suspensions were stored at 37 degrees C for 1 h in the blood bags, and metabolic changes in the platelets during storage were evaluated by the fluorescent spectroscopic technique. The surfaces of poly(vinyl chloride) and polyolefin elastomers, which are used for commercially available blood bags, enhanced the progress of platelet metabolism; i.e., there was a dramatic decrease in membrane fluidity and an increase in [Ca2+]i. Furthermore, the decrease in membrane fluidity was observed prior to the increase in [Ca2+]i. These results suggest that the decrease in membrane fluidity of platelets in contact with polymer surfaces can be the dominant stage in the activation of these platelets. In contrast, the surfaces of polyether-polyamide multiblock-copolymers exhibited few changes in either membrane fluidity or [Ca2+]i levels. These results suggest that the platelets in contact with the crystalline-amorphous microstructured copolymer surfaces can be inert and inactivated in terms of the prevention of a decrease in membrane fluidity.

  6. Contact Angle and Adhesion Dynamics and Hysteresis on Molecularly Smooth Chemically Homogeneous Surfaces.

    PubMed

    Chen, Szu-Ying; Kaufman, Yair; Schrader, Alex M; Seo, Dongjin; Lee, Dong Woog; Page, Steven H; Koenig, Peter H; Isaacs, Sandra; Gizaw, Yonas; Israelachvili, Jacob N

    2017-09-26

    Measuring truly equilibrium adhesion energies or contact angles to obtain the thermodynamic values is experimentally difficult because it requires loading/unloading or advancing/receding boundaries to be measured at rates that can be slower than 1 nm/s. We have measured advancing-receding contact angles and loading-unloading adhesion energies for various systems and geometries involving molecularly smooth and chemically homogeneous surfaces moving at different but steady velocities in both directions, ±V, focusing on the thermodynamic limit of ±V → 0. We have used the Bell Theory (1978) to derive expressions for the dynamic (velocity-dependent) adhesion energies and contact angles suitable for both (i) dynamic adhesion measurements using the classic Johnson-Kendall-Roberts (JKR, 1971) theory of "contact mechanics" and (ii) dynamic contact angle hysteresis measurements of both rolling droplets and syringe-controlled (sessile) droplets on various surfaces. We present our results for systems that exhibited both steady and varying velocities from V ≈ 10 mm/s to 1 nm/s, where in all cases but one, the advancing (V > 0) and receding (V < 0) adhesion energies and/or contact angles converged toward the same theoretical (thermodynamic) values as V → 0. Our equations for the dynamic contact angles are similar to the classic equations of Blake & Haynes (1969) and fitted the experimental adhesion data equally well over the range of velocities studied, although with somewhat different fitting parameters for the characteristic molecular length/dimension or area and characteristic bond formation/rupture lifetime or velocity. Our theoretical and experimental methods and results unify previous kinetic theories of adhesion and contact angle hysteresis and offer new experimental methods for testing kinetic models in the thermodynamic, quasi-static, limit. Our analyses are limited to kinetic effects only, and we conclude that hydrodynamic, i.e., viscous, and inertial effects

  7. Surface characterization of poly(L-lactic acid)-methoxy poly(ethylene glycol) diblock copolymers by static and dynamic contact angle measurements, FTIR, and ATR-FTIR.

    PubMed

    Mert, O; Doganci, E; Erbil, H Y; Demir, A S

    2008-02-05

    The surface composition and surface free energy properties of two types of amphiphilic and semicrystalline diblock copolymers consisting of poly(L-lactic acid) coupled to (methoxy poly(ethylene glycol) (PLLA-MePEG) having differing block lengths of PEG were investigated by using static and dynamic contact angle measurements, transmission Fourier infrared spectroscopy (FTIR), and attenuated total reflection spectroscopy (ATR-FTIR) and compared with results obtained from PLLA and MePEG homopolymers. The contact angle results were evaluated by using the van Oss-Good method (acid-base method), and it was determined that the Lewis base surface tension coefficient (gamma-) of the copolymers increased with an increase of the PEG molar content at the copolymer surface. This result is in good agreement with the transmission FTIR and ATR-FTIR results but not proportional to them, indicating that the surfaces of the copolymers are highly mobile and that the molecular rearrangement takes place upon contact with a polar liquid drop. The dynamic contact angle measurements showed that the strong acid-base interaction between the oxygen atoms in the copolymer backbone of the relatively more hydrophilic PEG segments with the Lewis acidic groups of the polar and hydrogen-bonding water molecules enabled the surface molecules to restructure (conformational change) at the contact area, so that the PEG segments moved upward, whereas the apolar methyl pendant groups of PLLA segments buried downward.

  8. 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.

  9. Determination of Surface Recombination Velocities at Contacts in Organic Semiconductor Devices Using Injected Carrier Reservoirs

    NASA Astrophysics Data System (ADS)

    Sandberg, Oskar J.; Sandén, Simon; Sundqvist, Anton; Smâtt, Jan-Henrik; Österbacka, Ronald

    2017-02-01

    A method to determine surface recombination velocities at collecting contacts in interface-limited organic semiconductor devices, based on the extraction of injected carrier reservoirs in a single-carrier sandwich-type structure, is presented. The analytical framework is derived and verified with drift-diffusion simulations. The method is demonstrated on solution-processed organic semiconductor devices with hole-blocking TiO2/organic and SiO2/organic interfaces, relevant for solar cell and transistor applications, respectively.

  10. [THE IMMUNOLOGIC INDICATORS IN PATIENTS WITH CARIES OF CONTACT SURFACES OF LATERAL TEETH].

    PubMed

    Heigetyan, A V; Bragin, E A; Maksiukov, S Yu; Labushkina, A V; Alutina, E L; Harseeva, G G

    2015-08-01

    The samplings of patients aged 18-45 years with caries of contact surfaces of lateral teeth (n=18) and healthy adults aged 18-20 years with intact teeth (n=18) were examined The saliva taken in rotary vial on empty stomach in amount of 3-4 mi served as assay for analysis. To identify secretory immunoglobulin A, interleukin lβ, interleukin-4 and interferon y saliva was centrifuged during 15 min under 1500 rpm. The supernatant fluid was analyzed using enzymoimmunoassay (test-systems "Vector-Best", Novosibirsk). The registration of reaction was implemented using multiscan Labsystem under wavelength 450 nm. The content of secretory immunoglobulin A was expressed in mg/l, cytokines - in pg/ml. It is demonstrated that in patients with caries average level of interleukin lβ was almost two times higher (p<0.05) than analogous indicator in healthy examined patients. In healthy patients average level of interferon γ significantly (more than in 10 times) exceeded upper limit of allowable standard and was higher (p<0.05) in comparison with such in patients with caries of contact surfaces. The analysis of content of secretory immunoglobulin A in saliva established that in healthy patients average values of the given indicator were higher (p<0.05) than in patients with caries of contact surfaces of lateral teeth. The lower content of secretory immunoglobulin A and interferon y against the background of increased level of interleukin lβ was detected in saliva of patients with caries of contact surfaces of lateral teeth. This occurrence can be considered as factor predisposing to development of caries process.

  11. Analysis of distribution rule of surface stress on cross wedge rolling contact zone by finite element method

    NASA Astrophysics Data System (ADS)

    Shu, Xuedao; Li, Lianpeng; Hu, Zhenghuan

    2005-12-01

    Contact surface of cross-wedge rolling is a complicated space surface and distribution rule of contact surface stress is very complicated. So far, its analyzed result was still based on slippery line method. Designing mould and actual production mainly depend on experiential factor. Application and development of cross-wedge rolling was baffled seriously. Based on the forming characteristics of cross-wedge rolling with flat wedge-shape, the ANSYS/DYNA software was developed secondly on the basis of itself, and the corresponding command program was compiled. Rolling process of cross-wedge rolling with flat wedge-shape was simulated successfully. Through simulation, space surface shape of contact surface was achieved, and distribution rule of contact surface stress was analyzed detailed and obtained. The results provide important theoretical foundation for avoiding appearing bug on surface of rolled part, instructing to design cross-wedge mould and confirming force and energy parameter.

  12. 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

  13. Contacts in the Office of Pesticide Programs, Pesticide Re-Evaluation Division

    EPA Pesticide Factsheets

    Contact the Pesticide Re-Evaluation Division (PRD) about registration review and reregistration follow up (including post-RED activities, product reregistration, and implementing certain tolerance reassessment decisions) for conventional pesticides.

  14. 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...

  15. 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...

  16. Contact mechanics analysis of oscillatory sliding of a rigid fractal surface against an elastic-plastic half-space

    NASA Astrophysics Data System (ADS)

    Song, Z.; Komvopoulos, K.

    2014-10-01

    Oscillatory sliding contact between a rigid rough surface and an elastic-plastic half-space is examined in the context of numerical simulations. Stick-slip at asperity contacts is included in the analysis in the form of a modified Mindlin theory. Two friction force components are considered - adhesion (depending on the real area of contact, shear strength and interfacial adhesive strength) and plowing (accounting for the deformation resistance of the plastically deformed half-space). Multi-scale surface roughness is described by fractal geometry, whereas the interfacial adhesive strength is represented by a floating parameter that varies between zero (adhesionless surfaces) and one (perfectly adhered surfaces). The effects of surface roughness, apparent contact pressure, oscillation amplitude, elastic-plastic properties of the half-space and interfacial adhesion on contact deformation are interpreted in the light of numerical results of the energy dissipation, maximum tangential (friction) force and slip index. A non-monotonic trend of the energy dissipation and maximum tangential force is observed with increasing surface roughness, which is explained in terms of the evolution of the elastic and plastic fractions of truncated asperity contact areas. The decrease of energy dissipation with increasing apparent contact pressure is attributed to the increase of the elastic contact area fraction and the decrease of the slip index. For a half-space with fixed yield strength, a lower elastic modulus produces a higher tangential force, whereas a higher elastic modulus yields a higher slip index. These two competing effects lead to a non-monotonic dependence of the energy dissipation on the elastic modulus-to-yield strength ratio of the half-space. The effect of interfacial adhesion on the oscillatory contact behaviour is more pronounced for smoother surfaces because the majority of asperity contacts deform elastically and adhesion is the dominant friction mechanism. For

  17. Simulated Contact Angle Hysteresis of a Three-Dimensional Drop on a Chemically Heterogeneous Surface: A Numerical Example

    PubMed

    Brandon; Wachs; Marmur

    1997-07-01

    A public domain software package is employed in the quasi-steady-state simulation of contact angle hysteresis. Three-dimensional sessile drops in equilibrium with a model chemically heterogeneous smooth solid surface are considered; evolving drop shapes, as a function of incremental changes in their volume, are investigated. Results are presented for a model system in which the intrinsic contact angle is assumed to vary along the surface in a periodic manner. Throughout the simulation, calculated contact angles show reasonable agreement with the local intrinsic contact angle values, and the computed drop shapes are found to be constant mean curvature surfaces. Significant hysteresis in the liquid-fluid interface curvature and average contact angle is found; a complete hysteresis loop is simulated. Advancing and receding contact angles exhibit the "stick-slip" behavior observed in experiments as well as in previous 2-D simulations.

  18. 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.

  19. 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.

  20. 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.

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

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1986-01-01

    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 220 C 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.

  2. Schottky-barrier-free contacts with two-dimensional semiconductors by surface-engineered MXenes

    DOE PAGES

    Liu, Yuanyue; Xiao, Hai; Goddard, III, William A.

    2016-11-22

    Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. Here we demonstrate their potential as Schottky-barrier-free metal contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. Based on first principles calculations, we find that the surface chemistry strongly affects the Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, while F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weakmore » Fermi level pinning, enable Schottky-barrier-free hole (or electron) injection into 2D semiconductors through van der Waals junctions with some of the O-terminated (or all the OH-terminated) MXenes. Furthermore, we suggest synthetic routes to control the surface terminations based on the calculated formation energies. Finally, this study enhances the understanding of the correlation between surface chemistry and electronic/transport properties of 2D materials, and also gives practical predictions for improving 2D electronics.« less

  3. Schottky-barrier-free contacts with two-dimensional semiconductors by surface-engineered MXenes

    SciTech Connect

    Liu, Yuanyue; Xiao, Hai; Goddard, III, William A.

    2016-11-22

    Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. Here we demonstrate their potential as Schottky-barrier-free metal contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. Based on first principles calculations, we find that the surface chemistry strongly affects the Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, while F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weak Fermi level pinning, enable Schottky-barrier-free hole (or electron) injection into 2D semiconductors through van der Waals junctions with some of the O-terminated (or all the OH-terminated) MXenes. Furthermore, we suggest synthetic routes to control the surface terminations based on the calculated formation energies. Finally, this study enhances the understanding of the correlation between surface chemistry and electronic/transport properties of 2D materials, and also gives practical predictions for improving 2D electronics.

  4. 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

  5. Susceptibility of opportunistic Burkholderia glumae to copper surfaces following wet or dry surface contact.

    PubMed

    Cui, Zhouqi; Ibrahim, Muhammad; Yang, Chunlan; Fang, Yuan; Annam, Hussain; Li, Bin; Wang, Yanli; Xie, Guan-Lin; Sun, Guochang

    2014-07-09

    Burkholderia glumae has been proposed to have a potential risk to vulnerable communities. In this work, we investigated the antibacterial activity and mechanism of copper surfaces against multi-drug resistant B. glumae from both patients and rice plants. The susceptibility of B. glumae to copper surfaces was noted by a significant decline in viable bacterial counts, relative to the slight reduction of stainless steel and polyvinylchloride, both of which were used as control surfaces. The mode of action of bacterial killing was determined by examing the mutagenicity, DNA damage, copper ions accumulation, and membrane damage in bacterial cells. The results indicated that the cells exposed to copper surfaces did not cause severe DNA lesions or increase the mutation frequencies, but resulted in a loss of cell membrane integrity within minutes. Furthermore, bacterial cells exposed to copper surfaces accumulated significantly higher amounts of copper compared to control surfaces. Overall, this study showed that metallic copper had strong antibacterial effect against B. glumae by causing DNA and membrane damage, cellular accumulation of copper, and cell death following DNA degradation, which could be utilized to reduce the risk of bacterial contamination and infection.

  6. 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

  7. 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.

  8. 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

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

    SciTech Connect

    Alimov, Mars M.; Kornev, Konstantin G.

    2016-01-15

    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.

  10. Periodic contact between piezoelectric materials and a rigid body with a wavy surface

    NASA Astrophysics Data System (ADS)

    Zhou, Yue-Ting; Kim, Tae-Won

    2015-01-01

    An exact analysis is conducted for periodic, two-dimensional (2D) contact of piezoelectric materials in contact with a rigid body with a wavy surface pressed by uniform stresses at infinity. For three cases of eigenvalue distribution, three harmonic functions automatically satisfying the periodicity conditions are carefully constructed to facilitate the derivation of the solution of the considered problem. The stresses and electric displacements are obtained as infinite series. It is found that for the full contact case, the disturbance stress and electric displacement fields remain only the first harmonic which has the slowest decay in the y-direction. The convergence behaviours of the infinite series are checked, which shows that the external loading p and different positions have a great effect on the convergence behaviours of the infinite series and 400 terms are enough to get accurate solution at each position. Numerical results are presented to justify the validity of the present derivation and show the effect of the external loading on the contact behaviours.

  11. 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.

  12. Feasibility study on the concept of thermal contact sensor for nanometre-level defect inspections on smooth surfaces

    NASA Astrophysics Data System (ADS)

    Shimizu, Yuki; Lu, Wenjian; Ohba, Yuta; Gao, Wei

    2014-06-01

    This paper presents a feasibility study on the concept of a thermal contact sensor that detects nanometre-scale defects on smoothly finished surfaces such as bare silicon wafers, magnetic disks and so on. The contact sensor has a thermal element, which is composed of thin-film structures with a thermally sensitive area of several tens of µm2 on its tip surface. In the proposed concept, the thermal element detects the existence of asperity-type defects on smooth surfaces by capturing frictional heats due to slight contacts between the thermal element surface and defects. During the defect detection, a gap between the thermal element surface and the smooth surface being rotated by a precision spindle would be maintained. By monitoring deviation of the electrical resistance of the thermal element while scanning the contact sensor across the rotating surface, defects on the target surface can be detected. In this paper, a fabrication process for the thermal element has been designed based on the photolithography process, and the first prototype of the thermal element has been fabricated. Results of laser exposure tests have revealed that the fabricated thermal element can detect a rate of heat supply of 10 µW, which is the same order as the rate of heat supply assumed to be generated at defect detection by the contact sensor. In addition, results of contact detection tests have confirmed the feasibility of the fabricated thermal element as a contact detection sensor.

  13. Resonance frequency analysis, insertion torque, and bone to implant contact of 4 implant surfaces: comparison and correlation study in sheep.

    PubMed

    Dagher, Maroun; Mokbel, Nadim; Jabbour, Gabriel; Naaman, Nada

    2014-12-01

    Primary stability is evaluated using resonance frequency analysis (RFA) and insertion torque (IT). Although there is a strong correlation between RFA and IT, studies failed to find a correlation between RFA and bone to implant contact (BIC) or IT and BIC. To compare RFA, IT, and BIC of SLA, SLActive, Euroteknika, and TiUnite implant surfaces and evaluate the correlation between them. Thirty-two implants were placed in 8 sheep. RFA and IT were recorded. Animals were killed at 1 and 2 months. A significant difference was found in RFA between the 4 surfaces. No significant difference was found for IT. Mean BIC was different between all 4 surfaces. A significant positive correlation was found between RFA and IT with SLA. No significant correlation was found between RFA and BIC and between IT and BIC at 1 and 2 months. Implants with 4 different surfaces have similar IT values but different RFA and BIC. Additionally irrespective of the implant surface, there is no correlation between IT and BIC and between RFA and BIC.

  14. Super-mercuryphobic and hydrophobic diamond surfaces with hierarchical structures: Vanishment of the contact angle hysteresis with mercury

    NASA Astrophysics Data System (ADS)

    Escobar, Juan V.; Garza, Cristina; Alonso, Juan Carlos; Castillo, Rolando

    2013-05-01

    Increased roughness is known to enhance the natural wetting properties of surfaces, making them either more hydrophobic or more hydrophilic. In this work we study the wetting properties of water and mercury drops in contact with boron doped diamond films with progressively increased surface roughnesses. We show how thermal oxidation of a microcrystalline film creates pyramids decorated with sub-micron protrusions that turn its naturally mercuryphobic surface into super-mercuryphobic. With this liquid, we observe the vanishment of the contact angle hysteresis that is expected for rough surfaces as the contact angle approaches 180˚, making small drops of mercury roll along out of the surface at an apparent zero tilt-angle. In contrast, the incorporation of nano-globules on the oxidized surface through a silanization process is necessary to increase the hydrophobic properties of the film for which the contact angle with water reaches 138°. The wetting states that dominate in each case are discussed.

  15. Study on surface topography of 446M stainless steel as a bipolar plate on interfacial contact resistance of polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Kim, Kwang Min; Kim, Seok Nyeon; Kim, Jong Hee; Lee, Yun Yong; Kim, Kyoo Young

    2012-12-01

    The effect of the surface topography of 446M ferritic stainless steel as a bipolar plate for polymer electrolyte membrane fuel cell (PEMFC) is evaluated by interfacial contact resistance (ICR) measurement and finite element method (FEM) simulation. When the surface of stainless steel is in contact with the carbon paper under load, the surface roughness of stainless steel can affect the degree of deformation of the carbon fiber. Moreover, the higher deformation of carbon fiber under load in the rougher stainless steel could lead to larger real contact area between stainless steel and carbon fiber, and consequently the rough one has a lower ICR value than the fine one. The results suggest that the topography of stainless steel as a bipolar plate significantly affects the ICR. Furthermore, it was found that topography of bipolar plate is one of the key factors to decrease ICR.

  16. Monolayer contact doping of silicon surfaces and nanowires using organophosphorus compounds.

    PubMed

    Hazut, Ori; Agarwala, Arunava; Subramani, Thangavel; Waichman, Sharon; Yerushalmi, Roie

    2013-12-02

    Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures(1). MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms. In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

  17. Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

    PubMed Central

    Hazut, Ori; Agarwala, Arunava; Subramani, Thangavel; Waichman, Sharon; Yerushalmi, Roie

    2013-01-01

    Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms. In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station. PMID:24326774

  18. Particle Separation inside a Sessile Droplet with Variable Contact Angle Using Surface Acoustic Waves.

    PubMed

    Destgeer, Ghulam; Jung, Jin Ho; Park, Jinsoo; Ahmed, Husnain; Sung, Hyung Jin

    2017-01-03

    A sessile droplet of water carrying polystyrene microparticles of different diameters was uniformly exposed to high frequency surface acoustic waves (SAWs) produced by an interdigitated transducer (IDT). We investigated the concentration behavior of the microparticles as the SAWs generated a strong acoustic streaming flow (ASF) inside the water droplet and exerted a direct acoustic radiation force (ARF) on the suspended particles, the magnitude of which depended upon the particle diameter. As a result of the ARF, the microparticles were concentrated according to their diameters at different positions inside the sessile droplet placed in the path of the SAW, right in front of the IDT. The microparticle concentration behavior changed as the sessile droplet contact angle with the substrate was varied by adding surfactant to the water or by gradually evaporating the water. The positions at which the smaller and larger microparticles were concentrated remained distinguishable, even at very different experimental conditions. The long-term exposure of the droplets to the SAWs was accompanied by the gradual evaporation of the carrier fluid, which dynamically changed the droplet contact angle as well as the concentration of particles. Complete evaporation of the fluid left behind several concentrated yet separated clusters of particles on the substrate surface. The effect of the droplet contact angle on particles' concentration behavior and consequent separation of particles has been uniquely studied in this SAW-based report.

  19. Pinning of the Contact Line during Evaporation on Heterogeneous Surfaces: Slowdown or Temporary Immobilization? Insights from a Nanoscale Study.

    PubMed

    Zhang, Jianguo; Müller-Plathe, Florian; Leroy, Frédéric

    2015-07-14

    The question of the effect of surface heterogeneities on the evaporation of liquid droplets from solid surfaces is addressed through nonequilibrium molecular dynamics simulations. The mechanism behind contact line pinning which is still unclear is discussed in detail on the nanoscale. Model systems with the Lennard-Jones interaction potential were employed to study the evaporation of nanometer-sized cylindrical droplets from a flat surface. The heterogeneity of the surface was modeled through alternating stripes of equal width but two chemical types. The first type leads to a contact angle of 67°, and the other leads to a contact angle of 115°. The stripe width was varied between 2 and 20 liquid-particle diameters. On the surface with the narrowest stripes, evaporation occurred at constant contact angle as if the surface was homogeneous, with a value of the contact angle as predicted by the regular Cassie-Baxter equation. When the width was increased, the contact angle oscillated during evaporation between two boundaries whose values depend on the stripe width. The evaporation behavior was thus found to be a direct signature of the typical size of the surface heterogeneity domains. The contact angle both at equilibrium and during evaporation could be predicted from a local Cassie-Baxter equation in which the surface composition within a distance of seven fluid-particle diameters around the contact line was considered, confirming the local nature of the interactions that drive the wetting behavior of droplets. More importantly, we propose a nanoscale explanation of pinning during evaporation. Pinning should be interpreted as a drastic slowdown of the contact line dynamics rather than a complete immobilization of it during a transition between two contact angle boundaries.

  20. Physical Modeling of Contact Processes on the Cutting Tools Surfaces of STM When Turning

    NASA Astrophysics Data System (ADS)

    Belozerov, V. A.; Uteshev, M. H.

    2016-08-01

    This article describes how to create an optimization model of the process of fine turning of superalloys and steel tools from STM on CNC machines, flexible manufacturing units (GPM), machining centers. Creation of the optimization model allows you to link (unite) contact processes simultaneously on the front and back surfaces of the tool from STM to manage contact processes and the dynamic strength of the cutting tool at the top of the STM. Established optimization model of management of the dynamic strength of the incisors of the STM in the process of fine turning is based on a previously developed thermomechanical (physical, heat) model, which allows the system thermomechanical approach to choosing brands STM (domestic and foreign) for cutting tools from STM designed for fine turning of heat resistant alloys and steels.

  1. Contact problem with wear for a foundation with a surface nonuniform coating

    NASA Astrophysics Data System (ADS)

    Manzhirov, A. V.; Kazakov, K. E.

    2017-07-01

    The plane contact problem with wear for an elastic foundation with a longitudinally nonuniform (surface nonuniform) coating and a rigid punch with a flat foundation has been solved for the first time. The case of linear wear is considered. The nonuniformity of the coating is described by a rapidly changing function. This strong nonuniformity arises when coatings are deposited using modern additive manufacturing technologies. The problem is reduced to the solution of an integral equation with two different integral operators: a compact self-adjoint positively defined operator with respect to the coordinate and the non-selfadjoint integral Volterra operator with respect to time. The solution is obtained in series using author's projection method. The efficiency of the proposed approach for constructing a high-accuracy approximate solution to the problem (with only a few expansion terms retained) is demonstrated. A simple engineering formula for estimating the contact stresses under a punch for large values of times is proposed.

  2. Employing polyethylene as contacting agent between ATR-crystals and solid samples with hard surfaces

    NASA Astrophysics Data System (ADS)

    Ivanovski, Vladimir; Mayerhöfer, Thomas G.; Popp, Jürgen

    2009-04-01

    Using a single crystal of fresnoite (Ba 2TiSiO 8), we demonstrate that polyethylene (PE) can be used as a contacting agent to enable the recording of ATR-spectra of materials with hard surfaces. The performance of our method is compared with the standard according to literature where CS 2 is used as an immersion liquid. A Harrick Seagull cell, equipped with a ZnSe semi-sphere ATR-crystal has been used in measuring s- and p-polarized spectra at different incidence angles. The experimental results were compared with model calculations based on the dielectric function tensor of fresnoite. The comparison reveals advantages of our method compared to the use of CS 2 like: closer resemblance between experimental and modeled spectra, repeatability and persistent optical contact. Moreover, our technique is easier to use.

  3. Characteristics of contact and distance osteogenesis around modified implant surfaces in rabbit tibiae

    PubMed Central

    2017-01-01

    Purpose Contact and distance osteogenesis occur around all endosseous dental implants. However, the mechanisms underlying these processes have not been fully elucidated. We hypothesized that these processes occur independently of each other. To test this, we used titanium (Ti) tubes to physically separate contact and distance osteogenesis, thus allowing contact osteogenesis to be measured in the absence of possible triggers from distance osteogenesis. Methods Sandblasted and acid-etched (SLA) and modified SLA (modSLA) implants were used. Both types had been sandblasted with large grit and then etched with acid. The modSLA implants then underwent additional treatment to increase hydrophilicity. The implants were implanted into rabbit tibiae, and half were implanted within Ti tubes. The bone-to-implant contact (BIC) ratio was calculated for each implant. Immunohistochemical analyses of bone morphogenetic protein (BMP)-2 expression and new bone formation (Masson trichrome stain) were performed. Results The implants outside of Ti tubes were associated with good bone formation along the implant surface. Implantation within a Ti tube significantly reduced the BIC ratio (P<0.001). Compared with the modSLA implants, the SLA implants were associated with significantly higher BIC ratios, regardless of the presence or absence of Ti tubes (P=0.043). In the absence of Ti tubes, the bone adjacent to the implant had areas of new bone formation that expressed BMP-2 at high levels. Conclusions This study disproved the null hypothesis and suggested that contact osteogenesis is initiated by signals from the old bone that undergoes distance osteogenesis after drilling. This signal may be BMP-2. PMID:28680714

  4. Cavitation on deterministically nanostructured surfaces in contact with an aqueous phase: a small-angle neutron scattering study.

    PubMed

    Melnichenko, Yuri B; Lavrik, N V; Popov, E; Bahadur, J; He, L; Kravchenko, I I; Smith, G; Pipich, V; Szekely, N K

    2014-08-26

    The structure of deterministically nanopatterned surfaces created using a combination of electron beam lithography and reactive ion etching was evaluated using small-angle neutron scattering (SANS). Samples exhibit 2D neutron scattering patterns that confirm the presence of ordered nanoscale cavities consistent with the targeted morphologies as well as with SEM data analysis. Comparison of SANS intensities obtained from samples in air and in contact with an aqueous phase (pure deuterium oxide, D2O, or a contrast matched mixture of D2O + H2O) reveals formation of stable gaseous nanobubbles trapped inside the cavities. The relative volume of nanobubbles depends strongly on the hydrophobicity of the cavity walls. In the case of hydrophobic surfaces, nanobubbles occupy up to 87% of the total cavity volume. The results demonstrate the high degree of sensitivity of SANS measurements for detecting and characterizing nano- and mesoscale bubbles with the volume fraction as low as ∼10(-6).

  5. Relationship between wettability and lubrication characteristics of the surfaces of contacting phospholipid-based membranes.

    PubMed

    Pawlak, Zenon; Petelska, Aneta D; Urbaniak, Wieslaw; Yusuf, Kehinde Q; Oloyede, Adekunle

    2013-04-01

    The wettability of the articular surface of cartilage depends on the condition of its surface active phospholipid overlay, which is structured as multi-bilayer. Based on a hypothesis that the surface of cartilage facilitates the almost frictionless lubrication of the joint, we examined the characteristics of this membrane surface entity in both its normal and degenerated conditions using a combination of atomic force microscopy, contact angle measurement, and friction test methods. The observations have led to the conclusions that (1) the acid-base equilibrium condition influences the lubrication effectiveness of the surface of cartilage and (2) the friction coefficient is significantly dependent on the hydrophobicity of the surface of the tissue, thereby confirming the hypothesis tested in this paper. Both wettability angle and interfacial energy were obtained for varying conditions of the cartilage surface both in its wet, dry and lipid-depleted conditions. The interfacial energy also increased with mole fraction of the lipid species reaching an asymptotic value after 0.6. Also, the friction coefficient was found to decrease to an asymptotic level as the wettability angle increased. The result reveal that the interfacial energy increased with pH till pH = 4.0, and then decreased from pH = 4.0 to reach equilibrium at pH = 7.0.

  6. The contact angle for a droplet on homogeneous and spherical concave surfaces

    NASA Astrophysics Data System (ADS)

    Hu, Ai-Jun; Lv, Bao-Zhan; Wang, Xiao-Song; Zhou, Long

    2016-03-01

    Wetting of droplets on homogeneous and spherical concave rough surfaces is investigated based on thermodynamics. In this study, neglecting the droplet gravity and the thickness of the precursor film of the liquid-vapor interface, the three-phase system is divided into six parts using Gibbs concept of dividing surface. The system Helmholtz free energy is established based on thermodynamics. Supposing the temperature and chemical potential to be constant, a new generalized Young’s equation of the equilibrium contact angle for a spherical droplet on a spherical concave rough surfaces is obtained including the line tension effects. Under certain conditions, this generalized Young’s equation is the same as the Rusanov’s equation.

  7. Motion of liquid drops on surfaces induced by asymmetric vibration: role of contact angle hysteresis.

    PubMed

    Mettu, Srinivas; Chaudhury, Manoj K

    2011-08-16

    Hysteresis of wetting, like the Coulombic friction at solid/solid interface, impedes the motion of a liquid drop on a surface when subjected to an external field. Here, we present a counterintuitive example, where some amount of hysteresis enables a drop to move on a surface when it is subjected to a periodic but asymmetric vibration. Experiments show that a surface either with a negligible or high hysteresis is not conducive to any drop motion. Some finite hysteresis of contact angle is needed to break the periodic symmetry of the forcing function for the drift to occur. These experimental results are consistent with simulations, in which a drop is approximated as a linear harmonic oscillator. The experiment also sheds light on the effect of the drop size on flow reversal, where drops of different sizes move in opposite directions due to the difference in the phase of the oscillation of their center of mass.

  8. Superlubricity in two-dimensional contacts of elastic solids with rough surfaces

    NASA Astrophysics Data System (ADS)

    Campañá, Carlos

    2007-04-01

    The recently developed Green’s-function molecular-dynamics technique is used to study the possibility for superlubricity in two dimensions. Elastic solid bodies in contact with rough surfaces are considered within the current approach. Surface topographies were either acquired from the results of atomic force microscopy experiments or created using a self-affine fractal generator algorithm. Interactions between the solids are modeled via hard-wall or exponentially repulsive potentials. Our results show evidence of a superlubric state whenever the hard-wall approximation is considered. In the case of exponential walls, the static friction coefficient on ideal surfaces appears to be only a function of the mean-square slope of the height profiles. Additionally, for experimental topographies, variations in the roughness of the very last layer prove to play a key role in achieving ultralow friction.

  9. Surface analysis of CdTe after various pre-contact treatments

    SciTech Connect

    Waters, D.M.; Niles, D.; Gessert, T.A.; Albin, D.; Rose, D.H.; Sheldon, P.

    1998-09-01

    The authors present surface analysis of close-spaced sublimated (CSS) CdTe after various pre-contact treatments. Methods include Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and grazing-incidence x-ray diffraction (GI-XRD). XPS and GI-XRD analyses of the surface residue left by the solution-based CdCl{sub 2} treatment do not indicate the presence of a significant amount of CdCl{sub 2}. In addition, the solubility properties and relatively high thermal stability of the residue suggest the presence of the oxychloride Cd{sub 3}Cl{sub 2}O{sub 2} rather than CdCl{sub 2} as the major chlorine-containing component. Of the methods tested for their effectiveness in removing the residue, only HNO{sub 3} etches removed all detectable traces of chlorine from the surface.

  10. Point-contacting by localised dielectric breakdown: Characterisation of a metallisation technique for the rear surface of a solar cell

    SciTech Connect

    Western, Ned J. Perez-Wurfl, Ivan; Wenham, Stuart R.; Bremner, Stephen P.

    2015-07-28

    Characterisation results are presented for ohmic contacts to passivated crystalline silicon, formed using the point-contacting by localised dielectric breakdown technique. Self aligned contact is made between the metal and heavily doped surface regions through an intrinsic a-Si:H passivation layer. Local doping is provided by a laser using a standard technique identical to that for selective emitter formation. Our results for gate metals of Au, Al, and Ti show that the technique does not rely on reactivity between the dielectric and the metal, excluding metal induced crystallisation from the contacting process. Diffusion of the gate metal into the dielectric is observed in transmission electron microscope images suggesting high temperatures are present locally during the breakdown process. The technique is equally applicable to contacting of n and p-type silicon, making it a potential alternative for ohmic contacting to silicon to passivated rear surfaces.

  11. Analysis of in-vivo articular cartilage contact surface of the knee during a step-up motion.

    PubMed

    Yin, Peng; Li, Jing-Sheng; Kernkamp, Willem A; Tsai, Tsung-Yuan; Baek, Seung-Hoon; Hosseini, Ali; Lin, Lin; Tang, Peifu; Li, Guoan

    2017-09-08

    Numerous studies have reported on the tibiofemoral articular cartilage contact kinematics, however, no data has been reported on the articular cartilage geometry at the contact area. This study investigated the in-vivo tibiofemoral articular cartilage contact biomechanics during a dynamic step-up motion. Ten healthy subjects were imaged using a validated magnetic resonance and dual fluoroscopic imaging technique during a step-up motion. Three-dimensional bone and cartilage models were constructed from the magnetic resonance images. The cartilage contact along the motion path was analyzed, including cartilage contact location and the cartilage surface geometry at the contact area. The cartilage contact excursions were similar in anteroposterior and mediolateral directions in the medial and lateral compartments of the tibia plateau (P>0.05). Both medial and lateral compartments were under convex (femur) to convex (tibia) contact in the sagittal plane, and under convex (femur) to concave (tibia) contact in the coronal plane. The medial tibial articular contact radius was larger than the lateral side in the sagittal plane along the motion path (P<0.001). These data revealed that both the medial and lateral compartments of the knee experienced convex (femur) to convex (tibia) contact in sagittal plane (or anteroposterior direction) during the dynamic step-up motion. These data could provide new insight into the in-vivo cartilage contact biomechanics research, and may provide guidelines for development of anatomical total knee arthroplasties that are aimed to reproduce normal knee joint kinematics. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. An Immunoassay for Quantification of Contamination by Raw Meat Juice on Food Contact Surfaces.

    PubMed

    Chen, Fur-Chi; Godwin, Sandria; Chambers, Edgar

    2016-11-01

    Raw chicken products often are contaminated with Salmonella and Campylobacter , which can be transmitted from packages to contact surfaces. Raw meat juices from these packages also provide potential media for cross-contamination. There are limited quantitative data on the levels of consumer exposure to raw meat juice during shopping for and handling of chicken products. An exposure assessment is needed to quantify the levels of transmission and to assess the risk. An enzyme-linked immunosorbent assay (ELISA) was developed and validated for quantitative detection of raw meat juice on hands and various food contact surfaces. Analytical procedures were designed to maximize the recovery of raw meat juice from various surfaces: hands, plastic, wood, stainless steel, laminated countertops, glass, and ceramics. The ELISA was based on the detection of a soluble muscle protein, troponin I (TnI), in the raw meat juice. The assay can detect levels as low as 1.25 ng of TnI, which is equivalent to less than 1 μl of the raw meat juice. The concentrations of TnI in the raw meat juices from 10 retail chicken packages, as determined by ELISA, were between 0.46 and 3.56 ng/μl, with an average of 1.69 ng/μl. The analytical procedures, which include swabbing, extraction, and concentration, enable the detection of TnI from various surfaces. The recoveries of raw meat juice from surfaces of hands were 92%, and recoveries from other tested surfaces were from 55% on plastic cutting boards to 75% on laminated countertops. The ELISA developed has been used for monitoring the transfer of raw meat juice during shopping for and handling of raw chicken products in our studies. The assay also can be applied to other raw meat products, such as pork and beef.

  13. High-precision drop shape analysis (HPDSA) of quasistatic contact angles on silanized silicon wafers with different surface topographies during inclining-plate measurements: Influence of the surface roughness on the contact line dynamics

    NASA Astrophysics Data System (ADS)

    Heib, F.; Hempelmann, R.; Munief, W. M.; Ingebrandt, S.; Fug, F.; Possart, W.; Groß, K.; Schmitt, M.

    2015-07-01

    Contact angles and wetting of solid surfaces are strongly influenced by the physical and chemical properties of the surfaces. These influence quantities are difficult to distinguish from each other if contact angle measurements are performed by measuring only the advancing θa and the receding θr contact angle. In this regard, time-dependent water contact angles are measured on two hydrophobic modified silicon wafers with different physical surface topographies. The first surface is nearly atomically flat while the second surface is patterned (alternating flat and nanoscale rough patterns) which is synthesized by a photolithography and etching procedure. The different surface topographies are characterized with atomic force microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy (FTIRRAS) and Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR). The resulting set of contact angle data obtained by the high-precision drop shape analysis approach is further analyzed by a Gompertzian fitting procedure and a statistical counting procedure in dependence on the triple line velocity. The Gompertzian fit is used to analyze overall properties of the surface and dependencies between the motion on the front and the back edge of the droplets. The statistical counting procedure results in the calculation of expectation values E(p) and standard deviations σ(p) for the inclination angle φ, contact angle θ, triple line velocity vel and the covered distance of the triple line dis relative to the first boundary points XB,10. Therefore, sessile drops during the inclination of the sample surface are video recorded and different specific contact angle events in dependence on the acceleration/deceleration of the triple line motion are analyzed. This procedure results in characteristically density distributions in dependence on the surface properties. The used procedures lead to the possibility to investigate influences on contact

  14. Wettability Tests of Polymer Films and Fabrics and Determination of Their Surface Energy by Contact-Angle Methods

    DTIC Science & Technology

    2007-03-01

    of two methods described in this section. For films, a static contact - angle setup using the sessile drop method was utilized. The setup consists...can’t be used, as fabric roughness causes absorption of the single drop . To measure the liquid-solid contact angle for fabrics, we use the Wilhelmy...polyethylene film. Prior to plasma exposure, a drop of water was placed on the film and the contact angle was 98°. In this case, the surface can be

  15. 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.

  16. Plasma-enhanced synthesis of surfaces that kill bacteria on contact

    NASA Astrophysics Data System (ADS)

    Jampala, Soujanya Naga

    High incidences of microbial contamination and infections are a major concern in all existing and evolving technologies of medicine and biology. The propensity towards infections is directly related to bacterial colonization and biofilms on surfaces. This dissertation presents the development of surfaces that can kill bacteria on contact by using cold plasma technology. Quaternary ammonium (QA) groups are known to exhibit antibacterial characteristics in water-based environments. To overcome the limitations of residual toxicity, alternative strategies involving covalent attachment of QA groups to metallic and cellulosic surfaces have been developed. Low pressure, non-equilibrium plasma-enhanced functionalization and subsequent ex situ chemical reactions were designed for step-by-step "bottom-up" chemical synthesis of QA groups covalently anchored to surfaces. The plasma processes under selected discharge parameters generated structure- and functionality-controlled crosslinked networks of macromolecular layers with high concentrations of reactive amine groups. Subsequent derivatization of the plasma-deposited films with alkyl halides yielded surface-bound QA groups rendering surfaces with high bactericidal efficacy against Gram-positive Staphylococcus aureus and Gram-negative Klebsiella pneumoniae. Stainless steel and cotton surfaces sequentially treated with ethylene diamine plasma, n-hexyl bromide and methyl iodide exhibited at least 99.9% and 98% kill of S. aureus and K. pneumoniae respectively. The influence of chemical architecture of QA groups with different alkyl substituents on the efficacy of bactericidal surfaces was quantified. Results from this work will permit the development of novel plasma-aided technologies for the synthesis of antibacterial surfaces with potential biomedical applications. The cold plasma approach can be used on any solid material surfaces including polymers, metals, ceramics and semiconductors.

  17. Contact angles of liquid drops on super hydrophobic surfaces: understanding the role of flattening of drops by gravity.

    PubMed

    Extrand, C W; Moon, Sung In

    2010-11-16

    Measurement of contact angles on super hydrophobic surfaces by conventional methods can produce ambiguous results. Experimental difficulties in constructing tangent lines, gravitational distortion or erroneous assumptions regarding the extent of spreading can lead to underestimation of contact angles. Three models were used to estimate drop shape and perceived contact angles on completely nonwetting super hydrophobic surfaces. One of the models employed the classic numerical solutions from Bashforth and Adams. Additionally, two approximate models were derived as part of this work. All three showed significant distortion of microliter-sized drops and similar trends in perceived contact angles. Liquid drops of several microliters are traditionally used in sessile contact angle measurements. Drops of this size are expected to and indeed undergo significant flattening on super hydrophobic surfaces, even if the wetting interactions are minimal. The distortion is more pronounced if the liquid has a lesser surface tension or greater density. For surfaces that are completely nonwetting, underestimation of contact angles can be tens of degrees. Our modeling efforts suggest that accurate contact angle measurements on super hydrophobic surfaces would require very small sessile drops, on the order of hundreds of picoliters.

  18. Morse potential-based model for contacting composite rough surfaces: Application to self-assembled monolayer junctions

    NASA Astrophysics Data System (ADS)

    Sierra-Suarez, Jonatan A.; Majumdar, Shubhaditya; McGaughey, Alan J. H.; Malen, Jonathan A.; Higgs, C. Fred

    2016-04-01

    This work formulates a rough surface contact model that accounts for adhesion through a Morse potential and plasticity through the Kogut-Etsion finite element-based approximation. Compared to the commonly used Lennard-Jones (LJ) potential, the Morse potential provides a more accurate and generalized description for modeling covalent materials and surface interactions. An extension of this contact model to describe composite layered surfaces is presented and implemented to study a self-assembled monolayer (SAM) grown on a gold substrate placed in contact with a second gold substrate. Based on a comparison with prior experimental measurements of the thermal conductance of this SAM junction [Majumdar et al., Nano Lett. 15, 2985-2991 (2015)], the more general Morse potential-based contact model provides a better prediction of the percentage contact area than an equivalent LJ potential-based model.

  19. Surface characterization of poly(methyl methacrylate) microgrooved for contact guidance of mammalian cells.

    PubMed

    Alaerts, J A; De Cupere, V M; Moser, S; Van den Bosh de Aguilar, P; Rouxhet, P G

    2001-06-01

    High-resolution patterns of grooves have been made in poly(methyl methacrylate) films, PMMA, by an electron-beam microlithographic process. The surface of films processed over a large width was characterized in terms of chemical composition (X-ray photoelectron spectroscopy (XPS). time of flight secondary ion mass spectroscopy), wettability (sessile drop) and topography (atomic force microscopy). Collagen adsorption was also studied (radiocounting, XPS) as such or in competition with Pluronic F68. The chemical alteration of the surface induced by the electron-beam irradiation disappeared after the dissolution involved in the development process. W138 human fibroblasts cultivated on microgrooved substrata (grooves 1 microm deep and 0.5-10 microm wide) showed a strong orientation parallel to the grooves. The contact guidance is induced by the topography of the surface and not by the alternation of zones with different physico-chemical properties. It may be explained in terms of probability of successful substratum contact by cell protrusions.

  20. Computational analysis of contact forces influence on cold forming processes in the dies with complex surfaces

    NASA Astrophysics Data System (ADS)

    Dragnea, D.; Lixandru, P.; Chereches, T.; Velicu, St.

    2016-08-01

    Interaction forces between the workpiece and the die appear during the cold forming process of metals in dies. Surface forces of high-intensity influence the mesh structure and internal structure of the finished piece by mechanical action. Frictional forces hinder the flow of the material in contact with the die walls, especially on surfaces of complex shape. Under certain conditions, the material can adhere to the wall of the die, leading to the blocking of the cold forming process. In order to highlight the influence of contact forces on cold forming processes in dies with complex surfaces there were used numerical simulation methods with finite elements. Numerical simulations of the process of axial cold forming in the die were carried out for analysis data acquisition necessary, in order to achieve HTD pulleys, for an ordinary range of friction coefficients. The analysis was directed to the gearing area of the HTD pulleys (head, flank and base of the tooth). The analysis highlighted the negative effects of friction forces on the shape and quality of the products and the need to use quality lubricants. Also, using the cold forming process they can be achieved substantial savings by redistribution of the material without removing it.

  1. Dynamic contact angle effects onto the maximum drop impact spreading on solid surfaces

    NASA Astrophysics Data System (ADS)

    Vadillo, D. C.; Soucemarianadin, A.; Delattre, C.; Roux, D. C. D.

    2009-12-01

    This paper reports experimental investigations of drop impacts onto chemically treated surfaces with wettability from 5° to 160°. To follow in time the drop spreading, a high speed video camera was used, and it allows us to determine precisely the expansion of the drop and the profile of the free surface at the contact line. By changing the impact velocity, between less than 0.5 and 5 m/s, and the viscosity, from 1 to 100 mPa s, at constant surface tension, a broad range of Reynolds and Weber numbers is explored. This paper is divided into two parts. In the first part, the experimental drop evolution during spreading is directly reported and compared with previous works. Secondly, the emphasis is on the importance of the apparent dynamic contact angle for the prediction of the maximum spreading diameter. This achievement is manifested at low Reynolds numbers at which the matching between the experiment and the model is improved greatly.

  2. Adaptive local surface refinement based on LR NURBS and its application to contact

    NASA Astrophysics Data System (ADS)

    Zimmermann, Christopher; Sauer, Roger A.

    2017-08-01

    A novel adaptive local surface refinement technique based on Locally Refined Non-Uniform Rational B-Splines (LR NURBS) is presented. LR NURBS can model complex geometries exactly and are the rational extension of LR B-splines. The local representation of the parameter space overcomes the drawback of non-existent local refinement in standard NURBS-based isogeometric analysis. For a convenient embedding into general finite element codes, the Bézier extraction operator for LR NURBS is formulated. An automatic remeshing technique is presented that allows adaptive local refinement and coarsening of LR NURBS. In this work, LR NURBS are applied to contact computations of 3D solids and membranes. For solids, LR NURBS-enriched finite elements are used to discretize the contact surfaces with LR NURBS finite elements, while the rest of the body is discretized by linear Lagrange finite elements. For membranes, the entire surface is discretized by LR NURBS. Various numerical examples are shown, and they demonstrate the benefit of using LR NURBS: Compared to uniform refinement, LR NURBS can achieve high accuracy at lower computational cost.

  3. Loss and replacement of small particles on the contact surfaces of footwear during successive exposures.

    PubMed

    Stoney, David A; Bowen, Andrew M; Stoney, Paul L

    2016-12-01

    On the contact surfaces of footwear loosely, moderately and strongly held particle fractions were separated and analyzed in an effort to detect different particle signals. Three environmental exposure sites were chosen to have different, characteristic particle types (soil minerals). Shoes of two types (work boots and tennis shoes) were tested, accumulating particles by walking 250m in each environment. Some shoes were exposed to only one environment; others were exposed to all three, in one of six different sequences. Sampling methods were developed to separate particles from the contact surface of the shoe based on how tightly they were held to the sole. Loosely held particles were removed by walking on paper, moderately held particles were removed by electrostatic lifting, and the most tightly held particles were removed by moist swabbing. The resulting numbers and types of particles were determined using forensic microscopy. Particle profiles from the different fractions were compared to test the ability to objectively distinguish the order of exposure to the three environments. Without exception, the samples resulting from differential sampling are dominated by the third site in the sequential footwear exposures. No noticeable differences are seen among the differential samplings of the loosely, moderately and strongly held particles: the same overwhelming presence of the third site is seen. It is clear from these results (1) that the third (final) exposure results in the nearly complete removal of any particles from prior exposures, and (2) that under the experimental conditions loosely, moderately and strongly held particles are affected similarly, without any detectable enrichment of the earlier exposures among the more tightly held particles. These findings have significant implications for casework, demonstrating that particles on the contact surfaces of footwear are rapidly lost and replaced. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  4. Tear Film Surface Quality with Soft Contact Lenses Using Dynamic Videokeratoscopy

    PubMed Central

    Kopf, Miriam; Yi, Fan; Robert Iskander, D.; Collins, Michael J.; Shaw, Alyra J.; Straker, Benjamin

    2010-01-01

    Purpose To investigate changes in tear film surface quality after commencing soft contact lens wear. Methods Tear film surface quality (TSQ) was assessed during the interblink period using dynamic videokeratoscopy at 25 Hz. A quantitative value of TSQ is derived for each raw Placido ring image. Eleven young subjects with normal tear characteristics participated in the study. Dynamic videokeratoscopy was taken three times per day; in the morning, at lunchtime, and in the afternoon. This was done on two baseline days (bare eye) and on the first and seventh days of lens wear for a conventional hydrogel lens and following a week of no lens wear, for a further week of silicone hydrogel lens wear. Additionally clinical tests to assess TSQ were conducted and subjects were also asked to rate the subjective dryness of their eyes. Results All lens wear measurements showed a significant worsening of TSQ compared to bare eye measurements (repeated measures ANOVA, P<0.01). A significant diurnal change was found on the first day of silicone hydrogel contact lens wear, where TSQ improved during the day (P=0.045). However, no diurnal changes were found in TSQ for the other lens wearing days or for the bare eye condition (P>0.05). The subjective rating of dryness correlated with TSQ values (Pearson's r=0.62, P<0.05) for the bare eye condition, but not during contact lens wear. TSQ derived from the right and left bare eyes of the same individuals showed a significant correlation (Pearson's r=0.61, P<0.05). Conclusions The measurement of TSQ using dynamic videokeratoscopy differentiates between bare eye and lens wearing conditions. It also shows a small systematic improvement in tear surface quality during the first day of silicone hydrogel lens wear and a significant association with subjective dryness for the bare eye condition.

  5. 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.

  6. Analysis of vegetable seedlings grown in contact with Apollo 14 lunar surface fines.

    NASA Technical Reports Server (NTRS)

    Walkinshaw, C. H.; Johnson, P. H.

    1971-01-01

    Study of plant seedlings treated with lunar material, grown for 14 to 21 days, and then subjected to chemical analyses and other measurements. The purpose of the study was to determine whether plants growing in contact with lunar-surface fines contained a different elemental composition compared with untreated seedlings. The results indicate a direct interaction between germfree plants and lunar material. Treated plants dissolved and absorbed significant quantities of Al, Fe, and Ti from the lunar fines. Cabbage and Brussel sprouts were particularly efficient in the dissolution and absorption of Mn.

  7. Investigation of the surface of implanted silicon crystal by the contact angle

    SciTech Connect

    Lebedeva, N.N.; Bakovets, V.V.; Sedymova, E.A.; Pridachin, N.B.

    1987-03-01

    The authors study the dependence of the critical contact angle of silicon upon the dose of its irradiation by argon and boron ions. It is established that the system of immiscible liquids ether-water can be successfully used to study the influence of ion implantation of silicon on its wettability by water. The change in the wettability of implanted silicon is related to the increase in the level of the defect state of the layer surface. Wetting of implanted silicon by melts at high temperatures can be used for studying the kinetics and the annealing mechanism of defects.

  8. Surface-plasmon Schottky contact detector based on a symmetric metal stripe in silicon.

    PubMed

    Scales, Christine; Breukelaar, Ian; Berini, Pierre

    2010-02-15

    A Schottky contact detector comprising a symmetric metal stripe buried in Si, capable of detecting surface plasmons at wavelengths below the bandgap of Si, is described. A model for the detector is proposed, and its performance is assessed at lambda(0)=1550 nm assuming a CoSi(2) stripe in p-type Si. End-fire coupled responsivities of about 0.1 A/W and minimum detectable powers of about -20 dBm are predicted at room temperature.

  9. Non-contact metrology of aspheric surfaces based on MWLI technology

    NASA Astrophysics Data System (ADS)

    Berger, G.; Petter, J.

    2013-09-01

    A non-contact optical scanning metrology solution measuring aspheric surfaces is presented, which is based on multi wavelength interferometry (MWLI). The technology yields high density 3D data in short measurement times (including set up time) and provides high, reproducible form measurement accuracy. It measures any asphere without restrictions in terms of spherical departures. In addition, measurement of a large variety of special optics is enabled, such as annular lenses, segmented optics, optics with diffractive steps, ground optics, optics made of opaque and transparent materials, and small and thin optics (e.g. smart phone lenses). The measurement instrument can be used under production conditions.

  10. Analysis of vegetable seedlings grown in contact with Apollo 14 lunar surface fines.

    NASA Technical Reports Server (NTRS)

    Walkinshaw, C. H.; Johnson, P. H.

    1971-01-01

    Study of plant seedlings treated with lunar material, grown for 14 to 21 days, and then subjected to chemical analyses and other measurements. The purpose of the study was to determine whether plants growing in contact with lunar-surface fines contained a different elemental composition compared with untreated seedlings. The results indicate a direct interaction between germfree plants and lunar material. Treated plants dissolved and absorbed significant quantities of Al, Fe, and Ti from the lunar fines. Cabbage and Brussel sprouts were particularly efficient in the dissolution and absorption of Mn.

  11. Dynamics of spider glue adhesion: effect of surface energy and contact area

    NASA Astrophysics Data System (ADS)

    Amarpuri, Gaurav; Chen, Yizhou; Blackledge, Todd; Dhinojwala, Ali

    Spider glue is a unique biological adhesive which is humidity responsive such that the adhesion continues to increase upto 100% relative humidity (RH) for some species. This is unlike synthetic adhesives that significantly drop in adhesion with an increase in humidity. However, most of adhesion data reported in literature have used clean hydrophilic glass substrate, unlike the hydrophobic, and charged insect cuticle surface that adheres to spider glue in nature. Previously, we have reported that the spider glue viscosity changes over five orders of magnitude with humidity. Here, we vary the surface energy and surface charge of the substrate to test the change in Larnioides cornutus spider glue adhesion with humidity. We find that an increase in both surface energy and surface charge density increases the droplet spreading and there exists an optimum droplet contact area where adhesion is maximized. Moreover, spider glue droplets act as reusable adhesive for low energy hydrophobic surface at the optimum humidity. These results explain why certain prey are caught more efficiently by spiders in their habitat. The mechanism by which spider species tune its glue adhesion for local prey capture can inspire new generation smart adhesives.

  12. Cold plasma rapid decontamination of food contact surfaces contaminated with Salmonella and Escherichia coli 0157:H7

    USDA-ARS?s Scientific Manuscript database

    Cross-contamination of fresh produce from persistent pathogen reservoirs is a known risk factor in processing environments. Industry requires a waterless, zero-contact, chemical-free method for removing pathogens from food-contact surfaces. Cold plasma was tested for its ability to remove biofilms f...

  13. Evaluation of midcarpal capitate contact mechanics in normal, injured and post-operative wrists.

    PubMed

    Modaresi, Saman; Kallem, Madhan S; Lee, Phil; McIff, Terence E; Toby, E Bruce; Fischer, Kenneth J

    2017-08-01

    Scapholunate ligament injury is a commonly occurring carpal ligament injury. Pathology associated with scapholunate ligament injury depends on several factors such as the time after injury, type of injury (instability) and the development of osteoarthritis. The aim of this study was to investigate and compare contact mechanics in the lunocapitate and scaphocapitate joints in the normal, injured (scapholunate dissociation) and repaired (postoperative) wrist. Four human subjects with scapholunate ligament dissociation participated in this