Ternary fluid mixture confined between surfaces: Surface-induced phase transition and long-range oscillatory forces

NARCIS (Netherlands)

Banerjee, S.; Mulder, P.; Kleijn, J.M.; Cohen Stuart, M.A.

2012-01-01

Surface forces between a soft cellulose surface and a hard silica particle were measured in wet hexane with or without the addition of a surfactant. In the absence of a surfactant, the adhesion force was enhanced as a result of capillary condensation of water. The effect of the surfactant in

The Effect of Non-Lambertian Surface Reflectance on Aerosol Radiative Forcing

Energy Technology Data Exchange (ETDEWEB)

Ricchiazzi, P.; O' Hirok, W.; Gautier, C.

2005-03-18

Surface reflectance is an important factor in determining the strength of aerosol radiative forcing. Previous studies of radiative forcing assumed that the reflected surface radiance is isotropic and does not depend on incident illumination angle. This Lambertian reflection model is not a very good descriptor of reflectance from real land and ocean surfaces. In this study we present computational results for the seasonal average of short and long wave aerosol radiative forcing at the top of the atmosphere and at the surface. The effect of the Lambertian assumption is found through comparison with calculations using a more detailed bi-direction reflectance distribution function (BRDF).

Atomic force microscopy characterization of the surface wettability of natural fibres

International Nuclear Information System (INIS)

Pietak, Alexis; Korte, Sandra; Tan, Emelyn; Downard, Alison; Staiger, Mark P.

2007-01-01

Natural fibres represent a readily available source of ecologically friendly and inexpensive reinforcement in composites with degradable thermoplastics, however chemical treatments of fibres are required to prepare feasible composites. It is desirable to characterize the surface wettability of fibres after chemical treatment as the polarity of cellulose-based fibres influences compatibility with a polymer matrix. Assessment of the surface wettability of natural fibres using conventional methods presents a challenge as the surfaces are morphologically and chemically heterogeneous, rough, and can be strongly wicking. In this work it is shown that under atmospheric conditions the adhesion force between an atomic force microscopy (AFM) tip and the fibre surface can estimate the water contact angle and surface wettability of the fibre. AFM adhesion force measurements are suitable for the more difficult surfaces of natural fibres and in addition allow for correlations between microstructural features and surface wettability characteristics

Probing surface charge potentials of clay basal planes and edges by direct force measurements.

Science.gov (United States)

Zhao, Hongying; Bhattacharjee, Subir; Chow, Ross; Wallace, Dean; Masliyah, Jacob H; Xu, Zhenghe

2008-11-18

The dispersion and gelation of clay suspensions have major impact on a number of industries, such as ceramic and composite materials processing, paper making, cement production, and consumer product formulation. To fundamentally understand controlling mechanisms of clay dispersion and gelation, it is necessary to study anisotropic surface charge properties and colloidal interactions of clay particles. In this study, a colloidal probe technique was employed to study the interaction forces between a silica probe and clay basal plane/edge surfaces. A muscovite mica was used as a representative of 2:1 phyllosilicate clay minerals. The muscovite basal plane was prepared by cleavage, while the edge surface was obtained by a microtome cutting technique. Direct force measurements demonstrated the anisotropic surface charge properties of the basal plane and edge surface. For the basal plane, the long-range forces were monotonically repulsive within pH 6-10 and the measured forces were pH-independent, thereby confirming that clay basal planes have permanent surface charge from isomorphic substitution of lattice elements. The measured interaction forces were fitted well with the classical DLVO theory. The surface potentials of muscovite basal plane derived from the measured force profiles were in good agreement with those reported in the literature. In the case of edge surfaces, the measured forces were monotonically repulsive at pH 10, decreasing with pH, and changed to be attractive at pH 5.6, strongly suggesting that the charge on the clay edge surfaces is pH-dependent. The measured force profiles could not be reasonably fitted with the classical DLVO theory, even with very small surface potential values, unless the surface roughness was considered. The surface element integration (SEI) method was used to calculate the DLVO forces to account for the surface roughness. The surface potentials of the muscovite edges were derived by fitting the measured force profiles with the

Friction and Adhesion Forces of Bacillus thuringiensis Spores on Planar Surfaces in Atmospheric Systems

Energy Technology Data Exchange (ETDEWEB)

Kweon, Hyojin [Georgia Inst. of Technology, Atlanta, GA (United States); Yiacoumi, Sotira [Georgia Inst. of Technology, Atlanta, GA (United States); Tsouris, Costas [Georgia Inst. of Technology, Atlanta, GA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2011-11-07

The kinetic friction force and the adhesion force of Bacillus thuringiensis spores on planar surfaces in atmospheric systems were studied using atomic force microscopy. The influence of relative humidity (RH) on these forces varied for different surface properties including hydrophobicity, roughness, and surface charge. The friction force of the spore was greater on a rougher surface than on mica, which is atomically flat. As RH increases, the friction force of the spores decreases on mica whereas it increases on rough surfaces. The influence of RH on the interaction forces between hydrophobic surfaces is not as strong as for hydrophilic surfaces. The friction force of the spore is linear to the sum of the adhesion force and normal load on the hydrophobic surface. In conclusion, the poorly defined surface structure of the spore and the adsorption of contaminants from the surrounding atmosphere are believed to cause a discrepancy between the calculated and measured adhesion forces.

Reynolds analogy for subcooled surface boiling under forced convection

International Nuclear Information System (INIS)

Avdeev, A.A.

1982-01-01

For the case of subcooled surface boiling under forced convection the analytic expression of analogy between the heat transfer and carry pulse (Reynolds analogy) is derived. It is concluded that the obtained dependence creates the basis for solution of a series of problems of surface boiling physics. On the basis of the performed analysis the method of coordinate calculation of the origin of intensive vapour generation is developed and the formula for calculation of the broken-off-bubble radius under forced convection is derived [ru

Origins of the Non-DLVO Force between Glass Surfaces in Aqueous Solution.

Science.gov (United States)

Adler, Joshua J.; Rabinovich, Yakov I.; Moudgil, Brij M.

2001-05-15

Direct measurement of surface forces has revealed that silica surfaces seem to have a short-range repulsion that is not accounted for in classical DLVO theory. The two leading hypotheses for the origin of the non-DLVO force are (i) structuring of water at the silica interface or (ii) water penetration into the surface resulting in a gel layer. In this article, the interaction of silica surfaces will be reviewed from the perspective of the non-DLVO force origin. In an attempt to more accurately describe the behavior of silica and glass surfaces, alternative models of how surfaces with gel layers should interact are proposed. It is suggested that a lessened van der Waals attraction originating from a thin gel layer may explain both the additional stability and the coagulation behavior of silica. It is important to understand the mechanisms underlying the existence of the non-DLVO force which is likely to have a major influence on the adsorption of polymers and surfactants used to modify the silica surface for practical applications in the ceramic, mineral, and microelectronic industries. Copyright 2001 Academic Press.

Improving the contact resistance at low force using gold coated carbon nanotube surfaces

Science.gov (United States)

McBride, J. W.; Yunus, E. M.; Spearing, S. M.

2010-04-01

Investigations to determine the electrical contact performance under repeated cycles at low force conditions for carbon-nanotube (CNT) coated surfaces were performed. The surfaces under investigation consisted of multi-walled CNT synthesized on a silicon substrate and coated with a gold film. These planar surfaces were mounted on the tip of a PZT actuator and contacted with a plated Au hemispherical probe. The dynamic applied force used was 1 mN. The contact resistance (Rc) of these surfaces was investigated with the applied force and with repeated loading cycles performed for stability testing. The surfaces were compared with a reference Au-Au contact under the same experimental conditions. This initial study shows the potential for the application of gold coated CNT surfaces as an interface in low force electrical contact applications.

Imaging surface nanobubbles at graphite–water interfaces with different atomic force microscopy modes

International Nuclear Information System (INIS)

Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

2013-01-01

We have imaged nanobubbles on highly ordered pyrolytic graphite (HOPG) surfaces in pure water with different atomic force microscopy (AFM) modes, including the frequency-modulation, the tapping, and the PeakForce techniques. We have compared the performance of these modes in obtaining the surface profiles of nanobubbles. The frequency-modulation mode yields a larger height value than the other two modes and can provide more accurate measurement of the surface profiles of nanobubbles. Imaging with PeakForce mode shows that a nanobubble appears smaller and shorter with increasing peak force and disappears above a certain peak force, but the size returns to the original value when the peak force is reduced. This indicates that imaging with high peak forces does not cause gas removal from the nanobubbles. Based on the presented findings and previous AFM observations, the existing models for nanobubbles are reviewed and discussed. The model of gas aggregate inside nanobubbles provides a better explanation for the puzzles of the high stability and the contact angle of surface nanobubbles. (paper)

Why must a solar forcing be larger than a CO2 forcing to cause the same global mean surface temperature change?

International Nuclear Information System (INIS)

Modak, Angshuman; Bala, Govindasamy; Cao, Long; Caldeira, Ken

2016-01-01

Many previous studies have shown that a solar forcing must be greater than a CO 2 forcing to cause the same global mean surface temperature change but a process-based mechanistic explanation is lacking in the literature. In this study, we investigate the physical mechanisms responsible for the lower efficacy of solar forcing compared to an equivalent CO 2 forcing. Radiative forcing is estimated using the Gregory method that regresses top-of-atmosphere (TOA) radiative flux against the change in global mean surface temperature. For a 2.25% increase in solar irradiance that produces the same long term global mean warming as a doubling of CO 2 concentration, we estimate that the efficacy of solar forcing is ∼80% relative to CO 2 forcing in the NCAR CAM5 climate model. We find that the fast tropospheric cloud adjustments especially over land and stratospheric warming in the first four months cause the slope of the regression between the TOA net radiative fluxes and surface temperature to be steeper in the solar forcing case. This steeper slope indicates a stronger net negative feedback and hence correspondingly a larger solar forcing than CO 2 forcing for the same equilibrium surface warming. Evidence is provided that rapid land surface warming in the first four months sets up a land-sea contrast that markedly affects radiative forcing and the climate feedback parameter over this period. We also confirm the robustness of our results using simulations from the Hadley Centre climate model. Our study has important implications for estimating the magnitude of climate change caused by volcanic eruptions, solar geoengineering and past climate changes caused by change in solar irradiance such as Maunder minimum. (letter)

Surface adhesion properties of graphene and graphene oxide studied by colloid-probe atomic force microscopy

International Nuclear Information System (INIS)

Ding Yanhuai; Zhang Ping; Ren Huming; Zhuo Qin; Yang Zhongmei; Jiang Xu; Jiang Yong

2011-01-01

Surface adhesion properties are important to various applications of graphene-based materials. Atomic force microscopy is powerful to study the adhesion properties of samples by measuring the forces on the colloidal sphere tip as it approaches and retracts from the surface. In this paper we have measured the adhesion force between the colloid probe and the surface of graphene (graphene oxide) nanosheet. The results revealed that the adhesion force on graphene and graphene oxide surface were 66.3 and 170.6 nN, respectively. It was found the adhesion force was mainly determined by the water meniscus, which was related to the surface contact angle of samples.

Superhydrophobic Zr-based metallic glass surface with high adhesive force

Science.gov (United States)

Li, Ning; Xia, Ting; Heng, Liping; Liu, Lin

2013-06-01

Micro/nano hierarchical structures were constructed on Zr35Ti30Be26.75Cu8.25 metallic glass surface by silicon moulding and subsequently chemical etching. The as-formed surface exhibited both superhydrophobicity and high adhesive force towards water. The superhydrophobicity is rationalized based on the modified Cassie-Baxter model [A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944)]. The origin of the robust adhesion is described in terms of intermolecular capillary forces. The present results not only provide a method to fabricate superhydrophobic metallic glasses surface but also explore an important industrial application as dry adhesives and transport of liquid microdroplets.

Nanophotonic force microscopy: characterizing particle-surface interactions using near-field photonics.

Science.gov (United States)

Schein, Perry; Kang, Pilgyu; O'Dell, Dakota; Erickson, David

2015-02-11

Direct measurements of particle-surface interactions are important for characterizing the stability and behavior of colloidal and nanoparticle suspensions. Current techniques are limited in their ability to measure pico-Newton scale interaction forces on submicrometer particles due to signal detection limits and thermal noise. Here we present a new technique for making measurements in this regime, which we refer to as nanophotonic force microscopy. Using a photonic crystal resonator, we generate a strongly localized region of exponentially decaying, near-field light that allows us to confine small particles close to a surface. From the statistical distribution of the light intensity scattered by the particle we are able to map out the potential well of the trap and directly quantify the repulsive force between the nanoparticle and the surface. As shown in this Letter, our technique is not limited by thermal noise, and therefore, we are able to resolve interaction forces smaller than 1 pN on dielectric particles as small as 100 nm in diameter.

Measuring adhesion on rough surfaces using atomic force microscopy with a liquid probe

Directory of Open Access Journals (Sweden)

Juan V. Escobar

2017-04-01

Full Text Available We present a procedure to perform and interpret pull-off force measurements during the jump-off-contact process between a liquid drop and rough surfaces using a conventional atomic force microscope. In this method, a micrometric liquid mercury drop is attached to an AFM tipless cantilever to measure the force required to pull this drop off a rough surface. We test the method with two surfaces: a square array of nanometer-sized peaks commonly used for the determination of AFM tip sharpness and a multi-scaled rough diamond surface containing sub-micrometer protrusions. Measurements are carried out in a nitrogen atmosphere to avoid water capillary interactions. We obtain information about the average force of adhesion between a single peak or protrusion and the liquid drop. This procedure could provide useful microscopic information to improve our understanding of wetting phenomena on rough surfaces.

AFM (Atomic force microscope and its use in studying the surface

Directory of Open Access Journals (Sweden)

Škvarla Jiří

1996-06-01

Full Text Available The paper summarizes the present knowledge about the use of AFM in the mineral processing research. First, the development and fundamentals of the AFM imaging are presented in relation to other imaging techniques (especially STM, Scanning tunneling microscope. Further, the role of the sensing tip-surface interactions is mentioned. Finally, the surface force measurements in the AFM force calibration mode are diskussed.

Atomic force microscopy analysis of different surface treatments of Ti dental implant surfaces

International Nuclear Information System (INIS)

Bathomarco, R.V.; Solorzano, G.; Elias, C.N.; Prioli, R.

2004-01-01

The surface of commercial unalloyed titanium, used in dental implants, was analyzed by atomic force microscopy. The morphology, roughness, and surface area of the samples, submitted to mechanically-induced erosion, chemical etching and a combination of both, were compared. The results show that surface treatments strongly influence the dental implant physical and chemical properties. An analysis of the length dependence of the implant surface roughness shows that, for scan sizes larger than 50 μm, the average surface roughness is independent of the scanning length and that the surface treatments lead to average surface roughness in the range of 0.37 up to 0.48 μm. It is shown that the implant surface energy is sensitive to the titanium surface area. As the area increases there is a decrease in the surface contact angle

Atomic force microscopy analysis of different surface treatments of Ti dental implant surfaces

Science.gov (United States)

Bathomarco, Ti R. V.; Solorzano, G.; Elias, C. N.; Prioli, R.

2004-06-01

The surface of commercial unalloyed titanium, used in dental implants, was analyzed by atomic force microscopy. The morphology, roughness, and surface area of the samples, submitted to mechanically-induced erosion, chemical etching and a combination of both, were compared. The results show that surface treatments strongly influence the dental implant physical and chemical properties. An analysis of the length dependence of the implant surface roughness shows that, for scan sizes larger than 50 μm, the average surface roughness is independent of the scanning length and that the surface treatments lead to average surface roughness in the range of 0.37 up to 0.48 μm. It is shown that the implant surface energy is sensitive to the titanium surface area. As the area increases there is a decrease in the surface contact angle.

Tracking Traction Force Changes of Single Cells on the Liquid Crystal Surface

Directory of Open Access Journals (Sweden)

Chin Fhong Soon

2015-01-01

Full Text Available Cell migration is a key contributor to wound repair. This study presents findings indicating that the liquid crystal based cell traction force transducer (LCTFT system can be used in conjunction with a bespoke cell traction force mapping (CTFM software to monitor cell/surface traction forces from quiescent state in real time. In this study, time-lapse photo microscopy allowed cell induced deformations in liquid crystal coated substrates to be monitored and analyzed. The results indicated that the system could be used to monitor the generation of cell/surface forces in an initially quiescent cell, as it migrated over the culture substrate, via multiple points of contact between the cell and the surface. Future application of this system is the real-time assaying of the pharmacological effects of cytokines on the mechanics of cell migration.

Bond-Strengthening in Staphylococcal Adhesion to Hydrophilic and Hydrophobic Surfaces Using Atomic Force Microscopy

NARCIS (Netherlands)

Boks, N.P.; Busscher, H.J.; Mei, van der H.C.; Norde, W.

2008-01-01

Time-dependent bacterial adhesion forces of four strains of Staphylococcus epidermidis to hydrophobic and hydrophilic surfaces were investigated. Initial adhesion forces differed significantly between the two surfaces and hovered around -0.4 nN. No unambiguous effect of substratum surface

Enhancement of vortex induced forces and motion through surface roughness control

Science.gov (United States)

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

2011-11-01

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

SURFACE ROUGHNESS AND CUTTING FORCES IN CRYOGENIC TURNING OF CARBON STEEL

Directory of Open Access Journals (Sweden)

T. C. YAP

2015-07-01

Full Text Available The effect of cryogenic liquid nitrogen on surface roughness, cutting forces, and friction coefficient of the machined surface when machining of carbon steel S45C in wet, dry and cryogenic condition was studied through experiments. The experimental results show that machining with liquid nitrogen increases the cutting forces, reduces the friction coefficient, and improves the chips produced. Beside this, conventional machining with cutting fluid is still the most suitable method to produce good surface in high speed machining of carbon steel S45C whereas dry machining produced best surface roughness in low speed machining. Cryogenic machining is not able to replace conventional cutting fluid in turning carbon steel.

Simultaneous measurement of dynamic force and spatial thin film thickness between deformable and solid surfaces by integrated thin liquid film force apparatus.

Science.gov (United States)

Zhang, Xurui; Tchoukov, Plamen; Manica, Rogerio; Wang, Louxiang; Liu, Qingxia; Xu, Zhenghe

2016-11-09

Interactions involving deformable surfaces reveal a number of distinguishing physicochemical characteristics that do not exist in interactions between rigid solid surfaces. A unique fully custom-designed instrument, referred to as integrated thin liquid film force apparatus (ITLFFA), was developed to study the interactions between one deformable and one solid surface in liquid. Incorporating a bimorph force sensor with interferometry, this device allows for the simultaneous measurement of the time-dependent interaction force and the corresponding spatiotemporal film thickness of the intervening liquid film. The ITLFFA possesses the specific feature of conducting measurement under a wide range of hydrodynamic conditions, with a displacement velocity of deformable surfaces ranging from 2 μm s -1 to 50 mm s -1 . Equipped with a high speed camera, the results of a bubble interacting with hydrophilic and partially hydrophobic surfaces in aqueous solutions indicated that ITLFFA can provide information on interaction forces and thin liquid film drainage dynamics not only in a stable film but also in films of the quick rupture process. The weak interaction force was extracted from a measured film profile. Because of its well-characterized experimental conditions, ITLFFA permits the accurate and quantitative comparison/validation between measured and calculated interaction forces and temporal film profiles.

Reduction of vortex induced forces and motion through surface roughness control

Science.gov (United States)

Bernitsas, Michael M; Raghavan, Kamaldev

2014-04-01

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

Forces on nuclei moving on autoionizing molecular potential energy surfaces.

Science.gov (United States)

Moiseyev, Nimrod

2017-01-14

Autoionization of molecular systems occurs in diatomic molecules and in small biochemical systems. Quantum chemistry packages enable calculation of complex potential energy surfaces (CPESs). The imaginary part of the CPES is associated with the autoionization decay rate, which is a function of the molecular structure. Molecular dynamics simulations, within the framework of the Born-Oppenheimer approximation, require the definition of a force field. The ability to calculate the forces on the nuclei in bio-systems when autoionization takes place seems to rely on an understanding of radiative damages in RNA and DNA arising from the release of slow moving electrons which have long de Broglie wavelengths. This work addresses calculation of the real forces on the nuclei moving on the CPES. By using the transformation of the time-dependent Schrödinger equation, previously used by Madelung, we proved that the classical forces on nuclei moving on the CPES correlated with the gradient of the real part of the CPES. It was proved that the force on the nuclei of the metastable molecules is time independent although the probability to detect metastable molecules exponentially decays. The classical force is obtained from the transformed Schrödinger equation when ℏ=0 and the Schrödinger equation is reduced to the classical (Newtonian) equations of motion. The forces on the nuclei regardless on what potential energy surface they move (parent CPES or product real PESs) vary in time due to the autoionization process.

Surface structure investigations using noncontact atomic force microscopy

International Nuclear Information System (INIS)

Kolodziej, J.J.; Such, B.; Goryl, M.; Krok, F.; Piatkowski, P.; Szymonski, M.

2006-01-01

Surfaces of several A III B V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination

Forces that Drive Nanoscale Self-assembly on Solid Surfaces

International Nuclear Information System (INIS)

Suo, Z.; Lu, W.

2000-01-01

Experimental evidence has accumulated in the recent decade that nanoscale patterns can self-assemble on solid surfaces. A two-component monolayer grown on a solid surface may separate into distinct phases. Sometimes the phases select sizes about 10 nm, and order into an array of stripes or disks. This paper reviews a model that accounts for these behaviors. Attention is focused on thermodynamic forces that drive the self-assembly. A double-welled, composition-dependent free energy drives phase separation. The phase boundary energy drives phase coarsening. The concentration-dependent surface stress drives phase refining. It is the competition between the coarsening and the refining that leads to size selection and spatial ordering. These thermodynamic forces are embodied in a nonlinear diffusion equation. Numerical simulations reveal rich dynamics of the pattern formation process. It is relatively fast for the phases to separate and select a uniform size, but exceedingly slow to order over a long distance, unless the symmetry is suitably broken

A transitioning Arctic surface energy budget: the impacts of solar zenith angle, surface albedo and cloud radiative forcing

Energy Technology Data Exchange (ETDEWEB)

Sedlar, Joseph; Tjernstroem, Michael; Leck, Caroline [Stockholm University, Department of Meteorology, Stockholm (Sweden); Mauritsen, Thorsten [Max-Planck-Institute for Meteorology, Hamburg (Germany); Shupe, Matthew D.; Persson, P.O.G. [University of Colorado, NOAA-ESRL-PSD, Boulder, CO (United States); Brooks, Ian M.; Birch, Cathryn E. [University of Leeds, School of Earth and Environment, Leeds (United Kingdom); Sirevaag, Anders [University of Bergen, Bjerknes Center for Climate Research, Bergen (Norway); Nicolaus, Marcel [Norwegian Polar Institute, Tromsoe (Norway); Alfred Wegener Institute for Polar and Marine Research, Bremerhaven (Germany)

2011-10-15

Snow surface and sea-ice energy budgets were measured near 87.5 N during the Arctic Summer Cloud Ocean Study (ASCOS), from August to early September 2008. Surface temperature indicated four distinct temperature regimes, characterized by varying cloud, thermodynamic and solar properties. An initial warm, melt-season regime was interrupted by a 3-day cold regime where temperatures dropped from near zero to -7 C. Subsequently mean energy budget residuals remained small and near zero for 1 week until once again temperatures dropped rapidly and the energy budget residuals became negative. Energy budget transitions were dominated by the net radiative fluxes, largely controlled by the cloudiness. Variable heat, moisture and cloud distributions were associated with changing air-masses. Surface cloud radiative forcing, the net radiative effect of clouds on the surface relative to clear skies, is estimated. Shortwave cloud forcing ranged between -50 W m{sup -2} and zero and varied significantly with surface albedo, solar zenith angle and cloud liquid water. Longwave cloud forcing was larger and generally ranged between 65 and 85 W m{sup -2}, except when the cloud fraction was tenuous or contained little liquid water; thus the net effect of the clouds was to warm the surface. Both cold periods occurred under tenuous, or altogether absent, low-level clouds containing little liquid water, effectively reducing the cloud greenhouse effect. Freeze-up progression was enhanced by a combination of increasing solar zenith angles and surface albedo, while inhibited by a large, positive surface cloud forcing until a new air-mass with considerably less cloudiness advected over the experiment area. (orig.)

Effects of Polishing Bur Application Force and Reuse on Sintered Zirconia Surface Topography.

Science.gov (United States)

Fischer, N G; Tsujimoto, A; Baruth, A G

2018-03-16

Limited information is available on how to polish and finish zirconia surfaces following computer-aided design/computer-aided manufacturing (CAD/CAM), specifically, how differing application forces and reuse of zirconia polishing systems affect zirconia topography. To determine the effect of differing, clinically relevant, polishing application forces and multiple usages of polishing burs on the surface topography of CAD/CAM zirconia. One hundred twenty 220-grit carbide finished zirconia disks were sintered according to manufacturer's directions and divided into two groups for the study of two coarse polishing bur types. Each group was divided into subgroups for polishing (15,000 rpm) at 15 seconds for 1.0 N, 4.5 N, or 11 N of force using a purpose-built fixture. Subgroups were further divided to study the effects of polishing for the first, fifth, 15th, and 30th bur use, simulating clinical procedures. Unpolished surfaces served as a control group. Surfaces were imaged with noncontact optical profilometry (OP) and atomic force microscopy (AFM) to measure average roughness values (Ra). Polishing burs were optically examined for wear. Scanning electron microscopy (SEM) was performed on burs and zirconia surfaces. One-way ANOVA with post hoc Tukey HSD (honest significant difference) tests (α=0.05) were used for statistical analyses. AFM and OP Ra values of all polished surfaces were significantly lower than those of the unpolished control. Different polishing forces and bur reuse showed no significant differences in AFM Ra. However, significant differences in OP Ra were found due to differing application forces and bur reuse between the first and subsequent uses. SEM and optical micrographs revealed notable bur wear, increasing with increasing reuse. SEM and AFM micrographs clearly showed polished, periodic zirconia surfaces. Nanoscale topography, as analyzed with kurtosis and average groove depth, was found dependent on the specific polishing bur type. These in

A comparative analysis of strategic approaches for Information Technology (IT) for Commander Naval Surface Forces

OpenAIRE

Johnson, Devine R.

2010-01-01

Approved for public release; distribution is unlimited As the lead organization for all United States Naval Surface Forces, Commander Naval Surface Forces (CNSF) is committed to providing operational commanders with well-trained, highly effective, and technologically relevant surface forces. Aligning itself with the Department of the Navy's Information Management (IM) and Information Technology (IT) strategic mission objectives, CNSF is dedicated to delivering secure, interoperable, and in...

Accurate fluid force measurement based on control surface integration

Science.gov (United States)

Lentink, David

2018-01-01

Nonintrusive 3D fluid force measurements are still challenging to conduct accurately for freely moving animals, vehicles, and deforming objects. Two techniques, 3D particle image velocimetry (PIV) and a new technique, the aerodynamic force platform (AFP), address this. Both rely on the control volume integral for momentum; whereas PIV requires numerical integration of flow fields, the AFP performs the integration mechanically based on rigid walls that form the control surface. The accuracy of both PIV and AFP measurements based on the control surface integration is thought to hinge on determining the unsteady body force associated with the acceleration of the volume of displaced fluid. Here, I introduce a set of non-dimensional error ratios to show which fluid and body parameters make the error negligible. The unsteady body force is insignificant in all conditions where the average density of the body is much greater than the density of the fluid, e.g., in gas. Whenever a strongly deforming body experiences significant buoyancy and acceleration, the error is significant. Remarkably, this error can be entirely corrected for with an exact factor provided that the body has a sufficiently homogenous density or acceleration distribution, which is common in liquids. The correction factor for omitting the unsteady body force, {{{ {ρ f}} {1 - {ρ f} ( {{ρ b}+{ρ f}} )}.{( {{{{ρ }}b}+{ρ f}} )}}} , depends only on the fluid, {ρ f}, and body, {{ρ }}b, density. Whereas these straightforward solutions work even at the liquid-gas interface in a significant number of cases, they do not work for generalized bodies undergoing buoyancy in combination with appreciable body density inhomogeneity, volume change (PIV), or volume rate-of-change (PIV and AFP). In these less common cases, the 3D body shape needs to be measured and resolved in time and space to estimate the unsteady body force. The analysis shows that accounting for the unsteady body force is straightforward to non

Raman-atomic force microscopy of the ommatidial surfaces of Dipteran compound eyes

Science.gov (United States)

Anderson, Mark S.; Gaimari, Stephen D.

2003-01-01

The ommatidial lens surfaces of the compound eyes in several species of files (Insecta: Diptera) and a related order (Mecoptera) were analyzed using a recently developed Raman-atomic force microscope. We demonstrate in this work that the atomic force microscope (AFM) is a potentially useful instrument for gathering phylogenetic data and that the newly developed Raman-AFM may extend this application by revealing nanometer-scale surface chemistry. This is the first demonstration of apertureless near-field Raman spectroscopy on an intact biological surface. For Chrysopilus testaceipes Bigot (Rhagionidae), this reveals unique cerebral cortex-like surface ridges with periodic variation in height and surface chemistry. Most other Brachyceran flies, and the "Nematoceran" Sylvicola fenestralis (Scopoli) (Anisopodidae), displayed the same morphology, while other taxa displayed various other characteristics, such as a nodule-like (Tipula (Triplicitipula) sp. (Tipulidae)) or coalescing nodule-like (Tabanus punctifer Osten Sacken (Tabanidae)) morphology, a smooth morphology with distinct pits and grooves (Dilophus orbatus (Say) (Bibionidae)), or an entirely smooth surface (Bittacus chlorostigma MacLachlan (Mecoptera: Bittacidae)). The variation in submicrometer structure and surface chemistry provides a new information source of potential phylogenetic importance, suggesting the Raman-atomic force microscope could provide a new tool useful to systematic and evolutionary inquiry.

Muscle force output and electromyographic activity in squats with various unstable surfaces.

Science.gov (United States)

Saeterbakken, Atle H; Fimland, Marius S

2013-01-01

The purpose of the study was to compare force output and muscle activity of leg and trunk muscles in isometric squats executed on stable surface (i.e., floor), power board, BOSU ball, and balance cone. Fifteen healthy men (23.3 ± 2.7 years, mass: 80.5 ± 8.5 kg, height: 1.81 ± 0.09 m) volunteered. The force output and electromyographic (EMG) activities of the rectus femoris, vastus medialis, vastus lateralis, biceps femoris, soleus, rectus abdominis, oblique external, and erector spinae were assessed. The order of the surfaces was randomized. One familiarization session was executed before the experimental test. Compared with stable surface (749 ± 222 N), the force output using power board was similar (-7%, p = 0.320) but lower for BOSU ball (-19%, p = 0.003) and balance cone (-24%, p ≤ 0.001). The force output using BOSU ball and balance cone was approximately 13% (p = 0.037) and approximately 18% (p = 0.001) less than the power board. There were similar EMG activities between the surfaces in all muscles except for rectus femoris, in which stable squat provided greater EMG activity than did the other exercises (p = 0.004-0.030). Lower EMG activity was observed in the rectus femoris using balance cone compared with the BOSU ball (p = 0.030). In conclusion, increasing the instability of the surface during maximum effort isometric squats usually maintains the muscle activity of lower-limb and superficial trunk muscles although the force output is reduced. This suggests that unstable surfaces in the squat may be beneficial in rehabilitation and as a part of periodized training programs, because similar muscle activity can be achieved with reduced loads.

Circuit Design of Surface Acoustic Wave Based Micro Force Sensor

Directory of Open Access Journals (Sweden)

Yuanyuan Li

2014-01-01

Full Text Available Pressure sensors are commonly used in industrial production and mechanical system. However, resistance strain, piezoresistive sensor, and ceramic capacitive pressure sensors possess limitations, especially in micro force measurement. A surface acoustic wave (SAW based micro force sensor is designed in this paper, which is based on the theories of wavelet transform, SAW detection, and pierce oscillator circuits. Using lithium niobate as the basal material, a mathematical model is established to analyze the frequency, and a peripheral circuit is designed to measure the micro force. The SAW based micro force sensor is tested to show the reasonable design of detection circuit and the stability of frequency and amplitude.

Surface force analysis of molecular interfacial interactions of proteins and lipids with polymeric biomaterials

International Nuclear Information System (INIS)

Hamilton-Brown, P.; Griesser, H.J.; Meagher, L.

2001-01-01

Full text: Adverse biological responses to biomedical devices are often caused by the irreversible accumulation of biological deposits onto the surfaces of devices. Such deposits cause blocking of artificial blood vessels, fibrous encapsulation of soft tissue regenerative devices, 'fouling' of contact lenses, secondary cataracts on intraocular lenses, and other undesirable events that interfere with the intended functions of biomedical devices. The formation of deposits is triggered by an initial stage in which various proteins and lipids rapidly adsorb onto the synthetic material surface; further biological molecules and ultimately cellular entities (e.g., host cells, bacteria) then settle onto the initial adsorbed layer. Hence, to avoid or control the accumulation of biological deposits, molecular understanding is required of the initial adsorption processes. Such adsorption is caused by attractive interfacial forces, which we are characterising by the use of a novel method. In the present study, polymeric thin film coatings, polyethylene oxide (PEO), and polysaccharide coatings have been analysed in terms of their surface forces and the ensuing propensity for protein and lipid adsorption. Interfacial forces are measured using atomic force microscopy (AFM) with a colloid-modified tip in a liquid cell using solutions of physiological pH and ionic strength. The chemical composition and uniformity of the coatings was characterised by X-ray Photon Spectroscopy (XPS). For a polymeric solid coating, repulsive forces have been measured against a silica colloid probe, and the dominant surface force is electrostatic. For the highly hydrated, 'soft' PEO and polysaccharide coatings, on the other hand, steric/entropic forces are also significant and contribute to interfacial interactions with proteins and lipids. In one system we have observed a time dependence of the electrostatic surface potential, which affects interaction with charged proteins. Force measurements were

Forces, surface finish and friction characteristics in surface engineered single- and multiple-point cutting edges

International Nuclear Information System (INIS)

Sarwar, M.; Gillibrand, D.; Bradbury, S.R.

1991-01-01

Advanced surface engineering technologies (physical and chemical vapour deposition) have been successfully applied to high speed steel and carbide cutting tools, and the potential benefits in terms of both performance and longer tool life, are now well established. Although major achievements have been reported by many manufacturers and users, there are a number of applications where surface engineering has been unsuccessful. Considerable attention has been given to the film characteristics and the variables associated with its properties; however, very little attention has been directed towards the benefits to the tool user. In order to apply surface engineering technology effectively to cutting tools, the coater needs to have accurate information relating to cutting conditions, i.e. cutting forces, stress and temperature etc. The present paper describes results obtained with single- and multiple-point cutting tools with examples of failures, which should help the surface coater to appreciate the significance of the cutting conditions, and in particular the magnitude of the forces and stresses present during cutting processes. These results will assist the development of a systems approach to cutting tool technology and surface engineering with a view to developing an improved product. (orig.)

Surface roughness and cutting force estimation in the CNC turning using artificial neural networks

Directory of Open Access Journals (Sweden)

Mohammad Ramezani

2015-04-01

Full Text Available Surface roughness and cutting forces are considered as important factors to determine machinability rate and the quality of product. A number of factors like cutting speed, feed rate, depth of cutting and tool noise radius influence the surface roughness and cutting forces in turning process. In this paper, an Artificial Neural Network (ANN model was used to forecast surface roughness and cutting forces with related inputs, including cutting speed, feed rate, depth of cut and tool noise radius. The machined surface roughness and cutting force parameters related to input parameters are the outputs of the ANN model. In this work, 24 samples of experimental data were used to train the network. Moreover, eight other experimental tests were implemented to test the network. The study concludes that ANN was a reliable and accurate method for predicting machining parameters in CNC turning operation.

Force control of a robot for surface contamination detection

International Nuclear Information System (INIS)

Petterson, B.J.; Jones, J.F.

1987-01-01

A system is under development at Sandia National Laboratories for use in understanding the issues relating to automated robotic handling of spent nuclear fuel shipping casks. The goal of robotic handling is reduction of personnel radiation exposure at the proposed geologic repositories. One of the major technology development areas has been the integration of sensors into the control of the robot system to allow operation in semi-structured environments. In particular, a multiaxis force sensor is used to make robot trajectory corrections based on the contact force between the robot and workpiece. This force feedback system allows contact swipes (smears) to be made on the cask surface in a repeatable manner. 8 refs., 3 figs

The Impacts of Daily Surface Forcing in the Upper Ocean over Tropical Pacific: A Numerical Study

Science.gov (United States)

Sui, C.-H.; Rienecker, Michele M.; Li, Xiaofan; Lau, William K.-M.; Laszlo, Istvan; Pinker, Rachel T.

2001-01-01

Tropical Pacific Ocean is an important region that affects global climate. How the ocean responds to the atmospheric surface forcing (surface radiative, heat and momentum fluxes) is a major topic in oceanographic research community. The ocean becomes warm when more heat flux puts into the ocean. The monthly mean forcing has been used in the past years since daily forcing was unavailable due to the lack of observations. The daily forcing is now available from the satellite measurements. This study investigates the response of the upper ocean over tropical Pacific to the daily atmospheric surface forcing. The ocean surface heat budgets are calculated to determine the important processes for the oceanic response. The differences of oceanic responses between the eastern and western Pacific are intensively discussed.

Influence of surface roughness on streptococcal adhesion forces to composite resins

NARCIS (Netherlands)

Mei, Li; Busscher, Henk J; van der Mei, Henny C; Ren, Yijin

OBJECTIVE: To determine streptococcal adhesion forces with composite resins with different surface roughness. METHODS: Polishing and grinding were applied to obtain smooth (roughness 20 nm), moderately rough (150 nm) and rough (350 nm) surfaces of two orthodontic, light-cured composites. Adhesion

Theoretical atomic-force-microscopy study of a stepped surface: Nonlocal effects in the probe

International Nuclear Information System (INIS)

Girard, C.

1991-01-01

The interaction force between a metallic tip and a nonplanar dielectric surface is derived from a nonlocal formalism. A general formulation is given for the case of a spherical tip of nanometer size and for surfaces of arbitrary shapes (stepped surfaces and single crystals adsorbed on a planar surface). The dispersion part of the attractive force is obtained from a nonlocal theory expressed in terms of generalized electric susceptibilities of the two constituents. Implications for atomic force microscopy in attractive modes are discussed. In this context, the present model indicates two different forms of corrugation: those due to the protuberance present on the tip leading to atomic corrugations; nanometer-sized corrugations detected in the attractive region by the spherical part of the tip

Surface radiative forcing of forest disturbances over northeastern China

International Nuclear Information System (INIS)

Zhang, Yuzhen; Liang, Shunlin

2014-01-01

Forests provide important climate forcing through biogeochemical and biogeophysical processes. In this study, we investigated the climatic effects of forest disturbances due to changes in forest biomass and surface albedo in terms of radiative forcing over northeastern China. Four types of forest disturbances were considered: fires, insect damage, logging, and afforestation and reforestation. The mechanisms of the influence of forest disturbances on climate were different. ‘Instantaneous’ net radiative forcings caused by fires, insect damage, logging, and afforestation and reforestation were estimated at 0.53 ± 0.08 W m −2 , 1.09 ± 0.14 W m −2 , 2.23 ± 0.27 W m −2 , and 0.14 ± 0.04 W m −2 , respectively. Trajectories of CO 2 -driven radiative forcing, albedo-driven radiative forcing, and net forcing were different with time for each type of disturbance. Over a decade, the estimated net forcings were 2.24 ± 0.11 W m −2 , 0.20 ± 0.31 W m −2 , 1.06 ± 0.41 W m −2 , and −0.47 ± 0.07 W m −2 , respectively. These estimated radiative forcings from satellite observations provided evidence for the mechanisms of the influences of forest disturbances on climate. (paper)

Surface and capillary forces encountered by zinc sulfide microspheres in aqueous electrolyte.

Science.gov (United States)

Gillies, Graeme; Kappl, Michael; Butt, Hans-Jürgen

2005-06-21

The colloid probe technique was used to investigate the interactions between individual zinc sulfide (ZnS) microspheres and an air bubble in electrolyte solution. Incorporation of zinc ions into the electrolyte solution overcomes the disproportionate zinc ion dissolution and mimics high-volume-fraction conditions common in flotation. Determined interaction forces revealed a distinct lack of long-ranged hydrophobic forces, indicated by the presence of a DLVO repulsion prior to particle engulfment. Single microsphere contact angles were determined from particle-bubble interactions. Contact angles increased with decreasing radii and with surface oxidation. Surface modification by the absorption of copper and subsequently potassium O-ethyldithiocarbonate (KED) reduced repulsive forces and strongly increased contact angles.

Characterization of local hydrophobicity on sapphire (0001) surfaces in aqueous environment by colloidal probe atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Wada, Tomoya; Yamazaki, Kenji; Isono, Toshinari; Ogino, Toshio, E-mail: ogino-toshio-rx@ynu.ac.jp

2017-02-28

Highlights: • Local hydrophobicity of phase-separated sapphire (0001) surfaces was investigated. • These surfaces are featured by coexistence of hydrophilic and hydrophobic domains. • Each domain was characterized by colloidal probe atomic force microscopy in water. • Both domains can be distinguished by adhesive forces of the probe to the surfaces. • Characterization in aqueous environment is important in bio-applications of sapphire. - Abstract: Sapphire (0001) surfaces exhibit a phase-separation into hydrophobic and hydrophilic domains upon high-temperature annealing, which were previously distinguished by the thickness of adsorbed water layers in air using atomic force microscopy (AFM). To characterize their local surface hydrophobicity in aqueous environment, we used AFM equipped with a colloidal probe and measured the local adhesive force between each sapphire domain and a hydrophilic SiO{sub 2} probe surface, or a hydrophobic polystyrene one. Two data acquisition modes for statistical analyses were used: one is force measurements at different positions of the surface and the other repeated measurement at a fixed position. We found that adhesive force measurements using the polystyrene probe allow us to distinctly separate the hydrophilic and hydrophobic domains. The dispersion in the force measurement data at different positions of the surface is larger than that in the repeated measurements at a fixed position. It indicates that the adhesive force measurement is repeatable although their data dispersion for the measurement positions is relatively large. From these results, we can conclude that the hydrophilic and hydrophobic domains on the sapphire (0001) surfaces are distinguished by a difference in their hydration degrees.

Finger-Shaped GelForce: Sensor for Measuring Surface Traction Fields for Robotic Hand.

Science.gov (United States)

Sato, K; Kamiyama, K; Kawakami, N; Tachi, S

2010-01-01

It is believed that the use of haptic sensors to measure the magnitude, direction, and distribution of a force will enable a robotic hand to perform dexterous operations. Therefore, we develop a new type of finger-shaped haptic sensor using GelForce technology. GelForce is a vision-based sensor that can be used to measure the distribution of force vectors, or surface traction fields. The simple structure of the GelForce enables us to develop a compact finger-shaped GelForce for the robotic hand. GelForce that is developed on the basis of an elastic theory can be used to calculate surface traction fields using a conversion equation. However, this conversion equation cannot be analytically solved when the elastic body of the sensor has a complicated shape such as the shape of a finger. Therefore, we propose an observational method and construct a prototype of the finger-shaped GelForce. By using this prototype, we evaluate the basic performance of the finger-shaped GelForce. Then, we conduct a field test by performing grasping operations using a robotic hand. The results of this test show that using the observational method, the finger-shaped GelForce can be successfully used in a robotic hand.

On the application of response surface methodology for predicting and optimizing surface roughness and cutting forces in hard turning by PVD coated insert

Directory of Open Access Journals (Sweden)

Hessainia Zahia

2015-04-01

Full Text Available This paper focuses on the exploitation of the response surface methodology (RSM to determine optimum cutting conditions leading to minimum surface roughness and cutting force components. The technique of RSM helps to create an efficient statistical model for studying the evolution of surface roughness and cutting forces according to cutting parameters: cutting speed, feed rate and depth of cut. For this purpose, turning tests of hardened steel alloy (AISI 4140 (56 HRC were carried out using PVD – coated ceramic insert under different cutting conditions. The equations of surface roughness and cutting forces were achieved by using the experimental data and the technique of the analysis of variance (ANOVA. The obtained results are presented in terms of mean values and confidence levels. It is shown that feed rate and depth of cut are the most influential factors on surface roughness and cutting forces, respectively. In addition, it is underlined that the surface roughness is mainly related to the cutting speed, whereas depth of cut has the greatest effect on the evolution of cutting forces. The optimal machining parameters obtained in this study represent reductions about 6.88%, 3.65%, 19.05% in cutting force components (Fa, Fr, Ft, respectively. The latters are compared with the results of initial cutting parameters for machining AISI 4140 steel in the hard turning process.

Tip-surface interactions at redox responsive poly(ferrocenylsilane) (PFS) interface by AFM-based force spectroscopy

International Nuclear Information System (INIS)

Chung Hongjing; Song Jing; Vancso, G. Julius

2009-01-01

Poly(ferrocenylsilanes) (PFS) belong to the class of redox responsive organometallic polymers. Atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) was used earlier to study single chain PFS response and redox energy driven single chain PFS molecular motors. Here we present further AFM investigations of force interactions between tip and a grafted PFS surface under potential control in electrochemical redox cycles. Typical tip-Au interaction is considered as reference in the force measurements. First the electrostatic component in the diffused double layer (DL) in NaClO 4 electrolyte environment was considered for a 'grafted to' PFS, which dominated the interplay between the tip and sample surface. The DL forces can also hinder the physisorption of PFS chain onto the tip when the voltage was applied at -0.1 V. On the other hand, if the tip contacted the PFS surface prior to the electrochemical process, physisorption of PFS chains governed the overall interaction regardless of subsequently applied surface potential. In addition, prolonged contact time, t c , may also contribute to the stability of tip-PFS bridging and detection of electrostatic forces between the tip-PFS interface. The results showed that tip-substrate interaction forces without PFS grafts have negligibly small force contributions under similar, electrochemically controlled, conditions used in single PFS chain based molecular motors.

The influence of rail surface irregularities on contact forces and local stresses

Science.gov (United States)

Andersson, Robin; Torstensson, Peter T.; Kabo, Elena; Larsson, Fredrik

2015-01-01

The effect of initial rail surface irregularities on promoting further surface degradation is investigated. The study concerns rolling contact fatigue formation, in particular in the form of the so-called squats. The impact of surface irregularities in the form of dimples is quantified by peak magnitudes of dynamic contact stresses and contact forces. To this end simulations of two-dimensional (later extended to three-dimensional) vertical dynamic vehicle-track interaction are employed. The most influencing parameters are identified. It is shown that even very shallow dimples might have a large impact on local contact stresses. Peak magnitudes of contact forces and stresses due to the influence of rail dimples are shown to exceed those due to rail corrugation.

The influence of the radiation pressure force on possible critical surfaces in binary systems

International Nuclear Information System (INIS)

Vanbeveren, D.

1978-01-01

Using a spherically symmetric approximation for the radiation pressure force to compute a possible critical surface for binary systems, previous authors found that the surface opens up at the far side of the companion. It is shown that this effect may be unreal, and could be a consequence of the simple approximation for the radiation pressure force, Due to the influence of the radiation force, mass will be lost over the whole surface of the star. In that way much mass could leave the system in massive binary systems. On the basis of evolutionary models, including mass loss by stellar wind, the results were applied on the X-ray binaries 3U 1700 - 37 and HD 77581. (Auth.)

Temporal step fluctuations on a conductor surface: electromigration force, surface resistivity and low-frequency noise

International Nuclear Information System (INIS)

Williams, E D; Bondarchuk, O; Tao, C G; Yan, W; Cullen, W G; Rous, P J; Bole, T

2007-01-01

Scattering of charge carriers from surface structures will become an increasing factor in the resistivity as the structure decreases in size to the nanoscale. The effects of scattering at the most basic surface defect, a kink in a step edge, are here analyzed using the continuum step model. Using a Langevin analysis, it has been shown that the electromigration force on the atoms at the step edge causes changes in the temporal evolution of the step-edge. For an electromigration force acting perpendicular to the average step edge and mass-transport dominated by step-edge diffusion, significant deviations from the usual t 1/4 scaling of the displacement correlation function occur dependent on a critical time τ and the direction of the force relative to the step edge (i.e. uphill or downhill). Experimental observations of step fluctuations on Ag(111) show the predicted changes among step fluctuations without current, and with current in the up- and down-hill directions for a current density of order 10 5 A cm -2 . The results yield the magnitude of the electromigration force acting on kinked sites at the step-edge. This in turn yields the contribution of the fluctuating steps to the surface resistivity, which exceeds 1% of the bulk resistivity as wire diameters decrease below 10s of nanometres. The temporal fluctuations of kink density can thus also be related to resistivity noise. Relating the known fluctuation spectrum of the step displacements to fluctuations in their lengths, the corresponding resistivity noise is predicted to show spectral signatures of ∼f -1/2 for step fluctuations governed by random attachment/detachment, and ∼f -3/4 for step fluctuations governed by step-edge diffusion

One-Channel Surface Electromyography Decomposition for Muscle Force Estimation

Directory of Open Access Journals (Sweden)

Wentao Sun

2018-05-01

Full Text Available Estimating muscle force by surface electromyography (sEMG is a non-invasive and flexible way to diagnose biomechanical diseases and control assistive devices such as prosthetic hands. To estimate muscle force using sEMG, a supervised method is commonly adopted. This requires simultaneous recording of sEMG signals and muscle force measured by additional devices to tune the variables involved. However, recording the muscle force of the lost limb of an amputee is challenging, and the supervised method has limitations in this regard. Although the unsupervised method does not require muscle force recording, it suffers from low accuracy due to a lack of reference data. To achieve accurate and easy estimation of muscle force by the unsupervised method, we propose a decomposition of one-channel sEMG signals into constituent motor unit action potentials (MUAPs in two steps: (1 learning an orthogonal basis of sEMG signals through reconstruction independent component analysis; (2 extracting spike-like MUAPs from the basis vectors. Nine healthy subjects were recruited to evaluate the accuracy of the proposed approach in estimating muscle force of the biceps brachii. The results demonstrated that the proposed approach based on decomposed MUAPs explains more than 80% of the muscle force variability recorded at an arbitrary force level, while the conventional amplitude-based approach explains only 62.3% of this variability. With the proposed approach, we were also able to achieve grip force control of a prosthetic hand, which is one of the most important clinical applications of the unsupervised method. Experiments on two trans-radial amputees indicated that the proposed approach improves the performance of the prosthetic hand in grasping everyday objects.

Intermolecular and surface forces

CERN Document Server

Israelachvili, Jacob N

2011-01-01

This reference describes the role of various intermolecular and interparticle forces in determining the properties of simple systems such as gases, liquids and solids, with a special focus on more complex colloidal, polymeric and biological systems. The book provides a thorough foundation in theories and concepts of intermolecular forces, allowing researchers and students to recognize which forces are important in any particular system, as well as how to control these forces. This third edition is expanded into three sections and contains five new chapters over the previous edition.· starts fr

Fusion of intraoperative force sensoring, surface reconstruction and biomechanical modeling

Science.gov (United States)

Röhl, S.; Bodenstedt, S.; Küderle, C.; Suwelack, S.; Kenngott, H.; Müller-Stich, B. P.; Dillmann, R.; Speidel, S.

2012-02-01

Minimally invasive surgery is medically complex and can heavily benefit from computer assistance. One way to help the surgeon is to integrate preoperative planning data into the surgical workflow. This information can be represented as a customized preoperative model of the surgical site. To use it intraoperatively, it has to be updated during the intervention due to the constantly changing environment. Hence, intraoperative sensor data has to be acquired and registered with the preoperative model. Haptic information which could complement the visual sensor data is still not established. In addition, biomechanical modeling of the surgical site can help in reflecting the changes which cannot be captured by intraoperative sensors. We present a setting where a force sensor is integrated into a laparoscopic instrument. In a test scenario using a silicone liver phantom, we register the measured forces with a reconstructed surface model from stereo endoscopic images and a finite element model. The endoscope, the instrument and the liver phantom are tracked with a Polaris optical tracking system. By fusing this information, we can transfer the deformation onto the finite element model. The purpose of this setting is to demonstrate the principles needed and the methods developed for intraoperative sensor data fusion. One emphasis lies on the calibration of the force sensor with the instrument and first experiments with soft tissue. We also present our solution and first results concerning the integration of the force sensor as well as accuracy to the fusion of force measurements, surface reconstruction and biomechanical modeling.

Single Cell Force Spectroscopy for Quantification of Cellular Adhesion on Surfaces

Science.gov (United States)

Christenson, Wayne B.

Cell adhesion is an important aspect of many biological processes. The atomic force microscope (AFM) has made it possible to quantify the forces involved in cellular adhesion using a technique called single cell force spectroscopy (SCFS). AFM based SCFS offers versatile control over experimental conditions for probing directly the interaction between specific cell types and specific proteins, surfaces, or other cells. Transmembrane integrins are the primary proteins involved in cellular adhesion to the extra cellular matix (ECM). One of the chief integrins involved in the adhesion of leukocyte cells is alpha Mbeta2 (Mac-1). The experiments in this dissertation quantify the adhesion of Mac-1 expressing human embryonic kidney (HEK Mac-1), platelets, and neutrophils cells on substrates with different concentrations of fibrinogen and on fibrin gels and multi-layered fibrinogen coated fibrin gels. It was shown that multi-layered fibrinogen reduces the adhesion force of these cells considerably. A novel method was developed as part of this research combining total internal reflection microscopy (TIRFM) with SCFS allowing for optical microscopy of HEK Mac-1 cells interacting with bovine serum albumin (BSA) coated glass after interacting with multi-layered fibrinogen. HEK Mac-1 cells are able to remove fibrinogen molecules from the multi-layered fibrinogen matrix. An analysis methodology for quantifying the kinetic parameters of integrin-ligand interactions from SCFS experiments is proposed, and the kinetic parameters of the Mac-1 fibrinogen bond are quantified. Additional SCFS experiments quantify the adhesion of macrophages and HEK Mac-1 cells on functionalized glass surfaces and normal glass surfaces. Both cell types show highest adhesion on a novel functionalized glass surface that was prepared to induce macrophage fusion. These experiments demonstrate the versatility of AFM based SCFS, and how it can be applied to address many questions in cellular biology offering

Simulated North Atlantic-Nordic Seas water mass exchanges in an isopycnic coordinate OGCM

OpenAIRE

Nilsen, Jan Even Øie; Gao, Yongqi; Drange, Helge; Furevik, Tore; Bentsen, Mats

2003-01-01

The variability in the volume exchanges between the North Atlantic and the Nordic Seas during the last 50 years is investigated using a synoptic forced, global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The simulated volume fluxes agree with the existing observations. The net volume flux across the Faroe-Shetland Channel (FSC) is positively correlated with the net flux through the Denmark Strait (DS; R = 0.74 for 3 years low pass filtering), but negatively correlated with ...

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

Science.gov (United States)

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

2017-12-15

Enteric viruses are recognized as major etiologies of U.S. foodborne infections. These viruses are easily transmitted via food contact surfaces. Understanding virus interactions with surfaces may facilitate the development of improved means for their removal, thus reducing transmission. Using MS2 coliphage as a virus surrogate, the strength of virus adhesion to common food processing and preparation surfaces of polyvinyl chloride (PVC) and glass was assessed by atomic force microscopy (AFM) and virus recovery assays. The interaction forces of MS2 with various surfaces were measured from adhesion peaks in force-distance curves registered using a spherical bead probe preconjugated with MS2 particles. MS2 in phosphate-buffered saline (PBS) demonstrated approximately 5 times less adhesion force to glass (0.54 nN) than to PVC (2.87 nN) ( P force for 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 potential means to mitigate virus adhesion to food contact surfaces. IMPORTANCE The spread of foodborne viruses is likely associated with their adhesive nature. Virus attachment on food contact surfaces has been evaluated by quantitating virus recoveries from inoculated surfaces. This study aimed to evaluate the microenvironment in which nanometer-sized viruses interact with food contact surfaces and to compare the virus adhesion differences using AFM. The virus surrogate MS2 demonstrated less adhesion force to glass than to PVC via AFM, with the force-contributing factors including the intrinsic nature and the topography of the contact surfaces. This adhesion finding is consistent with the virus recoveries, which were determined indirectly. Greater numbers of viruses were recovered from glass than from PVC, after application at the same levels. The stronger MS2 adhesion onto PVC could be interrupted by incorporating a

DNA adsorption and desorption on mica surface studied by atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Sun Lanlan [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate school of the Chinese Academy of Sciences, Chinese Academy of Sciences, Renmin Street 5625, Changchun 130022 (China); Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 16 East Nan-Hu Road, Open Economic Zone, Changchun 130033 (China); Zhao Dongxu [Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 16 East Nan-Hu Road, Open Economic Zone, Changchun 130033 (China); Zhang Yue; Xu Fugang [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate school of the Chinese Academy of Sciences, Chinese Academy of Sciences, Renmin Street 5625, Changchun 130022 (China); Li Zhuang, E-mail: zli@ciac.jl.cn [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate school of the Chinese Academy of Sciences, Chinese Academy of Sciences, Renmin Street 5625, Changchun 130022 (China)

2011-05-15

The adsorption of DNA molecules on mica surface and the following desorption of DNA molecules at ethanol-mica interface were studied using atomic force microscopy. By changing DNA concentration, different morphologies on mica surface have been observed. A very uniform and orderly monolayer of DNA molecules was constructed on the mica surface with a DNA concentration of 30 ng/{mu}L. When the samples were immersed into ethanol for about 15 min, various desorption degree of DNA from mica (0-99%) was achieved. It was found that with the increase of DNA concentration, the desorption degree of DNA from the mica at ethanol-mica interface decreased. And when the uniform and orderly DNA monolayers were formed on the mica surface, almost no DNA molecule desorbed from the mica surface in this process. The results indicated that the uniform and orderly DNA monolayer is one of the most stable DNA structures formed on the mica surface. In addition, we have studied the structure change of DNA molecules after desorbed from the mica surface with atomic force microscopy, and found that the desorption might be ascribed to the ethanol-induced DNA condensation.

DNA adsorption and desorption on mica surface studied by atomic force microscopy

International Nuclear Information System (INIS)

Sun Lanlan; Zhao Dongxu; Zhang Yue; Xu Fugang; Li Zhuang

2011-01-01

The adsorption of DNA molecules on mica surface and the following desorption of DNA molecules at ethanol-mica interface were studied using atomic force microscopy. By changing DNA concentration, different morphologies on mica surface have been observed. A very uniform and orderly monolayer of DNA molecules was constructed on the mica surface with a DNA concentration of 30 ng/μL. When the samples were immersed into ethanol for about 15 min, various desorption degree of DNA from mica (0-99%) was achieved. It was found that with the increase of DNA concentration, the desorption degree of DNA from the mica at ethanol-mica interface decreased. And when the uniform and orderly DNA monolayers were formed on the mica surface, almost no DNA molecule desorbed from the mica surface in this process. The results indicated that the uniform and orderly DNA monolayer is one of the most stable DNA structures formed on the mica surface. In addition, we have studied the structure change of DNA molecules after desorbed from the mica surface with atomic force microscopy, and found that the desorption might be ascribed to the ethanol-induced DNA condensation.

Investigation of graphite composite anodes surfaces by atomic force microscopy and related techniques

Energy Technology Data Exchange (ETDEWEB)

Hirasawa, Karen Akemi; Nishioka, Keiko; Sato, Tomohiro; Yamaguchi, Shoji; Mori, Shoichiro [Mitsubishi Chemical Corp., Tsukuba Research Center, Ibaraki (Japan)

1997-11-01

The surface of a synthetic graphite (KS-44) and polyvinylidene difluoride binder (PVDF) anode for lithium-ion secondary batteries is imaged using atomic force microscopy (AFM) and several related scanning probe microscope (SPM) instruments including: dynamic force microscopy (DFM), friction force microscopy (FFM), laterally-modulated friction force microscopy (LM-FFM), visco-elasticity atomic force microscopy (VE-AFM), and AFM/simultaneous current measurement mode (SCM). DFM is found to be an exceptional mode for topographic imaging while FFM results in the clearest contrast distinction between PVDF binder and KS-44 graphite regions. (orig.)

Evaluation of the roughness of the surface of porcelain systems with the atomic force microscope

International Nuclear Information System (INIS)

Chavarria Rodriguez, Bernal

2013-01-01

The surface of a dental ceramic was evaluated and compared with an atomic force microscope after being treated with different systems of polishing. 14 identical ceramic Lava® Zirconia discs were used to test the different polishing systems. 3 polishing systems from different matrix houses were used to polish dental porcelain. The samples were evaluated quantitatively with an atomic force microscope in order to study the real effectiveness of each system, on the roughness average (Ra) and the maximum peak to valley roughness (Ry) of the ceramic surfaces. A considerable reduction of the surface roughness was obtained by applying different polishing systems on the surface of dental ceramics. Very reliable values of Ra and Ry were obtained by making measurements on the structure reproduced by the atomic force microscope. The advanced ceramics of zirconium oxide presented the best physical characteristics and low levels of surface roughness. A smoother surface was achieved with the application of polishing systems, thus demonstrating the reduction of the surface roughness of a dental ceramic [es

Measuring the force of single protein molecule detachment from surfaces with AFM.

Science.gov (United States)

Tsapikouni, Theodora S; Missirlis, Yannis F

2010-01-01

Atomic force microscopy (AFM) was used to measure the non-specific detachment force of single fibrinogen molecules from glass surfaces. The identification of single unbinding events was based on the characteristics of the parabolic curves, recorded during the stretching of protein molecules. Fibrinogen molecules were covalently bound to Si(3)N(4) AFM tips, previously modified with 3-aminopropyl-dimethyl-ethoxysilane, through a homobifunctional poly(ethylene glycol) linker bearing two hydroxysulfosuccinimide esters. The most probable detachment force was found to be 210 pN, when the tip was retracting with a velocity of 1400 nm/s, while the distribution of the detachment distances indicated that the fibrinogen chain can be elongated beyond the length of the physical conformation before detachment. The dependence of the most probable detachment force on the loading rate was examined and the dynamics of fibrinogen binding to the surface were found amenable to the simple expression of the Bell-Evans theory. The theory's expansion, however, by incorporating the concept of the rupture of parallel residue-surface bonds could only describe the detachment of fibrinogen for a small number of such bonds. Finally, the mathematical expression of the Worm-Like Chain model was used to fit the stretching curves before rupture and two interpretations are suggested for the description of the AFM curves with multiple detachment events.

Naval Reserve Force: Cost and Benefit Analysis of Reducing the Number of Naval Surface Reserve Force Operating Budget Holders

National Research Council Canada - National Science Library

Young, Eric

1997-01-01

.... This thesis examines one of Commander Naval Surface Reserve Force's initiatives for reducing the current number of Operating Budget holder's Comptroller Departments without sacrificing efficiency...

Surface force measurements and simulations of mussel-derived peptide adhesives on wet organic surfaces.

Science.gov (United States)

Levine, Zachary A; Rapp, Michael V; Wei, Wei; Mullen, Ryan Gotchy; Wu, Chun; Zerze, Gül H; Mittal, Jeetain; Waite, J Herbert; Israelachvili, Jacob N; Shea, Joan-Emma

2016-04-19

Translating sticky biological molecules-such as mussel foot proteins (MFPs)-into synthetic, cost-effective underwater adhesives with adjustable nano- and macroscale characteristics requires an intimate understanding of the glue's molecular interactions. To help facilitate the next generation of aqueous adhesives, we performed a combination of surface forces apparatus (SFA) measurements and replica-exchange molecular dynamics (REMD) simulations on a synthetic, easy to prepare, Dopa-containing peptide (MFP-3s peptide), which adheres to organic surfaces just as effectively as its wild-type protein analog. Experiments and simulations both show significant differences in peptide adsorption on CH3-terminated (hydrophobic) and OH-terminated (hydrophilic) self-assembled monolayers (SAMs), where adsorption is strongest on hydrophobic SAMs because of orientationally specific interactions with Dopa. Additional umbrella-sampling simulations yield free-energy profiles that quantitatively agree with SFA measurements and are used to extract the adhesive properties of individual amino acids within the context of MFP-3s peptide adhesion, revealing a delicate balance between van der Waals, hydrophobic, and electrostatic forces.

Surface features on Sahara soil dust particles made visible by atomic force microscope (AFM phase images

Directory of Open Access Journals (Sweden)

M. O. Andreae

2008-10-01

Full Text Available We show that atomic force microscopy (AFM phase images can reveal surface features of soil dust particles, which are not evident using other microscopic methods. The non-contact AFM method is able to resolve topographical structures in the nanometer range as well as to uncover repulsive atomic forces and attractive van der Waals' forces, and thus gives insight to surface properties. Though the method does not allow quantitative assignment in terms of chemical compound description, it clearly shows deposits of distinguishable material on the surface. We apply this technique to dust aerosol particles from the Sahara collected over the Atlantic Ocean and describe micro-features on the surfaces of such particles.

Evidence of the no-slip boundary condition of water flow between hydrophilic surfaces using atomic force microscopy.

Science.gov (United States)

Maali, Abdelhamid; Wang, Yuliang; Bhushan, Bharat

2009-10-20

In this study we present measurements of the hydrodynamic force exerted on a glass sphere glued to an atomic force microscopy (AFM) cantilever approaching a mica surface in water. A large sphere was used to reduce the impact of the cantilever beam on the measurement. An AFM cantilever with large stiffness was used to accurately determine the actual contact position between the sphere and the sample surface. The measured hydrodynamic force with different approach velocities is in good agreement with the Taylor force calculated in the lubrication theory with the no-slip boundary conditions, which verifies that there is no boundary slip on the glass and mica surfaces. Moreover, a detailed procedure of how to subtract the electrostatic double-layer force is presented.

Construction of force-free fields which have toroidal surfaces about a given surface

International Nuclear Information System (INIS)

Bouligand, G.

1983-05-01

A study of two-fields (B vector, rotB vector) of conservative flux which admits a family of toroidal surfaces of parameter phi on a domain limited by a given surface S, suggests their construction by a Cauchy-Arzela method of step by step. Taking into account the Newcomb condition this method is consistent with force-free magnetic fields and with helical equilibria with scalar pressure. The method supposes that B vector is of class C 1 . This construction makes use of the remarkable property of the field B vector to be the surface gradient of a generating multivalued function Q on a closed surface. Consequently, the initial surface will be given with its normal metric coefficient K; that is to say, B vector admits a family F of homotopic surfaces on a infinitesimal domain about S, an element of F. From this, the periodic part of Q is a solution of a Beltrami equation for the flux conservation of which numerical resolution is envisaged. The study of these fields is made in a biorthogonal system of coordinates. The coeffficients of the two fundamental metric forms of magnetic surfaces vary with phi and are interrelated by a sixth order differential system of equations which gives their variation [fr

Effect of relative humidity on onset of capillary forces for rough surfaces.

Science.gov (United States)

Zarate, Nyah V; Harrison, Aaron J; Litster, James D; Beaudoin, Stephen P

2013-12-01

Atomic force microscopy (AFM) was used to investigate the effect of relative humidity (RH) on the adhesion forces between silicon nitride AFM probes, hydrophilic stainless steel, and hydrophobic Perspex® (polymethylmethacrylate, PMMA). In addition, AFM-based phase contrast imaging was used to quantify the amount and location of adsorbed water present on these substrates at RH levels ranging from 15% to 65% at 22°C. Both the adhesion forces and the quantities of adsorbed moisture were seen to vary with RH, and the nature of this variation depended on the hydrophobicity of the substrate. For the Perspex®, both the adhesion force and the amount of adsorbed moisture were essentially independent of RH. For the stainless steel substrate, adsorbed moisture increased continuously with increasing RH, while the adhesion force rose from a minimum at 15% RH to a broad maximum between 25% and 35% RH. From 35% to 55% RH, the adhesion force dropped continuously to an intermediate level before rising again as 65% RH was approached. The changes in adhesion force with increasing relative humidity in the case of the stainless steel substrate were attributed to a balance of effects associated with adsorbed, sub-continuum water on the cantilever and steel. Hydrogen bonding interactions between these adsorbed water molecules were thought to increase the adhesion force. However, when significant quantities of molecular water adsorbed, these molecules were expect to decrease adhesion by screening the van der Waals interactions between the steel and the cantilever tip, and by increasing the separation distance between these solid surfaces when they were 'in contact'. Finally, the slight increase in adhesion between 55% and 65% RH was attributed to true capillary forces exerted by continuum water on the two solid surfaces. Copyright © 2013 Elsevier Inc. All rights reserved.

Control of fingertip forces in young and older adults pressing against fixed low- and high-friction surfaces.

Directory of Open Access Journals (Sweden)

Kevin G Keenan

Full Text Available Mobile computing devices (e.g., smartphones and tablets that have low-friction surfaces require well-directed fingertip forces of sufficient and precise magnitudes for proper use. Although general impairments in manual dexterity are well-documented in older adults, it is unclear how these sensorimotor impairments influence the ability of older adults to dexterously manipulate fixed, low-friction surfaces in particular. 21 young and 18 older (65+ yrs adults produced maximal voluntary contractions (MVCs and steady submaximal forces (2.5 and 10% MVC with the fingertip of the index finger. A Teflon covered custom-molded splint was placed on the fingertip. A three-axis force sensor was covered with either Teflon or sandpaper to create low- and high-friction surfaces, respectively. Maximal downward forces (F(z were similar (p = .135 for young and older adults, and decreased by 15% (p<.001 while pressing on Teflon compared to sandpaper. Fluctuations in F(z during the submaximal force-matching tasks were 2.45× greater (p<.001 for older adults than in young adults, and reached a maximum when older adults pressed against the Teflon surface while receiving visual feedback. These age-associated changes in motor performance are explained, in part, by altered muscle activity from three hand muscles and out-of-plane forces. Quantifying the ability to produce steady fingertip forces against low-friction surfaces may be a better indicator of impairment and disability than the current practice of evaluating maximal forces with pinch meters. These age-associated impairments in dexterity while interacting with low-friction surfaces may limit the use of the current generation of computing interfaces by older adults.

Atomic force microscopy imaging and single molecule recognition force spectroscopy of coat proteins on the surface of Bacillus subtilis spore.

Science.gov (United States)

Tang, Jilin; Krajcikova, Daniela; Zhu, Rong; Ebner, Andreas; Cutting, Simon; Gruber, Hermann J; Barak, Imrich; Hinterdorfer, Peter

2007-01-01

Coat assembly in Bacillus subtilis serves as a tractable model for the study of the self-assembly process of biological structures and has a significant potential for use in nano-biotechnological applications. In the present study, the morphology of B. subtilis spores was investigated by magnetically driven dynamic force microscopy (MAC mode atomic force microscopy) under physiological conditions. B. subtilis spores appeared as prolate structures, with a length of 0.6-3 microm and a width of about 0.5-2 microm. The spore surface was mainly covered with bump-like structures with diameters ranging from 8 to 70 nm. Besides topographical explorations, single molecule recognition force spectroscopy (SMRFS) was used to characterize the spore coat protein CotA. This protein was specifically recognized by a polyclonal antibody directed against CotA (anti-CotA), the antibody being covalently tethered to the AFM tip via a polyethylene glycol linker. The unbinding force between CotA and anti-CotA was determined as 55 +/- 2 pN. From the high-binding probability of more than 20% in force-distance cycles it is concluded that CotA locates in the outer surface of B. subtilis spores. Copyright (c) 2007 John Wiley & Sons, Ltd.

Effect of SP-C on surface potential distribution in pulmonary surfactant: Atomic force microscopy and Kelvin probe force microscopy study

International Nuclear Information System (INIS)

Hane, Francis; Moores, Brad; Amrein, Matthias; Leonenko, Zoya

2009-01-01

The air-lung interface is covered by a molecular film of pulmonary surfactant (PS). The major function of the film is to reduce the surface tension of the lung's air-liquid interface, providing stability to the alveolar structure and reducing the work of breathing. Earlier we have shown that function of bovine lipid extract surfactant (BLES) is related to the specific molecular architecture of surfactant films. Defined molecular arrangement of the lipids and proteins of the surfactant film also give rise to a local highly variable electrical surface potential of the interface. In this work we investigated a simple model of artificial lung surfactant consisting of DPPC, eggPG, and surfactant protein C (SP-C). Effects of surface compression and the presence of SP-C on the monolayer structure and surface potential distribution were investigated using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We show that topography and locally variable surface potential of DPPC-eggPG lipid mixture are similar to those of pulmonary surfactant BLES in the presence of SP-C and differ in surface potential when SP-C is absent.

Characterization of polymer surface structure and surface mechanical behaviour by sum frequency generation surface vibrational spectroscopy and atomic force microscopy

International Nuclear Information System (INIS)

Opdahl, Aric; Koffas, Telly S; Amitay-Sadovsky, Ella; Kim, Joonyeong; Somorjai, Gabor A

2004-01-01

Sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM) have been used to study polymer surface structure and surface mechanical behaviour, specifically to study the relationships between the surface properties of polymers and their bulk compositions and the environment to which the polymer is exposed. The combination of SFG surface vibrational spectroscopy and AFM has been used to study surface segregation behaviour of polyolefin blends at the polymer/air and polymer/solid interfaces. SFG surface vibrational spectroscopy and AFM experiments have also been performed to characterize the properties of polymer/liquid and polymer/polymer interfaces, focusing on hydrogel materials. A method was developed to study the surface properties of hydrogel contact lens materials at various hydration conditions. Finally, the effect of mechanical stretching on the surface composition and surface mechanical behaviour of phase-separated polyurethanes, used in biomedical implant devices, has been studied by both SFG surface vibrational spectroscopy and AFM. (topical review)

Machining of bone: Analysis of cutting force and surface roughness by turning process.

Science.gov (United States)

Noordin, M Y; Jiawkok, N; Ndaruhadi, P Y M W; Kurniawan, D

2015-11-01

There are millions of orthopedic surgeries and dental implantation procedures performed every year globally. Most of them involve machining of bones and cartilage. However, theoretical and analytical study on bone machining is lagging behind its practice and implementation. This study views bone machining as a machining process with bovine bone as the workpiece material. Turning process which makes the basis of the actually used drilling process was experimented. The focus is on evaluating the effects of three machining parameters, that is, cutting speed, feed, and depth of cut, to machining responses, that is, cutting forces and surface roughness resulted by the turning process. Response surface methodology was used to quantify the relation between the machining parameters and the machining responses. The turning process was done at various cutting speeds (29-156 m/min), depths of cut (0.03 -0.37 mm), and feeds (0.023-0.11 mm/rev). Empirical models of the resulted cutting force and surface roughness as the functions of cutting speed, depth of cut, and feed were developed. Observation using the developed empirical models found that within the range of machining parameters evaluated, the most influential machining parameter to the cutting force is depth of cut, followed by feed and cutting speed. The lowest cutting force was obtained at the lowest cutting speed, lowest depth of cut, and highest feed setting. For surface roughness, feed is the most significant machining condition, followed by cutting speed, and with depth of cut showed no effect. The finest surface finish was obtained at the lowest cutting speed and feed setting. © IMechE 2015.

Electrostatic force microscopy on oriented graphite surfaces: coexistence of insulating and conducting behaviors.

Science.gov (United States)

Lu, Yonghua; Muñoz, M; Steplecaru, C S; Hao, Cheng; Bai, Ming; Garcia, N; Schindler, K; Esquinazi, P

2006-08-18

We present measurements of the electric potential fluctuations on the surface of highly oriented pyrolytic graphite using electrostatic force and atomic force microscopy. Micrometric domainlike potential distributions are observed even when the sample is grounded. Such potential distributions are unexpected given the good metallic conductivity of graphite because the surface should be an equipotential. Our results indicate the coexistence of regions with "metalliclike" and "insulatinglike" behaviors showing large potential fluctuations of the order of 0.25 V. In lower quality graphite, this effect is not observed. Experiments are performed in Ar and air atmospheres.

The electrical double layer on gold probed by electrokinetic and surface force measurements

NARCIS (Netherlands)

Giesbers, M.; Kleijn, J.M.; Cohen Stuart, M.A.

2002-01-01

Gold surfaces, obtained by vacuum deposition of 15-nm gold films on glass and silica wafers, were studied in aqueous solutions by streaming potential measurements and colloidal-probe AFM force measurements. In the force measurements both a bare and a gold-coated silica particle (6 m in diameter)

Near-field Light Scattering Techniques for Measuring Nanoparticle-Surface Interaction Energies and Forces.

Science.gov (United States)

Schein, Perry; Ashcroft, Colby K; O'Dell, Dakota; Adam, Ian S; DiPaolo, Brian; Sabharwal, Manit; Shi, Ce; Hart, Robert; Earhart, Christopher; Erickson, David

2015-08-15

Nanoparticles are quickly becoming commonplace in many commercial and industrial products, ranging from cosmetics to pharmaceuticals to medical diagnostics. Predicting the stability of the engineered nanoparticles within these products a priori remains an important and difficult challenge. Here we describe our techniques for measuring the mechanical interactions between nanoparticles and surfaces using near-field light scattering. Particle-surface interfacial forces are measured by optically "pushing" a particle against a reference surface and observing its motion using scattered near-field light. Unlike atomic force microscopy, this technique is not limited by thermal noise, but instead takes advantage of it. The integrated waveguide and microfluidic architecture allow for high-throughput measurements of about 1000 particles per hour. We characterize the reproducibility of and experimental uncertainty in the measurements made using the NanoTweezer surface instrument. We report surface interaction studies on gold nanoparticles with 50 nm diameters, smaller than previously reported in the literature using similar techniques.

Surface features on Sahara soil dust particles made visible by atomic force microscope (AFM) phase images

OpenAIRE

G. Helas; M. O. Andreae

2008-01-01

We show that atomic force microscopy (AFM) phase images can reveal surface features of soil dust particles, which are not evident using other microscopic methods. The non-contact AFM method is able to resolve topographical structures in the nanometer range as well as to uncover repulsive atomic forces and attractive van der Waals' forces, and thus gives insight to surface properties. Though the method does not allow quantitative assignment in terms of chemical compound description, it clearly...

Non-intrusive measurements of frictional forces between micro-spheres and flat surfaces

Science.gov (United States)

Lin, Wei-Hsun; Daraio, Chiara; Daraio's Group Team

2014-03-01

We report a novel, optical pump-probe experimental setup to study micro-friction phenomena between micro-particles and a flat surface. We present a case study of stainless steel microspheres, of diameter near 250 μm, in contact with different surfaces of variable roughness. In these experiments, the contact area between the particles and the substrates is only a few nanometers wide. To excite the particles, we deliver an impulse using a pulsed, high-power laser. The reaction force resulting from the surface ablation induced by the laser imparts a controlled initial velocity to the target particle. This initial velocity can be varied between 10-5 to 1 m/s. We investigate the vibrating and rolling motions of the micro-particles by detecting their velocity and displacement with a laser vibrometer and a high-speed microscope camera. We calculate the effective Hamaker constant from the vibrating motion of a particle, and study its relation to the substrate's surface roughness. We analyze the relation between rolling friction and the minimum momentum required to break surface bonding forces. This non-contact and non-intrusive technique could be employed to study a variety of contact and tribology problems at the microscale.

Sensitivity of surface temperature to radiative forcing by contrail cirrus in a radiative-mixing model

Directory of Open Access Journals (Sweden)

U. Schumann

2017-11-01

Full Text Available Earth's surface temperature sensitivity to radiative forcing (RF by contrail cirrus and the related RF efficacy relative to CO2 are investigated in a one-dimensional idealized model of the atmosphere. The model includes energy transport by shortwave (SW and longwave (LW radiation and by mixing in an otherwise fixed reference atmosphere (no other feedbacks. Mixing includes convective adjustment and turbulent diffusion, where the latter is related to the vertical component of mixing by large-scale eddies. The conceptual study shows that the surface temperature sensitivity to given contrail RF depends strongly on the timescales of energy transport by mixing and radiation. The timescales are derived for steady layered heating (ghost forcing and for a transient contrail cirrus case. The radiative timescales are shortest at the surface and shorter in the troposphere than in the mid-stratosphere. Without mixing, a large part of the energy induced into the upper troposphere by radiation due to contrails or similar disturbances gets lost to space before it can contribute to surface warming. Because of the different radiative forcing at the surface and at top of atmosphere (TOA and different radiative heating rate profiles in the troposphere, the local surface temperature sensitivity to stratosphere-adjusted RF is larger for SW than for LW contrail forcing. Without mixing, the surface energy budget is more important for surface warming than the TOA budget. Hence, surface warming by contrails is smaller than suggested by the net RF at TOA. For zero mixing, cooling by contrails cannot be excluded. This may in part explain low efficacy values for contrails found in previous global circulation model studies. Possible implications of this study are discussed. Since the results of this study are model dependent, they should be tested with a comprehensive climate model in the future.

Osteopontin adsorption to Gram-positive cells reduces adhesion forces and attachment to surfaces under flow

DEFF Research Database (Denmark)

Kristensen, M F; Zeng, G; Neu, T R

2017-01-01

caries or medical device-related infections. It further investigated if OPN's effect on adhesion is caused by blocking the accessibility of glycoconjugates on bacterial surfaces. Bacterial adhesion was determined in a shear-controlled flow cell system in the presence of different concentrations of OPN......The bovine milk protein osteopontin (OPN) may be an efficient means to prevent bacterial adhesion to dental tissues and control biofilm formation. This study sought to determine to what extent OPN impacts adhesion forces and surface attachment of different bacterial strains involved in dental......, and interaction forces of single bacteria were quantified using single-cell force spectroscopy before and after OPN exposure. Moreover, the study investigated OPN's effect on the accessibility of cell surface glycoconjugates through fluorescence lectin-binding analysis. OPN strongly affected bacterial adhesion...

Analysis of surface roughness and cutting force during turning of Ti6Al4V ELI in dry environment

Directory of Open Access Journals (Sweden)

V. G. Sargade

2016-04-01

Full Text Available This paper investigates the effect of cutting parameters on the surface roughness and cutting force of titanium alloy Ti-6Al-4V ELI when turning using PVD TiAlN coated tool in dry environment. Taguchi L9 orthogonal array design of experiment was used for the turning experiment 2 factors and 3 levels. Turning parameters studied were cutting speed (50, 65, 80 m/min, feed rate (0.08, 0.15, 0.2 mm/rev and depth of cut 0.5 mm constant. Linear and second order model of the surface roughness and cutting force has been developed in terms of cutting speed and feed. The results show that the feed rate was the most impact factor controlling the cutting force and surface roughness produced. MINITAB 17software was used to develop a linear and second order model of surface roughness and cutting force. Optimum condition was at 66.97 m/min of cutting speed, 0.08 mm/rev of feed rate. Surface roughness 0.57μm and cutting force 54.02 N were obtained at the optimum condition. A good agreement between the experimental and predicted surface roughness and cutting force were observed.

Photoassisted Kelvin probe force microscopy at GaN surfaces: The role of polarity

Science.gov (United States)

Wei, J. D.; Li, S. F.; Atamuratov, A.; Wehmann, H.-H.; Waag, A.

2010-10-01

The behavior of GaN surfaces during photoassisted Kelvin probe force microscopy is demonstrated to be strongly dependant on surface polarity. The surface photovoltage of GaN surfaces illuminated with above-band gap light is analyzed as a function of time and light intensity. Distinct differences between Ga-polar and N-polar surfaces could be identified, attributed to photoinduced chemisorption of oxygen during illumination. These differences can be used for a contactless, nondestructive, and easy-performable analysis of the polarity of GaN surfaces.

Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations. Part I: Surface fluxes

Science.gov (United States)

Josse, P.; Caniaux, G.; Giordani, H.; Planton, S.

1999-04-01

A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm-2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer to the atmosphere is

Relationship between cloud radiative forcing, cloud fraction and cloud albedo, and new surface-based approach for determining cloud albedo

OpenAIRE

Y. Liu; W. Wu; M. P. Jensen; T. Toto

2011-01-01

This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surfaced-based approach for measuring cloud albedo; (3) multiscale (diurnal, annual and inter-annual) variations and covariations of surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo. An analytical expression is first derived to quantify the relationship between cloud radiative forcing, cloud fractio...

INVESTIGATION OF POLYMER SURFACES USING SCANNING FORCE MICROSCOPY (SFM) - A NEW DIRECT LOOK ON OLD POLYMER PROBLEMS

NARCIS (Netherlands)

GRIM, PCM; BROUWER, HJ; SEYGER, RM; OOSTERGETEL, GT; BERGSMASCHUTTER, WG; ARNBERG, AC; GUTHNER, P; DRANSFELD, K; HADZIIOANNOU, G

In this contribution, the general concepts of force microscopy will be presented together with its application to polymer surfaces (Ref.1). Several examples will be presented to illustrate that force microscopy is a powerful and promising tool for investigation of (polymer) surfaces, such as the

An Oceanic General Circulation Model (OGCM) investigation of the Red Sea circulation: 2. Three-dimensional circulation in the Red Sea

Science.gov (United States)

Sofianos, Sarantis S.; Johns, William E.

2003-03-01

The three-dimensional circulation of the Red Sea is studied using a set of Miami Isopycnic Coordinate Ocean Model (MICOM) simulations. The model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation. The main findings of this analysis include an intensification of the along-axis flow toward the coasts, with a transition from western intensified boundary flow in the south to eastern intensified flow in the north, and a series of strong seasonal or permanent eddy-like features. Model experiments conducted with different forcing fields (wind-stress forcing only, surface buoyancy forcing only, or both forcings combined) showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind-driven part of the circulation. The main circulation pattern is related to the seasonal buoyancy flux (mostly due to the evaporation), which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface. The response of the eastern boundary to the associated mean cross-basin geostrophic current depends on the stratification and β-effect. In the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of Kelvin waves while in the south the traditional westward intensification due to Rossby waves takes place. The most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of Red Sea Outflow Water (RSOW). Beneath the surface boundary currents are similarly intensified southward undercurrents that carry the RSOW to the sill to flow out of the basin into the Indian Ocean.

Combined short scale roughness and surface dielectric function gradient effects on the determination of tip-sample force in atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Gusso, André, E-mail: gusso@metal.eeimvr.uff.br [Departamento de Ciências Exatas-EEIMVR, Universidade Federal Fluminense, Volta Redonda, RJ 27255-125 (Brazil)

2013-11-11

The contribution of tip roughness to the van der Waals force between an atomic force microscopy probe tip and the sample is calculated using the multilayer effective medium model, which allows us to consider the relevant case of roughness characterized by correlation length and amplitude in the nanometer scale. The effect of the surface dielectric function gradient is incorporated in the tip-sample force model. It is concluded that for rms roughness in the few nanometers range the effect of short scale tip roughness is quite significant.

Experimental investigation of Surface Roughness and Cutting force in CNC Turning - A Review

Directory of Open Access Journals (Sweden)

Dhiraj Patel

2014-08-01

Full Text Available The main purpose of this review paper is to check whether quality lies within desired tolerance level which can be accepted by the customers. So, experimental investigation surface roughness and cutting force using various CNC machining parameters including spindle speed (N, feed rate (f, and depth of cut (d,flow rate (Q and insert nose radius (r. As such, a solemn attempt is made in this paper to investigate the response parameters, viz., Cutting force and Surface Roughness (Ra a by experimentation on EN 19 turning process. The Design of experiments is carried-out considering Taguchi Technique with four input parameters, namely, spindle speed, feed rate, and depth of cut, flow rate and insert nose radius .The experiments are conducted considering the above materials for L16 and then the impact of each parameter is estimated by ANOAVA. Then the regression analysis is carried-out to find the trend of the response of each material. This experimental study aims at taguchi method has been applied for finding the effect on surface roughness and cutting force by various process parameters. And after that we can easily find out that which parameter will be more affect.

Surface wave effects in the NEMO ocean model: Forced and coupled experiments

Science.gov (United States)

Breivik, Øyvind; Mogensen, Kristian; Bidlot, Jean-Raymond; Balmaseda, Magdalena Alonso; Janssen, Peter A. E. M.

2015-04-01

The NEMO general circulation ocean model is extended to incorporate three physical processes related to ocean surface waves, namely the surface stress (modified by growth and dissipation of the oceanic wavefield), the turbulent kinetic energy flux from breaking waves, and the Stokes-Coriolis force. Experiments are done with NEMO in ocean-only (forced) mode and coupled to the ECMWF atmospheric and wave models. Ocean-only integrations are forced with fields from the ERA-Interim reanalysis. All three effects are noticeable in the extratropics, but the sea-state-dependent turbulent kinetic energy flux yields by far the largest difference. This is partly because the control run has too vigorous deep mixing due to an empirical mixing term in NEMO. We investigate the relation between this ad hoc mixing and Langmuir turbulence and find that it is much more effective than the Langmuir parameterization used in NEMO. The biases in sea surface temperature as well as subsurface temperature are reduced, and the total ocean heat content exhibits a trend closer to that observed in a recent ocean reanalysis (ORAS4) when wave effects are included. Seasonal integrations of the coupled atmosphere-wave-ocean model consisting of NEMO, the wave model ECWAM, and the atmospheric model of ECMWF similarly show that the sea surface temperature biases are greatly reduced when the mixing is controlled by the sea state and properly weighted by the thickness of the uppermost level of the ocean model. These wave-related physical processes were recently implemented in the operational coupled ensemble forecast system of ECMWF.

Faraday forcing of high-temperature levitated liquid metal drops for the measurement of surface tension.

Science.gov (United States)

Brosius, Nevin; Ward, Kevin; Matsumoto, Satoshi; SanSoucie, Michael; Narayanan, Ranga

2018-01-01

In this work, a method for the measurement of surface tension using continuous periodic forcing is presented. To reduce gravitational effects, samples are electrostatically levitated prior to forcing. The method, called Faraday forcing, is particularly well suited for fluids that require high temperature measurements such as liquid metals where conventional surface tension measurement methods are not possible. It offers distinct advantages over the conventional pulse-decay analysis method when the sample viscosity is high or the levitation feedback control system is noisy. In the current method, levitated drops are continuously translated about a mean position at a small, constant forcing amplitude over a range of frequencies. At a particular frequency in this range, the drop suddenly enters a state of resonance, which is confirmed by large executions of prolate/oblate deformations about the mean spherical shape. The arrival at this resonant condition is a signature that the parametric forcing frequency is equal to the drop's natural frequency, the latter being a known function of surface tension. A description of the experimental procedure is presented. A proof of concept is given using pure Zr and a Ti 39.5 Zr 39.5 Ni 21 alloy as examples. The results compare favorably with accepted literature values obtained using the pulse-decay method.

On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration

International Nuclear Information System (INIS)

Kim, W J; Brown-Hayes, M; Brownell, J H; Dalvit, D A R; Onofrio, R

2009-01-01

We report on measurements of forces acting between two conducting surfaces in a spherical-plane configuration in the 35 nm-1 μm separation range. The measurements are obtained by performing electrostatic calibrations followed by a residuals analysis after subtracting the electrostatic-dependent component. We find in all runs optimal fitting of the calibrations for exponents smaller than the one predicted by electrostatics for an ideal sphere-plane geometry. We also find that the external bias potential necessary to minimize the electrostatic contribution depends on the sphere-plane distance. In spite of these anomalies, by implementing a parametrization-dependent subtraction of the electrostatic contribution we have found evidence for short-distance attractive forces of magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss the relevance of our findings in the more general context of Casimir-Lifshitz force measurements, with particular regard to the critical issues of the electrical and geometrical characterization of the involved surfaces.

Comparison of the lateral retention forces on sessile and pendant water drops on a solid surface

Science.gov (United States)

de la Madrid, Rafael; Whitehead, Taylor; Irwin, George M.

2015-06-01

We present a simple experiment that demonstrates how a water drop hanging from a Plexiglas surface (pendant drop) experiences a lateral retention force that is comparable to, and in some cases larger than, the lateral retention force on a drop resting on top of the surface (sessile drop). The experiment also affords a simple demonstration of the Coriolis effect in two dimensions.

Air–water interface of submerged superhydrophobic surfaces imaged by atomic force microscopy

Directory of Open Access Journals (Sweden)

Markus Moosmann

2017-08-01

Full Text Available Underwater air retention of superhydrophobic hierarchically structured surfaces is of increasing interest for technical applications. Persistent air layers (the Salvinia effect are known from biological species, for example, the floating fern Salvinia or the backswimmer Notonecta. The use of this concept opens up new possibilities for biomimetic technical applications in the fields of drag reduction, antifouling, anticorrosion and under water sensing. Current knowledge regarding the shape of the air–water interface is insufficient, although it plays a crucial role with regards to stability in terms of diffusion and dynamic conditions. Optical methods for imaging the interface have been limited to the micrometer regime. In this work, we utilized a nondynamic and nondestructive atomic force microscopy (AFM method to image the interface of submerged superhydrophobic structures with nanometer resolution. Up to now, only the interfaces of nanobubbles (acting almost like solids have been characterized by AFM at these dimensions. In this study, we show for the first time that it is possible to image the air–water interface of submerged hierarchically structured (micro-pillars surfaces by AFM in contact mode. By scanning with zero resulting force applied, we were able to determine the shape of the interface and thereby the depth of the water penetrating into the underlying structures. This approach is complemented by a second method: the interface was scanned with different applied force loads and the height for zero force was determined by linear regression. These methods open new possibilities for the investigation of air-retaining surfaces, specifically in terms of measuring contact area and in comparing different coatings, and thus will lead to the development of new applications.

Experimental Research and Mathematical Modeling of Parameters Effecting on Cutting Force and SurfaceRoughness in CNC Turning Process

Science.gov (United States)

Zeqiri, F.; Alkan, M.; Kaya, B.; Toros, S.

2018-01-01

In this paper, the effects of cutting parameters on cutting forces and surface roughness based on Taguchi experimental design method are determined. Taguchi L9 orthogonal array is used to investigate the effects of machining parameters. Optimal cutting conditions are determined using the signal/noise (S/N) ratio which is calculated by average surface roughness and cutting force. Using results of analysis, effects of parameters on both average surface roughness and cutting forces are calculated on Minitab 17 using ANOVA method. The material that was investigated is Inconel 625 steel for two cases with heat treatment and without heat treatment. The predicted and calculated values with measurement are very close to each other. Confirmation test of results showed that the Taguchi method was very successful in the optimization of machining parameters for maximum surface roughness and cutting forces in the CNC turning process.

The study of dynamic force acted on water strider leg departing from water surface

Science.gov (United States)

Sun, Peiyuan; Zhao, Meirong; Jiang, Jile; Zheng, Yelong

2018-01-01

Water-walking insects such as water striders can skate on the water surface easily with the help of the hierarchical structure on legs. Numerous theoretical and experimental studies show that the hierarchical structure would help water strider in quasi-static case such as load-bearing capacity. However, the advantage of the hierarchical structure in the dynamic stage has not been reported yet. In this paper, the function of super hydrophobicity and the hierarchical structure was investigated by measuring the adhesion force of legs departing from the water surface at different lifting speed by a dynamic force sensor. The results show that the adhesion force decreased with the increase of lifting speed from 0.02 m/s to 0.4 m/s, whose mechanic is investigated by Energy analysis. In addition, it can be found that the needle shape setae on water strider leg can help them depart from water surface easily. Thus, it can serve as a starting point to understand how the hierarchical structure on the legs help water-walking insects to jump upward rapidly to avoid preying by other insects.

Simulated non-contact atomic force microscopy for GaAs surfaces based on real-space pseudopotentials

International Nuclear Information System (INIS)

Kim, Minjung; Chelikowsky, James R.

2014-01-01

We simulate non-contact atomic force microscopy (AFM) with a GaAs(1 1 0) surface using a real-space ab initio pseudopotential method. While most ab initio simulations include an explicit model for the AFM tip, our method does not introduce the tip modeling step. This approach results in a considerable reduction of computational work, and also provides complete AFM images, which can be directly compared to experiment. By analyzing tip-surface interaction forces in both our results and previous ab initio simulations, we find that our method provides very similar force profile to the pure Si tip results. We conclude that our method works well for systems in which the tip is not chemically active.

Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations Part I: Surface fluxes

Directory of Open Access Journals (Sweden)

P. Josse

1999-04-01

Full Text Available A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm-2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer

Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations Part I: Surface fluxes

Directory of Open Access Journals (Sweden)

H. Giordani

Full Text Available A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm-2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer

Low Temperature Scanning Force Microscopy of the Si(111)-( 7x7) Surface

International Nuclear Information System (INIS)

Lantz, M. A.; Hug, H. J.; Schendel, P. J. A. van; Hoffmann, R.; Martin, S.; Baratoff, A.; Abdurixit, A.; Guentherodt, H.-J.; Gerber, Ch.

2000-01-01

A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)-(7x7) surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few Angstrom of the surface. (c) 2000 The American Physical Society

Fabrication and properties of dual-level hierarchical structures mimicking gecko foot hairs.

Science.gov (United States)

Zhang, Peng; Liu, Shiyuan; Lv, Hao

2013-02-01

In nature, geckos have extraordinary adhesive capabilities. The multi-scale hierarchical structure of the gecko foot hairs, especially the high-aspect-ratio structure of its micro-scale seta and nano-scale spatulae is the critical factor of the gecko's ability to adopt and stick to any different surface with powerful adhesion force. In this paper, we present a simple and effective approach to fabricate dual-level hierarchical structures mimicking gecko foot hairs. Polydimethyl-siloxane (PDMS) hierarchical arrays were fabricated by demolding from a double stack mold that was composed of an SU-8 mold by thick film photolithography and a silicon mold by inductively coupled plasma (ICP) etching. Top pillars of the fabricated structures have 3 micom diameter and 18 microm in height, while base pillars have 25 microm diameter and 40 microm in height. The water droplet contact angle tests indicate that the hierarchical structures increase the hydrophobic property significantly compared with the single-level arrays and the unstructured polymers, exhibiting superhydrophobicity (154.2 degrees) like the Tokay gecko's (160.9 degrees). The shear force tests show that the top pillars make attachment through side contact with a value of about 0.25 N/cm2, and moreover, the hierarchical structures are demonstrated to be more suitable for contacting with rough surfaces.

Direct measurements of intermolecular forces by chemical force microscopy

Science.gov (United States)

Vezenov, Dmitri Vitalievich

1999-12-01

Detailed description of intermolecular forces is key to understanding a wide range of phenomena from molecular recognition to materials failure. The unique features of atomic force microscopy (AFM) to make point contact force measurements with ultra high sensitivity and to generate spatial maps of surface topography and forces have been extended to include measurements between well-defined organic molecular groups. Chemical modification of AFM probes with self-assembled monolayers (SAMs) was used to make them sensitive to specific molecular interactions. This novel chemical force microscopy (CFM) technique was used to probe forces between different molecular groups in a range of environments (vacuum, organic liquids and aqueous solutions); measure surface energetics on a nanometer scale; determine pK values of the surface acid and base groups; measure forces to stretch and unbind a short synthetic DNA duplex and map the spatial distribution of specific functional groups and their ionization state. Studies of adhesion forces demonstrated the important contribution of hydrogen bonding to interactions between simple organic functionalities. The chemical identity of the tip and substrate surfaces as well as the medium had a dramatic effect on adhesion between model monolayers. A direct correlation between surface free energy and adhesion forces was established. The adhesion between epoxy polymer and model mixed SAMs varied with the amount of hydrogen bonding component in the monolayers. A consistent interpretation of CFM measurements in polar solvents was provided by contact mechanics models and intermolecular force components theory. Forces between tips and surfaces functionalized with SAMs terminating in acid or base groups depended on their ionization state. A novel method of force titration was introduced for highly local characterization of the pK's of surface functional groups. The pH-dependent changes in friction forces were exploited to map spatially the

Potential dependent adhesion forces on bare and underpotential deposition modified electrode surfaces

Energy Technology Data Exchange (ETDEWEB)

Serafin, J.M.; Hsieh, S.J.; Monahan, J.; Gewirth, A.A. [Univ. of Illinois, Urbana, IL (United States)

1998-12-03

Adhesion force measurements are used to determine the potential dependence of the force of adhesion between a Si{sub 3}N{sub 4} cantilever and a Au(111) surface modified by the underpotential deposition (upd) of Bi or Cu in acid solution or by oxide formation. The measured work of adhesion is near zero for most of the potential region examined in Bi upd but rises after the formation of a full Bi monolayer. The work of adhesion is high at positive potentials for Cu upd but then decreases as the Cu partial and full monolayers are formed. The work of adhesion is low in the oxide region on Au(111) but rises following the sulfate disordering transition at 1.1 V vs NHE. These results are interpreted in terms of the degree of solvent order on the electrode surface.

Corrected direct force balance method for atomic force microscopy lateral force calibration

International Nuclear Information System (INIS)

Asay, David B.; Hsiao, Erik; Kim, Seong H.

2009-01-01

This paper reports corrections and improvements of the previously reported direct force balance method (DFBM) developed for lateral calibration of atomic force microscopy. The DFBM method employs the lateral force signal obtained during a force-distance measurement on a sloped surface and relates this signal to the applied load and the slope of the surface to determine the lateral calibration factor. In the original publication [Rev. Sci. Instrum. 77, 043903 (2006)], the tip-substrate contact was assumed to be pinned at the point of contact, i.e., no slip along the slope. In control experiments, the tip was found to slide along the slope during force-distance curve measurement. This paper presents the correct force balance for lateral force calibration.

Atomic force microscopy-based repeated machining theory for nanochannels on silicon oxide surfaces

Energy Technology Data Exchange (ETDEWEB)

Wang, Z.Q., E-mail: wangzhiqian@sia.cn [State Key Laboratory of Robotics, Shenyang Institute of Automation, CAS, Shenyang 110016 (China); Graduate University of the Chinese Academy of Sciences, Beijing 100049 (China); Jiao, N.D. [State Key Laboratory of Robotics, Shenyang Institute of Automation, CAS, Shenyang 110016 (China); Tung, S. [Department of Mechanical Engineering, University of Arkansas, Fayetteville, AR 72701 (United States); Dong, Z.L. [State Key Laboratory of Robotics, Shenyang Institute of Automation, CAS, Shenyang 110016 (China)

2011-02-01

The atomic force microscopy (AFM)-based repeated nanomachining of nanochannels on silicon oxide surfaces is investigated both theoretically and experimentally. The relationships of the initial nanochannel depth vs. final nanochannel depth at a normal force are systematically studied. Using the derived theory and simulation results, the final nanochannel depth can be predicted easily. Meanwhile, if a nanochannel with an expected depth needs to be machined, a right normal force can be selected simply and easily in order to decrease the wear of the AFM tip. The theoretical analysis and simulation results can be effectively used for AFM-based fabrication of nanochannels.

Analysis of cutting force signals by wavelet packet transform for surface roughness monitoring in CNC turning

Science.gov (United States)

García Plaza, E.; Núñez López, P. J.

2018-01-01

On-line monitoring of surface finish in machining processes has proven to be a substantial advancement over traditional post-process quality control techniques by reducing inspection times and costs and by avoiding the manufacture of defective products. This study applied techniques for processing cutting force signals based on the wavelet packet transform (WPT) method for the monitoring of surface finish in computer numerical control (CNC) turning operations. The behaviour of 40 mother wavelets was analysed using three techniques: global packet analysis (G-WPT), and the application of two packet reduction criteria: maximum energy (E-WPT) and maximum entropy (SE-WPT). The optimum signal decomposition level (Lj) was determined to eliminate noise and to obtain information correlated to surface finish. The results obtained with the G-WPT method provided an in-depth analysis of cutting force signals, and frequency ranges and signal characteristics were correlated to surface finish with excellent results in the accuracy and reliability of the predictive models. The radial and tangential cutting force components at low frequency provided most of the information for the monitoring of surface finish. The E-WPT and SE-WPT packet reduction criteria substantially reduced signal processing time, but at the expense of discarding packets with relevant information, which impoverished the results. The G-WPT method was observed to be an ideal procedure for processing cutting force signals applied to the real-time monitoring of surface finish, and was estimated to be highly accurate and reliable at a low analytical-computational cost.

Transport and diffusion on crystalline surfaces under external forces

International Nuclear Information System (INIS)

Lindenberg, Katja; Lacasta, A M; Sancho, J M; Romero, A H

2005-01-01

We present a numerical study of classical particles obeying a Langevin equation and moving on a solid crystalline surface under an external force that may either be constant or modulated by periodic oscillations. We focus on the particle drift velocity and diffusion. The roles of friction and equilibrium thermal fluctuations are studied for two nonlinear dynamical regimes corresponding to low and to high but finite friction. We identify a number of resonances and antiresonances, and provide phenomenological interpretations of the observed behaviour

The study of dynamic force acted on water strider leg departing from water surface

Directory of Open Access Journals (Sweden)

Peiyuan Sun

2018-01-01

Full Text Available Water-walking insects such as water striders can skate on the water surface easily with the help of the hierarchical structure on legs. Numerous theoretical and experimental studies show that the hierarchical structure would help water strider in quasi-static case such as load-bearing capacity. However, the advantage of the hierarchical structure in the dynamic stage has not been reported yet. In this paper, the function of super hydrophobicity and the hierarchical structure was investigated by measuring the adhesion force of legs departing from the water surface at different lifting speed by a dynamic force sensor. The results show that the adhesion force decreased with the increase of lifting speed from 0.02 m/s to 0.4 m/s, whose mechanic is investigated by Energy analysis. In addition, it can be found that the needle shape setae on water strider leg can help them depart from water surface easily. Thus, it can serve as a starting point to understand how the hierarchical structure on the legs help water-walking insects to jump upward rapidly to avoid preying by other insects.

Nonlinear dynamic response of cantilever beam tip during atomic force microscopy (AFM) nanolithography of copper surface

International Nuclear Information System (INIS)

Yeh, Y-L; Jang, M-J; Wang, C-C; Lin, Y-P; Chen, K-S

2008-01-01

This paper investigates the nonlinear dynamic response of an atomic force microscope (AFM) cantilever beam tip during the nanolithography of a copper (Cu) surface using a high-depth feed. The dynamic motion of the tip is modeled using a combined approach based on Newton's law and empirical observations. The cutting force is determined from experimental observations of the piling height on the Cu surface and the rotation angle of the cantilever beam tip. It is found that the piling height increases linearly with the cantilever beam carrier velocity. Furthermore, the cantilever beam tip is found to execute a saw tooth motion. Both this motion and the shear cutting force are nonlinear. The elastic modulus in the y direction is variable. Finally, the velocity of the cantilever beam tip as it traverses the specimen surface has a discrete characteristic rather than a smooth, continuous profile

The influence of Southern Ocean surface buoyancy forcing on glacial-interglacial changes in the global deep ocean stratification

OpenAIRE

Sun, S; Eisenman, I; Stewart, AL

2016-01-01

©2016. American Geophysical Union. All Rights Reserved. Previous studies have suggested that the global ocean density stratification below ∼3000 m is approximately set by its direct connection to the Southern Ocean surface density, which in turn is constrained by the atmosphere. Here the role of Southern Ocean surface forcing in glacial-interglacial stratification changes is investigated using a comprehensive climate model and an idealized conceptual model. Southern Ocean surface forcing is f...

An analytical model for force prediction in ball nose micro milling of inclined surfaces

DEFF Research Database (Denmark)

Bissacco, Giuliano; Hansen, Hans Nørgaard; De Chiffre, Leonardo

2010-01-01

Ball nose micro milling is a key process for the generation of free form surfaces and inclined surfaces often present in mould inserts for micro replication. This paper presents a new cutting force model for ball nose micro milling that is capable of taking into account the effect of the edge...

The correlation between surface electromyography and bite force of mastication muscles in Asian young adults.

Science.gov (United States)

Yen, Cheng-I; Mao, Shih-Hsuan; Chen, Chih-Hao; Chen, Chien-Tzung; Lee, Ming-Yih

2015-05-01

Mastication function is related to mandible movement, muscle strength, and bite force. No standard device for measuring bite force has been developed. A linear relationship between electromyographic activity and bite force has been reported by several investigators, but data on the reliability of this relationship remain limited in Asian young adults. The purpose of this study was to develop a clinically applicable, reliable, quantitative, and noninvasive system to measure the kinetic mastication function and observe the correlation between surface electromyography (sEMG) and bite force. The study group consisted of 41 young healthy adults (24 men and 17 women). Surface electromyography was used to evaluate bilateral temporalis and masseter muscle activities, and an occlusal bite force system was used concurrently to measure the bite force during maximal voluntary biting. Bilateral symmetry was compared, and the correlation between EMG and bite force was calculated. The sEMG signals were 107.7±55.0 μV and 106.0±56.0 μV (P=0.699) on right and left temporalis muscles and 183.7±86.2 μV and 194.8±94.3 μV (P=0.121) on right and left masseter muscles, respectively. The bite force was 5.0±3.2 kg on the right side and 5.7±4.0 kg on the left side (P=0.974). A positive correlation between sEMG and bite force was observed. The correlation coefficient between the temporalis muscle and bite force was 0.512, and that between the masseter muscle and bite force was 0.360. No significant difference between the bilateral electromyographic activities of the temporalis and masseter muscles and bilateral bite force was observed in young healthy adults in Taiwan. A positive correlation between sEMG signals and bite force was noted. By combining sEMG and bite force, we developed a clinically applicable, quantitative, reliable, and noninvasive system for evaluating mastication function by using characteristics of biofeedback.

Generating Converged Accurate Free Energy Surfaces for Chemical Reactions with a Force-Matched Semiempirical Model.

Science.gov (United States)

Kroonblawd, Matthew P; Pietrucci, Fabio; Saitta, Antonino Marco; Goldman, Nir

2018-04-10

We demonstrate the capability of creating robust density functional tight binding (DFTB) models for chemical reactivity in prebiotic mixtures through force matching to short time scale quantum free energy estimates. Molecular dynamics using density functional theory (DFT) is a highly accurate approach to generate free energy surfaces for chemical reactions, but the extreme computational cost often limits the time scales and range of thermodynamic states that can feasibly be studied. In contrast, DFTB is a semiempirical quantum method that affords up to a thousandfold reduction in cost and can recover DFT-level accuracy. Here, we show that a force-matched DFTB model for aqueous glycine condensation reactions yields free energy surfaces that are consistent with experimental observations of reaction energetics. Convergence analysis reveals that multiple nanoseconds of combined trajectory are needed to reach a steady-fluctuating free energy estimate for glycine condensation. Predictive accuracy of force-matched DFTB is demonstrated by direct comparison to DFT, with the two approaches yielding surfaces with large regions that differ by only a few kcal mol -1 .

Atomic force microscopy of surface topography of nitrogen plasma treated steel

CERN Document Server

Mahboubi, F

2002-01-01

Nitriding of steels, using plasma environments has been practiced for many years. A lot of efforts have been put on developing new methods, such as plasma immersion ion implantation (Pl sup 3) and radio frequency (RF) plasma nitriding, for mass transfer of nitrogen into the surface of the work piece. This article presents the results obtained from an in depth investigation of the surface morphology of the treated samples, carried out using an atomic force microscope. Samples from a microalloyed steel, were treated by both methods for 5 hours at different temperatures ranging from 350 to 550 sup d eg sup C in 75% N sub 2 -25% H sub 2 atmosphere. It has been found that the surface of the samples treated by PI sup 3 technique, although having more favorable properties, were rougher than the surfaces treated by RF plasma nitriding.

Aerosol Direct Radiative Forcing and Forcing Efficiencies at Surface from the shortwave Irradiance Measurements in Abu Dhabi, UAE

Science.gov (United States)

Beegum S, N.; Ben Romdhane, H.; Ghedira, H.

2013-12-01

Atmospheric aerosols are known to affect the radiation balance of the Earth-Atmospheric system directly by scattering and absorbing the solar and terrestrial radiation, and indirectly by affecting the lifetime and albedo of the clouds. Continuous and simultaneous measurements of short wave global irradiance in combination with synchronous spectral aerosol optical depth (AOD) measurements (from 340 nm to 1640 nm in 8 channels), for a period of 1 year from June 2012 to May 2013, were used for the determination of the surface direct aerosol radiative forcing and forcing efficiencies under cloud free conditions in Abu Dhabi (24.42°N, 54.61o E, 7m MSL), a coastal location in United Arab Emirates (UAE) in the Arabian Peninsula. The Rotating Shadow band Pyranometer (RSP, LI-COR) was used for the irradiance measurements (in the spectral region 400-1100 nm), whereas the AOD measurements were carried out using CIMEL Sunphotometer (CE 318-2, under AERONET program). The differential method, which is neither sensitive to calibration uncertainties nor model assumptions, has been employed for estimating forcing efficiencies from the changes in the measured fluxes. The forcing efficiency, which quantifies the net change in irradiance per unit change in AOD, is an appropriate parameter for the characterization of the aerosol radiative effects even if the microphysical and optical properties of the aerosols are not completely understood. The corresponding forcing values were estimated from the forcing efficiencies. The estimated radiative forcing and forcing efficiencies exhibited strong monthly variations. The forcing efficiencies (absolute magnitudes) were highest during March, and showed continuous decrease thereafter to reach the lowest value during September. In contrast, the forcing followed a slightly different pattern of variability, with the highest solar dimming during April ( -60 W m-2) and the minimum during February ( -20 W m-2). The results indicate that the aerosol

A global limit load solution for plates with surface cracks under combined end force and cross-thickness bending

International Nuclear Information System (INIS)

Lei Yuebao; Fox, Mike J.H.

2011-01-01

A global limit load solution for rectangular surface cracks in plates under combined end force and cross-thickness bending is derived, which allows any combination of positive/negative end force and positive/negative cross-thickness moment. The solution is based on the net-section plastic collapse concept and, therefore, gives limit load values based on the Tresca yielding criterion. Solutions for both cases with and without crack face contact are derived when whole or part of the crack is located in the compressive stress zone. From the solution, particular global limit load solutions for plates with extended surface cracks and through-thickness cracks under the same loading conditions are obtained. The solution is consistent with the limit load solution for surface cracks in plates under combined tension and positive bending due to Goodall and Webster and Lei when both the applied end force and bending moment are positive. The solution reduces to the limit load solution for plain plates under combined end force and cross-thickness bending when the crack vanishes. - Highlights: → A global limit load solution for plates with surface cracks in plates is derived. → Combined positive/negative end force and positive/negative cross-thickness moment are considered. → The solution is based on the net-section plastic collapse concept.

Interfacial force measurements using atomic force microscopy

NARCIS (Netherlands)

Chu, L.

2018-01-01

Atomic Force Microscopy (AFM) can not only image the topography of surfaces at atomic resolution, but can also measure accurately the different interaction forces, like repulsive, adhesive and lateral existing between an AFM tip and the sample surface. Based on AFM, various extended techniques have

Fire-induced albedo change and surface radiative forcing in sub-Saharan Africa savanna ecosystems: Implications for the energy balance

Science.gov (United States)

Dintwe, Kebonye; Okin, Gregory S.; Xue, Yongkang

2017-06-01

Surface albedo is a critical parameter that controls surface energy balance. In dryland ecosystems, fires play a significant role in decreasing surface albedo, resulting in positive radiative forcing. Here we investigate the long-term effect of fire on surface albedo. We devised a method to calculate short-, medium-, and long-term effect of fire-induced radiative forcing and their relative effects on energy balance. We used Moderate Resolution Imaging Spectroradiometer (MODIS) data in our analysis, covering different vegetation classes in sub-Saharan Africa (SSA). Our analysis indicated that mean short-term fire-induced albedo change in SSA was -0.022, -0.035, and -0.041 for savannas, shrubland, and grasslands, respectively. At regional scale, mean fire-induced albedo change in savannas was -0.018 and -0.024 for northern sub-Saharan of Africa and the southern hemisphere Africa, respectively. The short-term mean fire-induced radiative forcing in burned areas in sub-Saharan Africa (SSA) was 5.41 W m-2, which contributed continental and global radiative forcings of 0.25 and 0.058 W m-2, respectively. The impact of fire in surface albedo has long-lasting effects that varies with vegetation type. The long-term energetic effects of fire-induced albedo change and associated radiative forcing were, on average, more than 19 times greater across SSA than the short-term effects, suggesting that fires exerted far more radiative forcing than previously thought. Taking into account the actual duration of fire's effect on surface albedo, we conclude that the contribution of SSA fires, globally and throughout the year, is 0.12 W m-2. These findings provide crucial information on possible impact of fire on regional climate variability.

Analytical Model of the Nonlinear Dynamics of Cantilever Tip-Sample Surface Interactions for Various Acoustic-Atomic Force Microscopies

Science.gov (United States)

Cantrell, John H., Jr.; Cantrell, Sean A.

2008-01-01

A comprehensive analytical model of the interaction of the cantilever tip of the atomic force microscope (AFM) with the sample surface is developed that accounts for the nonlinearity of the tip-surface interaction force. The interaction is modeled as a nonlinear spring coupled at opposite ends to linear springs representing cantilever and sample surface oscillators. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a standard iteration procedure. Solutions are obtained for the phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) techniques including force modulation microscopy, atomic force acoustic microscopy, ultrasonic force microscopy, heterodyne force microscopy, resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), and the commonly used intermittent contact mode (TappingMode) generally available on AFMs. The solutions are used to obtain a quantitative measure of image contrast resulting from variations in the Young modulus of the sample for the amplitude and phase images generated by the A-AFM techniques. Application of the model to RDF-AFUM and intermittent soft contact phase images of LaRC-cp2 polyimide polymer is discussed. The model predicts variations in the Young modulus of the material of 24 percent from the RDF-AFUM image and 18 percent from the intermittent soft contact image. Both predictions are in good agreement with the literature value of 21 percent obtained from independent, macroscopic measurements of sheet polymer material.

Surface capillary currents: Rediscovery of fluid-structure interaction by forced evolving boundary theory

Science.gov (United States)

Wang, Chunbai; Mitra, Ambar K.

2016-01-01

Any boundary surface evolving in viscous fluid is driven with surface capillary currents. By step function defined for the fluid-structure interface, surface currents are found near a flat wall in a logarithmic form. The general flat-plate boundary layer is demonstrated through the interface kinematics. The dynamics analysis elucidates the relationship of the surface currents with the adhering region as well as the no-slip boundary condition. The wall skin friction coefficient, displacement thickness, and the logarithmic velocity-defect law of the smooth flat-plate boundary-layer flow are derived with the advent of the forced evolving boundary method. This fundamental theory has wide applications in applied science and engineering.

Track sensitivity and the surface roughness measurements of CR-39 with atomic force microscope

CERN Document Server

Yasuda, N; Amemiya, K; Takahashi, H; Kyan, A; Ogura, K

1999-01-01

Atomic Force Microscope (AFM) has been applied to evaluate the surface roughness and the track sensitivity of CR-39 track detector. We experimentally confirmed the inverse correlation between the track sensitivity and the roughness of the detector surface after etching. The surface of CR-39 (CR-39 doped with antioxidant (HARZLAS (TD-1)) and copolymer of CR-39/NIPAAm (TNF-1)) with high sensitivity becomes rough by the etching, while the pure CR-39 (BARYOTRAK) with low sensitivity keeps its original surface clarity even for the long etching.

Investigation of integrin expression on the surface of osteoblast-like cells by atomic force microscopy

International Nuclear Information System (INIS)

Caneva Soumetz, Federico; Saenz, Jose F.; Pastorino, Laura; Ruggiero, Carmelina; Nosi, Daniele; Raiteri, Roberto

2010-01-01

The transforming growth factor β1 (TGF-β1) is a human cytokine which has been demonstrated to modulate cell surface integrin repertoire. In this work integrin expression in response to TGF-β1 stimulation has been investigated on the surface of human osteoblast-like cells. We used atomic force microscopy (AFM) and confocal laser scanning microscopy to assess integrin expression and to evaluate their distribution over the dorsal side of the plasma membrane. AFM probes have been covalently functionalised with monoclonal antibodies specific to the β1 integrin subunit. Force curves have been collected in order to obtain maps of the interaction between the immobilized antibody and the respective cell membrane receptors. Adhesion peaks have been automatically detected by means of an ad hoc developed data analysis software. The specificity of the detected interactions has been assessed by adding free antibody in the solution and monitoring the dramatic decrease in the recorded interactions. In addition, the effect of TGF-β1 treatment on both the fluorescence signal and the adhesion events has been tested. The level of expression of the β1 integrin subunit was enhanced by TGF-β1. As a further analysis, the adhesion force of the single living cells to the substrate was measured by laterally pushing the cell with the AFM tip and measuring the force necessary to displace it. The treatment with TGF-β1 resulted in a decrease of the cell/substrate adhesion force. Results obtained by AFM have been validated by confocal laser scanning microscopy thus demonstrating the high potential of the AFM technique for the investigation of cell surface receptors distribution and trafficking at the nanoscale.

Investigation of integrin expression on the surface of osteoblast-like cells by atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Caneva Soumetz, Federico [Department of Communication, Computer and System Sciences, University of Genova, Via Opera Pia, 13-16145 Genova (Italy); Saenz, Jose F. [Biophysical and Electronic Engineering Department, University of Genova, Via All' Opera Pia 11a, 16145 Genova (Italy); Pastorino, Laura; Ruggiero, Carmelina [Department of Communication, Computer and System Sciences, University of Genova, Via Opera Pia, 13-16145 Genova (Italy); Nosi, Daniele [Department of Anatomy, Histology and Forensic Medicine, Bio-photonic Laboratory, University of Florence, viale Morgagni, 85 Firenze, CAP 50134 Florence (Italy); Raiteri, Roberto, E-mail: rr@unige.it [Biophysical and Electronic Engineering Department, University of Genova, Via All' Opera Pia 11a, 16145 Genova (Italy)

2010-03-15

The transforming growth factor {beta}1 (TGF-{beta}1) is a human cytokine which has been demonstrated to modulate cell surface integrin repertoire. In this work integrin expression in response to TGF-{beta}1 stimulation has been investigated on the surface of human osteoblast-like cells. We used atomic force microscopy (AFM) and confocal laser scanning microscopy to assess integrin expression and to evaluate their distribution over the dorsal side of the plasma membrane. AFM probes have been covalently functionalised with monoclonal antibodies specific to the {beta}1 integrin subunit. Force curves have been collected in order to obtain maps of the interaction between the immobilized antibody and the respective cell membrane receptors. Adhesion peaks have been automatically detected by means of an ad hoc developed data analysis software. The specificity of the detected interactions has been assessed by adding free antibody in the solution and monitoring the dramatic decrease in the recorded interactions. In addition, the effect of TGF-{beta}1 treatment on both the fluorescence signal and the adhesion events has been tested. The level of expression of the {beta}1 integrin subunit was enhanced by TGF-{beta}1. As a further analysis, the adhesion force of the single living cells to the substrate was measured by laterally pushing the cell with the AFM tip and measuring the force necessary to displace it. The treatment with TGF-{beta}1 resulted in a decrease of the cell/substrate adhesion force. Results obtained by AFM have been validated by confocal laser scanning microscopy thus demonstrating the high potential of the AFM technique for the investigation of cell surface receptors distribution and trafficking at the nanoscale.

Effects of surface design on aerodynamic forces of iced bridge cables

DEFF Research Database (Denmark)

Koss, Holger

2014-01-01

In recent years the relevance of ice accretion for wind-induced vibration of structural bridge cables has been recognised and became a subject of research in bridge engineering. Full-scale monitoring and observation indicate that light precipitation at moderate low temperatures between zero and -...... influences the accretion of ice to an extent that the aerodynamic forces differ significantly amongst the designs. The experiments were conducted in a wind tunnel facility capable amongst others to simulate in-cloud icing conditions........ The determination of these force coefficients require a proper simulation of the ice layer occurring under the specific climatic conditions, favouring real ice accretion over simplified artificial reproduction. The work presented in this paper was performed to study whether the design of bridge cable surface...

Quantification of the lift height for magnetic force microscopy using 3D surface parameters

International Nuclear Information System (INIS)

Nenadovic, M.; Strbac, S.; Rakocevic, Z.

2010-01-01

In this work, the quantitative conditions for the lift height for imaging of the magnetic field using magnetic force microscopy (MFM) were optimized. A thin cobalt film deposited on a monocrystalline silicon (1 0 0) substrate with a thickness of 55 nm and a thin nickel film deposited on a glass with a thickness of 600 nm were used as samples. The topography of the surface was acquired by tapping mode atomic force microscopy (AFM), while MFM imaging was performed in the lift mode for various lift heights. It was determined that the sensitivity of the measurements was about 10% higher for images obtained at a scan angle of 90 o compared to a scan angle of 0 deg. Therefore, the three-dimensional surface texture parameters, i.e., average roughness, skewness, kurtosis and the bearing ratio, were determined in dependence on the lift height for a scan angle of 90 deg. The results of the analyses of the surface parameters showed that the influence of the substrate and its texture on the magnetic force image could be neglected for lift heights above 40 nm and that the upper lift height limit is 100 nm. It was determined that the optimal values of the lift heights were in the range from 60 to 80 nm, depending on the nature of the sample and on the type of the tip used.

Atomic forces between noble gas atoms, alkali ions, and halogen ions for surface interactions

Science.gov (United States)

Wilson, J. W.; Outlaw, R. A.; Heinbockel, J. H.

1988-01-01

The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base developed from analysis of the two-body potential data, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas surfaces and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

Multi-objective optimization of surface roughness, cutting forces, productivity and Power consumption when turning of Inconel 718

Directory of Open Access Journals (Sweden)

Hamid Tebassi

2016-01-01

Full Text Available Nickel based super alloys are excellent for several applications and mainly in structural components submitted to high temperatures owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability such as in cases of jet engine and gas turbine components. The current work presents the experimental investigations of the cutting parameters effects (cutting speed, depth of cut and feed rate on the surface roughness, cutting force components, productivity and power consumption during dry conditions in straight turning using coated carbide tool. The mathematical models for output parameters have been developed using Box-Behnken design with 15 runs and Box-Cox transformation was used for improving normality. The results of the analysis have shown that the surface finish was statistically sensitive to the feed rate and cutting speed with the contribution of 43.58% and 23.85% respectively, while depth of cut had the greatest effect on the evolution of cutting force components with the contribution of 79.87% for feed force, 66.92% for radial force and 66.26% for tangential force. Multi-objective optimization procedure allowed minimizing roughness Ra, cutting forces and power consumption and maximizing material removal rate using desirability approach.

Acid-base properties and the chemical imaging of surface-bound functional groups studied with scanning force microscopy

NARCIS (Netherlands)

van der Vegte, E.W.; Hadziioannou, G

1997-01-01

In this paper we present a scanning force microscopy (SFM) study on electrostatic and hydrogen-bonding interactions between chemically modified SFM probes and surface functional groups. pH-dependent adhesion force measurements in aqueous media between various ionizable functional groups showed a

Attractive forces between hydrophobic solid surfaces measured by AFM on the first approach in salt solutions and in the presence of dissolved gases.

Science.gov (United States)

Azadi, Mehdi; Nguyen, Anh V; Yakubov, Gleb E

2015-02-17

Interfacial gas enrichment of dissolved gases (IGE) has been shown to cover hydrophobic solid surfaces in water. The atomic force microscopy (AFM) data has recently been supported by molecular dynamics simulation. It was demonstrated that IGE is responsible for the unexpected stability and large contact angle of gaseous nanobubbles at the hydrophobic solid-water interface. Here we provide further evidence of the significant effect of IGE on an attractive force between hydrophobic solid surfaces in water. The force in the presence of dissolved gas, i.e., in aerated and nonaerated NaCl solutions (up to 4 M), was measured by the AFM colloidal probe technique. The effect of nanobubble bridging on the attractive force was minimized or eliminated by measuring forces on the first approach of the AFM probe toward the flat hydrophobic surface and by using high salt concentrations to reduce gas solubility. Our results confirm the presence of three types of forces, two of which are long-range attractive forces of capillary bridging origin as caused by either surface nanobubbles or gap-induced cavitation. The third type is a short-range attractive force observed in the absence of interfacial nanobubbles that is attributed to the IGE in the form of a dense gas layer (DGL) at hydrophobic surfaces. Such a force was found to increase with increasing gas saturation and to decrease with decreasing gas solubility.

Topography and Mechanical Property Mapping of International Simple Glass Surfaces with Atomic Force Microscopy

Energy Technology Data Exchange (ETDEWEB)

Pierce, Eric M [ORNL

2014-01-01

Quantitative Nanomechanical Peak Force (PF-QNM) TappingModeTM atomic force microscopy measurements are presented for the first time on polished glass surfaces. The PF-QNM technique allows for topography and mechanical property information to be measured simultaneously at each pixel. Results for the international simple glass which represents a simplified version of SON68 glass suggests an average Young s modulus of 78.8 15.1 GPa is within the experimental error of the modulus measured for SON68 glass (83.6 2 GPa) with conventional approaches. Application of the PF-QNM technique will be extended to in situ glass corrosion experiments with the goal of gaining atomic-scale insights into altered layer development by exploiting the mechanical property differences that exist between silica gel (e.g., altered layer) and pristine glass surface.

Control of thumb force using surface functional electrical stimulation and muscle load sharing

Science.gov (United States)

2013-01-01

Background Stroke survivors often have difficulties in manipulating objects with their affected hand. Thumb control plays an important role in object manipulation. Surface functional electrical stimulation (FES) can assist movement. We aim to control the 2D thumb force by predicting the sum of individual muscle forces, described by a sigmoidal muscle recruitment curve and a single force direction. Methods Five able bodied subjects and five stroke subjects were strapped in a custom built setup. The forces perpendicular to the thumb in response to FES applied to three thumb muscles were measured. We evaluated the feasibility of using recruitment curve based force vector maps in predicting output forces. In addition, we developed a closed loop force controller. Load sharing between the three muscles was used to solve the redundancy problem having three actuators to control forces in two dimensions. The thumb force was controlled towards target forces of 0.5 N and 1.0 N in multiple directions within the individual’s thumb work space. Hereby, the possibilities to use these force vector maps and the load sharing approach in feed forward and feedback force control were explored. Results The force vector prediction of the obtained model had small RMS errors with respect to the actual measured force vectors (0.22±0.17 N for the healthy subjects; 0.17±0.13 N for the stroke subjects). The stroke subjects showed a limited work range due to limited force production of the individual muscles. Performance of feed forward control without feedback, was better in healthy subjects than in stroke subjects. However, when feedback control was added performances were similar between the two groups. Feedback force control lead, especially for the stroke subjects, to a reduction in stationary errors, which improved performance. Conclusions Thumb muscle responses to FES can be described by a single force direction and a sigmoidal recruitment curve. Force in desired direction can be

Single molecule force measurements delineate salt, pH and surface effects on biopolymer adhesion

International Nuclear Information System (INIS)

Pirzer, T; Geisler, M; Hugel, T; Scheibel, T

2009-01-01

In this paper we probe the influence of surface properties, pH and salt on the adhesion of recombinant spider silk proteins onto solid substrates with single molecule force spectroscopy. A single engineered spider silk protein (monomeric C 16 or dimeric (QAQ) 8 NR3) is covalently bound with one end to an AFM tip, which assures long-time measurements for hours with one and the same protein. The tip with the protein is brought into contact with various substrates at various buffer conditions and then retracted to desorb the protein. We observe a linear dependence of the adhesion force on the concentration of three selected salts (NaCl, NaH 2 PO 4 and NaI) and a Hofmeister series both for anions and cations. As expected, the more hydrophobic C 16 shows a higher adhesion force than (QAQ) 8 NR3, and the adhesion force rises with the hydrophobicity of the substrate. Unexpected is the magnitude of the dependences—we never observe a change of more than 30%, suggesting a surprisingly well-regulated balance between dispersive forces, water-structure-induced forces as well as co-solute-induced forces in biopolymer adhesion

Single molecule force measurements delineate salt, pH and surface effects on biopolymer adhesion

Science.gov (United States)

Pirzer, T.; Geisler, M.; Scheibel, T.; Hugel, T.

2009-06-01

In this paper we probe the influence of surface properties, pH and salt on the adhesion of recombinant spider silk proteins onto solid substrates with single molecule force spectroscopy. A single engineered spider silk protein (monomeric C16 or dimeric (QAQ)8NR3) is covalently bound with one end to an AFM tip, which assures long-time measurements for hours with one and the same protein. The tip with the protein is brought into contact with various substrates at various buffer conditions and then retracted to desorb the protein. We observe a linear dependence of the adhesion force on the concentration of three selected salts (NaCl, NaH2PO4 and NaI) and a Hofmeister series both for anions and cations. As expected, the more hydrophobic C16 shows a higher adhesion force than (QAQ)8NR3, and the adhesion force rises with the hydrophobicity of the substrate. Unexpected is the magnitude of the dependences—we never observe a change of more than 30%, suggesting a surprisingly well-regulated balance between dispersive forces, water-structure-induced forces as well as co-solute-induced forces in biopolymer adhesion.

Cantilever contribution to the total electrostatic force measured with the atomic force microscope

International Nuclear Information System (INIS)

Guriyanova, Svetlana; Golovko, Dmytro S; Bonaccurso, Elmar

2010-01-01

The atomic force microscope (AFM) is a powerful tool for surface imaging at the nanometer scale and surface force measurements in the piconewton range. Among long-range surface forces, the electrostatic forces play a predominant role. They originate if the electric potentials of the substrate and of the tip of the AFM cantilever are different. A quantitative interpretation of the AFM signal is often difficult because it depends in a complicated fashion on the cantilever–tip–surface geometry. Since the electrostatic interaction is a long-range interaction, the cantilever, which is many microns from the surface, contributes to the total electrostatic force along with the tip. Here we present results of the electrostatic interaction between a conducting flat surface and horizontal or tilted cantilevers, with and without tips, at various distances from the surface. As addressed in a previous work, we show that the contribution of the cantilever to the overall force cannot be neglected. Based on a predictive model and on 3D confocal measurements, we discuss the influence of the tilting angle of the cantilever

Nonlocal and surface effects on the flutter instability of cantilevered nanotubes conveying fluid subjected to follower forces

Energy Technology Data Exchange (ETDEWEB)

Bahaadini, Reza [Department of Mechanical Engineering, Sirjan University of Technology, 78137-33385 Sirjan, Islamic Republic of Iran (Iran, Islamic Republic of); Hosseini, Mohammad, E-mail: hosseini@sirjantech.ac.ir [Department of Mechanical Engineering, Sirjan University of Technology, 78137-33385 Sirjan, Islamic Republic of Iran (Iran, Islamic Republic of); Jamalpoor, Ali [Department of Mechanical Engineering, Iran University of Science and Technology, Tehran, Islamic Republic of Iran (Iran, Islamic Republic of)

2017-03-15

On the basis of nonlocal elasticity theory, this paper studies the dynamic structural instability behavior of cantilever nanotubes conveying fluid incorporating end concentrated follower force and distributed tangential load, resting on the visco-Pasternak substrate. In order to improve the accuracy of the results, surface effects, i.e. surface elasticity and residual stresses are considered. Extended Hamilton’s principle is implemented to obtain the nonlocal governing partial differential equation and related boundary conditions. Then, the extended Galerkin technique is used to convert partial differential equations into a general set of ordinary differential equations. Numerical results are expressed to reveal the variations of the critical flow velocity for flutter phenomenon of cantilever nanotubes with the various values of nonlocal parameter, mass ratios, nanotubes thickness, surface effects, various parameters of the visco-Pasternak medium, constant follower force and distributed compressive tangential load. Some numerical results of this research illustrated that the values of critical flutter flow velocity and stable region increase by considering surface effects. Also, critical flutter flow velocity decreases towards zero by increasing the value of the distributed compressive tangential load and constant follower force.

Effect of Cutting Parameters on Thrust Force and Surface Roughness in Drilling of Al-2219/B4C/Gr Metal Matrix Composites

Science.gov (United States)

Ravindranath, V. M.; Basavarajappa, G. S. Shiva Shankar S.; Suresh, R.

2016-09-01

In aluminium matrix composites, reinforcement of hard ceramic particle present inside the matrix which causes tool wear, high cutting forces and poor surface finish during machining. This paper focuses on effect of cutting parameters on thrust force, surface roughness and burr height during drilling of MMCs. In the present work, discuss the influence of spindle speed and feed rate on drilling the pure base alloy (Al-2219), mono composite (Al- 2219+8% B4C) and hybrid composite (Al-2219+8%B4C+3%Gr). The composites were fabricated using liquid metallurgy route. The drilling experiments were conducted by CNC machine with TiN coated HSS tool, M42 (Cobalt grade) and carbide tools at various spindle speeds and feed rates. The thrust force, surface roughness and burr height of the drilled hole were investigated in mono composite and hybrid composite containing graphite particles, the experimental results show that the feed rate has more influence on thrust force and surface roughness. Lesser thrust force and discontinuous chips were produced during machining of hybrid composites when compared with mono and base alloy during drilling process. It is due to solid lubricant property of graphite which reduces the lesser thrust force, burr height and lower surface roughness. When machining with Carbide tool at low feed and high speeds good surface finish was obtained compared to other two types of cutting tool materials.

Force mapping on a partially H-covered Si(111)-(7x7) surface: Influence of tip and surface reactivity

Czech Academy of Sciences Publication Activity Database

Yurtsever, A.; Sugimoto, Y.; Tanaka, H.; Abe, M.; Morita, S.; Ondráček, Martin; Pou, P.; Pérez, R.; Jelínek, Pavel

2013-01-01

Roč. 87, č. 15 (2013), "155403-1"-"155403-10" ISSN 1098-0121 R&D Projects: GA ČR(CZ) GPP204/11/P578; GA ČR GAP204/10/0952; GA AV ČR IAA100100905 Grant - others:GA AV ČR(CZ) M100101207 Institutional support: RVO:68378271 Keywords : atomic force microscopy * DFT simulations * silicon surface * surface passivation * electrostatic interaction Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.664, year: 2013 http://link.aps.org/doi/10.1103/PhysRevB.87.155403

Communication: Contrasting effects of glycerol and DMSO on lipid membrane surface hydration dynamics and forces

Energy Technology Data Exchange (ETDEWEB)

Schrader, Alex M. [Department of Chemical Engineering, University of California, Santa Barbara, California 93106 (United States); Cheng, Chi-Yuan [Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States); Israelachvili, Jacob N. [Department of Chemical Engineering, University of California, Santa Barbara, California 93106 (United States); Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States); Materials Department, University of California, Santa Barbara, California 93106 (United States); Han, Songi [Department of Chemical Engineering, University of California, Santa Barbara, California 93106 (United States); Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States)

2016-07-28

Glycerol and dimethyl sulfoxide (DMSO) are commonly used cryoprotectants in cellular systems, but due to the challenges of measuring the properties of surface-bound solvent, fundamental questions remain regarding the concentration, interactions, and conformation of these solutes at lipid membrane surfaces. We measured the surface water diffusivity at gel-phase dipalmitoylphosphatidylcholine (DPPC) bilayer surfaces in aqueous solutions containing ≤7.5 mol. % of DMSO or glycerol using Overhauser dynamic nuclear polarization. We found that glycerol similarly affects the diffusivity of water near the bilayer surface and that in the bulk solution (within 20%), while DMSO substantially increases the diffusivity of surface water relative to bulk water. We compare these measurements of water dynamics with those of equilibrium forces between DPPC bilayers in the same solvent mixtures. DMSO greatly decreases the range and magnitude of the repulsive forces between the bilayers, whereas glycerol increases it. We propose that the differences in hydrogen bonding capability of the two solutes leads DMSO to dehydrate the lipid head groups, while glycerol affects surface hydration only as much as it affects the bulk water properties. The results suggest that the mechanism of the two most common cryoprotectants must be fundamentally different: in the case of DMSO by decoupling the solvent from the lipid surface, and in the case of glycerol by altering the hydrogen bond structure and intermolecular cohesion of the global solvent, as manifested by increased solvent viscosity.

A Facile All-Solution-Processed Surface with High Water Contact Angle and High Water Adhesive Force.

Science.gov (United States)

Chen, Mei; Hu, Wei; Liang, Xiao; Zou, Cheng; Li, Fasheng; Zhang, Lanying; Chen, Feiwu; Yang, Huai

2017-07-12

A series of sticky superhydrophobicity surfaces with high water contact angle and high water adhesive force is facilely prepared via an all-solution-processed method based on polymerization-induced phase separation between liquid crystals (LCs) and epoxy resin, which produces layers of epoxy microspheres (EMSs) with nanofolds on the surface of a substrate. The morphologies and size distributions of EMSs are confirmed by scanning electron microscopy. Results reveal that the obtained EMS coated-surface exhibits high apparent contact angle of 152.0° and high water adhesive force up to 117.6 μN. By varying the composition of the sample or preparing conditions, the sizes of the produced EMSs can be artificially regulated and, thus, control the wetting properties and water adhesive behaviors. Also, the sticky superhydrophobic surface exhibits excellent chemical stability, as well as long-term durability. Water droplet transportation experiments further prove that the as-made surface can be effectively used as a mechanical hand for water transportation applications. Based on this, it is believed that the simple method proposed in this paper will pave a new way for producing a sticky superhydrophobic surface and obtain a wide range of use.

Thermal desorption study of physical forces at the PTFE surface

Science.gov (United States)

Wheeler, D. R.; Pepper, S. V.

1987-01-01

Thermal desorption spectroscopy (TDS) of the polytetrafluoroethylene (PTFE) surface was successfully employed to study the possible role of physical forces in the enhancement of metal-PTFE adhesion by radiation. The thermal desorption spectra were analyzed without assumptions to yield the activation energy for desorption over a range of xenon coverage from less than 0.1 monolayer to more than 100 monolayers. For multilayer coverage, the desorption is zero-order with an activation energy equal to the sublimation energy of xenon. For submonolayer coverages, the order for desorption from the unirradiated PTFE surface is 0.73 and the activation energy for desorption is between 3.32 and 3.36 kcal/mol; less than the xenon sublimation energy. The effect of irradiation is to increase the activation energy for desorption to as high as 4 kcal/mol at low coverage.

Dynamic analysis of a hollow cylinder subject to a dual traveling force imposed on its inner surface

Science.gov (United States)

Lee, Sooyoung; Seok, Jongwon

2015-03-01

The dynamic behavior of a hollow cylinder under a dual traveling force applied to the inner surface is investigated in this study. The cylinder is constrained at both the top and bottom surfaces not to move in the length direction but free in other directions. And a dual force travels at a constant velocity along the length direction on the inner surface of the hollow cylinder. The resulting governing field equations and the associated boundary conditions are ruled by the general Hooke's law. Due to the nature of the field equations, proper adjoint system of equations and biorthogonality conditions were derived in a precise and detailed manner. To solve these field equations in this study, the method of separation of variable is used and the method of Fro¨benius is employed for the differential equations in the radial direction. Using the field equations, the eigenanalyses on both the original and its adjoint system were performed with great care, which results in the eigenfunction sets of both systems. The biorthogonality conditions were applied to the field equations to obtain the discretized equation for each mode. Using the solutions of the discretized equations that account for the boundary forcing terms, the critical speed for a dual traveling force for each mode could be computed.

Generation of synthetic surface electromyography signals under fatigue conditions for varying force inputs using feedback control algorithm.

Science.gov (United States)

Venugopal, G; Deepak, P; Ghosh, Diptasree M; Ramakrishnan, S

2017-11-01

Surface electromyography is a non-invasive technique used for recording the electrical activity of neuromuscular systems. These signals are random, complex and multi-component. There are several techniques to extract information about the force exerted by muscles during any activity. This work attempts to generate surface electromyography signals for various magnitudes of force under isometric non-fatigue and fatigue conditions using a feedback model. The model is based on existing current distribution, volume conductor relations, the feedback control algorithm for rate coding and generation of firing pattern. The result shows that synthetic surface electromyography signals are highly complex in both non-fatigue and fatigue conditions. Furthermore, surface electromyography signals have higher amplitude and lower frequency under fatigue condition. This model can be used to study the influence of various signal parameters under fatigue and non-fatigue conditions.

Density Functional Theory and Atomic Force Microscopy Study of Oleate Functioned on Siderite Surface

Directory of Open Access Journals (Sweden)

Lixia Li

2018-01-01

Full Text Available Efficiently discovering the interaction of the collector oleate and siderite is of great significance for understanding the inherent function of siderite weakening hematite reverse flotation. For this purpose, investigation of the adsorption behavior of oleate on siderite surface was performed by density functional theory (DFT calculations associating with atomic force microscopy (AFM imaging. The siderite crystal geometry was computationally optimized via convergence tests. Calculated results of the interaction energy and the Mulliken population verified that the collector oleate adsorbed on siderite surface and the covalent bond was established as a result of electrons transferring from O1 atoms (in oleate molecule to Fe1 atoms (in siderite lattice. Therefore, valence-electrons’ configurations of Fe1 and O1 changed into 3d6.514s0.37 and 2s1.832p4.73 from 3d6.214s0.31 and 2s1.83p4.88 correspondingly. Siderite surfaces with or without oleate functioned were examined with the aid of AFM imaging in PeakForce Tapping mode, and the functioned siderite surface was found to be covered by vesicular membrane matters with the average roughness of 16.4 nm assuring the oleate adsorption. These results contributed to comprehending the interaction of oleate and siderite.

Film Thickness Formation in Nanoscale due to Effects of Elastohydrodynamic, Electrostatic and Surface force of Solvation and Van der Waals

Directory of Open Access Journals (Sweden)

M.F. Abd Al-Samieh

2017-03-01

Full Text Available The mechanism of oil film with a thickness in the nanoscale is discussed in this paper. A polar lubricant of propylene carbonate is used as the intervening liquid between contiguous bodies in concentrated contacts. A pressure caused by the hydrodynamic viscous action in addition to double layer electrostatic force, Van der Waals inter-molecular forces, and solvation pressure due to inter-surface forces is considered in calculating the ultrathin lubricating films. The numerical solution has been carried out, using the Newton-Raphson iteration technique, applied for the convergence of the hydrodynamic pressure. The results show that, at separations beyond about five molecular diameters of the intervening liquid, the formation of a lubricant film thickness is governed by combined effects of viscous action and surface force of an attractive Van der Waals force and a repulsive double layer force. At smaller separations below about five molecular diameters of the intervening liquid, the effect of solvation force is dominant in determining the oil film thickness

Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

Energy Technology Data Exchange (ETDEWEB)

Wang, R.; Williams, C. C., E-mail: clayton@physics.utah.edu [Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112 (United States)

2015-09-15

Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

Mapping of Proteomic Composition on the Surfaces of Bacillus spores by Atomic Force Microscopy-based Immunolabeling

Energy Technology Data Exchange (ETDEWEB)

Plomp, M; Malkin, A J

2008-06-02

Atomic force microscopy provides a unique capability to image high-resolution architecture and structural dynamics of pathogens (e.g. viruses, bacteria and bacterial spores) at near molecular resolution in native conditions. Further development of atomic force microscopy in order to enable the correlation of pathogen protein surface structures with specific gene products is essential to understand the mechanisms of the pathogen life cycle. We have applied an AFM-based immunolabeling technique for the proteomic mapping of macromolecular structures through the visualization of the binding of antibodies, conjugated with nanogold particles, to specific epitopes on Bacillus spore surfaces. This information is generated while simultaneously acquiring the surface morphology of the pathogen. The immunospecificity of this labeling method was established through the utilization of specific polyclonal and monoclonal antibodies that target spore coat and exosporium epitopes of Bacillus atrophaeus and Bacillus anthracis spores.

Interaction force measurement between E. coli cells and nanoparticles immobilized surfaces by using AFM.

Science.gov (United States)

Zhang, Wen; Stack, Andrew G; Chen, Yongsheng

2011-02-01

To better understand environmental behaviors of nanoparticles (NPs), we used the atomic force microscopy (AFM) to measure interaction forces between E. coli cells and NPs immobilized on surfaces in an aqueous environment. The results showed that adhesion force strength was significantly influenced by particle size for both hematite (α-Fe(2)O(3)) and corundum (α-Al(2)O(3)) NPs whereas the effect on the repulsive force was not observed. The adhesion force decreased from 6.3±0.7nN to 0.8±0.4nN as hematite NPs increased from 26nm to 98nm in diameter. Corundum NPs exhibited a similar dependence of adhesion force on particle size. The Johnson-Kendall-Roberts (JKR) model was employed to estimate the contact area between E. coli cells and NPs, and based on the JKR model a new model that considers local effective contact area was developed. The prediction of the new model matched the size dependence of adhesion force in experimental results. Size effects on adhesion forces may originate from the difference in local effective contact areas as supported by our model. These findings provide fundamental information for interpreting the environmental behaviors and biological interactions of NPs, which barely have been addressed. Copyright © 2010 Elsevier B.V. All rights reserved.

Synthesis of ZnS nanoparticles on a solid surface: Atomic force microscopy study

International Nuclear Information System (INIS)

Yuan Huizhen; Lian Wenping; Song Yonghai; Chen Shouhui; Chen Lili; Wang Li

2010-01-01

In this work, zinc sulfide (ZnS) nanoparticles had been synthesized on DNA network/mica and mica surface, respectively. The synthesis was carried out by first dropping a mixture of zinc acetate and DNA on a mica surface for the formation of the DNA networks or zinc acetate solution on a mica surface, and subsequently transferring the sample into a heated thiourea solution. The Zn 2+ adsorbed on DNA network/mica or mica surface would react with S 2- produced from thiourea and form ZnS nanoparticles on these surfaces. X-ray diffraction and atomic force microscopy (AFM) were used to characterize the ZnS nanoparticles in detail. AFM results showed that ZnS nanoparticles distributed uniformly on the mica surface and deposited preferentially on DNA networks. It was also found that the size and density of ZnS nanoparticles could be effectively controlled by adjusting reaction temperature and the concentration of Zn 2+ or DNA. The possible growth mechanisms have been discussed in detail.

Sensitivity of Horn of Africa Rainfall to Regional Sea Surface Temperature Forcing

Directory of Open Access Journals (Sweden)

Zewdu T. Segele

2015-05-01

Full Text Available The Abdus Salam International Center for Theoretical Physics (ICTP version 4.4 Regional Climate Model (RegCM4 is used to investigate the rainfall response to cooler/warmer sea surface temperature anomaly (SSTA forcing in the Indian and Atlantic Oceans. The effect of SSTA forcing in a specific ocean basin is identified by ensemble, averaging 10 individual simulations in which a constant or linearly zonally varying SSTA is prescribed in individual basins while specifying the 1971–2000 monthly varying climatological sea surface temperature (SST across the remaining model domain. The nonlinear rainfall response to SSTA amplitude also is investigated by separately specifying +1K, +2K, and +4K SSTA forcing in the Atlantic and Indian Oceans. The simulation results show that warm SSTs over the entire Indian Ocean produce drier conditions across the larger Blue Nile catchment, whereas warming ≥ +2K generates large positive rainfall anomalies exceeding 10 mm·day−1 over drought prone regions of Northeastern Ethiopia. However, the June–September rainy season tends to be wetter (drier when the SST warming (cooling is limited to either the Northern or Southern Indian Ocean. Wet rainy seasons generally are characterized by deepening of the monsoon trough, east of 40°E, intensification of the Mascarene high, strengthening of the Somali low level jet and the tropical easterly jet, enhanced zonal and meridional vertically integrated moisture fluxes, and steeply vertically decreasing moist static energy. The opposite conditions hold for dry monsoon seasons.

Prediction of surface roughness in turning of Ti-6Al-4V using cutting parameters, forces and tool vibration

Science.gov (United States)

Sahu, Neelesh Kumar; Andhare, Atul B.; Andhale, Sandip; Raju Abraham, Roja

2018-04-01

Present work deals with prediction of surface roughness using cutting parameters along with in-process measured cutting force and tool vibration (acceleration) during turning of Ti-6Al-4V with cubic boron nitride (CBN) inserts. Full factorial design is used for design of experiments using cutting speed, feed rate and depth of cut as design variables. Prediction model for surface roughness is developed using response surface methodology with cutting speed, feed rate, depth of cut, resultant cutting force and acceleration as control variables. Analysis of variance (ANOVA) is performed to find out significant terms in the model. Insignificant terms are removed after performing statistical test using backward elimination approach. Effect of each control variables on surface roughness is also studied. Correlation coefficient (R2 pred) of 99.4% shows that model correctly explains the experiment results and it behaves well even when adjustment is made in factors or new factors are added or eliminated. Validation of model is done with five fresh experiments and measured forces and acceleration values. Average absolute error between RSM model and experimental measured surface roughness is found to be 10.2%. Additionally, an artificial neural network model is also developed for prediction of surface roughness. The prediction results of modified regression model are compared with ANN. It is found that RSM model and ANN (average absolute error 7.5%) are predicting roughness with more than 90% accuracy. From the results obtained it is found that including cutting force and vibration for prediction of surface roughness gives better prediction than considering only cutting parameters. Also, ANN gives better prediction over RSM models.

Surface topography characterization using an atomic force microscope mounted on a coordinate measuring machine

DEFF Research Database (Denmark)

De Chiffre, Leonardo; Hansen, H.N; Kofod, N

1999-01-01

The paper describes the construction, testing and use of an integrated system for topographic characterization of fine surfaces on parts having relatively big dimensions. An atomic force microscope (AFM) was mounted on a manual three-coordinate measuring machine (CMM) achieving free positioning o...

Hydrological assessment of atmospheric forcing uncertainty in the Euro-Mediterranean area using a land surface model

Science.gov (United States)

Gelati, Emiliano; Decharme, Bertrand; Calvet, Jean-Christophe; Minvielle, Marie; Polcher, Jan; Fairbairn, David; Weedon, Graham P.

2018-04-01

Physically consistent descriptions of land surface hydrology are crucial for planning human activities that involve freshwater resources, especially in light of the expected climate change scenarios. We assess how atmospheric forcing data uncertainties affect land surface model (LSM) simulations by means of an extensive evaluation exercise using a number of state-of-the-art remote sensing and station-based datasets. For this purpose, we use the CO2-responsive ISBA-A-gs LSM coupled with the CNRM version of the Total Runoff Integrated Pathways (CTRIP) river routing model. We perform multi-forcing simulations over the Euro-Mediterranean area (25-75.5° N, 11.5° W-62.5° E, at 0.5° resolution) from 1979 to 2012. The model is forced using four atmospheric datasets. Three of them are based on the ERA-Interim reanalysis (ERA-I). The fourth dataset is independent from ERA-Interim: PGF, developed at Princeton University. The hydrological impacts of atmospheric forcing uncertainties are assessed by comparing simulated surface soil moisture (SSM), leaf area index (LAI) and river discharge against observation-based datasets: SSM from the European Space Agency's Water Cycle Multi-mission Observation Strategy and Climate Change Initiative projects (ESA-CCI), LAI of the Global Inventory Modeling and Mapping Studies (GIMMS), and Global Runoff Data Centre (GRDC) river discharge. The atmospheric forcing data are also compared to reference datasets. Precipitation is the most uncertain forcing variable across datasets, while the most consistent are air temperature and SW and LW radiation. At the monthly timescale, SSM and LAI simulations are relatively insensitive to forcing uncertainties. Some discrepancies with ESA-CCI appear to be forcing-independent and may be due to different assumptions underlying the LSM and the remote sensing retrieval algorithm. All simulations overestimate average summer and early-autumn LAI. Forcing uncertainty impacts on simulated river discharge are

Surface kinetic roughening caused by dental erosion: An atomic force microscopy study

Science.gov (United States)

Quartarone, Eliana; Mustarelli, Piercarlo; Poggio, Claudio; Lombardini, Marco

2008-05-01

Surface kinetic roughening takes place both in case of growth and erosion processes. Teeth surfaces are eroded by contact with acid drinks, such as those used to supplement mineral salts during sporting activities. Calcium-phosphate based (CPP-ACP) pastes are known to reduce the erosion process, and to favour the enamel remineralization. In this study we used atomic force microscopy (AFM) to investigate the surface roughening during dental erosion, and the mechanisms at the basis of the protection role exerted by a commercial CPP-ACP paste. We found a statistically significant difference (p<0.01) in the roughness of surfaces exposed and not exposed to the acid solutions. The treatment with the CPP-ACP paste determined a statistically significant reduction of the roughness values. By interpreting the AFM results in terms of fractal scaling concepts and continuum stochastic equations, we showed that the protection mechanism of the paste depends on the chemical properties of the acid solution.

Theoretical Investigation of Hydrogen Adsorption and Dissociation on Iron and Iron Carbide Surfaces Using the ReaxFF Reactive Force Field Method

Energy Technology Data Exchange (ETDEWEB)

Zou, Chenyu; van Duin, Adri C.T.; Sorescu, Dan C.

2012-06-01

We have developed a ReaxFF reactive force field to describe hydrogen adsorption and dissociation on iron and iron carbide surfaces relevant for simulation of Fischer–Tropsch (FT) synthesis on iron catalysts. This force field enables large system (>>1000 atoms) simulations of hydrogen related reactions with iron. The ReaxFF force field parameters are trained against a substantial amount of structural and energetic data including the equations of state and heats of formation of iron and iron carbide related materials, as well as hydrogen interaction with iron surfaces and different phases of bulk iron. We have validated the accuracy and applicability of ReaxFF force field by carrying out molecular dynamics simulations of hydrogen adsorption, dissociation and recombination on iron and iron carbide surfaces. The barriers and reaction energies for molecular dissociation on these two types of surfaces have been compared and the effect of subsurface carbon on hydrogen interaction with iron surface is evaluated. We found that existence of carbon atoms at subsurface iron sites tends to increase the hydrogen dissociation energy barrier on the surface, and also makes the corresponding hydrogen dissociative state relatively more stable compared to that on bare iron. These properties of iron carbide will affect the dissociation rate of H{sub 2} and will retain more surface hydride species, thus influencing the dynamics of the FT synthesis process.

Reversible electrochemical modification of the surface of a semiconductor by an atomic-force microscope probe

Energy Technology Data Exchange (ETDEWEB)

Kozhukhov, A. S., E-mail: antonkozhukhov@yandex.ru; Sheglov, D. V.; Latyshev, A. V. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

2017-04-15

A technique for reversible surface modification with an atomic-force-microscope (AFM) probe is suggested. In this method, no significant mechanical or topographic changes occur upon a local variation in the surface potential of a sample under the AFM probe. The method allows a controlled relative change in the ohmic resistance of a channel in a Hall bridge within the range 20–25%.

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

Science.gov (United States)

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.

Nanoscale Surface Photovoltage Mapping of 2D Materials and Heterostructures by Illuminated Kelvin Probe Force Microscopy

KAUST Repository

Shearer, Melinda J.

2018-02-01

Nanomaterials are interesting for a variety of applications, such as optoelectronics and photovoltaics. However, they often have spatial heterogeneity, i.e. composition change or physical change in the topography or structure, which can lead to varying properties that would influence their applications. New techniques must be developed to understand and correlate spatial heterogeneity with changes in electronic properties. Here we highlight the technique of surface photovoltage-Kelvin probe force microscopy (SPV-KFM), which is a modified version of non-contact atomic force microscopy capable of imaging not only the topography and surface potential, but also the surface photovoltage on the nanoscale. We demonstrate its utility in probing monolayer WSe2-MoS2 lateral heterostructures, which form an ultrathin p-n junction promising for photovoltaic and optoelectronic applications. We show surface photovoltage maps highlighting the different photoresponse of the two material regions as a result of the effective charge separation across this junction. Additionally, we study the variations between different heterostructure flakes and emphasize the importance of controlling the synthesis and transfer of these materials to obtain consistent properties and measurements.

Nanoscale Surface Photovoltage Mapping of 2D Materials and Heterostructures by Illuminated Kelvin Probe Force Microscopy

KAUST Repository

Shearer, Melinda J.; Li, Ming-yang; Li, Lain-Jong; Jin, Song; Hamers, Robert J

2018-01-01

Nanomaterials are interesting for a variety of applications, such as optoelectronics and photovoltaics. However, they often have spatial heterogeneity, i.e. composition change or physical change in the topography or structure, which can lead to varying properties that would influence their applications. New techniques must be developed to understand and correlate spatial heterogeneity with changes in electronic properties. Here we highlight the technique of surface photovoltage-Kelvin probe force microscopy (SPV-KFM), which is a modified version of non-contact atomic force microscopy capable of imaging not only the topography and surface potential, but also the surface photovoltage on the nanoscale. We demonstrate its utility in probing monolayer WSe2-MoS2 lateral heterostructures, which form an ultrathin p-n junction promising for photovoltaic and optoelectronic applications. We show surface photovoltage maps highlighting the different photoresponse of the two material regions as a result of the effective charge separation across this junction. Additionally, we study the variations between different heterostructure flakes and emphasize the importance of controlling the synthesis and transfer of these materials to obtain consistent properties and measurements.

Uncertainties of Large-Scale Forcing Caused by Surface Turbulence Flux Measurements and the Impacts on Cloud Simulations at the ARM SGP Site

Science.gov (United States)

Tang, S.; Xie, S.; Tang, Q.; Zhang, Y.

2017-12-01

Two types of instruments, the eddy correlation flux measurement system (ECOR) and the energy balance Bowen ratio system (EBBR), are used at the Atmospheric Radiation Measurement (ARM) program Southern Great Plains (SGP) site to measure surface latent and sensible fluxes. ECOR and EBBR typically sample different land surface types, and the domain-mean surface fluxes derived from ECOR and EBBR are not always consistent. The uncertainties of the surface fluxes will have impacts on the derived large-scale forcing data and further affect the simulations of single-column models (SCM), cloud-resolving models (CRM) and large-eddy simulation models (LES), especially for the shallow-cumulus clouds which are mainly driven by surface forcing. This study aims to quantify the uncertainties of the large-scale forcing caused by surface turbulence flux measurements and investigate the impacts on cloud simulations using long-term observations from the ARM SGP site.

Imaging stability in force-feedback high-speed atomic force microscopy

International Nuclear Information System (INIS)

Kim, Byung I.; Boehm, Ryan D.

2013-01-01

We studied the stability of force-feedback high-speed atomic force microscopy (HSAFM) by imaging soft, hard, and biological sample surfaces at various applied forces. The HSAFM images showed sudden topographic variations of streaky fringes with a negative applied force when collected on a soft hydrocarbon film grown on a grating sample, whereas they showed stable topographic features with positive applied forces. The instability of HSAFM images with the negative applied force was explained by the transition between contact and noncontact regimes in the force–distance curve. When the grating surface was cleaned, and thus hydrophilic by removing the hydrocarbon film, enhanced imaging stability was observed at both positive and negative applied forces. The higher adhesive interaction between the tip and the surface explains the improved imaging stability. The effects of imaging rate on the imaging stability were tested on an even softer adhesive Escherichia coli biofilm deposited onto the grating structure. The biofilm and planktonic cell structures in HSAFM images were reproducible within the force deviation less than ∼0.5 nN at the imaging rate up to 0.2 s per frame, suggesting that the force-feedback HSAFM was stable for various imaging speeds in imaging softer adhesive biological samples. - Highlights: ► We investigated the imaging stability of force-feedback HSAFM. ► Stable–unstable imaging transitions rely on applied force and sample hydrophilicity. ► The stable–unstable transitions are found to be independent of imaging rate

Chemical Force Spectroscopy Evidence Supporting the Layer-by-Layer Model of Organic Matter Binding to Iron (oxy)Hydroxide Mineral Surfaces

KAUST Repository

Chassé , Alexander W.; Ohno, Tsutomu; Higgins, Steven R.; Amirbahman, Aria; Yildirim, Nadir; Parr, Thomas B.

2015-01-01

© 2015 American Chemical Society. The adsorption of dissolved organic matter (DOM) to metal (oxy)hydroxide mineral surfaces is a critical step for C sequestration in soils. Although equilibrium studies have described some of the factors controlling this process, the molecular-scale description of the adsorption process has been more limited. Chemical force spectroscopy revealed differing adhesion strengths of DOM extracted from three soils and a reference peat soil material to an iron (oxy)hydroxide mineral surface. The DOM was characterized using ultrahigh-resolution negative ion mode electrospray ionization Fourier Transform ion cyclotron resonance mass spectrometry. The results indicate that carboxyl-rich aromatic and N-containing aliphatic molecules of DOM are correlated with high adhesion forces. Increasing molecular mass was shown to decrease the adhesion force between the mineral surface and the DOM. Kendrick mass defect analysis suggests that mechanisms involving two carboxyl groups result in the most stable bond to the mineral surface. We conceptualize these results using a layer-by-layer "onion" model of organic matter stabilization on soil mineral surfaces.

Chemical Force Spectroscopy Evidence Supporting the Layer-by-Layer Model of Organic Matter Binding to Iron (oxy)Hydroxide Mineral Surfaces

KAUST Repository

Chassé, Alexander W.

2015-08-18

© 2015 American Chemical Society. The adsorption of dissolved organic matter (DOM) to metal (oxy)hydroxide mineral surfaces is a critical step for C sequestration in soils. Although equilibrium studies have described some of the factors controlling this process, the molecular-scale description of the adsorption process has been more limited. Chemical force spectroscopy revealed differing adhesion strengths of DOM extracted from three soils and a reference peat soil material to an iron (oxy)hydroxide mineral surface. The DOM was characterized using ultrahigh-resolution negative ion mode electrospray ionization Fourier Transform ion cyclotron resonance mass spectrometry. The results indicate that carboxyl-rich aromatic and N-containing aliphatic molecules of DOM are correlated with high adhesion forces. Increasing molecular mass was shown to decrease the adhesion force between the mineral surface and the DOM. Kendrick mass defect analysis suggests that mechanisms involving two carboxyl groups result in the most stable bond to the mineral surface. We conceptualize these results using a layer-by-layer "onion" model of organic matter stabilization on soil mineral surfaces.

Development of a classical force field for the oxidized Si surface: application to hydrophilic wafer bonding.

Science.gov (United States)

Cole, Daniel J; Payne, Mike C; Csányi, Gábor; Spearing, S Mark; Colombi Ciacchi, Lucio

2007-11-28

We have developed a classical two- and three-body interaction potential to simulate the hydroxylated, natively oxidized Si surface in contact with water solutions, based on the combination and extension of the Stillinger-Weber potential and of a potential originally developed to simulate SiO(2) polymorphs. The potential parameters are chosen to reproduce the structure, charge distribution, tensile surface stress, and interactions with single water molecules of a natively oxidized Si surface model previously obtained by means of accurate density functional theory simulations. We have applied the potential to the case of hydrophilic silicon wafer bonding at room temperature, revealing maximum room temperature work of adhesion values for natively oxidized and amorphous silica surfaces of 97 and 90 mJm(2), respectively, at a water adsorption coverage of approximately 1 ML. The difference arises from the stronger interaction of the natively oxidized surface with liquid water, resulting in a higher heat of immersion (203 vs 166 mJm(2)), and may be explained in terms of the more pronounced water structuring close to the surface in alternating layers of larger and smaller densities with respect to the liquid bulk. The computed force-displacement bonding curves may be a useful input for cohesive zone models where both the topographic details of the surfaces and the dependence of the attractive force on the initial surface separation and wetting can be taken into account.

Observational determination of surface radiative forcing by CO2 from 2000 to 2010.

Science.gov (United States)

Feldman, D R; Collins, W D; Gero, P J; Torn, M S; Mlawer, E J; Shippert, T R

2015-03-19

The climatic impact of CO2 and other greenhouse gases is usually quantified in terms of radiative forcing, calculated as the difference between estimates of the Earth's radiation field from pre-industrial and present-day concentrations of these gases. Radiative transfer models calculate that the increase in CO2 since 1750 corresponds to a global annual-mean radiative forcing at the tropopause of 1.82 ± 0.19 W m(-2) (ref. 2). However, despite widespread scientific discussion and modelling of the climate impacts of well-mixed greenhouse gases, there is little direct observational evidence of the radiative impact of increasing atmospheric CO2. Here we present observationally based evidence of clear-sky CO2 surface radiative forcing that is directly attributable to the increase, between 2000 and 2010, of 22 parts per million atmospheric CO2. The time series of this forcing at the two locations-the Southern Great Plains and the North Slope of Alaska-are derived from Atmospheric Emitted Radiance Interferometer spectra together with ancillary measurements and thoroughly corroborated radiative transfer calculations. The time series both show statistically significant trends of 0.2 W m(-2) per decade (with respective uncertainties of ±0.06 W m(-2) per decade and ±0.07 W m(-2) per decade) and have seasonal ranges of 0.1-0.2 W m(-2). This is approximately ten per cent of the trend in downwelling longwave radiation. These results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions, and provide empirical evidence of how rising CO2 levels, mediated by temporal variations due to photosynthesis and respiration, are affecting the surface energy balance.

Force reconstruction from tapping mode force microscopy experiments

International Nuclear Information System (INIS)

Payam, Amir F; Martin-Jimenez, Daniel; Garcia, Ricardo

2015-01-01

Fast, accurate, and robust nanomechanical measurements are intensely studied in materials science, applied physics, and molecular biology. Amplitude modulation force microscopy (tapping mode) is the most established nanoscale characterization technique of surfaces for air and liquid environments. However, its quantitative capabilities lag behind its high spatial resolution and robustness. We develop a general method to transform the observables into quantitative force measurements. The force reconstruction algorithm has been deduced on the assumption that the observables (amplitude and phase shift) are slowly varying functions of the tip–surface separation. The accuracy and applicability of the method is validated by numerical simulations and experiments. The method is valid for liquid and air environments, small and large free amplitudes, compliant and rigid materials, and conservative and non-conservative forces. (paper)

Reductions in soil surface albedo as a function of biochar application rate: implications for global radiative forcing

International Nuclear Information System (INIS)

Verheijen, Frank G A; Bastos, Ana Catarina; Keizer, Jan Jacob; Jeffery, Simon; Van der Velde, Marijn; Penížek, Vít; Beland, Martin

2013-01-01

Biochar can be defined as pyrolysed (charred) biomass produced for application to soils with the aim of mitigating global climate change while improving soil functions. Sustainable biochar application to soils has been estimated to reduce global greenhouse gas emissions by 71–130 Pg CO 2 -C e over 100 years, indicating an important potential to mitigate climate change. However, these estimates ignored changes in soil surface reflection by the application of dark-coloured biochar. Through a laboratory experiment we show a strong tendency for soil surface albedo to decrease as a power decay function with increasing biochar application rate, depending on soil moisture content, biochar application method and land use. Surface application of biochar resulted in strong reductions in soil surface albedo even at relatively low application rates. As a first assessment of the implications for climate change mitigation of these biochar–albedo relationships, we applied a first order global energy balance model to compare negative radiative forcings (from avoided CO 2 emissions) with positive radiative forcings (from reduced soil surface albedos). For a global-scale biochar application equivalent to 120 t ha −1 , we obtained reductions in negative radiative forcings of 5 and 11% for croplands and 11 and 23% for grasslands, when incorporating biochar into the topsoil or applying it to the soil surface, respectively. For a lower global biochar application rate (equivalent to 10 t ha −1 ), these reductions amounted to 13 and 44% for croplands and 28 and 94% for grasslands. Thus, our findings revealed the importance of including changes in soil surface albedo in studies assessing the net climate change mitigation potential of biochar, and we discuss the urgent need for field studies and more detailed spatiotemporal modelling. (letter)

Origin of phase shift in atomic force microscopic investigation of the surface morphology of NR/NBR blend film

Energy Technology Data Exchange (ETDEWEB)

Thanawan, S. [Institute of Science and Technology for Research and Development, Mahidol University, Salaya, Nakhon Pathom 73170 (Thailand)], E-mail: ststw@mahidol.ac.th; Radabutra, S.; Thamasirianunt, P.; Amornsakchai, T.; Suchiva, K. [Department of Chemistry, Faculty of Science, Mahidol University, Salaya, Nakhon Pathom 73170 (Thailand)

2009-01-15

Atomic force microscopy (AFM) was used to study the morphology and surface properties of NR/NBR blend. Blends at 1/3, 1/1 and 3/1 weight ratios were prepared in benzene and formed film by casting. AFM phase images of these blends in tapping mode displayed islands in the sea morphology or matrix-dispersed structures. For blend 1/3, NR formed dispersed phase while in blends 1/1 and 3/1 phase inversion was observed. NR showed higher phase shift angle in AFM phase imaging for all blends. This circumstance was governed by adhesion energy hysteresis between the device tip and the rubber surface rather than surface stiffness of the materials, as proved by force distance measurements in the AFM contact mode.

Origin of phase shift in atomic force microscopic investigation of the surface morphology of NR/NBR blend film.

Science.gov (United States)

Thanawan, S; Radabutra, S; Thamasirianunt, P; Amornsakchai, T; Suchiva, K

2009-01-01

Atomic force microscopy (AFM) was used to study the morphology and surface properties of NR/NBR blend. Blends at 1/3, 1/1 and 3/1 weight ratios were prepared in benzene and formed film by casting. AFM phase images of these blends in tapping mode displayed islands in the sea morphology or matrix-dispersed structures. For blend 1/3, NR formed dispersed phase while in blends 1/1 and 3/1 phase inversion was observed. NR showed higher phase shift angle in AFM phase imaging for all blends. This circumstance was governed by adhesion energy hysteresis between the device tip and the rubber surface rather than surface stiffness of the materials, as proved by force distance measurements in the AFM contact mode.

Influence of the adhesion force crystal/heat exchanger surface on fouling mitigation

International Nuclear Information System (INIS)

Forster, M.; Augustin, W.; Bohnet, M.

1999-01-01

The accumulation of unwanted crystalline deposits (fouling) reduces the efficiency of heat exchangers considerably. In order to decrease the cost of fouling two strategies have been developed. The first fouling mitigation strategy is based on the modification of energy-and-geometry-related characteristics of the heat transfer surface to realize an increased duration of the induction period. By means of a drop-shape-analysis measurement device the interaction at the interface crystal/heat transfer surface is determined. The deployment of the fracture energy model and the interfacial defect model relates wetting characteristics to the adhesion phenomenon. Hence, a first estimation of the optimal choice of surface material is realized. Furthermore, the influence of surface topography on interfacial interactions has been analyzed. The second fouling mitigation strategy is based on the adjustment of the hydrodynamic flow conditions using a pulsation technique. Here, single strokes of higher velocity are superimposed on the stationary flow. These strokes shift the equilibrium of forces to an improved removal process. Fouling experiments have proved that pulsation is a powerful tool to mitigate the built-up of fouling layers on heat transfer surfaces. (author)

Localization of cesium on montmorillonite surface investigated by frequency modulation atomic force microscopy

Science.gov (United States)

Araki, Yuki; Satoh, Hisao; Okumura, Masahiko; Onishi, Hiroshi

2017-11-01

Cation exchange of clay mineral is typically analyzed without microscopic study of the clay surfaces. In order to reveal the distribution of exchangeable cations at the clay surface, we performed in situ atomic-scale observations of the surface changes in Na-rich montmorillonite due to exchange with Cs cations using frequency modulation atomic force microscopy (FM-AFM). Lines of protrusion were observed on the surface in aqueous CsCl solution. The amount of Cs of the montmorillonite particles analyzed by energy dispersive X-ray spectrometry was consistent with the ratio of the number of linear protrusions to all protrusions in the FM-AFM images. The results showed that the protrusions represent adsorbed Cs cations. The images indicated that Cs cations at the surface were immobile, and their occupancy remained constant at 10% of the cation sites at the surface with different immersion times in the CsCl solution. This suggests that the mobility and the number of Cs cations at the surface are controlled by the permanent charge of montmorillonite; however, the Cs distribution at the surface is independent of the charge distribution of the inner silicate layer. Our atomic-scale observations demonstrate that surface cations are distributed in different ways in montmorillonite and mica.

Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy.

Science.gov (United States)

Neff, Julia L; Milde, Peter; León, Carmen Pérez; Kundrat, Matthew D; Eng, Lukas M; Jacob, Christoph R; Hoffmann-Vogel, Regina

2014-04-22

In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces. We have found that, together with molecular islands of upright standing pentacene, a new phase of tilted molecules appears near step edges on KBr. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density functional theory calculations. Our images reveal that differently oriented molecules display different LCPD and that their value is independent of the number of molecular layers. These results point to the formation of an interface dipole, which may be explained by a partial charge transfer from the pentacene to the surface. Moreover, the monitoring of the evolution of the pentacene islands shows that they are strongly affected by dewetting: Multilayers build up at the expense of monolayers, and in the Kelvin images, previously unknown line defects appear, which reveal the epitaxial growth of pentacene crystals.

Reconstruction of the Tip-Surface Interaction Potential by Analysis of the Brownian Motion of an Atomic Force Microscope Tip

NARCIS (Netherlands)

Willemsen, O.H.; Kuipers, L.; van der Werf, Kees; de Grooth, B.G.; Greve, Jan

2000-01-01

The thermal movement of an atomic force microscope (AFM) tip is used to reconstruct the tip-surface interaction potential. If a tip is brought into the vicinity of a surface, its movement is governed by the sum of the harmonic cantilever potential and the tip-surface interaction potential. By

Enhanced solar evaporation of water from porous media, through capillary mediated forces and surface treatment

International Nuclear Information System (INIS)

Canbazoglu, F. M.; Fan, B.; Kargar, A.; Vemuri, K.; Bandaru, P. R.

2016-01-01

The relative influence of the capillary, Marangoni, and hydrophobic forces in mediating the evaporation of water from carbon foam based porous media, in response to incident solar radiation, are investigated. It is indicated that inducing hydrophilic interactions on the surface, through nitric acid treatment of the foams, has a similar effect to reduced pore diameter and the ensuing capillary forces. The efficiency of water evaporation may be parameterized through the Capillary number (Ca), with a lower Ca being preferred. The proposed study is of much relevance to efficient solar energy utilization.

Detachment of polystyrene particles from collector surfaces by surface tension forces induced by air-bubble passage through a parallel plate flow chamber

NARCIS (Netherlands)

Wit, PJ; vanderMei, HC; Busscher, HJ

1997-01-01

By allowing an air-bubble to pass through a parallel plate flow chamber with negatively charged, colloidal polystyrene particles adhering to the bottom collector plate of the chamber, the detachment of adhering particles stimulated by surface tension forces induced by the passage of a liquid-air

Surface forcing of non-stand-replacing fires in Siberian larch forests

Science.gov (United States)

Chen, Dong; Loboda, Tatiana V.

2018-04-01

Wildfires are the dominant disturbance agent in the Siberian larch forests. Extensive low- to mediate-intensity non-stand-replacing fires are a notable property of fire regime in these forests. Recent large scale studies of these fires have focused mostly on their impacts on carbon budget; however, their potential impacts on energy budget through post-fire albedo changes have not been considered. This study quantifies the post-fire surface forcing for Siberian larch forests that experienced non-stand-replacing fires between 2001 and 2012 using the full record of MODIS MCD43A3 albedo product and a burned area product developed specifically for the Russian forests. Despite a large variability, the mean effect of non-stand-replacing fires imposed through albedo is a negative forcing which lasts for at least 14 years. However, the magnitude of the forcing is much smaller than that imposed by stand-replacing fires, highlighting the importance of differentiating between the two fire types in the studies involving the fire impacts in the region. The results of this study also show that MODIS-based summer differenced normalized burn ratio (dNBR) provides a reliable metric for differentiating non-stand-replacing from stand-replacing fires with an overall accuracy of 88%, which is of considerable importance for future work on modeling post-fire energy budget and carbon budget in the region.

An Oceanic General Circulation Model (OGCM) investigation of the Red Sea circulation, 1. Exchange between the Red Sea and the Indian Ocean

Science.gov (United States)

Sofianos, Sarantis S.; Johns, William E.

2002-11-01

The mechanisms involved in the seasonal exchange between the Red Sea and the Indian Ocean are studied using an Oceanic General Circulation Model (OGCM), namely the Miami Isopycnic Coordinate Ocean Model (MICOM). The model reproduces the basic characteristics of the seasonal circulation observed in the area of the strait of Bab el Mandeb. There is good agreement between model results and available observations on the strength of the exchange and the characteristics of the water masses involved, as well as the seasonal flow pattern. During winter, this flow consists of a typical inverse estuarine circulation, while during summer, the surface flow reverses, there is an intermediate inflow of relatively cold and fresh water, and the hypersaline outflow at the bottom of the strait is significantly reduced. Additional experiments with different atmospheric forcing (seasonal winds, seasonal thermohaline air-sea fluxes, or combinations) were performed in order to assess the role of the atmospheric forcing fields in the exchange flow at Bab el Mandeb. The results of both the wind- and thermohaline-driven experiments exhibit a strong seasonality at the area of the strait, which is in phase with the observations. However, it is the combination of both the seasonal pattern of the wind stress and the seasonal thermohaline forcing that can reproduce the observed seasonal variability at the strait. The importance of the seasonal cycle of the thermohaline forcing on the exchange flow pattern is also emphasized by these results. In the experiment where the thermohaline forcing is represented by its annual mean, the strength of the exchange is reduced almost by half.

The vertical distribution of climate forcings and feedbacks from the surface to top of atmosphere

Energy Technology Data Exchange (ETDEWEB)

Previdi, Michael [Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY (United States); Liepert, Beate G. [NorthWest Research Associates, Redmond, WA (United States)

2012-08-15

The radiative forcings and feedbacks that determine Earth's climate sensitivity are typically defined at the top-of-atmosphere (TOA) or tropopause, yet climate sensitivity itself refers to a change in temperature at the surface. In this paper, we describe how TOA radiative perturbations translate into surface temperature changes. It is shown using first principles that radiation changes at the TOA can be equated with the change in energy stored by the oceans and land surface. This ocean and land heat uptake in turn involves an adjustment of the surface radiative and non-radiative energy fluxes, with the latter being comprised of the turbulent exchange of latent and sensible heat between the surface and atmosphere. We employ the radiative kernel technique to decompose TOA radiative feedbacks in the IPCC Fourth Assessment Report climate models into components associated with changes in radiative heating of the atmosphere and of the surface. (We consider the equilibrium response of atmosphere-mixed layer ocean models subjected to an instantaneous doubling of atmospheric CO{sub 2}). It is shown that most feedbacks, i.e., the temperature, water vapor and cloud feedbacks, (as well as CO{sub 2} forcing) affect primarily the turbulent energy exchange at the surface rather than the radiative energy exchange. Specifically, the temperature feedback increases the surface turbulent (radiative) energy loss by 2.87 W m{sup -2} K{sup -1} (0.60 W m{sup -2} K{sup -1}) in the multimodel mean; the water vapor feedback decreases the surface turbulent energy loss by 1.07 W m{sup -2} K{sup -1} and increases the surface radiative heating by 0.89 W m{sup -2} K{sup -1}; and the cloud feedback decreases both the turbulent energy loss and the radiative heating at the surface by 0.43 and 0.24 W m{sup -2} K{sup -1}, respectively. Since changes to the surface turbulent energy exchange are dominated in the global mean sense by changes in surface evaporation, these results serve to highlight

Quantification of Staphylococcus aureus adhesion forces on various dental restorative materials using atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Merghni, Abderrahmen, E-mail: abderrahmen_merghni@yahoo.fr [Laboratoire des Maladies Transmissibles et Substances biologiquement actives (LR99ES27) Faculté de Pharmacie de Monastir, Université de Monastir (Tunisia); Kammoun, Dorra [Laboratoire de Biomatériaux et Biotechnologie, Faculté de Médecine Dentaire, Monastir (Tunisia); Hentati, Hajer [Laboratoire de Recherche en Santé Orale et Réhabilitation Bucco-Faciale (LR12ES11), Faculté de Médecine Dentaire de Monastir, Université de Monastir (Tunisia); Janel, Sébastien [BioImaging Center Lille-FR3642, Lille (France); Popoff, Michka [Cellular Microbiology and Physics of Infection-CNRS UMR8204, INSERM U1019, Institut Pasteur de Lille, Lille University (France); Lafont, Frank [BioImaging Center Lille-FR3642, Lille (France); Cellular Microbiology and Physics of Infection-CNRS UMR8204, INSERM U1019, Institut Pasteur de Lille, Lille University (France); Aouni, Mahjoub [Laboratoire des Maladies Transmissibles et Substances biologiquement actives (LR99ES27) Faculté de Pharmacie de Monastir, Université de Monastir (Tunisia); Mastouri, Maha [Laboratoire des Maladies Transmissibles et Substances biologiquement actives (LR99ES27) Faculté de Pharmacie de Monastir, Université de Monastir (Tunisia); Laboratoire de Microbiologie, CHU Fattouma Bourguiba de Monastir (Tunisia)

2016-08-30

Highlights: • 4 dental restorative materials were characterized for roughness, angle contact water and surface free energy. • AFM adhesion forces of S. aureus to tested materials were achieved in presence and absence of salivary conditioning film. • S. aureus initial adhesion is dependent on the surface free energy and roughness. - Abstract: In the oral cavity dental restorative biomaterials can act as a reservoir for infection with opportunistic Staphylococcus aureus pathogen, which can lead to the occurrence of secondary caries and treatment failures. Our aim was to evaluate the adhesion forces by S. aureus on four dental restorative biomaterials and to correlate this finding to differences in specific surface characteristics. Additionally, the influence of salivary conditioning films in exerted adhesion forces was investigated. The substrate hydrophobicity was measured by goniometer and the surface free energy was calculated using the equilibrium advancing contact angle values of water, formamide, and diiodomethane on the tested surfaces. The surface roughness was determined using atomic force microscope (AFM). Additionally, cell force spectroscopy was achieved to quantify the forces that drive cell-substrate interactions. S. aureus bacterium exerted a considerable adhesion forces on various dental restorative materials, which decreased in the presence of saliva conditioning film. The influence of the surface roughness and free energy in initial adhesion appears to be more important than the effect of hydrophobicity, either in presence or absence of saliva coating. Hence, control of surface properties of dental restorative biomaterials is of crucial importance in preventing the attachment and subsequent the biofilm formation.

Quantification of Staphylococcus aureus adhesion forces on various dental restorative materials using atomic force microscopy

International Nuclear Information System (INIS)

Merghni, Abderrahmen; Kammoun, Dorra; Hentati, Hajer; Janel, Sébastien; Popoff, Michka; Lafont, Frank; Aouni, Mahjoub; Mastouri, Maha

2016-01-01

Highlights: • 4 dental restorative materials were characterized for roughness, angle contact water and surface free energy. • AFM adhesion forces of S. aureus to tested materials were achieved in presence and absence of salivary conditioning film. • S. aureus initial adhesion is dependent on the surface free energy and roughness. - Abstract: In the oral cavity dental restorative biomaterials can act as a reservoir for infection with opportunistic Staphylococcus aureus pathogen, which can lead to the occurrence of secondary caries and treatment failures. Our aim was to evaluate the adhesion forces by S. aureus on four dental restorative biomaterials and to correlate this finding to differences in specific surface characteristics. Additionally, the influence of salivary conditioning films in exerted adhesion forces was investigated. The substrate hydrophobicity was measured by goniometer and the surface free energy was calculated using the equilibrium advancing contact angle values of water, formamide, and diiodomethane on the tested surfaces. The surface roughness was determined using atomic force microscope (AFM). Additionally, cell force spectroscopy was achieved to quantify the forces that drive cell-substrate interactions. S. aureus bacterium exerted a considerable adhesion forces on various dental restorative materials, which decreased in the presence of saliva conditioning film. The influence of the surface roughness and free energy in initial adhesion appears to be more important than the effect of hydrophobicity, either in presence or absence of saliva coating. Hence, control of surface properties of dental restorative biomaterials is of crucial importance in preventing the attachment and subsequent the biofilm formation.

Experimental investigation and modelling of surface roughness and resultant cutting force in hard turning of AISI H13 Steel

Science.gov (United States)

Boy, M.; Yaşar, N.; Çiftçi, İ.

2016-11-01

In recent years, turning of hardened steels has replaced grinding for finishing operations. This process is compared to grinding operations; hard turning has higher material removal rates, the possibility of greater process flexibility, lower equipment costs, and shorter setup time. CBN or ceramic cutting tools are widely used hard part machining. For successful application of hard turning, selection of suitable cutting parameters for a given cutting tool is an important step. For this purpose, an experimental investigation was conducted to determine the effects of cutting tool edge geometry, feed rate and cutting speed on surface roughness and resultant cutting force in hard turning of AISI H13 steel with ceramic cutting tools. Machining experiments were conducted in a CNC lathe based on Taguchi experimental design (L16) in different levels of cutting parameters. In the experiments, a Kistler 9257 B, three cutting force components (Fc, Ff and Fr) piezoelectric dynamometer was used to measure cutting forces. Surface roughness measurements were performed by using a Mahrsurf PS1 device. For statistical analysis, analysis of variance has been performed and mathematical model have been developed for surface roughness and resultant cutting forces. The analysis of variance results showed that the cutting edge geometry, cutting speed and feed rate were the most significant factors on resultant cutting force while the cutting edge geometry and feed rate were the most significant factor for the surface roughness. The regression analysis was applied to predict the outcomes of the experiment. The predicted values and measured values were very close to each other. Afterwards a confirmation tests were performed to make a comparison between the predicted results and the measured results. According to the confirmation test results, measured values are within the 95% confidence interval.

Features of static and dynamic friction profiles in one and two dimensions on polymer and atomically flat surfaces using atomic force microscopy

International Nuclear Information System (INIS)

Watson, G S; Watson, J A

2008-01-01

In this paper we correlate the Atomic Force Microscope probe movement with surface location while scanning in the imaging and Force versus distance modes. Static and dynamic stick-slip processes are described on a scale of nanometres to microns on a range of samples. We demonstrate the limits and range of the tip apex being fixed laterally in the force versus distance mode and static friction slope dependence on probe parameters. Micron scale static and dynamic friction can be used to purposefully manipulate soft surfaces to produce well defined frictional gradients

Surface microstructure of bitumen characterized by atomic force microscopy.

Science.gov (United States)

Yu, Xiaokong; Burnham, Nancy A; Tao, Mingjiang

2015-04-01

Bitumen, also called asphalt binder, plays important roles in many industrial applications. It is used as the primary binding agent in asphalt concrete, as a key component in damping systems such as rubber, and as an indispensable additive in paint and ink. Consisting of a large number of hydrocarbons of different sizes and polarities, together with heteroatoms and traces of metals, bitumen displays rich surface microstructures that affect its rheological properties. This paper reviews the current understanding of bitumen's surface microstructures characterized by Atomic Force Microscopy (AFM). Microstructures of bitumen develop to different forms depending on crude oil source, thermal history, and sample preparation method. While some bitumens display surface microstructures with fine domains, flake-like domains, and dendrite structuring, 'bee-structures' with wavy patterns several micrometers in diameter and tens of nanometers in height are commonly seen in other binders. Controversy exists regarding the chemical origin of the 'bee-structures', which has been related to the asphaltene fraction, the metal content, or the crystallizing waxes in bitumen. The rich chemistry of bitumen can result in complicated intermolecular associations such as coprecipitation of wax and metalloporphyrins in asphaltenes. Therefore, it is the molecular interactions among the different chemical components in bitumen, rather than a single chemical fraction, that are responsible for the evolution of bitumen's diverse microstructures, including the 'bee-structures'. Mechanisms such as curvature elasticity and surface wrinkling that explain the rippled structures observed in polymer crystals might be responsible for the formation of 'bee-structures' in bitumen. Despite the progress made on morphological characterization of bitumen using AFM, the fundamental question whether the microstructures observed on bitumen surfaces represent its bulk structure remains to be addressed. In addition

Atomic force microscopy measurements of topography and friction on dotriacontane films adsorbed on a SiO2 surface

DEFF Research Database (Denmark)

Trogisch, S.; Simpson, M.J.; Taub, H.

2005-01-01

We report comprehensive atomic force microscopy (AFM) measurements at room temperature of the nanoscale topography and lateral friction on the surface of thin solid films of an intermediate-length normal alkane, dotriacontane (n-C32H66), adsorbed onto a SiO2 surface. Our topographic and frictional...

Study on Effect of Ultrasonic Vibration on Grinding Force and Surface Quality in Ultrasonic Assisted Micro End Grinding of Silica Glass

Directory of Open Access Journals (Sweden)

Zhang Jianhua

2014-01-01

Full Text Available Ultrasonic vibration assisted micro end grinding (UAMEG is a promising processing method for micro parts made of hard and brittle materials. First, the influence of ultrasonic assistance on the mechanism of this processing technology is theoretically analyzed. Then, in order to reveal the effects of ultrasonic vibration and grinding parameters on grinding forces and surface quality, contrast grinding tests of silica glass with and without ultrasonic assistance using micro radial electroplated diamond wheel are conducted. The grinding forces are measured using a three-component dynamometer. The surface characteristics are detected using the scanning electron microscope. The experiment results demonstrate that grinding forces are significantly reduced by introducing ultrasonic vibration into conventional micro end grinding (CMEG of silica glass; ultrasonic assistance causes inhibiting effect on variation percentages of tangential grinding force with grinding parameters; ductile machining is easier to be achieved and surface quality is obviously improved due to ultrasonic assistance in UAMEG. Therefore, larger grinding depth and feed rate adopted in UAMEG can lead to the improvement of removal rate and machining efficiency compared with CMEG.

Exploring Reaction Mechanism on Generalized Force Modified Potential Energy Surfaces (G-FMPES) for Diels-Alder Reaction

Science.gov (United States)

Jha, Sanjiv; Brown, Katie; Subramanian, Gopinath

We apply a recent formulation for searching minimum energy reaction path (MERP) and saddle point to atomic systems subjected to an external force. We demonstrate the effect of a loading modality resembling hydrostatic pressure on the trans to cis conformational change of 1,3-butadiene, and the simplest Diels-Alder reaction between ethylene and 1,3-butadiene. The calculated MERP and saddle points on the generalized force modified potential energy surface (G-FMPES) are compared with the corresponding quantities on an unmodified potential energy surface. Our study is performed using electronic structure calculations at the HF/6-31G** level as implemented in the AIMS-MOLPRO code. Our calculations suggest that the added compressive pressure lowers the energy of cis butadiene. The activation energy barrier for the concerted Diels-Alder reaction is found to decrease progressively with increasing compressive pressure.

Multiscale modeling of interaction of alane clusters on Al(111) surfaces : a reactive force field and infrared absorbtion spectroscopy approach

NARCIS (Netherlands)

Ojwang, J.G.O.; Chaudhuri, S.; Duin, van A.C.T.; Chabal, Y.J.; Veyan, J.-F.; Santen, van R.A.; Kramer, G.J.; Goddard III, W.A.

2010-01-01

We have used reactive force field (ReaxFF) to investigate the mechanism of interaction of alanes on Al(111) surface. Our simulations show that, on the Al(111) surface, alanes oligomerize into larger alanes. In addition, from our simulations, adsorption of atomic hydrogen on Al(111) surface leads to

Detecting onset of chain scission and crosslinking of γ-ray irradiated elastomer surfaces using frictional force microscopy

International Nuclear Information System (INIS)

Banerjee, S; Sinha, N K; Gayathri, N; Ponraju, D; Dash, S; Tyagi, A K; Raj, Baldev

2007-01-01

We report here that atomic force microscopy (AFM) in frictional force mode can be used to detect the onset of chain scission and crosslinking in polymeric and macromolecular samples upon irradiation. A systematic investigation to detect chain scission and crosslinking of two elastomers (1) ethylene-propylene-diene monomer rubber and (2) fluorocarbon rubber, upon γ-ray irradiation has been carried out using frictional force microscopy (FFM). From the AFM results we observed that both the elastomers show a systematic smoothening of its surfaces, as the γ-ray dose rate increases. However, the frictional property studied using FFM of the sample surfaces show an initial increase and then a decrease as a function of dose rate. This behaviour of increase in its frictional property has been attributed to the onset of chain scission, and the subsequent decrease in friction has been attributed to the onset of crosslinking of the polymer chains. The evaluated qualitative and semi-quantitative changes observed in the overall frictional property as a function of the γ-ray dose rate for the two elastomers are presented in this paper

Detecting onset of chain scission and crosslinking of {gamma}-ray irradiated elastomer surfaces using frictional force microscopy

Energy Technology Data Exchange (ETDEWEB)

Banerjee, S [Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 TN (India); Sinha, N K [Innovative Design Engineering and Synthesis Section, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 TN (India); Gayathri, N [Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 TN (India); Ponraju, D [Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 TN (India); Dash, S [Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 TN (India); Tyagi, A K [Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 TN (India); Raj, Baldev [Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 TN (India)

2007-02-07

We report here that atomic force microscopy (AFM) in frictional force mode can be used to detect the onset of chain scission and crosslinking in polymeric and macromolecular samples upon irradiation. A systematic investigation to detect chain scission and crosslinking of two elastomers (1) ethylene-propylene-diene monomer rubber and (2) fluorocarbon rubber, upon {gamma}-ray irradiation has been carried out using frictional force microscopy (FFM). From the AFM results we observed that both the elastomers show a systematic smoothening of its surfaces, as the {gamma}-ray dose rate increases. However, the frictional property studied using FFM of the sample surfaces show an initial increase and then a decrease as a function of dose rate. This behaviour of increase in its frictional property has been attributed to the onset of chain scission, and the subsequent decrease in friction has been attributed to the onset of crosslinking of the polymer chains. The evaluated qualitative and semi-quantitative changes observed in the overall frictional property as a function of the {gamma}-ray dose rate for the two elastomers are presented in this paper.

Probing the Surface Charge on the Basal Planes of Kaolinite Particles with High-Resolution Atomic Force Microscopy.

Science.gov (United States)

Kumar, N; Andersson, M P; van den Ende, D; Mugele, F; Siretanu, I

2017-12-19

High-resolution atomic force microscopy is used to map the surface charge on the basal planes of kaolinite nanoparticles in an ambient solution of variable pH and NaCl or CaCl 2 concentration. Using DLVO theory with charge regulation, we determine from the measured force-distance curves the surface charge distribution on both the silica-like and the gibbsite-like basal plane of the kaolinite particles. We observe that both basal planes do carry charge that varies with pH and salt concentration. The silica facet was found to be negatively charged at pH 4 and above, whereas the gibbsite facet is positively charged at pH below 7 and negatively charged at pH above 7. Investigations in CaCl 2 at pH 6 show that the surface charge on the gibbsite facet increases for concentration up to 10 mM CaCl 2 and starts to decrease upon further increasing the salt concentration to 50 mM. The increase of surface charge at low concentration is explained by Ca 2+ ion adsorption, while Cl - adsorption at higher CaCl 2 concentrations partially neutralizes the surface charge. Atomic resolution imaging and density functional theory calculations corroborate these observations. They show that hydrated Ca 2+ ions can spontaneously adsorb on the gibbsite facet of the kaolinite particle and form ordered surface structures, while at higher concentrations Cl - ions will co-adsorb, thereby changing the observed ordered surface structure.

Modulation of surface wettability of superhydrophobic substrates using Si nanowire arrays and capillary-force-induced nanocohesion

NARCIS (Netherlands)

Dawood, M.K.; Zheng, H.; Kurniawan, N.A.; Leong, K.C.; Foo, Y.L.; Rajagopalan, Raj; Khan, S.A.; Choi, W.K.

2012-01-01

We describe a new scalable method to fabricate large-area hybrid superhydrophobic surfaces with selective adhesion properties on silicon (Si) nanowire array substrates by exploiting liquid-medium-dependent capillary-force-induced nanocohesion. Gold (Au) nanoparticles were deposited on Si by glancing

Quantifying the importance of galactofuranose in Aspergillus nidulans hyphal wall surface organization by atomic force microscopy.

Science.gov (United States)

Paul, Biplab C; El-Ganiny, Amira M; Abbas, Mariam; Kaminskyj, Susan G W; Dahms, Tanya E S

2011-05-01

The fungal wall mediates cell-environment interactions. Galactofuranose (Galf), the five-member ring form of galactose, has a relatively low abundance in Aspergillus walls yet is important for fungal growth and fitness. Aspergillus nidulans strains deleted for Galf biosynthesis enzymes UgeA (UDP-glucose-4-epimerase) and UgmA (UDP-galactopyranose mutase) lacked immunolocalizable Galf, had growth and sporulation defects, and had abnormal wall architecture. We used atomic force microscopy and force spectroscopy to image and quantify cell wall viscoelasticity and surface adhesion of ugeAΔ and ugmAΔ strains. We compared the results for ugeAΔ and ugmAΔ strains with the results for a wild-type strain (AAE1) and the ugeB deletion strain, which has wild-type growth and sporulation. Our results suggest that UgeA and UgmA are important for cell wall surface subunit organization and wall viscoelasticity. The ugeAΔ and ugmAΔ strains had significantly larger surface subunits and lower cell wall viscoelastic moduli than those of AAE1 or ugeBΔ hyphae. Double deletion strains (ugeAΔ ugeBΔ and ugeAΔ ugmAΔ) had more-disorganized surface subunits than single deletion strains. Changes in wall surface structure correlated with changes in its viscoelastic modulus for both fixed and living hyphae. Wild-type walls had the largest viscoelastic modulus, while the walls of the double deletion strains had the smallest. The ugmAΔ strain and particularly the ugeAΔ ugmAΔ double deletion strain were more adhesive to hydrophilic surfaces than the wild type, consistent with changes in wall viscoelasticity and surface organization. We propose that Galf is necessary for full maturation of A. nidulans walls during hyphal extension.

The Role of the Electrostatic Force in Spore Adhesion

Energy Technology Data Exchange (ETDEWEB)

Chung, Eunhyea [Georgia Institute of Technology; Yiacoumi, Sotira [Georgia Institute of Technology; Lee, Ida [University of Tennessee, Knoxville (UTK); Tsouris, Costas [ORNL

2010-01-01

Electrostatic force is investigated as one of the components of the adhesion force between Bacillus thuringiensis (Bt) spores and planar surfaces. The surface potentials of a Bt spore and a mica surface are experimentally obtained using a combined atomic force microscopy (AFM)-scanning surface potential microscopy technique. On the basis of experimental information, the surface charge density of the spores is estimated at 0.03 {micro}C/cm{sup 2} at 20% relative humidity and decreases with increasing humidity. The Coulombic force is introduced for the spore-mica system (both charged, nonconductive surfaces), and an electrostatic image force is introduced to the spore-gold system because gold is electrically conductive. The Coulombic force for spore-mica is repulsive because the components are similarly charged, while the image force for the spore-gold system is attractive. The magnitude of both forces decreases with increasing humidity. The electrostatic forces are added to other force components, e.g., van der Waals and capillary forces, to obtain the adhesion force for each system. The adhesion forces measured by AFM are compared to the estimated values. It is shown that the electrostatic (Coulombic and image) forces play a significant role in the adhesion force between spores and planar surfaces.

Influence of the atomic force microscope tip on the multifractal analysis of rough surfaces

International Nuclear Information System (INIS)

Klapetek, Petr; Ohlidal, Ivan; Bilek, Jindrich

2004-01-01

In this paper, the influence of atomic force microscope tip on the multifractal analysis of rough surfaces is discussed. This analysis is based on two methods, i.e. on the correlation function method and the wavelet transform modulus maxima method. The principles of both methods are briefly described. Both methods are applied to simulated rough surfaces (simulation is performed by the spectral synthesis method). It is shown that the finite dimensions of the microscope tip misrepresent the values of the quantities expressing the multifractal analysis of rough surfaces within both the methods. Thus, it was concretely shown that the influence of the finite dimensions of the microscope tip changed mono-fractal properties of simulated rough surface to multifractal ones. Further, it is shown that a surface reconstruction method developed for removing the negative influence of the microscope tip does not improve the results obtained in a substantial way. The theoretical procedures concerning both the methods, i.e. the correlation function method and the wavelet transform modulus maxima method, are illustrated for the multifractal analysis of randomly rough gallium arsenide surfaces prepared by means of the thermal oxidation of smooth gallium arsenide surfaces and subsequent dissolution of the oxide films

Defects in oxide surfaces studied by atomic force and scanning tunneling microscopy

Directory of Open Access Journals (Sweden)

Thomas König

2011-01-01

Full Text Available Surfaces of thin oxide films were investigated by means of a dual mode NC-AFM/STM. Apart from imaging the surface termination by NC-AFM with atomic resolution, point defects in magnesium oxide on Ag(001 and line defects in aluminum oxide on NiAl(110, respectively, were thoroughly studied. The contact potential was determined by Kelvin probe force microscopy (KPFM and the electronic structure by scanning tunneling spectroscopy (STS. On magnesium oxide, different color centers, i.e., F0, F+, F2+ and divacancies, have different effects on the contact potential. These differences enabled classification and unambiguous differentiation by KPFM. True atomic resolution shows the topography at line defects in aluminum oxide. At these domain boundaries, STS and KPFM verify F2+-like centers, which have been predicted by density functional theory calculations. Thus, by determining the contact potential and the electronic structure with a spatial resolution in the nanometer range, NC-AFM and STM can be successfully applied on thin oxide films beyond imaging the topography of the surface atoms.

Quantified Differentiation of Surface Topography for Nano-materials As-Obtained from Atomic Force Microscopy Images

Science.gov (United States)

Gupta, Mousumi; Chatterjee, Somenath

2018-04-01

Surface texture is an important issue to realize the nature (crest and trough) of surfaces. Atomic force microscopy (AFM) image is a key analysis for surface topography. However, in nano-scale, the nature (i.e., deflection or crack) as well as quantification (i.e., height or depth) of deposited layers is essential information for material scientist. In this paper, a gradient-based K-means algorithm is used to differentiate the layered surfaces depending on their color contrast of as-obtained from AFM images. A transformation using wavelet decomposition is initiated to extract the information about deflection or crack on the material surfaces from the same images. Z-axis depth analysis from wavelet coefficients provides information about the crack present in the material. Using the above method corresponding surface information for the material is obtained. In addition, the Gaussian filter is applied to remove the unwanted lines, which occurred during AFM scanning. Few known samples are taken as input, and validity of the above approaches is shown.

Nanoscale fabrication and characterization of chemically modified silicon surfaces using conductive atomic force microscopy in liquids

Science.gov (United States)

Kinser, Christopher Reagan

This dissertation examines the modification and characterization of hydrogen-terminated silicon surfaces in organic liquids. Conductive atomic force microscope (cAFM) lithography is used to fabricate structures with sub-100 nm line width on H:Si(111) in n-alkanes, 1-alkenes, and 1-alkanes. Nanopatterning is accomplished by applying a positive (n-alkanes and 1-alkenes) or a negative (1-alkanes) voltage pulse to the silicon substrate with the cAFM tip connected to ground. The chemical and kinetic behavior of the patterned features is characterized using AFM, lateral force microscopy, time-of-flight secondary ion mass spectroscopy (TOF SIMS), and chemical etching. Features patterned in hexadecane, 1-octadecene, and undecylenic acid methyl ester exhibited chemical and kinetic behavior consistent with AFM field induced oxidation. The oxide features are formed due to capillary condensation of a water meniscus at the AFM tip-sample junction. A space-charge limited growth model is proposed to explain the observed growth kinetics. Surface modifications produced in the presence of neat 1-dodecyne and 1-octadecyne exhibited a reduced lateral force compared to the background H:Si(111) substrate and were resistant to a hydrofluoric acid etch, characteristics which indicate that the patterned features are not due to field induced oxidation and which are consistent with the presence of the methyl-terminated 1-alkyne bound directly to the silicon surface through silicon-carbon bonds. In addition to the cAFM patterned surfaces, full monolayers of undecylenic acid methyl ester (SAM-1) and undec-10-enoic acid 2-bromoethyl ester (SAM-2) were grown on H:Si(111) substrates using ultraviolet light. The structure and chemistry of the monolayers were characterized using AFM, TOF SIMS, X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), X-ray standing waves (XSW), and X-ray fluorescence (XRF). These combined analyses provide evidence that SAM-1 and SAM-2 form dense monolayers

Incorporating contact angles in the surface tension force with the ACES interface curvature scheme

Science.gov (United States)

Owkes, Mark

2017-11-01

In simulations of gas-liquid flows interacting with solid boundaries, the contact line dynamics effect the interface motion and flow field through the surface tension force. The surface tension force is directly proportional to the interface curvature and the problem of accurately imposing a contact angle must be incorporated into the interface curvature calculation. Many commonly used algorithms to compute interface curvatures (e.g., height function method) require extrapolating the interface, with defined contact angle, into the solid to allow for the calculation of a curvature near a wall. Extrapolating can be an ill-posed problem, especially in three-dimensions or when multiple contact lines are near each other. We have developed an accurate methodology to compute interface curvatures that allows for contact angles to be easily incorporated while avoiding extrapolation and the associated challenges. The method, known as Adjustable Curvature Evaluation Scale (ACES), leverages a least squares fit of a polynomial to points computed on the volume-of-fluid (VOF) representation of the gas-liquid interface. The method is tested by simulating canonical test cases and then applied to simulate the injection and motion of water droplets in a channel (relevant to PEM fuel cells).

Characterizing the surface forces between two individual nanowires using optical microscopy based nanomanipulation

Science.gov (United States)

Xie, Hongtao; Mead, James L.; Wang, Shiliang; Fatikow, Sergej; Huang, Han

2018-06-01

The adhesion and friction between two Al2O3 nanowires (NWs) was characterized by the use of optical microscopy based nanomanipulation, with which peeling, shearing and sliding was performed. The elastically deformed shape of the NWs during peeling and shearing was used to calculate the adhesion and frictional forces; force sensing was not required. The obtained adhesion stress between two Al2O3 NWs varied from 0.14 to 0.25 MPa, lower than that observed for carbon nanotube junctions, and was attributed to van der Waals attraction. Stick-slip was observed during the shearing and sliding of two NWs, and was the consequence of discrete contact between surface asperities. The obtained static and kinetic frictional stresses varied from 0.7 to 1.3 MPa and 0.4 to 0.8 MPa, respectively; significantly greater than the obtained adhesion stress.

Force Measurement with a Piezoelectric Cantilever in a Scanning Force Microscope

OpenAIRE

Tansock, J.; Williams, C. C.

1992-01-01

Detection of surface forces between a tip and sample has been demonstrated with a piezoelectric cantilever in a scanning force microscope (SFM). The use of piezoelectric force sensing is particularly advantageous in semiconductor applications where stray light from conventional optical force-sensing methods can significantly modify the local carrier density. Additionally, the piezoelectric sensors are simple, provide good sensitivity to force, and can be batch fabricated. Our piezoelectric fo...

Restless behavior increases over time, but not with compressibility of the flooring surface, during forced standing at the feed bunk.

Science.gov (United States)

Krebs, N; Berry, S L; Tucker, C B

2011-01-01

Interest in the use of rubber flooring in freestall barns has increased, but little is known about which design features of these surfaces are important for cattle. In 2 experiments, we evaluated how the type and compressibility of the flooring surface in front of the feed bunk influenced the behavioral response to 4 h of forced standing after morning milking. Two flooring types were compared: rubber and concrete. Rubber was tested at 3 levels of compressibility: 2, 4, and 35 times as compressible as concrete. Four hours of forced standing was evaluated because it mimicked conditions that can occur on dairies, particularly when waiting for artificial insemination or veterinary treatment. The effects of cow weight and hoof surface area, gait score, and hoof health on the response to treatment were evaluated. Restless behavior, as measured by number of steps, almost doubled over the 4h of forced standing, regardless of flooring material. Cows lay down, on average, within 5 min after access to the lying area was provided. These results indicate that the 4 h of forced standing was uncomfortable. No differences in restless behavior were observed in association with the type or compressibility of the flooring surface in front of the feed bunk. Cow size, hoof health, or gait score did not consistently explain the response to the flooring treatments or stepping rate, although these populations of animals were generally healthy. It is unclear if comfort did not differ between the flooring options tested during 4 h of forced standing or if alterative methodology, such as measuring more subtle shifts in weight, is required to assess design features of rubber flooring. Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Surface tension effect on the mechanical properties of nanomaterials measured by atomic force microscopy

Science.gov (United States)

Cuenot, Stéphane; Frétigny, Christian; Demoustier-Champagne, Sophie; Nysten, Bernard

2004-04-01

The effect of reduced size on the elastic properties measured on silver and lead nanowires and on polypyrrole nanotubes with an outer diameter ranging between 30 and 250 nm is presented and discussed. Resonant-contact atomic force microscopy (AFM) is used to measure their apparent elastic modulus. The measured modulus of the nanomaterials with smaller diameters is significantly higher than that of the larger ones. The latter is comparable to the macroscopic modulus of the materials. The increase of the apparent elastic modulus for the smaller diameters is attributed to surface tension effects. The surface tension of the probed material may be experimentally determined from these AFM measurements.

Atomic force microscopic study of the effects of ethanol on yeast cell surface morphology.

Science.gov (United States)

Canetta, Elisabetta; Adya, Ashok K; Walker, Graeme M

2006-02-01

The detrimental effects of ethanol toxicity on the cell surface morphology of Saccharomyces cerevisiae (strain NCYC 1681) and Schizosaccharomyces pombe (strain DVPB 1354) were investigated using an atomic force microscope (AFM). In combination with culture viability and mean cell volume measurements AFM studies allowed us to relate the cell surface morphological changes, observed on nanometer lateral resolution, with the cellular stress physiology. Exposing yeasts to increasing stressful concentrations of ethanol led to decreased cell viabilities and mean cell volumes. Together with the roughness and bearing volume analyses of the AFM images, the results provided novel insight into the relative ethanol tolerance of S. cerevisiae and Sc. pombe.

Analysis of atomic force microscopy data for surface characterization using fuzzy logic

International Nuclear Information System (INIS)

Al-Mousa, Amjed; Niemann, Darrell L.; Niemann, Devin J.; Gunther, Norman G.; Rahman, Mahmud

2011-01-01

In this paper we present a methodology to characterize surface nanostructures of thin films. The methodology identifies and isolates nanostructures using Atomic Force Microscopy (AFM) data and extracts quantitative information, such as their size and shape. The fuzzy logic based methodology relies on a Fuzzy Inference Engine (FIE) to classify the data points as being top, bottom, uphill, or downhill. The resulting data sets are then further processed to extract quantitative information about the nanostructures. In the present work we introduce a mechanism which can consistently distinguish crowded surfaces from those with sparsely distributed structures and present an omni-directional search technique to improve the structural recognition accuracy. In order to demonstrate the effectiveness of our approach we present a case study which uses our approach to quantitatively identify particle sizes of two specimens each with a unique gold nanoparticle size distribution. - Research Highlights: → A Fuzzy logic analysis technique capable of characterizing AFM images of thin films. → The technique is applicable to different surfaces regardless of their densities. → Fuzzy logic technique does not require manual adjustment of the algorithm parameters. → The technique can quantitatively capture differences between surfaces. → This technique yields more realistic structure boundaries compared to other methods.

Controlling electron transfer processes on insulating surfaces with the non-contact atomic force microscope.

Science.gov (United States)

Trevethan, Thomas; Shluger, Alexander

2009-07-01

We present the results of theoretical modelling that predicts how a process of transfer of single electrons between two defects on an insulating surface can be induced using a scanning force microscope tip. A model but realistic system is employed which consists of a neutral oxygen vacancy and a noble metal (Pt or Pd) adatom on the MgO(001) surface. We show that the ionization potential of the vacancy and the electron affinity of the metal adatom can be significantly modified by the electric field produced by an ionic tip apex at close approach to the surface. The relative energies of the two states are also a function of the separation of the two defects. Therefore the transfer of an electron from the vacancy to the metal adatom can be induced either by the field effect of the tip or by manipulating the position of the metal adatom on the surface.

Distinction of heterogeneity on Au nanostructured surface based on phase contrast imaging of atomic force microscopy

International Nuclear Information System (INIS)

Jung, Mi; Choi, Jeong-Woo

2010-01-01

The discrimination of the heterogeneity of different materials on nanostructured surfaces has attracted a great deal of interest in biotechnology as well as nanotechnology. Phase imaging through tapping mode of atomic force microscopy (TMAFM) can be used to distinguish the heterogeneity on a nanostructured surface. Nanostructures were fabricated using anodic aluminum oxide (AAO). An 11-mercaptoundecanoic acid (11-MUA) layer adsorbed onto the Au nanodots through self-assembly to improve the bio-compatibility. The Au nanostructures that were modified with 11-MUA and the concave surfaces were investigated using the TMAFM phase images to compare the heterogeneous and homogeneous nanostructured surfaces. Although the topography and phase images were taken simultaneously, the images were different. Therefore, the contrast in the TMAFM phase images revealed the different compositional materials on the heterogeneous nanostructure surface.

Theoretical investigation of the distance dependence of capillary and van der Waals forces in scanning force microscopy

International Nuclear Information System (INIS)

Stifter, Thomas; Marti, Othmar; Bhushan, Bharat

2000-01-01

The capillary and van der Waals forces between a tip and a plane in a scanning force microscope (SFM) are calculated. The forces are calculated for a fixed distance of tip and sample, as well as during retracting of the tip from the sample surface. The exact geometric shape of the meniscus is considered, with the boundary condition of fixed liquid volume during retraction. The starting volume is given by the operating and environmental conditions (surface tension, humidity, and tip geometry) at the point of lowest distance between tip and surface. The influence of the different parameters, namely, humidity, tip geometry, tip-sample starting distance, surface tension, and contact angles are studied. For each force curve also the geometric shape of the meniscus is calculated. The capillary forces are compared with van der Waals forces to understand their relative importance in various operating conditions. In addition to application in SFM, this analysis is useful in the design of surface roughness in microdevices for low adhesion in operating environments

Controller design for automatic micro-assembly systems under the influence of surface forces, hysteresis and quantizer

NARCIS (Netherlands)

Ouyang, Ruiyue; Jayawardhana, Bayu

In this paper, we design nonlinear controllers for micro-magnetic levitation systems. The controller takes into account the influence of the surface forces and hysteresis/quantizer. We show the exponential convergence of the error signal and its time derivative to a compact set, which is determined

Localization and force analysis at the single virus particle level using atomic force microscopy

International Nuclear Information System (INIS)

Liu, Chih-Hao; Horng, Jim-Tong; Chang, Jeng-Shian; Hsieh, Chung-Fan; Tseng, You-Chen; Lin, Shiming

2012-01-01

Highlights: ► Localization of single virus particle. ► Force measurements. ► Force mapping. -- Abstract: Atomic force microscopy (AFM) is a vital instrument in nanobiotechnology. In this study, we developed a method that enables AFM to simultaneously measure specific unbinding force and map the viral glycoprotein at the single virus particle level. The average diameter of virus particles from AFM images and the specificity between the viral surface antigen and antibody probe were integrated to design a three-stage method that sets the measuring area to a single virus particle before obtaining the force measurements, where the influenza virus was used as the object of measurements. Based on the purposed method and performed analysis, several findings can be derived from the results. The mean unbinding force of a single virus particle can be quantified, and no significant difference exists in this value among virus particles. Furthermore, the repeatability of the proposed method is demonstrated. The force mapping images reveal that the distributions of surface viral antigens recognized by antibody probe were dispersed on the whole surface of individual virus particles under the proposed method and experimental criteria; meanwhile, the binding probabilities are similar among particles. This approach can be easily applied to most AFM systems without specific components or configurations. These results help understand the force-based analysis at the single virus particle level, and therefore, can reinforce the capability of AFM to investigate a specific type of viral surface protein and its distributions.

Capillary force between wetted nanometric contacts and its application to atomic force microscopy.

Science.gov (United States)

Crassous, Jérôme; Ciccotti, Matteo; Charlaix, Elisabeth

2011-04-05

We extend to the case of perfect wetting the exact calculation of Orr et al. (J. Fluid. Mech. 1975, 67, 723) for a pendular ring connecting two dry surfaces. We derive an approximate analytical expression for the capillary force between two highly curved surfaces covered by a wetting liquid film. The domain of validity of this expression is assessed and extended by a custom-made numerical simulation based on the full exact mathematical description. In the case of attractive liquid-solid van der Waals interactions, the capillary force increases monotonically with decreasing vapor pressure up to several times its saturation value. This accurate description of the capillary force makes it possible to estimate the adhesion force between wet nanoparticles; it can also be used to quantitatively interpret pull-off forces measured by atomic force microscopy.

Mathematical Modelling and Optimization of Cutting Force, Tool Wear and Surface Roughness by Using Artificial Neural Network and Response Surface Methodology in Milling of Ti-6242S

Directory of Open Access Journals (Sweden)

Erol Kilickap

2017-10-01

Full Text Available In this paper, an experimental study was conducted to determine the effect of different cutting parameters such as cutting speed, feed rate, and depth of cut on cutting force, surface roughness, and tool wear in the milling of Ti-6242S alloy using the cemented carbide (WC end mills with a 10 mm diameter. Data obtained from experiments were defined both Artificial Neural Network (ANN and Response Surface Methodology (RSM. ANN trained network using Levenberg-Marquardt (LM and weights were trained. On the other hand, the mathematical models in RSM were created applying Box Behnken design. Values obtained from the ANN and the RSM was found to be very close to the data obtained from experimental studies. The lowest cutting force and surface roughness were obtained at high cutting speeds and low feed rate and depth of cut. The minimum tool wear was obtained at low cutting speed, feed rate, and depth of cut.

Atomic imaging of an InSe single-crystal surface with atomic force microscope

OpenAIRE

Uosaki, Kohei; Koinuma, Michio

1993-01-01

The atomic force microscope was employed to observed in air the surface atomic structure of InSe, one of III-VI compound semiconductors with layered structures. Atomic arrangements were observed in both n-type and p-type materials. The observed structures are in good agreement with those expected from bulk crystal structures. The atomic images became less clear by repeating the imaging process. Wide area imaging after the imaging of small area clearly showed that a mound was created at the sp...

Characterizing the effect of polymyxin B antibiotics to lipopolysaccharide on Escherichia coli surface using atomic force microscopy.

Science.gov (United States)

Oh, Yoo Jin; Plochberger, Birgit; Rechberger, Markus; Hinterdorfer, Peter

2017-06-01

Lipopolysaccharide (LPS) on gram-negative bacterial outer membranes is the first target for antimicrobial agents, due to their spatial proximity to outer environments of microorganisms. To develop antibacterial compounds with high specificity for LPS binding, the understanding of the molecular nature and their mode of recognition is of key importance. In this study, atomic force microscopy (AFM) and single molecular force spectroscopy were used to characterize the effects of antibiotic polymyxin B (PMB) to the bacterial membrane at the nanoscale. Isolated LPS layer and the intact bacterial membrane were examined with respect to morphological changes at different concentrations of PMB. Our results revealed that 3 hours of 10 μg/mL of PMB exposure caused the highest roughness changes on intact bacterial surfaces, arising from the direct binding of PMB to LPS on the bacterial membrane. Single molecular force spectroscopy was used to probe specific interaction forces between the isolated LPS layer and PMB coupled to the AFM tip. A short range interaction regime mediated by electrostatic forces was visible. Unbinding forces between isolated LPS and PMB were about 30 pN at a retraction velocity of 500 nm/s. We further investigated the effects of the polycationic peptide PMB on bacterial outer membranes and monitored its influences on the deterioration of the bacterial membrane structure. Polymyxin B binding led to rougher appearances and wrinkles on the outer membranes surface, which may finally lead to lethal membrane damage of bacteria. Our studies indicate the potential of AFM for applications in pathogen recognition and nano-resolution approaches in microbiology. Copyright © 2017 John Wiley & Sons, Ltd.

The Mechanical of the Small Axisymmetric Oscillations of the Liquid with the Surface Tension Forces in Elastic Tank

Directory of Open Access Journals (Sweden)

D. A. Goncharov

2015-01-01

Full Text Available In this paper we investigate small axisymmetric oscillations of a liquid in an elastic tank. We also take into account the influence of surface tension forces. For this, we turn to the mechanical analogue of the considered mechanical system. To realize the transition to mechanical analogue we use the energy method: postulating the equality of kinetic and potential energy for the investigated mechanical system and the mechanical system analog. Due to this transition we can further investigate the oscillations of a mechanical analogue. As a mechanical analogue, we consider the oscillator in the spring. The mass of the oscillator is calculated as the weight of the fluid to make oscillations. The oscillator spring constant is calculated using the identity of equations, namely, equation of free small oscillations of the oscillator and equation of free small oscillations of the system under investigation: the fluid in the elastic tank. The identity of equations allows us to draw conclusion about the identity of the natural frequencies for the source mechanical system and the system of a mechanical analogue. Next, we take into consideration the action of the surface tension. We record the Laplace condition for excess pressure because of the forces of surface tension. Then we compile the expression for the generalized force, taking into account the phenomenon of the surface tension. Next, we write the equation of oscillations of a mechanical analogue. The surface tension, due to the introduction of the generalized force in the equation for small oscillations of the mechanical analogue will change the natural frequency of the mechanical analogue. The paper presents the appropriate dependencies. The abovementioned allows us to investigate the stability of small motions of fluid in microgravity or low gravity by studying the stability of small motions of mechanical analogue. The latter is especially important due to the design and development of advanced

Surface EMG and intra-socket force measurement to control a prosthetic device

Science.gov (United States)

Sanford, Joe; Patterson, Rita; Popa, Dan

2015-06-01

Surface electromyography (SEMG) has been shown to be a robust and reliable interaction method allowing for basic control of powered prosthetic devices. Research has shown a marked decrease in EMG-classification efficiency throughout activities of daily life due to socket shift and movement and fatigue as well as changes in degree of fit of the socket throughout the subject's lifetime. Users with the most severe levels of amputation require the most complex devices with the greatest number of degrees of freedom. Controlling complex dexterous devices with limited available inputs requires the addition of sensing and interaction modalities. However, the larger the amputation severity, the fewer viable SEMG sites are available as control inputs. Previous work reported the use of intra-socket pressure, as measured during wrist flexion and extension, and has shown that it is possible to control a powered prosthetic device with pressure sensors. In this paper, we present data correlations of SEMG data with intra-socket pressure data. Surface EMG sensors and force sensors were housed within a simulated prosthetic cuff fit to a healthy-limbed subject. EMG and intra-socket force data was collected from inside the cuff as a subject performed pre-defined grip motions with their dominant hand. Data fusion algorithms were explored and allowed a subject to use both intra-socket pressure and SEMG data as control inputs for a powered prosthetic device. This additional input modality allows for an improvement in input classification as well as information regarding socket fit through out activities of daily life.

Quantitative 3D-KPFM imaging with simultaneous electrostatic force and force gradient detection

International Nuclear Information System (INIS)

Collins, L; Rodriguez, B J; Okatan, M B; Li, Q; Kravenchenko, I I; Lavrik, N V; Kalinin, S V; Jesse, S

2015-01-01

Kelvin probe force microscopy (KPFM) is a powerful characterization technique for imaging local electrochemical and electrostatic potential distributions and has been applied across a broad range of materials and devices. Proper interpretation of the local KPFM data can be complicated, however, by convolution of the true surface potential under the tip with additional contributions due to long range capacitive coupling between the probe (e.g. cantilever, cone, tip apex) and the sample under test. In this work, band excitation (BE)-KPFM is used to negate such effects. In contrast to traditional single frequency KPFM, multifrequency BE-KPFM is shown to afford dual sensitivity to both the electrostatic force and the force gradient detection, analogous to simultaneous amplitude modulated and frequency modulated KPFM imaging. BE-KPFM is demonstrated on a Pt/Au/SiO x test structure and electrostatic force gradient detection is found to lead to an improved lateral resolution compared to electrostatic force detection. Finally, a 3D-KPFM imaging technique is developed. Force volume (FV) BE-KPFM allows the tip–sample distance dependence of the electrostatic interactions (force and force gradient) to be recorded at each point across the sample surface. As such, FVBE-KPFM provides a much needed pathway towards complete tip–sample capacitive de-convolution in KPFM measurements and will enable quantitative surface potential measurements with nanoscale resolution. (paper)

Localization and force analysis at the single virus particle level using atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Liu, Chih-Hao [Institute of Applied Mechanics, Nation Taiwan University, Roosevelt Road, Taipei 10617, Taiwan (China); Horng, Jim-Tong [Department of Biochemistry, Chang Gung University, 259 Wen-Hwa First Road, Kweishan, Taoyuan 333, Taiwan (China); Chang, Jeng-Shian [Institute of Applied Mechanics, Nation Taiwan University, Roosevelt Road, Taipei 10617, Taiwan (China); Hsieh, Chung-Fan [Graduate Institute of Biomedical Sciences, Chang Gung University, Kweishan, Taoyuan 333, Taiwan (China); Tseng, You-Chen [Institute of Applied Mechanics, Nation Taiwan University, Roosevelt Road, Taipei 10617, Taiwan (China); Lin, Shiming, E-mail: til@ntu.edu.tw [Institute of Applied Mechanics, Nation Taiwan University, Roosevelt Road, Taipei 10617, Taiwan (China); Center for Optoelectronic Biomedicine, College of Medicine, Nation Taiwan University, 1-1 Jen-Ai Road, Taipei 10051, Taiwan (China)

2012-01-06

Highlights: Black-Right-Pointing-Pointer Localization of single virus particle. Black-Right-Pointing-Pointer Force measurements. Black-Right-Pointing-Pointer Force mapping. -- Abstract: Atomic force microscopy (AFM) is a vital instrument in nanobiotechnology. In this study, we developed a method that enables AFM to simultaneously measure specific unbinding force and map the viral glycoprotein at the single virus particle level. The average diameter of virus particles from AFM images and the specificity between the viral surface antigen and antibody probe were integrated to design a three-stage method that sets the measuring area to a single virus particle before obtaining the force measurements, where the influenza virus was used as the object of measurements. Based on the purposed method and performed analysis, several findings can be derived from the results. The mean unbinding force of a single virus particle can be quantified, and no significant difference exists in this value among virus particles. Furthermore, the repeatability of the proposed method is demonstrated. The force mapping images reveal that the distributions of surface viral antigens recognized by antibody probe were dispersed on the whole surface of individual virus particles under the proposed method and experimental criteria; meanwhile, the binding probabilities are similar among particles. This approach can be easily applied to most AFM systems without specific components or configurations. These results help understand the force-based analysis at the single virus particle level, and therefore, can reinforce the capability of AFM to investigate a specific type of viral surface protein and its distributions.

Sensitivity of Surface Temperature to Oceanic Forcing via q-Flux Green’s Function Experiments. Part I: Linear Response Function

Energy Technology Data Exchange (ETDEWEB)

Liu, Fukai; Lu, Jian; Garuba, Oluwayemi A.; Leung, Lai-Yung; Luo, Yiyong; Wan, Xiuquan

2018-05-01

This paper explores the use of linear response function (LRF) to relate the mean sea surface temperature (SST) response to prescribed ocean heat convergence (q-flux) forcings. Two methods for constructing the LRF based on the fluctuation-dissipation theorem (FDT) and Green’s function (GRF) are examined. A 900-year preindustrial simulation from the Community Earth System Model with a slab ocean (CESM-SOM) is used to estimate the LRF using FDT. For GRF, 106 pairs of CESM-SOM simulations with warm and cold q-flux patches are performed. FDT is found to have skill in estimating the SST response to a q-flux forcing when the local SST response is strong, but it fails in inverse estimation of the q-flux forcing for a given SST pattern. In contrast, GRF is shown to be reasonably accurate in estimating both SST response and q-flux forcing. Possible degradation in FDT may be attributed to insufficient data sampling, significant departures of the SST data from Gaussian, and the non-normality of the constructed operator. The accurately estimated GRF-based LRF is used to (i) generate a global surface temperature sensitivity map that shows the q-flux forcing in higher latitudes to be three to four times more effective than in low latitudes in producing global surface warming; (ii) identify the most excitable SST mode (neutral vector) resembling Interdecadal Pacific Oscillation; and (iii) estimate a time-invariant q-flux forcing needed for maintaining the GHG-induced SST warming pattern. The GRF experiments will be used to construct LRF for other variables to further explore climate sensitivities and feedbacks.

MM99.50 - Surface Topography Characterization Using an Atomic Force Microscope Mounted on a Coordinate Measuring Machine

DEFF Research Database (Denmark)

Chiffre, Leonardo De; Hansen, Hans Nørgaard; Kofod, Niels

1999-01-01

The paper describes the construction, testing and use of an integrated system for topographic characterization of fine surfaces on parts having relatively big dimensions. An atomic force microscope (AFM) was mounted on a manual three-coordinate measuring machine (CMM) achieving free positioning o...

EXPERIMENTAL INVESTIGATION OF THE EFFECT OF MACHINIG PARAMETERS OVER CUTTING FORCE AND SURFACE ROUGHNESS IN THE MACHINABILITY OF AA5052 ALLOY

Directory of Open Access Journals (Sweden)

Hasan GÖKKAYA

2006-03-01

Full Text Available In this study, the effects of different cutting and feed rates over average surface roughness and main cutting force during the machinability of AA5052 aluminum alloy with uncoated cemented carbide insert were evaluated. In the experiments, stable depth of cut (1.5 mm, four different cutting speeds (200, 300, 400, 500 m/min and five different feed rates (0.10, 0.15, 0.20, 0.25, 0.30 mm/rev were used. Based on cutting and feed rates, the lowest main cutting force was obtained as 113 in 500 m/min cutting speed and 0.10 mm/rev feed rate and the highest cutting force was obtained as 332 N in 200 m/min cutting speed and 0.30 mm/rev feed rate. The lowest average surface roughness was obtained as 0.95 µm in 200 m/min cutting speed and 0.10 mm/rev feed rate and the highest average surface roughness was obtained as 6.65 µm in 300 m/min cutting speed and 0.30 mm/rev feed rate.

Surface interaction forces of cellulose nanocrystals grafted with thermoresponsive polymer brushes.

Science.gov (United States)

Zoppe, Justin O; Osterberg, Monika; Venditti, Richard A; Laine, Janne; Rojas, Orlando J

2011-07-11

The colloidal stability and thermoresponsive behavior of poly(N-isopropylacrylamide) brushes grafted from cellulose nanocrystals (CNCs) of varying graft densities and molecular weights was investigated. Indication of the grafted polymer brushes was obtained after AFM imaging of CNCs adsorbed on silica. Also, aggregation of the nanoparticles carrying grafts of high degree of polymerization was observed. The responsiveness of grafted CNCs in aqueous dispersions and as an ultrathin film was evaluated by using light scattering, viscosimetry, and colloidal probe microscopy (CPM). Light transmittance measurements showed temperature-dependent aggregation originating from the different graft densities and molecular weights. The lower critical solution temperature (LCST) of grafted poly(NiPAAm) brushes was found to decrease with the ionic strength, as is the case for free poly(NiPAAm) in aqueous solution. Thermal responsive behavior of grafted CNCs in aqueous dispersions was observed by a sharp increase in dispersion viscosity as the temperature approached the LCST. CPM in liquid media for asymmetric systems consisting of ultrathin films of CNCs and a colloidal silica probe showed the distinctive effects of the grafted polymer brushes on interaction and adhesive forces. The origin of such forces was found to be mainly electrostatic and steric in the case of bare and grafted CNCs, respectively. A decrease in the onset of attractive and adhesion forces of grafted CNCs films were observed with the ionic strength of the aqueous solution. The decreased mobility of polymer brushes upon partial collapse and decreased availability of hydrogen bonding sites with higher electrolyte concentration were hypothesized as the main reasons for the less prominent polymer bridging between interacting surfaces.

Single-Molecule Tribology: Force Microscopy Manipulation of a Porphyrin Derivative on a Copper Surface.

Science.gov (United States)

Pawlak, Rémy; Ouyang, Wengen; Filippov, Alexander E; Kalikhman-Razvozov, Lena; Kawai, Shigeki; Glatzel, Thilo; Gnecco, Enrico; Baratoff, Alexis; Zheng, Quanshui; Hod, Oded; Urbakh, Michael; Meyer, Ernst

2016-01-26

The low-temperature mechanical response of a single porphyrin molecule attached to the apex of an atomic force microscope (AFM) tip during vertical and lateral manipulations is studied. We find that approach-retraction cycles as well as surface scanning with the terminated tip result in atomic-scale friction patterns induced by the internal reorientations of the molecule. With a joint experimental and computational effort, we identify the dicyanophenyl side groups of the molecule interacting with the surface as the dominant factor determining the observed frictional behavior. To this end, we developed a generalized Prandtl-Tomlinson model parametrized using density functional theory calculations that includes the internal degrees of freedom of the side group with respect to the core and its interactions with the underlying surface. We demonstrate that the friction pattern results from the variations of the bond length and bond angles between the dicyanophenyl side group and the porphyrin backbone as well as those of the CN group facing the surface during the lateral and vertical motion of the AFM tip.

A hybrid scanning force and light microscope for surface imaging and three-dimensional optical sectioning in differential interference contrast.

Science.gov (United States)

Stemmer, A

1995-04-01

The design of a scanned-cantilever-type force microscope is presented which is fully integrated into an inverted high-resolution video-enhanced light microscope. This set-up allows us to acquire thin optical sections in differential interference contrast (DIC) or polarization while the force microscope is in place. Such a hybrid microscope provides a unique platform to study how cell surface properties determine, or are affected by, the three-dimensional dynamic organization inside the living cell. The hybrid microscope presented in this paper has proven reliable and versatile for biological applications. It is the only instrument that can image a specimen by force microscopy and high-power DIC without having either to translate the specimen or to remove the force microscope. Adaptation of the design features could greatly enhance the suitability of other force microscopes for biological work.

Investigation on the Effect of a Pre-Center Drill Hole and Tool Material on Thrust Force, Surface Roughness, and Cylindricity in the Drilling of Al7075.

Science.gov (United States)

Ghasemi, Amir Hossein; Khorasani, Amir Mahyar; Gibson, Ian

2018-01-16

Drilling is one of the most useful metal cutting processes and is used in various applications, such as aerospace, electronics, and automotive. In traditional drilling methods, the thrust force, torque, tolerance, and tribology (surface roughness) are related to the cutting condition and tool geometry. In this paper, the effects of a pre-center drill hole, tool material, and drilling strategy (including continuous and non-continuous feed) on thrust force, surface roughness, and dimensional accuracy (cylindricity) have been investigated. The results show that using pre-center drill holes leads to a reduction of the engagement force and an improvement in the surface quality and cylindricity. Non-continuous drilling reduces the average thrust force and cylindricity value, and High Speed Steels HSS-Mo (high steel speed + 5-8% Mo) reduces the maximum quantity of cutting forces. Moreover, cylindricity is directly related to cutting temperature and is improved by using a non-continuous drilling strategy.

Investigation on the Effect of a Pre-Center Drill Hole and Tool Material on Thrust Force, Surface Roughness, and Cylindricity in the Drilling of Al7075

Directory of Open Access Journals (Sweden)

Amir Hossein Ghasemi

2018-01-01

Full Text Available Drilling is one of the most useful metal cutting processes and is used in various applications, such as aerospace, electronics, and automotive. In traditional drilling methods, the thrust force, torque, tolerance, and tribology (surface roughness are related to the cutting condition and tool geometry. In this paper, the effects of a pre-center drill hole, tool material, and drilling strategy (including continuous and non-continuous feed on thrust force, surface roughness, and dimensional accuracy (cylindricity have been investigated. The results show that using pre-center drill holes leads to a reduction of the engagement force and an improvement in the surface quality and cylindricity. Non-continuous drilling reduces the average thrust force and cylindricity value, and High Speed Steels HSS-Mo (high steel speed + 5–8% Mo reduces the maximum quantity of cutting forces. Moreover, cylindricity is directly related to cutting temperature and is improved by using a non-continuous drilling strategy.

Functionalization of gold and nanocrystalline diamond atomic force microscope tips for single molecule force spectroscopy

Science.gov (United States)

Drew, Michael E.

The atomic force microscope (AFM) has fueled interest in nanotechnology because of its ability to image surfaces at the nanometer level and act as a molecular force sensor. Functionalization of the surface of an AFM tip surface in a stable, controlled manner expands the capabilities of the AFM and enables additional applications in the fields of single molecule force spectroscopy and nanolithography. Two AFM tip functionalizations are described: the assembly of tripodal molecular tips onto gold AFM tips and the photochemical attachment of terminal alkenes to nanocrystalline diamond (NCD) AFM tips. Two separate tripodal molecules with different linker lengths and a monopodal molecule terminated with biotin were synthesized to attach to a gold AFM tip for single molecule force spectroscopy. The immobilization of these molecules was examined by contact angle measurements, spectroscopic ellipsometry, infrared, and near edge x-ray absorption fine structure (NEXAFS) spectroscopy. All three molecules displayed rupture forces that agreed with previously reported values for the biotin--avidin rupture. The tripodal molecular tip displayed narrower distribution in their force histograms than the monopodal molecular tip. The performance of the tripodal molecular tip was compared to the monopodal molecular tip in single molecule force spectroscopy studies. Over repeated measurements, the distribution of forces for the monopodal molecular tip shifted to lower forces, whereas the distribution for the tripodal molecular tip remained constant throughout. Loading rate dependence and control experiments further indicated that the rupture forces of the tripod molecular tips were specific to the biotin--NeutrAvidin interaction. The second functionalization method used the photochemical attachment of undecylenic acid to NCD AFM tips. The photochemical attachment of undecylenic acid to hydrogen-terminated NCD wafer surfaces was investigated by contact angle measurements, x

Micropatterning of bacteria on two-dimensional lattice protein surface observed by atomic force microscopy

International Nuclear Information System (INIS)

Oh, Y.J.; Jo, W.; Lim, J.; Park, S.; Kim, Y.S.; Kim, Y.

2008-01-01

In this study, we characterized the two-dimensional lattice of bovine serum albumin (BSA) as a chemical and physical barrier against bacterial adhesion, using fluorescence microscopy and atomic force microscopy (AFM). The lattice of BSA on glass surface was fabricated by micro-contact printing (μCP), which is a useful way to pattern a wide range of molecules into microscale features on different types of substrates. The contact-mode AFM measurements showed that the average height of the printed BSA monolayer was 5-6 nm. Escherichia coli adhered rapidly on bare glass slide, while the bacterial adhesion was minimized on the lattices in the range of 1-3 μm 2 . Especially, the bacterial adhesion was completely inhibited on a 1 μm 2 lattice. The results suggest that the anti-adhesion effects are due by the steric repulsion forces exerted by BSA

In situ atomic force microscopy studies of reversible light-induced switching of surface roughness and adhesion in azobenzene-containing PMMA films

International Nuclear Information System (INIS)

Mueller, M.; Gonzalez-Garcia, Y.; Pakula, C.; Zaporojtchenko, V.; Strunskus, T.; Faupel, F.; Herges, R.; Zargarani, D.; Magnussen, O.M.

2011-01-01

Thin films in the range 40-80 nm of a blend of PMMA with an azobenzene derivative have been studied directly during UV and blue light irradiation by atomic force microscopy (AFM), revealing highly reversible changes in the surface roughness and the film adhesion. UV light induces an ∼80% increase in surface roughness, whereas illumination by blue light completely reverses these changes. Based on the observed surface topography and transition kinetics a reversible mass flow mechanisms is suggested, where the polarity changes upon switching trigger a wetting-dewetting transition in a surface segregation layer of the chromophore. Similar AFM measurements of the pull-off force indicate a decrease upon UV and an increase after blue light illumination with a complex kinetic behavior: a rapid initial change, attributed to the change in the cis isomer fraction of the azobenzene derivative, and a more gradual change, indicative of slow structural reorganization.

Ex situ investigation of the step bunching on crystal surfaces by atomic force microscopy

Science.gov (United States)

Krasinski, Mariusz J.

1997-07-01

We are describing ex situ observation of step bunching on the surfaces of solution grown potassium dihydrogen phosphate (KDP) and sodium chlorate monocrystals. The measurements have been done with the use of atomic force microscope. The use of this equipment allowed us to see directly the structure of macrosteps. Observation confirmed the existence of step pinning which is one of the proposed mechanisms of step bunching. Despite the very high resolution of AFM it was not possible to determine the nature of pinning point. The monatomic steps on KDP and sodium chlorate crystal surfaces are mainly one unit cell high what seems to be the result of the steps pairing. The origin of observed step pattern is discussed in frames of existing theories.

The contribution of the electrostatic proximity force to atomic force microscopy with insulators

International Nuclear Information System (INIS)

Stanley Czarnecki, W.; Schein, L.B.

2005-01-01

Measurements, using atomic force microscopy, of the force and force derivative on a charged insulating micron sized sphere as a function of gap between the sphere and a conductive plane have revealed attractive forces at finite gaps that are larger than predicted by either van der Waals or conventional electrostatic forces. We suggest that these observations may be due to an electrostatic force that we have identified theoretically and call the proximity force. This proximity force is due to the discrete charges on the surface of the sphere in close proximity to the plane

The contribution of the electrostatic proximity force to atomic force microscopy with insulators

Energy Technology Data Exchange (ETDEWEB)

Stanley Czarnecki, W. [Aetas Technology Corporation, P.O. Box 53398, Irvine, CA 92619-3398 (United States); IBM Corporation, 5600 Cottle Rd., Building 13, San Jose, CA 95193 (United States); Schein, L.B. [Aetas Technology Corporation, P.O. Box 53398, Irvine, CA 92619-3398 (United States)]. E-mail: schein@prodigy.net

2005-05-16

Measurements, using atomic force microscopy, of the force and force derivative on a charged insulating micron sized sphere as a function of gap between the sphere and a conductive plane have revealed attractive forces at finite gaps that are larger than predicted by either van der Waals or conventional electrostatic forces. We suggest that these observations may be due to an electrostatic force that we have identified theoretically and call the proximity force. This proximity force is due to the discrete charges on the surface of the sphere in close proximity to the plane.

Effect of Surface Forces on the Rheology of Particle-Liquid Systems and the Consolidation of Ceramic Powders

Science.gov (United States)

1994-01-31

isxeduced by the addition of citric acid, a potential determining ion. The addition of potassium nitrate, an indifferent ion, did not affect the yield...Leong, T.W. Healy, D.V. Boger, "Surface Chemistry and Rheology of ZrO2 Suspensions Containing Polyacrylate : Effects of Molecular Weight and ZrO2...REPORT DOCUMENTATION PAGE Fr 1 940131 ANNUAL REPORT 2/l/93-1/31/94 "EFFECT OF SURFACE FORCES ON THE RHEOLOGY OF PARTICLE-I LIQUID SYSTEMS AND THE

The influence of cooling techniques on cutting forces and surface roughness during cryogenic machining of titanium alloys

Directory of Open Access Journals (Sweden)

Wstawska Iwona

2016-12-01

Full Text Available Titanium alloys are one of the materials extensively used in the aerospace industry due to its excellent properties of high specific strength and corrosion resistance. On the other hand, they also present problems wherein titanium alloys are extremely difficult materials to machine. In addition, the cost associated with titanium machining is also high due to lower cutting velocities and shorter tool life. The main objective of this work is a comparison of different cooling techniques during cryogenic machining of titanium alloys. The analysis revealed that applied cooling technique has a significant influence on cutting force and surface roughness (Ra parameter values. Furthermore, in all cases observed a positive influence of cryogenic machining on selected aspects after turning and milling of titanium alloys. This work can be also the starting point to the further research, related to the analysis of cutting forces and surface roughness during cryogenic machining of titanium alloys.

Casimir-lifshitz force out of thermal equilibrium and asymptotic nonadditivity

NARCIS (Netherlands)

Antezza, Mauro; Pitaevskii, Lev P.; Stringari, Sandro; Svetovoy, Vitaly

2006-01-01

We investigate the force acting between two parallel plates held at different temperatures. The force reproduces, as limiting cases, the well-known Casimir-Lifshitz surface-surface force at thermal equilibrium and the surface-atom force out of thermal equilibrium recently derived by M. Antezza et

Distributed Surface Force

Science.gov (United States)

2014-06-01

surface missile SSN nuclear powered attack submarine ST Singapore Technologies T-AKE Lewis and Clarke class TDSI Temasek Defense Systems Institute TRL...total of 313 (Department of the Navy N8 Department 2013). This 306-ship plan includes 12 SSBNs, 48 SSNs , 11 aircraft carriers, 88 cruisers and...MoCil • • West Reef Barque Canada Stloal frinc2 of wales Bank • Reef fat Grair9r Bani< Aneoyna Cltf •Mari\\eles • • • • Nlenwl Bank Ardaser n Dalas

Influence of ion pairing in ionic liquids on electrical double layer structures and surface force using classical density functional approach.

Science.gov (United States)

Ma, Ke; Forsman, Jan; Woodward, Clifford E

2015-05-07

We explore the influence of ion pairing in room temperature ionic liquids confined by planar electrode surfaces. Using a coarse-grained model for the aromatic ionic liquid [C4MIM(+)][BF4 (-)], we account for an ion pairing component as an equilibrium associating species within a classical density functional theory. We investigated the resulting structure of the electrical double layer as well as the ensuing surface forces and differential capacitance, as a function of the degree of ion association. We found that the short-range structure adjacent to surfaces was remarkably unaffected by the degree of ion pairing, up to several molecular diameters. This was even the case for 100% of ions being paired. The physical implications of ion pairing only become apparent in equilibrium properties that depend upon the long-range screening of charges, such as the asymptotic behaviour of surface forces and the differential capacitance, especially at low surface potential. The effect of ion pairing on capacitance is consistent with their invocation as a source of the anomalous temperature dependence of the latter. This work shows that ion pairing effects on equilibrium properties are subtle and may be difficult to extract directly from simulations.

Sub-Angstrom oscillation amplitude non-contact atomic force microscopy for lateral force gradient measurement

International Nuclear Information System (INIS)

Atabak, Mehrdad; Unverdi, Ozhan; Ozer, H. Ozguer; Oral, Ahmet

2009-01-01

We report the first results from novel sub-Angstrom oscillation amplitude non-contact atomic force microscopy developed for lateral force gradient measurements. Quantitative lateral force gradients between a tungsten tip and Si(1 1 1)-(7 x 7) surface can be measured using this microscope. Simultaneous lateral force gradient and scanning tunnelling microscope images of single and multi atomic steps are obtained. In our measurement, tunnel current is used as feedback. The lateral stiffness contrast has been observed to be 2.5 N/m at single atomic step, in contrast to 13 N/m at multi atomic step on Si(1 1 1) surface. We also carried out a series of lateral stiffness-distance spectroscopy. We observed lateral stiffness-distance curves exhibit sharp increase in the stiffness as the sample is approached towards the surface. We usually observed positive stiffness and sometimes going into slightly negative region.

Students’ understanding of forces: Force diagrams on horizontal and inclined plane

Science.gov (United States)

Sirait, J.; Hamdani; Mursyid, S.

2018-03-01

This study aims to analyse students’ difficulties in understanding force diagrams on horizontal surfaces and inclined planes. Physics education students (pre-service physics teachers) of Tanjungpura University, who had completed a Basic Physics course, took a Force concept test which has six questions covering three concepts: an object at rest, an object moving at constant speed, and an object moving at constant acceleration both on a horizontal surface and on an inclined plane. The test is in a multiple-choice format. It examines the ability of students to select appropriate force diagrams depending on the context. The results show that 44% of students have difficulties in solving the test (these students only could solve one or two items out of six items). About 50% of students faced difficulties finding the correct diagram of an object when it has constant speed and acceleration in both contexts. In general, students could only correctly identify 48% of the force diagrams on the test. The most difficult task for the students in terms was identifying the force diagram representing forces exerted on an object on in an inclined plane.

Forced synchronization of large-scale circulation to increase predictability of surface states

Science.gov (United States)

Shen, Mao-Lin; Keenlyside, Noel; Selten, Frank; Wiegerinck, Wim; Duane, Gregory

2016-04-01

Numerical models are key tools in the projection of the future climate change. The lack of perfect initial condition and perfect knowledge of the laws of physics, as well as inherent chaotic behavior limit predictions. Conceptually, the atmospheric variables can be decomposed into a predictable component (signal) and an unpredictable component (noise). In ensemble prediction the anomaly of ensemble mean is regarded as the signal and the ensemble spread the noise. Naturally the prediction skill will be higher if the signal-to-noise ratio (SNR) is larger in the initial conditions. We run two ensemble experiments in order to explore a way to reduce the SNR of surface winds and temperature. One ensemble experiment is AGCM with prescribing sea surface temperature (SST); the other is AGCM with both prescribing SST and nudging the high-level temperature and winds to ERA-Interim. Each ensemble has 30 members. Larger SNR is expected and found over the tropical ocean in the first experiment because the tropical circulation is associated with the convection and the associated surface wind convergence as these are to a large extent driven by the SST. However, small SNR is found over high latitude ocean and land surface due to the chaotic and non-synchronized atmosphere states. In the second experiment the higher level temperature and winds are forced to be synchronized (nudged to reanalysis) and hence a larger SNR of surface winds and temperature is expected. Furthermore, different nudging coefficients are also tested in order to understand the limitation of both synchronization of large-scale circulation and the surface states. These experiments will be useful for the developing strategies to synchronize the 3-D states of atmospheric models that can be later used to build a super model.

Investigation of the range of validity of the pairwise summation method applied to the calculation of the surface roughness correction to the van der Waals force

Science.gov (United States)

Gusso, André; Burnham, Nancy A.

2016-09-01

It has long been recognized that stochastic surface roughness can considerably change the van der Waals (vdW) force between interacting surfaces and particles. However, few analytical expressions for the vdW force between rough surfaces have been presented in the literature. Because they have been derived using perturbative methods or the proximity force approximation the expressions are valid when the roughness correction is small and for a limited range of roughness parameters and surface separation. In this work, a nonperturbative approach, the effective density method (EDM) is proposed to circumvent some of these limitations. The method simplifies the calculations of the roughness correction based on pairwise summation (PWS), and allows us to derive simple expressions for the vdW force and energy between two semispaces covered with stochastic rough surfaces. Because the range of applicability of PWS and, therefore, of our results, are not known a priori, we compare the predictions based on the EDM with those based on the multilayer effective medium model, whose range of validity can be defined more properly and which is valid when the roughness correction is comparatively large. We conclude that the PWS can be used for roughness characterized by a correlation length of the order of its rms amplitude, when this amplitude is of the order of or smaller than a few nanometers, and only for typically insulating materials such as silicon dioxide, silicon nitride, diamond, and certain glasses, polymers and ceramics. The results are relevant for the correct modeling of systems where the vdW force can play a significant role such as micro and nanodevices, for the calculation of the tip-sample force in atomic force microscopy, and in problems involving adhesion.

Investigation of the surface potential of TiO2 (110) by frequency-modulation Kelvin probe force microscopy

Science.gov (United States)

Kou, Lili; Li, Yan Jun; Kamijyo, Takeshi; Naitoh, Yoshitaka; Sugawara, Yasuhiro

2016-12-01

We investigate the surface potential distribution on a TiO2 (110)-1 × 1 surface by Kelvin probe force microscopy (KPFM) and atom-dependent bias-distance spectroscopic mapping. The experimental results demonstrate that the local contact potential difference increases on twofold-coordinated oxygen sites, and decreases on OH defects and fivefold-coordinated Ti sites. We propose a qualitative model to explain the origin of the surface potential of TiO2 (110). We qualitatively calculate the surface potential induced by chemical potential and permanent surface dipole. The calculated results agree with our experimental ones. Therefore, we suggest that the surface potential of TiO2 (110) is dominated not only by the permanent surface dipole between the tip apex atom and surface, but also by the dipoles induced by the chemical interaction between the tip and sample. The KPFM technique demonstrate the possibility of investigation of the charge transfer phenomenon on TiO2 surface under gas conditions. It is useful for the elucidation of the mechanism of the catalytic reactions.

Continuous surface force based lattice Boltzmann equation method for simulating thermocapillary flow

International Nuclear Information System (INIS)

Zheng, Lin; Zheng, Song; Zhai, Qinglan

2016-01-01

In this paper, we extend a lattice Boltzmann equation (LBE) with continuous surface force (CSF) to simulate thermocapillary flows. The model is designed on our previous CSF LBE for athermal two phase flow, in which the interfacial tension forces and the Marangoni stresses as the results of the interface interactions between different phases are described by a conception of CSF. In this model, the sharp interfaces between different phases are separated by a narrow transition layers, and the kinetics and morphology evolution of phase separation would be characterized by an order parameter via Cahn–Hilliard equation which is solved in the frame work of LBE. The scalar convection–diffusion equation for temperature field is resolved by thermal LBE. The models are validated by thermal two layered Poiseuille flow, and two superimposed planar fluids at negligibly small Reynolds and Marangoni numbers for the thermocapillary driven convection, which have analytical solutions for the velocity and temperature. Then thermocapillary migration of two/three dimensional deformable droplet are simulated. Numerical results show that the predictions of present LBE agreed with the analytical solution/other numerical results. - Highlights: • A CSF LBE to thermocapillary flows. • Thermal layered Poiseuille flows. • Thermocapillary migration.

Continuous surface force based lattice Boltzmann equation method for simulating thermocapillary flow

Energy Technology Data Exchange (ETDEWEB)

Zheng, Lin, E-mail: lz@njust.edu.cn [School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Zheng, Song [School of Mathematics and Statistics, Zhejiang University of Finance and Economics, Hangzhou 310018 (China); Zhai, Qinglan [School of Economics Management and Law, Chaohu University, Chaohu 238000 (China)

2016-02-05

In this paper, we extend a lattice Boltzmann equation (LBE) with continuous surface force (CSF) to simulate thermocapillary flows. The model is designed on our previous CSF LBE for athermal two phase flow, in which the interfacial tension forces and the Marangoni stresses as the results of the interface interactions between different phases are described by a conception of CSF. In this model, the sharp interfaces between different phases are separated by a narrow transition layers, and the kinetics and morphology evolution of phase separation would be characterized by an order parameter via Cahn–Hilliard equation which is solved in the frame work of LBE. The scalar convection–diffusion equation for temperature field is resolved by thermal LBE. The models are validated by thermal two layered Poiseuille flow, and two superimposed planar fluids at negligibly small Reynolds and Marangoni numbers for the thermocapillary driven convection, which have analytical solutions for the velocity and temperature. Then thermocapillary migration of two/three dimensional deformable droplet are simulated. Numerical results show that the predictions of present LBE agreed with the analytical solution/other numerical results. - Highlights: • A CSF LBE to thermocapillary flows. • Thermal layered Poiseuille flows. • Thermocapillary migration.

A facile and cost-effective approach to engineer surface roughness for preparation of large-scale superhydrophobic substrate with high adhesive force

Science.gov (United States)

Zhou, Bingpu; Tian, Jingxuan; Wang, Cong; Gao, Yibo; Wen, Weijia

2016-12-01

This study presents a convenient avenue to fabricate polydimethylsiloxane (PDMS) with controllable surface morphologies and wetting characteristics via standard molding technique. The templates with engineered surface roughness were simply prepared by combinations of microfluidics and photo-polymerization of N-Isopropylacrylamide (NIPAM). The surface morphology of mold could be adjusted via ultraviolet-curing duration or the grafting density, which means that the surface of PDMS sample replicated from the mold could also be easily controlled based on the proposed method. Furthermore, via multiple grafting and replication processes, we have successfully demonstrated that hydrophobicity properties of prepared PDMS samples could be swiftly enhanced to ∼154° with highly adhesive force with resident water droplets. The obtained PDMS samples exhibited well resistance to external mechanical deformation even up to 100 cycles. The proposed scheme is timesaving, cost-effective and suitable for large-scale production of superhydrophobic PDMS substrates. We believe that the presented approach can provide a promising method for preparing superhydrophobic surface with highly adhesive force for on-chip liquid transport, localized reaction, etc.

Rubber friction and force transmission during the shearing process of actively-driven vacuum grippers on rough surfaces

International Nuclear Information System (INIS)

Kern, Patrick

2016-01-01

Nowadays, vacuum grippers come in many different shapes and sizes. Their stability is guaranteed through specially manufactured metal fittings. These fittings are non-positively and positively connected to the elastic part of the vacuum gripper. The design of the elastic part may vary, though. Elastomer components are used to ensure tightness for the negative pressure in the active cave chamber of the vacuum gripper, as well as for the transfer of shearing forces, which acting parallel to the surface. Some vacuum grippers feature one elastomer for both the sealing function and the transfer of shear forces; other gripper types are equipped with various elastomers for those applications. The vacuum grippers described in this work are equipped with structured rubber friction pads, their tightness being ensured by sealing lips made of a flexible foam rubber. A restraint system consisting of one or several vacuum grippers must be sized prior to its actual practical use. For the transmission of shearing forces, which acting parallel to the surface, it is necessary to take the tribological system, consisting of the suction element's elastomer and the base material, into account since these loads put shearing stress on the vacuum gripper. In practice, however, a standardized value is given for the coefficient of friction μ; i.e. the ratio of transmissible frictional force to the normal force. This does neither include a detailed description of the elastomer used nor of the roughness of the base material. The standardized friction coefficients cannot be applied to the practical design of restraint systems. The present work includes the analysis of the load transmission and the modeling of the friction coefficients μ on rough surfaces during the shearing process of actively-driven vacuum grippers. Based on current theories, the phenomenon of elastomeric friction can be attributed to the two main components of hysteresis and adhesion friction. Both components are presented

Influence of the Molecular Adhesion Force on the Indentation Depth of a Particle into the Wafer Surface in the CMP Process

Directory of Open Access Journals (Sweden)

Zhou Jianhua

2014-01-01

Full Text Available By theoretical calculation, the external force on the particle conveyed by pad asperities and the molecular adhesion force between particle and wafer are compared and analyzed quantitatively. It is confirmed that the molecular adhesion force between particle and wafer has a great influence on the chemical mechanical polishing (CMP material removal process. Considering the molecular adhesion force between particle and wafer, a more precise model for the indentation of a particle into the wafer surface is developed in this paper, and the new model is compared with the former model which neglected the molecular adhesion force. Through theoretical analyses, an approach and corresponding critical values are applied to estimate whether the molecular adhesion force in CMP can be neglected. These methods can improve the precision of the material removal model of CMP.

Stiction in surface micromachining

NARCIS (Netherlands)

Tas, Niels Roelof; Sonnenberg, A.H.; Jansen, Henricus V.; Legtenberg, R.; Legtenberg, Rob; Elwenspoek, Michael Curt

1996-01-01

Due to the smoothness of the surfaces in surface micromachining, large adhesion forces between fabricated structures and the substrate are encountered. Four major adhesion mechanisms have been analysed: capillary forces, hydrogen bridging, electrostatic forces and van der Waals forces. Once contact

Revised model for the radiation force exerted by standing surface acoustic waves on a rigid cylinder

Science.gov (United States)

Liang, Shen; Chaohui, Wang

2018-03-01

In this paper, a model for the radiation force exerted by standing surface acoustic waves (SSAWs) on a rigid cylinder in inviscid fluids is extended to account for the dependence on the Rayleigh angle. The conventional model for the radiation force used in the SSAW-based applications is developed in plane standing waves, which fails to predict the movement of the cylinder in the SSAW. Our revised model reveals that, in the direction normal to the piezoelectric substrate on which the SSAW is generated, acoustic radiation force can be large enough to drive the cylinder even in the long-wavelength limit. Furthermore, the force in this direction can not only push the cylinder away, but also pull it back toward the substrate. In the direction parallel to the substrate, the equilibrium positions for particles can be actively tuned by changing Rayleigh angle. As an example considered in the paper, with the reduction of Rayleigh angle the equilibrium positions for steel cylinders in water change from pressure nodes to pressure antinodes. The model can thus be used in the design of SSAWs for particle manipulations.

Evaluation of surface roughness of orthodontic wires by means of atomic force microscopy.

Science.gov (United States)

D'Antò, Vincenzo; Rongo, Roberto; Ametrano, Gianluca; Spagnuolo, Gianrico; Manzo, Paolo; Martina, Roberto; Paduano, Sergio; Valletta, Rosa

2012-09-01

To compare the surface roughness of different orthodontic archwires. Four nickel-titanium wires (Sentalloy(®), Sentalloy(®) High Aesthetic, Titanium Memory ThermaTi Lite(®), and Titanium Memory Esthetic(®)), three β-titanium wires (TMA(®), Colored TMA(®), and Beta Titanium(®)), and one stainless-steel wire (Stainless Steel(®)) were considered for this study. Three samples for each wire were analyzed by atomic force microscopy (AFM). Three-dimensional images were processed using Gwiddion software, and the roughness average (Ra), the root mean square (Rms), and the maximum height (Mh) values of the scanned surface profile were recorded. Statistical analysis was performed by one-way analysis of variance (ANOVA) followed by Tukey's post hoc test (P Sentalloy High Aesthetic was the roughest (Ra  =  133.5 ± 10.8; Rms  =  165.8 ± 9.8; Mh  =  949.6 ± 192.1) of the archwires. The surface quality of the wires investigated differed significantly. Ion implantation effectively reduced the roughness of TMA. Moreover, Teflon(®)-coated Titanium Memory Esthetic was less rough than was ion-implanted Sentalloy High Aesthetic.

Effects of Cement, Abutment Surface Pretreatment, and Artificial Aging on the Force Required to Detach Cantilever Fixed Dental Prostheses from Dental Implants.

Science.gov (United States)

Kappel, Stefanie; Chepura, Taras; Schmitter, Marc; Rammelsberg, Peter; Rues, Stefan

To examine the in vitro effects of different cements, abutment surface preconditioning, and artificial aging on the maximum tensile force needed to detach cantilever fixed dental prostheses (FDPs) from dental implants with titanium abutments. A total of 32 tissue-level implants were combined with standardized titanium abutments. For each test group, eight cantilever FDPs were fabricated using selective laser melting (cobalt-chromium [CoCr] alloy). The inner surfaces of the cantilever FDPs and half of the abutments were sandblasted and then joined by use of four different cements (two permanent and two semi-permanent) in two different amounts per cement. Subgroups were tested after either artificial aging (thermocycling and chewing simulation) or 3 days of water storage. Finally, axial pull off-tests were performed for each abutment separately. Cement type and surface pretreatment significantly affected decementation behavior. The highest retention forces (approximately 1,200 N) were associated with sandblasted abutments and permanent cements. With unconditioned abutments, temporary cements (Fu cement (Fu ≈ 100 N), resulted in rather low retention forces. Zinc phosphate cement guaranteed high retention forces. After aging, retention was sufficient only for cementation with zinc phosphate cement and for the combination of sandblasted abutments and glass-ionomer cement. When glass-ionomer cement is used to fix cantilever FDPs on implants, sandblasting of standard titanium abutments may help prevent loss of retention. Retention forces were still high for FDPs fixed with zinc phosphate cement, even when the abutments were not pretreated. Use of permanent cements only, however, is recommended to prevent unwanted loosening of cantilever FDPs.

Using Force to Probe Single-Molecule Receptor-Cytoskeletal Anchoring Beneath the Surface of a Living Cell

DEFF Research Database (Denmark)

Evans, Evan; Kinoshita, Koji

2007-01-01

-cytoskeletal unbinding increased exponentially with the level of force, suggesting disruption at a site of single-molecule interaction. Since many important enzymes and signaling molecules are closely associated with a membrane receptor-cytoskeletal linkage, pulling on a receptor could alter interactions among its......The ligation of cell surface receptors often communicates a signal that initiates a cytoplasmic chemical cascade to implement an important cell function. Less well understood is how physical stress applied to a cell surface adhesive bond propagates throughout the cytostructure to catalyze...... or trigger important steps in these chemical processes. Probing the nanoscale impact of pulling on cell surface bonds, we discovered that receptors frequently detach prematurely from the interior cytostructure prior to failure of the exterior adhesive bond [Evans, E., Heinrich, V., Leung, A., and Kinoshita...

Contributions of developed and developing countries to global climate forcing and surface temperature change

International Nuclear Information System (INIS)

Ward, D S; Mahowald, N M

2014-01-01

Understanding the relative contributions of individual countries to global climate change for different time periods is essential for mitigation strategies that seek to hold nations accountable for their historical emissions. Previous assessments of this kind have compared countries by their greenhouse gas emissions, but have yet to consider the full spectrum of the short-lived gases and aerosols. In this study, we use the radiative forcing of anthropogenic emissions of long-lived greenhouse gases, ozone precursors, aerosols, and from albedo changes from land cover change together with a simple climate model to evaluate country contributions to climate change. We assess the historical contribution of each country to global surface temperature change from anthropogenic forcing ( Δ T s ), future Δ T s through year 2100 given two different emissions scenarios, and the Δ T s that each country has committed to from past activities between 1850 and 2010 (committed Δ T s ). By including forcings in addition to the long-lived greenhouse gases the contribution of developed countries, particularly the United States, to Δ T s from 1850 to 2010 (58%) is increased compared to an assessment of CO 2 -equivalent emissions for the same time period (52%). Contributions to committed Δ T s evaluated at year 2100, dominated by long-lived greenhouse gas forcing, are more evenly split between developed and developing countries (55% and 45%, respectively). The portion of anthropogenic Δ T s attributable to developing countries is increasing, led by emissions from China and India, and we estimate that this will surpass the contribution from developed countries around year 2030. (paper)

Simultaneous fitting of a potential-energy surface and its corresponding force fields using feedforward neural networks

Science.gov (United States)

Pukrittayakamee, A.; Malshe, M.; Hagan, M.; Raff, L. M.; Narulkar, R.; Bukkapatnum, S.; Komanduri, R.

2009-04-01

An improved neural network (NN) approach is presented for the simultaneous development of accurate potential-energy hypersurfaces and corresponding force fields that can be utilized to conduct ab initio molecular dynamics and Monte Carlo studies on gas-phase chemical reactions. The method is termed as combined function derivative approximation (CFDA). The novelty of the CFDA method lies in the fact that although the NN has only a single output neuron that represents potential energy, the network is trained in such a way that the derivatives of the NN output match the gradient of the potential-energy hypersurface. Accurate force fields can therefore be computed simply by differentiating the network. Both the computed energies and the gradients are then accurately interpolated using the NN. This approach is superior to having the gradients appear in the output layer of the NN because it greatly simplifies the required architecture of the network. The CFDA permits weighting of function fitting relative to gradient fitting. In every test that we have run on six different systems, CFDA training (without a validation set) has produced smaller out-of-sample testing error than early stopping (with a validation set) or Bayesian regularization (without a validation set). This indicates that CFDA training does a better job of preventing overfitting than the standard methods currently in use. The training data can be obtained using an empirical potential surface or any ab initio method. The accuracy and interpolation power of the method have been tested for the reaction dynamics of H+HBr using an analytical potential. The results show that the present NN training technique produces more accurate fits to both the potential-energy surface as well as the corresponding force fields than the previous methods. The fitting and interpolation accuracy is so high (rms error=1.2 cm-1) that trajectories computed on the NN potential exhibit point-by-point agreement with corresponding

Simultaneous Force Regression and Movement Classification of Fingers via Surface EMG within a Unified Bayesian Framework.

Science.gov (United States)

Baldacchino, Tara; Jacobs, William R; Anderson, Sean R; Worden, Keith; Rowson, Jennifer

2018-01-01

This contribution presents a novel methodology for myolectric-based control using surface electromyographic (sEMG) signals recorded during finger movements. A multivariate Bayesian mixture of experts (MoE) model is introduced which provides a powerful method for modeling force regression at the fingertips, while also performing finger movement classification as a by-product of the modeling algorithm. Bayesian inference of the model allows uncertainties to be naturally incorporated into the model structure. This method is tested using data from the publicly released NinaPro database which consists of sEMG recordings for 6 degree-of-freedom force activations for 40 intact subjects. The results demonstrate that the MoE model achieves similar performance compared to the benchmark set by the authors of NinaPro for finger force regression. Additionally, inherent to the Bayesian framework is the inclusion of uncertainty in the model parameters, naturally providing confidence bounds on the force regression predictions. Furthermore, the integrated clustering step allows a detailed investigation into classification of the finger movements, without incurring any extra computational effort. Subsequently, a systematic approach to assessing the importance of the number of electrodes needed for accurate control is performed via sensitivity analysis techniques. A slight degradation in regression performance is observed for a reduced number of electrodes, while classification performance is unaffected.

Interannual Variation of Surface Circulation in the Japan/East Sea due to External Forcings and Intrinsic Variability

Science.gov (United States)

Choi, Byoung-Ju; Cho, Seong Hun; Jung, Hee Seok; Lee, Sang-Ho; Byun, Do-Seong; Kwon, Kyungman

2018-03-01

The interannual variation of surface ocean currents can be as large as seasonal variation in the Japan/East Sea (JES). To identify the major factors that cause such interannual variability of surface ocean circulation in the JES, surface circulation was simulated from 1998 to 2009 using a three-dimensional model. Contributions of atmospheric forcing (ATM), open boundary data (OBC), and intrinsic variability (ITV) of the surface flow in the JES on the interannual variability of surface ocean circulation were separately examined using numerical simulations. Variability in surface circulation was quantified in terms of variance in sea surface height, 100-m depth water temperature, and surface currents. ITV was found to be the dominant factor that induced interannual variabilities of surface circulation, the main path of the East Korea Warm Current (EKWC), and surface kinetic energy on a time scale of 2-4 years. OBC and ATM were secondary factors contributing to the interannual variation of surface circulation. Interannual variation of ATM changed the separation latitude of EKWC and increased the variability of surface circulation in the Ulleung Basin. Interannual variation of OBC enhanced low-frequency changes in surface circulation and eddies in the Yamato Basin. It also modulated basin-wide uniform oscillations of sea level. This study suggests that precise estimation of initial conditions using data assimilation is essential for long-term prediction of surface circulation in the JES.

Surface and electron emission properties of hydrogen-free diamond-like carbon films investigated by atomic force microscopy

International Nuclear Information System (INIS)

Liu Dongping; Zhang, Sam; Ong, S.-E.; Benstetter, Guenther; Du Hejun

2006-01-01

In this study, we have deposited hydrogen-free diamond-like carbon (DLC) films by using DC magnetron sputtering of graphite target at various r.f. bias voltages. Surface and nanoscale emission properties of these DLC films have been investigated using a combination of atomic force microscopy (AFM)-based nanowear tests and conducting-AFM, by simultaneously measuring the topography and the conductivity of the samples. Nanowear tests show that these DLC films are covered with the thin (1.5-2.0 nm) graphite-like layers at surfaces. Compared to the film bulk structure, the graphite-like surface layers are more conductive. The graphite-like surface layers significantly influence the electron emission properties of these films. Low-energy carbon species can be responsible for the formation of graphite-like surface layers. Nanoscale electron emission measurements have revealed the inhomogeneous emission nature of these films. The low-field emission from these films can be attributed to the existence of sp 2 -configured nanoclusters inside the films

Reduction of Liquid Bridge Force for 3D Microstructure Measurements

Directory of Open Access Journals (Sweden)

Hiroshi Murakami

2016-05-01

Full Text Available Recent years have witnessed an increased demand for a method for precise measurement of the microstructures of mechanical microparts, microelectromechanical systems, micromolds, optical devices, microholes, etc. This paper presents a measurement system for three-dimensional (3D microstructures that use an optical fiber probe. This probe consists of a stylus shaft with a diameter of 2.5 µm and a glass ball with a diameter of 5 µm attached to the stylus tip. In this study, the measurement system, placed in a vacuum vessel, is constructed suitably to prevent adhesion of the stylus tip to the measured surface caused by the surface force resulting from the van der Waals force, electrostatic force, and liquid bridge force. First, these surface forces are analyzed with the aim of investigating the causes of adhesion. Subsequently, the effects of pressure inside the vacuum vessel on surface forces are evaluated. As a result, it is found that the surface force is 0.13 µN when the pressure inside the vacuum vessel is 350 Pa. This effect is equivalent to a 60% reduction in the surface force in the atmosphere.

Effect of the interaction conditions of the probe of an atomic-force microscope with the n-GaAs surface on the triboelectrization phenomenon

Energy Technology Data Exchange (ETDEWEB)

Baklanov, A. V., E-mail: baklanov@mail.ioffe.ru [St. Petersburg State Polytechnical University, Institute of Physics, Nanotechnology, and Telecommunications (Russian Federation); Gutkin, A. A.; Kalyuzhnyy, N. A. [Russian Academy of Sciences, Ioffe Institute (Russian Federation); Brunkov, P. N. [St. Petersburg State Polytechnical University, Institute of Physics, Nanotechnology, and Telecommunications (Russian Federation)

2015-08-15

Triboelectrization as a result of the scanning of an atomic-force-microscope probe over an n-GaAs surface in the contact mode is investigated. The dependences of the local potential variation on the scanning rate and the pressing force of the probe are obtained. The results are explained by point-defect formation in the surface layers of samples under the effect of deformation of these layers during probe scanning. The charge localized at these defects in the case of equilibrium changes the potential of surface, which is subject to triboelectrization. It is shown that, for qualitative explanation of the observed dependences, it is necessary to take into account both the generation and annihilation of defects in the region experiencing deformation.

Force microscopy of layering and friction in an ionic liquid

International Nuclear Information System (INIS)

Hoth, Judith; Hausen, Florian; Bennewitz, Roland; Müser, Martin H

2014-01-01

The mechanical properties of the ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py 1,4 ][FAP]) in confinement between a SiO x and a Au(1 1 1) surface are investigated by means of atomic force microscopy (AFM) under electrochemical control. Up to 12 layers of ion pairs can be detected through force measurements while approaching the tip of the AFM to the surface. The particular shape of the force versus distance curve is explained by a model for the interaction between tip, gold surface and ionic liquid, which assumes an exponentially decaying oscillatory force originating from bulk liquid density correlations. Jumps in the tip–sample distance upon approach correspond to jumps of the compliant force sensor between branches of the oscillatory force curve. Frictional force between the laterally moving tip and the surface is detected only after partial penetration of the last double layer between tip and surface. (paper)

Following the surface response of caffeine cocrystals to controlled humidity storage by atomic force microscopy.

Science.gov (United States)

Cassidy, A M C; Gardner, C E; Jones, W

2009-09-08

Active pharmaceutical ingredient (API) stability in solid state tablet formulation is frequently a function of the relative humidity (RH) environment in which the drug is stored. Caffeine is one such problematic API. Previously reported caffeine cocrystals, however, were found to offer increased resistance to caffeine hydrate formation. Here we report on the use of atomic force microscopy (AFM) to image the surface of two caffeine cocrystal systems to look for differences between the surface and bulk response of the cocrystal to storage in controlled humidity environments. Bulk responses have previously been assessed by powder X-ray diffraction. With AFM, pinning sites were identified at step edges on caffeine/oxalic acid, with these sites leading to non-uniform step movement on going from ambient to 0% RH. At RH >75%, areas of fresh crystal growth were seen on the cocrystal surface. In the case of caffeine/malonic acid the cocrystals were observed to absorb water anisotropically after storage at 75% RH for 2 days, affecting the surface topography of the cocrystal. These results show that AFM expands on the data gathered by bulk analytical techniques, such as powder X-ray diffraction, by providing localised surface information. This surface information may be important for better predicting API stability in isolation and at a solid state API-excipient interface.

Measurements of the Casimir-Lifshitz force in fluids: The effect of electrostatic forces and Debye screening

Science.gov (United States)

Munday, J. N.; Capasso, Federico; Parsegian, V. Adrian; Bezrukov, Sergey M.

2008-09-01

We present detailed measurements of the Casimir-Lifshitz force between two gold surfaces (a sphere and a plate) immersed in ethanol and study the effect of residual electrostatic forces, which are dominated by static fields within the apparatus and can be reduced with proper shielding. Electrostatic forces are further reduced by Debye screening through the addition of salt ions to the liquid. Additionally, the salt leads to a reduction of the Casimir-Lifshitz force by screening the zero-frequency contribution to the force; however, the effect is small between gold surfaces at the measured separations and within experimental error. An improved calibration procedure is described and compared with previous methods. Finally, the experimental results are compared with Lifshitz’s theory and found to be consistent for the materials used in the experiment.

Scratch direction and threshold force in nanoscale scratching using atomic force microscopes

Energy Technology Data Exchange (ETDEWEB)

Tseng, Ampere A., E-mail: ampere.tseng@asu.edu [Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Kuo, Chung-Feng Jeffrey; Jou, Shyankay [Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Nishimura, Shinya; Shirakashi, Jun-ichi [Department of Electrical and Electronic Engineering, Tokyo University of Agriculture and Technology, Tokyo 184-8588 (Japan)

2011-09-01

The nanoscaled tip in an AFM (atomic force microscope) has become an effective scratching tool for material removing in nanofabrication. In this article, the characteristics of using a diamond-coated pyramidal tip to scratch Ni-Fe thin film surfaces was experimentally investigated with the focus on the evaluation of the influence of the scratch or scan direction on the final shape of the scratched geometry as well as the applied scratch force. Results indicated that both the scratched profile and the scratch force were greatly affected by the scratch direction. It has been found that, to minimize the formation of protuberances along the groove sides and to have a better control of the scratched geometry, the tip face should be perpendicular to the scratching direction, which is also known as orthogonal cutting condition. To demonstrate the present findings, three groove patterns have been scratched with the tip face perpendicular to the scratching direction and very little amount of protuberances was observed. The threshold scratch force was also predicted based on the Hertz contact theory. Without considering the surface friction and adhesive forces between the tip and substrate, the threshold force predicted was twice smaller than the measurement value. Finally, recommendations for technical improvement and research focuses are provided.

Scratch direction and threshold force in nanoscale scratching using atomic force microscopes

International Nuclear Information System (INIS)

Tseng, Ampere A.; Kuo, Chung-Feng Jeffrey; Jou, Shyankay; Nishimura, Shinya; Shirakashi, Jun-ichi

2011-01-01

The nanoscaled tip in an AFM (atomic force microscope) has become an effective scratching tool for material removing in nanofabrication. In this article, the characteristics of using a diamond-coated pyramidal tip to scratch Ni-Fe thin film surfaces was experimentally investigated with the focus on the evaluation of the influence of the scratch or scan direction on the final shape of the scratched geometry as well as the applied scratch force. Results indicated that both the scratched profile and the scratch force were greatly affected by the scratch direction. It has been found that, to minimize the formation of protuberances along the groove sides and to have a better control of the scratched geometry, the tip face should be perpendicular to the scratching direction, which is also known as orthogonal cutting condition. To demonstrate the present findings, three groove patterns have been scratched with the tip face perpendicular to the scratching direction and very little amount of protuberances was observed. The threshold scratch force was also predicted based on the Hertz contact theory. Without considering the surface friction and adhesive forces between the tip and substrate, the threshold force predicted was twice smaller than the measurement value. Finally, recommendations for technical improvement and research focuses are provided.

Dependence of Pin Surface Roughness for Friction Forces of Ultrathin Perfluoropolyether Lubricant Film on Magnetic Disks by Pin-on-Disk Test

Directory of Open Access Journals (Sweden)

H. Tani

2012-01-01

Full Text Available We fabricated supersmooth probes for use in pin-on-disk sliding tests by applying gas cluster ion beam irradiation to glass convex lenses. In the fabrication process, various changes were made to the irradiation conditions; these included one-step irradiation of Ar clusters or two-step irradiation of Ar and N2 clusters, with or without Ar cluster-assisted tough carbon deposition prior to N2 irradiation, and the application of various ion doses onto the surface. We successfully obtained probes with a centerline averaged surface roughness that ranged widely from 1.08 to 4.30 nm. Using these probes, we measured the friction forces exerted on magnetic disks coated with a molecularly thin lubricant film. Perfluoropolyether lubricant films with different numbers of hydroxyl end groups were compared, and our results indicated that the friction force increases as the surface roughness of the pin decreases and that increases as the number of hydroxyl end groups increases.

A multilinear regression methodology to analyze the effect of atmospheric and surface forcing on Arctic clouds

Science.gov (United States)

Boeke, R.; Taylor, P. C.; Li, Y.

2017-12-01

Arctic cloud amount as simulated in CMIP5 models displays large intermodel spread- models disagree on the processes important for cloud formation as well as the radiative impact of clouds. The radiative response to cloud forcing can be better assessed when the drivers of Arctic cloud formation are known. Arctic cloud amount (CA) is a function of both atmospheric and surface conditions, and it is crucial to separate the influences of unique processes to understand why the models are different. This study uses a multilinear regression methodology to determine cloud changes using 3 variables as predictors: lower tropospheric stability (LTS), 500-hPa vertical velocity (ω500), and sea ice concentration (SIC). These three explanatory variables were chosen because their effects on clouds can be attributed to unique climate processes: LTS is a thermodynamic indicator of the relationship between clouds and atmospheric stability, SIC determines the interaction between clouds and the surface, and ω500 is a metric for dynamical change. Vertical, seasonal profiles of necessary variables are obtained from the Coupled Model Intercomparison Project 5 (CMIP5) historical simulation, an ocean-atmosphere couple model forced with the best-estimate natural and anthropogenic radiative forcing from 1850-2005, and statistical significance tests are used to confirm the regression equation. A unique heuristic model will be constructed for each climate model and for observations, and models will be tested by their ability to capture the observed cloud amount and behavior. Lastly, the intermodel spread in Arctic cloud amount will be attributed to individual processes, ranking the relative contributions of each factor to shed light on emergent constraints in the Arctic cloud radiative effect.

Importance of Preserving Cross-correlation in developing Statistically Downscaled Climate Forcings and in estimating Land-surface Fluxes and States

Science.gov (United States)

Das Bhowmik, R.; Arumugam, S.

2015-12-01

Multivariate downscaling techniques exhibited superiority over univariate regression schemes in terms of preserving cross-correlations between multiple variables- precipitation and temperature - from GCMs. This study focuses on two aspects: (a) develop an analytical solutions on estimating biases in cross-correlations from univariate downscaling approaches and (b) quantify the uncertainty in land-surface states and fluxes due to biases in cross-correlations in downscaled climate forcings. Both these aspects are evaluated using climate forcings available from both historical climate simulations and CMIP5 hindcasts over the entire US. The analytical solution basically relates the univariate regression parameters, co-efficient of determination of regression and the co-variance ratio between GCM and downscaled values. The analytical solutions are compared with the downscaled univariate forcings by choosing the desired p-value (Type-1 error) in preserving the observed cross-correlation. . For quantifying the impacts of biases on cross-correlation on estimating streamflow and groundwater, we corrupt the downscaled climate forcings with different cross-correlation structure.

Combined use of atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry for cell surface analysis.

Science.gov (United States)

Dague, Etienne; Delcorte, Arnaud; Latgé, Jean-Paul; Dufrêne, Yves F

2008-04-01

Understanding the surface properties of microbial cells is a major challenge of current microbiological research and a key to efficiently exploit them in biotechnology. Here, we used three advanced surface analysis techniques with different sensitivity, probing depth, and lateral resolution, that is, in situ atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry, to gain insight into the surface properties of the conidia of the human fungal pathogen Aspergillus fumigatus. We show that the native ultrastructure, surface protein and polysaccharide concentrations, and amino acid composition of three mutants affected in hydrophobin production are markedly different from those of the wild-type, thereby providing novel insight into the cell wall architecture of A. fumigatus. The results demonstrate the power of using multiple complementary techniques for probing microbial cell surfaces.

Hoof accelerations and ground reaction forces of Thoroughbred racehorses measured on dirt, synthetic, and turf track surfaces.

Science.gov (United States)

Setterbo, Jacob J; Garcia, Tanya C; Campbell, Ian P; Reese, Jennifer L; Morgan, Jessica M; Kim, Sun Y; Hubbard, Mont; Stover, Susan M

2009-10-01

To compare hoof acceleration and ground reaction force (GRF) data among dirt, synthetic, and turf surfaces in Thoroughbred racehorses. 3 healthy Thoroughbred racehorses. Forelimb hoof accelerations and GRFs were measured with an accelerometer and a dynamometric horseshoe during trot and canter on dirt, synthetic, and turf track surfaces at a racecourse. Maxima, minima, temporal components, and a measure of vibration were extracted from the data. Acceleration and GRF variables were compared statistically among surfaces. The synthetic surface often had the lowest peak accelerations, mean vibration, and peak GRFs. Peak acceleration during hoof landing was significantly smaller for the synthetic surface (mean + or - SE, 28.5g + or - 2.9g) than for the turf surface (42.9g + or - 3.8g). Hoof vibrations during hoof landing for the synthetic surface were dirt and turf surfaces. Peak GRF for the synthetic surface (11.5 + or - 0.4 N/kg) was 83% and 71% of those for the dirt (13.8 + or - 0.3 N/kg) and turf surfaces (16.1 + or - 0.7 N/kg), respectively. The relatively low hoof accelerations, vibrations, and peak GRFs associated with the synthetic surface evaluated in the present study indicated that synthetic surfaces have potential for injury reduction in Thoroughbred racehorses. However, because of the unique material properties and different nature of individual dirt, synthetic, and turf racetrack surfaces, extending the results of this study to encompass all track surfaces should be done with caution.

Ductile cutting of silicon microstructures with surface inclination measurement and compensation by using a force sensor integrated single point diamond tool

International Nuclear Information System (INIS)

Chen, Yuan-Liu; Cai, Yindi; Shimizu, Yuki; Ito, So; Gao, Wei; Ju, Bing-Feng

2016-01-01

This paper presents a measurement and compensation method of surface inclination for ductile cutting of silicon microstructures by using a diamond tool with a force sensor based on a four-axis ultra-precision lathe. The X- and Y-directional inclinations of a single crystal silicon workpiece with respect to the X- and Y-motion axes of the lathe slides were measured respectively by employing the diamond tool as a touch-trigger probe, in which the tool-workpiece contact is sensitively detected by monitoring the force sensor output. Based on the measurement results, fabrication of silicon microstructures can be thus carried out directly along the tilted silicon workpiece by compensating the cutting motion axis to be parallel to the silicon surface without time-consuming pre-adjustment of the surface inclination or turning of a flat surface. A diamond tool with a negative rake angle was used in the experiment for superior ductile cutting performance. The measurement precision by using the diamond tool as a touch-trigger probe was investigated. Experiments of surface inclination measurement and ultra-precision ductile cutting of a micro-pillar array and a micro-pyramid array with inclination compensation were carried out respectively to demonstrate the feasibility of the proposed method. (paper)

Static and kinetic friction force and surface roughness of different archwire-bracket sliding contacts.

Science.gov (United States)

Carrion-Vilches, Francisco J; Bermudez, María-Dolores; Fructuoso, Paula

2015-01-01

The aim of this study was to determine the static and kinetic friction forces of the contact bracket-archwire with different dental material compositions in order to select those materials with lower resistance to sliding. We carried out sliding friction tests by means of a universal testing machine following an experimental procedure as described in ASTM D1894 standard. We determined the static and kinetic friction forces under dry and lubricating conditions using an artificial saliva solution at 36.5ºC. The bracket-archwire pairs studied were: stainless steel-stainless steel; stainless steel-glass fiber composite; stainless steel-Nitinol 60; sapphire-stainless steel; sapphire-glass fiber composite; and sapphire-Nitinol 60. The best performance is obtained for Nitinol 60 archwire sliding against a stainless steel bracket, both under dry and lubricated conditions. These results are in agreement with the low surface roughness of Nitinol 60 with respect to the glass fiber composite archwire. The results described here contribute to establishing selection criteria for materials for dental archwire-brackets.

Impact of Dust Radiative Forcing upon Climate. Chapter 13

Science.gov (United States)

Miller, Ronald L.; Knippertz, Peter; Perez Garcia-Pando, Carlos; Perlwitz, Jan P.; Tegan, Ina

2014-01-01

Dust aerosols perturb the atmospheric radiative flux at both solar and thermal wavelengths, altering the energy and water cycles. The climate adjusts by redistributing energy and moisture, so that local temperature perturbations, for example, depend upon the forcing over the entire extent of the perturbed circulation. Within regions frequently mixed by deep convection, including the deep tropics, dust particles perturb the surface air temperature primarily through radiative forcing at the top of the atmosphere (TOA). Many models predict that dust reduces global precipitation. This reduction is typically attributed to the decrease of surface evaporation in response to dimming of the surface. A counterexample is presented, where greater shortwave absorption by dust increases evaporation and precipitation despite greater dimming of the surface. This is attributed to the dependence of surface evaporation upon TOA forcing through its influence upon surface temperature and humidity. Perturbations by dust to the surface wind speed and vegetation (through precipitation anomalies) feed back upon the dust aerosol concentration. The current uncertainty of radiative forcing attributed to dust and the resulting range of climate perturbations calculated by models remain a useful test of our understanding of the mechanisms relating dust radiative forcing to the climate response.

Localization of the phantom force induced by the tunneling current

Science.gov (United States)

Wutscher, Thorsten; Weymouth, Alfred J.; Giessibl, Franz J.

2012-05-01

The phantom force is an apparently repulsive force, which can dominate the atomic contrast of an AFM image when a tunneling current is present. We described this effect with a simple resistive model, in which the tunneling current causes a voltage drop at the sample area underneath the probe tip. Because tunneling is a highly local process, the areal current density is quite high, which leads to an appreciable local voltage drop that in turn changes the electrostatic attraction between tip and sample. However, Si(111)-7×7 has a metallic surface state and it might be proposed that electrons should instead propagate along the surface state, as through a thin metal film on a semiconducting surface, before propagating into the bulk. In this paper, we first measure the phantom force on a sample that displays a metallic surface state [here, Si(111)-7×7] using tips with various radii. If the metallic surface state would lead to a constant electrostatic potential on the surface, we would expect a direct dependence of the phantom force with tip radius. In a second set of experiments, we study H/Si(100), a surface that does not have a metallic surface state. We conclude that a metallic surface state does not suppress the phantom force, but that the local resistance Rs has a strong effect on the magnitude of the phantom force.

Grip Force and 3D Push-Pull Force Estimation Based on sEMG and GRNN

Directory of Open Access Journals (Sweden)

Changcheng Wu

2017-06-01

Full Text Available The estimation of the grip force and the 3D push-pull force (push and pull force in the three dimension space from the electromyogram (EMG signal is of great importance in the dexterous control of the EMG prosthetic hand. In this paper, an action force estimation method which is based on the eight channels of the surface EMG (sEMG and the Generalized Regression Neural Network (GRNN is proposed to meet the requirements of the force control of the intelligent EMG prosthetic hand. Firstly, the experimental platform, the acquisition of the sEMG, the feature extraction of the sEMG and the construction of GRNN are described. Then, the multi-channels of the sEMG when the hand is moving are captured by the EMG sensors attached on eight different positions of the arm skin surface. Meanwhile, a grip force sensor and a three dimension force sensor are adopted to measure the output force of the human's hand. The characteristic matrix of the sEMG and the force signals are used to construct the GRNN. The mean absolute value and the root mean square of the estimation errors, the correlation coefficients between the actual force and the estimated force are employed to assess the accuracy of the estimation. Analysis of variance (ANOVA is also employed to test the difference of the force estimation. The experiments are implemented to verify the effectiveness of the proposed estimation method and the results show that the output force of the human's hand can be correctly estimated by using sEMG and GRNN method.

The effect of uranium on bacterial viability and cell surface morphology using atomic force microscopy in the presence of bicarbonate ions

Energy Technology Data Exchange (ETDEWEB)

Sepulveda-Medina, Paola; Katsenovich, Yelena; Musaramthota, Vishal; Lee, Michelle; Lee, Brady; Dua, Rupak; Lagos, Leonel

2015-06-01

Nuclear production facilities during the Cold War have caused liquid waste to leak and soak into the ground creating multiple radionuclide plumes. The Arthrobacter bacteria are one of the most common groups in soils and are found in large numbers in subsurface environments contaminated with radionuclides. This study experimentally analyzed changes on the bacteria surface after uranium exposure and evaluated the effect of bicarbonate ions on U(VI) toxicity of a less uranium tolerant Arthrobacter strain, G968, by investigating changes in adhesion forces and cells dimensions via atomic force microscopy (AFM). AFM and viability studies showed that samples containing bicarbonate are able to acclimate and withstand uranium toxicity. Samples containing no bicarbonate exhibited deformed surfaces and a low height profile, which might be an indication that the cells are not alive.

Resonant difference-frequency atomic force ultrasonic microscope

Science.gov (United States)

Cantrell, John H. (Inventor); Cantrell, Sean A. (Inventor)

2010-01-01

A scanning probe microscope and methodology called resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), employs an ultrasonic wave launched from the bottom of a sample while the cantilever of an atomic force microscope, driven at a frequency differing from the ultrasonic frequency by one of the contact resonance frequencies of the cantilever, engages the sample top surface. The nonlinear mixing of the oscillating cantilever and the ultrasonic wave in the region defined by the cantilever tip-sample surface interaction force generates difference-frequency oscillations at the cantilever contact resonance. The resonance-enhanced difference-frequency signals are used to create images of nanoscale near-surface and subsurface features.

The effect of drive frequency and set point amplitude on tapping forces in atomic force microscopy: simulation and experiment

International Nuclear Information System (INIS)

Legleiter, Justin

2009-01-01

In tapping mode atomic force microscopy (AFM), a sharp probe tip attached to an oscillating cantilever is allowed to intermittently strike a surface. By raster scanning the probe while monitoring the oscillation amplitude of the cantilever via a feedback loop, topographical maps of surfaces with nanoscale resolution can be acquired. While numerous studies have employed numerical simulations to elucidate the time-resolved tapping force between the probe tip and surface, until recent technique developments, specific read-outs from such models could not be experimentally verified. In this study, we explore, via numerical simulation, the impact of imaging parameters, i.e. set point ratio and drive frequency as a function of resonance, on time-varying tip-sample force interactions, which are directly compared to reconstructed tapping forces from real AFM experiments. As the AFM model contains a feedback loop allowing for the simulation of the entire scanning process, we further explore the impact that various tip-sample force have on the entire imaging process.

Adsorption of chitosan onto carbonaceous surfaces and its application: atomic force microscopy study

International Nuclear Information System (INIS)

Tan Shengnan; Liu Zhiguo; Zu Yuangang; Fu Yujie; Xing Zhimin; Zhao Lin; Sun Tongze; Zhou Zhen

2011-01-01

The adsorption of chitosan onto highly ordered pyrolytic graphite(HOPG) surfaces and its applications have been studied by atomic force microscopy (AFM). The results indicated that chitosan topography formed on the HOPG surface significantly depends on the pH conditions and its concentration for the incubation. Under strongly acidic conditions (pH -1 , chitosan formed into uniform network structures composed of fine chains. When the solution pH was changed from 3.5 to 6.5, chitosan tends to form a thicker film. Under neutral and basic conditions, chitosan changed into spherical nanoparticles, and their sizes were increased with increasing pH. Dendritic structures have been observed when the chitosan concentration was increased up to 5 mg ml -1 . In addition, the chitosan topography can also be influenced by ionic strength and the addition of different metal ions. When 0.1 M metal ions Na + , Mg 2+ , Ca 2+ and Cu 2+ were added into the chitosan solution at pH 3.0 for the incubation, network structures, branched chains, block structures and dense networks attached with many small particles were observed, respectively. The potential applications of these chitosan structures on HOPG have been explored. Preliminary results characterized by AFM and XPS indicated that the chitosan network formed on the HOPG surface can be used for AFM lithography, selective adsorption of gold nanoparticles and DNA molecules.

Rigid two-axis MEMS force plate for measuring cellular traction force

International Nuclear Information System (INIS)

Takahashi, Hidetoshi; Jung, Uijin G; Shimoyama, Isao; Kan, Tetsuo; Tsukagoshi, Takuya; Matsumoto, Kiyoshi

2016-01-01

Cellular traction force is one of the important factors for understanding cell behaviors, such as spreading, migration and differentiation. Cells are known to change their behavior according to the mechanical stiffness of the environment. However, the measurement of cell traction forces on a rigid environment has remained difficult. This paper reports a micro-electromechanical systems (MEMS) force plate that provides a cellular traction force measurement on a rigid substrate. Both the high force sensitivity and high stiffness of the substrate were obtained using piezoresistive sensing elements. The proposed force plate consists of a 70 µ m  ×  15 µ m  ×  5 µ m base as the substrate for cultivating a bovine aortic smooth muscle cell, and the supporting beams with piezoresistors on the sidewall and the surface were used to measure the forces in both the horizontal and vertical directions. The spring constant and force resolution of the fabricated force plate in the horizontal direction were 0.2 N m −1 and less than 0.05 µ N, respectively. The cell traction force was measured, and the traction force increased by approximately 1 µ N over 30 min. These results demonstrate that the proposed force plate is applicable as an effective traction force measurement. (paper)

Compliment Graphene Oxide Coating on Silk Fiber Surface via Electrostatic Force for Capacitive Humidity Sensor Applications.

Science.gov (United States)

Han, Kook In; Kim, Seungdu; Lee, In Gyu; Kim, Jong Pil; Kim, Jung-Ha; Hong, Suck Won; Cho, Byung Jin; Hwang, Wan Sik

2017-02-19

Cylindrical silk fiber (SF) was coated with Graphene oxide (GO) for capacitive humidity sensor applications. Negatively charged GO in the solution was attracted to the positively charged SF surface via electrostatic force without any help from adhesive intermediates. The magnitude of the positively charged SF surface was controlled through the static electricity charges created on the SF surface. The GO coating ability on the SF improved as the SF's positive charge increased. The GO-coated SFs at various conditions were characterized using an optical microscope, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and LCR meter. Unlike the intact SF, the GO-coated SF showed clear response-recovery behavior and well-behaved repeatability when it was exposed to 20% relative humidity (RH) and 90% RH alternatively in a capacitive mode. This approach allows humidity sensors to take advantage of GO's excellent sensing properties and SF's flexibility, expediting the production of flexible, low power consumption devices at relatively low costs.

Direct observation of deformation of nafion surfaces induced by methanol treatment by using atomic force microscopy

International Nuclear Information System (INIS)

Umemura, Kazuo; Kuroda, Reiko; Gao Yanfeng; Nagai, Masayuki; Maeda, Yuta

2008-01-01

We successfully characterized the effect of methanol treatment on the nanoscopic structures of a nafion film, which is widely used in direct methanol fuel cells (DMFCs). Atomic force microscopy (AFM) was used to repetitively image a particular region of a nafion sample before and after methanol solutions were dropped onto the nafion film and dried in air. When the surface was treated with 20% methanol for 5 min, many nanopores appeared on the surface. The number of nanopores increased when the sample was treated twice or thrice. By repetitive AFM imaging of a particular region of the same sample, we found that the shapes of the nanopores were deformed by the repeated methanol treatment, although the size of the nanopores had not significantly changed. The creation of the nanopores was affected by the concentration of methanol. Our results directly visualized the effects of methanol treatment on the surface structures of a nafion film at nanoscale levels for the first time

Training the People’s Liberation Army Air Force Surface-to-Air Missile (SAM) Forces

Science.gov (United States)

2016-01-01

Kyle Brady, and Lyle J. Morris , The U.S.-China Military Scorecard: Forces, Geography, and the Evolving Balance of Power, 1996–2017, Santa Monica, Calif...training articles from January 1, 2004, to December 31, 2006.72 At that time, KJB was published only three times a week ( Tuesdays , Thursdays, and...DeLuca, David A. Shlapak, David R. Frelinger, Burgess Laird, Kyle Brady, and Lyle J. Morris , The U.S.-China Military Scorecard: Forces, Geography

Mapping land water and energy balance relations through conditional sampling of remote sensing estimates of atmospheric forcing and surface states

Science.gov (United States)

Farhadi, Leila; Entekhabi, Dara; Salvucci, Guido

2016-04-01

In this study, we develop and apply a mapping estimation capability for key unknown parameters that link the surface water and energy balance equations. The method is applied to the Gourma region in West Africa. The accuracy of the estimation method at point scale was previously examined using flux tower data. In this study, the capability is scaled to be applicable with remotely sensed data products and hence allow mapping. Parameters of the system are estimated through a process that links atmospheric forcing (precipitation and incident radiation), surface states, and unknown parameters. Based on conditional averaging of land surface temperature and moisture states, respectively, a single objective function is posed that measures moisture and temperature-dependent errors solely in terms of observed forcings and surface states. This objective function is minimized with respect to parameters to identify evapotranspiration and drainage models and estimate water and energy balance flux components. The uncertainty of the estimated parameters (and associated statistical confidence limits) is obtained through the inverse of Hessian of the objective function, which is an approximation of the covariance matrix. This calibration-free method is applied to the mesoscale region of Gourma in West Africa using multiplatform remote sensing data. The retrievals are verified against tower-flux field site data and physiographic characteristics of the region. The focus is to find the functional form of the evaporative fraction dependence on soil moisture, a key closure function for surface and subsurface heat and moisture dynamics, using remote sensing data.

An improved method for calculation of interface pressure force in PLIC-VOF methods

International Nuclear Information System (INIS)

Sefollahi, M.; Shirani, E.

2004-08-01

Conventional methods for the modeling of surface tension force in Piecewise Linear Interface Calculation-Volume of Fluid (PLIC-VOF) methods, such as Continuum Surface Force (CSF), Continuum Surface Stress (CSS) and also Meier's method, convert the surface tension force into a body force. Not only do they include the force in the interfacial cells but also in the neighboring cells. Thus they produce spurious currents. Also the pressure jump, due to the surface tension, is not calculated accurately in these methods. In this paper a more accurate method for the application of interface force in the computational modeling of free surfaces and interfaces which use PLIC-VOF methods is developed. This method is based on the evaluation of the surface tension force only in the interfacial cells and not the neighboring cells. Also the normal and the interface surface area needed for the calculation of the surface tension force is calculated more accurately. The present method is applied to a two-dimensional motionless drop of liquid and a bubble of gas as well as a non-circular two-dimensional drop, which oscillates due to the surface tension force, in an initially stagnant fluid with no gravity force. The results are compared with the results of the cases when CSF, CSS and Meier's methods are used. It is shown that the present method calculates pressure jump at the interface more accurately and produces less spurious currents comparing to CSS an CSF models. (author)

Single-cell force spectroscopy of pili-mediated adhesion

Science.gov (United States)

Sullan, Ruby May A.; Beaussart, Audrey; Tripathi, Prachi; Derclaye, Sylvie; El-Kirat-Chatel, Sofiane; Li, James K.; Schneider, Yves-Jacques; Vanderleyden, Jos; Lebeer, Sarah; Dufrêne, Yves F.

2013-12-01

Although bacterial pili are known to mediate cell adhesion to a variety of substrates, the molecular interactions behind this process are poorly understood. We report the direct measurement of the forces guiding pili-mediated adhesion, focusing on the medically important probiotic bacterium Lactobacillus rhamnosus GG (LGG). Using non-invasive single-cell force spectroscopy (SCFS), we quantify the adhesion forces between individual bacteria and biotic (mucin, intestinal cells) or abiotic (hydrophobic monolayers) surfaces. On hydrophobic surfaces, bacterial pili strengthen adhesion through remarkable nanospring properties, which - presumably - enable the bacteria to resist high shear forces under physiological conditions. On mucin, nanosprings are more frequent and adhesion forces larger, reflecting the influence of specific pili-mucin bonds. Interestingly, these mechanical responses are no longer observed on human intestinal Caco-2 cells. Rather, force curves exhibit constant force plateaus with extended ruptures reflecting the extraction of membrane nanotethers. These single-cell analyses provide novel insights into the molecular mechanisms by which piliated bacteria colonize surfaces (nanosprings, nanotethers), and offer exciting avenues in nanomedicine for understanding and controlling the adhesion of microbial cells (probiotics, pathogens).

Probing living bacterial adhesion by single cell force spectroscopy using atomic force microscopy

DEFF Research Database (Denmark)

Zeng, Guanghong; Ogaki, Ryosuke; Regina, Viduthalai R.

be considered. We have therefore developed a simple and versatile method to make single-cell bacterial probes for measuring single cell adhesion with atomic force microscopy (AFM).[1] A single-cell probe was readily made by picking up a bacterial cell from a glass surface using a tipless AFM cantilever coated...... random immobilization is obtained by submerging the cantilever in a bacterial suspension. The reported method provides a general platform for investigating single cell interactions of bacteria with different surfaces and other cells by AFM force spectroscopy, thus improving our understanding....... The strain-dependent susceptibility to bacterial colonization on conventional PLL-g-PEG illustrates how bacterial diversity challenges development of “universal” antifouling coatings, and AFM single-cell force spectroscopy was proven to be a powerful tool to provide insights into the molecular mechanisms...

Climate Implications of the Heterogeneity of Anthropogenic Aerosol Forcing

Science.gov (United States)

Persad, Geeta Gayatri

Short-lived anthropogenic aerosols are concentrated in regions of high human activity, where they interact with radiation and clouds, causing horizontally heterogeneous radiative forcing between polluted and unpolluted regions. Aerosols can absorb shortwave energy in the atmosphere, but deplete it at the surface, producing opposite radiative perturbations between the surface and atmosphere. This thesis investigates climate and policy implications of this horizontal and vertical heterogeneity of anthropogenic aerosol forcing, employing the Geophysical Fluid Dynamics Laboratory's AM2.1 and AM3 models, both at a global scale and using East Asia as a regional case study. The degree of difference between spatial patterns of climate change due to heterogeneous aerosol forcing versus homogeneous greenhouse gas forcing deeply impacts the detection, attribution, and prediction of regional climate change. This dissertation addresses a gap in current understanding of these two forcings' response pattern development, using AM2.1 historical forcing simulations. The results indicate that fast atmospheric and land-surface processes alone substantially homogenize the global pattern of surface energy flux response to heterogeneous aerosol forcing. Aerosols' vertical redistribution of energy significantly impacts regional climate, but is incompletely understood. It is newly identified here, via observations and historical and idealized forcing simulations, that increased aerosol-driven atmospheric absorption may explain half of East Asia's recent surface insolation decline. Further, aerosols' surface and atmospheric effects counteract each other regionally---atmospheric heating enhances summer monsoon circulation, while surface dimming suppresses it---but absorbing aerosols' combined effects reduce summer monsoon rainfall. This thesis constitutes the first vertical decomposition of aerosols' impacts in this high-emissions region and elucidates the monsoonal response to aerosols

Modelling of deformation process for the layer of elastoviscoplastic media under surface action of periodic force of arbitrary type

Science.gov (United States)

Mikheyev, V. V.; Saveliev, S. V.

2018-01-01

Description of deflected mode for different types of materials under action of external force plays special role for wide variety of applications - from construction mechanics to circuits engineering. This article con-siders the problem of plastic deformation of the layer of elastoviscolastic soil under surface periodic force. The problem was solved with use of the modified lumped parameters approach which takes into account close to real distribution of normal stress in the depth of the layer along with changes in local mechanical properties of the material taking place during plastic deformation. Special numeric algorithm was worked out for computer modeling of the process. As an example of application suggested algorithm was realized for the deformation of the layer of elasoviscoplastic material by the source of external lateral force with the parameters of real technological process of soil compaction.

Irrigation as an Historical Climate Forcing

Science.gov (United States)

Cook, Benjamin I.; Shukla, Sonali P.; Puma, Michael J.; Nazarenko, Larissa S.

2014-01-01

Irrigation is the single largest anthropogenic water use, a modification of the land surface that significantly affects surface energy budgets, the water cycle, and climate. Irrigation, however, is typically not included in standard historical general circulation model (GCM) simulations along with other anthropogenic and natural forcings. To investigate the importance of irrigation as an anthropogenic climate forcing, we conduct two 5-member ensemble GCM experiments. Both are setup identical to the historical forced (anthropogenic plus natural) scenario used in version 5 of the Coupled Model Intercomparison Project, but in one experiment we also add water to the land surface using a dataset of historically estimated irrigation rates. Irrigation has a negligible effect on the global average radiative balance at the top of the atmosphere, but causes significant cooling of global average surface air temperatures over land and dampens regional warming trends. This cooling is regionally focused and is especially strong in Western North America, the Mediterranean, the Middle East, and Asia. Irrigation enhances cloud cover and precipitation in these same regions, except for summer in parts of Monsoon Asia, where irrigation causes a reduction in monsoon season precipitation. Irrigation cools the surface, reducing upward fluxes of longwave radiation (increasing net longwave), and increases cloud cover, enhancing shortwave reflection (reducing net shortwave). The relative magnitude of these two processes causes regional increases (northern India) or decreases (Central Asia, China) in energy availability at the surface and top of the atmosphere. Despite these changes in net radiation, however, climate responses are due primarily to larger magnitude shifts in the Bowen ratio from sensible to latent heating. Irrigation impacts on temperature, precipitation, and other climate variables are regionally significant, even while other anthropogenic forcings (anthropogenic aerosols

Spatiotemporal variation of surface shortwave forcing from fire-induced albedo change in interior Alaska

Science.gov (United States)

Huang, Shengli; Dahal, Devendra; Liu, Heping; Jin, Suming; Young, Claudia J.; Liu, Shuang; Liu, Shu-Guang

2015-01-01

The albedo change caused by both fires and subsequent succession is spatially heterogeneous, leading to the need to assess the spatiotemporal variation of surface shortwave forcing (SSF) as a component to quantify the climate impacts of high-latitude fires. We used an image reconstruction approach to compare postfire albedo with the albedo assuming fires had not occurred. Combining the fire-caused albedo change from the 2001-2010 fires in interior Alaska and the monthly surface incoming solar radiation, we examined the spatiotemporal variation of SSF in the early successional stage of around 10 years. Our results showed that while postfire albedo generally increased in fall, winter, and spring, some burned areas could show an albedo decrease during these seasons. In summer, the albedo increased for several years and then declined again. The spring SSF distribution did not show a latitudinal decrease from south to north as previously reported. The results also indicated that although the SSF is usually largely negative in the early successional years, it may not be significant during the first postfire year. The annual 2005-2010 SSF for the 2004 fire scars was -1.30, -4.40, -3.31, -4.00, -3.42, and -2.47 Wm-2. The integrated annual SSF map showed significant spatial variation with a mean of -3.15 Wm-2 and a standard deviation of 3.26 Wm-2, 16% of burned areas having positive SSF. Our results suggest that boreal deciduous fires would be less positive for climate change than boreal evergreen fires. Future research is needed to comprehensively investigate the spatiotemporal radiative and non-radiative forcings to determine the effect of boreal fires on climate.

An isometric muscle force estimation framework based on a high-density surface EMG array and an NMF algorithm

Science.gov (United States)

Huang, Chengjun; Chen, Xiang; Cao, Shuai; Qiu, Bensheng; Zhang, Xu

2017-08-01

Objective. To realize accurate muscle force estimation, a novel framework is proposed in this paper which can extract the input of the prediction model from the appropriate activation area of the skeletal muscle. Approach. Surface electromyographic (sEMG) signals from the biceps brachii muscle during isometric elbow flexion were collected with a high-density (HD) electrode grid (128 channels) and the external force at three contraction levels was measured at the wrist synchronously. The sEMG envelope matrix was factorized into a matrix of basis vectors with each column representing an activation pattern and a matrix of time-varying coefficients by a nonnegative matrix factorization (NMF) algorithm. The activation pattern with the highest activation intensity, which was defined as the sum of the absolute values of the time-varying coefficient curve, was considered as the major activation pattern, and its channels with high weighting factors were selected to extract the input activation signal of a force estimation model based on the polynomial fitting technique. Main results. Compared with conventional methods using the whole channels of the grid, the proposed method could significantly improve the quality of force estimation and reduce the electrode number. Significance. The proposed method provides a way to find proper electrode placement for force estimation, which can be further employed in muscle heterogeneity analysis, myoelectric prostheses and the control of exoskeleton devices.

An atomic force microscopy study on the transition from mushrooms to octopus surface ''micelles'' by changing the solvent quality

NARCIS (Netherlands)

Stamouli, A.; Pelletier, E.; Koutsos, V; van der Vegte, E.W.; Hadziioannou, G

1996-01-01

Atomic force microscopy (AFM) is used to study the behavior of a diblock copolymer onto a solid surface while the solvent quality is changed. In a first step, the copolymer poly(2-vinylpyridine)/polystyrene (P2VP/PS) is adsorbed onto mica from a selective solvent (the PS block is well solvated and

Electrical Double-Layer and Ion Bridging Forces between Symmetric and Asymmetric Charged Surfaces in the Presence of Mono- and Divalent Ions

DEFF Research Database (Denmark)

Liu, Xiaoyan; Feilberg, Karen Louise; Yan, Wei

2017-01-01

charged (3-aminopropyl)trimethoxysilane, and the negatively charged (3-mercaptopropyl)trimethoxysilane. The interactions between the three symmetric systems, as well as between the three asymmetric combinations of surfaces, were measured and compared to calculated electrical double-layer forces...

Probing the nanoscale interaction forces and elastic properties of organic and inorganic materials using force-distance (F-D) spectroscopy

Science.gov (United States)

Vincent, Abhilash

Due to their therapeutic applications such as radical scavenging, MRI contrast imaging, Photoluminescence imaging, drug delivery, etc., nanoparticles (NPs) have a significant importance in bio-nanotechnology. The reason that prevents the utilizing NPs for drug delivery in medical field is mostly due to their biocompatibility issues (incompatibility can lead to toxicity and cell death). Changes in the surface conditions of NPs often lead to NP cytotoxicity. Investigating the role of NP surface properties (surface charges and surface chemistry) on their interactions with biomolecules (Cells, protein and DNA) could enhance the current understanding of NP cytotoxicity. Hence, it is highly beneficial to the nanotechnology community to bring more attention towards the enhancement of surface properties of NPs to make them more biocompatible and less toxic to biological systems. Surface functionalization of NPs using specific ligand biomolecules have shown to enhance the protein adsorption and cellular uptake through more favorable interaction pathways. Cerium oxide NPs (CNPs also known as nanoceria) are potential antioxidants in cell culture models and understanding the nature of interaction between cerium oxide NPs and biological proteins and cells are important due to their therapeutic application (especially in site specific drug delivery systems). The surface charges and surface chemistry of CNPs play a major role in protein adsorption and cellular uptake. Hence, by tuning the surface charges and by selecting proper functional molecules on the surface, CNPs exhibiting strong adhesion to biological materials can be prepared. By probing the nanoscale interaction forces acting between CNPs and protein molecules using Atomic Force Microscopy (AFM) based force-distance (F-D) spectroscopy, the mechanism of CNP-protein adsorption and CNP cellular uptake can be understood more quantitatively. The work presented in this dissertation is based on the application of AFM in

Accurate measurement of Atomic Force Microscope cantilever deflection excluding tip-surface contact with application to force calibration

Energy Technology Data Exchange (ETDEWEB)

Slattery, Ashley D.; Blanch, Adam J.; Quinton, Jamie S.; Gibson, Christopher T., E-mail: christopher.gibson@flinders.edu.au

2013-08-15

calibrate the cantilever spring constant using the thermal noise method, allowing complete force calibration to be accurately performed without tip-sample contact. - Highlights: • A technique for determining AFM cantilever sensitivity is developed and tested. • The error on the method is between 2–5% and does not require tip surface contact. • The method is simple to implement and can be applied to any type of cantilever. • The current method can be used to determine the spring constant of the cantilever.

Semi-implicit surface tension formulation with a Lagrangian surface mesh on an Eulerian simulation grid

KAUST Repository

Schroeder, Craig; Zheng, Wen; Fedkiw, Ronald

2012-01-01

-implicit and fully-coupled viscosity, pressure, and Lagrangian forces. We apply our new framework for forces on a Lagrangian mesh to the case of a surface tension force, which when treated explicitly leads to a tight time step restriction. By applying surface tension

A force-based protein biochip

Science.gov (United States)

Blank, K.; Mai, T.; Gilbert, I.; Schiffmann, S.; Rankl, J.; Zivin, R.; Tackney, C.; Nicolaus, T.; Spinnler, K.; Oesterhelt, F.; Benoit, M.; Clausen-Schaumann, H.; Gaub, H. E.

2003-09-01

A parallel assay for the quantification of single-molecule binding forces was developed based on differential unbinding force measurements where ligand-receptor interactions are compared with the unzipping forces of DNA hybrids. Using the DNA zippers as molecular force sensors, the efficient discrimination between specific and nonspecific interactions was demonstrated for small molecules binding to specific receptors, as well as for protein-protein interactions on protein arrays. Finally, an antibody sandwich assay with different capture antibodies on one chip surface and with the detection antibodies linked to a congruent surface via the DNA zippers was used to capture and quantify a recombinant hepatitis C antigen from solution. In this case, the DNA zippers enable not only discrimination between specific and nonspecific binding, but also allow for the local application of detection antibodies, thereby eliminating false-positive results caused by cross-reactive antibodies and nonspecific binding.

Sample preparation method for scanning force microscopy

CERN Document Server

Jankov, I R; Szente, R N; Carreno, M N P; Swart, J W; Landers, R

2001-01-01

We present a method of sample preparation for studies of ion implantation on metal surfaces. The method, employing a mechanical mask, is specially adapted for samples analysed by Scanning Force Microscopy. It was successfully tested on polycrystalline copper substrates implanted with phosphorus ions at an acceleration voltage of 39 keV. The changes of the electrical properties of the surface were measured by Kelvin Probe Force Microscopy and the surface composition was analysed by Auger Electron Spectroscopy.

Nanoscopic morphological changes in yeast cell surfaces caused by oxidative stress: an atomic force microscopic study.

Science.gov (United States)

Canetta, Elisabetta; Walker, Graeme M; Adya, Ashok K

2009-06-01

Nanoscopic changes in the cell surface morphology of the yeasts Saccharomyces cerevisiae (strain NCYC 1681) and Schizosaccharomyces pombe (strain DVPB 1354), due to their exposure to varying concentrations of hydrogen peroxide (oxidative stress), were investigated using an atomic force microscope (AFM). Increasing hydrogen peroxide concentration led to a decrease in cell viabilities and mean cell volumes, and an increase in the surface roughness of the yeasts. In addition, AFM studies revealed that oxidative stress caused cell compression in both S. cerevisiae and Schiz. pombe cells and an increase in the number of aged yeasts. These results confirmed the importance and usefulness of AFM in investigating the morphology of stressed microbial cells at the nanoscale. The results also provided novel information on the relative oxidative stress tolerance of S. cerevisiae and Schiz. pombe.

Digital force-feedback for protein unfolding experiments using atomic force microscopy

Science.gov (United States)

Bippes, Christian A.; Janovjak, Harald; Kedrov, Alexej; Muller, Daniel J.

2007-01-01

Since its invention in the 1990s single-molecule force spectroscopy has been increasingly applied to study protein (un-)folding, cell adhesion, and ligand-receptor interactions. In most force spectroscopy studies, the cantilever of an atomic force microscope (AFM) is separated from a surface at a constant velocity, thus applying an increasing force to folded bio-molecules or bio-molecular bonds. Recently, Fernandez and co-workers introduced the so-called force-clamp technique. Single proteins were subjected to a defined constant force allowing their life times and life time distributions to be directly measured. Up to now, the force-clamping was performed by analogue PID controllers, which require complex additional hardware and might make it difficult to combine the force-feedback with other modes such as constant velocity. These points may be limiting the applicability and versatility of this technique. Here we present a simple, fast, and all-digital (software-based) PID controller that yields response times of a few milliseconds in combination with a commercial AFM. We demonstrate the performance of our feedback loop by force-clamp unfolding of single Ig27 domains of titin and the membrane proteins bacteriorhodopsin (BR) and the sodium/proton antiporter NhaA.

Digital force-feedback for protein unfolding experiments using atomic force microscopy

International Nuclear Information System (INIS)

Bippes, Christian A; Janovjak, Harald; Kedrov, Alexej; Muller, Daniel J

2007-01-01

Since its invention in the 1990s single-molecule force spectroscopy has been increasingly applied to study protein (un-)folding, cell adhesion, and ligand-receptor interactions. In most force spectroscopy studies, the cantilever of an atomic force microscope (AFM) is separated from a surface at a constant velocity, thus applying an increasing force to folded bio-molecules or bio-molecular bonds. Recently, Fernandez and co-workers introduced the so-called force-clamp technique. Single proteins were subjected to a defined constant force allowing their life times and life time distributions to be directly measured. Up to now, the force-clamping was performed by analogue PID controllers, which require complex additional hardware and might make it difficult to combine the force-feedback with other modes such as constant velocity. These points may be limiting the applicability and versatility of this technique. Here we present a simple, fast, and all-digital (software-based) PID controller that yields response times of a few milliseconds in combination with a commercial AFM. We demonstrate the performance of our feedback loop by force-clamp unfolding of single Ig27 domains of titin and the membrane proteins bacteriorhodopsin (BR) and the sodium/proton antiporter NhaA

The Impact of Model and Rainfall Forcing Errors on Characterizing Soil Moisture Uncertainty in Land Surface Modeling

Science.gov (United States)

Maggioni, V.; Anagnostou, E. N.; Reichle, R. H.

2013-01-01

The contribution of rainfall forcing errors relative to model (structural and parameter) uncertainty in the prediction of soil moisture is investigated by integrating the NASA Catchment Land Surface Model (CLSM), forced with hydro-meteorological data, in the Oklahoma region. Rainfall-forcing uncertainty is introduced using a stochastic error model that generates ensemble rainfall fields from satellite rainfall products. The ensemble satellite rain fields are propagated through CLSM to produce soil moisture ensembles. Errors in CLSM are modeled with two different approaches: either by perturbing model parameters (representing model parameter uncertainty) or by adding randomly generated noise (representing model structure and parameter uncertainty) to the model prognostic variables. Our findings highlight that the method currently used in the NASA GEOS-5 Land Data Assimilation System to perturb CLSM variables poorly describes the uncertainty in the predicted soil moisture, even when combined with rainfall model perturbations. On the other hand, by adding model parameter perturbations to rainfall forcing perturbations, a better characterization of uncertainty in soil moisture simulations is observed. Specifically, an analysis of the rank histograms shows that the most consistent ensemble of soil moisture is obtained by combining rainfall and model parameter perturbations. When rainfall forcing and model prognostic perturbations are added, the rank histogram shows a U-shape at the domain average scale, which corresponds to a lack of variability in the forecast ensemble. The more accurate estimation of the soil moisture prediction uncertainty obtained by combining rainfall and parameter perturbations is encouraging for the application of this approach in ensemble data assimilation systems.

EVALUATION OF MACHINABILITY OF DUCTILE IRONS ALLOYED WITH Ni AND Cu IN TERMS OF CUTTING FORCES AND SURFACE QUALITY

Directory of Open Access Journals (Sweden)

Yücel AŞKUN

2003-02-01

Full Text Available Due to the enhanced strength, ductility and thoughness of Ductile Iron (DI when compared to the other types cast iron, its machinability is relatively poor. When a steel part is replaced with ductile iron, however, better machinability is considered to be the most important gain. This study presents the results of machining tests of ductile irons alloyed with Ni and Cu at various contents to determine the effect of their microstructure and mechanical properties on cutting forces and surface roughness. Six different specimen groups of ductile iron alloyed with various amounts of nickel and copper were subjected to machining tests and their machinabilities were investigated based on cutting forces and surface roughness criteria. The results were evaluated according to microstructure and mechanical properties of specimens determined before. In terms of both criterion, the best result obtained was specimen added 0.7 % Ni and 0.7 % Cu. When the specimens were evaluated according to their mechanical properties, the specimens alloyed 1 % Ni and 0.65 % Cu seemed promising.

Method for lateral force calibration in atomic force microscope using MEMS microforce sensor.

Science.gov (United States)

Dziekoński, Cezary; Dera, Wojciech; Jarząbek, Dariusz M

2017-11-01

In this paper we present a simple and direct method for the lateral force calibration constant determination. Our procedure does not require any knowledge about material or geometrical parameters of an investigated cantilever. We apply a commercially available microforce sensor with advanced electronics for direct measurement of the friction force applied by the cantilever's tip to a flat surface of the microforce sensor measuring beam. Due to the third law of dynamics, the friction force of the equal value tilts the AFM cantilever. Therefore, torsional (lateral force) signal is compared with the signal from the microforce sensor and the lateral force calibration constant is determined. The method is easy to perform and could be widely used for the lateral force calibration constant determination in many types of atomic force microscopes. Copyright © 2017 Elsevier B.V. All rights reserved.

Investigating the Interannual Variability of the Circulation and Water Mass Formation in the Red Sea

Science.gov (United States)

Sofianos, S. S.; Papadopoulos, V. P.; Denaxa, D.; Abualnaja, Y.

2014-12-01

The interannual variability of the circulation and water mass formation in the Red Sea is investigated with the use of a numerical model and the combination of satellite and in-situ observations. The response of Red Sea to the large-scale variability of atmospheric forcing is studied through a 30-years simulation experiment, using MICOM model. The modeling results demonstrate significant trends and variability that are mainly located in the central and northern parts of the basin. On the other hand, the exchange pattern between the Red Sea and the Indian Ocean at the strait of Bab el Mandeb presents very weak interannual variability. The results verify the regularity of the water mass formation processes in the northern Red Sea but also show significant variability of the circulation and thermohaline conditions in the areas of formation. Enhanced water mass formation conditions are observed during specific years of the simulation (approximately five years apart). Analysis of recent warm and cold events in the northernmost part of the basin, based on a combination of atmospheric reanalysis results and oceanic satellite and in-situ observations, shows the importance of the cyclonic gyre that is prevailing in this part of the basin. This gyre can effectively influence the sea surface temperature (SST) and intensify or mitigate the winter effect of the atmospheric forcing. Upwelling induced by persistent periods of the gyre functioning drops the SST over the northernmost part of the Red Sea and can produce colder than normal winter SST even without extreme atmospheric forcing. These mechanisms are crucial for the formation of intermediate and deep water masses in the Red Sea and the strength of the subsequent thermohaline cells.

How drops start sliding over solid surfaces

Science.gov (United States)

Gao, Nan; Geyer, Florian; Pilat, Dominik W.; Wooh, Sanghyuk; Vollmer, Doris; Butt, Hans-Jürgen; Berger, Rüdiger

2018-02-01

It has been known for more than 200 years that the maximum static friction force between two solid surfaces is usually greater than the kinetic friction force--the force that is required to maintain the relative motion of the surfaces once the static force has been overcome. But the forces that impede the lateral motion of a drop of liquid on a solid surface are not as well characterized, and there is a lack of understanding about liquid-solid friction in general. Here, we report that the lateral adhesion force between a liquid drop and a solid can also be divided into a static and a kinetic regime. This striking analogy with solid-solid friction is a generic phenomenon that holds for liquids of different polarities and surface tensions on smooth, rough and structured surfaces.

Analysis of the problem of forced landing of aircraft on water surface and methods of simulation of aircraft crews at aircraft accidents of this type

Directory of Open Access Journals (Sweden)

V. M. Nedilko

2017-06-01

Full Text Available The article is devoted to an actual problem of emergency incidents of forced landing of aircraft on the water surface. The main content of the research is the analysis of statistical data and classification splashdown. The article reveals the main reasons that lead to the forced landing of aircraft. Analysis of accidents is interesting for us, as it can reveal the shortcomings and problems in the Rescue and disadvantages of rescue equipment. Considerable attention is paid to the analysis of simulators for flight and cabin crew. Based on the analysis of the problem the need for regular training and exercises is established. To conduct a full-fledged study on the problem of forced landing of airborne vessels on the water surface, the following methods were used: comparison method, generalization method, data analysis method.

Three-dimensional hydration layer mapping on the (10.4) surface of calcite using amplitude modulation atomic force microscopy.

Science.gov (United States)

Marutschke, Christoph; Walters, Deron; Walters, Deron; Hermes, Ilka; Bechstein, Ralf; Kühnle, Angelika

2014-08-22

Calcite, the most stable modification of calcium carbonate, is a major mineral in nature. It is, therefore, highly relevant in a broad range of fields such as biomineralization, sea water desalination and oil production. Knowledge of the surface structure and reactivity of the most stable cleavage plane, calcite (10.4), is pivotal for understanding the role of calcite in these diverse areas. Given the fact that most biological processes and technical applications take place in an aqueous environment, perhaps the most basic - yet decisive - question addresses the interaction of water molecules with the calcite (10.4) surface. In this work, amplitude modulation atomic force microscopy is used for three-dimensional (3D) mapping of the surface structure and the hydration layers above the surface. An easy-to-use scanning protocol is implemented for collecting reliable 3D data. We carefully discuss a comprehensible criterion for identifying the solid-liquid interface within our data. In our data three hydration layers form a characteristic pattern that is commensurate with the underlying calcite surface.

Three-dimensional hydration layer mapping on the (10.4) surface of calcite using amplitude modulation atomic force microscopy

International Nuclear Information System (INIS)

Marutschke, Christoph; Hermes, Ilka; Bechstein, Ralf; Kühnle, Angelika; Walters, Deron; Cleveland, Jason

2014-01-01

Calcite, the most stable modification of calcium carbonate, is a major mineral in nature. It is, therefore, highly relevant in a broad range of fields such as biomineralization, sea water desalination and oil production. Knowledge of the surface structure and reactivity of the most stable cleavage plane, calcite (10.4), is pivotal for understanding the role of calcite in these diverse areas. Given the fact that most biological processes and technical applications take place in an aqueous environment, perhaps the most basic—yet decisive—question addresses the interaction of water molecules with the calcite (10.4) surface. In this work, amplitude modulation atomic force microscopy is used for three-dimensional (3D) mapping of the surface structure and the hydration layers above the surface. An easy-to-use scanning protocol is implemented for collecting reliable 3D data. We carefully discuss a comprehensible criterion for identifying the solid–liquid interface within our data. In our data three hydration layers form a characteristic pattern that is commensurate with the underlying calcite surface. (paper)

Nanoconfined ionic liquids: Disentangling electrostatic and viscous forces

Science.gov (United States)

Lhermerout, Romain; Perkin, Susan

2018-01-01

Recent reports of surface forces across nanoconfined ionic liquids have revealed the existence of an anomalously long-ranged interaction apparently of electrostatic origin. Ionic liquids are viscous, and therefore it is important to inspect rigorously whether the observed repulsive forces are indeed equilibrium forces or, rather, arise from the viscous force during drainage of the fluid between two confining surfaces. In this paper we present our direct measurements of surface forces between mica sheets approaching in the ionic liquid [C2C1Im ] [NTf2] , exploring three orders of magnitude in approach velocity. Trajectories are systematically fitted by solving the equation of motion, allowing us to disentangle the viscous and equilibrium contributions. First, we find that the drainage obeys classical hydrodynamics with a negative slip boundary condition in the range of the structural force, implying that a nanometer -thick portion of the liquid in the vicinity of the solid surface is composed of ordered molecules that do not contribute to the flow. Second, we show that a long-range static force must indeed be invoked, in addition to the viscous force, in order to describe the data quantitatively. This equilibrium interaction decays exponentially and with decay length in agreement with the screening length reported for the same system in previous studies. In those studies the decay was simply checked to be independent of velocity and measured at a low approach rate, rather than explicitly taking account of viscous effects: we explain why this gives indistinguishable outcomes for the screening length by noting that the viscous force is linear to very good approximation over a wide range of distances.

Simulation of Changes in the Near-Surface Soil Freeze/Thaw Cycle Using CLM4.5 With Four Atmospheric Forcing Data Sets

Science.gov (United States)

Guo, Donglin; Wang, Aihui; Li, Duo; Hua, Wei

2018-03-01

Change in the near-surface soil freeze/thaw cycle is critical for assessments of hydrological activity, ecosystems, and climate change. Previous studies investigated the near-surface soil freeze/thaw cycle change mostly based on in situ observations and satellite monitoring. Here numerical simulation method is tested to estimate the long-term change in the near-surface soil freeze/thaw cycle in response to recent climate warming for its application to predictions. Four simulations are performed at 0.5° × 0.5° resolution from 1979 to 2009 using the Community Land Model version 4.5, each driven by one of the four atmospheric forcing data sets (i.e., one default Climate Research Unit-National Centers for Environmental Prediction [CRUNCEP] and three newly developed Modern Era Retrospective-Analysis for Research and Applications, Climate Forecast System Reanalysis, and European Centre for Medium-Range Weather Forecasts Reanalysis Interim). The observations from 299 weather stations in both Russia and China are employed to validate the simulated results. The results show that all simulations reasonably reproduce the observed variations in the ground temperature, the freeze start and end dates, and the freeze duration (the correlation coefficients range from 0.47 to 0.99, and the Nash-Sutcliffe efficiencies range from 0.19 to 0.98). Part of the simulations also exactly simulate the trends of the ground temperature, the freeze start and end dates, and the freeze duration. Of the four simulations, the results from the simulation using the CRUNCEP data set show the best overall agreement with the in situ observations, indicating that the CRUNCEP data set could be preferentially considered as the basic atmospheric forcing data set for future prediction. The simulated area-averaged annual freeze duration shortened by 8.03 days on average from 1979 to 2009, with an uncertainty (one standard deviation) of 0.67 days caused by the different atmospheric forcing data sets. These

Vibrations of a molecule in an external force field.

Science.gov (United States)

Okabayashi, Norio; Peronio, Angelo; Paulsson, Magnus; Arai, Toyoko; Giessibl, Franz J

2018-05-01

The oscillation frequencies of a molecule on a surface are determined by the mass distribution in the molecule and the restoring forces that occur when the molecule bends. The restoring force originates from the atomic-scale interaction within the molecule and with the surface, which plays an essential role in the dynamics and reactivity of the molecule. In 1998, a combination of scanning tunneling microscopy with inelastic tunneling spectroscopy revealed the vibrational frequencies of single molecules adsorbed on a surface. However, the probe tip itself exerts forces on the molecule, changing its oscillation frequencies. Here, we combine atomic force microscopy with inelastic tunneling spectroscopy and measure the influence of the forces exerted by the tip on the lateral vibrational modes of a carbon monoxide molecule on a copper surface. Comparing the experimental data to a mechanical model of the vibrating molecule shows that the bonds within the molecule and with the surface are weakened by the proximity of the tip. This combination of techniques can be applied to analyze complex molecular vibrations and the mechanics of forming and loosening chemical bonds, as well as to study the mechanics of bond breaking in chemical reactions and atomic manipulation.

Electrostatic forces on grains near asteroids and comets

Directory of Open Access Journals (Sweden)

Hartzell Christine

2017-01-01

Full Text Available Dust on and near the surface of small planetary bodies (e.g. asteroids, the Moon, Mars’ moons is subject to gravity, cohesion and electrostatic forces. Due to the very low gravity on small bodies, the behavior of small dust grains is driven by non-gravitational forces. Recent work by Scheeres et al. has shown that cohesion, specifically van der Waals force, is significant for grains on asteroids. In addition to van der Waals cohesion, dust grains also experience electrostatic forces, arising from their interaction with each other (through tribocharging and the solar wind plasma (which produces both grain charging and an external electric field. Electrostatic forces influence both the interactions of grains on the surface of small bodies as well as the dynamics of grains in the plasma sheath above the surface. While tribocharging between identical dielectric grains remains poorly understood, we have recently expanded an existing charge transfer model to consider continuous size distributions of grains and are planning an experiment to test the charge predictions produced. Additionally, we will present predictions of the size of dust grains that are capable of detaching from the surface of small bodies.

Atomic force microscopy recognition of protein A on Staphylococcus aureus cell surfaces by labelling with IgG-Au conjugates.

Science.gov (United States)

Tatlybaeva, Elena B; Nikiyan, Hike N; Vasilchenko, Alexey S; Deryabin, Dmitri G

2013-01-01

The labelling of functional molecules on the surface of bacterial cells is one way to recognize the bacteria. In this work, we have developed a method for the selective labelling of protein A on the cell surfaces of Staphylococcus aureus by using nanosized immunogold conjugates as cell-surface markers for atomic force microscopy (AFM). The use of 30-nm size Au nanoparticles conjugated with immunoglobulin G (IgG) allowed the visualization, localization and distribution of protein A-IgG complexes on the surface of S. aureus. The selectivity of the labelling method was confirmed in mixtures of S. aureus with Bacillus licheniformis cells, which differed by size and shape and had no IgG receptors on the surface. A preferential binding of the IgG-Au conjugates to S. aureus was obtained. Thus, this novel approach allows the identification of protein A and other IgG receptor-bearing bacteria, which is useful for AFM indication of pathogenic microorganisms in poly-component associations.

Atomic force microscopy recognition of protein A on Staphylococcus aureus cell surfaces by labelling with IgG–Au conjugates

Directory of Open Access Journals (Sweden)

Elena B. Tatlybaeva

2013-11-01

Full Text Available The labelling of functional molecules on the surface of bacterial cells is one way to recognize the bacteria. In this work, we have developed a method for the selective labelling of protein A on the cell surfaces of Staphylococcus aureus by using nanosized immunogold conjugates as cell-surface markers for atomic force microscopy (AFM. The use of 30-nm size Au nanoparticles conjugated with immunoglobulin G (IgG allowed the visualization, localization and distribution of protein A–IgG complexes on the surface of S. aureus. The selectivity of the labelling method was confirmed in mixtures of S. aureus with Bacillus licheniformis cells, which differed by size and shape and had no IgG receptors on the surface. A preferential binding of the IgG–Au conjugates to S. aureus was obtained. Thus, this novel approach allows the identification of protein A and other IgG receptor-bearing bacteria, which is useful for AFM indication of pathogenic microorganisms in poly-component associations.

Atomic force microscopy recognition of protein A on Staphylococcus aureus cell surfaces by labelling with IgG–Au conjugates

Science.gov (United States)

Tatlybaeva, Elena B; Vasilchenko, Alexey S; Deryabin, Dmitri G

2013-01-01

Summary The labelling of functional molecules on the surface of bacterial cells is one way to recognize the bacteria. In this work, we have developed a method for the selective labelling of protein A on the cell surfaces of Staphylococcus aureus by using nanosized immunogold conjugates as cell-surface markers for atomic force microscopy (AFM). The use of 30-nm size Au nanoparticles conjugated with immunoglobulin G (IgG) allowed the visualization, localization and distribution of protein A–IgG complexes on the surface of S. aureus. The selectivity of the labelling method was confirmed in mixtures of S. aureus with Bacillus licheniformis cells, which differed by size and shape and had no IgG receptors on the surface. A preferential binding of the IgG–Au conjugates to S. aureus was obtained. Thus, this novel approach allows the identification of protein A and other IgG receptor-bearing bacteria, which is useful for AFM indication of pathogenic microorganisms in poly-component associations. PMID:24367742

Effects of additional inertia force on bubble breakup

International Nuclear Information System (INIS)

Pan Liangming; Zhang Wenzhi; Chen Deqi; Xu Jianhui; Xu Jianjun; Huang Yanping

2011-01-01

Through VOF two-phase flow model, the single bubble deformation and breakup in a vertical narrow channel is numerically investigated in the study based on the force balance at the process of bubble breakup. The effect of surface tension force, the additional inertia force and bubble initial shape on bubble breakup are analyzed according to the velocity variation at the break-up point and the minimum necking size when the bubble is breaking up. It is found that the surface tension force, the additional inertia force and the bubble initial shape have significant effects on the bubble breakup through the fluid injection toward to the bubble, which finally induces the onset of bubble breakup. (authors)

Facile fabrication of functional PDMS surfaces with tunable wettablity and high adhesive force via femtosecond laser textured templating

Directory of Open Access Journals (Sweden)

Yanlei Hu

2014-12-01

Full Text Available Femtosecond laser processing is emerged as a promising tool to functionalize surfaces of various materials, including metals, semiconductors, and polymers. However, the productivity of this technique is limited by the low efficiency of laser raster scanning. Here we report a facile approach for efficiently producing large-area functional polymer surfaces, by which metal is firstly textured by a femtosecond laser, and the as-prepared hierarchical structures are subsequently transferred onto polydimethylsiloxane (PDMS surfaces. Aluminum pieces covered by laser induced micro/nano-structures act as template masters and their performance of displaying diverse colors are investigated. Polymer replicas are endowed with tunable wetting properties, which are mainly attributed to the multi-scale surface structures. Furthermore, the surfaces are found to have extremely high adhesive force for water drops because of the high water penetration depth and the resultant high contact angle hysteresis. This characteristic facilitates many potential applications like loss-free tiny water droplets transportation. The reusability of metal master and easiness of soft lithography make it to be a very simple, fast and cost-efficient way for mass production of functional polymeric surfaces.

The influence of local volume forces on surface relaxation of pure metals and alloys: Applications to Ni, Al, Ni3Al

International Nuclear Information System (INIS)

Savino, E.J.; Farkas, D.

1987-11-01

We present an analysis of the relative influence of the interatomic potential, lattice structure and defect symmetry on the calculated and measured distortion for the free surfaces of alloys and pure metals. In particular, the effect of using local ''volume'' dependent interactions is studied, as opposed to simple pair interatomic forces. The dependence of the relaxation on the lattice structure is examined by comparing pure metals with ordered alloys. A Green function method for surface relaxation is presented and used for the above analysis as well as for studying the influence of different surface symmetries. Examples based on computer simulation of Ni, Al and Ni 3 Al for some surface orientations are presented. (author). 33 refs, 4 figs

Meniscus and viscous forces during normal separation of liquid-mediated contacts

International Nuclear Information System (INIS)

Cai Shaobiao; Bhushan, Bharat

2007-01-01

Menisci form between two solid surfaces with the presence of an ultra-thin liquid film. Meniscus and viscous forces contribute to an adhesive force when two surfaces are separated. The adhesive force can be very large and can result in high friction, stiction and possibly high wear. The situation may become more pronounced when the contacting surfaces are ultra-smooth and the normal load is small, as is common for micro-/nanodevices. In this study, equations for meniscus and viscous forces during separation of two flat surfaces, and a sphere and a flat surface, are developed, and the corresponding adhesive forces contributed by these two types of forces are examined. The geometric meniscus curvatures and break point are theoretically determined, and the role of meniscus and viscous forces is evaluated during separation. The influence of separation distance, liquid thickness, meniscus area, separation time, liquid properties and contact angles are analyzed. Critical meniscus areas at which transition in the dominance of meniscus to viscous forces occurs for different given conditions, i.e. various initial liquid thicknesses, contact angles and designated separation time, are identified. The analysis provides a fundamental understanding of the physics of separation process, and insights into the relationships between meniscus and viscous forces. It is also valuable for the design of the interface for various devices

Compliment Graphene Oxide Coating on Silk Fiber Surface via Electrostatic Force for Capacitive Humidity Sensor Applications

Directory of Open Access Journals (Sweden)

Kook In Han

2017-02-01

Full Text Available Cylindrical silk fiber (SF was coated with Graphene oxide (GO for capacitive humidity sensor applications. Negatively charged GO in the solution was attracted to the positively charged SF surface via electrostatic force without any help from adhesive intermediates. The magnitude of the positively charged SF surface was controlled through the static electricity charges created on the SF surface. The GO coating ability on the SF improved as the SF’s positive charge increased. The GO-coated SFs at various conditions were characterized using an optical microscope, scanning electron microscopy (SEM, energy-dispersive X-ray spectroscopy (EDS, Raman spectroscopy, and LCR meter. Unlike the intact SF, the GO-coated SF showed clear response-recovery behavior and well-behaved repeatability when it was exposed to 20% relative humidity (RH and 90% RH alternatively in a capacitive mode. This approach allows humidity sensors to take advantage of GO’s excellent sensing properties and SF’s flexibility, expediting the production of flexible, low power consumption devices at relatively low costs.

Topographic characterization of the self-assembled nanostructures of chitosan on mica surface by atomic force microscopy

International Nuclear Information System (INIS)

Wang, Li; Wu, Jiafeng; Guo, Yan; Gong, Coucong; Song, Yonghai

2015-01-01

Graphical abstract: - Highlights: • Nanocomposites of chitosan film were prepared by simple self-assembly from solvent media. • Chitosan molecules assembled on mica surface of nanoparticles, fibril and membrane with varied chitosan concentration. • Chitosan molecules assembled with different nanostructure under varied pH. • The optimum drying temperature for forming chitosan membrane is about 65 °C. - Abstract: In this work, the self-assembled nanostructures of chitosan on mica surface formed from various solvents were investigated by using atomic force microscopy. The effects of various factors on the self-assembled nanostructures of chitosan on mica surface, including solvents, the concentration of chitosan, the pH of solution and the drying temperature, were explored in detail. Our experimental data resulted in the conclusion that chitosan molecules could self-assemble on mica surface to form various nanostructures such as nanoparticles, fibril and film. Nanoparticles were always formed on mica surface from CCl_4, C_6H_6, CH_2Cl_2 solution, fibril preferred to form on mica surface from CH_3CH_2OH and CH_3OH solution and the optimal solvent to form film was found to be CH_3CN. Low concentration, pH and temperature were helpful for the formation of nanoparticles, medium concentration, pH and temperature resulted in fibril and high concentration, pH and temperature were often beneficial to forming chitosan films. The study of self-assembled nanostructures of chitosan on mica surface would provide new insight into the development of chitosan-based load-bearing materials.

Comparison of frictional forces on graphene and graphite

International Nuclear Information System (INIS)

Lee, Hyunsoo; Lee, Naesung; Seo, Yongho; Eom, Jonghwa; Lee, SangWook

2009-01-01

We report on the frictional force between an SiN tip and graphene/graphite surfaces using lateral force microscopy. The cantilever we have used was made of an SiN membrane and has a low stiffness of 0.006 N m -1 . We prepared graphene flakes on a Si wafer covered with silicon oxides. The frictional force on graphene was smaller than that on the Si oxide and larger than that on graphite (multilayer of graphene). Force spectroscopy was also employed to study the van der Waals force between the graphene and the tip. Judging that the van der Waals force was also in graphite-graphene-silicon oxide order, the friction is suspected to be related to the van der Waals interactions. As the normal force acting on the surface was much weaker than the attractive force, such as the van der Waals force, the friction was independent of the normal force strength. The velocity dependency of the friction showed a logarithmic behavior which was attributed to the thermally activated stick-slip effect.

Contactless and non-invasive delivery of micro-particles lying on a non-customized rigid surface by using acoustic radiation force.

Science.gov (United States)

Meng, Jianxin; Mei, Deqing; Jia, Kun; Fan, Zongwei; Yang, Keji

2014-07-01

In the existing acoustic micro-particle delivery methods, the micro-particles always lie and slide on the surface of platform in the whole delivery process. To avoid the damage and contamination of micro-particles caused by the sliding motion, this paper deals with a novel approach to trap micro-particles from non-customized rigid surfaces and freely manipulate them. The delivery process contains three procedures: detaching, transporting, and landing. Hence, the micro-particles no longer lie on the surface, but are levitated in the fluid, during the long range transporting procedure. It is very meaningful especially for the fragile and easily contaminated targets. To quantitatively analyze the delivery process, a theoretical model to calculate the acoustic radiation force exerting upon a micro-particle near the boundary in half space is built. An experimental device is also developed to validate the delivery method. A 100 μm diameter micro-silica bead adopted as the delivery target is detached from the upper surface of an aluminum platform and levitated in the fluid. Then, it is transported along the designated path with high precision in horizontal plane. The maximum deviation is only about 3.3 μm. During the horizontal transportation, the levitation of the micro-silica bead is stable, the maximum fluctuation is less than 1 μm. The proposed method may extend the application of acoustic radiation force and provide a promising tool for microstructure or cell manipulation. Copyright © 2014 Elsevier B.V. All rights reserved.

In-depth Study on Cylinder Wake Controlled by Lorentz Force

International Nuclear Information System (INIS)

Zhang Hui; Fan Bao-Chun; Chen Zhi-Hua

2011-01-01

The underlying mechanisms of the electromagnetic control of cylinder wake are investigated and discussed. The effects of Lorentz force are found to be composed of two parts, one is its direct action on the cylinder (the wall Lorentz force) and the other is applied to the fluid (called the field Lorentz force) near the cylinder surface. Our results show that the wall Lorentz force can generate thrust and reduce the drag; the field Lorentz force increases the drag. However, the cylinder drag is dominated by the wall Lorentz force. In addition, the field Lorentz force above the upper surface decreases the lift, while the upper wall Lorentz force increases it. The total lift is dominated by the upper wall Lorentz force. (fundamental areas of phenomenology(including applications))

Intermittent contact atomic force microscopy in electrochemical environment

Energy Technology Data Exchange (ETDEWEB)

Haering, P; Koetz, R [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Siegenthaler, H [Bern Univ., Bern (Switzerland)

1997-06-01

In situ measurements with Atomic Force Microscopy may cause surface modifications due to the tip-surface interactions. As an alternative and less destructive method, Intermittent Contact Atomic Force Microscopy (ICAFM) has been tested in an electrolytic environment. In the ICAFM mode the tip is not constantly in contact with the surface under investigation but is tapping onto the surface with a certain frequency. A commercial Park Scientific Instruments Microscopy has been modified to enable in situ experiment with ICAFM. It was possible to image iridium oxide films with ICAFM in the electrolytic environment without any noticeable surface modifications. (author) 3 figs., 4 refs.

Direct imaging by atomic force microscopy of surface-localized self-assembled monolayers on a cuprate superconductor and surface X-ray scattering analysis of analogous monolayers on the surface of water

DEFF Research Database (Denmark)

Schougaard, Steen B.; Reitzel, Niels; Bjørnholm, Thomas

2007-01-01

A self-assembled monolayer of CF3(CF2)(3)(CH2)(11)NH2 atop the (001) surface of the high-temperature superconductor YBa2Cu3O7-x was imaged by atomic force microscopy (AFM). The AFM images provide direct 2D-structural evidence for the epitaxial 5.5 angstrom square root 2 x root 2R45 degrees unit...... was studied by grazing-incidence X-ray diffraction and specular X-ray reflectivity. Structural differences and similarities between the water-supported and superconductor-localized monolayers are discussed....

Molecular dynamics simulation of sodium aluminosilicate glass structures and glass surface-water reactions using the reactive force field (ReaxFF)

Science.gov (United States)

Dongol, R.; Wang, L.; Cormack, A. N.; Sundaram, S. K.

2018-05-01

Reactive potentials are increasingly used to study the properties of glasses and glass water reactions in a reactive molecular dynamics (MD) framework. In this study, we have simulated a ternary sodium aluminosilicate glass and investigated the initial stages of the glass surface-water reactions at 300 K using reactive force field (ReaxFF). On comparison of the simulated glass structures generated using ReaxFF and classical Buckingham potentials, our results show that the atomic density profiles calculated for the surface glass structures indicate a bond-angle distribution dependency. The atomic density profiles also show higher concentrations of non-bridging oxygens (NBOs) and sodium ions at the glass surface. Additionally, we present our results of formation of silanol species and the diffusion of water molecules at the glass surface using ReaxFF.

Computation and Evaluation of Features of Surface Electromyogram to Identify the Force of Muscle Contraction and Muscle Fatigue

Directory of Open Access Journals (Sweden)

Sridhar P. Arjunan

2014-01-01

Full Text Available The relationship between force of muscle contraction and muscle fatigue with six different features of surface electromyogram (sEMG was determined by conducting experiments on thirty-five volunteers. The participants performed isometric contractions at 50%, 75%, and 100% of their maximum voluntary contraction (MVC. Six features were considered in this study: normalised spectral index (NSM5, median frequency, root mean square, waveform length, normalised root mean square (NRMS, and increase in synchronization (IIS index. Analysis of variance (ANOVA and linear regression analysis were performed to determine the significance of the feature with respect to the three factors: muscle force, muscle fatigue, and subject. The results show that IIS index of sEMG had the highest correlation with muscle fatigue and the relationship was statistically significant (P0.05.

Computation and evaluation of features of surface electromyogram to identify the force of muscle contraction and muscle fatigue.

Science.gov (United States)

Arjunan, Sridhar P; Kumar, Dinesh K; Naik, Ganesh

2014-01-01

The relationship between force of muscle contraction and muscle fatigue with six different features of surface electromyogram (sEMG) was determined by conducting experiments on thirty-five volunteers. The participants performed isometric contractions at 50%, 75%, and 100% of their maximum voluntary contraction (MVC). Six features were considered in this study: normalised spectral index (NSM5), median frequency, root mean square, waveform length, normalised root mean square (NRMS), and increase in synchronization (IIS) index. Analysis of variance (ANOVA) and linear regression analysis were performed to determine the significance of the feature with respect to the three factors: muscle force, muscle fatigue, and subject. The results show that IIS index of sEMG had the highest correlation with muscle fatigue and the relationship was statistically significant (P 0.05).

Thickness and morphology of polyelectrolyte coatings on silica surfaces before and after protein exposure studied by atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Haselberg, Rob, E-mail: r.haselberg@vu.nl [Biomolecular Analysis, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (Netherlands); AIMMS Division of BioMolecular Analysis, VU University Amsterdam, de Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Flesch, Frits M. [Biomolecular Analysis, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (Netherlands); Boerke, Arjan [Department of Biochemistry and Cell Biology, Utrecht University, Yalelaan 2, 3508 TD Utrecht (Netherlands); Somsen, Govert W. [Biomolecular Analysis, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (Netherlands); AIMMS Division of BioMolecular Analysis, VU University Amsterdam, de Boelelaan 1083, 1081 HV Amsterdam (Netherlands)

2013-05-24

Graphical abstract: -- Highlights: •Atomic force microscopy is used to characterize polyelectrolyte coatings. •Coating procedure leads to nm-thick layers on a silica surface. •Polyelectrolyte coatings effectively prevent protein adsorption. •AFM provides the high resolution to investigate these thin films. •AFM results support earlier findings obtained with capillary electrophoresis. -- Abstract: Analyte–wall interaction is a significant problem in capillary electrophoresis (CE) as it may compromise separation efficiencies and migration time repeatability. In CE, self-assembled polyelectrolyte multilayer films of Polybrene (PB) and dextran sulfate (DS) or poly(vinylsulfonic acid) (PVS) have been used to coat the capillary inner wall and thereby prevent analyte adsorption. In this study, atomic force microscopy (AFM) was employed to investigate the layer thickness and surface morphology of monolayer (PB), bilayer, (PB-DS and PB-PVS), and trilayer (PB-DS-PB and PB-PVS-PB) coatings on glass surfaces. AFM nanoshaving experiments providing height distributions demonstrated that the coating procedures led to average layer thicknesses between 1 nm (PB) and 5 nm (PB-DS-PB), suggesting the individual polyelectrolytes adhere flat on the silica surface. Investigation of the surface morphology of the different coatings by AFM revealed that the PB coating does not completely cover the silica surface, whereas full coverage was observed for the trilayer coatings. The DS-containing coatings appeared on average 1 nm thicker than the corresponding PVS-containing coatings, which could be attributed to the molecular structure of the anionic polymers applied. Upon exposure to the basic protein cytochrome c, AFM measurements showed an increase of the layer thickness for bare (3.1 nm) and PB-DS-coated (4.6 nm) silica, indicating substantial protein adsorption. In contrast, a very small or no increase of the layer thickness was observed for the PB and PB-DS-PB coatings

Influence of the forces on the adhesion behavior of graphite dust in HTGR

International Nuclear Information System (INIS)

Peng Wei; Sun Xiaokai; Zhang Tianqi; Yu Suyuan

2015-01-01

The behavior of the graphite dust is important to the safety of High Temperature Gas-cooled Reactors. The present study focuses on the forces which make the graphite dust attach or detach from the surface in HTGR. The effect of graphite dust size, the fluid velocity and the surface energy between the particles and the substrate were investigated. The result showed that van der Waals adhesion force is the main factors affecting the dust attach on the surface, the gravity force and the electrostatic force were much smaller than it. For small particles, both the aerodynamic lift and drag are smaller than van der Waals adhesion force. While for the large particles, the coupled effects of aerodynamic lift and drag can make the dust detach from the substrate easier. Both the aerodynamic lift and drag forces will increase quickly as the fluid velocity increases. The surface energy is an important parameter for van der Waals adhesion force, which will decrease as the surface energy decreases. (author)

Casimir-Lifshitz force out of thermal equilibrium

NARCIS (Netherlands)

Antezza, M.; Pitaevskii, L.P.; Stringari, S.; Svetovoy, Vitaly

We study the Casimir-Lifshitz interaction out of thermal equilibrium, when the interacting objects are at different temperatures. The analysis is focused on the surface-surface, surface-rarefied body, and surface-atom configurations. A systematic investigation of the contributions to the force

How weather impacts the forced climate response

Energy Technology Data Exchange (ETDEWEB)

Kirtman, Ben P. [University of Miami, Division of Meteorology and Physical Oceanography, Rosenstiel School for Atmospheric and Marine Science, Miami, FL (United States); Center for Ocean-Land-Atmosphere Studies, Calverton, MD (United States); Schneider, Edwin K.; Straus, David M. [George Mason University, Department of Atmospheric, Oceanic and Earth Sciences, Fairfax, VA (United States); Center for Ocean-Land-Atmosphere Studies, Calverton, MD (United States); Min, Dughong; Burgman, Robert [University of Miami, Division of Meteorology and Physical Oceanography, Rosenstiel School for Atmospheric and Marine Science, Miami, FL (United States)

2011-12-15

The new interactive ensemble modeling strategy is used to diagnose how noise due to internal atmospheric dynamics impacts the forced climate response during the twentieth century (i.e., 1870-1999). The interactive ensemble uses multiple realizations of the atmospheric component model coupled to a single realization of the land, ocean and ice component models in order to reduce the noise due to internal atmospheric dynamics in the flux exchange at the interface of the component models. A control ensemble of so-called climate of the twentieth century simulations of the Community Climate Simulation Model version 3 (CCSM3) are compared with a similar simulation with the interactive ensemble version of CCSM3. Despite substantial differences in the overall mean climate, the global mean trends in surface temperature, 500 mb geopotential and precipitation are largely indistinguishable between the control ensemble and the interactive ensemble. Large differences in the forced response; however, are detected particularly in the surface temperature of the North Atlantic. Associated with the forced North Atlantic surface temperature differences are local differences in the forced precipitation and a substantial remote rainfall response in the deep tropical Pacific. We also introduce a simple variance analysis to separately compare the variance due to noise and the forced response. We find that the noise variance is decreased when external forcing is included. In terms of the forced variance, we find that the interactive ensemble increases this variance relative to the control. (orig.)

Contributions of greenhouse gas forcing and the Southern Annular Mode to historical Southern Ocean surface temperature trends

OpenAIRE

Kostov, Yavor; Ferreira, David; Marshall, John; Armour, Kyle

2018-01-01

We examine the 1979-2014 Southern Ocean (SO) sea surface temperature (SST) trends simulated in an ensemble of coupled general circulation models and evaluate possible causes of the models’ inability to reproduce the observed 1979-2014 SO cooling. For each model we estimate the response of SO SST to step changes in greenhouse gas (GHG) forcing and in the seasonal indices of the Southern Annular Mode (SAM). Using these step-response functions, we skillfully reconstruct the models’ 1979-2014 SO ...

MEMS two-axis force plate array used to measure the ground reaction forces during the running motion of an ant

International Nuclear Information System (INIS)

Takahashi, Hidetoshi; Thanh-Vinh, Nguyen; Jung, Uijin G; Shimoyama, Isao; Matsumoto, Kiyoshi

2014-01-01

A terrestrial insect can perform agile running maneuvers. However, the balance of ground reaction forces (GRFs) between each leg in an insect have remained poorly characterized. In this report, we present a micro force plate array for the simultaneous measurement of the anterior and vertical components of GRFs of multiple legs during the running motion of an ant. The proposed force plate, which consists of a 2000 µm × 980 µm × 20 µm plate base as the contact surface of an ant's leg, and the supported beams with piezoresistors on the sidewall and surface are sufficiently compact to be adjacently arrayed along the anterior direction. Eight plates arrayed in parallel were fabricated on the same silicon-on-insulator substrate to narrow the gap between each plate to 20 µm. We compartmented the plate surface into 32 blocks and evaluated the sensitivities to two-axis forces in each block so that the exerted forces could be detected wherever a leg came into contact. The force resolutions in both directions were under 1 µN within ±20 µN. Using the fabricated force plate array, we achieved a simultaneous measurement of the GRFs of three legs on one side while an ant was running. (paper)

Simultaneous current, force and dissipation measurements on the Si(111 7×7 surface with an optimized qPlus AFM/STM technique

Directory of Open Access Journals (Sweden)

Zsolt Majzik

2012-03-01

Full Text Available We present the results of simultaneous scanning-tunneling and frequency-modulated dynamic atomic force microscopy measurements with a qPlus setup. The qPlus sensor is a purely electrical sensor based on a quartz tuning fork. If both the tunneling current and the force signal are to be measured at the tip, a cross-talk of the tunneling current with the force signal can easily occur. The origin and general features of the capacitive cross-talk will be discussed in detail in this contribution. Furthermore, we describe an experimental setup that improves the level of decoupling between the tunneling-current and the deflection signal. The efficiency of this experimental setup is demonstrated through topography and site-specific force/tunneling-spectroscopy measurements on the Si(111 7×7 surface. The results show an excellent agreement with previously reported data measured by optical interferometric deflection.

Analytical prediction of friction factors and Nusselt numbers of turbulent forced convection in rod bundles with smooth and rough surfaces

International Nuclear Information System (INIS)

Su Jian; Silva Freire, Atila P.

2002-01-01

A simple analytical method was developed for the prediction of the friction factor, f, of fully developed turbulent flow and the Nusselt number, Nu, of fully developed turbulent forced convection in rod bundles arranged in square or hexagonal arrays. The friction factor equation for smooth rod bundles was presented in a form similar to the friction factor equation for turbulent flow in a circular pipe. An explicit equation for the Nusselt number of turbulent forced convection in rod bundles with smooth surface was developed. In addition, we extended the analysis to rod bundles with rough surface and provided a method for the prediction of the friction factor and the Nusselt number. The method was based on the law of the wall for velocity and the law of the wall for the temperature, which were integrated over the entire flow area to yield algebraic equations for the prediction of f and Nu. The present method is applicable to infinite rod bundles in square and hexagonal arrays with low pitch to rod diameter ratio, P/D<1.2

The surface characteristics of Al-7%Si aluminum alloy manufactured by thixo/rheoforming process through nanoindentation/atomic force microscopy

International Nuclear Information System (INIS)

Cho, S.H.; Kang, C.G.; Lee, S.M.

2008-01-01

This study investigated nano/microsturcture and mechanical/tribological properties in the thixo/rheoformed A356 alloy parts using nano/microindentation and nanoscratch, incorporated with optical microscopy and atomic force microscopy (AFM). As a result, thixo-cast sample exhibited higher mechanical properties than rheo-cast, irrespective of grain size. The reason that mechanical properties of thixo-cast part was higher than that of rheo-cast, was interpreted by the effect of the eutectic region surrounded by the primary α phase on the hardness. It was also observed that shape and distribution of Si particles in the adjacent eutectic region to the primary α-Al phase of the thixo/rheo-cast products were different. By scratching surface of thixo/rheo-cast parts using a nanoindentor, friction forces and coefficients for the primary α-Al and eutectic phases in thixo-cast products were resulted to be higher than those in the rheo-cast. Nanoscratch for the thixo-cast product also revealed a rough and irregular surface compared to that for the rheo-cast, providing the evidence for the effect of eutectic entrapped by primary α-Al phase on mechanical properties

Atomic Force Microscope

Energy Technology Data Exchange (ETDEWEB)

Day, R.D.; Russell, P.E.

1988-12-01

The Atomic Force Microscope (AFM) is a recently developed instrument that has achieved atomic resolution imaging of both conducting and non- conducting surfaces. Because the AFM is in the early stages of development, and because of the difficulty of building the instrument, it is currently in use in fewer than ten laboratories worldwide. It promises to be a valuable tool for obtaining information about engineering surfaces and aiding the .study of precision fabrication processes. This paper gives an overview of AFM technology and presents plans to build an instrument designed to look at engineering surfaces.

Identification of 6H-SiC polar faces with pull-off force of atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Gan, Di; Song, Youting; Yang, Junwei; Chen, Hongxiang [Research & development Center for Functional Crystals, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Guo, Liwei, E-mail: lwguo@iphy.ac.cn [Research & development Center for Functional Crystals, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Chen, Xiaolong, E-mail: chenx29@iphy.ac.cn [Research & development Center for Functional Crystals, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)

2016-12-30

Highlights: • A new method is proposed and demonstrated to distinguish the polar faces of 6H-SiC by pull-off forces which are clearly different on the Si-face and the C-face of 6H-SiC. • The reliability of this method is confirmed on 6H-SiC samples treated with different surface processing procedures. • The essence of different pull-off forces on different polar faces of 6H-SiC is that the surface energies between them are obviously different. • Theoretical calculations are consistent with our experimental results. - Abstract: Distinguishing SiC (0001) Si-face from SiC (000-1) C-face without any damages is extremely important because the two polar faces have different physical and chemical properties which seriously influence the quality of a homoepitaxy or heteroepitaxy thin film on it. Here, a convenient and nondestructive detection method is developed to distinguish the Si-face and C-face of a (0001) oriented SiC wafer by employing a pull-off force measurement using atomic force microscopy. It is found that the pull-off force from a Si-face of 6H-SiC is about two times of that from a C-face, no matter it is a two-face chemical mechanical polishing or etched 6H-SiC wafer. The method developed here is suitable to identify polar faces of materials only if the two polar faces having different surface energy.

Force Field Benchmark of Organic Liquids: Density, Enthalpy of Vaporization, Heat Capacities, Surface Tension, Isothermal Compressibility, Volumetric Expansion Coefficient, and Dielectric Constant.

Science.gov (United States)

Caleman, Carl; van Maaren, Paul J; Hong, Minyan; Hub, Jochen S; Costa, Luciano T; van der Spoel, David

2012-01-10

The chemical composition of small organic molecules is often very similar to amino acid side chains or the bases in nucleic acids, and hence there is no a priori reason why a molecular mechanics force field could not describe both organic liquids and biomolecules with a single parameter set. Here, we devise a benchmark for force fields in order to test the ability of existing force fields to reproduce some key properties of organic liquids, namely, the density, enthalpy of vaporization, the surface tension, the heat capacity at constant volume and pressure, the isothermal compressibility, the volumetric expansion coefficient, and the static dielectric constant. Well over 1200 experimental measurements were used for comparison to the simulations of 146 organic liquids. Novel polynomial interpolations of the dielectric constant (32 molecules), heat capacity at constant pressure (three molecules), and the isothermal compressibility (53 molecules) as a function of the temperature have been made, based on experimental data, in order to be able to compare simulation results to them. To compute the heat capacities, we applied the two phase thermodynamics method (Lin et al. J. Chem. Phys.2003, 119, 11792), which allows one to compute thermodynamic properties on the basis of the density of states as derived from the velocity autocorrelation function. The method is implemented in a new utility within the GROMACS molecular simulation package, named g_dos, and a detailed exposé of the underlying equations is presented. The purpose of this work is to establish the state of the art of two popular force fields, OPLS/AA (all-atom optimized potential for liquid simulation) and GAFF (generalized Amber force field), to find common bottlenecks, i.e., particularly difficult molecules, and to serve as a reference point for future force field development. To make for a fair playing field, all molecules were evaluated with the same parameter settings, such as thermostats and barostats

Gecko adhesion pad: a smart surface?

Science.gov (United States)

Pesika, Noshir S.; Zeng, Hongbo; Kristiansen, Kai; Zhao, Boxin; Tian, Yu; Autumn, Kellar; Israelachvili, Jacob

2009-11-01

Recently, it has been shown that humidity can increase the adhesion of the spatula pads that form the outermost (adhesive) surface of the tokay gecko feet by 50% relative to the main adhesion mechanism (i.e. van der Waals adhesive forces), although the mechanism by which the enhancement is realized is still not well understood. A change in the surface hydrophobicity of a gecko setal array is observed when the array, which supports the spatulae, is exposed to a water drop for more than 20 min, suggesting a change in the hydrophilic-lyophilic balance (HLB), and therefore of the conformation of the surface proteins. A surface force apparatus (SFA) was used to quantify these changes, i.e. in the adhesion and friction forces, while shearing the setal array against a silica surface under (i) dry conditions, (ii) 100% humidity and (iii) when fully immersed in water. The adhesion increased in the humid environment but greatly diminished in water. Although the adhesion forces changed significantly, the friction forces remained unaffected, indicating that the friction between these highly textured surfaces is 'load-controlled' rather than 'adhesion-controlled'. These results demonstrate that the gecko adhesive pads have the ability to exploit environmental conditions to maximize their adhesion and stabilize their friction forces. Future designs of synthetic dry adhesives inspired by the gecko can potentially include similar 'smart' surfaces that adapt to their environment.

Gecko adhesion pad: a smart surface?

International Nuclear Information System (INIS)

Pesika, Noshir S; Zeng Hongbo; Kristiansen, Kai; Israelachvili, Jacob; Zhao, Boxin; Tian Yu; Autumn, Kellar

2009-01-01

Recently, it has been shown that humidity can increase the adhesion of the spatula pads that form the outermost (adhesive) surface of the tokay gecko feet by 50% relative to the main adhesion mechanism (i.e. van der Waals adhesive forces), although the mechanism by which the enhancement is realized is still not well understood. A change in the surface hydrophobicity of a gecko setal array is observed when the array, which supports the spatulae, is exposed to a water drop for more than 20 min, suggesting a change in the hydrophilic-lyophilic balance (HLB), and therefore of the conformation of the surface proteins. A surface force apparatus (SFA) was used to quantify these changes, i.e. in the adhesion and friction forces, while shearing the setal array against a silica surface under (i) dry conditions, (ii) 100% humidity and (iii) when fully immersed in water. The adhesion increased in the humid environment but greatly diminished in water. Although the adhesion forces changed significantly, the friction forces remained unaffected, indicating that the friction between these highly textured surfaces is 'load-controlled' rather than 'adhesion-controlled'. These results demonstrate that the gecko adhesive pads have the ability to exploit environmental conditions to maximize their adhesion and stabilize their friction forces. Future designs of synthetic dry adhesives inspired by the gecko can potentially include similar 'smart' surfaces that adapt to their environment.

Near field plasmon and force microscopy

NARCIS (Netherlands)

de Hollander, R.B.G.; van Hulst, N.F.; Kooyman, R.P.H.

1995-01-01

A scanning plasmon near field optical microscope (SPNM) is presented which combines a conventional far field surface plasmon microscope with a stand-alone atomic force microscope (AFM). Near field plasmon and force images are recorded simultaneously both with a lateral resolution limited by the

Computing Thermal Imbalance Forces On Satellites

Science.gov (United States)

Vigue, Yvonne; Schutz, Robert E.; Sewell, Granville; Abusali, Pothai A. M.

1994-01-01

HEAT.PRO computer program calculates imbalance force caused by heating of surfaces of satellite. Calculates thermal imbalance force and determines its effect on orbit of satellite, especially where shadow cast by Earth Causes periodic changes in thermal environment around satellite. Written in FORTRAN 77.

Lateral Casimir-Polder forces by breaking time-reversal symmetry

Science.gov (United States)

Oude Weernink, Ricardo R. Q. P. T.; Barcellona, Pablo; Buhmann, Stefan Yoshi

2018-03-01

We examine the lateral Casimir-Polder force acting on a circular rotating emitter near a dielectric plane surface. As the circular motion breaks time-reversal symmetry, the spontaneous emission in a direction parallel to the surface is in general anisotropic. We show that a lateral force arises which can be interpreted as a recoil force because of this asymmetric emission. The force is an oscillating function of the distance between the emitter and the surface, and the lossy character of the dielectric strongly influences the results in the near-field regime. The force exhibits also a population-induced dynamics, decaying exponentially with respect to time on time scales of the inverse of the spontaneous decay rate. We propose that this effect could be detected measuring the velocity acquired by the emitter, following different cycles of excitation and spontaneous decay. Our results are expressed in terms of the Green's tensor and can therefore easily be applied to more complex geometries.

MDM2–MDM4 molecular interaction investigated by atomic force spectroscopy and surface plasmon resonance

Directory of Open Access Journals (Sweden)

Moscetti I

2016-08-01

Full Text Available Ilaria Moscetti,1 Emanuela Teveroni,2,3 Fabiola Moretti,3 Anna Rita Bizzarri,1 Salvatore Cannistraro1 1Biophysics and Nanoscience Centre, Department DEB, Università della Tuscia, Viterbo, Italy; 2Department of Endocrinology and Metabolism, Università Cattolica di Roma, Roma, Italy; 3Institute of Cell Biology and Neurobiology, Consiglio Nazionale delle Ricerche (CNR, Roma, Italy Abstract: Murine double minute 2 (MDM2 and 4 (MDM4 are known as the main negative regulators of p53, a tumor suppressor. They are able to form heterodimers that are much more effective in the downregulation of p53. Therefore, the MDM2–MDM4 complex could be a target for promising therapeutic restoration of p53 function. To this aim, a deeper understanding of the molecular mechanisms underlining the heterodimerization is needed. The kinetic and thermodynamic characterization of the MDM2–MDM4 complex was performed with two complementary approaches: atomic force spectroscopy and surface plasmon resonance. Both techniques revealed an equilibrium dissociation constant (KD in the micromolar range for the MDM2–MDM4 heterodimer, similar to related complexes involved in the p53 network. Furthermore, the MDM2–MDM4 complex is characterized by a relatively high free energy, through a single energy barrier, and by a lifetime in the order of tens of seconds. New insights into the MDM2–MDM4 interaction could be highly important for developing innovative anticancer drugs focused on p53 reactivation. Keywords: MDM2, MDM4, atomic force spectroscopy, surface plasmon resonance

Effects of Mach Numbers on Side Force, Yawing Moment and Surface Pressure

Science.gov (United States)

Sohail, Muhammad Amjad; Muhammad, Zaka; Husain, Mukkarum; Younis, Muhammad Yamin

2011-09-01

In this research, CFD simulations are performed for air vehicle configuration to compute the side force effect and yawing moment coefficients variations at high angle of attack and Mach numbers. As the angle of attack is increased then lift and drag are increased for cylinder body configurations. But when roll angle is given to body then side force component is also appeared on the body which causes lateral forces on the body and yawing moment is also produced. Now due to advancement of CFD methods we are able to calculate these forces and moment even at supersonic and hypersonic speed. In this study modern CFD techniques are used to simulate the hypersonic flow to calculate the side force effects and yawing moment coefficient. Static pressure variations along the circumferential and along the length of the body are also calculated. The pressure coefficient and center of pressure may be accurately predicted and calculated. When roll angle and yaw angle is given to body then these forces becomes very high and cause the instability of the missile body with fin configurations. So it is very demanding and serious problem to accurately predict and simulate these forces for the stability of supersonic vehicles.

Changes in force, surface and motor unit EMG during post-exercise development of low frequency fatigue in vastus lateralis muscle.

Science.gov (United States)

de Ruiter, C J; Elzinga, M J H; Verdijk, P W L; van Mechelen, W; de Haan, A

2005-08-01

We investigated the effects of low frequency fatigue (LFF) on post-exercise changes in rectified surface EMG (rsEMG) and single motor unit EMG (smuEMG) in vastus lateralis muscle (n = 9). On two experimental days the knee extensors were fatigued with a 60-s-isometric contraction (exercise) at 50% maximal force capacity (MFC). On the first day post-exercise (15 s, 3, 9, 15, 21 and 27 min) rsEMG and electrically-induced (surface stimulation) forces were investigated. SmuEMG was obtained on day two. During short ramp and hold (5 s) contractions at 50% MFC, motor unit discharges of the same units were followed over time. Post-exercise MFC and tetanic force (100 Hz stimulation) recovered to about 90% of the pre-exercise values, but recovery with 20 Hz stimulation was less complete: the 20-100 Hz force ratio (mean +/- SD) decreased from 0.65+/-0.06 (pre-exercise) to 0.56+/-0.04 at 27 min post-exercise (Pexercise rsEMG (% pre-exercise maximum) and motor unit discharge rate were 51.1 +/- 12.7% and 14.1 +/- 3.7 (pulses per second; pps) respectively, 15 s post-exercise the respective values were 61.4 +/- 15.4% (P0.05). Thereafter, rsEMG (at 50% MFC) remained stable but motor unit discharge rate significantly increased to 17.7 +/- 3.9 pps 27 min post-exercise. The recruitment threshold decreased (Pexercise to 25.2 +/- 6.7% 27 min post-exercise. The increase in discharge rate was significantly greater than could be expected from the decrease in recruitment threshold. Thus, post-exercise LFF was compensated by increased motor unit discharge rates which could only partly be accounted for by the small decrease in motor unit recruitment threshold.

CHARACTERIZATION OF SURFACE OF THE (010 FACE OF BORAX CRYSTALS USING EX SITU ATOMIC FORCE MICROSCOPY (AFM:

Directory of Open Access Journals (Sweden)

Suharso Suharso

2010-06-01

Full Text Available The surface topology of borax crystals grown at a relative supersaturation of 0.21 has been investigated using ex situ atomic force microscopy (AFM. It was found that the cleavage of borax crystals along the (010 face planes has features of the cleavage of layered compounds, exhibiting cleavage steps of low heights. The step heights of the cleavage of the (010 face of borax crystal are from one unit cell to three unit cells of this face.   Keywords: AFM, cleavage, borax.

Surface adhesion and confinement variation of Staphylococcus aurius on SAM surfaces

Science.gov (United States)

Amroski, Alicia; Olsen, Morgan; Calabrese, Joseph; Senevirathne, Reshani; Senevirathne, Indrajith

2012-02-01

Controlled surface adhesion of non - pathogenic gram positive strain, Staphylococcus aureus is interesting as a model system due to possible development of respective biosensors for prevention and detection of the pathogenic strain methicillin resistant Staphylococcus aureus (MRSA) and further as a study for bio-machine interfacing. Self Assembled Monolayers (SAM) with engineered surfaces of linear thiols on Au(111) were used as the substrate. Sub cultured S. aureus were used for the analysis. The SAM layered surfaces were dipped in 2 -- 4 Log/ml S. aureus solution. Subsequent surface adhesion at different bacterial dilutions on surfaces will be discussed, and correlated with quantitative and qualitative adhesion properties of bacteria on the engineered SAM surfaces. The bacteria adhered SAM surfaces were investigated using intermittent contact, noncontact, lateral force and contact modes of Atomic Force Microscopy (AFM).

Characterization of deep nanoscale surface trenches with AFM using thin carbon nanotube probes in amplitude-modulation and frequency-force-modulation modes

International Nuclear Information System (INIS)

Solares, Santiago D

2008-01-01

The characterization of deep surface trenches with atomic force microscopy (AFM) presents significant challenges due to the sharp step edges that disturb the instrument and prevent it from faithfully reproducing the sample topography. Previous authors have developed AFM methodologies to successfully characterize semiconductor surface trenches with dimensions on the order of tens of nanometers. However, the study of imaging fidelity for features with dimensions smaller than 10 nm has not yet received sufficient attention. Such a study is necessary because small features in some cases lead to apparently high-quality images that are distorted due to tip and sample mechanical deformation. This paper presents multi-scale simulations, illustrating common artifacts affecting images of nanoscale trenches taken with fine carbon nanotube probes within amplitude-modulation and frequency-force-modulation AFM (AM-AFM and FFM-AFM, respectively). It also describes a methodology combining FFM-AFM with a step-in/step-out algorithm analogous to that developed by other groups for larger trenches, which can eliminate the observed artifacts. Finally, an overview of the AFM simulation methods is provided. These methods, based on atomistic and continuum simulation, have been previously used to study a variety of samples including silicon surfaces, carbon nanotubes and biomolecules

Contributions of Greenhouse Gas Forcing and the Southern Annular Mode to Historical Southern Ocean Surface Temperature Trends

Science.gov (United States)

Kostov, Yavor; Ferreira, David; Armour, Kyle C.; Marshall, John

2018-01-01

We examine the 1979-2014 Southern Ocean (SO) sea surface temperature (SST) trends simulated in an ensemble of coupled general circulation models and evaluate possible causes of the models' inability to reproduce the observed 1979-2014 SO cooling. For each model we estimate the response of SO SST to step changes in greenhouse gas (GHG) forcing and in the seasonal indices of the Southern Annular Mode (SAM). Using these step-response functions, we skillfully reconstruct the models' 1979-2014 SO SST trends. Consistent with the seasonal signature of the Antarctic ozone hole and the seasonality of SO stratification, the summer and fall SAM exert a large impact on the simulated SO SST trends. We further identify conditions that favor multidecadal SO cooling: (1) a weak SO warming response to GHG forcing, (2) a strong multidecadal SO cooling response to a positive SAM trend, and (3) a historical SAM trend as strong as in observations.

Nonlinear Dynamics of Cantilever-Sample Interactions in Atomic Force Microscopy

Science.gov (United States)

Cantrell, John H.; Cantrell, Sean A.

2010-01-01

The interaction of the cantilever tip of an atomic force microscope (AFM) with the sample surface is obtained by treating the cantilever and sample as independent systems coupled by a nonlinear force acting between the cantilever tip and a volume element of the sample surface. The volume element is subjected to a restoring force from the remainder of the sample that provides dynamical equilibrium for the combined systems. The model accounts for the positions on the cantilever of the cantilever tip, laser probe, and excitation force (if any) via a basis set of set of orthogonal functions that may be generalized to account for arbitrary cantilever shapes. The basis set is extended to include nonlinear cantilever modes. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a matrix iteration procedure. The effects of oscillatory excitation forces applied either to the cantilever or to the sample surface (or to both) are obtained from the solution set and applied to the to the assessment of phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) modalities. The influence of bistable cantilever modes of on AFM signal generation is discussed. The effects on the cantilever-sample surface dynamics of subsurface features embedded in the sample that are perturbed by surface-generated oscillatory excitation forces and carried to the cantilever via wave propagation are accounted by the Bolef-Miller propagating wave model. Expressions pertaining to signal generation and image contrast in A-AFM are obtained and applied to amplitude modulation (intermittent contact) atomic force microscopy and resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM). The influence of phase accumulation in A-AFM on image contrast is discussed, as is the effect of hard contact and maximum nonlinearity regimes of A-AFM operation.

Elephant overflows: Multi-annual variability in Weddell Sea Deep Water driven by surface forcing

Science.gov (United States)

Meijers, Andrew; Meredith, Michael; Abrahamsen, Povl; Naviera-Garabato, Alberto; Ángel Morales Maqueda, Miguel; Polzin, Kurt

2015-04-01

The volume of the deepest and densest water mass in Drake Passage, Lower Weddell Sea Deep Water (LWSDW), is shown to have been decreasing over the last 20 years of observations, with an associated reduction in density driven by freshening. Superimposed on this long term trend is a multi-annual oscillation with a period of 3-5 years. This variability only appears in Drake Passage; observations in the east of the Scotia Sea show a similar long term trend, but with no apparent multi-annual variability. Clues as to the source of this variability may be found on the continental slope at approximately 1000 m immediately north of Elephant Island on the northern tip of the Antarctic Peninsula. Here there is an intermittent westward flowing cold/fresh slope current whose volume and properties are strongly correlated with the LWSDW multi-annual variability, although leading the LWSDW by around one year. As the slope current and LWSDW are separated from each other both geographically and in water mass characteristics, their co-variability implies that they are responding to a common forcing, while the lag between deep LWSDW and shallow slope current provides information on the timescale of this response. A newly available high resolution temperature and salinity multi-year time series from the Elephant Island slope at 1000 m is compared with reanalysis and model derived surface fluxes, sea ice extent and wind stress. We find that there are strong positive relationships between the surface wind stress and heat flux over the shelf at the tip of the Antarctic Peninsula and the properties of the slope current at 1000 m on seasonal to annual timescales. We use tracer release experiments in the Southern Ocean State Estimate (SOSE) model to investigate the lag between the slope current and LWSDW timeseries and hypothesise that the observed multi-annual variability in both water masses is driven by surface forcing over the shelf and the overflow of modified water from the slope in

Vibrotactile Compliance Feedback for Tangential Force Interaction.

Science.gov (United States)

Heo, Seongkook; Lee, Geehyuk

2017-01-01

This paper presents a method to generate a haptic illusion of compliance using a vibrotactile actuator when a tangential force is applied to a rigid surface. The novel method builds on a conceptual compliance model where a physical object moves on a textured surface in response to a tangential force. The method plays vibration patterns simulating friction-induced vibrations as an applied tangential force changes. We built a prototype consisting of a two-dimensional tangential force sensor and a surface transducer to test the effectiveness of the model. Participants in user experiments with the prototype perceived the rigid surface of the prototype as a moving, rubber-like plate. The main findings of the experiments are: 1) the perceived stiffness of a simulated material can be controlled by controlling the force-playback transfer function, 2) its perceptual properties such as softness and pleasantness can be controlled by changing friction grain parameters, and 3) the use of the vibrotactile compliance feedback reduces participants' workload including physical demand and frustration while performing a force repetition task.

Transition States from Empirical Force Fields

DEFF Research Database (Denmark)

Jensen, Frank; Norrby, Per-Ola

2003-01-01

This is an overview of the use of empirical force fields in the study of reaction mechanisms. EVB-type methods (including RFF and MCMM) produce full reaction surfaces by mixing, in the simplest case, known force fields describing reactants and products. The SEAM method instead locates approximate...

Influence of post-stroke spasticity on EMG-force coupling and force steadiness in biceps brachii.

Science.gov (United States)

Carlyle, Jennilee K; Mochizuki, George

2018-02-01

Individuals with spasticity after stroke experience a decrease in force steadiness which can impact function. Alterations in the strength of EMG-force coupling may contribute to the reduction in force steadiness observed in spasticity. The aim was to determine the extent to which force steadiness and EMG-force coupling is affected by post-stroke spasticity. This cross-sectional study involved individuals with upper limb spasticity after stroke. Participants were required to generate and maintain isometric contractions of the elbow flexors at varying force levels. Coefficient of variation of force, absolute force, EMG-force cross-correlation function peak and peak latency was measured from both limbs with surface electromyography and isometric dynamometry. Statistically significant differences were observed between the affected and less affected limbs for all outcome measures. Significant main effects of force level were also observed. Force steadiness was not statistically significantly correlated with EMG-force coupling; however, both force steadiness and absolute force were associated with the level of impairment as measured by the Chedoke McMaster Stroke Assessment Scale. Spasticity after stroke uncouples the relationship between EMG and force and is associated with reduced force steadiness during isometric contractions; however, these features of control are not associated in individuals with spasticity. Copyright © 2017 Elsevier Ltd. All rights reserved.

Reducing detrimental electrostatic effects in Casimir-force measurements and Casimir-force-based microdevices

Science.gov (United States)

Xu, Jun; Klimchitskaya, G. L.; Mostepanenko, V. M.; Mohideen, U.

2018-03-01

It is well known that residual electrostatic forces create significant difficulties in precise measurements of the Casimir force and the wide use of Casimir-operated microdevices. We experimentally demonstrate that, with the help of Ar-ion cleaning of the surfaces, it is possible to make electrostatic effects negligibly small compared to the Casimir interaction. Our experimental setup consists of a dynamic atomic force microscope supplemented with an Ar-ion gun and argon reservoir. The residual potential difference between the Au-coated surfaces of a sphere and those of a plate was measured both before and after in situ Ar-ion cleaning. It is shown that this cleaning decreases the magnitude of the residual potential by up to an order of magnitude and makes it almost independent of the separation. The gradient of the Casimir force was measured using ordinary samples subjected to Ar-ion cleaning. The obtained results are shown to be in good agreement both with previous precision measurements using specially selected samples and with theoretical predictions of the Lifshitz theory. The conclusion is made that the suggested method of in situ Ar-ion cleaning is effective in reducing the electrostatic effects and therefore is a great resource for experiments on measuring the Casimir interaction and for Casimir-operated microdevices.

Micro and nanostructural characterization of surfaces and interfaces of Portland cement mortars using atomic force microscopy

International Nuclear Information System (INIS)

Barreto, M.F.O.; Brandao, P.R.G.

2014-01-01

The characterization of Portland cement mortars is very important in the study the interfaces and surfaces that make up the system grout/ceramic block. In this sense, scanning electron microscopy and energy-dispersive (X-ray) spectrometer are important tools in investigating the morphology and chemical aspects. However, more detailed topographic information can be necessary in the characterization process. In this work, the aim was to characterize topographically surfaces and interfaces of mortars applied onto ceramic blocks. This has been accomplished by using the atomic force microscope (AFM) - MFP-3D-SA Asylum Research. To date, the results obtained from this research show that the characterization of cementitious materials with the help of AFM has an important contribution in the investigation and differentiation of hydrated calcium silicates (CSH), calcium hydroxide (Ca(OH)2, ettringite and calcium carbonate by providing morphological and micro topographical data, which are extremely important and reliable for the understanding of cementitious materials. (author)

The Kadomtsev endash Petviashvili equation under rapid forcing

International Nuclear Information System (INIS)

Moroz, I.M.

1997-01-01

We consider the initial value problem for the forced Kadomtsev endash Petviashvili equation (KP) when the forcing is assumed to be fast compared to the evolution of the unforced equation. This suggests the introduction of two time scales. Solutions to the forced KP are sought by expanding the dependent variable in powers of a small parameter, which is inversely related to the forcing time scale. The unforced system describes weakly nonlinear, weakly dispersive, weakly two-dimensional wave propagation and is studied in two forms, depending upon whether gravity dominates surface tension or vice versa. We focus on the effect that the forcing has on the one-lump solution to the KPI equation (where surface tension dominates) and on the one- and two-line soliton solutions to the KPII equation (when gravity dominates). Solutions to second order in the expansion are computed analytically for some specific choices of the forcing function, which are related to the choice of initial data. copyright 1997 American Institute of Physics

Gecko adhesion pad: a smart surface?

Energy Technology Data Exchange (ETDEWEB)

Pesika, Noshir S [Chemical and Biomolecular Engineering Department, Tulane University, New Orleans, LA 70118 (United States); Zeng Hongbo [Chemical and Materials Engineering Department, University of Alberta, Edmonton, AB, T6G 2V4 (Canada); Kristiansen, Kai; Israelachvili, Jacob [Chemical Engineering Department, University of California, Santa Barbara, CA 93117 (United States); Zhao, Boxin [Chemical Engineering Department and Waterloo Institute of Nanotechnology, University of Waterloo, Ontario, N2L 3G1 (Canada); Tian Yu [State Key Laboratory of Tribology, Department of Precision Instruments, Tsinghua University, Beijing 100084 (China); Autumn, Kellar, E-mail: npesika@tulane.ed [Department of Biology, Lewis and Clark College, Portland, OR 97219 (United States)

2009-11-18

Recently, it has been shown that humidity can increase the adhesion of the spatula pads that form the outermost (adhesive) surface of the tokay gecko feet by 50% relative to the main adhesion mechanism (i.e. van der Waals adhesive forces), although the mechanism by which the enhancement is realized is still not well understood. A change in the surface hydrophobicity of a gecko setal array is observed when the array, which supports the spatulae, is exposed to a water drop for more than 20 min, suggesting a change in the hydrophilic-lyophilic balance (HLB), and therefore of the conformation of the surface proteins. A surface force apparatus (SFA) was used to quantify these changes, i.e. in the adhesion and friction forces, while shearing the setal array against a silica surface under (i) dry conditions, (ii) 100% humidity and (iii) when fully immersed in water. The adhesion increased in the humid environment but greatly diminished in water. Although the adhesion forces changed significantly, the friction forces remained unaffected, indicating that the friction between these highly textured surfaces is 'load-controlled' rather than 'adhesion-controlled'. These results demonstrate that the gecko adhesive pads have the ability to exploit environmental conditions to maximize their adhesion and stabilize their friction forces. Future designs of synthetic dry adhesives inspired by the gecko can potentially include similar 'smart' surfaces that adapt to their environment.

Osteopontin Reduces the Adhesion Force of Dental Bacteria Without Blocking Bacterial Cell Surface Glycoconjugates

DEFF Research Database (Denmark)

Kristensen, Mathilde Frost; Zeng, Guanghong; Neu, Thomas R.

2017-01-01

. paracasei, and lectins VGA and WGA to S. mitis. Immobilized bacteria were incubated with these lectins in the presence and absence of OPN. For each combination, 12 confocal images were acquired with fixed microscope settings, and average fluorescence intensities were determined. Experiments were performed......The bovine milk protein osteopontin (OPN) has been shown to reduce the adhesion of oral bacteria to saliva-coated surfaces, which reduces biofilm formation and may contribute to caries control. We now quantified the effect of OPN (Lacprodan OPN-10) treatment on the adhesion force of Lactobacillus...... and after OPN treatment. Adhesion energy was found to be reduced by 94% for L. paracasei and 61% for A. naeslundii (pbacteria was screened. Lectins BanLec, ConA, VGA and WGA bound well to A. naeslundii, lectins ABA and HPA to L...

Molecular dimensions of dried glucose oxidase on a Au(1 1 1) surface studied by dynamic mode scanning force microscopy

International Nuclear Information System (INIS)

Otsuka, Ichiro; Yaoita, Masashi; Nagashima, Seiichi; Higano, Michi

2005-01-01

We have investigated the molecular dimensions of a dried single glucose oxidase (GO) molecule adsorbed on a Au(1 1 1) surface with the UHV non-contact atomic force microscopy (NC-AFM) and tapping mode atomic force microcopy (TMAFM). The smallest air-dried GO particles in a TMAFM-measured size distribution are found to be 10-11 nm wide and 0.3-0.4 nm high. We find each collapsed ellipsoidal feature with a groove in a NC-AFM image, which measured 12 nm x 10 nm x 0.5 nm. The lateral dimensions (12 nm x 10 nm) of the observed feature is close to those of a GO monomer measured by scanning tunneling microscopy (STM) [Quijin et al., 12.2 nm x 8.9 nm as the size of one wing of an opening butterfly (dimer) appeared in a STM image] and by contact mode AFM [Quinto et al., 14 nm x 8 nm]. Our value of the vertical dimension (0.5 nm) is consistent with AFM results and molecular dynamics simulations that suggest a surface-induced complete unfolding, showing the average diameter of amino acid residues

Nature of bonding forces between two hydrogen-passivated silicon wafers

DEFF Research Database (Denmark)

Stokbro, Kurt; Nielsen, E.; Hult, E.

1998-01-01

The nature and strength of the bonding forces between two II-passivated Si surfaces are studied with the density-functional theory, using an approach based on recent theoretical advances in understanding of van der Waals forces between two surfaces. Contrary to previous suggestions of van der Waals...

Standardization Plan for Fiber Optics Optional Phase. Volume 2.

Science.gov (United States)

1984-01-01

Langley 1 ERADCOM 7 Johnson 1 ETL-TD-E 1 Johnson 1 MICOM 2 Ames 1 MIRADCOM 1 AVRADCOM 7 DARCOMW 14 Army Human Engineering 1 Laboratories NAVY DEPARTMENT...34- .- . . "-",..- -? ., .. .- " - , -- , - .--- ’- -.... . : ...- . . ..-. ..- ;.- SPECIFICATIONS DATA BASE Page 44 170. Automiated Sampled Data Instrumentation System CASDIS) Transmission Group CI 0042137 Number: S-M-X

Force spectroscopy of hepatocytic extracellular matrix components

Energy Technology Data Exchange (ETDEWEB)

Yongsunthon, R., E-mail: YongsuntR@Corning.com [Corning Incorporated, SP-FR-01, R1S32D, Corning, NY 14831 (United States); Baker, W.A.; Bryhan, M.D.; Baker, D.E.; Chang, T.; Petzold, O.N.; Walczak, W.J.; Liu, J.; Faris, R.A.; Senaratne, W.; Seeley, L.A.; Youngman, R.E. [Corning Incorporated, SP-FR-01, R1S32D, Corning, NY 14831 (United States)

2009-07-15

We present atomic force microscopy and force spectroscopy data of live hepatocytes (HEPG2/C3A liver cell line) grown in Eagle's Minimum Essential Medium, a complex solution of salts and amino acids commonly used for cell culture. Contact-mode imaging and force spectroscopy of this system allowed correlation of cell morphology and extracellular matrix (ECM) properties with substrate properties. Force spectroscopy analysis of cellular 'footprints' indicated that the cells secrete large polymers (e.g., 3.5 {mu}m contour length and estimated MW 1000 kDa) onto their substrate surface. Although definitive identification of the polymers has not yet been achieved, fluorescent-labeled antibody staining has specified the presence of ECM proteins such as collagen and laminin in the cellular footprints. The stretched polymers appear to be much larger than single molecules of known ECM components, such as collagen and heparan sulfate proteoglycan, thus suggesting that the cells create larger entangled, macromolecular structures from smaller components. There is strong evidence which suggests that the composition of the ECM is greatly influenced by the hydrophobicity of the substrate surface, with preferential production and/or adsorption of larger macromolecules on hydrophobic surfaces.

Defect forces, defect couples and path integrals in fracture mechanics

International Nuclear Information System (INIS)

Roche, R.L.

1979-07-01

In this work, it is shown that the path integrals can be introduced without any reference to the material behavior. The method is based on the definition in a continuous medium of a set of vectors and couples having the dimension of a force or a moment. More precisely, definitions are given of volume defect forces, surface defect forces, volume defect couples, and surface defect couples. This is done with the help of the stress working variation of a particule moving through the solid. The most important result is: the resultant of all the defect forces included in a volume V is the J integral on the surface surrounding V and the moment resultant is the L integral. So these integrals are defined without any assumption on the material constitutive equation. Another result is the material form of the virtual work principle - defect forces are acting like conventional forces in the conventional principles of virtual work. This lead to the introduction of the energy momentum tensor and of the associated couple stress. Application of this method is made to fracture mechanics in studying the defect forces distribution around a crack [fr

Differential magnetic force microscope imaging.

Science.gov (United States)

Wang, Ying; Wang, Zuobin; Liu, Jinyun; Hou, Liwei

2015-01-01

This paper presents a method for differential magnetic force microscope imaging based on a two-pass scanning procedure to extract differential magnetic forces and eliminate or significantly reduce background forces with reversed tip magnetization. In the work, the difference of two scanned images with reversed tip magnetization was used to express the local magnetic forces. The magnetic sample was first scanned with a low lift distance between the MFM tip and the sample surface, and the magnetization direction of the probe was then changed after the first scan to perform the second scan. The differential magnetic force image was obtained through the subtraction of the two images from the two scans. The theoretical and experimental results have shown that the proposed method for differential magnetic force microscope imaging is able to reduce the effect of background or environment interference forces, and offers an improved image contrast and signal to noise ratio (SNR). © Wiley Periodicals, Inc.

Three-dimensional scanning force/tunneling spectroscopy at room temperature

International Nuclear Information System (INIS)

Sugimoto, Yoshiaki; Ueda, Keiichi; Abe, Masayuki; Morita, Seizo

2012-01-01

We simultaneously measured the force and tunneling current in three-dimensional (3D) space on the Si(111)-(7 × 7) surface using scanning force/tunneling microscopy at room temperature. The observables, the frequency shift and the time-averaged tunneling current were converted to the physical quantities of interest, i.e. the interaction force and the instantaneous tunneling current. Using the same tip, the local density of states (LDOS) was mapped on the same surface area at constant height by measuring the time-averaged tunneling current as a function of the bias voltage at every lateral position. LDOS images at negative sample voltages indicate that the tip apex is covered with Si atoms, which is consistent with the Si-Si covalent bonding mechanism for AFM imaging. A measurement technique for 3D force/current mapping and LDOS imaging on the equivalent surface area using the same tip was thus demonstrated. (paper)

Flow and Displacement of Non-Newtonian Fluid(Power-Law Model) by Surface Tension and Gravity Force in Inclined Circular Tube

International Nuclear Information System (INIS)

Moh, Jeong Hah; Cho, Y. I.

2014-01-01

This paper presents the theoretical analysis of a flow driven by surface tension and gravity in an inclined circular tube. A governing equation is developed for describing the displacement of a non-Newtonian fluid(Power-law model) that continuously flows into a circular tube owing to surface tension, which represents a second-order, nonlinear, non-homogeneous, and ordinary differential form. It was found that quantitatively, the theoretical predictions of the governing equation were in excellent agreement with the solutions of the equation for horizontal tubes and the past experimental data. In addition, the predictions compared very well with the results of the force balance equation for steady

Current-induced forces: a simple derivation

International Nuclear Information System (INIS)

Todorov, Tchavdar N; Dundas, Daniel; Lü, Jing-Tao; Brandbyge, Mads; Hedegård, Per

2014-01-01

We revisit the problem of forces on atoms under current in nanoscale conductors. We derive and discuss the five principal kinds of force under steady-state conditions from a simple standpoint that—with the help of background literature—should be accessible to physics undergraduates. The discussion aims at combining methodology with an emphasis on the underlying physics through examples. We discuss and compare two forces present only under current—the non-conservative electron wind force and a Lorentz-like velocity-dependent force. It is shown that in metallic nanowires both display significant features at the wire surface, making it a candidate for the nucleation of current-driven structural transformations and failure. Finally we discuss the problem of force noise and the limitations of Ehrenfest dynamics. (paper)

Studying the InAs quantum points on the vicinal surface of a GaAs crystal by the atomic force microscopy

CERN Document Server

Evtikhiev, V P; Kotelnikov, E Y; Matveentsev, A V; Titkov, A N; Shkolnik, A S

2002-01-01

The methodology for processing the images, obtained through the atomic force microscopy, is proposed. It is shown by the concrete example, how the parameters of the InAs clusters on the vicinal surface of the GaAs crystal are determined. This makes it possible to calculate the energy levels of the electrons and holes in the quantum point with application of the previously developed cluster spherical model

Correlating yeast cell stress physiology to changes in the cell surface morphology: atomic force microscopic studies.

Science.gov (United States)

Canetta, Elisabetta; Walker, Graeme M; Adya, Ashok K

2006-07-06

Atomic Force Microscopy (AFM) has emerged as a powerful biophysical tool in biotechnology and medicine to investigate the morphological, physical, and mechanical properties of yeasts and other biological systems. However, properties such as, yeasts' response to environmental stresses, metabolic activities of pathogenic yeasts, cell-cell/cell-substrate adhesion, and cell-flocculation have rarely been investigated so far by using biophysical tools. Our recent results obtained by AFM on one strain each of Saccharomyces cerevisiae and Schizosaccharomyces pombe show a clear correlation between the physiology of environmentally stressed yeasts and the changes in their surface morphology. The future directions of the AFM related techniques in relation to yeasts are also discussed.

Surface modifications by field induced diffusion.

Directory of Open Access Journals (Sweden)

Martin Olsen

Full Text Available By applying a voltage pulse to a scanning tunneling microscope tip the surface under the tip will be modified. We have in this paper taken a closer look at the model of electric field induced surface diffusion of adatoms including the van der Waals force as a contribution in formations of a mound on a surface. The dipole moment of an adatom is the sum of the surface induced dipole moment (which is constant and the dipole moment due to electric field polarisation which depends on the strength and polarity of the electric field. The electric field is analytically modelled by a point charge over an infinite conducting flat surface. From this we calculate the force that cause adatoms to migrate. The calculated force is small for voltage used, typical 1 pN, but due to thermal vibration adatoms are hopping on the surface and even a small net force can be significant in the drift of adatoms. In this way we obtain a novel formula for a polarity dependent threshold voltage for mound formation on the surface for positive tip. Knowing the voltage of the pulse we then can calculate the radius of the formed mound. A threshold electric field for mound formation of about 2 V/nm is calculated. In addition, we found that van der Waals force is of importance for shorter distances and its contribution to the radial force on the adatoms has to be considered for distances smaller than 1.5 nm for commonly used voltages.

Mechanism underlying bioinertness of self-assembled monolayers of oligo(ethyleneglycol)-terminated alkanethiols on gold: protein adsorption, platelet adhesion, and surface forces.

Science.gov (United States)

Hayashi, Tomohiro; Tanaka, Yusaku; Koide, Yuki; Tanaka, Masaru; Hara, Masahiko

2012-08-07

The mechanism underlying the bioinertness of the self-assembled monolayers of oligo(ethylene glycol)-terminated alkanethiol (OEG-SAM) was investigated with protein adsorption experiments, platelet adhesion tests, and surface force measurements with an atomic force microscope (AFM). In this work, we performed systematic analysis with SAMs having various terminal groups (-OEG, -OH, -COOH, -NH(2), and -CH(3)). The results of the protein adsorption experiment by the quartz crystal microbalance (QCM) method suggested that having one EG unit and the neutrality of total charges of the terminal groups are essential for protein-resistance. In particular, QCM with energy dissipation analyses indicated that proteins absorb onto the OEG-SAM via a very weak interaction compared with other SAMs. Contrary to the protein resistance, at least three EG units as well as the charge neutrality of the SAM are found to be required for anti-platelet adhesion. When the identical SAMs were formed on both AFM probe and substrate, our force measurements revealed that only the OEG-SAMs possessing more than two EG units showed strong repulsion in the range of 4 to 6 nm. In addition, we found that the SAMs with other terminal groups did not exhibit such repulsion. The repulsion between OEG-SAMs was always observed independent of solution conditions [NaCl concentration (between 0 and 1 M) and pH (between 3 and 11)] and was not observed in solution mixed with ethanol, which disrupts the three-dimensional network of the water molecules. We therefore concluded that the repulsion originated from structured interfacial water molecules. Considering the correlation between the above results, we propose that the layer of the structured interfacial water with a thickness of 2 to 3 nm (half of the range of the repulsion observed in the surface force measurements) plays an important role in deterring proteins and platelets from adsorption or adhesion.

A study on fixing force generation mechanism of ER gel

International Nuclear Information System (INIS)

Tanaka, H; Kakinuma, Y; Aoyama, T; Anzai, H

2009-01-01

Electro-rheological Gel (ERG) is a new functional elastomer which changes its surface frictional and adhesive property according to the intensity of applied electrical field. This unique property is called ERG effect. The upper sliding electrode placed on the surface of ERG is fixed by the adhesive effect of ERG under electrical field. Variable fixing forces due to adhesion are generated by this effect. However, relationship between physical factors and generated fixing force has not yet been clarified. In this study, physical mechanism of fixing phenomenon is elucidated experimentally from the view point of frictional force and adhesive force. From the results, empirical equation of generated fixing force is originally derived to establish the theory of ERG effect.

A study on fixing force generation mechanism of ER gel

Energy Technology Data Exchange (ETDEWEB)

Tanaka, H; Kakinuma, Y; Aoyama, T [School of Integrated Design Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Anzai, H [Fujikura kasei Co., Ltd., 2-6-15 Shibakouen, Minato-ku, Tokyo (Japan)], E-mail: h-tanaka@ina.sd.keio.ac.jp

2009-02-01

Electro-rheological Gel (ERG) is a new functional elastomer which changes its surface frictional and adhesive property according to the intensity of applied electrical field. This unique property is called ERG effect. The upper sliding electrode placed on the surface of ERG is fixed by the adhesive effect of ERG under electrical field. Variable fixing forces due to adhesion are generated by this effect. However, relationship between physical factors and generated fixing force has not yet been clarified. In this study, physical mechanism of fixing phenomenon is elucidated experimentally from the view point of frictional force and adhesive force. From the results, empirical equation of generated fixing force is originally derived to establish the theory of ERG effect.