Science.gov

Sample records for surface force measurements

  1. Measurement of Surface Forces

    DTIC Science & Technology

    1990-11-16

    hydration forces were observed in solutions containing chloride salts of Li+ , K+ , Na 4 , and Cs+ , resulting from electrostatic binding of the cation...concentrated solutions of a series of tetraalkylammonium bromide salts [46] [Fig. 13]. In these measurements, the distance of closest approach of the two...solid metal electrodes separated by an electrolytic solution . Electrostatic forces, which are intimately related to electrode kinetics and adsorption

  2. Interfacial forces between silica surfaces measured by atomic force microscopy.

    PubMed

    Duan, Jinming

    2009-01-01

    Colloidal particle stability and some other interfacial phenomena are governed by interfacial force interactions. The two well known forces are van der Waals force and electrostatic force, as documented by the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. Moreover, advances in modern instrumentation and colloid science suggested that some short-ranged forces or structure forces are important for relevant colloidal systems. The interfacial and/or molecular forces can be measured as a resultant force as function of separation distance by atomic force microscopy (AFM) colloid probe. This article presents a discussion on AFM colloid probe measurement of silica particle and silica wafer surfaces in solutions with some technical notifications in measurement and data convolution mechanisms. The measured forces are then analyzed and discussed based on the 'constant charge' and 'constant potential' models of DLVO theory. The difference between the prediction of DLVO theory and the measured results indicates that there is a strong short-range structure force between the two hydrophilic surfaces, even at extremely low ionic concentration, such as Milli-Q water purity solution.

  3. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements.

    PubMed

    Zou, Yi; Jayasuriya, Sunil; Manke, Charles W; Mao, Guangzhao

    2015-09-29

    Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken

  4. Bite force measurements with hard and soft bite surfaces.

    PubMed

    Serra, C M; Manns, A E

    2013-08-01

    Bite force has been measured by different methods and over a wide variety of designs. In several instruments, the fact that bite surface has been manufactured with stiff materials might interfere in obtaining reliable data, by a more prompt activation of inhibitory reflex mechanisms. The purpose of this study was to compare the maximum voluntary bite force measured by a digital occlusal force gauge (GM10 Nagano Keiki, Japan) between different opponent teeth, employing semi-hard or soft bite surfaces. A sample of 34 young adults with complete natural dentition was studied. The original semi-hard bite surface was exchanged by a soft one, made of leather and rubber. Maximum voluntary bite force recordings were made for each tooth group and for both bite surfaces. Statistical analyses (Student's t-test) revealed significant differences, with higher scores while using the soft surface across sexes and tooth groups (P < 0·05). Differential activation of periodontal mechanoreceptors of a specific tooth group is mainly conditioned by the hardness of the bite surface; a soft surface induces greater activation of elevator musculature, while a hard one induces inhibition more promptly. Thus, soft bite surfaces are recommended for higher reliability in maximum voluntary bite force recordings.

  5. Capillary-force measurement on SiC surfaces

    NASA Astrophysics Data System (ADS)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-06-01

    Capillary forces have been measured by atomic force microscopy in the sphere-plate geometry, in a controlled humidity environment, between smooth silicon carbide and borosilicate glass spheres. The force measurements were performed as a function of the rms surface roughness ˜4-14 nm mainly due to sphere morphology, the relative humidity (RH) ˜0%-40%, the applied load on the cantilever, and the contact time. The pull-off force was found to decrease by nearly two orders of magnitude with increasing rms roughness from 8 to 14 nm due to formation of a few capillary menisci for the roughest surfaces, while it remained unchanged for rms roughness <8 nm implying fully wetted surface features leading to a single meniscus. The latter reached a steady state in less than 5 s for the smoothest surfaces, as force measurements versus contact time indicated for increased RH˜40%. Finally, the pull-off force increases and reaches a maximum with applied load, which is associated with plastic deformation of surface asperities, and decreases at higher loads.

  6. A Simple Instrument for Measuring Surface Forces in Liquids

    NASA Astrophysics Data System (ADS)

    Hannon, James; Tromp, Rudolf; Haight, Richard; Ellis, Arthur

    2015-03-01

    We have constructed a simple instrument to measure the interaction force between two surfaces in solution, or in vacuum. Specifically, we measure the interaction between a lens and a thin silicon cantilever. Either the lens, or the cantilever (or both) can be coated with the species of interest. When the lens is brought close to the cantilever surface, the force of interaction causes the cantilever to bend. By measuring the deflection as a function of the distance between the lens and cantilever, the long-range interactions between the two surfaces can be determined. Our approach includes three important innovations. First, a commercial lens with a radius of ~ 1 cm is used for one surface. The relatively large radius of curvature enhances force sensitivity of the method. Second, we use optical interference (Newton's Rings) to determine the distance between lens and cantilever with ~ 1 nm accuracy. Third, we make use of thin crystalline cantilevers (100 μm thick) whose elastic properties can be easily measured. We have achieved a force sensitivity F / R better than 0.001 mN/m. I will discuss the theory of operation of the new instrument and describe measurements made on SiO2 and metal oxide surfaces in water.

  7. Theoretical Models for Surface Forces and Adhesion and Their Measurement Using Atomic Force Microscopy

    PubMed Central

    Leite, Fabio L.; Bueno, Carolina C.; Da Róz, Alessandra L.; Ziemath, Ervino C.; Oliveira, Osvaldo N.

    2012-01-01

    The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of AFS, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution. PMID:23202925

  8. Theoretical models for surface forces and adhesion and their measurement using atomic force microscopy.

    PubMed

    Leite, Fabio L; Bueno, Carolina C; Da Róz, Alessandra L; Ziemath, Ervino C; Oliveira, Osvaldo N

    2012-10-08

    The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of afs, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution.

  9. Drag force and surface roughness measurements on freshwater biofouled surfaces.

    PubMed

    Andrewartha, J; Perkins, K; Sargison, J; Osborn, J; Walker, G; Henderson, A; Hallegraeff, G

    2010-05-01

    The detrimental effect of biofilms on skin friction for near wall flows is well known. The diatom genera Gomphonema and Tabellaria dominated the biofilm mat in the freshwater open channels of the Tarraleah Hydropower Scheme in Tasmania, Australia. A multi-faceted approach was adopted to investigate the drag penalty for biofouled 1.0 m x 0.6 m test plates which incorporated species identification, drag measurement in a recirculating water tunnel and surface characterisation using close-range photogrammetry. Increases in total drag coefficient of up to 99% were measured over clean surface values for biofouled test plates incubated under flow conditions in a hydropower canal. The effective roughness of the biofouled surfaces was found to be larger than the physical roughness; the additional energy dissipation was caused in part by the vibration of the biofilms in three-dimensions under flow conditions. The data indicate that there was a roughly linear relationship between the maximum peak-to-valley height of a biofilm and the total drag coefficient.

  10. Interpreting atomic force microscopy measurements of hydrodynamic and surface forces with nonlinear parametric estimation.

    PubMed

    Cui, Song; Manica, Rogerio; Tabor, Rico F; Chan, Derek Y C

    2012-10-01

    A nonlinear parameter estimation method has been developed to extract the separation-dependent surface force and cantilever spring constant from atomic force microscope data taken at different speeds for the interaction between a silica colloidal probe and plate in aqueous solution. The distinguishing feature of this approach is that it exploits information from the velocity dependence of the force-displacement data due to hydrodynamic interaction to provide an unbiased estimate of the functional form of the separation-dependent surface force. An assumed function for the surface force with unknown parameters is not required. In addition, the analysis also yields a consistent estimate of the in situ cantilever spring constant. In combination with data from static force measurements, this approach can further be used to quantify the extent of hydrodynamic slip.

  11. Wettability and surface forces measured by atomic force microscopy: the role of roughness

    NASA Astrophysics Data System (ADS)

    Gavoille, J.; Takadoum, J.; Martin, N.; Durand, D.

    2009-10-01

    Thin films of titanium, copper and silver with various roughnesses were prepared by physical vapour deposition technique: dc magnetron sputtering. By varying the deposition time from few minutes to one hour it was possible to obtain metallic films with surface roughness average ranging from 1 to 20 nm. The wettability of these films was studied by measuring the contact angle using the sessile drop method and surface forces were investigated using the atomic force microscopy (AFM) by measuring the pull-off force between the AFM tip and the surfaces. Experimental results have been mainly discussed in terms of metal surface reactivity, Young modulus of the materials and real surface of contact between the AFM tip and the film surfaces.

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

    PubMed

    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.

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

    PubMed Central

    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

    2016-01-01

    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. PMID:27036002

  14. Dynamic measurement of the force required to move a liquid drop on a solid surface.

    PubMed

    Pilat, D W; Papadopoulos, P; Schäffel, D; Vollmer, D; Berger, R; Butt, H-J

    2012-12-11

    We measured the forces required to slide sessile drops over surfaces. The forces were measured by means of a vertical deflectable capillary stuck in the drop. The drop adhesion force instrument (DAFI) allowed the investigation of the dynamic lateral adhesion force of water drops of 0.1 to 2 μL volume at defined velocities. On flat PDMS surfaces, the dynamic lateral adhesion force increases linearly with the diameter of the contact area of the solid-liquid interface and linearly with the sliding velocity. The movement of the drop relative to the surfaces enabled us to resolve the pinning of the three-phase contact line to individual defects. We further investigated a 3D superhydrophobic pillar array. The depinning of the receding part of the rim of the drop occurred almost simultaneously from four to five pillars, giving rise to peaks in the lateral adhesion force.

  15. A relationship between three-dimensional surface hydration structures and force distribution measured by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Miyazawa, Keisuke; Kobayashi, Naritaka; Watkins, Matthew; Shluger, Alexander L.; Amano, Ken-Ichi; Fukuma, Takeshi

    2016-03-01

    Hydration plays important roles in various solid-liquid interfacial phenomena. Very recently, three-dimensional scanning force microscopy (3D-SFM) has been proposed as a tool to visualise solvated surfaces and their hydration structures with lateral and vertical (sub) molecular resolution. However, the relationship between the 3D force map obtained and the equilibrium water density, ρ(r), distribution above the surface remains an open question. Here, we investigate this relationship at an interface of an inorganic mineral, fluorite, and water. The force maps measured in pure water are directly compared to force maps generated using the solvent tip approximation (STA) model and from explicit molecular dynamics simulations. The results show that the simulated STA force map describes the major features of the experimentally obtained force image. The agreement between the STA data and the experiment establishes the correspondence between the water density used as an input to the STA model and the experimental hydration structure and thus provides a tool to bridge the experimental force data and atomistic solvation structures. Further applications of this method should improve the accuracy and reliability of both interpretation of 3D-SFM force maps and atomistic simulations in a wide range of solid-liquid interfacial phenomena.Hydration plays important roles in various solid-liquid interfacial phenomena. Very recently, three-dimensional scanning force microscopy (3D-SFM) has been proposed as a tool to visualise solvated surfaces and their hydration structures with lateral and vertical (sub) molecular resolution. However, the relationship between the 3D force map obtained and the equilibrium water density, ρ(r), distribution above the surface remains an open question. Here, we investigate this relationship at an interface of an inorganic mineral, fluorite, and water. The force maps measured in pure water are directly compared to force maps generated using the solvent

  16. Understanding gas-surface interactions from direct force measurements using a specialized torsion balance

    NASA Technical Reports Server (NTRS)

    Cook, S. R.; Hoffbauer, M. A.

    1996-01-01

    The first comprehensive measurements of the magnitude and direction of the forces exerted on surfaces by molecular beams are discussed and used to obtain information about the microscopic properties of the gas-surface interactions. This unique approach is not based on microscopic measurements of the scattered molecules. The reduced force coefficients are introduced as a new set of parameters that completely describe the macroscopic average momentum transfer to a surface by an incident molecular beam. By using a specialized torsion balance and molecular beams of N2, CO, CO2, and H2, the reduced force coefficients are determined from direct measurements of the force components exerted on surface of a solar panel array material, Kapton, SiO2-coated Kapton, and Z-93 as a function of the angle of incidence ranging from 0 degrees to 85 degrees. The absolute flux densities of the molecular beams were measured using a different torsion balance with a beam-stop that nullified the force of the scattered molecules. Standard time-of-flight techniques were used to determine the flux-weighted average velocities of the various molecular beams ranging from 1600 m/s to 4600 m/s. The reduced force coefficients can be used to directly obtain macroscopic average properties of the scattered molecules, such as the flux-weighted average velocity and translational energy, that can then be used to determine microscopic details concerning gas-surface interactions without the complications associated with averaging microscopic measurements.

  17. An aspect of denture base retention: direct measurement of force due to surface tension.

    PubMed

    Murray, M D; Darvell, B W

    1991-01-01

    A fixed-volume drop of liquid between a pair of parallel surfaces has been a common model for the denture-mucosa system. The reported one-term equation for the model, the derivation of which is suspect, implies that the acting force is inversely proportional to the square of the separation. Direct measurement of the force, however, showed that a better approximation is given by a two-term equation, with force varying as the inverse of the separation. The need for rigorous theoretical derivation is thereby emphasized. The experimental data suggest that a maximum retention force might occur for denture bases at separations of about 15 microns.

  18. Simultaneous scanning tunneling microscopy and stress measurements to elucidate the origins of surface forces.

    PubMed

    Narushima, Tetsuya; Kinahan, Niall T; Boland, John J

    2007-05-01

    We have developed a new combined measurement system to investigate the underlying origins of forces on solid state surfaces from the viewpoint of atomic surface morphology. This system consists of two main parts: the measurements of force based on displacements and detailed atomic resolution observations of the surface morphology. The former involves a large sample cantilever and a capacitive detection method that provide sufficient resolution to detect changes of a few meV/atom or pN/atom at surfaces. For the latter, a scanning tunneling microscope was incorporated to observe structural changes occurring on the surface of the cantilever sample. Although this combined observation is not trivial, it was accomplished by carefully designing sample dimensions while suppressing the self-oscillation of the cantilever. To demonstrate the performance of this system a preliminary study of the room temperature adsorption of Br(2) on the clean Si(111)-7x7 surface is presented.

  19. Understanding gas-surface interactions from direct force measurements using a specialized torsion balance

    SciTech Connect

    Cook, S.R.; Hoffbauer, M.A.

    1996-12-31

    The first comprehensive measurements of the magnitude and direction of the forces exerted on surfaces by molecular beams are discussed and used to obtain information about the microscopic properties of the gas-surface interactions. This unique approach is not based on microscopic measurements of the scattered molecules. The reduced force coefficients are introduced as a new set of parameters that completely describe the macroscopic average momentum transfer to a surface by an incident molecular beam. By using a specialized torsion balance and molecular beams of N{sub 2}, CO, CO{sub 2}, and H{sub 2}, the reduced force coefficients are determined from direct measurements of the force components exerted on surface of a solar panel array material, Kapton, SiO{sub 2}-coated Kapton, and Z-93 as a function of the angle of incidence ranging from 0{degrees} to 85{degrees}. The absolute flux densities of the molecular beams were measured using a different torsion balance with a beam-stop that nullified the force of the scattered molecules. Standard time-of-flight techniques were used to determine the flux-weighted average velocities of the various molecular beams ranging from 1600 m/s to 4600 m/s. The reduced force coefficients can be used to directly obtain macroscopic average properties of the scattered molecules, such as the flux-weighted average velocity and translational energy, that can then be used to determine microscopic details concerning gas-surface interactions without the complications associated with averaging microscopic measurements.

  20. Surface force measurements at the basal planes of ordered kaolinite particles.

    PubMed

    Gupta, Vishal; Miller, Jan D

    2010-04-15

    An experimental procedure is presented to order kaolinite particles on substrates for interrogation of the two basal plane surfaces by atomic force microscopy. Surface force measurements were performed between a silicon nitride tip and each of the two faces (silica tetrahedral face and alumina octahedral face) of kaolinite in 1 mM KCl solution at pH 4, 5, 6, 8 and 10, using atomic force microscopy. The colloidal force measurements reveal that the silica tetrahedral face of kaolinite is negatively charged at pH>4, whereas the alumina octahedral face of kaolinite is positively charged at pH<6, and negatively charged at pH>8. Such measurements have not been reported previously and the results suggest that the iso-electric point of the silica tetrahedral face is at pH<4, and that the iso-electric point of the alumina octahedral face lies between pH 6 and 8. These results contradict the generally accepted view that basal plane surfaces of kaolinite carry a permanent negative charge due to minor substitution of Al(3+) for Si(4+) in the silica tetrahedral layer, and suggest some surface charge dependency of the two faces with respect to solution pH. With this new information it may be possible to further explain the electrokinetic behavior of kaolinite particles, and their interactions in aqueous suspensions.

  1. Surface summertime radiative forcing by shallow cumuli at the Atmospheric Radiation Measurement Southern Great Plains site

    SciTech Connect

    Berg, Larry K.; Kassianov, Evgueni I.; Long, Charles N.; Mills Jr., David L.

    2011-01-08

    Although shallow cumuli are common over large areas of the globe, their impact on the surface radiative forcing has not been carefully evaluated. This study addresses this shortcoming by analyzing data from days with shallow cumuli collected over eight summers (2000-2007) at the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Climate Research Facility (collectively ACRF) Southern Great Plains site. During periods with clouds, the average shortwave and longwave radiative forcings are 45.5 W m-2 and +11.6 W m-2, respectively. The forcing has been defined so that a negative (positive) forcing indicates a surface cooling (warming). On average, the shortwave forcing is negative, however, instances with positive shortwave forcing are observed approximately 20% of the time. These positive values of shortwave forcing are associated with three-dimensional radiative effects of the clouds. The three-dimensional effects are shown to be largest for intermediate cloud amounts. The magnitude of the three-dimensional effects decreased with averaging time, but it is not negligibly small even for large averaging times as long as four hours.

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

    SciTech Connect

    Zhang, Wen; Chen, Yongsheng

    2011-01-01

    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 ( -Fe2 O3 ) and corundum ( -Al2 O3 ) NPs whereas the effect on the repulsive force was not observed. The adhesion force decreased from 6.3 0.7 nN to 0.8 0.4 nN as hematite NPs increased from 26 nm to 98 nm 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.

  3. Probing three-dimensional surface force fields with atomic resolution: Measurement strategies, limitations, and artifact reduction.

    PubMed

    Baykara, Mehmet Z; Dagdeviren, Omur E; Schwendemann, Todd C; Mönig, Harry; Altman, Eric I; Schwarz, Udo D

    2012-01-01

    Noncontact atomic force microscopy (NC-AFM) is being increasingly used to measure the interaction force between an atomically sharp probe tip and surfaces of interest, as a function of the three spatial dimensions, with picometer and piconewton accuracy. Since the results of such measurements may be affected by piezo nonlinearities, thermal and electronic drift, tip asymmetries, and elastic deformation of the tip apex, these effects need to be considered during image interpretation.In this paper, we analyze their impact on the acquired data, compare different methods to record atomic-resolution surface force fields, and determine the approaches that suffer the least from the associated artifacts. The related discussion underscores the idea that since force fields recorded by using NC-AFM always reflect the properties of both the sample and the probe tip, efforts to reduce unwanted effects of the tip on recorded data are indispensable for the extraction of detailed information about the atomic-scale properties of the surface.

  4. Reconstruction of Energy Surfaces from Friction Force Microscopy Measurements with the Jarzynski Equality

    NASA Astrophysics Data System (ADS)

    Berkovich, Ronen; Klafter, Joseph; Urbakh, Michael

    Free energy is one of the most fundamental thermodynamic functions, determining relative phase stability and serving as a generating function for other thermodynamic quantities. The calculation of free energies is a challenging enterprise. In equilibrium statistical mechanics, the free energy is related to the canonical partition function. The partition function itself involves integrations over all degrees of freedom in the system and, in most cases, cannot be easily calculated directly. In 1997, Jarzynski proved a remarkable equality that allows computing the equilibrium free-energy difference between two states from the probability distribution of the nonequilibrium work done on the system to switch between the two states. The Jarzynski equality provides a powerful free-energy difference estimator from a set of irreversible experiments. This method is closely related to free-energy perturbation approach, which is also a computational technique for estimating free-energy differences. The ability to map potential profiles and topologies is of major significance to areas as diverse as biological recognition and nanoscale friction. This capability has been demonstrated for frictional studies where a force between the tip of the scanning force microscope and the surface is probed. The surface free-energy corrugation produces a detectable friction forces. Thus, friction force microscopy (FFM) should be able to discriminate between energetically different areas on the probed surface. Here, we apply the Jarzynski equality for the analysis of FFM measurements and thus obtain a variation of the free energy along a surface.

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

    PubMed Central

    O'Dell, Dakota; Adam, Ian S.; DiPaolo, Brian; Sabharwal, Manit; Shi, Ce; Hart, Robert; Earhart, Christopher; Erickson, David

    2015-01-01

    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. PMID:26855473

  6. Measurement of adhesive forces between bacteria and protein-coated surfaces using optical tweezers

    NASA Astrophysics Data System (ADS)

    Simpson, Kathryn H.; Bowden, Gabriela; Hook, Magnus; Anvari, Bahman

    2002-05-01

    Bacterial adhesion is a primary cause of failure in implanted medical devices. Bacteria commonly found in device-related infections, such as S. aureus, have multiple cell surface adhesins which mediate specific adhesion to molecules found in extracellular matrix and blood plasma. Adhesins recognizing fibrinogen, fibronectin, collagen, and elastin molecules have been isolated in S. aureus. We have used optical tweezers to measure the adhesive force between a single bacterium and a protein-coated surface. Various concentrations of fibronectin, fibrinogen, or whole plasma were immobilized onto 10-micrometers diameter polystyrene microspheres. We optically trapped a bacterium with a titanium-sapphire laser tuned to 830 nm and contacted the cell with a coated bead. We determined the minimum force necessary to separate the cell and bead. For beads coated with fibronectin and fibrinogen, detachment force values occurred as approximate integer multiples of an estimated single bond detachment force. With plasma-coated beads, only cells lacking the fibrinogen adhesin could be detached; therefore, we believe that either this adhesin is prevalent on wilde-type cells, or it is preferentially adsorbed onto the beads. Additionally, the whole plasma detachment forces appeared random; therefore, we believe that many adhesins participate in boding to plasma.

  7. Non-additivity of molecule-surface van der Waals potentials from force measurements

    PubMed Central

    Wagner, Christian; Fournier, Norman; Ruiz, Victor G.; Li, Chen; Müllen, Klaus; Rohlfing, Michael; Tkatchenko, Alexandre; Temirov, Ruslan; Tautz, F. Stefan

    2014-01-01

    Van der Waals (vdW) forces act ubiquitously in condensed matter. Despite being weak on an atomic level, they substantially influence molecular and biological systems due to their long range and system-size scaling. The difficulty to isolate and measure vdW forces on a single-molecule level causes our present understanding to be strongly theory based. Here we show measurements of the attractive potential between differently sized organic molecules and a metal surface using an atomic force microscope. Our choice of molecules and the large molecule-surface separation cause this attraction to be purely of vdW type. The experiment allows testing the asymptotic vdW force law and its validity range. We find a superlinear growth of the vdW attraction with molecular size, originating from the increased deconfinement of electrons in the molecules. Because such non-additive vdW contributions are not accounted for in most first-principles or empirical calculations, we suggest further development in that direction. PMID:25424490

  8. Fast, high-resolution surface potential measurements in air with heterodyne Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Garrett, Joseph L.; Munday, Jeremy N.

    2016-06-01

    Kelvin probe force microscopy (KPFM) adapts an atomic force microscope to measure electric potential on surfaces at nanometer length scales. Here we demonstrate that Heterodyne-KPFM enables scan rates of several frames per minute in air, and concurrently maintains spatial resolution and voltage sensitivity comparable to frequency-modulation KPFM, the current spatial resolution standard. Two common classes of topography-coupled artifacts are shown to be avoidable with H-KPFM. A second implementation of H-KPFM is also introduced, in which the voltage signal is amplified by the first cantilever resonance for enhanced sensitivity. The enhanced temporal resolution of H-KPFM can enable the imaging of many dynamic processes, such as such as electrochromic switching, phase transitions, and device degredation (battery, solar, etc), which take place over seconds to minutes and involve changes in electric potential at nanometer lengths.

  9. Defect localization in fibre-reinforced composites by computing external volume forces from surface sensor measurements

    NASA Astrophysics Data System (ADS)

    Binder, F.; Schöpfer, F.; Schuster, T.

    2015-02-01

    We suggest a prospective method for detecting and visualizing defects in fibre-reinforced composites by computing external volume forces from measurements acquired by sensors that are integrated on the surface of the structure. Anisotropic materials like carbon fibre-reinforced composites are widely used in light weight construction which can exhibit damages that are not optically detectable. The key idea of our method is the interpretation of defects in such structures as if they were induced by an external volume force. This idea is based on the observation that a propagating elastic wave interferes with a damaged area by reflecting the wave. In that sense a damage can be seen as an additional source. Thus identifying the external volume force which has caused this wave is supposed to reveal the location of the defect. This approach leads to the inverse problem of determining the inhomogeneity of a hyperbolic initial-boundary value problem. We tackle this ill-posed problem by minimizing a Tikhonov functional which takes the oberservation points of our surface measurements into account. In the article we address the solvability of the direct problem, state and analyze the PDE-based optimization problem that aims for computing the external force and develop a numerical realization of its solution using the conjugate gradient method. First numerical results for a simple model case with different sensor adjustments show that the defects in fact are detectable. In that sense this article might be seen as starting point of future research which should comprehend deeper numerical studies and analysis of the problem.

  10. Polymer Droplet Dynamic Wetting Measurement at the Nanometer Scale on Smooth Surfaces Using Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Soleymaniha, Mohammadreza; Felts, Jonathan Robert; Anml Team

    2016-11-01

    Fluid spreading is a complex phenomenon driven strongly by intermolecular forces that requires nanometer scale microscopy to observe and understand. We present a technique for measuring molten polymer spreading dynamics with nanometer scale spatial resolution at elevated temperatures on sapphire, silicon oxide and mica using tapping-mode atomic force microscopy (AFM). The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 μ m diameters at 115-175 C. Custom image processing algorithms realize the droplet height, radius, volume and contact angle of the droplet over time. The contact angle evolution followed a power law with time with experimental exponent values of -0.26, -0.08, and -0.2 for sapphire, silicon oxide, and mica, respectively at 115 C. The non-zero steady state contact angles result in a slower evolution of contact angle with time compared to Tanner's Law, as expected. We observe local crystallinity on the molten droplet surface, where crystalline structures appear to nucleate at the contact line and migrate toward the top of the droplet. Increasing the temperature from 115 C to 175 C reduced surface crystallinity from 35% to 12%, consistent with increasingly energetically favorable amorphous phase as the temperature approaches the melting temperature. This platform provides a way to measure spreading dynamics of extremely small volumes of heterogeneously complex fluids not possible through other means. Dr.Jonathan Felts is the principal investigator of the ANML research group in Mechanical Engineering Department of Texas A&M University.

  11. Orthoclase surface structure dissolution measured in situ by x-ray reflectivity and atomic force microscopy.

    SciTech Connect

    Sturchio, N. C.; Fenter, P.; Cheng, L.; Teng, H.

    2000-11-28

    Orthoclase (001) surface topography and interface structure were measured during dissolution by using in situ atomic force microscopy (AFM) and synchrotrons X-ray reflectivity at pH 1.1-12.9 and T = 25-84 C. Terrace roughening at low pH and step motion at high pH were the main phenomena observed, and dissolution rates were measured precisely. Contrasting dissolution mechanisms are inferred for low- and high-pH conditions. These observations clarify differences in alkali feldspar dissolution mechanisms as a function of pH, demonstrate a new in situ method for measuring face-specific dissolution rates on single crystals, and improve the fundamental basis for understanding alkali feldspar weathering processes.

  12. Nanofluids mediating surface forces.

    PubMed

    Pilkington, Georgia A; Briscoe, Wuge H

    2012-11-01

    Fluids containing nanostructures, known as nanofluids, are increasingly found in a wide array of applications due to their unique physical properties as compared with their base fluids and larger colloidal suspensions. With several tuneable parameters such as the size, shape and surface chemistry of nanostructures, as well as numerous base fluids available, nanofluids also offer a new paradigm for mediating surface forces. Other properties such as local surface plasmon resonance and size dependent magnetism of nanostructures also present novel mechanisms for imparting tuneable surface interactions. However, our fundamental understanding, experimentally and theoretically, of how these parameters might affect surface forces remains incomplete. Here we review recent results on equilibrium and dynamic surface forces between macroscopic surfaces in nanofluids, highlighting the overriding trends in the correlation between the physical parameters that characterise nanofluids and the surface forces they mediate. We also discuss the challenges that confront existing surface force knowledge as a result of this new paradigm.

  13. Optical measurements of dynamic adhesive forces between bacteria and protein-coated surfaces

    NASA Astrophysics Data System (ADS)

    Simpson, Kathryn H.; Bowden, Gabriela; Hook, Magnus; Anvari, Bahman

    2003-06-01

    Bacterial adhesion to host tissue is an initial step in the infectious process. Staphylococcus aureus, a major human pathogen, has covalently anchored cell surface adhesins called microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) which mediate specific adhesion to extracellular matrix (ECM) molecules. Understanding MSCRAMM binding is potentially useful in developing effective antibacterial drugs. In this study, optical tweezers were used in conjunction with a quadrant photodetector to measure adhesive forces between MSCRAMMs and surfaces coated with the ECM molecule fibronectin. Using a piezoelectrically driven stage, a fibronectin-coated microsphere adherent to a coverslip was brought into contact with a cell optically trapped at 830 nm. The microsphere was subsequently moved away from the cell, and a quadrant photodiode monitored the cell displacement from the trap center during the detachment process. The photodetector voltage signals were subsequently converted into the adhesive forces between MSCRAMMs and fibronectin based on a calibration using Stoke"s law for viscous drag. Optical detection of the trapped bead displacement allowed us to study both the dynamics of the detachment process and observe the effects of various loading rates. This technique can be extended to identify the contributions of various MSCRAMM domains to adhesion in order to develop new methods of treating infections.

  14. Estimations of Forest fire Smoke Forcing From Surface Measurements, Satellite Data, and Trajectory Modeling

    NASA Astrophysics Data System (ADS)

    Cox, S. J.; Stackhouse, P. W.; Baum, B. A.; Pierce, R. B.; Harvey, V. L.; Mikovitz, J. C.; Chiacchio, M.

    2002-05-01

    Methods of using satellite and surface measurements along with trajectory modeling to determine the radiative effect of large boreal forest fires are developed. We present results of surface and top of atmosphere shortwave radiative forcings due to smoke from a very large forest fire outbreak in Manitoba, Canada in July and August 1989. These fires resulted in a large smoke plume over a wide area over the two months. The LaRC trajectory model (LTM) (Pierce et al., 1997) was run in time forward mode for the July-August 1989 time period. The model was seeded with fire pixels as recognized by the Baum and Trepte (1999) smoke/fire/cloud mask. Meteorological data was taken from the European Centre for Medium-Range Weather Forecasts 15-year reanalysis (ERA-15). Air parcels were traced from fire regions over a period of five days globally on a 2.5o equal angle grid. Areas with large numbers of trajectories originating from boundary layer air in fire regions were considered to be likely to be influenced by smoke. An analysis of the effects of the smoke from the Manitoba fires at Canadian surface radiometric sites was performed. Hourly shortwave surface fluxes were compared to a variety of radiative transfer model calculations, satellite data products, and trajectory model results. Numbers and ages of fire-originating trajectories passing within a two degree adius of each of the sites were collected. A theoretical "clean sky" (i.e., with no aerosols or clouds) surface shortwave flux was calculated at each surface site for each hour in July and August using the Fu-Liou radiative transfer code with TOMS ozone values and GEOS-1 meteorology. July 23, 1989 was taken as a first test case. Smoke was heavy over the fire region of Manitoba and Ontario, and both the trajectory model and TOMS showed a tongue of smoke advected far east of the fire region, over the Canadian maritime provinces. At solar noon over each of five stations (Winnipeg, Moosonee, Big Trout Lake, Fredericton, and

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

    PubMed

    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.

  16. Force measurements on myelin basic protein adsorbed to mica and lipid bilayer surfaces done with the atomic force microscope.

    PubMed Central

    Mueller, H; Butt, H J; Bamberg, E

    1999-01-01

    The mechanical and adhesion properties of myelin basic protein (MBP) are important for its function, namely the compaction of the myelin sheath. To get more information about these properties we used atomic force microscopy to study tip-sample interaction of mica and mixed dioleoylphosphatidylserine (DOPS) (20%)/egg phosphatidylcholine (EPC) (80%) lipid bilayer surfaces in the absence and presence of bovine MBP. On mica or DOPS/EPC bilayers a short-range repulsive force (decay length 1.0-1.3 nm) was observed during the approach. The presence of MBP always led to an attractive force between tip and sample. When retracting the tip again, force curves on mica and on lipid layers were different. While attached to the mica surface, the MBP molecules exhibited elastic stretching behavior that agreed with the worm-like chain model, yielding a persistence length of 0.5 +/- 0.25 nm and an average contour length of 53 +/- 19 nm. MBP attached to a lipid bilayer did not show elastic stretching behavior. This shows that the protein adopts a different conformation when in contact with lipids. The lipid bilayer is strongly modified by MBP attachment, indicating formation of MBP-lipid complexes and possibly disruption of the original bilayer structure. PMID:9916039

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Fabrication and measurement of nanostructures on the micro ball surface using a modified atomic force microscope.

    PubMed

    Zhao, X S; Geng, Y Q; Li, W B; Yan, Y D; Hu, Z J; Sun, T; Liang, Y C; Dong, S

    2012-11-01

    In order to machine and measure nanostructures on the micro ball surface, a modified atomic force microscope (AFM) combining a commercial AFM system with a home built precision air bearing spindle is established. Based on this system, motions of both the AFM scanner and the air bearing spindle are controlled to machine nanostructures on the micro ball based on the AFM tip-based nano mechanical machining approach. The eccentric error between the axis of the micro ball and the axis of the spindle is reduced to 3-4 μm by the provided fine adjusting method. A 1000 nano lines array, 36 square pits structure, 10 square pits structure, and a zig-zag structure on the circumference of the micro ball with the diameter of 1.5 mm are machined successfully. The measurement results achieved by the same system reveal that the profiles and mode-power spectra curves of the micro ball are influenced by the artificially machined nanostructures significantly according to their distributions. This work is an useful attempt for modifying the micro ball profile and manufacture of the spherical modulation targets to study the experimental performance of the micro ball in implosion.

  19. Fabrication and measurement of nanostructures on the micro ball surface using a modified atomic force microscope

    NASA Astrophysics Data System (ADS)

    Zhao, X. S.; Geng, Y. Q.; Li, W. B.; Yan, Y. D.; Hu, Z. J.; Sun, T.; Liang, Y. C.; Dong, S.

    2012-11-01

    In order to machine and measure nanostructures on the micro ball surface, a modified atomic force microscope (AFM) combining a commercial AFM system with a home built precision air bearing spindle is established. Based on this system, motions of both the AFM scanner and the air bearing spindle are controlled to machine nanostructures on the micro ball based on the AFM tip-based nano mechanical machining approach. The eccentric error between the axis of the micro ball and the axis of the spindle is reduced to 3-4 μm by the provided fine adjusting method. A 1000 nano lines array, 36 square pits structure, 10 square pits structure, and a zig-zag structure on the circumference of the micro ball with the diameter of 1.5 mm are machined successfully. The measurement results achieved by the same system reveal that the profiles and mode-power spectra curves of the micro ball are influenced by the artificially machined nanostructures significantly according to their distributions. This work is an useful attempt for modifying the micro ball profile and manufacture of the spherical modulation targets to study the experimental performance of the micro ball in implosion.

  20. Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration

    SciTech Connect

    Andersson, Martin; Madgavkar, Ashwin; Stjerndahl, Maria; Wu, Yanrong; Tan, Weihong; Duran, Randy; Niehren, Stefan; Mustafa, Kamal; Arvidson, Kristina; Wennerberg, Ann

    2007-07-15

    Optical tweezers were used to study the interaction and attachment of human bone cells to various types of medical implant materials. Ideally, the implant should facilitate cell attachment and promote migration of the progenitor cells in order to decrease the healing time. It is therefore of interest, in a controlled manner, to be able to monitor the cell adhesion process. Results from such studies would help foresee the clinical outcome of integrating medical implants. The interactions between two primary cell culture models, human gingival fibroblasts and bone forming human osteoblast cells, and three different implant materials, glass, titanium, and hydroxyapatite, were studied. A novel type of optical tweezers, which has a newly designed quadrant detector and a powerful 3 W laser was constructed and force calibrated using two different methods: one method in which the stiffness of the optical trap was obtained by monitoring the phase lag between the trap and the moved object when imposing a forced oscillation on the trapped object and another method in which the maximum trapping force was derived from the critical velocity at which the object escapes the trap. Polystyrene beads as well as cells were utilized for the calibrations. This is the first time that cells have been used directly for these types of force calibrations and, hence, direct measurements of forces exerted on cells can be performed, thus avoiding the difficulties often encountered when translating the results obtained from cell measurements to the calibrations obtained with reference materials. This more straightforward approach represents an advantage in comparison to established methods.

  1. Measuring forces and spatiotemporal evolution of thin water films between an air bubble and solid surfaces of different hydrophobicity.

    PubMed

    Shi, Chen; Cui, Xin; Xie, Lei; Liu, Qingxia; Chan, Derek Y C; Israelachvili, Jacob N; Zeng, Hongbo

    2015-01-27

    A combination of atomic force microscopy (AFM) and reflection interference contrast microscopy (RICM) was used to measure simultaneously the interaction force and the spatiotemporal evolution of the thin water film between a bubble in water and mica surfaces with varying degrees of hydrophobicity. Stable films, supported by the repulsive van der Waals-Casimir-Lifshitz force were always observed between air bubble and hydrophilic mica surfaces (water contact angle, θ(w) < 5°) whereas bubble attachment occurred on hydrophobized mica surfaces. A theoretical model, based on the Reynolds lubrication theory and the augmented Young-Laplace equation including the effects of disjoining pressure, provided excellent agreement with experiment results, indicating the essential physics involved in the interaction between air bubble and solid surfaces can be elucidated. A hydrophobic interaction free energy per unit area of the form: WH(h) = -γ(1 - cos θ(w))exp(-h/D(H)) can be used to quantify the attraction between bubble and hydrophobized solid substrate at separation, h, with γ being the surface tension of water. For surfaces with water contact angle in the range 45° < θ(w) < 90°, the decay length DH varied between 0.8 and 1.0 nm. This study quantified the hydrophobic interaction in asymmetric system between air bubble and hydrophobic surfaces, and provided a feasible method for synchronous measurements of the interaction forces with sub-nN resolution and the drainage dynamics of thin films down to nm thickness.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Force-Measuring Clamps

    NASA Technical Reports Server (NTRS)

    Nunnelee, Mark

    2003-01-01

    Force-measuring clamps have been invented to facilitate and simplify the task of measuring the forces or pressures applied to clamped parts. There is a critical need to measure clamping forces or pressures in some applications for example, while bonding sensors to substrates or while clamping any sensitive or delicate parts. Many manufacturers of adhesives and sensors recommend clamping at specific pressures while bonding sensors or during adhesive bonding between parts in general. In the absence of a force-measuring clamp, measurement of clamping force can be cumbersome at best because of the need for additional load sensors and load-indicating equipment. One prior method of measuring clamping force involved the use of load washers or miniature load cells in combination with external power sources and load-indicating equipment. Calibrated spring clamps have also been used. Load washers and miniature load cells constitute additional clamped parts in load paths and can add to the destabilizing effects of loading mechanisms. Spring clamps can lose calibration quickly through weakening of the springs and are limited to the maximum forces that the springs can apply. The basic principle of a force-measuring clamp can be implemented on a clamp of almost any size and can enable measurement of a force of almost any magnitude. No external equipment is needed because the component(s) for transducing the clamping force and the circuitry for supplying power, conditioning the output of the transducers, and displaying the measurement value are all housed on the clamp. In other words, a force-measuring clamp is a complete force-application and force-measurement system all in one package. The advantage of unitary packaging of such a system is that it becomes possible to apply the desired clamping force or pressure with precision and ease.

  4. The effect of surface properties on the strength of attachment of fungal spores using AFM perpendicular force measurements.

    PubMed

    Whitehead, Kathryn A; Deisenroth, Ted; Preuss, Andrea; Liauw, Christopher M; Verran, Joanna

    2011-02-01

    Polymeric substrata may be biodegraded by fungal species resulting in damaged, weakened and unsightly materials. This process typically begins with fungal spore attachment to the surface. In order to better understand the processes that precedes a biofouling event, fungal spore attachment to a range of surfaces, was determined using perpendicular force measurements. This was carried out using atomic force microscope cantilevers modified with fungal spores from Aspergillus niger 1957 (5μm diameter, non-wettable, spherical), Aspergillus niger 1988 (5μm diameter non-wettable, spikey) or Aureobasidium pullulans (5μm-10μm sized, wettable, ellipsoidal). The strength of attachment of the spores was determined in combination with seven surfaces (nitric acid cleaned glass, cast poly(methylmethacrylate) sheet [c-PMMA], polytetrafluoroethylene [PTFE], silicon wafers spin coated with poly(3-methacryloxypropyltrimethoxy silane (γ-MPS)-co-methylmethacrylate (MMA)) [p(γ-MPS-co-MMA)], poly (γ-MPS-co-lauryl methacrylate) [p(γ-MPS-co-LMA)] [both in a ratio of 10-90], PMMA dissolved in a solvent [PMMAsc] and silicon wafers). Perpendicular force measurements could not be related to the R(a) values of the surfaces, but surface wettability was shown to have an effect. All three spore types interacted comparably with the surfaces. All spores attached strongly to c-PMMA and glass (wettable surfaces), and weakly to PTFE, (p(γ- MPS-co-LMA)) (non-wettable) and (p(γ-MPS-co-MMA)). Spore shape also affected the strength of attachment. Aureobasidium pullulans spores attached with the widest range of forces whilst A. niger 1957 attached with the smallest. Findings will inform the selection of surfaces for use in environments where biofouling is an important consideration.

  5. A method for the direct measurement of surface tension of collected atmospherically relevant aerosol particles using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Hritz, Andrew D.; Raymond, Timothy M.; Dutcher, Dabrina D.

    2016-08-01

    Accurate estimates of particle surface tension are required for models concerning atmospheric aerosol nucleation and activation. However, it is difficult to collect the volumes of atmospheric aerosol required by typical instruments that measure surface tension, such as goniometers or Wilhelmy plates. In this work, a method that measures, ex situ, the surface tension of collected liquid nanoparticles using atomic force microscopy is presented. A film of particles is collected via impaction and is probed using nanoneedle tips with the atomic force microscope. This micro-Wilhelmy method allows for direct measurements of the surface tension of small amounts of sample. This method was verified using liquids, whose surface tensions were known. Particles of ozone oxidized α-pinene, a well-characterized system, were then produced, collected, and analyzed using this method to demonstrate its applicability for liquid aerosol samples. It was determined that oxidized α-pinene particles formed in dry conditions have a surface tension similar to that of pure α-pinene, and oxidized α-pinene particles formed in more humid conditions have a surface tension that is significantly higher.

  6. Atomic force microscopy of orb-spider-web-silks to measure surface nanostructuring and evaluate silk fibers per strand

    NASA Astrophysics Data System (ADS)

    Kane, D. M.; Naidoo, N.; Staib, G. R.

    2010-10-01

    Atomic force microscopy (AFM) study is used to measure the surface topology and roughness of radial and capture spider silks on the micro- and nanoscale. This is done for silks of the orb weaver spider Argiope keyserlingi. Capture silk has a surface roughness that is five times less than that for radial silk. The capture silk has an equivalent flatness of λ /100 (5-6 nm deep surface features) as an optical surface. This is equivalent to a very highly polished optical surface. AFM does show the number of silk fibers that make up a silk thread but geometric distortion occurs during sample preparation. This prevented AFM from accurately measuring the silk topology on the microscale in this study.

  7. Effect of the charge and roughness of surfaces on normal and friction forces measured in aqueous solutions.

    PubMed

    McNamee, Cathy E; Higashitani, Ko

    2013-04-23

    We used the atomic force microscope (AFM) to determine how the roughness and charge on a surface affect the adhesion and friction when measured against a smooth surface (colloid probe) in an aqueous solution. The effect of roughness was investigated by coating TiO2 crystal substrates with TiO2 nano- or micro-sized particles, where an increase in the particle size increased the RMS roughness of the substrate. The charge of the substrate was varied by changing the pH of the aqueous solution. Force-separation curves and friction-load data were measured for the smooth colloid probe-rough substrate systems. The adhesion and friction between two surfaces in solution were seen to depend on the surface charge and roughness. A noncharged surface gave the greatest adhesion, while a charged surface gave weaker adhesions. Increasing the roughness of the surface resulted in a stronger adhesion. The magnitude and range of the adhesions were not affected by the measuring velocity in the case of a noncharged substrate but decreased with an increasing velocity for charged surfaces. The friction was seen not to depend on roughness in the case of a noncharged surface. However, in the case of a charged surface, the friction decreased with an increased roughness for low loads and then showed no dependence on the surface roughness for high loads. The results of this experiment show that the adhesion and friction of a system can be decreased via the roughness and charge of the substrate and the ion types in the solution.

  8. Oriented covalent immobilization of antibodies for measurement of intermolecular binding forces between zipper-like contact surfaces of split inteins

    PubMed Central

    Sorci, Mirco; Dassa, Bareket; Liu, Hongwei; Anand, Gaurav; Dutta, Amit K.; Pietrokovski, Shmuel; Belfort, Marlene; Belfort, Georges

    2013-01-01

    In order to measure the intermolecular binding forces between two halves (or partners) of naturally split protein splicing elements called inteins, a novel thiol-hydrazide linker was designed and used to orient immobilized antibodies specific for each partner. Activation of the surfaces was achieved in one step allowing direct force measurements of the formation of a peptide bond catalyzed by the binding of the two partners of the split intein (called protein trans-splicing). Through this binding process, a whole functional intein is formed resulting in subsequent splicing. Atomic force microscopy (AFM) was used to directly measure the split intein partner binding at 1µm/s between native (wild-type) and mixed pairs of C- and N-terminal partners of naturally occurring split inteins from three cyanobacteria. Native and mixed pairs exhibit similar binding forces within the error of the measurement technique (~52 pN). Bioinformatic sequence analysis and computational structural analysis discovered a zipper-like contact between the two partners with electrostatic and non-polar attraction between multiple aligned ion pairs and hydrophobic residues. Also, we tested the Jarzynski’s equality and demonstrated, as expected, that non-equilibrium dissipative measurements obtained here gave larger energies of interaction as compared with those for equilibrium. Hence, AFM coupled with our immobilization strategy and computational studies provides a useful analytical tool for the direct measurement of intermolecular association of split inteins and could be extended to any interacting protein pair. PMID:23679912

  9. Force-Measuring Clamp

    NASA Technical Reports Server (NTRS)

    Nunnelee, Mark (Inventor)

    2004-01-01

    A precision clamp that accurately measures force over a wide range of conditions is described. Using a full bridge or other strain gage configuration. the elastic deformation of the clamp is measured or detected by the strain gages. Thc strain gages transmit a signal that corresponds to the degree of stress upon the clamp. Thc strain gage signal is converted to a numeric display. Calibration is achieved by ero and span potentiometers which enable accurate measurements by the force-measuring clamp.

  10. Extracting local surface charges and charge regulation behavior from atomic force microscopy measurements at heterogeneous solid-electrolyte interfaces

    NASA Astrophysics Data System (ADS)

    Zhao, Cunlu; Ebeling, Daniel; Siretanu, Igor; van den Ende, Dirk; Mugele, Frieder

    2015-10-01

    We present a method to determine the local surface charge of solid-liquid interfaces from Atomic Force Microscopy (AFM) measurements that takes into account shifts of the adsorption/desorption equilibria of protons and ions as the cantilever tip approaches the sample. We recorded AFM force distance curves in dynamic mode with sharp tips on heterogeneous silica surfaces partially covered by gibbsite nano-particles immersed in an aqueous electrolyte with variable concentrations of dissolved NaCl and KCl at pH 5.8. Forces are analyzed in the framework of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory in combination with a charge regulation boundary that describes adsorption and desorption reactions of protons and ions. A systematic method to extract the equilibrium constants of these reactions by simultaneous least-squared fitting to experimental data for various salt concentrations is developed and is shown to yield highly consistent results for silica-electrolyte interfaces. For gibbsite-electrolyte interfaces, the surface charge can be determined, yet, an unambiguous identification of the relevant surface speciation reactions is not possible, presumably due to a combination of intrinsic chemical complexity and heterogeneity of the nano-particle surfaces.

  11. Attachment forces of ants measured with a centrifuge: better 'wax-runners' have a poorer attachment to a smooth surface.

    PubMed

    Federle, W; Rohrseitz, K; Hölldobler, B

    2000-02-01

    The symbiotic ant partners of glaucous Macaranga ant-plants show an exceptional capacity to run on the slippery epicuticular wax crystals covering the plant stem without any difficulty. We test the hypothesis that these specialised 'wax-runners' have a general, superior attachment capacity. We compared attachment on a smooth surface for 11 ant species with different wax-running capacities. The maximum force that could be withstood before an ant became detached was quantified using a centrifuge recorded by a high-speed video camera. This technique has the advantage of causing minimum disruption and allows measurements in very small animals. When strong centrifugal forces were applied, the ants showed a conspicuous 'freezing reflex' advantageous to attachment. Attachment forces differed strongly among the ant species investigated. This variation could not be explained by different surface area/weight ratios of smaller and larger ants. Within species, however, detachment force per body weight (F/W) scaled with the predicted value of W(-)(0.33), where W is body weight in newtons. Surprisingly, our results not only disprove the hypothesis that 'wax-runners' generally attach better but also provide evidence for the reverse effect. Superior 'wax-runners' (genera Technomyrmex and Crematogaster) did not cling better to smooth Perspex, but performed significantly worse than closely related congeners that are unable to climb up waxy stems. This suggests an inverse relationship between adaptations to run on wax and to attach to a smooth surface.

  12. Evidence for water structuring forces between surfaces

    SciTech Connect

    Stanley, Christopher B; Rau, Dr. Donald

    2011-01-01

    Structured water on apposing surfaces can generate significant energies due to reorganization and displacement as the surfaces encounter each other. Force measurements on a multitude of biological structures using the osmotic stress technique have elucidated commonalities that point toward an underlying hydration force. In this review, the forces of two contrasting systems are considered in detail: highly charged DNA and nonpolar, uncharged hydroxypropyl cellulose. Conditions for both net repulsion and attraction, along with the measured exclusion of chemically different solutes from these macromolecular surfaces, are explored and demonstrate features consistent with a hydration force origin. Specifically, the observed interaction forces can be reduced to the effects of perturbing structured surface water.

  13. Correlating steric hydration forces with water dynamics through surface force and diffusion NMR measurements in a lipid–DMSO–H2O system

    PubMed Central

    Schrader, Alex M.; Donaldson, Stephen H.; Song, Jinsuk; Cheng, Chi-Yuan; Lee, Dong Woog; Han, Songi; Israelachvili, Jacob N.

    2015-01-01

    Dimethyl sulfoxide (DMSO) is a common solvent and biological additive possessing well-known utility in cellular cryoprotection and lipid membrane permeabilization, but the governing mechanisms at membrane interfaces remain poorly understood. Many studies have focused on DMSO–lipid interactions and the subsequent effects on membrane-phase behavior, but explanations often rely on qualitative notions of DMSO-induced dehydration of lipid head groups. In this work, surface forces measurements between gel-phase dipalmitoylphosphatidylcholine membranes in DMSO–water mixtures quantify the hydration- and solvation-length scales with angstrom resolution as a function of DMSO concentration from 0 mol% to 20 mol%. DMSO causes a drastic decrease in the range of the steric hydration repulsion, leading to an increase in adhesion at a much-reduced intermembrane distance. Pulsed field gradient NMR of the phosphatidylcholine (PC) head group analogs, dimethyl phosphate and tetramethylammonium ions, shows that the ion hydrodynamic radius decreases with increasing DMSO concentration up to 10 mol% DMSO. The complementary measurements indicate that, at concentrations below 10 mol%, the primary effect of DMSO is to decrease the solvated volume of the PC head group and that, from 10 mol% to 20 mol%, DMSO acts to gradually collapse head groups down onto the surface and suppress their thermal motion. This work shows a connection between surface forces, head group conformation and dynamics, and surface water diffusion, with important implications for soft matter and colloidal systems. PMID:26261313

  14. Electrostatic patch potentials in Casimir force measurements

    NASA Astrophysics Data System (ADS)

    Garrett, Joseph; Somers, David; Munday, Jeremy

    2015-03-01

    Measurements of the Casimir force require the elimination of the electrostatic force between interacting surfaces. The force can be minimized by applying a potential to one of the two surfaces. However, electrostatic patch potentials remain and contribute an additional force which can obscure the Casimir force signal. We will discuss recent measurements of patch potentials made with Heterodyne Amplitude-Modulated Kelvin Probe Force Microscopy that suggest patches could be responsible for >1% of the signal in some Casimir force measurements, and thus make the distinction between different theoretical models of the Casimir force (e.g. a Drude-model or a plasma-model for the dielectric response) difficult to discern.

  15. Shear rheology of mixed protein adsorption layers vs their structure studied by surface force measurements.

    PubMed

    Danov, Krassimir D; Kralchevsky, Peter A; Radulova, Gergana M; Basheva, Elka S; Stoyanov, Simeon D; Pelan, Eddie G

    2015-08-01

    The hydrophobins are proteins that form the most rigid adsorption layers at liquid interfaces in comparison with all other investigated proteins. The mixing of hydrophobin HFBII with other conventional proteins is expected to reduce the surface shear elasticity and viscosity, E(sh) and η(sh), proportional to the fraction of the conventional protein. However, the experiments show that the effect of mixing can be rather different depending on the nature of the additive. If the additive is a globular protein, like β-lactoglobulin and ovalbumin, the surface rigidity is preserved, and even enhanced. The experiments with separate foam films indicate that this is due to the formation of a bilayer structure at the air/water interface. The more hydrophobic HFBII forms the upper layer adjacent to the air phase, whereas the conventional globular protein forms the lower layer that faces the water phase. Thus, the elastic network formed by the adsorbed hydrophobin remains intact, and even reinforced by the adjacent layer of globular protein. In contrast, the addition of the disordered protein β-casein leads to softening of the HFBII adsorption layer. Similar (an even stronger) effect is produced by the nonionic surfactant Tween 20. This can be explained with the penetration of the hydrophobic tails of β-casein and Tween 20 between the HFBII molecules at the interface, which breaks the integrity of the hydrophobin interfacial elastic network. The analyzed experimental data for the surface shear rheology of various protein adsorption layers comply with a viscoelastic thixotropic model, which allows one to determine E(sh) and η(sh) from the measured storage and loss moduli, G' and G″. The results could contribute for quantitative characterization and deeper understanding of the factors that control the surface rigidity of protein adsorption layers with potential application for the creation of stable foams and emulsions with fine bubbles or droplets.

  16. Contact sensing from force measurements

    NASA Technical Reports Server (NTRS)

    Bicchi, Antonio; Salisbury, J. K.; Brock, David L.

    1993-01-01

    This article addresses contact sensing (i.e., the problem of resolving the location of a contact, the force at the interface, and the moment about the contact normals). Called 'intrinsic' contact sensing for the use of internal force and torque measurements, this method allows for practical devices that provide simple, relevant contact information in practical robotic applications. Such sensors have been used in conjunction with robot hands to identify objects, determine surface friction, detect slip, augment grasp stability, measure object mass, probe surfaces, and control collision and for a variety of other useful tasks. This article describes the theoretical basis for their operation and provides a framework for future device design.

  17. Surface forces: Surface roughness in theory and experiment

    SciTech Connect

    Parsons, Drew F. Walsh, Rick B.; Craig, Vincent S. J.

    2014-04-28

    A method of incorporating surface roughness into theoretical calculations of surface forces is presented. The model contains two chief elements. First, surface roughness is represented as a probability distribution of surface heights around an average surface height. A roughness-averaged force is determined by taking an average of the classic flat-surface force, weighing all possible separation distances against the probability distributions of surface heights. Second the model adds a repulsive contact force due to the elastic contact of asperities. We derive a simple analytic expression for the contact force. The general impact of roughness is to amplify the long range behaviour of noncontact (DLVO) forces. The impact of the elastic contact force is to provide a repulsive wall which is felt at a separation between surfaces that scales with the root-mean-square (RMS) roughness of the surfaces. The model therefore provides a means of distinguishing between “true zero,” where the separation between the average centres of each surface is zero, and “apparent zero,” defined by the onset of the repulsive contact wall. A normal distribution may be assumed for the surface probability distribution, characterised by the RMS roughness measured by atomic force microscopy (AFM). Alternatively the probability distribution may be defined by the histogram of heights measured by AFM. Both methods of treating surface roughness are compared against the classic smooth surface calculation and experimental AFM measurement.

  18. Direct Measurement of the Effect of Surface Roughness on the Colloidal Forces between a Particle and Flat Plate.

    PubMed

    Suresh; Walz

    1997-12-15

    The van der Waals and electrostatic interaction energies between a single particle and a flat plate were measured using the optical technique of total internal reflection microscopy (TIRM). The particles used were 15-µm-diameter polystyrene latex spheres and the flat plate was a polished BK-7 glass slide. The measurements were performed in aqueous solutions of ionic strength ranging from 3 to 7 mM, and the particle-plate separation distances ranged from approximately 25 to 300 nm. During measurement, the particle was trapped in a secondary energy well formed by the repulsive electrostatic and attractive van der Waals forces; however, the particle was free to undergo Brownian motion at all times. These measurements, which capitalize on the extreme sensitivity of the TIRM technique, are believed to be the first direct measurement of the van der Waals interaction energy in aqueous solutions at separation distances where retardation effects are substantial. Comparison of the measured energy wells with predictions made with traditional energy equations produced only fair agreement; specifically, the measured well depths were consistently lower than predicted. However, when the measured results were compared with predictions made using the recent model of L. Suresh and J. Y. Walz ([J. Colloid Interface Sci. 183, 199 (1996)] for rough surfaces, very good agreement was obtained. The asperity heights yielding the best agreement ranged between 14 and 33 nm, with an average height of 26 nm. This value is consistent with previous estimates of the roughness height obtained by measuring the particle sedimentation velocity [J. Y. Walz and L. Suresh, J. Chem. Phys. 103, 10714 (1995)]. Copyright 1997 Academic Press.

  19. Measuring Roughnesses Of Optical Surfaces

    NASA Technical Reports Server (NTRS)

    Coulter, Daniel R.; Al-Jumaily, Gahnim A.; Raouf, Nasrat A.; Anderson, Mark S.

    1994-01-01

    Report discusses use of scanning tunneling microscopy and atomic force microscopy to measure roughnesses of optical surfaces. These techniques offer greater spatial resolution than other techniques. Report notes scanning tunneling microscopes and atomic force microscopes resolve down to 1 nm.

  20. Gravity Forcing Of Surface Waves

    NASA Astrophysics Data System (ADS)

    Kenyon, K. E.

    2005-12-01

    Surface waves in deep water are forced entirely by gravity at the air-sea interface when no other forces act tangent to the surface. Then according to Newton's second law, the fluid acceleration parallel to the surface must equal the component of gravity parallel to the surface. Between crest and trough the fluid accelerates; between trough and crest the fluid decelerates. By replacing Bernoulli's law, gravity forcing becomes the dynamic boundary condition needed to solve the mathematical problem of these waves. Irrotational waves with a sinusoidal profile satisfy the gravity forcing condition, with the usual dispersion relation, provided the slope is small compared to one, as is true also of the Stokes development. However, the exact wave shape can be calculated using the gravity forcing method in a way that is less complex and less time consuming than that of the Stokes perturbation expansion. To the second order the surface elevation is the same as the Stokes result; the third order calculation has not been made yet. Extensions of the gravity forcing method can easily be carried out for multiple wave trains, solitary waves and bores, waves in finite constant mean depths, and internal waves in a two-layer system. For shoaling surface waves gravity forcing provides a physical understanding of the progressive steepening often observed near shore.

  1. Junction formation of Cu3BiS3 investigated by Kelvin probe force microscopy and surface photovoltage measurements

    PubMed Central

    Mesa, Fredy; Chamorro, William; Vallejo, William; Baier, Robert; Dittrich, Thomas; Grimm, Alexander; Lux-Steiner, Martha C

    2012-01-01

    Summary Recently, the compound semiconductor Cu3BiS3 has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu3BiS3 absorber layer and the junction formation with CdS, ZnS and In2S3 buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20–100 nm, and a considerably smaller work-function distribution for In2S3 compared to that of CdS and ZnS. For In2S3 and CdS buffer layers the KPFM experiments indicate negatively charged Cu3BiS3 grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In2S3 buffer layer. Our findings indicate that Cu3BiS3 may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased. PMID:22497001

  2. Force, Surface Pressure, and Flowfield Measurements on a Slender Missile Configuration with Square Cross-Section at Supersonic Speeds

    NASA Technical Reports Server (NTRS)

    Wilcox, Floyd J., Jr.; Birch, Trevor J.; Allen, Jerry M.

    2004-01-01

    A wind-tunnel investigation of a square cross-section missile configuration has been conducted to obtain force and moment measurements, surface pressure measurements, and vapor screen flow visualization photographs for comparison with computational fluid dynamics studies conducted under the auspices of The Technical Cooperation Program (TTCP). Tests were conducted on three configurations which included: (1) body alone, (2) body plus tail fins mounted on the missile corners, and (3) body plus tail fins mounted on the missile side. This test was conducted in test section #2 of the NASA Langley Unitary Plan Wind Tunnel at Mach numbers of 2.50 and 4.50 and at a Reynolds number of 4 million per ft. The data were obtained over an angle of attack range from -4 deg. to 24 deg. and roll angles from 0 deg. to 45 deg., i.e., from a diamond shape (as viewed from the rear) at a roll angle of 0 deg. to a square shape at 45 deg.

  3. Nanometer-Sized Water Bridge and Pull-Off Force in AFM at Different Relative Humidities: Reproducibility Measurement and Model Based on Surface Tension Change.

    PubMed

    Bartošík, Miroslav; Kormoš, Lukáš; Flajšman, Lukáš; Kalousek, Radek; Mach, Jindřich; Lišková, Zuzana; Nezval, David; Švarc, Vojtěch; Šamořil, Tomáš; Šikola, Tomáš

    2017-01-26

    This article deals with the analysis of the relationship between the pull-off force measured by atomic force microscopy and the dimensions of water bridge condensed between a hydrophilic silicon oxide tip and a silicon oxide surface under ambient conditions. Our experiments have shown that the pull-off force increases linearly with the radius of the tip and nonmonotonically with the relative humidity (RH). The latter dependence generally consists of an initial constant part changing to a convex-concave-like increase of the pull-off force and finally followed by a concave-like decrease of this force. The reproducibility tests have demonstrated that the precision limits have to be taken into account for comparing these measurements carried out under atmospheric conditions. The results were fitted by a classical thermodynamic model based on water-bridge envelope calculations using the numerical solution of the Kelvin equation in the form of axisymmetric differential equations and consequent calculation of adhesive forces. To describe the measured data more precisely, a decrease of the water surface tension for low RH was incorporated into the calculation. Such a decrease can be expected as a consequence of the high surface curvature in the nanometer-sized water bridge between the tip and the surface.

  4. Local viscoelasticity of the surfaces of individual Gram-negative bacterial cells measured using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Vadillo-Rodriguez, Virginia; Beveridge, Terry; Dutcher, John

    2008-03-01

    The cell wall of Gram-negative bacteria performs many important biological functions: it plays a structural role, it allows the selective movement of molecules across itself, and it allows for growth and division. These functions not only suggest that the cell wall is dynamic, but that its mechanical properties are very important. We have used a novel, AFM-based approach to probe the mechanical properties of single bacterial cells by applying a constant compressive force to the cell under physiological conditions while measuring the time-dependent displacement (creep) of the AFM tip due to the viscoelastic properties of the cell. For these experiments, we chose a representative Gram-negative bacterium, P. aeruginosa PAO1, and we used AFM tips of different size and geometry. We find that the cell response is well described by a three element mechanical model with an effective cell spring constant k and an effective time constant τ for the creep motion. Adding glutaraldehyde, which increases the covalent bonding of the cell surface, produced a significant increase in k and a significant decrease in τ.

  5. Influence of radioactivity on surface interaction forces.

    PubMed

    Walker, M E; McFarlane, J; Glasgow, D C; Chung, E; Taboada-Serrano, P; Yiacoumi, S; Tsouris, C

    2010-10-15

    Although some differences have been observed, the transport behavior of radioactive aerosol particles has often been assumed to be analogous to the behavior of nonradioactive aerosols in dispersion models. However, radioactive particles can become electrostatically charged as a result of the decay process. Theories have been proposed to describe this self-charging phenomenon, which may have a significant effect on how these particles interact with one another and with charged surfaces in the environment. In this study, atomic force microscopy (AFM) was employed to quantify surface forces between a particle and a planar surface and to compare measurements with and without the involvement of radioactivity. The main objective of this work is to assess directly the effects of radioactivity on the surface interactions of radioactive aerosols via the measurement of the adhesion force. The adhesion force between a silicon nitride AFM tip and an activated gold substrate was measured so that any possible effects due to radioactivity could be observed. The adhesion force between the tip and the gold surface increased significantly when the gold substrate (25 mm(2) surface area) was activated to a level of approximately 0.6 mCi. The results of this investigation will prompt further work into the effects of radioactivity in particle-surface interactions.

  6. Uncertainty in NIST Force Measurements.

    PubMed

    Bartel, Tom

    2005-01-01

    This paper focuses upon the uncertainty of force calibration measurements at the National Institute of Standards and Technology (NIST). The uncertainty of the realization of force for the national deadweight force standards at NIST is discussed, as well as the uncertainties associated with NIST's voltage-ratio measuring instruments and with the characteristics of transducers being calibrated. The combined uncertainty is related to the uncertainty of dissemination for force transfer standards sent to NIST for calibration.

  7. Measurement of the interaction forces at various pH levels by using AFM for the interpretation of DNA adsorption on silanized surfaces

    NASA Astrophysics Data System (ADS)

    Han, Seung Pil; Suga, Kosaku; Fujihara, Masamichi; Park, Byung-Eun

    2014-09-01

    Various surfaces have been used for deoxyribonucleic acid (DNA) immobilization, one example being a silanized surface. This is useful for determining DNA lengths and, thus, locating specific gene sequences in DNA by using fluorescence microscopy and scanning probe microscopy. In this study, we deposited DNA by using the molecular combing method and, we used fluorescence microscopy to study how the chain lengths of n-alkylsilanes affected the surface density of DNA deposited on the silanized surfaces in a tris-ethylenediaminetetraacetic acid (TE) buffer. The forces between a cleaned silicon-nitride (Si3N4) tip and each substrate surface in aqueous buffers at various pH levels (1.0 ~ 9.0) were also studied by using atomic force microscopy to measure the force-distance curves. We explain why the density of lambda bacteriophage DNA (λ-DNA) deposited by using the molecular combing method at pH 8 was lower on the silanized surface with the shorter alkyl chain than it was on the silanized surface with the longer alkyl chain in terms of the electrical double layer (EDL) and the adhesive force.

  8. Direct measurement of critical Casimir forces

    NASA Astrophysics Data System (ADS)

    Hertlein, C.; Helden, L.; Gambassi, A.; Dietrich, S.; Bechinger, C.

    2008-01-01

    When fluctuating fields are confined between two surfaces, long-range forces arise. A famous example is the quantum-electrodynamical Casimir force that results from zero-point vacuum fluctuations confined between two conducting metal plates. A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture close to its critical point and arises from the confinement of concentration fluctuations within the thin film of fluid separating the surfaces. So far, all experimental evidence for the existence of this effect has been indirect. Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6-lutidine near its critical point. We use total internal reflection microscopy to determine in situ the forces between the sphere and the surface, with femtonewton resolution. Depending on whether the adsorption preferences of the sphere and the surface for water and 2,6-lutidine are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system. We expect that these features of critical Casimir forces may result in novel uses of colloids as model systems.

  9. Direct measurement of critical Casimir forces.

    PubMed

    Hertlein, C; Helden, L; Gambassi, A; Dietrich, S; Bechinger, C

    2008-01-10

    When fluctuating fields are confined between two surfaces, long-range forces arise. A famous example is the quantum-electrodynamical Casimir force that results from zero-point vacuum fluctuations confined between two conducting metal plates. A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture close to its critical point and arises from the confinement of concentration fluctuations within the thin film of fluid separating the surfaces. So far, all experimental evidence for the existence of this effect has been indirect. Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6-lutidine near its critical point. We use total internal reflection microscopy to determine in situ the forces between the sphere and the surface, with femtonewton resolution. Depending on whether the adsorption preferences of the sphere and the surface for water and 2,6-lutidine are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system. We expect that these features of critical Casimir forces may result in novel uses of colloids as model systems.

  10. Force based displacement measurement in micromechanical devices

    SciTech Connect

    O {close_quote}Shea, S. J.; Ng, C. K.; Tan, Y. Y.; Xu, Y.; Tay, E. H.; Chua, B. L.; Tien, N. C.; Tang, X. S.; Chen, W. T.

    2001-06-18

    We demonstrate how force detection methods based on atomic force microscopy can be used to measure displacement in micromechanical devices. We show the operation of a simple microfabricated accelerometer, the proof mass of which incorporates a tip which can be moved towards an opposing surface. Both noncontact operation using long range electrostatic forces and tapping mode operation are demonstrated. The displacement sensitivity of the present device using feedback to control the tip-surface separation is approximately 1 nm. {copyright} 2001 American Institute of Physics.

  11. Jaw bite force measurement device.

    PubMed

    Flanagan, Dennis; Ilies, Horea; O'Brien, Brendan; McManus, Anne; Larrow, Beau

    2012-08-01

    We describe a cost-effective device that uses an off-the-shelf force transducer to measure patient bite force as a diagnostic aid in determining dental implant size, number of implants, and prosthetic design for restoring partial edentulism. The main advantages of the device are its accuracy, simplicity, modularity, ease of manufacturing, and low cost.

  12. Cooling Force Measurements at CELSIUS

    SciTech Connect

    Ga ring lnander, B.; Lofnes, T.; Ziemann, V.; Fedotov, A. V.; Litvinenko, V. N.; Sidorin, A. O.; Smirnov, A. V.

    2006-03-20

    The design of future high energy coolers relies heavily on extending the results of cooling force measurements into new regimes by using simulation codes. In order to carefully benchmark these codes we have accurately measured the longitudinal friction force in CELSIUS by recording the phase shift between the beam and the RF voltage while varying the RF frequency. Moreover, parameter dependencies on the electron current, solenoid magnetic field and magnetic field alignment were carried out.

  13. COOLING FORCE MEASUREMENTS IN CELSIUS.

    SciTech Connect

    GALNANDER, B.; FEDOTOV, A.V.; LITVINENKO, V.N.; ET AL.

    2005-09-18

    The design of future high energy coolers relies heavily on extending the results of cooling force measurements into new regimes by using simulation codes. In order to carefully benchmark these codes we have accurately measured the longitudinal friction force in CELSIUS by recording the phase shift between the beam and the RF voltage while varying the RF frequency. Moreover, parameter dependencies on the electron current, solenoid magnetic field and magnetic field alignment were carried out.

  14. Reduced hydrophobic interaction of polystyrene surfaces by spontaneous segregation of block copolymers with oligo (ethylene glycol) methyl ether methacrylate blocks: force measurements in water using atomic force microscope with hydrophobic probes.

    PubMed

    Zhang, Rui; Seki, Akiko; Ishizone, Takashi; Yokoyama, Hideaki

    2008-05-20

    Reduction of hydrophobic interaction in water is important in biological interfaces. In our previous work, we have found that poly(styrene- b-triethylene glycol methyl ether methacrylate) (PS-PME3MA) segregates the PME3MA block to the surface in hydrophobic environment, such as in air or in a vacuum, and shows remarkable resistance against adsorption or adhesion of proteins, platelets, and cells in water. In this paper, we report that atomic force microscopy (AFM) with hydrophobic probes can directly monitor the reduced hydrophobic interaction of the PS surfaces modified by poly(styrene- b-origoethylene glycol methyl ether methacrylate) (PS-PME NMA), where N is the number of ethylene glycol units. The pull-off forces between the hydrophobic probes that are coated with octyltrichlorosilane (OLTS) and the PS-PME NMA modified polystyrene (PS) surfaces in water were measured. The absolute spring constants and tip-curvatures of the AFM cantilevers were measured to compute the work of adhesion by the Johnson, Kendall, and Roberts (JKR) theory, which relates the pull-off force at which the separation occurs between a hemisphere and a plane to the work of adhesion. The hydrophobic interactions between the hydrophobic tip and polymer surfaces in water were greatly reduced with the segregated PME NMA blocks. The hydrophobic interactions decrease with increasing N of the series of PS-PME NMA and show a correlation with the amount of protein adsorbed.

  15. The electrochemical surface forces apparatus: the effect of surface roughness, electrostatic surface potentials, and anodic oxide growth on interaction forces, and friction between dissimilar surfaces in aqueous solutions.

    PubMed

    Valtiner, Markus; Banquy, Xavier; Kristiansen, Kai; Greene, George W; Israelachvili, Jacob N

    2012-09-11

    We present a newly designed electrochemical surface forces apparatus (EC-SFA) that allows control and measurement of surface potentials and interfacial electrochemical reactions with simultaneous measurement of normal interaction forces (with nN resolution), friction forces (with μN resolution), and distances (with Å resolution) between apposing surfaces. We describe three applications of the developed EC-SFA and discuss the wide-range of potential other applications. In particular, we describe measurements of (1) force-distance profiles between smooth and rough gold surfaces and apposing self-assembled monolayer-covered smooth mica surfaces; (2) the effective changing thickness of anodically growing oxide layers with Å-accuracy on rough and smooth surfaces; and (3) friction forces evolving at a metal-ceramic contact, all as a function of the applied electrochemical potential. Interaction forces between atomically smooth surfaces are well-described using DLVO theory and the Hogg-Healy-Fuerstenau approximation for electric double layer interactions between dissimilar surfaces, which unintuitively predicts the possibility of attractive double layer forces between dissimilar surfaces whose surface potentials have similar sign, and repulsive forces between surfaces whose surface potentials have opposite sign. Surface roughness of the gold electrodes leads to an additional exponentially repulsive force in the force-distance profiles that is qualitatively well described by an extended DLVO model that includes repulsive hydration and steric forces. Comparing the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer allowed the identification of its chemical structure as a hydrated Au(OH)(3) phase formed at the gold surface at high positive potentials. The EC-SFA allows, for the first time, one to look at complex long-term transient effects of dynamic processes (e.g., relaxation times), which are also reflected in friction

  16. Automatic HTS force measurement instrument

    DOEpatents

    Sanders, Scott T.; Niemann, Ralph C.

    1999-01-01

    A device for measuring the levitation force of a high temperature superconductor sample with respect to a reference magnet includes a receptacle for holding several high temperature superconductor samples each cooled to superconducting temperature. A rotatable carousel successively locates a selected one of the high temperature superconductor samples in registry with the reference magnet. Mechanism varies the distance between one of the high temperature superconductor samples and the reference magnet, and a sensor measures levitation force of the sample as a function of the distance between the reference magnet and the sample. A method is also disclosed.

  17. Automatic HTS force measurement instrument

    DOEpatents

    Sanders, S.T.; Niemann, R.C.

    1999-03-30

    A device is disclosed for measuring the levitation force of a high temperature superconductor sample with respect to a reference magnet includes a receptacle for holding several high temperature superconductor samples each cooled to superconducting temperature. A rotatable carousel successively locates a selected one of the high temperature superconductor samples in registry with the reference magnet. Mechanism varies the distance between one of the high temperature superconductor samples and the reference magnet, and a sensor measures levitation force of the sample as a function of the distance between the reference magnet and the sample. A method is also disclosed. 3 figs.

  18. Measuring Adhesion And Friction Forces

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa

    1991-01-01

    Cavendish balance adapted to new purpose. Apparatus developed which measures forces of adhesion and friction between specimens of solid materials in vacuum at temperatures from ambient to 900 degrees C. Intended primarily for use in studying adhesion properties of ceramics and metals, including silicon carbide, aluminum oxide, and iron-base amorphous alloys.

  19. Intrinsic adhesion force of lubricants to steel surface.

    PubMed

    Lee, Jonghwi

    2004-09-01

    The intrinsic adhesion forces of lubricants and other pharmaceutical materials to a steel surface were quantitatively compared using Atomic Force Microscopy (AFM). A steel sphere was attached to the tip of an AFM cantilever, and its adhesion forces to the substrate surfaces of magnesium stearate, sodium stearyl fumarate, lactose, 4-acetamidophenol, and naproxen were measured. Surface roughness varied by an order of magnitude among the materials. However, the results clearly showed that the two lubricants had about half the intrinsic adhesion force as lactose, 4-acetamidophenol, and naproxen. Differences in the intrinsic adhesion forces of the two lubricants were insignificant. The lubricant molecules were unable to cover the steel surface during AFM measurements. Intrinsic adhesion force can slightly be modified by surface treatment and compaction, and its tip-to-tip variation was not greater than its difference between lubricants and other pharmaceutical particles. This study provides a quantitative fundamental basis for understanding adhesion related issues.

  20. Detecting chameleons through Casimir force measurements

    SciTech Connect

    Brax, Philippe; Davis, Anne-Christine; Shaw, Douglas; Mota, David F.

    2007-12-15

    The best laboratory constraints on strongly coupled chameleon fields come not from tests of gravity per se but from precision measurements of the Casimir force. The chameleonic force between two nearby bodies is more akin to a Casimir-like force than a gravitational one: The chameleon force behaves as an inverse power of the distance of separation between the surfaces of two bodies, just as the Casimir force does. Additionally, experimental tests of gravity often employ a thin metallic sheet to shield electrostatic forces; however, this sheet masks any detectable signal due to the presence of a strongly coupled chameleon field. As a result of this shielding, experiments that are designed to specifically test the behavior of gravity are often unable to place any constraint on chameleon fields with a strong coupling to matter. Casimir force measurements do not employ a physical electrostatic shield and as such are able to put tighter constraints on the properties of chameleons fields with a strong matter coupling than tests of gravity. Motivated by this, we perform a full investigation on the possibility of testing chameleon models with both present and future Casimir experiments. We find that present-day measurements are not able to detect the chameleon. However, future experiments have a strong possibility of detecting or rule out a whole class of chameleon models.

  1. Covalent Immobilization of Microtubules on Glass Surfaces for Molecular Motor Force Measurements and Other Single-Molecule Assays

    PubMed Central

    Nicholas, Matthew P.; Rao, Lu; Gennerich, Arne

    2014-01-01

    Rigid attachment of microtubules (MTs) to glass cover slip surfaces is a prerequisite for a variety of microscopy experiments in which MTs are used as substrates for MT-associated proteins, such as the molecular motors kinesin and cytoplasmic dynein. We present an MT-surface coupling protocol in which aminosilanized glass is formylated using the cross-linker glutaraldehyde, fluorescence-labeled MTs are covalently attached, and the surface is passivated with highly pure beta-casein. The technique presented here yields rigid MT immobilization while simultaneously blocking the remaining glass surface against nonspecific binding by polystyrene optical trapping microspheres. This surface chemistry is straightforward and relatively cheap and uses a minimum of specialized equipment or hazardous reagents. These methods provide a foundation for a variety of optical tweezers experiments with MT-associated molecular motors and may also be useful in other assays requiring surface-immobilized proteins. PMID:24633798

  2. The effect of patch potentials in Casimir force measurements determined by heterodyne Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Garrett, Joseph L.; Somers, David; Munday, Jeremy N.

    2015-06-01

    Measurements of the Casimir force require the elimination of the electrostatic force between the surfaces. However, due to electrostatic patch potentials, the voltage required to minimize the total force may not be sufficient to completely nullify the electrostatic interaction. Thus, these surface potential variations cause an additional force, which can obscure the Casimir force signal. In this paper, we inspect the spatially varying surface potential of e-beamed, sputtered, sputtered and annealed, and template stripped gold surfaces with Heterodyne amplitude modulated Kelvin probe force microscopy (HAM-KPFM). It is demonstrated that HAM-KPFM improves the spatial resolution of surface potential measurements compared to amplitude modulated Kelvin probe force microscopy. We find that patch potentials vary depending on sample preparation, and that the calculated pressure can be similar to the pressure difference between Casimir force calculations employing the plasma and Drude models.

  3. Surface potential measurement on contact resistance of amorphous-InGaZnO thin film transistors by Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Han, Zhiheng; Xu, Guangwei; Wang, Wei; Lu, Congyan; Lu, Nianduan; Ji, Zhuoyu; Li, Ling; Liu, Ming

    2016-07-01

    Contact resistance plays an important role in amorphous InGaZnO (a-IGZO) thin film transistors (TFTs). In this paper, the surface potential distributions along the channel have been measured by using Kelvin probe force microscopy (KPFM) on operating a-IGZO TFTs, and sharp potential drops at the edges of source and drain were observed. The source and drain contact resistances can be extracted by dividing sharp potential drops with the corresponding drain to source current. It is found that the contact resistances could not be neglected compared with the whole channel resistances in the a-IGZO TFT, and the contact resistances decrease remarkably with increasing gate biased voltage. Our results suggest that the contact resistances can be controlled by tuning the gate biased voltage. Moreover, a transition from gradual channel approximation to space charge region was observed through the surface potential map directly when TFT operating from linear regime to saturation regime.

  4. Forces and Holes in Liquid Surfaces and Soap Films: A Simple Measurement of a Not-So-Simple Effect

    ERIC Educational Resources Information Center

    Gratton, Luigi M.; Oss, Stefano

    2004-01-01

    In this article we show how to verify that in a fluid surface or film the value of the surface tension (i.e. the free energy per unit area) does not depend on the area of the film itself. The experimental evidence discussed can be obtained extremely simply yet with great accuracy. This experiment is important in that it leads to a deeper…

  5. Direct measurements of drag forces in C. elegans crawling locomotion.

    PubMed

    Rabets, Yegor; Backholm, Matilda; Dalnoki-Veress, Kari; Ryu, William S

    2014-10-21

    With a simple and versatile microcantilever-based force measurement technique, we have probed the drag forces involved in Caenorhabditis elegans locomotion. As a worm crawls on an agar surface, we found that substrate viscoelasticity introduces nonlinearities in the force-velocity relationships, yielding nonconstant drag coefficients that are not captured by original resistive force theory. A major contributing factor to these nonlinearities is the formation of a shallow groove on the agar surface. We measured both the adhesion forces that cause the worm's body to settle into the agar and the resulting dynamics of groove formation. Furthermore, we quantified the locomotive forces produced by C. elegans undulatory motions on a wet viscoelastic agar surface. We show that an extension of resistive force theory is able to use the dynamics of a nematode's body shape along with the measured drag coefficients to predict the forces generated by a crawling nematode.

  6. Short wave Aerosol Radiative Forcing estimates over a semi urban coastal environment in south-east India and validation with surface flux measurements

    NASA Astrophysics Data System (ADS)

    Aruna, K.; Lakshmi Kumar, T. V.; Krishna Murthy, B. V.; Babu, S. Suresh; Ratnam, M. Venkat; Rao, D. Narayana

    2016-01-01

    The short wave direct Aerosol Radiative Forcing (ARF) at a semi urban coastal location near Chennai (12.81 °N, 80.03 °E, ˜45 m amsl), a mega city on the east coast of India has been estimated for all the four seasons in the year 2013 using the SBDART (Santa Barbara Discrete ordinate Atmospheric Radiative Transfer) model. As inputs to this model, measured aerosol parameters together with modeled aerosol and atmospheric parameters are used. The ARF in the atmosphere is found to be higher in the pre-monsoon and winter seasons compared to the other seasons whereas at the surface, it is found to be higher in the south-west (SW) monsoon and winter seasons. The estimated ARF values are compared with those reported over other locations in India. The effect of Relative Humidity on ARF has been investigated for the first time in the present study. It is found that the ARF increases with increasing RH in the SW monsoon and winter seasons. An unique feature of the present study is the comparison of the net surface short wave fluxes estimated from the model (SBDART) and measured fluxes using CNR 4 net radiometer. This comparison between the estimated and measured fluxes showed good agreement, providing a 'closure' for the estimates.

  7. Structural and functional changes of the articular surface in a post-traumatic model of early osteoarthritis measured by atomic force microscopy.

    PubMed

    Desrochers, Jane; Amrein, Matthias A; Matyas, John R

    2010-12-01

    The functional integrity of the articulating cartilage surface is a critical determinant of joint health. Although a variety of techniques exist to characterize the structural changes in the tissue with osteoarthritis (OA), some with extremely high resolution, most lack the ability to detect and monitor the functional changes that accompany the structural deterioration of this essential bearing surface. Atomic force microscopy (AFM) enables the acquisition of both structural and mechanical properties of the articular cartilage surface, with up to nanoscale resolution, making it particularly useful for evaluating the functional behavior of the macromolecular network forming the cartilage surface, which disintegrates in OA. In the present study, AFM was applied to the articular cartilage surfaces from six pairs of canine knee joints with post-traumatic OA. Microstructure (RMS roughness) and micromechanics (dynamic indentation modulus, E* of medial femoral condyle cartilages were compared between contralateral controls and cruciate-transected knee joints, which develop early signs of OA by three months after surgery. Results reveal a significant increase in RMS roughness and a significant four-fold decrease in E* in cartilages from cruciate-transected joints versus contralateral controls. Compared to previous reports of changes in bulk mechanics, AFM was considerably more sensitive at detecting early cartilage changes due to cruciate-deficiency. The use of AFM in this study provides important new information on early changes in the natural history of OA because of its ability to sensitively detect and measure local structural and functional changes of the articular cartilage surface, the presumptive site of osteoarthritic initiation.

  8. Microscale friction investigation of polysilicon surface using scanning force microscopy

    NASA Astrophysics Data System (ADS)

    Flueraru, C.; Cobianu, C.; Dascalu, D.; Flueraru, M.

    1998-07-01

    Microscale phenomena between the surface of chemically vapour deposited silicon films and a silicon nitride tip was investigated using Scanning Force Microscopy. An analysis of friction forces for different scan directions is presented. For different applied forces, the friction forces were measured and consequently the friction coefficient was calculated. We found that the average friction force linearly increases with the applied force and is reversible when unloading. Connection between the surface roughness and the friction coefficient was experimentally demonstrated. On a étudié par Microscopie à Force Atomique des phénomènes à échelle microscopique au niveau de la jonction pointe de nitrure de silicium et surface de films de silicium, obtenus par déposition chimique en phase vapeur. Dans cet article, nous présentons une analyse des forces de friction pour différentes directions de balayage. On a déterminé les forces de friction et, en conséquence, nous avons calculé le coefficient de friction pour différentes forces appliquées. Les résultats montrent que la force moyenne de friction augmente en fonction de la force appliquée, et qu'elle est reversible lorsque la charge diminue. Une dépendance entre la rugosité de la surface et le coefficient de friction est déduite.

  9. Influence of roughness on capillary forces between hydrophilic surfaces.

    PubMed

    van Zwol, P J; Palasantzas, G; De Hosson, J Th M

    2008-09-01

    Capillary forces have been measured by atomic force microscopy in the plate-sphere setup between gold, borosilicate glass, GeSbTe, titanium, and UV-irradiated amorphous titanium-dioxide surfaces. The force measurements were performed as a function contact time and surface roughness in the range 0.2-15 nm rms and relative humidity ranging between 2% and 40%. It is found that even for the lowest attainable relative humidity ( approximately 2%+/-1%) very large capillary forces are still present. The latter suggests the persistence of a nanometers-thick adsorbed water layer that acts as a capillary bridge between contacting surfaces. Moreover, we found a significantly different scaling behavior of the force with rms roughness for materials with different hydrophilicity as compared to gold-gold surfaces.

  10. Adhesion force between cyclopentane hydrate and mineral surfaces.

    PubMed

    Aman, Zachary M; Leith, William J; Grasso, Giovanny A; Sloan, E Dendy; Sum, Amadeu K; Koh, Carolyn A

    2013-12-17

    Clathrate hydrate adhesion forces play a critical role in describing aggregation and deposition behavior in conventional energy production and transportation. This manuscript uses a unique micromechanical force apparatus to measure the adhesion force between cyclopentane hydrate and heterogeneous quartz and calcite substrates. The latter substrates represent models for coproduced sand and scale often present during conventional energy production and transportation. Micromechanical adhesion force data indicate that clathrate hydrate adhesive forces are 5-10× larger for calcite and quartz minerals than stainless steel. Adhesive forces further increased by 3-15× when increasing surface contact time from 10 to 30 s. In some cases, liquid water from within the hydrate shell contacted the mineral surface and rapidly converted to clathrate hydrate. Further measurements on mineral surfaces with physical control of surface roughness showed a nonlinear dependence of water wetting angle on surface roughness. Existing adhesive force theory correctly predicted the dependence of clathrate hydrate adhesive force on calcite wettability, but did not accurately capture the dependence on quartz wettability. This comparison suggests that the substrate surface may not be inert, and may contribute positively to the strength of the capillary bridge formed between hydrate particles and solid surfaces.

  11. Anisotropic particles near surfaces: Propulsion force and friction

    NASA Astrophysics Data System (ADS)

    Müller, Boris; Krüger, Matthias

    2016-03-01

    We theoretically study the phenomenon of propulsion through Casimir forces in thermal nonequilibrium. Using fluctuational electrodynamics, we derive a formula for the propulsion force for an arbitrary small object in two scenarios: (i) for the object being isolated, and (ii) for the object being close to a planar surface. In the latter case, the propulsion force (i.e., the force parallel to the surface) increases with decreasing distance, i.e., it couples to the near field. We numerically calculate the lateral force acting on a hot spheroid near a surface and show that it can be as large as the gravitational force, thus being potentially measurable in fly-by experiments. We close by linking our results to well-known relations of linear-response theory in fluctuational electrodynamics: Looking at the friction of the anisotropic object for constant velocity, we identify a correction term that is additional to the typically used approach.

  12. Assimilation of high-frequency radar surface currents measurements to optimize tidal boundary conditions and wind forcing (Outstanding Young Scientist Lecture)

    NASA Astrophysics Data System (ADS)

    Barth, Alexander; Alvera-Azcárate, Aida; Gurgel, Klaus-Werner; Staneva, Joanna; Beckers, Jean-Marie; Port, Alexander; Stanev, Emil

    2010-05-01

    An ensemble smoother scheme is presented to assimilate high-frequency (HF) radar surface currents to improve tidal boundary conditions and wind forcings of a circulation model of the German Bight. To create an ensemble of dynamically realistic tidal boundary conditions, a cost function is formulated which is directly related to the probability of each perturbation. This cost function ensures that the perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained using all observations within the assimilation period using the covariances of the ensemble simulation. The approach acts like a smoother scheme since past and future observations are taken into account. The final analysis is obtained by rerunning the model using the optimal perturbation of the boundary conditions. The analyzed model solution satisfies thus the model equations exactly and does not suffer from spurious adjustments often observed with sequential assimilation schemes. Model results are also compared to independent tide gage data. The assimilation also reduces the model error compared to those sea level observations. The same scheme is also used to correct surface winds. Surface winds are crucial for accurately modeling the marine circulation in coastal waters. The method is validated directly by comparing the analyzed wind speed to in situ measurements and indirectly by assessing the impact of the corrected winds on sea surface temperature (SST) relative to satellite SST.

  13. Unsteady Aerodynamic Force Sensing from Measured Strain

    NASA Technical Reports Server (NTRS)

    Pak, Chan-Gi

    2016-01-01

    A simple approach for computing unsteady aerodynamic forces from simulated measured strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, aerodynamic forces over the wing are computed using modal aerodynamic influence coefficient matrices, a rational function approximation, and a time-marching algorithm. A cantilevered rectangular wing built and tested at the NASA Langley Research Center (Hampton, Virginia, USA) in 1959 is used to validate the simple approach. Unsteady aerodynamic forces as well as wing deflections, velocities, accelerations, and strains are computed using the CFL3D computational fluid dynamics (CFD) code and an MSC/NASTRAN code (MSC Software Corporation, Newport Beach, California, USA), and these CFL3D-based results are assumed as measured quantities. Based on the measured strains, wing deflections, velocities, accelerations, and aerodynamic forces are computed using the proposed approach. These computed deflections, velocities, accelerations, and unsteady aerodynamic forces are compared with the CFL3D/NASTRAN-based results. In general, computed aerodynamic forces based on the lifting surface theory in subsonic speeds are in good agreement with the target aerodynamic forces generated using CFL3D code with the Euler equation. Excellent aeroelastic responses are obtained even with unsteady strain data under the signal to noise ratio of -9.8dB. The deflections, velocities, and accelerations at each sensor location are independent of structural and aerodynamic models. Therefore, the distributed strain data together with the current proposed approaches can be used as distributed deflection

  14. Surface Biology of DNA by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Hansma, Helen G.

    2001-10-01

    The atomic force microscope operates on surfaces. Since surfaces occupy much of the space in living organisms, surface biology is a valid and valuable form of biology that has been difficult to investigate in the past owing to a lack of good technology. Atomic force microscopy (AFM) of DNA has been used to investigate DNA condensation for gene therapy, DNA mapping and sizing, and a few applications to cancer research and to nanotechnology. Some of the most exciting new applications for atomic force microscopy of DNA involve pulling on single DNA molecules to obtain measurements of single-molecule mechanics and thermodynamics.

  15. Surface forces of colloidal particles from micrometer to nanometer

    NASA Astrophysics Data System (ADS)

    Cho, Jeong-Min

    2003-10-01

    Surface forces of colloidal particles play critical roles in the macroscopic behavior of particulate systems such as dispersion and coagulation, adhesion and coating, and the rheological behavior of ceramic slurries. As particle size is decreased from micrometer to nanometer range, surface forces are increasingly important. Polyelectrolytes are the chemical additives commonly used to efficiently control the stabilization of the colloidal system. Their conformations on the solid surfaces as well as the interactions between the adsorbed polyelectrolytes are important issues in colloidal processing. Most experimental and theoretical approaches to the surface forces are based on particle sizes in the micrometer range. However, nanoparticles at close proximity or high solids loading are expected to show different behavior than what can be estimated from conventional theories such as continuum or mean field theories. My study examined the effect of pH, ionic strength, and molecular weight of the polyelectrolytes on the surface forces of colloidal particles by the interplay with the adsorption, turbidity, and direct surface force measurement in terms of the conformation on the solid surfaces. The colloid probe technique based on atomic force microscopy (AFM) is well established for micron size particles; and could be extended for nanosize particles by using carbon nanotubes as proximal probes. Nanotubes with their high aspect ratio avoid the contribution from cone shapes that happens with AFM tips. The difference in particle size significantly influences surface forces for sterically dispersed colloidal systems.

  16. Measuring the structure of thin soft matter films under confinement: A surface-force type apparatus for neutron reflection, based on a flexible membrane approach

    NASA Astrophysics Data System (ADS)

    de Vos, Wiebe M.; Mears, Laura L. E.; Richardson, Robert M.; Cosgrove, Terence; Dalgliesh, Robert M.; Prescott, Stuart W.

    2012-11-01

    A unique surface force type apparatus that allows the investigation of a confined thin film using neutron reflection is described. The central feature of the setup consists of a solid substrate (silicon) and a flexible polymer membrane (Melinex®). We show that inflation of the membrane against the solid surface provides close and even contact between the interfaces over a large surface area. Both heavy water and air can be completely squeezed out from between the flexible film and the solid substrate, leaving them in molecular contact. The strength of confinement is controlled by the pressure used to inflate the membrane. Dust provides a small problem for this approach as it can get trapped between membrane and substrate to prevent a small part of the membrane from making good contact with the substrate. This results in the measured neutron reflectivity containing a small component of an unwanted reflection, between 10% and 20% at low confining pressures (1 bar) and between 1% and 5% at high confining pressures (5 bar). However, we show that this extra signal does not prevent good and clear information on the structure of thin films being extracted from the neutron reflectivity. The effects of confinement are illustrated with data from a poly(vinyl pyrollidone) gel layer in water, a polyelectrolyte multilayer in water, and with data from a stack of supported lipid-bilayers swollen with D2O vapor. The data demonstrates the potential of this apparatus to provide information on the structure of thin films under confinement for a known confining pressure.

  17. Measuring the structure of thin soft matter films under confinement: A surface-force type apparatus for neutron reflection, based on a flexible membrane approach

    SciTech Connect

    Vos, Wiebe M. de; Mears, Laura L. E.; Richardson, Robert M.; Cosgrove, Terence; Prescott, Stuart W.; Dalgliesh, Robert M.

    2012-11-15

    A unique surface force type apparatus that allows the investigation of a confined thin film using neutron reflection is described. The central feature of the setup consists of a solid substrate (silicon) and a flexible polymer membrane (Melinex{sup Registered-Sign }). We show that inflation of the membrane against the solid surface provides close and even contact between the interfaces over a large surface area. Both heavy water and air can be completely squeezed out from between the flexible film and the solid substrate, leaving them in molecular contact. The strength of confinement is controlled by the pressure used to inflate the membrane. Dust provides a small problem for this approach as it can get trapped between membrane and substrate to prevent a small part of the membrane from making good contact with the substrate. This results in the measured neutron reflectivity containing a small component of an unwanted reflection, between 10% and 20% at low confining pressures (1 bar) and between 1% and 5% at high confining pressures (5 bar). However, we show that this extra signal does not prevent good and clear information on the structure of thin films being extracted from the neutron reflectivity. The effects of confinement are illustrated with data from a poly(vinyl pyrollidone) gel layer in water, a polyelectrolyte multilayer in water, and with data from a stack of supported lipid-bilayers swollen with D{sub 2}O vapor. The data demonstrates the potential of this apparatus to provide information on the structure of thin films under confinement for a known confining pressure.

  18. Force-Control Algorithm for Surface Sampling

    NASA Technical Reports Server (NTRS)

    Acikmese, Behcet; Quadrelli, Marco B.; Phan, Linh

    2008-01-01

    A G-FCON algorithm is designed for small-body surface sampling. It has a linearization component and a feedback component to enhance performance. The algorithm regulates the contact force between the tip of a robotic arm attached to a spacecraft and a surface during sampling.

  19. Surface cleanliness measurement procedure

    DOEpatents

    Schroder, Mark Stewart; Woodmansee, Donald Ernest; Beadie, Douglas Frank

    2002-01-01

    A procedure and tools for quantifying surface cleanliness are described. Cleanliness of a target surface is quantified by wiping a prescribed area of the surface with a flexible, bright white cloth swatch, preferably mounted on a special tool. The cloth picks up a substantial amount of any particulate surface contamination. The amount of contamination is determined by measuring the reflectivity loss of the cloth before and after wiping on the contaminated system and comparing that loss to a previous calibration with similar contamination. In the alternative, a visual comparison of the contaminated cloth to a contamination key provides an indication of the surface cleanliness.

  20. Graphene thickness dependent adhesion force and its correlation to surface roughness

    SciTech Connect

    Pourzand, Hoorad; Tabib-Azar, Massood

    2014-04-28

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

  1. Controlling adhesion force by means of nanoscale surface roughness.

    PubMed

    Ramakrishna, Shivaprakash N; Clasohm, Lucy Y; Rao, Akshata; Spencer, Nicholas D

    2011-08-16

    Control of adhesion is a crucial aspect in the design of microelectromechanical and nanoelectromechanical devices. To understand the dependence of adhesion on nanometer-scale surface roughness, a roughness gradient has been employed. Monomodal roughness gradients were fabricated by means of silica nanoparticles (diameter ∼12 nm) to produce substrates with varying nanoparticle density. Pull-off force measurements on the gradients were performed using (polyethylene) colloidal-probe microscopy under perfluorodecalin, in order to restrict interactions to van der Waals forces. The influence of normal load on pull-off forces was studied and the measured forces compared with existing Hamaker-approximation-based models. We observe that adhesion force reaches a minimum value at an optimum particle density on the gradient sample, where the mean particle spacing becomes comparable with the diameter of the contact area with the polyethylene sphere. We also observe that the effect on adhesion of increasing the normal load depends on the roughness of the surface.

  2. Adhesion force of staphylococcus aureus on various biomaterial surfaces.

    PubMed

    Alam, Fahad; Balani, Kantesh

    2017-01-01

    Staphylococcus comprises of more than half of all pathogens in orthopedic implant infections and they can cause major bone infection which can result in destruction of joint and bone. In the current study, adhesion force of bacteria on the surface of various biomaterial surfaces is measured using atomic force microscope (AFM). Staphylococcus aureus was immobilized on an AFM tipless cantilever as a force probe to measure the adhesion force between bacteria and biomaterials (viz. ultra-high molecular weight poly ethylene (UHMWPE), stainless steel (SS), Ti-6Al-4V alloy, hydroxyapatite (HA)). At the contact time of 10s, UHMWPE shows weak adhesion force (~4nN) whereas SS showed strong adhesion force (~15nN) due to their surface energy and surface roughness. Bacterial retention and viability experiment (3M™ petrifilm test, agar plate) dictates that hydroxyapatite shows the lowest vaibility of bacteria, whereas lowest bacterial retention is observed on UHMWPE surface. Similar results were obtained from live/dead staining test, where HA shows 65% viability, whereas on UHMWPE, SS and Ti-6Al-4V, the bacterial viability is 78%, 94% and 97%, respectively. Lower adhesion forces, constrained pull-off distance (of bacterial) and high antibacterial resistance of bioactive-HA makes it a potential biomaterial for bone-replacement arthroplasty.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    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 µm  ×  15 µm  ×  5 µm 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 µN, respectively. The cell traction force was measured, and the traction force increased by approximately 1 µN over 30 min. These results demonstrate that the proposed force plate is applicable as an effective traction force measurement.

  4. Dynamic Force Measurement with Strain Gauges

    ERIC Educational Resources Information Center

    Lee, Bruce E.

    1974-01-01

    Discusses the use of four strain gauges, a Wheatstone bridge, and an oscilloscope to measure forces dynamically. Included is an example of determining the centripetal force of a pendulum in a general physics laboratory. (CC)

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

    SciTech Connect

    Kweon, Hyojin; Yiacoumi, Sotira; Tsouris, Costas

    2011-01-01

    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. 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.

  6. The impact of rubbing fabric type on surface roughness and tribological properties of some semi-alicyclic polyimides evaluated from atomic force measurements

    NASA Astrophysics Data System (ADS)

    Stoica, Iuliana; Barzic, Andreea Irina; Hulubei, Camelia

    2013-03-01

    The morphology of some polyimides (PI) prepared from a flexible and alicyclic dianhydride, in combination with aromatic diamines was investigated in detail before and after rubbing with two types of fabric: cotton velvet (CV) and cellulose diacetate velvet (CDV). Atomic force microscopy was employed to evaluate the correlation between rubbing-induced grooves in PI film and size/flexibility of textile fibers. For both samples surface isotropy decreased appreciatively with 91% after patterning since the appearance of ordered nanostructures in the direction of rubbing. The angular spectra reveal the generation of a surface anisotropy after rubbing process and a higher surface regularity and uniformity when using CV. This result is confirmed by decrease of texture direction index with 75% and of surface texture aspect ratio with 89%. These parameters together with the rubbing fiber characteristics are key factors in controlling liquid crystal alignment on patterned PI surfaces.

  7. Adhesion force mapping on wood by atomic force microscopy: influence of surface roughness and tip geometry.

    PubMed

    Jin, X; Kasal, B

    2016-10-01

    This study attempts to address the interpretation of atomic force microscopy (AFM) adhesion force measurements conducted on the heterogeneous rough surface of wood and natural fibre materials. The influences of wood surface roughness, tip geometry and wear on the adhesion force distribution are examined by cyclic measurements conducted on wood surface under dry inert conditions. It was found that both the variation of tip and surface roughness of wood can widen the distribution of adhesion forces, which are essential for data interpretation. When a common Si AFM tip with nanometre size is used, the influence of tip wear can be significant. Therefore, control experiments should take the sequence of measurements into consideration, e.g. repeated experiments with used tip. In comparison, colloidal tips provide highly reproducible results. Similar average values but different distributions are shown for the adhesion measured on two major components of wood surface (cell wall and lumen). Evidence supports the hypothesis that the difference of the adhesion force distribution on these two locations was mainly induced by their surface roughness.

  8. Adhesion force mapping on wood by atomic force microscopy: influence of surface roughness and tip geometry

    NASA Astrophysics Data System (ADS)

    Jin, X.; Kasal, B.

    2016-10-01

    This study attempts to address the interpretation of atomic force microscopy (AFM) adhesion force measurements conducted on the heterogeneous rough surface of wood and natural fibre materials. The influences of wood surface roughness, tip geometry and wear on the adhesion force distribution are examined by cyclic measurements conducted on wood surface under dry inert conditions. It was found that both the variation of tip and surface roughness of wood can widen the distribution of adhesion forces, which are essential for data interpretation. When a common Si AFM tip with nanometre size is used, the influence of tip wear can be significant. Therefore, control experiments should take the sequence of measurements into consideration, e.g. repeated experiments with used tip. In comparison, colloidal tips provide highly reproducible results. Similar average values but different distributions are shown for the adhesion measured on two major components of wood surface (cell wall and lumen). Evidence supports the hypothesis that the difference of the adhesion force distribution on these two locations was mainly induced by their surface roughness.

  9. Adhesion force mapping on wood by atomic force microscopy: influence of surface roughness and tip geometry

    PubMed Central

    Kasal, B.

    2016-01-01

    This study attempts to address the interpretation of atomic force microscopy (AFM) adhesion force measurements conducted on the heterogeneous rough surface of wood and natural fibre materials. The influences of wood surface roughness, tip geometry and wear on the adhesion force distribution are examined by cyclic measurements conducted on wood surface under dry inert conditions. It was found that both the variation of tip and surface roughness of wood can widen the distribution of adhesion forces, which are essential for data interpretation. When a common Si AFM tip with nanometre size is used, the influence of tip wear can be significant. Therefore, control experiments should take the sequence of measurements into consideration, e.g. repeated experiments with used tip. In comparison, colloidal tips provide highly reproducible results. Similar average values but different distributions are shown for the adhesion measured on two major components of wood surface (cell wall and lumen). Evidence supports the hypothesis that the difference of the adhesion force distribution on these two locations was mainly induced by their surface roughness. PMID:27853541

  10. Adhesive force mapping of friction-transferred PTFE film surface

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Mashiko, S.

    The adhesive force of a friction-transferred polytetrafluoroethylene (PTFE) film was mapped by using an atomic force microscope (AFM) system driven by custom software. The friction-transferred PTFE film, which was made by sliding a PTFE polymer rod on a heated glass, consisted of many PTFE ridges running parallel to the sliding direction on the glass surface. The adhesive force on the sample was derived from force curve measurement. A triangular wave amplified with a custom high-voltage amplifier was fed into the Z piezo of the AFM head through an AFM controller unit to obtain force curves while the AFM cantilever scanned a single line of the sample. The force curves both of the PTFE ridges and of the bare glass surface could be obtained by scanning the region perpendicular to the sliding direction. The deflection signal of the cantilever was sampled and stored in a computer through an AD converter. The adhesive force on the PTFE region was about half that on the glass surface. This difference was explained by the difference in capillary force of the surface water.

  11. A constant compliance force modulation technique for scanning force microscopy (SFM) imaging of polymer surface elasticity.

    PubMed

    Stroup, E W; Pungor, A; Hlady, V

    1996-12-01

    A new method of force modulation scanning force microscopy (SFM) imaging based on a constant compliance feedback loop is presented. The feedback adjusts the loading force applied by the SFM tip to the surface in order to maintain a constant compliance beneath the tip. The new method, constant compliance force modulation (CCFM), has the advantage of being able to quantify the loading force exerted by the tip onto the sample surface and thus to estimate the elastic modulus of the material probed by the SFM tip. Once the elastic modulus of one region is known, the elastic moduli of other surface regions can be estimated from the spatial map of loading forces using the Hertz model of deformation. Force vs. displacement measurements made on one surface locality could also be used to estimate the local modulus. Several model surfaces, including a rubber-toughened epoxy polymer blend which showed clearly resolved compliant rubber phases within the harder epoxy matrix, were analyzed with the CCFM technique to illustrate the method's application.

  12. Surface force spectroscopic point load measurements and viscoelastic modelling of the micromechanical properties of air flow sensitive hairs of a spider (Cupiennius salei).

    PubMed

    McConney, Michael E; Schaber, Clemens F; Julian, Michael D; Eberhardt, William C; Humphrey, Joseph A C; Barth, Friedrich G; Tsukruk, Vladimir V

    2009-08-06

    The micromechanical properties of spider air flow hair sensilla (trichobothria) were characterized with nanometre resolution using surface force spectroscopy (SFS) under conditions of different constant deflection angular velocities theta (rad s(-1)) for hairs 900-950 microm long prior to shortening for measurement purposes. In the range of angular velocities examined (4 x 10(-4) - 2.6 x 10(-1) rad s(-1)), the torque T (Nm) resisting hair motion and its time rate of change (Nm s(-1)) were found to vary with deflection velocity according to power functions. In this range of angular velocities, the motion of the hair is most accurately captured by a three-parameter solid model, which numerically describes the properties of the hair suspension. A fit of the three-parameter model (3p) to the experimental data yielded the two torsional restoring parameters, S(3p)=2.91 x 10(-11) Nm rad(-1) and =2.77 x 10(-11) Nm rad(-1) and the damping parameter R(3p)=1.46 x 10(-12) Nm s rad(-1). For angular velocities larger than 0.05 rad s(-1), which are common under natural conditions, a more accurate angular momentum equation was found to be given by a two-parameter Kelvin solid model. For this case, the multiple regression fit yielded S(2p)=4.89 x 10(-11) Nm rad(-1) and R(2p)=2.83 x 10(-14) Nm s rad(-1) for the model parameters. While the two-parameter model has been used extensively in earlier work primarily at high hair angular velocities, to correctly capture the motion of the hair at both low and high angular velocities it is necessary to employ the three-parameter model. It is suggested that the viscoelastic mechanical properties of the hair suspension work to promote the phasic response behaviour of the sensilla.

  13. Micromechanical cohesion force measurements to determine cyclopentane hydrate interfacial properties.

    PubMed

    Aman, Zachary M; Joshi, Sanjeev E; Sloan, E Dendy; Sum, Amadeu K; Koh, Carolyn A

    2012-06-15

    Hydrate aggregation and deposition are critical factors in determining where and when hydrates may plug a deepwater flowline. We present the first direct measurement of structure II (cyclopentane) hydrate cohesive forces in the water, liquid hydrocarbon and gas bulk phases. For fully annealed hydrate particles, gas phase cohesive forces were approximately twice that obtained in a liquid hydrocarbon phase, and approximately six times that obtained in the water phase. Direct measurements show that hydrate cohesion force in a water-continuous bulk may be only the product of solid-solid cohesion. When excess water was present on the hydrate surface, gas phase cohesive forces increased by a factor of three, suggesting the importance of the liquid or quasi-liquid layer (QLL) in determining cohesive force. Hydrate-steel adhesion force measurements show that, when the steel surface is coated with hydrophobic wax, forces decrease up to 96%. As the micromechanical force technique is uniquely capable of measuring hydrate-surface forces with variable contact time, the present work contains significant implications for hydrate applications in flow assurance.

  14. Indium adhesion provides quantitative measure of surface cleanliness

    NASA Technical Reports Server (NTRS)

    Krieger, G. L.; Wilson, G. J.

    1968-01-01

    Indium tipped probe measures hydrophobic and hydrophilic contaminants on rough and smooth surfaces. The force needed to pull the indium tip, which adheres to a clean surface, away from the surface provides a quantitative measure of cleanliness.

  15. Measuring the force of drag on air sheared sessile drops

    NASA Astrophysics Data System (ADS)

    Milne, Andrew J. B.; Fleck, Brian; Amirfazli, Alidad

    2012-11-01

    To blow a drop along or off of a surface (i.e. to shed the drop), the drag force on the drop (based on flow conditions, drop shape, and fluid properties) must overcome the adhesion force between the drop and the surface (based on surface tension, drop shape, and contact angle). While the shedding of sessile drops by shear flow has been studied [Milne, A. J. B. & Amirfazli, A. Langmuir 25, 14155 (2009).], no independent measurements of the drag or adhesion forces have been made. Likewise, analytic predictions are limited to hemispherical drops and low air velocities. We present, therefore, measurements of the drag force on sessile drops at air velocities up to the point of incipient motion. Measurements were made using a modified floating element shear sensor in a laminar low speed wind tunnel to record drag force over the surface with the drop absent, and over the combined system of the surface and drop partially immersed in the boundary layer. Surfaces of different wettabilities were used to study the effects of drop shape and contact angles, with drop volume ranged between approximately 10 and 100 microlitres. The drag force for incipient motion (which by definition equals the maximum of the adhesion force) is compared to simplified models for drop adhesion such as that of Furmidge

  16. Frictional forces and surface topography of a new ceramic bracket.

    PubMed

    Tanne, K; Matsubara, S; Hotei, Y; Sakuda, M; Yoshida, M

    1994-09-01

    The present study was designed to measure the frictional forces between orthodontic wires and a new ceramic bracket and to investigate the differences in the frictional forces with the new and two previously available ceramic brackets. Frictional forces were measured during the sliding of 0.016 x 0.022-inch and 0.017 x 0.022-inch cobalt-chromium alloy wire through three brackets bonded to a simulated tooth. The wires were not ligated into the brackets, so as to eliminate the influences of ligation on the bracket-wire friction. Further, slot surfaces of the three brackets were examined by scanning electron microscope (SEM). The magnitude of frictional forces produced by the new ceramic bracket was significantly less for both the wires than that produced by the two ceramic brackets at 1% level of confidence. The frictional forces with all the brackets exhibited a slight increase as the wire size became larger. The magnitude of frictional forces decreased substantially as the retraction point shifted more cervically. Slot surfaces of the new ceramic bracket were substantially smoother than those surfaces of the two other ceramic brackets. It is shown that refinements of slot surfaces of the ceramic bracket may be effective to reduce friction, although the bracket-wire frictions in this in vitro study were somewhat underestimated because of the lack of ligation of the wire into the bracket.

  17. Measurement of non-monotonic Casimir forces between silicon nanostructures

    NASA Astrophysics Data System (ADS)

    Tang, L.; Wang, M.; Ng, C. Y.; Nikolic, M.; Chan, C. T.; Rodriguez, A. W.; Chan, H. B.

    2017-01-01

    Casimir forces are of fundamental interest because they originate from quantum fluctuations of the electromagnetic field. Apart from controlling this force via the optical properties of materials, a number of novel geometries have been proposed to generate repulsive and/or non-monotonic Casimir forces between bodies separated by vacuum gaps. Experimental realization of these geometries, however, is hindered by the difficulties in alignment when the bodies are brought into close proximity. Here, using an on-chip platform with integrated force sensors and actuators, we circumvent the alignment problem and measure the Casimir force between two surfaces with nanoscale protrusions. We demonstrate that the force depends non-monotonically on the displacement. At some displacements, the Casimir force leads to an effective stiffening of the nanomechanical spring. Our findings pave the way for exploiting the Casimir force in nanomechanical systems using structures of complex and non-conventional shapes.

  18. Influence of surface roughness on dispersion forces.

    PubMed

    Svetovoy, V B; Palasantzas, G

    2015-02-01

    Surface roughness occurs in a wide variety of processes where it is both difficult to avoid and control. When two bodies are separated by a small distance the roughness starts to play an important role in the interaction between the bodies, their adhesion, and friction. Control of this short-distance interaction is crucial for micro and nanoelectromechanical devices, microfluidics, and for micro and nanotechnology. An important short-distance interaction is the dispersion forces, which are omnipresent due to their quantum origin. These forces between flat bodies can be described by the Lifshitz theory that takes into account the actual optical properties of interacting materials. However, this theory cannot describe rough bodies. The problem is complicated by the nonadditivity of the dispersion forces. Evaluation of the roughness effect becomes extremely difficult when roughness is comparable with the distance between bodies. In this paper we review the current state of the problem. Introduction for non-experts to physical origin of the dispersion forces is given in the paper. Critical experiments demonstrating the nonadditivity of the forces and strong influence of roughness on the interaction between bodies are reviewed. We also describe existing theoretical approaches to the problem. Recent advances in understanding the role of high asperities on the forces at distances close to contact are emphasized. Finally, some opinions about currently unsolved problems are also presented.

  19. Knee joint forces: prediction, measurement, and significance

    PubMed Central

    D’Lima, Darryl D.; Fregly, Benjamin J.; Patil, Shantanu; Steklov, Nikolai; Colwell, Clifford W.

    2011-01-01

    Knee forces are highly significant in osteoarthritis and in the survival and function of knee arthroplasty. A large number of studies have attempted to estimate forces around the knee during various activities. Several approaches have been used to relate knee kinematics and external forces to internal joint contact forces, the most popular being inverse dynamics, forward dynamics, and static body analyses. Knee forces have also been measured in vivo after knee arthroplasty, which serves as valuable validation of computational predictions. This review summarizes the results of published studies that measured knee forces for various activities. The efficacy of various methods to alter knee force distribution, such as gait modification, orthotics, walking aids, and custom treadmills are analyzed. Current gaps in our knowledge are identified and directions for future research in this area are outlined. PMID:22468461

  20. Isoelectric point of fluorite by direct force measurements using atomic force microscopy.

    PubMed

    Assemi, Shoeleh; Nalaskowski, Jakub; Miller, Jan D; Johnson, William P

    2006-02-14

    Interaction forces between a fluorite (CaF2) surface and colloidal silica were measured by atomic force microscopy (AFM) in 1 x 10(-3) M NaNO3 at different pH values. Forces between the silica colloid and fluorite flat were measured at a range of pH values above the isoelectric point (IEP) of silica so that the forces were mainly controlled by the fluorite surface charge. In this way, the IEP of the fluorite surface was deduced from AFM force curves at pH approximately 9.2. Experimental force versus separation distance curves were in good agreement with theoretical predictions based on long-range electrostatic interactions, allowing the potential of the fluorite surface to be estimated from the experimental force curves. AFM-deduced surface potentials were generally lower than the published zeta potentials obtained from electrokinetic methods for powdered samples. Differences in methodology, orientation of the fluorite, surface carbonation, and equilibration time all could have contributed to this difference.

  1. Intermolecular forces and scaling relations between heterogeneous macromolecular surfaces

    NASA Astrophysics Data System (ADS)

    Rosenberg, Kenneth J.

    Most theories regarding the behavior of intermolecular forces assume perfectly smooth surfaces with well-defined chemical and material properties. In this thesis, three separate systems are studied to explore the accuracy of this assumption in very different situations. In the first system, the effects of milli-molar amounts of dissolved gas (the amount typically present in normal atmospheric conditions) have been studied at a pristine oil/water interface. It was found that the removal of the dissolved gas significantly increased the lifetime of the oil droplets, effectively reducing the long-range hydrophobic attractive force present under standard conditions. In the second system, the effect of varying normal and lateral roughness of solid surfaces in understanding the long-range steric forces and shorter-range adhesive (van der Waals) forces are studied. Various techniques to reproducibly control and vary the roughness were developed for a number of different types of polymeric surfaces. A strong correlation between the roughness and the repulsive steric force was observed for randomly rough surfaces. Similar scaling relations between the roughness and the magnitude of the adhesive force were measured. Friction measurements between these surfaces show that even a few nanometers of roughness significantly reduces the critical shear stress required to initiate sliding. However, the coefficient of friction was relatively unaffected by the range of roughness considered, in agreement with the macroscopic Amontons' law. The third and final system dealt with the properties of adsorbed layers of polyampholytes (containing both positively and negatively charged groups), as opposed to the more common classes of neutral polymers or polyelectrolytes. These measurements took advantage of a naturally occurring family of proteins (a class of polyampholytes), known as tau, which exist in six different well-defined lengths and charge densities. Force measurements were made with

  2. Axial force measurement for esophageal function testing

    PubMed Central

    Gravesen, Flemming H; Funch-Jensen, Peter; Gregersen, Hans; Drewes, Asbjørn Mohr

    2009-01-01

    The esophagus serves to transport food and fluid from the pharynx to the stomach. Manometry has been the “golden standard” for the diagnosis of esophageal motility diseases for many decades. Hence, esophageal function is normally evaluated by means of manometry even though it reflects the squeeze force (force in radial direction) whereas the bolus moves along the length of esophagus in a distal direction. Force measurements in the longitudinal (axial) direction provide a more direct measure of esophageal transport function. The technique used to record axial force has developed from external force transducers over in-vivo strain gauges of various sizes to electrical impedance based measurements. The amplitude and duration of the axial force has been shown to be as reliable as manometry. Normal, as well as abnormal, manometric recordings occur with normal bolus transit, which have been documented using imaging modalities such as radiography and scintigraphy. This inconsistency using manometry has also been documented by axial force recordings. This underlines the lack of information when diagnostics are based on manometry alone. Increasing the volume of a bag mounted on a probe with combined axial force and manometry recordings showed that axial force amplitude increased by 130% in contrast to an increase of 30% using manometry. Using axial force in combination with manometry provides a more complete picture of esophageal motility, and the current paper outlines the advantages of using this method. PMID:19132762

  3. Measurement of surface microtopography

    NASA Technical Reports Server (NTRS)

    Wall, S. D.; Farr, T. G.; Muller, J.-P.; Lewis, P.; Leberl, F. W.

    1991-01-01

    Acquisition of ground truth data for use in microwave interaction modeling requires measurement of surface roughness sampled at intervals comparable to a fraction of the microwave wavelength and extensive enough to adequately represent the statistics of a surface unit. Sub-centimetric measurement accuracy is thus required over large areas, and existing techniques are usually inadequate. A technique is discussed for acquiring the necessary photogrammetric data using twin film cameras mounted on a helicopter. In an attempt to eliminate tedious data reduction, an automated technique was applied to the helicopter photographs, and results were compared to those produced by conventional stereogrammetry. Derived root-mean-square (RMS) roughness for the same stereo-pair was 7.5 cm for the automated technique versus 6.5 cm for the manual method. The principal source of error is probably due to vegetation in the scene, which affects the automated technique but is ignored by a human operator.

  4. Surface force spectroscopic point load measurements and viscoelastic modelling of the micromechanical properties of air flow sensitive hairs of a spider (Cupiennius salei)

    PubMed Central

    McConney, Michael E.; Schaber, Clemens F.; Julian, Michael D.; Eberhardt, William C.; Humphrey, Joseph A.C.; Barth, Friedrich G.; Tsukruk, Vladimir V.

    2009-01-01

    The micromechanical properties of spider air flow hair sensilla (trichobothria) were characterized with nanometre resolution using surface force spectroscopy (SFS) under conditions of different constant deflection angular velocities (rad s−1) for hairs 900–950 μm long prior to shortening for measurement purposes. In the range of angular velocities examined (4×10−4−2.6×10−1 rad s−1), the torque T (Nm) resisting hair motion and its time rate of change (Nm s−1) were found to vary with deflection velocity according to power functions. In this range of angular velocities, the motion of the hair is most accurately captured by a three-parameter solid model, which numerically describes the properties of the hair suspension. A fit of the three-parameter model (3p) to the experimental data yielded the two torsional restoring parameters, S 3p=2.91×10−11 Nm rad−1 and =2.77×10−11 Nm rad−1 and the damping parameter R 3p=1.46×10−12 Nm s rad−1. For angular velocities larger than 0.05 rad s−1, which are common under natural conditions, a more accurate angular momentum equation was found to be given by a two-parameter Kelvin solid model. For this case, the multiple regression fit yielded S 2p=4.89×10−11 Nm rad−1 and R 2p=2.83×10−14 Nm s rad−1 for the model parameters. While the two-parameter model has been used extensively in earlier work primarily at high hair angular velocities, to correctly capture the motion of the hair at both low and high angular velocities it is necessary to employ the three-parameter model. It is suggested that the viscoelastic mechanical properties of the hair suspension work to promote the phasic response behaviour of the sensilla. PMID:19091682

  5. Determination of dynamic surface forces using piezoelectric arrays

    NASA Astrophysics Data System (ADS)

    Nitsche, W.; Mirow, P.

    The experimental determination of static and dynamic surface forces on flow bodies using piezoelectric arrays is outlined. The fundamentals of the piezo-array sensor technique (sensor construction, signal separation, and signal transmission) are presented. Practical applications of piezo-arrays in the fields of airfoil aerodynamics and general flow investigations are explained. The obtained measuring results are purely qualitative.

  6. Influence of aerosols on surface reaching spectral irradiance and introduction to a new technique for estimating aerosol radiative forcing from spectral flux measurements

    NASA Astrophysics Data System (ADS)

    Rao, R. R.

    2015-12-01

    Aerosol radiative forcing estimates with high certainty are required in climate change studies. The approach in estimating the aerosol radiative forcing by using the chemical composition of aerosols is not effective as the chemical composition data with radiative properties are not widely available. In this study we look into the approach where ground based spectral radiation flux measurements along with an RT model is used to estimate radiative forcing. Measurements of spectral flux were made using an ASD spectroradiometer with 350 - 1050 nm wavelength range and 3nm resolution for around 54 clear-sky days during which AOD range was around 0.1 to 0.7. Simultaneous measurements of black carbon were also made using Aethalometer (Magee Scientific) which ranged from around 1.5 ug/m3 to 8 ug/m3. All the measurements were made in the campus of Indian Institute of Science which is in the heart of Bangalore city. The primary study involved in understanding the sensitivity of spectral flux to change in the mass concentration of individual aerosol species (Optical properties of Aerosols and Clouds -OPAC classified aerosol species) using the SBDART RT model. This made us clearly distinguish the region of influence of different aerosol species on the spectral flux. Following this, a new technique has been introduced to estimate an optically equivalent mixture of aerosol species for the given location. The new method involves an iterative process where the mixture of aerosol species are changed in OPAC model and RT model is run as long as the mixture which mimics the measured spectral flux within 2-3% deviation from measured spectral flux is obtained. Using the optically equivalent aerosol mixture and RT model aerosol radiative forcing is estimated. The new method is limited to clear sky scenes and its accuracy to derive an optically equivalent aerosol mixture reduces when diffuse component of flux increases. Our analysis also showed that direct component of spectral flux is

  7. Laser Photon Force Measurements using a CW Laser

    NASA Technical Reports Server (NTRS)

    Gray, Perry; Edwards, David L.; Carruth, M. Ralph, Jr.; Munafo, Paul M. (Technical Monitor)

    2002-01-01

    The photon force resulting from the non-damaging impact of laser derived photons on a metallic target was measured using a vacuum compatible microbalance. This experiment quantitatively verified that the force resulting from laser photons impacting a reflective surface is measurable and predictable. The photon wavelength is 1064 mn and the laser is a multi-mode 30OW Nd YAG continuous wave (CW) laser.

  8. Measurement of edgewise torque force in vitro.

    PubMed

    Steyn, C L

    1977-05-01

    The construction of a model for the measurement of palatal root torque is described. It was demonstrated that: 1. Halfway between the apex of a tooth and the arch wire the force was double that which was delivered at the apex. 2. The lateral incisors were subjected to appreciably more force than the central incisors. 3. The smaller the number of teeth acted upon, the greater the force they received.

  9. Force Measurement Device for ARIANE 5 Payloads

    NASA Astrophysics Data System (ADS)

    Brunner, O.; Braeken, R.

    2004-08-01

    ESTEC uses since 1991 a Force Measurement Device (FMD) for the measurement of dynamic mechanical forces and moments. This tool allows the determination of forces and moments applied to the test hardware at its interface to the test facilities during dynamic testing. Three forces and three moments are calculated from the measurements of eight tri-axial force links and used to either characterize the dynamic mechanical behaviour of the test item and/or to control forces and moments during vibration testing (force limited vibration control). The current FMD is limited to test items with an interface diameter of up to about 1.2 m (adapter already available) and a mass compatible with ARIANE 4 payloads. The limitations of the current system come from the maximum of eight tri-axial force links and from the analogue technique of the Signal Processing Unit (SPU) that allows only a limited number of geometric configurations for the mechanical interface. Following the success of the FMD during former test campaigns, e.g. ROSETTA STM + FM, the need for a FMD, compatible with ARIANE 5 payloads has been established. Therefore ESA decided to develop a new FMD system. The system will include a digital real time SPU with 72 force input channels, corresponding to 24 tri-axes force sensors or 72 mono axial force sensors. The SPU design will allow extending the number of force input channels to 144. The set-up of the FMD will be done via a standard PC interface. The user will enter for each force sensor the location and the measurement direction in the reference coordinate system. Based on the geometrical information and the maximum forces and moments expected the PC will calculate the optimum range settings for the charge-amplifiers and the corresponding matrix with weighting factors which will allow to perform a fast calculation of the six output forces and moments from the 72 (or 144) input forces. The six output channels with forces and moments can then be connected either to the

  10. Force measurement enabling precise analysis by dynamic force spectroscopy.

    PubMed

    Taninaka, Atsushi; Hirano, Yuuichi; Takeuchi, Osamu; Shigekawa, Hidemi

    2012-01-01

    Dynamic force spectroscopy (DFS) makes it possible to investigate specific interactions between two molecules such as ligand-receptor pairs at the single-molecule level. In the DFS method based on the Bell-Evans model, the unbinding force applied to a molecular bond is increased at a constant rate, and the force required to rupture the molecular bond is measured. By analyzing the relationship between the modal rupture force and the logarithm of the loading rate, microscopic potential barrier landscapes and the lifetimes of bonds can be obtained. However, the results obtained, for example, in the case of streptavidin/biotin complexes, have differed among previous studies and some results have been inconsistent with theoretical predictions. In this study, using an atomic force microscopy technique that enables the precise analysis of molecular interactions on the basis of DFS, we investigated the effect of the sampling rate on DFS analysis. The shape of rupture force histograms, for example, was significantly deformed at a sampling rate of 1 kHz in comparison with that of histograms obtained at 100 kHz, indicating the fundamental importance of ensuring suitable experimental conditions for further advances in the DFS method.

  11. Augmented Computer Mouse Would Measure Applied Force

    NASA Technical Reports Server (NTRS)

    Li, Larry C. H.

    1993-01-01

    Proposed computer mouse measures force of contact applied by user. Adds another dimension to two-dimensional-position-measuring capability of conventional computer mouse; force measurement designated to represent any desired continuously variable function of time and position, such as control force, acceleration, velocity, or position along axis perpendicular to computer video display. Proposed mouse enhances sense of realism and intuition in interaction between operator and computer. Useful in such applications as three-dimensional computer graphics, computer games, and mathematical modeling of dynamics.

  12. Measurement and analysis of forces in grinding of silicon nitride

    SciTech Connect

    Jahanmir, S.; Hwang, T.; Whitenton, E.P.; Job, L.S.; Evans, C.J.

    1995-12-31

    Using an instrumented surface grinder, the two components of grinding forces (normal and tangential) were measured for different types of silicon nitride ceramics. The influences of grinding parameters, such as down feed and table speed, and grinding fluids on forces were determined. In addition to these measurements, the specific grinding energy defined as the energy per unit volume of removed material was calculated. This parameter and the measured forces were then analyzed to determine possible correlations with mechanical properties of the silicon nitrides. It was found that, in general, the grinding forces and the specific grinding energy increase with the hardness. Both the grinding forces and the specific grinding energy were influenced by the grinding fluid and the grinding parameters. The implication of these results on the mechanisms of material removal in grinding of silicon nitride and the possible tribological effects are discussed.

  13. Phoretic Force Measurement for Microparticles Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Davis, E. J.; Zheng, R.

    1999-01-01

    This theoretical and experimental investigation of the collisional interactions between gas molecules and solid and liquid surfaces of microparticles involves fundamental studies of the transfer of energy, mass and momentum between gas molecules and surfaces. The numerous applications include particle deposition on semiconductor surfaces and on surfaces in combustion processes, containerless processing, the production of nanophase materials, pigments and ceramic precursors, and pollution abatement technologies such as desulfurization of gaseous effluents from combustion processes. Of particular emphasis are the forces exerted on microparticles present in a nonuniform gas, that is, in gaseous surroundings involving temperature and concentration gradients. These so-called phoretic forces become the dominant forces when the gravitational force is diminished, and they are strongly dependent on the momentum transfer between gas molecules and the surface. The momentum transfer, in turn, depends on the gas and particle properties and the mean free path and kinetic energy of the gas molecules. The experimental program involves the particle levitation system shown. A micrometer size particle is held between two heat exchangers enclosed in a vacuum chamber by means of ac and dc electric fields. The ac field keeps the particle centered on the vertical axis of the chamber, and the dc field balances the gravitational force and the thermophoretic force. Some measurements of the thermophoretic force are presented in this paper.

  14. Micromechanical apparatus for measurement of forces

    DOEpatents

    Tanner, Danelle Mary; Allen, James Joe

    2004-05-25

    A new class of micromechanical dynamometers has been disclosed which are particularly suited to fabrication in parallel with other microelectromechanical apparatus. Forces in the microNewton regime and below can be measured with such dynamometers which are based on a high-compliance deflection element (e.g. a ring or annulus) suspended above a substrate for deflection by an applied force, and one or more distance scales for optically measuring the deflection.

  15. Forced wetting of a reactive surface.

    PubMed

    Blake, T D

    2012-11-01

    The dynamic wetting of water on gelatin-coated poly(ethylene terephthalate) (GC-PET) has been investigated by forced wetting over a wide speed range and compared with earlier data obtained with unmodified PET. The results were analysed according to the molecular-kinetic theory of dynamic wetting (MKT). Both substrates show complex behaviour, with separate low- and high-speed modes. For the GC-PET, this is attributed to a rapid change in the wettability of the substrate on contact with water, specifically a surface molecular transformation from hydrophobic to hydrophilic. This results in a smooth wetting transition from one mode to the other. For the PET, the bimodal behaviour is attributed to surface heterogeneity, with the low-speed dynamics dominated by interactions with polar sites on the substrate that become masked at higher speeds. In this case, the transition is discontinuous. The study has general ramifications for the investigation of any wetting processes in which a physicochemical transformation takes place at the solid surface on contact with the liquid. In particular, it shows how forced wetting, combined with the MKT, can reveal subtle details of the processes involved. It is unlikely that similar insight could be gained from spontaneous wetting studies, such as spreading drops.

  16. Instrument for measuring human biting force

    NASA Astrophysics Data System (ADS)

    Kopola, Harri K.; Mantyla, Olavi; Makiniemi, Matti; Mahonen, Kalevi; Virtanen, Kauko

    1995-02-01

    Alongside EMG activity, biting force is the primary parameter used for assessing the biting problems of dentulous patients and patients with dentures. In a highly conductive oral cavity, dielectric measurement methods are preferred, for safety reasons. The maximum biting force for patients with removable dentures is not more than 100 ... 300 N. We report here on an instrument developed for measuring human biting force which consists of three units: a mouthpiece, a signal processing and interface unit (SPI), and a PC. The mouthpiece comprises a sensor head of thickness 3.4 mm, width 20 mm and length 30 mm constructed of two stainless steel plates and with a fiber optic microbending sensor between them. This is connected to the SPI unit by a three-meter fiber optic cable, and the SPI unit to the PC by an RS connection. A computer program has been developed that includes measurement, display, zeroing, and calibration operations. The instrument measures biting force as a function of time and displays the time-dependent force profile and maximum force on a screen or plots it in hard copy. The dynamic measurement range of the mouthpiece is from 0 to 1000 N, and the resolution of the instrument is 10 N. The results of preliminary clinical measurements and repeatability tests are reported.

  17. Force measurements in skinned muscle fibres

    PubMed Central

    Hellam, D. C.; Podolsky, R. J.

    1969-01-01

    1. Isometric force was measured in skinned segments of frog semitendinosus muscle fibres exposed to solutions in which the calcium ion concentration was controlled with EGTA. 2. The threshold for force development, calculated from an apparent stability constant for the CaEGTA complex of 106.69 M-1 at pH 7·0, was generally close to pCa 7·5. Maximum force was reached at about pCa 6·0. 3. Maximum force is proportional to the cross-sectional area of the fibres. 4. The rate of force development was slower than that expected from simple diffusion of a substance from the bathing solution into the fibre. The delay appears to be due to slow equilibration of the EGTA buffer system during calcium uptake by the sarcoplasmic reticulum. 5. Addition of deoxycholate (DOC) to the bathing solution produced a reversible increase in the rate of force development. The steady force was also increased for values of pCa that gave less than maximum force, which shifted the force—pCa relation toward lower calcium concentrations by about 0·5 pCa unit. 6. The length—force relation in partially activated preparations is similar to that reported for electrically activated intact fibres. This result suggests that in the region of myofilament overlap the affinity of the binding sites for calcium is uniform along the length of the calciumbinding myofilament. PMID:5765859

  18. Atomic force microscopy study of tooth surfaces.

    PubMed

    Farina, M; Schemmel, A; Weissmüller, G; Cruz, R; Kachar, B; Bisch, P M

    1999-03-01

    Atomic force microscopy (AFM) was used to study tooth surfaces in order to compare the pattern of particle distribution in the outermost layer of the tooth surfaces. Human teeth and teeth from a rodent (Golden hamster), from a fish (piranha), and from a grazing mollusk (chiton) with distinct feeding habits were analyzed in terms of particle arrangement, packing, and size distribution. Scanning electron microscopy and transmission electron microscopy were used for comparison. It was found that AFM gives high-contrast, high-resolution images and is an important tool as a source of complementary and/or new structural information. All teeth were cleaned and some were etched with acidic solutions before analysis. It was observed that human enamel (permanent teeth) presents particles tightly packed in the outer surface, whereas enamel from the hamster (continuously growing teeth) shows particles of less dense packing. The piranha teeth have a thin cuticle covering the long apatite crystals of the underlying enameloid. This cuticle has a rough surface of particles that have a globular appearance after the brief acidic treatment. The similar appearance of the in vivo naturally etched tooth surface suggests that the pattern of globule distribution may be due to the presence of an organic material. Elemental analysis of this cuticle indicated that calcium, phosphorus, and iron are the main components of the structure while electron microdiffraction of pulverized cuticle particles showed a pattern consistent with hydroxyapatite. The chiton mineralized tooth cusp had a smooth surface in an unabraded region and a very rough structure with the magnetite crystals (already known to make part of the structure) protruding from the surface. It was concluded that the structures analyzed are optimized for efficiency in feeding mechanism and life span of the teeth.

  19. Measurement of tool forces in diamond turning

    SciTech Connect

    Drescher, J.; Dow, T.A.

    1988-12-01

    A dynamometer has been designed and built to measure forces in diamond turning. The design includes a 3-component, piezoelectric transducer. Initial experiments with this dynamometer system included verification of its predicted dynamic characteristics as well as a detailed study of cutting parameters. Many cutting experiments have been conducted on OFHC Copper and 6061-T6 Aluminum. Tests have involved investigation of velocity effects, and the effects of depth and feedrate on tool forces. Velocity has been determined to have negligible effects between 4 and 21 m/s. Forces generally increase with increasing depth of cut. Increasing feedrate does not necessarily lead to higher forces. Results suggest that a simple model may not be sufficient to describe the forces produced in the diamond turning process.

  20. Fusion of intraoperative force sensoring, surface reconstruction and biomechanical modeling

    NASA Astrophysics Data System (ADS)

    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.

  1. Probing surface adhesion forces of Enterococcus faecalis to medical-grade polymers using atomic force microscopy.

    PubMed

    Sénéchal, Annie; Carrigan, Shawn D; Tabrizian, Maryam

    2004-05-11

    The aim of this study was to compare the initial adhesion forces of the uropathogen Enterococcus faecalis with the medical-grade polymers polyurethane (PU), polyamide (PA), and poly(tetrafluoroethylene) (PTFE). To quantify the cell-substrate adhesion forces, a method was developed using atomic force microscopy (AFM) in liquid that allows for the detachment of individual live cells from a polymeric surface through the application of increasing force using unmodified cantilever tips. Results show that the lateral force required to detach E. faecalis cells from a substrate differed depending on the nature of the polymeric surface: a force of 19 +/- 4 nN was required to detach cells from PU, 6 +/- 4 nN from PA, and 0.7 +/- 0.3 nN from PTFE. Among the unfluorinated polymers (PU and PA), surface wettability was inversely proportional to the strength of adhesion. AFM images also demonstrated qualitative differences in bacterial adhesion; PU was covered by clusters of cells with few cell singlets present, whereas PA was predominantly covered by individual cells. Moreover, extracellular material could be observed on some clusters of PU-adhered cells as well as in the adjacent region surrounding cells adhered on PA. E. faecalis adhesion to the fluorinated polymer (PTFE) showed different characteristics; only a few individual cells were found, and bacteria were easily damaged, and thus detached, by the tip. This work demonstrates the utility of AFM for measurement of cell-substrate lateral adhesion forces and the contribution these forces make toward understanding the initial stages of bacterial adhesion. Further, it suggests that initial adhesion can be controlled, through appropriate biomaterial design, to prevent subsequent formation of aggregates and biofilms.

  2. Measurements of human force control during a constrained arm motion using a force-actuated joystick.

    PubMed

    McIntyre, J; Gurfinkel, E V; Lipshits, M I; Droulez, J; Gurfinkel, V S

    1995-03-01

    1. When interacting with the environment, human arm movements may be prevented in certain directions (i.e., when sliding the hand along a surface) resulting in what is called a "constrained motion." In the directions that the movement is restricted, the subject is instead free to control the forces against the constraint. 2. Control strategies for constrained motion may be characterized by two extreme models. Under the active compliance model, an essentially feedback-based approach, measurements of contact force may be used in real time to modify the motor command and precisely control the forces generated against the constraint. Under the passive compliance model the motion would be executed in a feedforward manner, using an internal model of the constraint geometry. The feedforward model relies on the compliant behavior of the passive mechanical system to maintain contact while avoiding excessive contact forces. 3. Subjects performed a task in which they were required to slide the hand along a rigid surface. This task was performed in a virtual force environment in which contact forces were simulated by a two-dimensional force-actuated joystick. Unknown to the subject, the orientation of the surface constraint was varied from trial to trial, and contact force changes induced by these perturbations were measured. 4. Subjects showed variations in contact force correlated with the direction of the orientation perturbation. "Upward" tilts resulted in higher contact forces, whereas "downward" tilts resulted in lower contact forces. This result is consistent with a feedforward-based control of a passively compliant system. 5. Subject responses did not, however, correspond exactly to the predictions of a static analysis of a passive, feedforward-controlled system. A dynamic analysis reveals a much closer resemblance between a passive, feedforward model and the observed data. Numerical simulations demonstrate that a passive, dynamic system model of the movement captures

  3. The Kilogram and Measurements of Mass and Force

    PubMed Central

    Jabbour, Z. J.; Yaniv, S. L.

    2001-01-01

    This paper describes the facilities, measurement capabilities, and ongoing research activities in the areas of mass and force at the National Institute of Standards and Technology (NIST). The first section of the paper is devoted to mass metrology and starts with a brief historical perspective on the developments that led to the current definition of the kilogram. An overview of mass measurement procedures is given with a brief discussion of current research on alternative materials for mass standards and surface profiles of the U.S. national prototype kilograms. A brief outlook into the future possible redefinition of the unit of mass based on fundamental principles is included. The second part of this paper focuses on the unit of force and describes the realization of the unit, measurement procedures, uncertainty in the realized force, facilities, and current efforts aimed at the realization of small forces. PMID:27500016

  4. Surface energy budget responses to radiative forcing at Summit, Greenland

    NASA Astrophysics Data System (ADS)

    Miller, Nathaniel B.; Shupe, Matthew D.; Cox, Christopher J.; Noone, David; Persson, P. Ola G.; Steffen, Konrad

    2017-02-01

    Greenland Ice Sheet surface temperatures are controlled by an exchange of energy at the surface, which includes radiative, turbulent, and ground heat fluxes. Data collected by multiple projects are leveraged to calculate all surface energy budget (SEB) terms at Summit, Greenland, for the full annual cycle from July 2013 to June 2014 and extend to longer periods for the radiative and turbulent SEB terms. Radiative fluxes are measured directly by a suite of broadband radiometers. Turbulent sensible heat flux is estimated via the bulk aerodynamic and eddy correlation methods, and the turbulent latent heat flux is calculated via a two-level approach using measurements at 10 and 2 m. The subsurface heat flux is calculated using a string of thermistors buried in the snow pack. Extensive quality-control data processing produced a data set in which all terms of the SEB are present 75 % of the full annual cycle, despite the harsh conditions. By including a storage term for a near-surface layer, the SEB is balanced in this data set to within the aggregated uncertainties for the individual terms. November and August case studies illustrate that surface radiative forcing is driven by synoptically forced cloud characteristics, especially by low-level, liquid-bearing clouds. The annual cycle and seasonal diurnal cycles of all SEB components indicate that the non-radiative terms are anticorrelated to changes in the total radiative flux and are hence responding to cloud radiative forcing. Generally, the non-radiative SEB terms and the upwelling longwave radiation component compensate for changes in downwelling radiation, although exact partitioning of energy in the response terms varies with season and near-surface characteristics such as stability and moisture availability. Substantial surface warming from low-level clouds typically leads to a change from a very stable to a weakly stable near-surface regime with no solar radiation or from a weakly stable to neutral

  5. A force plate system for measuring low-magnitude reaction forces in small laboratory animals.

    PubMed

    Handley, D E; Ross, J F; Carr, G J

    1998-07-01

    We present a force plate system which measures low-magnitude vertical reaction forces generated by small laboratory animals. The force plate mechanical design minimizes radiated transverse waves, acoustic reverberation, and standing waves caused by impacts on the force plate surface. A secondary force plate and PC-based software algorithm minimize floor vibrational artifact. The force plate was used to measure function of rats during two tests: forelimb/hindlimb hopping reaction and surface righting reaction. In control rats, forelimb hopping rate exceeded hindlimb hopping rate during 16 weeks of repeated testing. Subchronic intraperitoneal (i.p.) dosing of 10 mg/kg/day acrylamide produced a selective impairment of hindlimb hopping. In contrast, single doses of haloperidol (1-5 mg/kg, i.p.) slowed the righting reaction and produced a relatively selective impairment of forelimb hopping. The force plate system presents new opportunities for performing quantitative neurological assessments of small laboratory animals when previously such tests had been performed subjectively and qualitatively.

  6. Armor Plate Surface Roughness Measurements

    DTIC Science & Technology

    2005-04-01

    Armor Plate Surface Roughness Measurements by Brian Stanton, William Coburn, and Thomas J. Pizzillo ARL-TR-3498 April 2005... Armor Plate Surface Roughness Measurements Brian Stanton, William Coburn and Thomas J. Pizzillo Sensors and Electron Devices Directorate...October 2004 5a. CONTRACT NUMBER 5b. GRANT NUMBER 4. TITLE AND SUBTITLE Armor Plate Surface Roughness Measurements 5c. PROGRAM ELEMENT NUMBER

  7. Does an instrumented treadmill correctly measure the ground reaction forces?

    PubMed Central

    Willems, Patrick A.; Gosseye, Thierry P.

    2013-01-01

    Summary Since the 1990s, treadmills have been equipped with multi-axis force transducers to measure the three components of the ground reaction forces during walking and running. These measurements are correctly performed if the whole treadmill (including the motor) is mounted on the transducers. In this case, the acceleration of the treadmill centre of mass relative to the reference frame of the laboratory is nil. The external forces exerted on one side of the treadmill are thus equal in magnitude and opposite in direction to the external forces exerted on the other side. However, uncertainty exists about the accuracy of these measures: due to friction between the belt and the tread-surface, due to the motor pulling the belt, some believe that it is not possible to correctly measure the horizontal components of the forces exerted by the feet on the belt. Here, we propose a simple model of an instrumented treadmill and we demonstrate (1) that the forces exerted by the subject moving on the upper part of the treadmill are accurately transmitted to the transducers placed under it and (2) that all internal forces – including friction – between the parts of the treadmill are cancelling each other. PMID:24285705

  8. Measuring the Drag Force on a Falling Ball

    NASA Astrophysics Data System (ADS)

    Cross, Rod; Lindsey, Crawford

    2014-03-01

    The effect of the aerodynamic drag force on an object in flight is well known and has been described in this and other journals many times. At speeds less than about 1 m/s, the drag force on a sphere is proportional to the speed and is given by Stokes' law. At higher speeds, the drag force is proportional to the velocity squared and is usually small compared with the gravitational force if the object mass is large and its speed is low. In order to observe a significant effect, or to measure the terminal velocity, experiments are often conducted with very light objects such as a balloon or coffee filter3 or muffin cup,4 or are conducted in a liquid rather than in air. The effect of the drag force can also be increased by increasing the surface area of the object.

  9. Friction of ice measured using lateral force microscopy

    SciTech Connect

    Bluhm, Hendrik; Inoue, Takahito; Salmeron, Miquel

    2000-03-15

    The friction of nanometer thin ice films grown on mica substrates is investigated using atomic force microscopy (AFM). Friction was found to be of similar magnitude as the static friction of ice reported in macroscopic experiments. The possible existence of a lubricating film of water due to pressure melting, frictional heating, and surface premelting is discussed based on the experimental results using noncontact, contact, and lateral force microscopy. We conclude that AFM measures the dry friction of ice due to the low scan speed and the squeezing out of the water layer between the sharp AFM tip and the ice surface. (c) 2000 The American Physical Society.

  10. Surface texture generation during cylindrical milling in the aspect of cutting force variations

    NASA Astrophysics Data System (ADS)

    Wojciechowski, S.; Twardowski, P.; Pelic, M.

    2014-03-01

    The work presented here concentrates on surface texture analysis, after cylindrical milling of hardened steel. Cutting force variations occurring in the machining process have direct influence on the cutter displacements and thus on the generated surface texture. Therefore, in these experiments, the influence of active number of teeth (zc) on the cutting force variations was investigated. Cutting forces and cutter displacements were measured during machining process (online) using, namely piezoelectric force dynamometer and 3D laser vibrometer. Surface roughness parameters were measured using stylus surface profiler. The surface roughness model including cutting parameters (fz, D) and cutting force variations was also developed. The research revealed that in cylindrical milling process, cutting force variations have immediate influence on surface texture generation.

  11. Hydrodynamic boundary conditions and dynamic forces between bubbles and surfaces.

    PubMed

    Manor, Ofer; Vakarelski, Ivan U; Tang, Xiaosong; O'Shea, Sean J; Stevens, Geoffrey W; Grieser, Franz; Dagastine, Raymond R; Chan, Derek Y C

    2008-07-11

    Dynamic forces between a 50 microm radius bubble driven towards and from a mica plate using an atomic force microscope in electrolyte and in surfactant exhibit different hydrodynamic boundary conditions at the bubble surface. In added surfactant, the forces are consistent with the no-slip boundary condition at the mica and bubble surfaces. With no surfactant, a new boundary condition that accounts for the transport of trace surface impurities explains variations of dynamic forces at different speeds and provides a direct connection between dynamic forces and surface transport effects at the air-water interface.

  12. Hydrodynamic Boundary Conditions and Dynamic Forces between Bubbles and Surfaces

    NASA Astrophysics Data System (ADS)

    Manor, Ofer; Vakarelski, Ivan U.; Tang, Xiaosong; O'Shea, Sean J.; Stevens, Geoffrey W.; Grieser, Franz; Dagastine, Raymond R.; Chan, Derek Y. C.

    2008-07-01

    Dynamic forces between a 50μm radius bubble driven towards and from a mica plate using an atomic force microscope in electrolyte and in surfactant exhibit different hydrodynamic boundary conditions at the bubble surface. In added surfactant, the forces are consistent with the no-slip boundary condition at the mica and bubble surfaces. With no surfactant, a new boundary condition that accounts for the transport of trace surface impurities explains variations of dynamic forces at different speeds and provides a direct connection between dynamic forces and surface transport effects at the air-water interface.

  13. Direct Aerosol Radiative Forcing: Calculations and Measurements from the Tropospheric

    NASA Technical Reports Server (NTRS)

    Russell, P. B.; Hignett, P.; Stowe, L. L.; Livingston, J. M.; Kinne, S.; Wong, J.; Chan, K. Roland (Technical Monitor)

    1997-01-01

    Radiative forcing is defined as the change in the net (downwelling minus upwelling) radiative flux at a given level in the atmosphere. This net flux is the radiative power density available to drive climatic processes in the earth-atmosphere system below that level. Recent research shows that radiative forcing by aerosol particles is a major source of uncertainty in climate predictions. To reduce those uncertainties, TARFOX was designed to determine direct (cloud-free) radiative forcing by the aerosols in one of the world's major industrial pollution plumes--that flowing from the east coast of the US over the Atlantic Ocean. TARFOX measured a variety of aerosol radiative effects (including direct forcing) while simultaneously measuring the chemical, physical, and optical properties of the aerosol particles causing those effects. The resulting data sets permit a wide variety of tests of the consistency, or closure, among the measurements and the models that link them. Because climate predictions use the same or similar model components, closure tests help to assess and reduce prediction uncertainties. In this work we use the TARFOX-determined aerosol, gas, and surface properties to compute radiative forcing for a variety of aerosol episodes, with inadvisable optical depths ranging from 0.07 to 0.6. We calculate forcing by several techniques with varying degrees of sophistication, in part to test the range of applicability of simplified techniques--which are often the only ones feasible in climate predictions by general circulation models (GCMs). We then compare computed forcing to that determined from: (1) Upwelling and downwelling fluxes (0.3-0.7 mm and 0.7-3.0 mm) measured by radiometers on the UK MRF C-130. and (2) Daily average cloud-free absorbed solar and emitted thermal radiative flux at the top of the atmosphere derived from the AVHRR radiometer on the NOAA- 14 satellite. The calculations and measurements all yield aerosol direct radiative forcing in the

  14. A MEMS sensor for microscale force measurements

    NASA Astrophysics Data System (ADS)

    Majcherek, S.; Aman, A.; Fochtmann, J.

    2016-02-01

    This paper describes the development and testing of a new MEMS-based sensor device for microscale contact force measurements. A special MEMS cell was developed to reach higher lateral resolution than common steel-based load cells with foil-type strain gauges as mechanical-electrical converters. The design provided more than one normal force measurement point with spatial resolution in submillimeter range. Specific geometric adaption of the MEMS-device allowed adjustability of its measurement range between 0.5 and 5 N. The thin film nickel-chromium piezo resistors were used to achieve a mechanical-electrical conversion. The production process was realized by established silicon processing technologies such as deep reactive ion etching and vapor deposition (sputtering). The sensor was tested in two steps. Firstly, the sensor characteristics were carried out by application of defined loads at the measurement points by a push-pull tester. As a result, the sensor showed linear behavior. A measurement system analysis (MSA1) was performed to define the reliability of the measurement system. The measured force values had the maximal relative deviation of 1% to average value of 1.97 N. Secondly, the sensor was tested under near-industrial conditions. In this context, the thermal induced relaxation behavior of the electrical connector contact springs was investigated. The handling of emerging problems during the characterization process of the sensor is also described.

  15. Critical Casimir forces between homogeneous and chemically striped surfaces.

    PubMed

    Parisen Toldin, Francesco; Tröndle, Matthias; Dietrich, S

    2013-11-01

    Recent experiments have measured the critical Casimir force acting on a colloid immersed in a binary liquid mixture near its continuous demixing phase transition and exposed to a chemically structured substrate. Motivated by these experiments, we study the critical behavior of a system, which belongs to the Ising universality class, for the film geometry with one planar wall chemically striped, such that there is a laterally alternating adsorption preference for the two species of the binary liquid mixture, which is implemented by surface fields. For the opposite wall we employ alternatively a homogeneous adsorption preference or homogeneous Dirichlet boundary conditions, which within a lattice model are realized by open boundary conditions. By means of mean-field theory, Monte Carlo simulations, and finite-size scaling analysis we determine the critical Casimir force acting on the two parallel walls and its corresponding universal scaling function. We show that in the limit of stripe widths small compared with the film thickness, on the striped surface the system effectively realizes Dirichlet boundary conditions, which generically do not hold for actual fluids. Moreover, the critical Casimir force is found to be attractive or repulsive, depending on the width of the stripes of the chemically patterned surface and on the boundary condition applied to the opposing surface.

  16. Intermodulation electrostatic force microscopy for imaging surface photo-voltage

    SciTech Connect

    Borgani, Riccardo Forchheimer, Daniel; Thorén, Per-Anders; Haviland, David B.; Bergqvist, Jonas; Inganäs, Olle

    2014-10-06

    We demonstrate an alternative to Kelvin Probe Force Microscopy for imaging surface potential. The open-loop, single-pass technique applies a low-frequency AC voltage to the atomic force microscopy tip while driving the cantilever near its resonance frequency. Frequency mixing due to the nonlinear capacitance gives intermodulation products of the two drive frequencies near the cantilever resonance, where they are measured with high signal to noise ratio. Analysis of this intermodulation response allows for quantitative reconstruction of the contact potential difference. We derive the theory of the method, validate it with numerical simulation and a control experiment, and we demonstrate its utility for fast imaging of the surface photo-voltage on an organic photo-voltaic material.

  17. Sublattice identification in noncontact atomic force microscopy of the NaCl(001) surface

    SciTech Connect

    Hoffmann, R.; Weiner, D.; Schirmeisen, A.; Foster, A. S.

    2009-09-15

    We compare the three-dimensional force field obtained from frequency-distance measurements above the NaCl(001) surface to atomistic calculations using various tip models. In the experiments, long-range forces cause a total attractive force even on the similarly charged site. Taking force differences between two sites minimizes the influence of such long-range forces. The magnitude of the measured force differences are by a factor of 6.5-10 smaller than the calculated forces. This is an indication that for the particular tip used in this experiment several atoms of the tip interact with the surface atoms at close tip-sample distances. The interaction of these additional atoms with the surface is small at the imaging distance, because symmetric images are obtained. The force distance characteristics resemble those of a negative tip apex ion which could be explained, e.g., by a neutral Si tip.

  18. Quantitative surface parameter maps using Intermodulation Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Forchheimer, Daniel; Platz, Daniel; Tholén, Erik; Hutter, Carsten; Haviland, David

    2011-03-01

    It is well known that the phase image in amplitude modulation atomic force microscopy (AM-AFM) is sensitive to material properties of the surface. However that information is not enough to fully quantify the tip-surface interaction. We have developed Intermodulation AFM, based on a spectral analysis of the cantilever's nonlinear dynamics, which increases the amount of information obtained without increasing scan time. We show how it is possible to extract quantitative material properties of the surface from this additional information. The method works under the assumption of a tip-surface force model, such as the DMT model, fitting the model parameters to the measured spectral data. The parameters are obtained at each pixel of the AFM image and form surface property maps which can be displayed together with topography. We demonstrate this on different surfaces such as polymer blends, extracting stiffness and adhesive properties. D. Platz, E. A. Tholen, D. Pesen, and D. B. Haviland, Appl. Phys. Lett., 92, 153106 (2008)

  19. Quantitative evaluation of interaction force of fibrinogen at well-defined surfaces with various structures.

    PubMed

    Chen, Weixin; Inoue, Yuuki; Ishihara, Kazuhiko

    2014-01-01

    The effects of functional groups and structures at the surface of biomaterials on protein adsorption were examined using direct interaction force measurements. Three kinds of surface structures were evaluated: polymer brushes, self-assembled monolayers with low molecular weight compounds, and surfaces with conventional polymer coatings. These surfaces had various functional groups including phosphorylcholine (PC) group. The surface characterization demonstrated that surface wettability and flexibility depended on both the structure of the surface and the functional groups at the surface. The interactions of protein with these surfaces were evaluated by a force vs. distance curve using an atomic force microscope (AFM). We used fibrinogen as the protein, and the fibrinogen was immobilized on the surface of the AFM cantilever by a conventional technique. It was observed that the interaction force of fibrinogen was strongly related to surface hydrophobic nature and flexibility. That is, the interaction force increased with the increasing hydrophobic nature of the surface. The relationship between the amount of fibrinogen adsorbed on the surface and the interaction force showed good correlation in the range of fibrinogen adsorption from 0 to 250 ng/cm(2), that is, in a monolayered adsorption region. The interaction force decreased with increasing surface viscoelasticity. The most effective surface for preventing fibrinogen adsorption was the polymer brush surface with phosphorylcholine (PC) groups, that is, poly(2-methacryloyloxyethyl phosphorylcholine) brush. The interaction force of this sample was less than 0.1 nN and the amount of fibrinogen adsorbed on the surface was minimal. It was found that the evaluation of protein adsorption based on the interaction force measurement is useful for low-protein adsorption surfaces. It was demonstrated that an extremely hydrophilic and flexible surface could weaken the protein interactions at the surface, resulting in

  20. Measurement methods in atomic force microscopy.

    PubMed

    Torre, Bruno; Canale, Claudio; Ricci, Davide; Braga, Pier Carlo

    2011-01-01

    This chapter is introductory to the measurements: it explains different measurement techniques both for imaging and for force spectroscopy, on which most of the AFM experiments rely. It gives a general overview of the different techniques and of the output expected from the instrument; therefore it is, at a basic level, a good tool to properly start a new experiment. Concepts introduced in this chapter give the base for understanding the applications shown in the following chapters. Subheading 1 introduces the distinction between spectroscopy and imaging experiments and, within the last ones, between DC and AC mode. Subheading 2 is focused on DC mode (contact), explaining the topography and the lateral force channel. Subheading 3 introduces AC mode, both in noncontact and intermittent contact case. Phase imaging and force modulation are also discussed. Subheading 4 explains how the AFM can be used to measure local mechanical and adhesive properties of specimens by means of force spectroscopy technique. An overview on the state of the art and future trends in this field is also given.

  1. Surface roughness measurements

    NASA Astrophysics Data System (ADS)

    Howard, Thomas G.

    1994-10-01

    The Optics Division is currently in the research phase of producing grazing-incidence mirrors to be used in x-ray detector applications. The traditional method of construction involves labor-intensive glass grinding. This also culminates in a relatively heavy mirror. For lower resolution applications, the mirrors may be of a replicated design which involves milling a mandrel as a negative of the final shape and electroplating the cylindrical mirror onto it. The mirror is then separated from the mandrel by cooling. The mandrel will shrink more than the 'shell' (mirror) allowing it to be pulled from the mandrel. Ulmer (2) describes this technique and its variations in more detail. To date, several mirrors have been tested at MSFC by the Optical Fabrication Branch by focusing x-ray energy onto a detector with limited success. Little is known about the surface roughness of the actual mirror. Hence, the attempt to gather data on these surfaces. The test involves profiling the surface of a sample, replicating the surface as described above, and then profiling the replicated surface.

  2. Motion recognition from contact force measurement.

    PubMed

    Yabuki, Takumi; Venture, Gentiane

    2013-01-01

    Optical motion capture systems, which are used in broad fields of research, are costly; they need large installation space and calibrations. We find difficulty in applying it in typical homes and care centers. Therefore we propose to use low cost contact force measurement systems to develop rehabilitation and healthcare monitoring tools. Here, we propose a novel algorithm for motion recognition using the feature vector from force data solely obtained during a daily exercise program. We recognized 7 types of movement (Radio Exercises) of two candidates (mean age 22, male). The results show that the recognition rate of each motion has high score (mean: 86.9%). The results also confirm that there is a clustering of each movement in personal exercises data, and a similarity of the clustering even for different candidates thus that motion recognition is possible using contact force data.

  3. Trends of Measured Climate Forcing Agents

    NASA Technical Reports Server (NTRS)

    Hansen, James E.; Sato, Makiko; Einaudi, Franco (Technical Monitor)

    2002-01-01

    The growth rate of climate forcing by measured greenhouse gases peaked near 1980 at almost 5 W/sq m per century. This growth rate has since declined to approximately equal to 3 W/sq m per century, largely because of cooperative international actions. We argue that trends can be reduced to the level needed for the moderate "alternative" climate scenario (approximately equal to 2 W/M2 per century for the next 50 years) by means of concerted actions that have other benefits, but the forcing reductions are not automatic "co-benefits" of actions that slow CO2 emissions. Current trends of climate forcings by aerosols remain very uncertain. Nevertheless, practical constraints on changes in emission levels suggest that global warming at a rate + 0.15 +/- 0.05 C per decade will occur over the next several decades.

  4. Interaction forces between asphaltene surfaces in organic solvents.

    PubMed

    Wang, Shengqun; Liu, Jianjun; Zhang, Liyan; Masliyah, Jacob; Xu, Zhenghe

    2010-01-05

    The colloidal interactions between asphaltene surfaces in heptol, a mixture of n-heptane and toluene, were studied for the first time by colloidal force measurements using an atomic force microscope (AFM). Asphaltenes were deposited on silica wafers and silica spheres using the Langmuir-Blodgett upstroke technique. The results showed that the ratio of toluene to heptane can significantly change solvent quality in terms of the ability to solubilize asphaltenes and hence the nature and the magnitude of the interaction forces between asphaltene surfaces. In pure toluene, there is a steric long-range repulsion which can be well fitted by the scaling theory of polymer brushes. As toluene volume fraction in heptol (Phi(T)) is gradually decreased from Phi(T) = 1 (pure toluene) to Phi(T) = 0 (pure n-heptane), the steric repulsion reduced and changed to weak attraction when Phi(T) < 0.2. The attraction in heptane can be fitted by van der Waals forces alone which are thus believed to promote asphaltene aggregation, leading to asphaltene precipitation. The results obtained in this study provide an insight into interactions that determine asphaltene behavior in an organic medium and hence in crude oils.

  5. Combined atomic force microscopy and voltage pulse technique to accurately measure electrostatic force

    NASA Astrophysics Data System (ADS)

    Inami, Eiichi; Sugimoto, Yoshiaki

    2016-08-01

    We propose a new method of extracting electrostatic force. The technique is based on frequency modulation atomic force microscopy (FM-AFM) combined with a voltage pulse. In this method, the work that the electrostatic field does on the oscillating tip is measured through the cantilever energy dissipation. This allows us to directly extract capacitive forces including the longer range part, to which the conventional FM-AFM is insensitive. The distance-dependent contact potential difference, which is modulated by local charges distributed on the surfaces of the tip and/or sample, could also be correctly obtained. In the absence of local charges, our method can perfectly reproduce the electrostatic force as a function of the distance and the bias voltage. Furthermore, we demonstrate that the system serves as a sensitive sensor enabling us to check the existence of the local charges such as trapped charges and patch charges.

  6. Forced free-shear layer measurements

    NASA Technical Reports Server (NTRS)

    Leboeuf, Richard L.

    1994-01-01

    Detailed three-dimensional three-component phase averaged measurements of the spanwise and streamwise vorticity formation and evolution in acoustically forced plane free-shear flows have been obtained. For the first time, phase-averaged measurements of all three velocity components have been obtained in both a mixing layer and a wake on three-dimensional grids, yielding the spanwise and streamwise vorticity distributions without invoking Taylor's hypothesis. Initially, two-frequency forcing was used to phase-lock the roll-up and first pairing of the spanwise vortical structures in a plane mixing layer. The objective of this study was to measure the near-field vortical structure morphology in a mixing layer with 'natural' laminar initial boundary layers. For the second experiment the second and third subharmonics of the fundamental roll-up frequency were added to the previous two-frequency forcing in order to phase-lock the roll-up and first three pairings of the spanwise rollers in the mixing layer. The objective of this study was to determine the details of spanwise scale changes observed in previous time-averaged measurements and flow visualization of unforced mixing layers. For the final experiment, single-frequency forcing was used to phase-lock the Karman vortex street in a plane wake developing from nominally two-dimensional laminar initial boundary layers. The objective of this study was to compare measurements of the three-dimensional structure in a wake developing from 'natural' initial boundary layers to existing models of wake vortical structure.

  7. Measurement-only topological quantum computation without forced measurements

    NASA Astrophysics Data System (ADS)

    Zheng, Huaixiu; Dua, Arpit; Jiang, Liang

    2016-12-01

    We investigate the measurement-only topological quantum computation (MOTQC) approach proposed by Bonderson et al (2008 Phys. Rev. Lett. 101 010501) where the braiding operation is shown to be equivalent to a series of topological charge ‘forced measurements’ of anyons. In a forced measurement, the charge measurement is forced to yield the desired outcome (e.g. charge 0) via repeatedly measuring charges in different bases. This is a probabilistic process with a certain success probability for each trial. In practice, the number of measurements needed will vary from run to run. We show that such an uncertainty associated with forced measurements can be removed by simulating the braiding operation using a fixed number of three measurements supplemented by a correction operator. Furthermore, we demonstrate that in practice we can avoid applying the correction operator in hardware by implementing it in software. Our findings greatly simplify the MOTQC proposal and only require the capability of performing charge measurements to implement topologically protected transformations generated by braiding exchanges without physically moving anyons.

  8. Surface temperature measurement errors

    SciTech Connect

    Keltner, N.R.; Beck, J.V.

    1983-05-01

    Mathematical models are developed for the response of surface mounted thermocouples on a thick wall. These models account for the significant causes of errors in both the transient and steady-state response to changes in the wall temperature. In many cases, closed form analytical expressions are given for the response. The cases for which analytical expressions are not obtained can be easily evaluated on a programmable calculator or a small computer.

  9. Modeling and experiments of the adhesion force distribution between particles and a surface.

    PubMed

    You, Siming; Wan, Man Pun

    2014-06-17

    Due to the existence of surface roughness in real surfaces, the adhesion force between particles and the surface where the particles are deposited exhibits certain statistical distributions. Despite the importance of adhesion force distribution in a variety of applications, the current understanding of modeling adhesion force distribution is still limited. In this work, an adhesion force distribution model based on integrating the root-mean-square (RMS) roughness distribution (i.e., the variation of RMS roughness on the surface in terms of location) into recently proposed mean adhesion force models was proposed. The integration was accomplished by statistical analysis and Monte Carlo simulation. A series of centrifuge experiments were conducted to measure the adhesion force distributions between polystyrene particles (146.1 ± 1.99 μm) and various substrates (stainless steel, aluminum and plastic, respectively). The proposed model was validated against the measured adhesion force distributions from this work and another previous study. Based on the proposed model, the effect of RMS roughness distribution on the adhesion force distribution of particles on a rough surface was explored, showing that both the median and standard deviation of adhesion force distribution could be affected by the RMS roughness distribution. The proposed model could predict both van der Waals force and capillary force distributions and consider the multiscale roughness feature, greatly extending the current capability of adhesion force distribution prediction.

  10. A measurement of the hysteresis loop in force-spectroscopy curves using a tuning-fork atomic force microscope.

    PubMed

    Lange, Manfred; van Vörden, Dennis; Möller, Rolf

    2012-01-01

    Measurements of the frequency shift versus distance in noncontact atomic force microscopy (NC-AFM) allow measurements of the force gradient between the oscillating tip and a surface (force-spectroscopy measurements). When nonconservative forces act between the tip apex and the surface the oscillation amplitude is damped. The dissipation is caused by bistabilities in the potential energy surface of the tip-sample system, and the process can be understood as a hysteresis of forces between approach and retraction of the tip. In this paper, we present the direct measurement of the whole hysteresis loop in force-spectroscopy curves at 77 K on the PTCDA/Ag/Si(111) √3 × √3 surface by means of a tuning-fork-based NC-AFM with an oscillation amplitude smaller than the distance range of the hysteresis loop. The hysteresis effect is caused by the making and breaking of a bond between PTCDA molecules on the surface and a PTCDA molecule at the tip. The corresponding energy loss was determined to be 0.57 eV by evaluation of the force-distance curves upon approach and retraction. Furthermore, a second dissipation process was identified through the damping of the oscillation while the molecule on the tip is in contact with the surface. This dissipation process occurs mainly during the retraction of the tip. It reaches a maximum value of about 0.22 eV/cycle.

  11. Combining the effect of crops surface albedo variability on the radiative forcing together with crop GHG budgets calculated from in situ flux measurements in a life cycle assessment approach: methodology and results

    NASA Astrophysics Data System (ADS)

    Ceschia, E.; Ferlicoq, M.; Brut, A.; Tallec, T.

    2013-12-01

    The carbon and GHG budgets (GHGB) of the 2 crop sites with contrasted management located in South West France was estimated over a complete rotation by combining a classical LCA approach with on site CO2 flux measurements. At both sites, carbon inputs (organic fertilization, seeds), carbon exports (harvest) and net ecosystem production (NEP), measured with the eddy covariance technique, were estimated. The variability of the different terms and their relative contributions to the net ecosystem carbon budget (NECB) were analyzed for all site-years, and the effect of management on NECB was assessed. To account for GHG fluxes that were not directly measured on site, we estimated the emissions caused by field operations (EFO) for each site using emission factors from the literature. The EFO were added to the NECB to calculate the total GHGB for a range of cropping systems and management regimes. N2O emissions were calculated following the IPCC (2007) guidelines or and CH4 emissions were assumed to be negligible. Albedo was calculated continuously using the short wave incident and reflected radiation measurements in the field from CNR1 sensors. Rapid changes in surface albedo typical from those ecosystems and resulting from management and crop phenology were analysed. The annual radiative forcing for each plot was estimated by calculating the difference between a mean annual albedo for each crop and a reference bare soil albedo value calculated over 5 years for each plot. To finalize the radiative forcing calculation, the method developed by Muñoz et al (2010) using up and down atmospheric transmittance had to be corrected so it would only account for up-going atmospheric transmittance. Annual differences in radiative forcing between crops were then converted in g C equivalent m-2 in order to add this effect to the GHG budget of each crop within a rotation. This methodology could be applied to all ICOS/NEON cropland sites. We found that the differences in radiative

  12. Probing anisotropic surface properties and interaction forces of chrysotile rods by atomic force microscopy and rheology.

    PubMed

    Yang, Dingzheng; Xie, Lei; Bobicki, Erin; Xu, Zhenghe; Liu, Qingxia; Zeng, Hongbo

    2014-09-16

    Understanding the surface properties and interactions of nonspherical particles is of both fundamental and practical importance in the rheology of complex fluids in various engineering applications. In this work, natural chrysotile, a phyllosilicate composed of 1:1 stacked silica and brucite layers which coil into cylindrical structure, was chosen as a model rod-shaped particle. The interactions of chrysotile brucite-like basal or bilayered edge planes and a silicon nitride tip were measured using an atomic force microscope (AFM). The force-distance profiles were fitted using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which demonstrates anisotropic and pH-dependent surface charge properties of brucite-like basal plane and bilayered edge surface. The points of zero charge (PZC) of the basal and edge planes were estimated to be around pH 10-11 and 6-7, respectively. Rheology measurements of 7 vol % chrysotile (with an aspect ratio of 14.5) in 10 mM NaCl solution showed pH-dependent yield stress with a local maximum around pH 7-9, which falls between the two PZC values of the edge and basal planes of the rod particles. On the basis of the surface potentials of the edge and basal planes obtained from AFM measurements, theoretical analysis of the surface interactions of edge-edge, basal-edge, and basal-basal planes of the chrysotile rods suggests the yield stress maximum observed could be mainly attributed to the basal-edge attractions. Our results indicate that the anisotropic surface properties (e.g., charges) of chrysotile rods play an important role in the particle-particle interaction and rheological behavior, which also provides insight into the basic understanding of the colloidal interactions and rheology of nonspherical particles.

  13. Direct Measurements of Drag Forces in C. elegans Crawling Locomotion

    PubMed Central

    Rabets, Yegor; Backholm, Matilda; Dalnoki-Veress, Kari; Ryu, William S.

    2014-01-01

    With a simple and versatile microcantilever-based force measurement technique, we have probed the drag forces involved in Caenorhabditis elegans locomotion. As a worm crawls on an agar surface, we found that substrate viscoelasticity introduces nonlinearities in the force-velocity relationships, yielding nonconstant drag coefficients that are not captured by original resistive force theory. A major contributing factor to these nonlinearities is the formation of a shallow groove on the agar surface. We measured both the adhesion forces that cause the worm’s body to settle into the agar and the resulting dynamics of groove formation. Furthermore, we quantified the locomotive forces produced by C. elegans undulatory motions on a wet viscoelastic agar surface. We show that an extension of resistive force theory is able to use the dynamics of a nematode’s body shape along with the measured drag coefficients to predict the forces generated by a crawling nematode. PMID:25418179

  14. Measured long-range repulsive Casimir–Lifshitz forces

    PubMed Central

    Munday, J. N.; Capasso, Federico; Parsegian, V. Adrian

    2014-01-01

    Quantum fluctuations create intermolecular forces that pervade macroscopic bodies1–3. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces4. However, as recognized in the theories of Casimir, Polder and Lifshitz5–7, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies8–11. Here we show experimentally that, in accord with theoretical prediction12, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir–Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction13–15. PMID:19129843

  15. Uncertainty quantification in nanomechanical measurements using the atomic force microscope.

    PubMed

    Wagner, Ryan; Moon, Robert; Pratt, Jon; Shaw, Gordon; Raman, Arvind

    2011-11-11

    Quantifying uncertainty in measured properties of nanomaterials is a prerequisite for the manufacture of reliable nanoengineered materials and products. Yet, rigorous uncertainty quantification (UQ) is rarely applied for material property measurements with the atomic force microscope (AFM), a widely used instrument that can measure properties at nanometer scale resolution of both inorganic and biological surfaces and nanomaterials. We present a framework to ascribe uncertainty to local nanomechanical properties of any nanoparticle or surface measured with the AFM by taking into account the main uncertainty sources inherent in such measurements. We demonstrate the framework by quantifying uncertainty in AFM-based measurements of the transverse elastic modulus of cellulose nanocrystals (CNCs), an abundant, plant-derived nanomaterial whose mechanical properties are comparable to Kevlar fibers. For a single, isolated CNC the transverse elastic modulus was found to have a mean of 8.1 GPa and a 95% confidence interval of 2.7-20 GPa. A key result is that multiple replicates of force-distance curves do not sample the important sources of uncertainty, which are systematic in nature. The dominant source of uncertainty is the nondimensional photodiode sensitivity calibration rather than the cantilever stiffness or Z-piezo calibrations. The results underscore the great need for, and open a path towards, quantifying and minimizing uncertainty in AFM-based material property measurements of nanoparticles, nanostructured surfaces, thin films, polymers and biomaterials.

  16. Comparison of Shortwave Cloud Radiative Forcing Derived from ARM SGP Surface and GOES-8 Satellite Measurements During ARESE I and ARESE II

    NASA Technical Reports Server (NTRS)

    Rapp, A. D.; Doelling, D. R.; Khaiyer, M. M.; Minnis, P.; Smith, W. L., Jr.; Nguyen, L.; Haeffelin, M. P.; Valero, F. P. J.; Asano, S.

    2001-01-01

    One of the objectives of the ARM Enhanced Shortwave Experiment (ARESE) is to investigate the absorption of solar radiation by clouds over the ARM Southern Great Plains central facility. A variety of techniques employing various combinations Of Surface, aircraft, and satellite data have been used to estimate the absorption empirically. During ARESE-I conducted during fall 1995, conflicting results were produced from different analyses of the combined datasets leading to the need for a more controlled experiment. ARESE-II was conducted during spring 2000. Improved calibrations, different sampling strategies, and broadband satellite data were all available to minimize some of the sources of uncertainty in the data. In this paper, cloud absorption or its parametric surrogates (e.g., Cess et al. 1995) are derived from collocated and coincident surface and satellite radiometer data from both ARESE-I and ARESE-II using the latest satellite and surface instrument calibrations.

  17. A measurement of the hysteresis loop in force-spectroscopy curves using a tuning-fork atomic force microscope

    PubMed Central

    van Vörden, Dennis; Möller, Rolf

    2012-01-01

    Summary Measurements of the frequency shift versus distance in noncontact atomic force microscopy (NC-AFM) allow measurements of the force gradient between the oscillating tip and a surface (force-spectroscopy measurements). When nonconservative forces act between the tip apex and the surface the oscillation amplitude is damped. The dissipation is caused by bistabilities in the potential energy surface of the tip–sample system, and the process can be understood as a hysteresis of forces between approach and retraction of the tip. In this paper, we present the direct measurement of the whole hysteresis loop in force-spectroscopy curves at 77 K on the PTCDA/Ag/Si(111) √3 × √3 surface by means of a tuning-fork-based NC-AFM with an oscillation amplitude smaller than the distance range of the hysteresis loop. The hysteresis effect is caused by the making and breaking of a bond between PTCDA molecules on the surface and a PTCDA molecule at the tip. The corresponding energy loss was determined to be 0.57 eV by evaluation of the force–distance curves upon approach and retraction. Furthermore, a second dissipation process was identified through the damping of the oscillation while the molecule on the tip is in contact with the surface. This dissipation process occurs mainly during the retraction of the tip. It reaches a maximum value of about 0.22 eV/cycle. PMID:22496993

  18. Tools for measuring surface cleanliness

    DOEpatents

    Schroder, Mark Stewart; Woodmansee, Donald Ernest; Beadie, Douglas Frank

    2002-01-01

    A procedure and tools for quantifying surface cleanliness are described. Cleanliness of a target surface is quantified by wiping a prescribed area of the surface with a flexible, bright white cloth swatch, preferably mounted on a special tool. The cloth picks up a substantial amount of any particulate surface contamination. The amount of contamination is determined by measuring the reflectivity loss of the cloth before and after wiping on the contaminated system and comparing that loss to a previous calibration with similar contamination. In the alternative, a visual comparison of the contaminated cloth to a contamination key provides an indication of the surface cleanliness.

  19. Atmosphere-surface exchange measurements.

    PubMed

    Dabberdt, W F; Lenschow, D H; Horst, T W; Zimmerman, P R; Oncley, S P; Delany, A C

    1993-06-04

    The exchange of various trace species and energy at the earth's surface plays an important role in climate, ecology, and human health and welfare. Surface exchange measurements can be difficult to obtain yet are important to understand physical processes, assess environmental and global change impacts, and develop robust parameterizations of atmospheric processes. The physics and turbulent structure of the atmospheric boundary layer are reviewed as they contribute to dry surface exchange rates (fluxes). Micrometeorological, budget, and enclosure techniques used to measure or estimate surface fluxes are described, along with their respective advantages and limitations. Various measurement issues (such as site characteristics, sampling considerations, sensor attributes, and flow distortion) impact on the ability to obtain representative surface-based and airborne flux data.

  20. Surface Polarity Of Beta-hmx Crystal And The Related Adhesive Forces With Estane Binder

    SciTech Connect

    Yang, Lu; Hanson, David E

    2008-01-01

    Here we present the results on the study of surface properties of {beta}-HMX crystal utilizing molecular simulations. The surface polarity of three principal crystal surfaces are investigated by measuring the water contact angles. The calculated contact angles agree excellently with the values measured by experiment and show that the surface polarity of three crystal surfaces are different. The free energies and forces of detaching an Estane chain with and without nitroplasticizer from the three principal crystal surfaces were calculated using umbrella sampling technique. We find that the detaching free energy/force increases with the increasing HMX surface polarity. In addition, our results also show that nitroplasticizer plays an important role in the adhesion forces between Estane and HMX surfaces.

  1. The relation between the surface electromyogram and muscular force.

    PubMed Central

    Milner-Brown, H S; Stein, R B

    1975-01-01

    1. Motor units in the first dorsal interosseus muscle of normal human subjects were recorded by needle electrodes, together with the surface electromyogram (e.m.g.). The wave form contributed by each motor unit to the surface e.m.g. was determined by signal averaging. 2. The peak-to-peak amplitude of the wave form contributed to the surface e.m.g. by a motor unit increased approximately as the square root of the threshold force at which the unit was recruited. The peak-to-peak duration of the wave form was independent of the threshold force. 3. Large and small motor units are uniformly distributed throughout this muscle, and the muscle fibres making up a motor unit may be widely dispersed. 4. The rectified surface e.m.g. was computed as a function of force, based on the sample of motor units recorded. The largest contribution of motor unit recruitment occurs at low force levels, while the contribution of increased firing rate becomes more important at higher force levels. 5. Possible bases for the common experimental observation that the mean rectified surface e.m.g. varies linearly with the force generated by a muscle are discussed. E.m.g. potentials and contractile responses may both sum non-linearly at moderate to high force levels, but in such a way that the rectified surface e.m.g. is still approximately linearly related to the force produced by the muscle. PMID:1133787

  2. Shear force microscopy using piezoresistive cantilevers in surface metrology

    NASA Astrophysics Data System (ADS)

    Gotszalk, Teodor; Kopiec, Daniel; Sierakowski, Andrzej; Janus, Paweł; Grabiec, Piotr; Rangelow, Ivo W.

    2014-09-01

    In this article we describe application of piezoresistive cantilevers in surface investigations carried out with the use of shear force microscopy (ShFM). The novel piezoresistive cantilevers integrate a Wheatstone piezoresistive bridge was used to detect the cantilever deflection, thermal deflection detector and planar tip protruding out of the spring beam. Because the planar tip deflection can be detected and controlled electronically the described technology is very flexible and can be applied in many surface investigations. In this article we will present operation theory of the described solution, experimental setup, methods for calibration of the tip deflection detection and actuation The analysis will be illustrated with example results of topography measurements performed using the described technology.

  3. Quantitative evaluation of interaction force between functional groups in protein and polymer brush surfaces.

    PubMed

    Sakata, Sho; Inoue, Yuuki; Ishihara, Kazuhiko

    2014-03-18

    To understand interactions between polymer surfaces and different functional groups in proteins, interaction forces were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Various polymer brush surfaces were systematically prepared by surface-initiated atom transfer radical polymerization as well-defined model surfaces to understand protein adsorption behavior. The polymer brush layers consisted of phosphorylcholine groups (zwitterionic/hydrophilic), trimethylammonium groups (cationic/hydrophilic), sulfonate groups (anionic/hydrophilic), hydroxyl groups (nonionic/hydrophilic), and n-butyl groups (nonionic/hydrophobic) in their side chains. The interaction forces between these polymer brush surfaces and different functional groups (carboxyl groups, amino groups, and methyl groups, which are typical functional groups existing in proteins) were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Furthermore, the amount of adsorbed protein on the polymer brush surfaces was quantified by surface plasmon resonance using albumin with a negative net charge and lysozyme with a positive net charge under physiological conditions. The amount of proteins adsorbed on the polymer brush surfaces corresponded to the interaction forces generated between the functional groups on the cantilever and the polymer brush surfaces. The weakest interaction force and least amount of protein adsorbed were observed in the case of the polymer brush surface with phosphorylcholine groups in the side chain. On the other hand, positive and negative surfaces generated strong forces against the oppositely charged functional groups. In addition, they showed significant adsorption with albumin and lysozyme, respectively. These results indicated that the interaction force at the functional group level might be

  4. Robust high-resolution imaging and quantitative force measurement with tuned-oscillator atomic force microscopy.

    PubMed

    Dagdeviren, Omur E; Götzen, Jan; Hölscher, Hendrik; Altman, Eric I; Schwarz, Udo D

    2016-02-12

    Atomic force microscopy (AFM) and spectroscopy are based on locally detecting the interactions between a surface and a sharp probe tip. For highest resolution imaging, noncontact modes that avoid tip-sample contact are used; control of the tip's vertical position is accomplished by oscillating the tip and detecting perturbations induced by its interaction with the surface potential. Due to this potential's nonlinear nature, however, achieving reliable control of the tip-sample distance is challenging, so much so that despite its power vacuum-based noncontact AFM has remained a niche technique. Here we introduce a new pathway to distance control that prevents instabilities by externally tuning the oscillator's response characteristics. A major advantage of this operational scheme is that it delivers robust position control in both the attractive and repulsive regimes with only one feedback loop, thereby providing an easy-to-implement route to atomic resolution imaging and quantitative tip-sample interaction force measurement.

  5. Muscle force estimation with surface EMG during dynamic muscle contractions: a wavelet and ANN based approach.

    PubMed

    Bai, Fengjun; Chew, Chee-Meng

    2013-01-01

    Human muscle force estimation is important in biomechanics studies, sports and assistive devices fields. Therefore, it is essential to develop an efficient algorithm to estimate force exerted by muscles. The purpose of this study is to predict force/torque exerted by muscles under dynamic muscle contractions based on continuous wavelet transform (CWT) and artificial neural networks (ANN) approaches. Mean frequency (MF) of the surface electromyography (EMG) signals power spectrum was calculated from CWT. ANN models were trained to derive the MF-force relationships from the subset of EMG signals and the measured forces. Then we use the networks to predict the individual muscle forces for different muscle groups. Fourteen healthy subjects (10 males and 4 females) were voluntarily recruited in this study. EMG signals were collected from the biceps brachii, triceps, hamstring and quadriceps femoris muscles to evaluate the proposed method. Root mean square errors (RMSE) and correlation coefficients between the predicted forces and measured actual forces were calculated.

  6. Some results from 50 years' research on surface forces

    NASA Astrophysics Data System (ADS)

    Derjaguin, B. V.

    1992-05-01

    A review is presented about research on surface forces and surface interactions conducted over the past half-century, with some emphasis on the pioneering contributions of the Department of Surface Phenomena at the Institute of Physical Chemistry of the USSR Academy of Sciences.

  7. Investigating biomolecular recognition at the cell surface using atomic force microscopy.

    PubMed

    Wang, Congzhou; Yadavalli, Vamsi K

    2014-05-01

    Probing the interaction forces that drive biomolecular recognition on cell surfaces is essential for understanding diverse biological processes. Force spectroscopy has been a widely used dynamic analytical technique, allowing measurement of such interactions at the molecular and cellular level. The capabilities of working under near physiological environments, combined with excellent force and lateral resolution make atomic force microscopy (AFM)-based force spectroscopy a powerful approach to measure biomolecular interaction forces not only on non-biological substrates, but also on soft, dynamic cell surfaces. Over the last few years, AFM-based force spectroscopy has provided biophysical insight into how biomolecules on cell surfaces interact with each other and induce relevant biological processes. In this review, we focus on describing the technique of force spectroscopy using the AFM, specifically in the context of probing cell surfaces. We summarize recent progress in understanding the recognition and interactions between macromolecules that may be found at cell surfaces from a force spectroscopy perspective. We further discuss the challenges and future prospects of the application of this versatile technique.

  8. Strong Casimir force reduction through metallic surface nanostructuring

    PubMed Central

    Intravaia, Francesco; Koev, Stephan; Jung, Il Woong; Talin, A. Alec; Davids, Paul S.; Decca, Ricardo S.; Aksyuk, Vladimir A.; Dalvit, Diego A. R.; López, Daniel

    2013-01-01

    The Casimir force between bodies in vacuum can be understood as arising from their interaction with an infinite number of fluctuating electromagnetic quantum vacuum modes, resulting in a complex dependence on the shape and material of the interacting objects. Becoming dominant at small separations, the force has a significant role in nanomechanics and object manipulation at the nanoscale, leading to a considerable interest in identifying structures where the Casimir interaction behaves significantly different from the well-known attractive force between parallel plates. Here we experimentally demonstrate that by nanostructuring one of the interacting metal surfaces at scales below the plasma wavelength, an unexpected regime in the Casimir force can be observed. Replacing a flat surface with a deep metallic lamellar grating with sub-100 nm features strongly suppresses the Casimir force and for large inter-surfaces separations reduces it beyond what would be expected by any existing theoretical prediction. PMID:24071657

  9. Molecular interaction forces generated during protein adsorption to well-defined polymer brush surfaces.

    PubMed

    Sakata, Sho; Inoue, Yuuki; Ishihara, Kazuhiko

    2015-03-17

    The molecular interaction forces generated during the adsorption of proteins to surfaces were examined by the force-versus-distance (f-d) curve measurements of atomic force microscopy using probes modified with appropriate molecules. Various substrates with polymer brush layers bearing zwitterionic, cationic, anionic, and hydrophobic groups were systematically prepared by surface-initiated atom transfer radical polymerization. Surface interaction forces on these substrates were analyzed by the f-d curve measurements using probes with the same polymer brush layer as the substrate. Repulsive forces, which decreased depending on the ionic strength, were generated between cationic or anionic polyelectrolyte brush layers; these were considered to be electrostatic interaction forces. A strong adhesive force was detected between hydrophobic polymer brush layers during retraction; this corresponded to the hydrophobic interaction between two hydrophobic polymer layers. In contrast, no significant interaction forces were detected between zwitterionic polymer brush layers. Direct interaction forces between proteins and polymer brush layers were then quantitatively evaluated by the f-d curve measurements using protein-immobilized probes consisting of negatively charged albumin and positively charged lysozyme under physiological conditions. In addition, the amount of protein adsorbed on the polymer brush layer was quantified by surface plasmon resonance measurements. Relatively large amounts of protein adsorbed to the polyelectrolyte brush layers with opposite charges. It was considered that the detachment of the protein after contact with the polymer brush layer hardly occurred due to salt formation at the interface. Both proteins adsorbed significantly on the hydrophobic polymer brush layer, which was due to hydrophobic interactions at the interface. In contrast, the zwitterionic polymer brush layer exhibited no significant interaction force with proteins and suppressed

  10. Tip-surface forces, amplitude, and energy dissipation in amplitude-modulation (tapping mode) force microscopy

    NASA Astrophysics Data System (ADS)

    Paulo, Álvaro San; García, Ricardo

    2001-11-01

    Amplitude-modulation (tapping mode) atomic force microscopy is a technique for high resolution imaging of a wide variety of surfaces in air and liquid environments. Here by using the virial theorem and energy conservation principles we have derived analytical relationships between the oscillation amplitude, phase shift, and average tip-surface forces. We find that the average value of the interaction force and oscillation and the average power dissipated by the tip-surface interaction are the quantities that control the amplitude reduction. The agreement obtained between analytical and numerical results supports the analytical method.

  11. Measurements of the rotordynamic shroud forces for centrifugal pumps

    NASA Technical Reports Server (NTRS)

    Guinzburg, A.; Brennen, C. E.; Acosta, A. J.; Caughey, T. K.

    1990-01-01

    An experiment was designed to measure the rotordynamic shroud forces on a centrifugal pump impeller. The measurements were done for various whirl/impeller speed ratios and for different flow rates. A destabilizing tangential force was measured for small positive whirl ratios and this force decreased with increasing flow rate.

  12. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    PubMed Central

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-01-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained. PMID:27587276

  13. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    DOE PAGES

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; ...

    2016-09-02

    In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements aremore » sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.« less

  14. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    SciTech Connect

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-09-02

    In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  15. Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

    2016-09-01

    Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

  16. Measuring shear force transmission across a biomimetic glycocalyx

    NASA Astrophysics Data System (ADS)

    Bray, Isabel; Young, Dylan; Scrimgeour, Jan

    Human blood vessels are lined with a low-density polymer brush known as the glycocalyx. This brush plays an active role in defining the mechanical and biochemical environment of the endothelial cell in the blood vessel wall. In addition, it is involved in the detection of mechanical stimuli, such as the shear stress from blood flowing in the vessel. In this work, we construct a biomimetic version of the glycocalyx on top of a soft deformable substrate in order to measure its ability to modulate the effects of shear stress at the endothelial cell surface. The soft substrate is stamped on to a glass substrate and then enclosed inside a microfluidic device that generates a controlled flow over the substrate. The hydrogel chemistry has been optimized so that it reliably stamps into a defined shape and has consistent mechanical properties. Fluorescent microbeads embedded in the gel allow measurement of the surface deformation, and subsequently, calculation of the shear force at the surface of the soft substrate. We investigate the effect of the major structural elements of the glycocalyx, hyaluronic acid and charged proteoglycans, on the magnitude of the shear force transmitted to the surface of the hydrogel.

  17. A force vector and surface orientation sensor for intelligent grasping

    NASA Technical Reports Server (NTRS)

    Mcglasson, W. D.; Lorenz, R. D.; Duffie, N. A.; Gale, K. L.

    1991-01-01

    The paper discusses a force vector and surface orientation sensor suitable for intelligent grasping. The use of a novel four degree-of-freedom force vector robotic fingertip sensor allows efficient, real time intelligent grasping operations. The basis of sensing for intelligent grasping operations is presented and experimental results demonstrate the accuracy and ease of implementation of this approach.

  18. Surface Gravity and Hawking Temperature from Entropic Force Viewpoint

    NASA Astrophysics Data System (ADS)

    Aaltonen, T.; Adelman, J.; Álvarez González, B.; Amerio, S.; Amidei, D.; Anastassov, A.; Annovi, A.; Antos, J.; Apollinari, G.; Appel, J.; Apresyan, A.; Arisawa, T.; Artikov, A.; Asaadi, J.; Ashmanskas, W.; Attal, A.; Aurisano, A.; Azfar, F.; Badgett, W.; Barbaro-Galtieri, A.; Barnes, V. E.; Barnett, B. A.; Barria, P.; Bartos, P.; Bauer, G.; Beauchemin, P.-H.; Bedeschi, F.; Beecher, D.; Behari, S.; Bellettini, G.; Bellinger, J.; Benjamin, D.; Beretvas, A.; Bhatti, A.; Binkley, M.; Bisello, D.; Bizjak, I.; Blair, R. E.; Blocker, C.; Blumenfeld, B.; Bocci, A.; Bodek, A.; Boisvert, V.; Bortoletto, D.; Boudreau, J.; Boveia, A.; Brau, B.; Bridgeman, A.; Brigliadori, L.; Bromberg, C.; Brubaker, E.; Budagov, J.; Budd, H. S.; Budd, S.; Burkett, K.; Busetto, G.; Bussey, P.; Buzatu, A.; Byrum, K. L.; Cabrera, S.; Calancha, C.; Camarda, S.; Campanelli, M.; Campbell, M.; Canelli, F.; Canepa, A.; Carls, B.; Carlsmith, D.; Carosi, R.; Carrillo, S.; Carron, S.; Casal, B.; Casarsa, M.; Castro, A.; Catastini, P.; Cauz, D.; Cavaliere, V.; Cavalli-Sforza, M.; Cerri, A.; Cerrito, L.; Chang, S. H.; Chen, Y. C.; Chertok, M.; Chiarelli, G.; Chlachidze, G.; Chlebana, F.; Cho, K.; Chokheli, D.; Chou, J. P.; Chung, K.; Chung, W. H.; Chung, Y. S.; Chwalek, T.; Ciobanu, C. I.; Ciocci, M. A.; Clark, A.; Clark, D.; Compostella, G.; Convery, M. E.; Conway, J.; Corbo, M.; Cordelli, M.; Cox, C. A.; Cox, D. J.; Crescioli, F.; Cuenca Almenar, C.; Cuevas, J.; Culbertson, R.; Cully, J. C.; Dagenhart, D.; D'Ascenzo, N.; Datta, M.; Davies, T.; de Barbaro, P.; de Cecco, S.; Deisher, A.; de Lorenzo, G.; Dell'Orso, M.; Deluca, C.; Demortier, L.; Deng, J.; Deninno, M.; D'Errico, M.; di Canto, A.; di Ruzza, B.; Dittmann, J. R.; D'Onofrio, M.; Donati, S.; Dong, P.; Dorigo, T.; Dube, S.; Ebina, K.; Elagin, A.; Erbacher, R.; Errede, D.; Errede, S.; Ershaidat, N.; Eusebi, R.; Fang, H. C.; Farrington, S.; Fedorko, W. T.; Feild, R. G.; Feindt, M.; Fernandez, J. P.; Ferrazza, C.; Field, R.; Flanagan, G.; Forrest, R.; Frank, M. J.; Franklin, M.; Freeman, J. C.; Furic, I.; Gallinaro, M.; Galyardt, J.; Garberson, F.; Garcia, J. E.; Garfinkel, A. F.; Garosi, P.; Gerberich, H.; Gerdes, D.; Gessler, A.; Giagu, S.; Giakoumopoulou, V.; Giannetti, P.; Gibson, K.; Gimmell, J. L.; Ginsburg, C. M.; Giokaris, N.; Giordani, M.; Giromini, P.; Giunta, M.; Giurgiu, G.; Glagolev, V.; Glenzinski, D.; Gold, M.; Goldschmidt, N.; Golossanov, A.; Gomez, G.; Gomez-Ceballos, G.; Goncharov, M.; González, O.; Gorelov, I.; Goshaw, A. T.; Goulianos, K.; Gresele, A.; Grinstein, S.; Grosso-Pilcher, C.; Group, R. C.; Grundler, U.; Guimaraes da Costa, J.; Gunay-Unalan, Z.; Haber, C.; Hahn, S. R.; Halkiadakis, E.; Han, B.-Y.; Han, J. Y.; Happacher, F.; Hara, K.; Hare, D.; Hare, M.; Harr, R. F.; Hartz, M.; Hatakeyama, K.; Hays, C.; Heck, M.; Heinrich, J.; Herndon, M.; Heuser, J.; Hewamanage, S.; Hidas, D.; Hill, C. S.; Hirschbuehl, D.; Hocker, A.; Hou, S.; Houlden, M.; Hsu, S.-C.; Hughes, R. E.; Hurwitz, M.; Husemann, U.; Hussein, M.; Huston, J.; Incandela, J.; Introzzi, G.; Iori, M.; Ivanov, A.; James, E.; Jang, D.; Jayatilaka, B.; Jeon, E. J.; Jha, M. K.; Jindariani, S.; Johnson, W.; Jones, M.; Joo, K. K.; Jun, S. Y.; Jung, J. E.; Junk, T. R.; Kamon, T.; Kar, D.; Karchin, P. E.; Kato, Y.; Kephart, R.; Ketchum, W.; Keung, J.; Kietzman, B.; Khotilovich, V.; Kilminster, B.; Kim, D. H.; Kim, H. S.; Kim, H. W.; Kim, J. E.; Kim, M. J.; Kim, S. B.; Kim, S. H.; Kim, Y. K.; Kimura, N.; Kirsch, L.; Klimenko, S.; Kondo, K.; Kong, D. J.; Konigsberg, J.; Korytov, A.; Kotwal, A. V.; Kreps, M.; Kroll, J.; Krop, D.; Krumnack, N.; Kruse, M.; Krutelyov, V.; Kuhr, T.; Kulkarni, N. P.; Kurata, M.; Kwang, S.; Laasanen, A. T.; Lami, S.; Lammel, S.; Lancaster, M.; Lander, R. L.; Lannon, K.; Lath, A.; Latino, G.; Lazzizzera, I.; Lecompte, T.; Lee, E.; Lee, H. S.; Lee, J. S.; Lee, S. W.; Leone, S.; Lewis, J. D.; Lin, C.-J.; Linacre, J.; Lindgren, M.; Lipeles, E.; Lister, A.; Litvintsev, D. O.; Liu, C.; Liu, T.; Lockyer, N. S.; Loginov, A.; Lovas, L.; Lucchesi, D.; Lueck, J.; Lujan, P.; Lukens, P.; Lungu, G.; Lys, J.; Lysak, R.; MacQueen, D.; Madrak, R.; Maeshima, K.; Makhoul, K.; Maksimovic, P.; Malde, S.; Malik, S.; Manca, G.; Manousakis-Katsikakis, A.; Margaroli, F.; Marino, C.; Marino, C. P.; Martin, A.; Martin, V.; Martínez, M.; Martínez-Ballarín, R.; Mastrandrea, P.; Mathis, M.; Mattson, M. E.; Mazzanti, P.; McFarland, K. S.; McIntyre, P.; McNulty, R.; Mehta, A.; Mehtala, P.; Menzione, A.; Mesropian, C.; Miao, T.; Mietlicki, D.; Miladinovic, N.; Miller, R.; Mills, C.; Milnik, M.; Mitra, A.; Mitselmakher, G.; Miyake, H.; Moed, S.; Moggi, N.; Mondragon, M. N.; Moon, C. S.; Moore, R.; Morello, M. J.; Morlock, J.; Movilla Fernandez, P.; Mülmenstädt, J.; Mukherjee, A.; Muller, Th.; Murat, P.; Mussini, M.; Nachtman, J.; Nagai, Y.; Naganoma, J.; Nakamura, K.; Nakano, I.; Napier, A.; Nett, J.; Neu, C.; Neubauer, M. S.; Neubauer, S.; Nielsen, J.; Nodulman, L.; Norman, M.; Norniella, O.; Nurse, E.; Oakes, L.; Oh, S. H.; Oh, Y. D.; Oksuzian, I.; Okusawa, T.; Orava, R.; Osterberg, K.; Pagan Griso, S.; Pagliarone, C.; Palencia, E.; Papadimitriou, V.; Papaikonomou, A.; Paramanov, A. A.; Parks, B.; Pashapour, S.; Patrick, J.; Pauletta, G.; Paulini, M.; Paus, C.; Peiffer, T.; Pellett, D. E.; Penzo, A.; Phillips, T. J.; Piacentino, G.; Pianori, E.; Pinera, L.; Pitts, K.; Plager, C.; Pondrom, L.; Potamianos, K.; Poukhov, O.; Prokoshin, F.; Pronko, A.; Ptohos, F.; Pueschel, E.; Punzi, G.; Pursley, J.; Rademacker, J.; Rahaman, A.; Ramakrishnan, V.; Ranjan, N.; Redondo, I.; Renton, P.; Renz, M.; Rescigno, M.; Richter, S.; Rimondi, F.; Ristori, L.; Robson, A.; Rodrigo, T.; Rodriguez, T.; Rogers, E.; Rolli, S.; Roser, R.; Rossi, M.; Rossin, R.; Roy, P.; Ruiz, A.; Russ, J.; Rusu, V.; Rutherford, B.; Saarikko, H.; Safonov, A.; Sakumoto, W. K.; Santi, L.; Sartori, L.; Sato, K.; Saveliev, V.; Savoy-Navarro, A.; Schlabach, P.; Schmidt, A.; Schmidt, E. E.; Schmidt, M. A.; Schmidt, M. P.; Schmitt, M.; Schwarz, T.; Scodellaro, L.; Scribano, A.; Scuri, F.; Sedov, A.; Seidel, S.; Seiya, Y.; Semenov, A.; Sexton-Kennedy, L.; Sforza, F.; Sfyrla, A.; Shalhout, S. Z.; Shears, T.; Shepard, P. F.; Shimojima, M.; Shiraishi, S.; Shochet, M.; Shon, Y.; Shreyber, I.; Simonenko, A.; Sinervo, P.; Sisakyan, A.; Slaughter, A. J.; Slaunwhite, J.; Sliwa, K.; Smith, J. R.; Snider, F. D.; Snihur, R.; Soha, A.; Somalwar, S.; Sorin, V.; Squillacioti, P.; Stanitzki, M.; St. Denis, R.; Stelzer, B.; Stelzer-Chilton, O.; Stentz, D.; Strologas, J.; Strycker, G. L.; Suh, J. S.; Sukhanov, A.; Suslov, I.; Taffard, A.; Takashima, R.; Takeuchi, Y.; Tanaka, R.; Tang, J.; Tecchio, M.; Teng, P. K.; Thom, J.; Thome, J.; Thompson, G. A.; Thomson, E.; Tipton, P.; Ttito-Guzmán, P.; Tkaczyk, S.; Toback, D.; Tokar, S.; Tollefson, K.; Tomura, T.; Tonelli, D.; Torre, S.; Torretta, D.; Totaro, P.; Trovato, M.; Tsai, S.-Y.; Tu, Y.; Turini, N.; Ukegawa, F.; Uozumi, S.; van Remortel, N.; Varganov, A.; Vataga, E.; Vázquez, F.; Velev, G.; Vellidis, C.; Vidal, M.; Vila, I.; Vilar, R.; Vogel, M.; Volobouev, I.; Volpi, G.; Wagner, P.; Wagner, R. G.; Wagner, R. L.; Wagner, W.; Wagner-Kuhr, J.; Wakisaka, T.; Wallny, R.; Wang, S. M.; Warburton, A.; Waters, D.; Weinberger, M.; Weinelt, J.; Wester, W. C., III; Whitehouse, B.; Whiteson, D.; Wicklund, A. B.; Wicklund, E.; Wilbur, S.; Williams, G.; Williams, H. H.; Wilson, P.; Winer, B. L.; Wittich, P.; Wolbers, S.; Wolfe, C.; Wolfe, H.; Wright, T.; Wu, X.; Würthwein, F.; Yagil, A.; Yamamoto, K.; Yamaoka, J.; Yang, U. K.; Yang, Y. C.; Yao, W. M.; Yeh, G. P.; Yi, K.; Yoh, J.; Yorita, K.; Yoshida, T.; Yu, G. B.; Yu, I.; Yu, S. S.; Yun, J. C.; Zanetti, A.; Zeng, Y.; Zhang, X.; Zheng, Y.; Zucchelli, S.; CDF Collaboration

    We consider a freely falling holographic screen for the Schwarzschild and Reissner-Nordström black holes and evaluate the entropic force à la Verlinde. When the screen crosses the event horizon, the temperature of the screen agrees to the Hawking temperature and the entropic force gives rise to the surface gravity for both of the black holes.

  19. Impact of surface imperfections on the Casimir force for lenses of centimeter-size curvature radii

    SciTech Connect

    Bezerra, V. B.; Romero, C.; Klimchitskaya, G. L.; Mohideen, U.; Mostepanenko, V. M.

    2011-02-15

    The impact of imperfections, which are always present on surfaces of lenses with centimeter-size curvature radii, on the Casimir force in the lens-plate geometry is investigated. It is shown that the commonly used formulation of the proximity force approximation is inapplicable for spherical lenses with surface imperfections, such as bubbles and pits. More general expressions for the Casimir force are derived that take surface imperfections into account. Using these expressions, we show that surface imperfections can both increase and decrease the magnitude of the Casimir force up to a few tens percent when compared with the case of a perfectly spherical lens. We demonstrate that the Casimir force between a perfectly spherical lens and a plate described by the Drude model can be made approximately equal to the force between a sphere with some surface imperfection and a plate described by the plasma model, and vice versa. In the case of a metallic sphere and a semiconductor plate, approximately the same Casimir forces are obtained for four different descriptions of charge carriers in the semiconductor if appropriate surface imperfections on the lens surface are present. The conclusion is made that there is a fundamental problem in the interpretation of measurement data for the Casimir force using spherical lenses of centimeter-size radii.

  20. Vertical and lateral force mapping on the Si(111)-(7×7) surface by dynamic force microscopy

    NASA Astrophysics Data System (ADS)

    Sugimoto, Yoshiaki; Namikawa, Takashi; Miki, Koutaro; Abe, Masayuki; Morita, Seizo

    2008-05-01

    The topographic image of dynamic force microscopy (DFM) keeping the frequency shift (Δfz) constant at tiny cantilever oscillation amplitudes corresponds to the constant-vertical force (Fz) gradient surface, while the interpretation becomes complicated at larger oscillation amplitudes. We discuss how Fz and the potential energy (U) act on the tip during DFM topographic scan at various cantilever oscillation amplitudes by measuring the Δfz map on the Si(111)-(7×7) surface at room temperature. The Δfz map is numerically converted into Fz and U maps. DFM topographic curves at various cantilever oscillation amplitudes are numerically derived by using the experimentally obtained Fz map. In addition, we discuss how the lateral force (Fx) acts on the tip at various tip-surface distances on various surface sites by an Fx map converted from a U map. The positions at which Fx becomes zero are identified as U minimum sites, such as the top of adatom sites, and U maximum sites (equilibrium positions of Fx ), such as the center positions among three center adatoms. The tip deviated from these sites is then laterally attracted toward the U minimum sites. It is also demonstrated that lateral force microscopy performed at 1Å cantilever oscillation enables direct measurement of the lateral force gradient by numerically deriving the frequency shift (Δfx) caused by Fx .

  1. Uncertainty quantification in nanomechanical measurements using the atomic force microscope

    NASA Astrophysics Data System (ADS)

    Wagner, Ryan; Moon, Robert; Pratt, Jon; Shaw, Gordon; Raman, Arvind

    2011-11-01

    Quantifying uncertainty in measured properties of nanomaterials is a prerequisite for the manufacture of reliable nanoengineered materials and products. Yet, rigorous uncertainty quantification (UQ) is rarely applied for material property measurements with the atomic force microscope (AFM), a widely used instrument that can measure properties at nanometer scale resolution of both inorganic and biological surfaces and nanomaterials. We present a framework to ascribe uncertainty to local nanomechanical properties of any nanoparticle or surface measured with the AFM by taking into account the main uncertainty sources inherent in such measurements. We demonstrate the framework by quantifying uncertainty in AFM-based measurements of the transverse elastic modulus of cellulose nanocrystals (CNCs), an abundant, plant-derived nanomaterial whose mechanical properties are comparable to Kevlar fibers. For a single, isolated CNC the transverse elastic modulus was found to have a mean of 8.1 GPa and a 95% confidence interval of 2.7-20 GPa. A key result is that multiple replicates of force-distance curves do not sample the important sources of uncertainty, which are systematic in nature. The dominant source of uncertainty is the nondimensional photodiode sensitivity calibration rather than the cantilever stiffness or Z-piezo calibrations. The results underscore the great need for, and open a path towards, quantifying and minimizing uncertainty in AFM-based material property measurements of nanoparticles, nanostructured surfaces, thin films, polymers and biomaterials. This work is a partial contribution of the USDA Forest Service and NIST, agencies of the US government, and is not subject to copyright.

  2. Surface roughtness and its influence on particle adhesion using atomic force microscope techniques

    SciTech Connect

    Gady, B.; Schaefer, D.; Reifenberger, R.; Rimai, D.; DeMejo, L.P.

    1996-12-31

    The surface force interactions between individual 8 {mu}m diameter spheres and atomically flat substrates have been systematically investigated using atomic force techniques. The lift-off force of glass, polystyrene and tin particles from atomically smooth mica and highly oriented pyrolytic graphite substrates was determined as a function of the applied loading force in an inert nitrogen environment. While the relative magnitudes of the measured lift-off force was found to scale as expected between the various systems studied, the absolute values were a factor of {approximately}50 smaller than expected from the Johnson, Kendall, and Roberts theory. The surface topography of representative spheres was characterized with atomic force microscopy, allowing a quantitative assessment of the role that surface roughness plays in the adhesion of micrometer-size particles to substrates. Taking into account the radius of curvature of the asperities measured from the atomic force scans, agreement between the measured and theoretical estimates for the lift-off forces was improved, with the corrected experimental forces about a factor of 3 smaller than theoretical expectations.

  3. Shortwave Spectral Radiative Forcing of Cumulus Clouds from Surface Observations

    SciTech Connect

    Kassianov, Evgueni I.; Barnard, James C.; Berg, Larry K.; Long, Charles N.; Flynn, Connor J.

    2011-04-02

    The spectral changes of the total cloud radiative forcing (CRF) and its diffuse and direct components are examined by using spectrally resolved (visible spectral range) all-sky surface irradiances measured by Multi-Filter Rotating Shadowband Radiometer. We demonstrate: (i) the substantial contribution of the diffuse component to the total CRF, (ii) the well-defined spectral variations of total CRF in the visible spectral region, and (iii) the strong statistical relationship between spectral (500 nm) and shortwave broadband values of total CRF. Our results suggest that the framework based on the visible narrowband fluxes can provide important radiative quantities for rigorous evaluation of radiative transfer parameterizations and can be applied for estimation of the shortwave total CRF.

  4. Measuring Wind Ventilation of Dense Surface Snow

    NASA Astrophysics Data System (ADS)

    Drake, S. A.; Huwald, H.; Selker, J. S.; Higgins, C. W.; Lehning, M.; Thomas, C. K.

    2014-12-01

    Wind ventilation enhances exposure of suspended, canopy-captured and corniced snow to subsaturated air and can significantly increase sublimation rate. Although sublimation rate may be high for highly ventilated snow this snow regime represents a small fraction snow that resides in a basin potentially minimizing its influence on snow mass balance. In contrast, the vast majority of a seasonal snowpack typically resides as poorly ventilated surface snow. The sublimation rate of surface snow is often locally so small as to defy direct measurement but regionally pervasive enough that the integrated mass loss of frozen water across a basin may be significant on a seasonal basis. In a warming climate, sublimation rate increases even in subfreezing conditions because the equilibrium water vapor pressure over ice increases exponentially with temperature. To better understand the process of wintertime surface snow sublimation we need to quantify the depth to which turbulent and topographically driven pressure perturbations effect air exchange within the snowpack. Hypothetically, this active layer depth increases the effective ventilated snow surface area, enhancing sublimation above that given by a plane, impermeable snow surface. We designed and performed a novel set of field experiments at two sites in the Oregon Cascades during the 2014 winter season to examine the spectral attenuation of pressure perturbations with depth for dense snow as a function of turbulence intensity and snow permeability. We mounted a Campbell Scientific Irgason Integrated CO2 and H2O Open Path Gas Analyzer and 3-D Sonic Anemometer one meter above the snow to capture mean and turbulent wind forcing and placed outlets of four high precision ParoScientific 216B-102 pressure transducers at different depths to measure the depth-dependent pressure response to wind forcing. A GPS antenna captured data acquisition time with sufficient precision to synchronize a Campbell Scientific CR-3000 acquiring

  5. Atomic force microscopy of lead iodide crystal surfaces

    NASA Astrophysics Data System (ADS)

    George, M. A.; Azoulay, M.; Jayatirtha, H. N.; Biao, Y.; Burger, A.; Collins, W. E.; Silberman, E.

    1994-03-01

    Atomic force microscopy (AFM) was used to characterize the surface of lead iodide crystals. The high vapor pressure of lead iodide prohibits the use of traditional high resolution surface study techniques that require high vacuum conditions. AFM was used to image numerous insulating surface in various ambients, with very little sample preparation techniques needed. Freshly cleaved and modified surfaces, including, chemical and vacuum etched, and air aged surfaces, were examined. Both intrinsic and induced defects were imaged with high resolution. The results were compared to a similar AFM study of mercuric iodide surfaces and it was found that, at ambient conditions, lead iodide is significantly more stable than mercuric iodide.

  6. Force measurement reveals structure of a confined liquid: Observation of the impenetrable space

    NASA Astrophysics Data System (ADS)

    Amano, Ken-ichi; Tanaka, Eisuke; Kobayashi, Kazuya; Onishi, Hiroshi; Nishi, Naoya; Sakka, Tetsuo

    2015-11-01

    Understanding of the structure of a confined liquid is an important subject for developments in surface science, tribology, biophysics, etc. In this study, we propose its measurement theory and conduct a test of the theory. The measurement theory uses a force curve obtained by surface force apparatus and transforms the force curve into the confined liquid structure. To check the validity of the measurement theory, we perform a verification test in a computer. It is found that the theory can semi-quantitatively reproduce the confined liquid structure. The theory will lead to the first step toward measuring a liquid structure confined between optically impenetrable substrates.

  7. ForceFit: a code to fit classical force fields to quantum mechanical potential energy surfaces.

    PubMed

    Waldher, Benjamin; Kuta, Jadwiga; Chen, Samuel; Henson, Neil; Clark, Aurora E

    2010-09-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under UNIX and is written in C++, is an easy-to-use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field, and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program.

  8. Measuring the Magnetic Force on a Current-Carrying Conductor.

    ERIC Educational Resources Information Center

    Herreman, W.; Huysentruyt, R.

    1995-01-01

    Describes a fast and simple method for measuring the magnetic force acting on a current-carrying conductor using a digital balance. Discusses the influence of current intensity and wire length on the magnetic force on the conductor. (JRH)

  9. Dynamometer for measuring machining forces in two perpendicular directions

    NASA Technical Reports Server (NTRS)

    Sutherland, I. A.

    1974-01-01

    Published report discusses development of two-component force dynamometer which is used for dynamic measurement of machining forces in cutting and thrust directions. Resulting data suggest that faster metal-cutting machines may be developed that have reduced vibrations.

  10. Cantilevers orthodontics forces measured by fiber sensors

    NASA Astrophysics Data System (ADS)

    Schneider, Neblyssa; Milczewski, Maura S.; de Oliveira, Valmir; Guariza Filho, Odilon; Lopes, Stephani C. P. S.; Kalinowski, Hypolito J.

    2015-09-01

    Fibers Bragg Gratings were used to evaluate the transmission of the forces generates by orthodontic mechanic based one and two cantilevers used to move molars to the upright position. The results showed levels forces of approximately 0,14N near to the root of the molar with one and two cantilevers.

  11. Measurement of dynamic bite force during mastication.

    PubMed

    Shimada, A; Yamabe, Y; Torisu, T; Baad-Hansen, L; Murata, H; Svensson, P

    2012-05-01

    Efficient mastication of different types and size of food depends on fast integration of sensory information from mechanoreceptors and central control mechanisms of jaw movements and applied bite force. The neural basis underlying mastication has been studied for decades but little progress in understanding the dynamics of bite force has been made mainly due to technical limitations of bite force recorders. The aims of this study were to develop a new intraoral bite force recorder which would allow the study of natural mastication without an increase in the occlusal vertical dimension and subsequently to analyze the relation between electromyographic (EMG) activity of jaw-closing muscles, jaw movements and bite force during mastication of five different types of food. Customized force recorders based on strain gauge sensors were fitted to the upper and lower molar teeth on the preferred chewing side in fourteen healthy and dentate subjects (21-39 years), and recordings were carried out during voluntary mastication of five different kinds of food. Intraoral force recordings were successively obtained from all subjects. anova showed that impulse of bite force as well as integrated EMG was significantly influenced by food (P<0·05), while time-related parameters were significantly affected by chewing cycles (P<0·001). This study demonstrates that intraoral force recordings are feasible and can provide new information on the dynamics of human mastication with direct implications for oral rehabilitation. We also propose that the control of bite force during mastication is achieved by anticipatory adjustment and encoding of bolus characteristics.

  12. Direct Measurement of Lateral Force Using Dual Cantilevers

    PubMed Central

    Ishikawa, Makoto; Ichikawa, Masaya; Miura, Kouji

    2012-01-01

    We have constructed an experimental system to measure a piconewton lateral force using dual cantilevers which cross with each other. The resolution of the lateral force is estimated to be 3.3 p ± 0.2 pN, which is comparable to forces due to thermal fluctuation. This experimental apparatus works so easily that it will enable us to determine forces during nano-manipulation and nano-tribological measurements. PMID:22737001

  13. Study of DNA adsorption on mica surfaces using a surface force apparatus

    NASA Astrophysics Data System (ADS)

    Kan, Yajing; Tan, Qiyan; Wu, Gensheng; Si, Wei; Chen, Yunfei

    2015-02-01

    We report our studies on the adsorption properties of double-stranded DNA molecules on mica surfaces in a confined environment using a surface force apparatus. Specifically, we studied the influence of cation species and concentrations on DNA adsorption properties. Our results indicated that divalent cations (Mg2+ and Co2+) preferred to form uniform and moderately dense DNA layers on a mica substrate. By measuring the interactions between DNA-coated mica and bare mica in an aqueous solution, obvious adhesion was observed in a cobalt chloride solution, possibly due to the ion-correlation attraction between negatively charged DNA and the mica surface. Furthermore, the interaction differences that were observed with MgCl2 and CoCl2 solutions reveal that the specific adsorption behaviors of DNA molecules on a mica substrate were mediated by these two salts. Our results are helpful to elucidate the dynamics of DNA binding on a solid substrate.

  14. Modeling noncontact atomic force microscopy resolution on corrugated surfaces.

    PubMed

    Burson, Kristen M; Yamamoto, Mahito; Cullen, William G

    2012-01-01

    Key developments in NC-AFM have generally involved atomically flat crystalline surfaces. However, many surfaces of technological interest are not atomically flat. We discuss the experimental difficulties in obtaining high-resolution images of rough surfaces, with amorphous SiO(2) as a specific case. We develop a quasi-1-D minimal model for noncontact atomic force microscopy, based on van der Waals interactions between a spherical tip and the surface, explicitly accounting for the corrugated substrate (modeled as a sinusoid). The model results show an attenuation of the topographic contours by ~30% for tip distances within 5 Å of the surface. Results also indicate a deviation from the Hamaker force law for a sphere interacting with a flat surface.

  15. Lateral hydrodynamic interactions between an emulsion droplet and a flat surface evaluated by frictional force microscopy.

    PubMed

    Vakarelski, Ivan U; Dagastine, Raymond R; Chan, Derek Y C; Stevens, Geoffrey W; Higashitani, Ko; Grieser, Franz

    2010-06-01

    We introduce a lateral atomic force microscopy (AFM) method to measure the hydrodynamic drag force acting on a microscopic emulsion droplet moving parallel to a flat surface. A tetradecane oil droplet formed in an aqueous solution of sodium dodecylsulfate was attached to a V-shaped atomic force microscopy cantilever, and lateral hydrodynamic interactions between the droplet and a flat glass surface were measured using a range of scanning velocities. The droplet was positioned either far from the oscillating surface or was pressed to the surface under a constant applied load. These measurements demonstrate the feasibility of using AFM to study lateral hydrodynamic interactions and lubricity between soft matter materials relevant to a large number of applications in areas as diverse as flavor delivery in foods to the applications of emulsions or emollients in personal care products.

  16. Surface flow measurements from drones

    NASA Astrophysics Data System (ADS)

    Tauro, Flavia; Porfiri, Maurizio; Grimaldi, Salvatore

    2016-09-01

    Drones are transforming the way we sense and interact with the environment. However, despite their increased capabilities, the use of drones in geophysical sciences usually focuses on image acquisition for generating high-resolution maps. Motivated by the increasing demand for innovative and high performance geophysical observational methodologies, we posit the integration of drone technology and optical sensing toward a quantitative characterization of surface flow phenomena. We demonstrate that a recreational drone can be used to yield accurate surface flow maps of sub-meter water bodies. Specifically, drone's vibrations do not hinder surface flow observations, and velocity measurements are in agreement with traditional techniques. This first instance of quantitative water flow sensing from a flying drone paves the way to novel observations of the environment.

  17. Infrared Aerosol Radiative Forcing at the Surface and the Top of the Atmosphere

    NASA Technical Reports Server (NTRS)

    Markowicz, Krzysztof M.; Flatau, Piotr J.; Vogelmann, Andrew M.; Quinn, Patricia K.; Welton, Ellsworth J.

    2003-01-01

    We study the clear-sky aerosol radiative forcing at infrared wavelengths using data from the Aerosol Characterization Experiment (ACE-Asia) cruise of the NOAA R/V Ronald H. Brown. Limited number of data points is analyzed mostly from ship and collocated satellite values. An optical model is derived from chemical measurements, lidar profiles, and visible extinction measurements which is used to and estimate the infrared aerosol optical thickness and the single scattering albedo. The IR model results are compared to detailed Fourier Transform Interferometer based infrared aerosol forcing estimates, pyrgeometer based infrared downward fluxes, and against the direct solar forcing observations. This combined approach attests for the self-consistency of the optical model and allows to derive quantities such as the infrared forcing at the top of the atmosphere or the infrared optical thickness. The mean infrared aerosol optical thickness at 10 microns is 0.08 and the single scattering albedo is 0.55. The modeled infrared aerosol forcing reaches 10 W/sq m during the cruise, which is a significant contribution to the total direct aerosol forcing. The surface infrared aerosol radiative forcing is between 10 to 25% of the shortwave aerosol forcing. The infrared aerosol forcing at the top of the atmosphere can go up to 19% of the solar aerosol forcing. We show good agreement between satellite (CERES instrument) retrievals and model results at the top of the atmosphere. Over the Sea of Japan, the average infrared radiative forcing is 4.6 W/sq m in the window region at the surface and it is 1.5 W/sq m at top of the atmosphere. The top of the atmosphere IR forcing efficiency is a strong function of aerosol temperature while the surface IR forcing efficiency varies between 37 and 55 W/sq m (per infrared optical depth unit). and changes between 10 to 18 W/sq m (per infrared optical depth unit).

  18. Spikes removal in surface measurement

    NASA Astrophysics Data System (ADS)

    Podulka, P.; Pawlus, P.; Dobrzański, P.; Lenart, A.

    2014-03-01

    Several cylinder surface topographies made from grey cast iron were measured by Talysurf CCI white light interferometer with and without use of spikes filter. They were plateau honed by abrasive stones. Measured area was 3.3 mm × 3.3 mm, height resolution was 0.01 nm. The forms were eliminated using polynomial of the 3rd degree. After it, spikes were removed using four methods. These approaches were compared. Parameters of the smaller and highest sensitivity on spikes presence were selected.

  19. Forces on nuclei moving on autoionizing molecular potential energy surfaces.

    PubMed

    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.

  20. Unbinding forces and energies between a siRNA molecule and a dendrimer measured by force spectroscopy

    NASA Astrophysics Data System (ADS)

    Dumitru, Andra C.; Herruzo, Elena T.; Rausell, Estrella; Ceña, Valentin; Garcia, Ricardo

    2015-11-01

    We have measured the intermolecular forces between small interference RNA (siRNA) and polyamidoamine dendrimers at the single molecular level. A single molecule force spectroscopy approach has been developed to measure the unbinding forces and energies between a siRNA molecule and polyamidoamine dendrimers deposited on a mica surface in a buffer solution. We report three types of unbinding events which are characterized by forces and free unbinding energies, respectively, of 28 pN, 0.709 eV; 38 pN, 0.722 eV; and 50 pN, 0.724 eV. These events reflect different possible electrostatic interactions between the positive charges of one or two dendrimers and the negatively charged phosphate groups of a single siRNA. We have evidence of a high binding affinity of siRNA towards polyamidoamine dendrimers that leads to a 45% probability of measuring specific unbinding events.

  1. Unbinding forces and energies between a siRNA molecule and a dendrimer measured by force spectroscopy.

    PubMed

    Dumitru, Andra C; Herruzo, Elena T; Rausell, Estrella; Ceña, Valentin; Garcia, Ricardo

    2015-12-21

    We have measured the intermolecular forces between small interference RNA (siRNA) and polyamidoamine dendrimers at the single molecular level. A single molecule force spectroscopy approach has been developed to measure the unbinding forces and energies between a siRNA molecule and polyamidoamine dendrimers deposited on a mica surface in a buffer solution. We report three types of unbinding events which are characterized by forces and free unbinding energies, respectively, of 28 pN, 0.709 eV; 38 pN, 0.722 eV; and 50 pN, 0.724 eV. These events reflect different possible electrostatic interactions between the positive charges of one or two dendrimers and the negatively charged phosphate groups of a single siRNA. We have evidence of a high binding affinity of siRNA towards polyamidoamine dendrimers that leads to a 45% probability of measuring specific unbinding events.

  2. Two techniques for measuring locomotion impact forces during zero G

    NASA Technical Reports Server (NTRS)

    Greenisen, Michael C.; Smith, Richard A.; Klute, Glenn K.; Mccaulley, James B.

    1993-01-01

    A load-cell-instrumented treadmill mated to a Kistler force plate was used to investigate two methods of force measurement instrumentation during treadmill ambulation in zero g, created by parabolic flight on NASA's KC-135 aircraft. Current spaceflight treadmills do not have adequate instrumentation to determine the resultant foot impact force applied during restrained ambulation. Accurate measurement of foot-ground reaction forces is critical in attaining proper one-g loading, therefore ensuring proper musculoskeletal conditioning. Treadmill instrumentation and force plate measurements were compared for frequency response and linearity. Locomotion impact data were also collected under one-g laboratory settings and in Keplerian flight. The first resonant frequency for both techniques was found to be well above the primary frequency content of the locomotive forces. Peak impact forces measured by the two systems compared to within 10 percent.

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

    PubMed

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

    2014-08-12

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

  4. Dynamic forces between bubbles and surfaces and hydrodynamic boundary conditions.

    PubMed

    Manor, Ofer; Vakarelski, Ivan U; Stevens, Geoffrey W; Grieser, Franz; Dagastine, Raymond R; Chan, Derek Y C

    2008-10-21

    A bubble attached to the end of an atomic force microscope cantilever and driven toward or away from a flat mica surface across an aqueous film is used to characterize the dynamic force that arises from hydrodynamic drainage and electrical double layer interactions across the nanometer thick intervening aqueous film. The hydrodynamic response of the air/water interface can range from a classical fully immobile, no-slip surface in the presence of added surfactants to a partially mobile interface in an electrolyte solution without added surfactants. A model that includes the convection and diffusion of trace surface contaminants can account for the observed behavior presented. This model predicts quantitatively different interfacial dynamics to the Navier slip model that can also be used to fit dynamic force data with a post hoc choice of a slip length.

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  6. Measurement of polyamide and polystyrene adhesion with coated-tip atomic force microscopy.

    PubMed

    Thio, Beng Joo Reginald; Meredith, J Carson

    2007-10-01

    This work presents atomic force microscopy (AFM) measurements of adhesion forces between polyamides, polystyrene and AFM tips coated with the same materials. The polymers employed were polyamide 6 (PA6), PA66, PA12 and polystyrene (PS). All adhesion forces between the various unmodified or modified AFM tips and the polymer surfaces were in the range -1.5 to -8 nN. The weakest force was observed for an unmodified AFM tip with a PS surface and the strongest was between a PS-coated tip and PS surface. The results point to both the benefits and drawbacks of coated-tip AFM force-distance measurements. Adhesion forces between the two most dissimilar (PA6-PS and PA66-PS) materials were significantly asymmetric, e.g., the forces were different depending on the relative placement of each polymer on the AFM tip or substrate. Materials with similar chemistry and intermolecular interactions yielded forces in close agreement regardless of placement on tip or substrate. Using experimental forces, we calculated the contact radii via four models: Derjaguin, Muller, and Toporov; Johnson, Kendall, and Roberts; parametric tip-force-distance relation; and a square pyramid-flat surface (SPFS) model developed herein. The SPFS model gave the most reasonable contact tip radius estimate. Hamaker constants calculated from the SPFS model using this radius agreed in both magnitude and trends with experiment and Lifshitz theory.

  7. Interferometric measurement of functional surfaces

    NASA Astrophysics Data System (ADS)

    Lehmann, Peter; Xie, Weichang; Kühnhold, Peter; Niehues, Jan

    2013-06-01

    Increasing capabilities in precision manufacturing and micro technology are accompanied by increasing demands of high precision industrial metrology systems. Especially for measuring functional surfaces, areal optical principles are widely used. If, in addition, nanometer height resolution is needed interferometers seem to be the most promising instruments. First, this contribution focuses on the transfer characteristics of white-light interferometers with microscopic field of view. In general, microscopic instruments suffer from their limited lateral resolution capabilities. Hence, the transfer function of these instruments is typically assumed to show a linear low-pass characteristic. We studied the transfer characteristics of white-light interferometers by theoretical simulations and experimental investigations. Our results show that in most practical cases these instruments behave nonlinear, i.e. the output surface profile cannot be obtained from the input profile by a simple linear filter operation. Although they are well-established, there are some further limitations of white-light interferometers if they are used to measure micro or even sub-microstructures. If edges, steeper slopes or abrupt slope changes are present on a measuring object characteristic errors such as batwings occur. Furthermore, a high effort concerning the correction of chromatic aberration is necessary in order to avoid dispersion effects. Otherwise, there will be systematic discrepancies between profiles obtained from evaluation of the coherence peak and those resulting from the phase of the interference signals. These may lead to 2π phase jumps if the fringe order is obtained from the position of the coherence peak. Finally, measurement artifacts may also result if the measured micro-structure shows discontinuities of the surface slope. This contribution analyses the different phenomena and discusses approaches to overcome existing limitations.

  8. Subminiature transducers for measuring forces and deformation of heart muscle

    NASA Technical Reports Server (NTRS)

    Feldstein, C.; Osher, J. V.; Lewis, G. W.; Silver, R. H.; Duran, E. N.

    1975-01-01

    Two subminiature transducers, one measuring muscle forces and one measuring muscle displacement, can be inserted into heart muscle without interfering with it. Probe, approximately 1 mm (0.04 in), causes no damage to heart muscle. Probe can be rotated to different positions to measure muscle forces from various directions.

  9. Surface forces and properties of foam films from rhamnolipid biosurfactants.

    PubMed

    Cohen, R; Exerowa, D

    2007-10-31

    Foam films are considered as a convenient model to study the interaction behaviour and surface properties of microbial rhamnolipid type biosurfactants. The Scheludko-Exerowa microinterferometric methodology of film thickness measurements is employed for experimental studies of microscopic foam films formed from aqueous solutions of a single rhamnolipid Rh1 (with one rhamnosyl head group) and of mixtures of rhamnolipid surfactants Rh1 and Rh2 (with two rhamnosyl head groups) at ratios Rh2/Rh1=1.2 and Rh2/Rh1=0.69. The measurements of the equilibrium thickness (h) of the obtained films as a function of surfactant concentration (Cs) and electrolyte (NaCl) concentration (C el) determine the conditions for obtaining common, common black and Newton black films. The saturation values of the diffuse electric layer potential phi 0 approximately 60 mV for the Rh1.2 and phi 0 approximately 94 mV for the Rh0.69 common films conform the ionic character of the rhamnolipids. The h(C el) curves of the rhamnolipid foam films and the directly measured disjoining pressure (Pi(h)) isotherms indicate the ranges of action of the DLVO and non-DLVO surface forces. The obtained foam film parameters allow their practical use in ecology and in various technological processes where rhamnolipid surfactants are used. Experiments with model lung surfactant (Infasurf) foam films with rhamnolipid added outline a perspective for the potential application of the foam film for investigating the effect of rhamnolipids on human alveoli.

  10. Critical Casimir forces in colloidal suspensions on chemically patterned surfaces.

    PubMed

    Soyka, Florian; Zvyagolskaya, Olga; Hertlein, Christopher; Helden, Laurent; Bechinger, Clemens

    2008-11-14

    We investigate the behavior of colloidal particles immersed in a binary liquid mixture of water and 2,6-lutidine in the presence of a chemically patterned substrate. Close to the critical point of the mixture, the particles are subjected to critical Casimir interactions with force components normal and parallel to the surface. Because the strength and sign of these interactions can be tuned by variations in the surface properties and the mixtures temperature, critical Casimir forces allow the formation of highly ordered monolayers but also extend the use of colloids as model systems.

  11. Critical Casimir Forces in Colloidal Suspensions on Chemically Patterned Surfaces

    NASA Astrophysics Data System (ADS)

    Soyka, Florian; Zvyagolskaya, Olga; Hertlein, Christopher; Helden, Laurent; Bechinger, Clemens

    2008-11-01

    We investigate the behavior of colloidal particles immersed in a binary liquid mixture of water and 2,6-lutidine in the presence of a chemically patterned substrate. Close to the critical point of the mixture, the particles are subjected to critical Casimir interactions with force components normal and parallel to the surface. Because the strength and sign of these interactions can be tuned by variations in the surface properties and the mixtures temperature, critical Casimir forces allow the formation of highly ordered monolayers but also extend the use of colloids as model systems.

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

    NASA Technical Reports Server (NTRS)

    Holm, Ragnar

    1944-01-01

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

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

    PubMed Central

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

    2015-01-01

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

  14. Probing the interaction between air bubble and sphalerite mineral surface using atomic force microscope.

    PubMed

    Xie, Lei; Shi, Chen; Wang, Jingyi; Huang, Jun; Lu, Qiuyi; Liu, Qingxia; Zeng, Hongbo

    2015-03-03

    The interaction between air bubbles and solid surfaces plays important roles in many engineering processes, such as mineral froth flotation. In this work, an atomic force microscope (AFM) bubble probe technique was employed, for the first time, to directly measure the interaction forces between an air bubble and sphalerite mineral surfaces of different hydrophobicity (i.e., sphalerite before/after conditioning treatment) under various hydrodynamic conditions. The direct force measurements demonstrate the critical role of the hydrodynamic force and surface forces in bubble-mineral interaction and attachment, which agree well with the theoretical calculations based on Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. The hydrophobic disjoining pressure was found to be stronger for the bubble-water-conditioned sphalerite interaction with a larger hydrophobic decay length, which enables the bubble attachment on conditioned sphalerite at relatively higher bubble approaching velocities than that of unconditioned sphalerite. Increasing the salt concentration (i.e., NaCl, CaCl2) leads to weakened electrical double layer force and thereby facilitates the bubble-mineral attachment, which follows the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory by including the effects of hydrophobic interaction. The results provide insights into the basic understanding of the interaction mechanism between bubbles and minerals at nanoscale in froth flotation processes, and the methodology on probing the interaction forces of air bubble and sphalerite surfaces in this work can be extended to many other mineral and particle systems.

  15. Long Term Surface Salinity Measurements

    NASA Technical Reports Server (NTRS)

    Schmitt, Raymond W.; Brown, Neil L.

    2005-01-01

    Our long-term goal is to establish a reliable system for monitoring surface salinity around the global ocean. Salinity is a strong indicator of the freshwater cycle and has a great influence on upper ocean stratification. Global salinity measurements have potential to improve climate forecasts if an observation system can be developed. This project is developing a new internal field conductivity cell that can be protected from biological fouling for two years. Combined with a temperature sensor, this foul-proof cell can be deployed widely on surface drifters. A reliable in-situ network of surface salinity sensors will be an important adjunct to the salinity sensing satellite AQUARIUS to be deployed by NASA in 2009. A new internal-field conductivity cell has been developed by N Brown, along with new electronics. This sensor system has been combined with a temperature sensor to make a conductivity - temperature (UT) sensor suitable for deployment on drifters. The basic sensor concepts have been proven on a high resolution CTD. A simpler (lower cost) circuit has been built for this application. A protection mechanism for the conductivity cell that includes antifouling protection has also been designed and built. Mr. A.Walsh of our commercial partner E-Paint has designed and delivered time-release formulations of antifoulants for our application. Mr. G. Williams of partner Clearwater Instrumentation advised on power and communication issues and supplied surface drifters for testing.

  16. Reflectance measurements from particulate surfaces

    NASA Astrophysics Data System (ADS)

    Peltoniemi, J.; Gritsevich, M.; Hakala, T.; Penttilä, A.; Eskelinen, J.; Dagsson-Waldhauserova, P.; Arnalds, O.; Guirado, D.; Muinonen, K.

    2014-07-01

    Asteroids consists of, e.g., metals and rocky materials, and comets consist of, e.g., icy and rocky materials and dust. Their surfaces can be covered by small particles. To certain extent, these surfaces can resemble some natural or artificial surfaces on the Earth, such as snow layers, sand, gravels, or silt. By measuring the reflectance from such surfaces, one can gain better understanding on how to interpret astronomical observations of asteroids and comets. Even if not completely analogous, these samples and measurements provide a strict test bed for the scattering models applied to interpret observations of small Solar System bodies. FIGIFIGO (Finnish Geodetic Institute's Field Gonio-spectro-polari- radiometer) can measure the bidirectional reflectance factor (BRF) of surface targets of a diameter of around 10 cm, in a selected angular range and resolution, in the spectral range of 400-2400 nm, at about 10-nm resolution, including linear polarisation (Stokes I, Q, and U, or reflection coefficient matrix elements R_{11}, R_{12}, and R_{13}). Using FIGIFIGO, over 500 samples have been measured over the past years, including over 100 snow samples and almost 100 samples resembling sand, silt, soil, dust, or gravel. For planetary studies, especially interesting are dark volcanic ash and silt samples from Eyjafjallajökull and Grímsvönt eruptions. These have been measured loose and compressed, smooth and rough, purely and deposited on snow. Further single-scattering measurements using the Granada setup and measurements using the Univ. Helsinki integrating sphere complement the picture. Generally, we have observed that the reflectance from volcanic materials behaves mostly as expected and modelled. BRF shows typical bowl shape with strong phase-angle dependence. Spectral features are smooth, with slight angular dependence. Polarisation depends strongly on the phase angle, weaker on other angles defining the scattering geometry, and smoothly on the wavelength. There

  17. Adhesion forces in liquid media: effect of surface topography and wettability.

    PubMed

    Serro, A P; Colaço, R; Saramago, B

    2008-09-15

    This work was motivated by the unexpected values of adhesion forces measured between an atomic force microscopy tip and the hydrophobic surface of ultra-high-molecular-weight polyethylene. Two types of samples with different roughness but similar wettability were tested. Adhesion forces of similar magnitude were obtained in air and in polar liquids (water and Hank's Balanced Salt Solution, a saline solution) with the rougher sample. In contrast, the adhesion forces measured on the smoother sample in air were much higher than those measured in water or in the aqueous solution. Those experimental results suggested the presence of nanobubbles at the interface between the rough sample and the polar liquids. The existence of the nanobubbles was further confirmed by the images of the interface obtained in noncontact tapping mode. The adhesion forces measured in a nonpolar liquid (hexadecane) were small and of the same order of magnitude for both samples and their values were in good agreement with the predictions of the London-Hamaker approach for the van der Waals interactions. Finally, we correlate the appearance of nanobubbles with surface topography. The conclusion of this work is that adhesion forces measured in aqueous media may be strongly affected by the presence of nanobubbles if the surface presents topographical accidents.

  18. Fermi surface measurements of lutetium

    NASA Astrophysics Data System (ADS)

    Johanson, W. R.; Crabtree, G. W.; Schmidt, F. A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (101¯0) and (112¯0) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  19. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  20. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-01-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of Lutetium at temperatures down to .3K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a non-magnetic prototype of the structurally similar (hcp), trivalent, heavy rare-earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  1. Characterization of the surface charge distribution on kaolinite particles using high resolution atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Kumar, Naveen; Zhao, Cunlu; Klaassen, Aram; van den Ende, Dirk; Mugele, Frieder; Siretanu, Igor

    2016-02-01

    Most solid surfaces, in particular clay minerals and rock surfaces, acquire a surface charge upon exposure to an aqueous environment due to adsorption and/or desorption of ionic species. Macroscopic techniques such as titration and electrokinetic measurements are commonly used to determine the surface charge and ζ -potential of these surfaces. However, because of the macroscopic averaging character these techniques cannot do justice to the role of local heterogeneities on the surfaces. In this work, we use dynamic atomic force microscopy (AFM) to determine the distribution of surface charge on the two (gibbsite-like and silica-like) basal planes of kaolinite nanoparticles immersed in aqueous electrolyte with a lateral resolution of approximately 30 nm. The surface charge density is extracted from force-distance curves using DLVO theory in combination with surface complexation modeling. While the gibbsite-like and the silica-like facet display on average positive and negative surface charge values as expected, our measurements reveal lateral variations of more than a factor of two on seemingly atomically smooth terraces, even if high resolution AFM images clearly reveal the atomic lattice on the surface. These results suggest that simple surface complexation models of clays that attribute a unique surface chemistry and hence homogeneous surface charge densities to basal planes may miss important aspects of real clay surfaces.

  2. Application of the FlexiForce contact surface force sensor to continuous extraocular compression monitoring during craniotomy for cerebral aneurysms.

    PubMed

    Mutoh, Tatsushi; Ishikawa, Tatsuya; Nishimura, Hiromi; Yasui, Nobuyuki

    2010-01-01

    The aims of this study were to introduce our newly developed device equipped with a contact surface force sensor (FlexiForce) for monitoring extraocular compression continuously, and to illustrate its potential clinical application using this device in patients undergoing uncomplicated frontotemporal or bifrontal craniotomy for surgical clipping of unruptured anterior circulation aneurysms. In a pilot study with volunteers, we determined the critical force of 100 gf to cause painful ocular sensation. Then we performed the bilateral extraocular force measurements in 15 patients undergoing uncomplicated frontotemporal or bifrontal craniotomy for surgical clipping of unruptured anterior circulation aneurysms. Extraocular force increased immediately after retraction of the flap, increased to 144+/-26 gf (mean+/-SD) during lower craniotomy close to the orbit, was maintained at 91+/-18 gf during microsurgery, and returned close to baseline at 24+/-14 gf after restoration of skin flap retraction. Such changes were observed only on the surgical side in frontotemporal craniotomy. Abnormal increase in extraocular force was effectively reduced by placing a real-time digital panel meter to warn surgeons to avoid excessive skin flap retraction during the surgical procedure. In conclusion, this new tool may allow us to monitor the external forces that can be applied intraoperatively to the ocular globe in the supine position.

  3. Measuring the Forces between Magnetic Dipoles

    ERIC Educational Resources Information Center

    Gayetsky, Lisa E.; Caylor, Craig L.

    2007-01-01

    We describe a simple undergraduate lab in which students determine how the force between two magnetic dipoles depends on their separation. We consider the case where both dipoles are permanent and the case where one of the dipoles is induced by the field of the other (permanent) dipole. Agreement with theoretically expected results is quite good.

  4. Spatial spectrograms of vibrating atomic force microscopy cantilevers coupled to sample surfaces

    SciTech Connect

    Wagner, Ryan; Raman, Arvind; Proksch, Roger

    2013-12-23

    Many advanced dynamic Atomic Force Microscopy (AFM) techniques such as contact resonance, force modulation, piezoresponse force microscopy, electrochemical strain microscopy, and AFM infrared spectroscopy exploit the dynamic response of a cantilever in contact with a sample to extract local material properties. Achieving quantitative results in these techniques usually requires the assumption of a certain shape of cantilever vibration. We present a technique that allows in-situ measurements of the vibrational shape of AFM cantilevers coupled to surfaces. This technique opens up unique approaches to nanoscale material property mapping, which are not possible with single point measurements alone.

  5. Force plate for measuring small animal forces by digital speckle pattern interferometry

    NASA Astrophysics Data System (ADS)

    Arroyo, M. Pilar; Bea, José Antonio; Andrés, Nieves; Osta, Rosario; Doblaré, Manuel

    2007-06-01

    This paper presents a force plate specially designed for measuring ground reaction forces in small animals. Digital Speckle Pattern Interferometry (DSPI) is used to measure the plate deformation produced by the animal. Elasticity theory is used to obtain force magnitude and application position from the vertical displacement field measured with DSPI. The force plate has been tested with static weights of 5g and 10g at various locations on the plate. Some experiments with 20g body weight transgenic mice are also reported.

  6. Method for measuring surface temperature

    DOEpatents

    Baker, Gary A.; Baker, Sheila N.; McCleskey, T. Mark

    2009-07-28

    The present invention relates to a method for measuring a surface temperature using is a fluorescent temperature sensor or optical thermometer. The sensor includes a solution of 1,3-bis(1-pyrenyl)propane within a 1-butyl-1-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid solvent. The 1,3-bis(1-pyrenyl)propane remains unassociated when in the ground state while in solution. When subjected to UV light, an excited state is produced that exists in equilibrium with an excimer. The position of the equilibrium between the two excited states is temperature dependent.

  7. Adhesive Force of a Spider Mite, Tetranychus urticae, to a Flat Smooth Surface

    NASA Astrophysics Data System (ADS)

    Mizutani, Katsumi; Egashira, Kai; Toukai, Tadashi; Ogushi, Jun

    The adhesion of a spider mite to a surface of a flat smooth plate is investigated as a model for micromachine parts to adhere to and move on such surfaces. The measurement of adhesive force is carried out under various conditions in which plate material, surface roughness of a plate and environmental humidity are differed. The adhesion mechanism is also discussed. Of the forces acting between a spider mite and a surface, one from dispersion interaction is the most dominant because (1) there is a high correlation between the adhesive force and the dispersion force component of surface energy with adhesive forces of 8.2µN for glass, 9.7µN for mica, 9.9µN for silicon and 12.1µN for gold, and because (2) high humidity and high surface roughness reduce the adhesive force. For strong adhesion based on work of adhesion, spider mites have tenent hairs with a bell-shaped end.

  8. "Magic" surface clustering of borazines driven by repulsive intermolecular forces.

    PubMed

    Kervyn, Simon; Kalashnyk, Nataliya; Riello, Massimo; Moreton, Ben; Tasseroul, Jonathan; Wouters, Johan; Jones, Tim S; De Vita, Alessandro; Costantini, Giovanni; Bonifazi, Davide

    2013-07-15

    It's a kind of magic: Hydroxy pentaaryl borazine molecules self-assemble into small clusters (see structure) on Cu(111) surfaces, whereas with symmetric hexaaryl borazine molecules large islands are obtained. Simulations indicate that the observed "magic" cluster sizes result from long-range repulsive Coulomb forces arising from the deprotonation of the B-OH groups of the hydroxy pentaaryl borazine.

  9. Probing characteristics of collagen molecules on various surfaces via atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Su, Hao-Wei; Ho, Mon-Shu; Cheng, Chao-Min

    2012-06-01

    We examine, herein, specific dynamic responses of collagen molecules (i.e., observations of self-assembly and nanometric adhesion force measurements of type-I collagen molecules) as they interact with either a hydrophobic or a hydrophilic surface at two distinct temperatures, using a liquid-type atomic force microscope. We conclude that, regardless of surface hydrophobicity/hydrophilicity, assembled microfibrils eventually distribute homogeneously in accordance with changes in surface-related mechanical properties of collagen molecules at different self-assembly stages.

  10. Radiative forcing by light absorbing impurities in snow from MODIS surface reflectance data

    NASA Astrophysics Data System (ADS)

    Painter, Thomas H.; Bryant, Ann C.; Skiles, S. McKenzie

    2012-09-01

    The episodic deposition of dust and carbonaceous particles to snow decreases snow surface albedo and enhances absorption of solar radiation, leading to accelerated snowmelt, negative glacier mass balance, and the snow-albedo feedback. Until now, no remote sensing retrieval has captured the spatial and temporal variability of this forcing. Here we present the MODIS Dust Radiative Forcing in Snow (MODDRFS) model that retrieves surface radiative forcing by light absorbing impurities in snow cover from Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data. Validation of MODDRFS with a 7-year record of in situ measurements indicates the radiative forcing retrieval has positive bias at lower values and slight negative bias above 200 W m-2, subject to mixed pixel uncertainties. With bias-correction, MODDRFS has a root mean squared error of 32 W m-2 and mean absolute error of 25 W m-2. We demonstrate MODDRFS in the Upper Colorado River Basin and Hindu Kush-Himalaya.

  11. Modifications of the structure of the pericellular matrix measured via optical force probe microscopy

    NASA Astrophysics Data System (ADS)

    McLane, Louis; Kramer, Anthony; Chang, Patrick; Curtis, Jennifer

    2013-03-01

    The pericellular matrix is a large protein and polysaccharide rich polymer layer attached to the surface of many cells, and which often extends several microns out from the cell surface into the surrounding extracellular space. Here we study the intrinsic nature and modifications of the structure of the pericellular coat on rat chondrocytes with the use of optical force probe microscopy. Optical force probe studies allow us to make both dynamic force measurements as well as equilibrium force measurements throughout the coat. These force measurements are used to observe the structural change in the coat with the addition of exogenous aggrecan. Not only does addition of exogenous aggrecan dramatically swell our coat to well over twice in size, our analysis indicates that the addition of exogenous aggrecan decreases the mesh size throughout the coat. We speculate that the added aggrecan binds to available binding sites along the hyaluronan chain, both enlarging the coat's size as well as tightening up the opening within the coat. We further suggest that the available binding sites for the exogenous aggrecan are abundant in the outer edges of the coat, as both the dynamic and equilibrium forces in this region are changed. Here, both force measurements show that forces closest to the cell membrane remain relatively unchanged, while the forces in the outer region of the coat are increased. These results are consistent with those obtained with complementary measurements using quantitative particle exclusion assays.

  12. Precision Measurement of the Casimir Force for Au Using a Dynamic Afm

    NASA Astrophysics Data System (ADS)

    Chang, C.-C.; Banishev, A. A.; Castillo-Garza, R.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Mohideen, U.

    2012-07-01

    The gradient of the Casimir force between carefully cleaned Au surfaces of a sphere and a plate is measured using a dynamic atomic force microscope in the frequency modulation regime in high vacuum. The electrostatic calibration of the setup did not reveal any effect of patches or surface contaminants. The experimental data for the force gradient are found to be consistent with theory using the plasma model approach over the entire measurement range. The Drude model approach is excluded by the data at separations from 235 to 400 nm at a 67% confidence level.

  13. Parallel force measurement with a polymeric microbeam array using an optical microscope and micromanipulator.

    PubMed

    Sasoglu, F Mert; Bohl, Andrew J; Allen, Kathleen B; Layton, Bradley E

    2009-01-01

    An image analysis method and its validation are presented for tracking the displacements of parallel mechanical force sensors. Force is measured using a combination of beam theory, optical microscopy, and image analysis. The primary instrument is a calibrated polymeric microbeam array mounted on a micromanipulator with the intended purpose of measuring traction forces on cell cultures or cell arrays. One application is the testing of hypotheses involving cellular mechanotransduction mechanisms. An Otsu-based image analysis code calculates displacement and force on cellular or other soft structures by using edge detection and image subtraction on digitally captured optical microscopy images. Forces as small as 250+/-50 nN and as great as 25+/-2.5 microN may be applied and measured upon as few as one or as many as hundreds of structures in parallel. A validation of the method is provided by comparing results from a rigid glass surface and a compliant polymeric surface.

  14. Microsystems for cellular force measurement: a review

    NASA Astrophysics Data System (ADS)

    Rayne Zheng, Xiaoyu; Zhang, Xin

    2011-05-01

    Microsystems are providing key advances in studying single cell mechanical behavior. The mechanical interaction of cells with their extracellular matrix is fundamentally important for cell migration, division, phagocytosis and aptoptosis. This review reports the development of microsystems on studying cell forces. Microsystems provide advantages of studying single cells since the scale of cells is on the micron level. The components of microsystems provide culture, loading, guiding, trapping and on chip analysis of cellular mechanical forces. This paper gives overviews on how MEMS are advancing in the field of cell biomechno sensory systems. It presents different materials, and mode of studying cell mechanics. Finally, we comment on the future directions and challenges on the state of art techniques.

  15. Force Measurement on the GLAST Delta II Flight

    NASA Technical Reports Server (NTRS)

    Gordon, Scott; Kaufman, Daniel

    2009-01-01

    This viewgraph presentation reviews the interface force measurement at spacecraft separation of GLAST Delta II. The contents include: 1) Flight Force Measurement (FFM) Background; 2) Team Members; 3) GLAST Mission Overview; 4) Methodology Development; 5) Ground Test Validation; 6) Flight Data; 7) Coupled Loads Simulation (VCLA & Reconstruction); 8) Basedrive Simulation; 9) Findings; and 10) Summary and Conclusions.

  16. Measurements of particle-wall interaction forces using simultaneous position and force detection (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Kashchuk, Anatolii V.; Bui, Ann A. M.; Stilgoe, Alexander B.; Carberry, David M.; Nieminen, Timo A.; Rubinsztein-Dunlop, Halina

    2016-09-01

    Particle-wall interactions are important in biology, micromachining, coagulation studies, and many other areas of science. As a contactless tool, optical tweezers are ideal for measuring these kind of interactions. Here we will present a new method for calculating the non-optical forces acting on a trapped particle using simultaneous position and force detection. Analysis of the particle's Brownian motion when trapped gives a measure of all the forces experienced by the particle. In contrast, measuring only the light's momentum change directly gives the solely optical force. This is achieved measuring the changes in the scattered light. The difference between the forces recorded by the two techniques reveals the external forces acting on the trapped particle. Therefore, by trapping the particle close to a wall, one can study the particle-wall interaction force in details. The simulation were done using the optical tweezer toolbox [1] to find the optical force acting on a particle. The net force was calculated from a Brownian motion's statistics of a trapped particle in the presence of the exponential external force. By using the proposed method, we were able to successfully reconstruct the external force. The experiment was done on a trapped spherical PMMA particle (d=2.2um) close to the 3D-printed wall. For the particle-wall distance 0.7um the non-optical force is 100fN . The experiment and simulation results confirm the efficiency of the proposed method for an external force measurements. [1] Nieminen et al., J. Opt. A 9, S196-S203 (2007).

  17. Recent Investments by NASA's National Force Measurement Technology Capability

    NASA Technical Reports Server (NTRS)

    Commo, Sean A.; Ponder, Jonathan D.

    2016-01-01

    The National Force Measurement Technology Capability (NFMTC) is a nationwide partnership established in 2008 and sponsored by NASA's Aeronautics Evaluation and Test Capabilities (AETC) project to maintain and further develop force measurement capabilities. The NFMTC focuses on force measurement in wind tunnels and provides operational support in addition to conducting balance research. Based on force measurement capability challenges, strategic investments into research tasks are designed to meet the experimental requirements of current and future aerospace research programs and projects. This paper highlights recent and force measurement investments into several areas including recapitalizing the strain-gage balance inventory, developing balance best practices, improving calibration and facility capabilities, and researching potential technologies to advance balance capabilities.

  18. Impact of Thermal Gradients on Wind Tunnel Force Measurements

    NASA Technical Reports Server (NTRS)

    Hereford, James; Parker, Peter A.; Rhew, Ray D.

    1999-01-01

    In a wind tunnel facility, the direct measurement of forces and moments induced on the model are performed by a force measurement balance. The measurement balance is a precision-machined device that has strain gages at strategic locations to measure the strain (i.e., deformations) due to applied forces and moments. The strain gages convert the strain (and hence the applied force) to an electrical voltage that is measured by external meters. Thermal gradients can complicate the process, however. Thermal gradients on the balance cause differential expansion (or contraction) of various parts of the balance that induce a strain that is detected by the strain gages and is indistinguishable from an external applied force. The thermal gradients can result when testing is done at elevated temperatures or at cryogenic temperatures such as at the National Transonic Facility (NTF) at NASA Langley Research Center (LaRC).

  19. The role of deformable structured surfaces on viscous forces during peeling

    NASA Astrophysics Data System (ADS)

    Dhong, Charles; Frechette, Joelle

    It is known that tree frogs are able to adhere well in flooded environments, presumably due to their interconnected network of drainage channels formed by hexagonal epithelial cells in their toe pads. To investigate this effect, a patterned surface of hexagonally arranged cylindrical posts was brought close to a stationary substrate in a submerged, viscous fluid via a normal load, and then peeled off to measure a retraction force. Because these structured surfaces were made from PDMS, they are able to deform throughout the process. We find that these deformable surfaces further reduce the work required to peel apart the two surfaces, even when compared to previous studies in the same system with rigid structures, and we isolated these contributions independent of conservative forces. We then conducted experiments to compare the effect of deformation on the viscous forces and conservative forces. We find that there are several regimes where deformation either increases or decreases the retraction force since we have found that elasticity decreases retraction forces when considering viscous contributions but is also known to increase adhesion in the context of conservative forces. Office of Naval Research, National Science Foundation, Hopkins Extreme Materials Institute.

  20. Magnetic tweezers: micromanipulation and force measurement at the molecular level.

    PubMed Central

    Gosse, Charlie; Croquette, Vincent

    2002-01-01

    Cantilevers and optical tweezers are widely used for micromanipulating cells or biomolecules for measuring their mechanical properties. However, they do not allow easy rotary motion and can sometimes damage the handled material. We present here a system of magnetic tweezers that overcomes those drawbacks while retaining most of the previous dynamometers properties. Electromagnets are coupled to a microscope-based particle tracking system through a digital feedback loop. Magnetic beads are first trapped in a potential well of stiffness approximately 10(-7) N/m. Thus, they can be manipulated in three dimensions at a speed of approximately 10 microm/s and rotated along the optical axis at a frequency of 10 Hz. In addition, our apparatus can work as a dynamometer relying on either usual calibration against the viscous drag or complete calibration using Brownian fluctuations. By stretching a DNA molecule between a magnetic particle and a glass surface, we applied and measured vertical forces ranging from 50 fN to 20 pN. Similarly, nearly horizontal forces up to 5 pN were obtained. From those experiments, we conclude that magnetic tweezers represent a low-cost and biocompatible setup that could become a suitable alternative to the other available micromanipulators. PMID:12023254

  1. Direct measurement of the intermolecular forces between counterion-condensed DNA double helices. Evidence for long range attractive hydration forces.

    PubMed

    Rau, D C; Parsegian, V A

    1992-01-01

    Rather than acting by modifying van der Waals or electrostatic double layer interactions or by directly bridging neighboring molecules, polyvalent ligands bound to DNA double helices appear to act by reconfiguring the water between macromolecular surfaces to create attractive long range hydration forces. We have reached this conclusion by directly measuring the repulsive forces between parallel B-form DNA double helices pushed together from the separations at which they have self organized into hexagonal arrays of parallel rods. For all of the wide variety of "condensing agents" from divalent Mn to polymeric protamines, the resulting intermolecular force varies exponentially with a decay rate of 1.4-1.5 A, exactly one-half that seen previously for hydration repulsion. Such behavior qualitatively contradicts the predictions of all electrostatic double layer and van der Waals force potentials previously suggested. It fits remarkably well with the idea, developed and tested here, that multivalent counterion adsorption reorganizes the water at discrete sites complementary to unadsorbed sites on the apposing surface. The measured strength and range of these attractive forces together with their apparent specificity suggest the presence of a previously unexpected force in molecular organization.

  2. Direct measurement of the intermolecular forces between counterion-condensed DNA double helices. Evidence for long range attractive hydration forces.

    PubMed Central

    Rau, D C; Parsegian, V A

    1992-01-01

    Rather than acting by modifying van der Waals or electrostatic double layer interactions or by directly bridging neighboring molecules, polyvalent ligands bound to DNA double helices appear to act by reconfiguring the water between macromolecular surfaces to create attractive long range hydration forces. We have reached this conclusion by directly measuring the repulsive forces between parallel B-form DNA double helices pushed together from the separations at which they have self organized into hexagonal arrays of parallel rods. For all of the wide variety of "condensing agents" from divalent Mn to polymeric protamines, the resulting intermolecular force varies exponentially with a decay rate of 1.4-1.5 A, exactly one-half that seen previously for hydration repulsion. Such behavior qualitatively contradicts the predictions of all electrostatic double layer and van der Waals force potentials previously suggested. It fits remarkably well with the idea, developed and tested here, that multivalent counterion adsorption reorganizes the water at discrete sites complementary to unadsorbed sites on the apposing surface. The measured strength and range of these attractive forces together with their apparent specificity suggest the presence of a previously unexpected force in molecular organization. Images FIGURE 1 PMID:1540693

  3. Coalescence and noncoalescence of sessile drops: impact of surface forces.

    PubMed

    Karpitschka, Stefan; Hanske, Christoph; Fery, Andreas; Riegler, Hans

    2014-06-17

    Due to capillarity, sessile droplets of identical liquids will instantaneously fuse when they come in contact at their three-phase lines. However, with drops of different, completely miscible liquids, instantaneous coalescence can be suppressed. Instead, the drops remain in a state of noncoalescence for some time, with the two drop bodies connected only by a thin neck. The reason for this noncoalescence is the surface tension difference, Δγ, between the liquids. If Δγ is sufficiently large, then it induces a sufficiently strong Marangoni flow, which keeps the main drop bodies temporarily separated. Studies with spreading drops have revealed that the boundary between instantaneous coalescence and noncoalescence is sharp (Karpitschka, S.; Riegler, H. J. Fluid. Mech. 2014, 743, R1). The boundary is a function of two parameters only: Δγ and Θ(a), the arithmetic mean of the contact angles in the moment of drop-drop contact. It appears plausible that surface forces (the disjoining pressure) could also influence the coalescence behavior. However, in experiments with spreading drops, surface forces always promote coalescence and their influence might be obscured. Therefore, we present here coalescence experiments with partially wetting liquids and compare the results to the spreading case. We adjust different equilibrium contact angles (i.e., different surface forces) with different substrate surface coatings. As for spreading drops, we observe a sharp boundary between regimes of coalescence and noncoalescence. The boundary follows the same power law relation for both partially and completely wetting cases. Therefore, we conclude that surface forces have no significant, explicit influence on the coalescence behavior of sessile drops from different miscible liquids.

  4. Atomically resolved graphitic surfaces in air by atomic force microscopy.

    PubMed

    Wastl, Daniel S; Weymouth, Alfred J; Giessibl, Franz J

    2014-05-27

    Imaging at the atomic scale using atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomic resolution of graphite and hydrogen-intercalated graphene on SiC in air. The main challenges arise from the overall surface cleanliness and the water layers which form on almost all surfaces. To further investigate the influence of the water layers, we compare data taken with a hydrophilic bulk-silicon tip to a hydrophobic bulk-sapphire tip. While atomic resolution can be achieved with both tip materials at moderate interaction forces, there are strong differences in force versus distance spectra which relate to the water layers on the tips and samples. Imaging at very low tip-sample interaction forces results in the observation of large terraces of a naturally occurring stripe structure on the hydrogen-intercalated graphene. This structure has been previously reported on graphitic surfaces that are not covered with disordered adsorbates in ambient conditions (i.e., on graphite and bilayer graphene on SiC, but not on monolayer graphene on SiC). Both these observations indicate that hydrogen-intercalated graphene is close to an ideal graphene sample in ambient environments.

  5. Understanding nanorheology and surface forces of confined thin films

    NASA Astrophysics Data System (ADS)

    Huang, Jun; Yan, Bin; Faghihnejad, Ali; Xu, Haolan; Zeng, Hongbo

    2014-02-01

    Understanding the nanorheology and associated intermolecular/surface forces of fluids in confined geometries or porous media is of both fundamental and practical importance, providing significant insights into various applications such as lubrication and micro/nanoelectromechanical systems. In this work, we briefly reviewed the fundamentals of nanoreheolgy, advances in experimental techniques and theoretical simulation methods, as well as important progress in the nanorheology of confined thin films. The advent of advanced experimental techniques such as surface forces apparatus (SFA), X-ray surface forces apparatus (XSFA) and atomic force microscope (AFM) and computational methods such as molecular dynamics simulations provides powerful tools to study a wide range of rheological phenomena at molecular level and nano scale. One of the most challenging issues unresolved is to elucidate the relationship between the rheological properties and structural evolution of the confined fluid films and particles suspensions. Some of the emerging research areas in the nanorheology field include, but are not limited to, the development of more advanced characterization techniques, design of multifunctional rheological fluids, bio-related nanorheology, and polymer brushes.

  6. Physical forces exerted by microbubbles on a surface in a traveling wave field.

    PubMed

    Brems, S; Hauptmann, M; Camerotto, E; Mertens, P W; Heyns, M; Struyf, H; De Gendt, S

    2014-02-01

    The effect of a wave with a varying traveling component on the bubble activity as well as the physical force generated by microbubbles on a surface has been studied. The acoustic emission from a collection of bubbles is measured in a 928 kHz sound field. Particle removal tests on a surface, which actually measures the applied physical force by the bubbles on that surface, indicate a very strong dependence on the angle of incidence. In other words, when the traveling wave component is maximized, the average physical force applied by microbubbles reaches a maximum. Almost complete particle removal for 78 nm silica particles was obtained for a traveling wave, while particle removal efficiency was reduced to only a few percent when a standing wave was applied. This increase in particle removal for a traveling wave is probably caused by a decrease in bubble trapping at nodes and antinodes in a standing wave field.

  7. Development of cylindrical-type finger force measuring system using force sensors and its characteristics evaluation

    NASA Astrophysics Data System (ADS)

    Kim, Hyeon-Min; Yoon, Joungwon; Shin, Hee-Suk; Kim, Gab-Soon

    2012-02-01

    Some patients cannot use their hands because of the paralysis of their fingers. Their fingers can recover with rehabilitative training, and the extent of rehabilitation can be judged by grasping a cylindrical-object with their fingers. At present, the cylindrical-object used in hospitals is only a plastic cylinder, which cannot measure grasping force of the fingers. Therefore, doctors must judge the extent of rehabilitation by watching patients' fingers as they grasp the plastic cylinder. In this paper, the development of two cylindrical-type finger force measuring systems with four force sensors for left hand and right hand were developed. The developed finger force measuring system can measure the grasping force of patients' each finger (forefinger, middle finger, ring finger and little finger), and the measured results could be used to judge the rehabilitation extent of a finger patient. The grasping force tests of men and women were performed using the developed cylindrical-type finger force measuring systems. The tests confirm that the average finger forces of right hand and left hand for men were about 194 N and 179 N, and for women, 108 N and 95 N.

  8. Calculation of Excavation Force for ISRU on Lunar Surface

    NASA Technical Reports Server (NTRS)

    Zeng, Xiangwu (David); Burnoski, Louis; Agui, Juan H.; Wilkinson, Allen

    2007-01-01

    Accurately predicting the excavation force that will be encountered by digging tools on the lunar surface is a crucial element of in-situ resource utilization (ISRU). Based on principles of soil mechanics, this paper develops an analytical model that is relatively simple to apply and uses soil parameters that can be determined by traditional soil strength tests. The influence of important parameters on the excavation force is investigated. The results are compared with that predicted by other available theories. Results of preliminary soil tests on lunar stimulant are also reported.

  9. A measurable force driven by an excitonic condensate

    SciTech Connect

    Hakioğlu, T.; Özgün, Ege; Günay, Mehmet

    2014-04-21

    Free energy signatures related to the measurement of an emergent force (≈10{sup −9}N) due to the exciton condensate (EC) in Double Quantum Wells are predicted and experiments are proposed to measure the effects. The EC-force is attractive and reminiscent of the Casimir force between two perfect metallic plates, but also distinctively different from it by its driving mechanism and dependence on the parameters of the condensate. The proposed experiments are based on a recent experimental work on a driven micromechanical oscillator. Conclusive observations of EC in recent experiments also provide a strong promise for the observation of the EC-force.

  10. Correct height measurement in noncontact atomic force microscopy.

    PubMed

    Sadewasser, Sascha; Lux-Steiner, Martha Ch

    2003-12-31

    We demonstrate that topography measurements by noncontact atomic force microscopy are subject to residual electrostatic forces. On highly oriented pyrolitic graphite (HOPG) with a submonolayer coverage of C60, we monitor the step height from C60 to HOPG as a function of dc bias between tip and sample. Because of the different contact potential of C60 and HOPG ( approximately 50 mV), the step height is strongly dependent on the dc bias. The presented results and additional simulations demonstrate clearly that for correct height measurements it is mandatory to use a Kelvin probe force microscopy method with active compensation of electrostatic forces.

  11. A Revised Force Restore Model for Land Surface Modeling.

    NASA Astrophysics Data System (ADS)

    Ren, Diandong; Xue, Ming

    2004-11-01

    To clarify the definition of the equation for the temperature toward which the soil skin temperature is restored, the prediction equations in the commonly used force restore model for soil temperature are rederived from the heat conduction equation. The derivation led to a deep-layer temperature, commonly denoted T2, that is defined as the soil temperature at depth πd plus a transient term, where d is the e-folding damping depth of soil temperature diurnal oscillations. The corresponding prediction equation for T2 has the same form as the commonly used one except for an additional term involving the lapse rate of the “seasonal mean” soil temperature and the damping depth d. A term involving the same also appears in the skin temperature prediction equation, which also includes a transient term. In the literature, T2 was initially defined as the short-term (over several days) mean of the skin temperature, but in practice it is often used as the deep-layer temperature. Such inconsistent use can lead to drift in T2 prediction over a several-day period, as is documented in this paper. When T2 is properly defined and initialized, large drift in T2 prediction is avoided and the surface temperature prediction is usually improved. This is confirmed by four sets of experiments, each for a period during each season of 2000, that are initialized using and verified against measurements of the Oklahoma Atmospheric Surface-Layer Instrumentation System (OASIS) project.


  12. Hydrophobic pore array surfaces: wetting and interaction forces in water/ethanol mixtures.

    PubMed

    Hansson, Petra M; Hormozan, Yashar; Brandner, Birgit D; Linnros, Jan; Claesson, Per M; Swerin, Agne; Schoelkopf, Joachim; Gane, Patrick A C; Thormann, Esben

    2013-04-15

    Interactions between and wetting behavior of structured hydrophobic surfaces using different concentrations of water/ethanol mixtures have been investigated. Silica surfaces consisting of pore arrays with different pore spacings and pore depths were made hydrophobic by silanization. Their static and dynamic contact angles were found to be independent of the pore depth while fewer pores on the surface, i.e. a closer resemblance to a flat surface, gave a lower contact angle. As expected, a higher amount of ethanol facilitated wetting on all the surfaces tested. Confocal Raman microscopy measurements proved both water and ethanol to penetrate into the pores. AFM colloidal probe force measurements clearly showed that formation of air cavitation was hindered between the hydrophobic surfaces in presence of ethanol, and an increase in ethanol concentration was followed by a smaller jump-in distance and a weaker adhesion force. On separation, an immediate jump-out of contact occurred. The measured forces were interpreted as being due to capillary condensation of ethanol between the surfaces giving rise to very unstable cavities immediately rupturing on surface separation.

  13. Direct measurement of cell detachment force on single cells using a new electromechanical method.

    PubMed

    Francis, G W; Fisher, L R; Gamble, R A; Gingell, D

    1987-05-01

    We describe a new device in which an accurately measured force is applied to individual adherent cells while the topography of the adhesion zone is simultaneously monitored. The force is applied via a flexible glass micropipette, attached by suction to the cell under study, and is calculated directly from the measured pipette deflection. Regions of close contact in the adhesion zone are observed using interference reflection microscopy. We have used the device to measure the force required to detach human red blood cells from hydrophobic and hydrophilic glass surfaces, and to detach Dictyostelium discoideum amoebae from a hydrophobic glass surface. The measured forces per unit length of contact perimeter are within an order of magnitude of the tensions required for membrane rupture.

  14. Measurement of axial forces via natural frequency

    NASA Astrophysics Data System (ADS)

    Petro, Samer H.; Reynolds, Don; EnChen, Shen; GangaRao, Hota V. S.

    1998-03-01

    This paper presents results from testing several suspender ropes of the Delaware Memorial Bridge using vibration measurements and a non-destructive evaluation (NDE) instrument called the Axial Load Monitor (ALM). The testing consisted of measuring the frequencies of suspender ropes and determining their tension levels. Results were compared to theoretical predictions. This paper presents the results of the testing and discusses the problems associated with vibration measurements on actual bridges.

  15. Measuring thermal rupture force distributions from an ensemble of trajectories.

    PubMed

    Swan, J W; Shindel, M M; Furst, E M

    2012-11-09

    Rupture, bond breaking, or extraction from a deep and narrow potential well requires considerable force while producing minimal displacement. In thermally fluctuating systems, there is not a single force required to achieve rupture, but a spectrum, as thermal forces can both augment and inhibit the bond breaking. We demonstrate measurement and interpretation of the distribution of rupture forces between pairs of colloidal particles bonded via the van der Waals attraction. The otherwise irreversible bond is broken by pulling the particles apart with optical tweezers. We show that an ensemble of the particle trajectories before, during and after the rupture event may be used to produce a high fidelity description of the distribution of rupture forces. This analysis is equally suitable for describing rupture forces in molecular and biomolecular contexts with a number of measurement techniques.

  16. Adhesion force interactions between cyclopentane hydrate and physically and chemically modified surfaces.

    PubMed

    Aman, Zachary M; Sloan, E Dendy; Sum, Amadeu K; Koh, Carolyn A

    2014-12-07

    Interfacial interactions between liquid-solid and solid-solid phases/surfaces are of fundamental importance to the formation of hydrate deposits in oil and gas pipelines. This work establishes the effect of five categories of physical and chemical modification to steel on clathrate hydrate adhesive force: oleamide, graphite, citric acid ester, nonanedithiol, and Rain-X anti-wetting agent. Hydrate adhesive forces were measured using a micromechanical force apparatus, under both dry and water-wet surface conditions. The results show that the graphite coating reduced hydrate-steel adhesion force by 79%, due to an increase in the water wetting angle from 42 ± 8° to 154 ± 7°. Two chemical surface coatings (nonanedithiol and the citric acid ester) induced rapid hydrate growth in the hydrate particles; nonanedithiol increased hydrate adhesive force by 49% from the baseline, while the citric acid ester coating reduced hydrate adhesion force by 98%. This result suggests that crystal growth may enable a strong adhesive pathway between hydrate and other crystalline structures, however this effect may be negated in cases where water-hydrocarbon interfacial tension is minimised. When a liquid water droplet was placed on the modified steel surfaces, the graphite and citric acid ester became less effective at reducing adhesive force. In pipelines containing a free water phase wetting the steel surface, chemical or physical surface modifications alone may be insufficient to eliminate hydrate deposition risk. In further tests, the citric acid ester reduced hydrate cohesive forces by 50%, suggesting mild activity as a hybrid anti-agglomerant suppressing both hydrate deposition and particle agglomeration. These results demonstrate a new capability to develop polyfunctional surfactants, which simultaneously limit the capability for hydrate particles to aggregate and deposit on the pipeline wall.

  17. Measured force/current relations in solid magnetic thrust bearings

    SciTech Connect

    Allaire, P.E.; Fittro, R.L.; Maslen, E.H.; Wakefield, W.C.

    1997-01-01

    When magnetic bearings are employed in a pump, compressor, turbine, or other rotating machine, measurement of the current in the bearing coils provides knowledge of the forces imposed on the bearings. This can be a significant indicator of machine problems. Additionally, magnetic bearings can be utilized as a load cell for measuring impeller forces in test rigs. The forces supported by magnetic bearings are directly related to the currents, air gaps, and other parameters in the bearings. This paper discusses the current/force relation for magnetic thrust bearings. Force versus current measurements were made on a particular magnetic bearing in a test rig as the bearing coil currents were cycled at various time rates of change.d the quasi-static force versus current relations were measured for a variety of air gaps and currents. The thrust bearing exhibits a hysteresis effect, which creates a significant difference between the measured force when the current is increasing as compared to that when the current is decreasing. For design current loops, 0.95 A to 2.55 A, at the time rate of change of 0.1 A/s, the difference between increasing and decreasing current curves due to hysteresis ranged from 4 to 8%. If the bearing is operated in small trajectories about a fixed (nonzero) operation point on the F/I (force/current) curve, the scatter in the measurement error could be expected to be on the order of 4%. A quasi-static nonlinear current/force equation was developed to model the data and curve-fit parameters established for the measured data. The effects of coercive force and iron reluctance, obtained from conventional magnetic materials tests, were included to improve the model, but theoretically calculated values from simple magnetic circuit theory do not produce accurate results. Magnetic fringing, leakage, and other effects must be included.

  18. Surface-charge differentiation of streptavidin and avidin by atomic force microscopy-force spectroscopy.

    PubMed

    Almonte, Lisa; Lopez-Elvira, Elena; Baró, Arturo M

    2014-09-15

    Chemical information can be obtained by using atomic force microscopy (AFM) and force spectroscopy (FS) with atomic or molecular resolution, even in liquid media. The aim of this paper is to demonstrate that single molecules of avidin and streptavidin anchored to a biotinylated bilayer can be differentiated by using AFM, even though AFM topographical images of the two proteins are remarkably alike. At physiological pH, the basic glycoprotein avidin is positively charged, whereas streptavidin is a neutral protein. This charge difference can be determined with AFM, which can probe electrostatic double-layer forces by using FS. The force curves, owing to the electrostatic interaction, show major differences when measured on top of each protein as well as on the lipid substrate. FS data show that the two proteins are negatively charged. Nevertheless, avidin and streptavidin can be clearly distinguished, thus demonstrating the sensitivity of AFM to detect small changes in the charge state of macromolecules.

  19. Nanonewton force measurement using a modified Michelson interferometer

    NASA Astrophysics Data System (ADS)

    Tahviliyan, Masoud; Charsooghi, Mohammad A.; Akhlaghi, Ehsan A.; Taghi Tavassoly, Mohammad

    2017-04-01

    In this paper, we introduce a new method to measure forces in the nanonewton range. The method is based on modification of a Michelson interferometer in which the rigid mirrors are replaced with two thin rod-like mirrors. One of the rod-like mirrors is fixed at both ends and the other has one free end. As the mirror with free end deflects in response to an applied force the spatial interference pattern is changed. Analysis of the interference fringes provides a readout of the rod deflection and thereby the applied force. The device is calibrated by applying known forces to the mirror with a free end and measuring the resulting displacement. Two different methods, mechanical and electrostatic, are used for calibration. The precision of the measurements and the propagation of the calibration uncertainty are investigated. The results show that this optical method is a good candidate for detecting small forces in the nanonewton range.

  20. Direct measurement of the forces generated by an undulatory microswimmer

    NASA Astrophysics Data System (ADS)

    Schulman, Rafael; Backholm, Matilda; Ryu, William; Dalnoki-Veress, Kari

    2014-11-01

    C. elegans is a millimeter-sized nematode which has served as a model organism in biology for several decades, primarily due to its simple anatomy. Employing an undulatory form of locomotion, this worm is capable of propelling itself through various media. Using a micropipette deflection technique, in conjunction with high speed imaging, we directly measure the time-varying forces generated by C. elegans. We observe excellent agreement between our measured forces and the predictions of resistive force theory, through which we determine the drag coefficients of the worm. We also perform the direct force measurements at controlled distances from a single solid boundary as well as between two solid boundaries. We extract the drag coefficients of the worm to quantify the influence of the boundary on the swimming and the hydrodynamic forces involved.

  1. Surface Instability of Liquid Propellant under Vertical Oscillatory Forcing

    NASA Technical Reports Server (NTRS)

    Yang, H. Q.; Peugeot, John

    2011-01-01

    Fluid motion in a fuel tank produced during thrust oscillations can circulate sub-cooled hydrogen near the liquid-vapor interface resulting in increased condensation and ullage pressure collapse. The first objective of this study is to validate the capabilities of a Computational Fluid Dynamics (CFD) tool, CFD-ACE+, in modeling the fundamental interface transition physics occurring at the propellant surface. The second objective is to use the tool to assess the effects of thrust oscillations on surface dynamics. Our technical approach is to first verify the CFD code against known theoretical solutions, and then validate against existing experiments for small scale tanks and a range of transition regimes. A 2D axisymmetric, multi-phase model of gases, liquids, and solids is used to verify that CFD-ACE+ is capable of modeling fluid-structure interaction and system resonance in a typical thrust oscillation environment. Then, the 3D mode is studied with an assumed oscillatory body force to simulate the thrust oscillating effect. The study showed that CFD modeling can capture all of the transition physics from solid body motion to standing surface wave and to droplet ejection from liquid-gas interface. Unlike the analytical solutions established during the 1960 s, CFD modeling is not limited to the small amplitude regime. It can extend solutions to the nonlinear regime to determine the amplitude of surface waves after the onset of instability. The present simulation also demonstrated consistent trends from numerical experiments through variation of physical properties from low viscous fluid to high viscous fluids, and through variation of geometry and input forcing functions. A comparison of surface wave patterns under various forcing frequencies and amplitudes showed good agreement with experimental observations. It is concluded that thrust oscillations can cause droplet formation at the interface, which results in increased surface area and enhanced heat transfer

  2. Force Measurements in Magnetic Suspension and Balance System

    NASA Technical Reports Server (NTRS)

    Kuzin, Alexander; Shapovalov, George; Prohorov, Nikolay

    1996-01-01

    The description of an infrared telemetry system for measurement of drag forces in Magnetic Suspension and Balance Systems (MSBS) is presented. This system includes a drag force sensor, electronic pack and transmitter placed in the model which is of special construction, and receiver with a microprocessor-based measuring device, placed outside of the test section. Piezosensitive resonators as sensitive elements and non-magnetic steel as the material for the force sensor are used. The main features of the proposed system for load measurements are discussed and the main characteristics are presented.

  3. Temporal Modulations of Contact Force during Haptic Surface Exploration

    PubMed Central

    Martin, Sven; Schwarz, Michael

    2016-01-01

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

  4. Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces.

    PubMed

    Boks, Niels P; Norde, Willem; van der Mei, Henny C; Busscher, Henk J

    2008-10-01

    Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F(prev)) and to detach adhering bacteria (F(det)) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the following three hypotheses. 1. A strong hydrodynamic shear force to prevent adhesion relates to a strong hydrodynamic shear force to detach an adhering organism. 2. A weak hydrodynamic shear force to detach adhering bacteria implies that more bacteria will be stimulated to detach by passing an air-liquid interface (an air bubble) through the flow chamber. 3. DLVO (Derjaguin, Landau, Verwey, Overbeek) interactions determine the characteristic hydrodynamic shear forces to prevent adhesion and to detach adhering micro-organisms as well as the detachment induced by a passing air-liquid interface. F(prev) varied from 0.03 to 0.70 pN, while F(det) varied from 0.31 to over 19.64 pN, suggesting that after initial contact, strengthening of the bond occurs. Generally, it was more difficult to detach bacteria from DDS-coated glass than from hydrophilic glass, which was confirmed by air bubble detachment studies. Calculated attractive forces based on the DLVO theory (F(DLVO)) towards the secondary interaction minimum were higher on glass than on DDS-coated glass. In general, all three hypotheses had to be rejected, showing that it is important to distinguish between forces acting parallel (hydrodynamic shear) and perpendicular (DLVO, air-liquid interface passages) to the substratum surface.

  5. Vehicle Lateral State Estimation Based on Measured Tyre Forces

    PubMed Central

    Tuononen, Ari J.

    2009-01-01

    Future active safety systems need more accurate information about the state of vehicles. This article proposes a method to evaluate the lateral state of a vehicle based on measured tyre forces. The tyre forces of two tyres are estimated from optically measured tyre carcass deflections and transmitted wirelessly to the vehicle body. The two remaining tyres are so-called virtual tyre sensors, the forces of which are calculated from the real tyre sensor estimates. The Kalman filter estimator for lateral vehicle state based on measured tyre forces is presented, together with a simple method to define adaptive measurement error covariance depending on the driving condition of the vehicle. The estimated yaw rate and lateral velocity are compared with the validation sensor measurements. PMID:22291535

  6. Report of the Task Force on Institutional Effectiveness Measures.

    ERIC Educational Resources Information Center

    Arizona State Board of Directors for Community Colleges, Phoenix.

    The Task Force on Institutional Effectiveness Measures was formed by the State Board of Directors for Community Colleges of Arizona to develop a statewide plan for systematically demonstrating the degree to which community colleges accomplish their diverse missions. Two subgroups were formed in the Task Force on transfer and college programs and…

  7. From static to animated: Measuring mechanical forces in tissues.

    PubMed

    Nelson, Celeste M

    2017-01-02

    Cells are physical objects that exert mechanical forces on their surroundings as they migrate and take their places within tissues. New techniques are now poised to enable the measurement of cell-generated mechanical forces in intact tissues in vivo, which will illuminate the secret dynamic lives of cells and change our current perception of cell biology.

  8. Oceanic Precipitation Measurement - Surface Validation

    NASA Astrophysics Data System (ADS)

    Klepp, Christian

    2013-04-01

    State-of-the-art satellite derived and reanalysis based precipitation climatologies still show remarkably large differences in frequency, amount, intensity, variability and temporal behavior of precipitation over the oceans. Additionally so far appropriate in-situ validation instruments were not available for shipboard use. The uncertainties are largest for light precipitation within the ITCZ and subtropics and for cold season high-latitude precipitation including mix-phase and snowfall. Hence, a long-term issue on which IPWG and GPM-GV is urging more attention is the provision of high quality surface validation data in oceanic areas using innovative ship-based instruments. Precipitation studies would greatly benefit from systematic dataset collection and analysis as such data could also be used to constrain precipitation retrievals. To achieve this goal, the KlimaCampus and Max Planck Institute for Meteorology in Hamburg, Germany funded this project that uses automated shipboard optical disdrometers, called Eigenbrodt ODM470, that are capable of measuring liquid and solid precipitation using drop size distributions in minute intervals on moving ships with high accuracy even under high wind speeds and rough sea states. Since the project start in 2009 the statistical basis for a conclusive validation has significantly improved with comprehensive data collection of more than 3 million minutes of precipitation measurements onboard six ships. Currently, six ODM470 instrument systems are available of which three are long-term mounted onboard the German research icebreaker R/V Polarstern (Alfred Wegner Institut) since June 2010, on R/V Akademik Ioffe (P.P.Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia) since September 2010 and on R/V Maria S. Merian (Brise Research, University of Hamburg) since December 2011. Three instruments are used for additional short-term shipboard campaigns and intercomparison projects. The core regions for these

  9. Simulation of Forces between Humid Amorphous Silica Surfaces: A Comparison of Empirical Atomistic Force Fields

    PubMed Central

    2012-01-01

    Atmospheric humidity strongly influences the interactions between dry granular particles in process containers. To reduce the energy loss in industrial production processes caused by particle agglomeration, a basic understanding of the dependence of particle interactions on humidity is necessary. Hence, in this study, molecular dynamic simulations were carried out to calculate the adhesion between silica surfaces in the presence of adsorbed water. For a realistic description, the choice of force field is crucial. Because of their frequent use and transferability to biochemical systems, the Clay and CWCA force fields were investigated with respect to their ability to describe the water–silica interface in comparison to the more advanced Reax force field, ab initio calculations, and experiments. PMID:23378869

  10. Annual Cycle of Cloud Forcing of Surface Radiation Budget

    NASA Technical Reports Server (NTRS)

    Wilber, Anne C.; Smith, G. Louis; Stackhouse, Paul W., Jr.; Gupta, Shashi K.

    2006-01-01

    The climate of the Earth is determined by its balance of radiation. The incoming and outgoing radiation fluxes are strongly modulated by clouds, which are not well understood. The Earth Radiation Budget Experiment (Barkstrom and Smith, 1986) provided data from which the effects of clouds on radiation at the top of the atmosphere (TOA) could be computed (Ramanathan, 1987). At TOA, clouds increase the reflected solar radiation, tending to cool the planet, and decrease the OLR, causing the planet to retain its heat (Ramanathan et al., 1989; Harrison et al., 1990). The effects of clouds on radiation fluxes are denoted cloud forcing. These shortwave and longwave forcings counter each other to various degrees, so that in the tropics the result is a near balance. Over mid and polar latitude oceans, cloud forcing at TOA results in large net loss of radiation. Here, there are large areas of stratus clouds and cloud systems associated with storms. These systems are sensitive to surface temperatures and vary strongly with the annual cycle. During winter, anticyclones form over the continents and move to the oceans during summer. This movement of major cloud systems causes large changes of surface radiation, which in turn drives the surface temperature and sensible and latent heat released to the atmosphere.

  11. Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy

    SciTech Connect

    Balke, Nina; Jesse, Stephen; Yu, Pu; Carmichael, Ben; Kalinin, Sergei V.; Tselev, Alexander

    2016-09-15

    Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ~1–3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip–sample contact stiffness. The approach has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. Furthermore, this analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques.

  12. Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy

    DOE PAGES

    Balke, Nina; Jesse, Stephen; Yu, Pu; ...

    2016-09-15

    Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ~1–3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip–sample contact stiffness. The approachmore » has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. Furthermore, this analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques.« less

  13. Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Balke, Nina; Jesse, Stephen; Yu, Pu; Carmichael, Ben; Kalinin, Sergei V.; Tselev, Alexander

    2016-10-01

    Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ˜1-3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip-sample contact stiffness. The approach has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. This analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques.

  14. Boundary slip study on hydrophilic, hydrophobic, and superhydrophobic surfaces with dynamic atomic force microscopy.

    PubMed

    Bhushan, Bharat; Wang, Yuliang; Maali, Abdelhamid

    2009-07-21

    Slip length has been measured using the dynamic atomic force microscopy (AFM) method. Unlike the contact AFM method, the sample surface approaches an oscillating sphere with a very low velocity in the dynamic AFM method. During this process, the amplitude and phase shift data are recorded to calculate the hydrodynamic damping coefficient, which is then used to obtain slip length. In this study, a glass sphere with a large radius was glued to the end of an AFM cantilever to measure the slip length on rough surfaces. Experimental results for hydrophilic, hydrophobic, and superhydrophobic surfaces show that the hydrodynamic damping coefficient decreases from the hydrophilic surface to the hydrophobic surface and from the hydrophobic one to the superhydrophobic one. The slip lengths obtained on the hydrophobic and superhydrophobic surfaces are 43 and 236 nm, respectively, which indicates increasing boundary slip from the hydrophobic surface to the superhydrophobic one.

  15. Direct measurement of Vorticella contraction force by micropipette deflection.

    PubMed

    France, Danielle; Tejada, Jonathan; Matsudaira, Paul

    2017-02-01

    The ciliated protozoan Vorticella convallaria is noted for its exceptionally fast adenosine triphosphate-independent cellular contraction, but direct measurements of contractile force have proven difficult given the length scale, speed, and forces involved. We used high-speed video microscopy to image live Vorticella stalled in midcontraction by deflection of an attached micropipette. Stall forces correlate with both distance contracted and the resting stalk length. Estimated isometric forces range from 95 to 177 nanonewtons (nN), or 1.12 nN·μm(-1) of the stalk. Maximum velocity and work are also proportional to distance contracted. These parameters constrain proposed biochemical/physical models of the contractile mechanism.

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

    NASA Astrophysics Data System (ADS)

    Wada, Tomoya; Yamazaki, Kenji; Isono, Toshinari; Ogino, Toshio

    2017-02-01

    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 SiO2 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.

  17. Force Developments. The Measurement of Effectiveness

    DTIC Science & Technology

    1973-01-01

    14309 Prevention and Control of Cormmunicable Diseases oi Animals . 14689 Analysis to Identify Non-Divisional TOE Combat FSarvi~e Support Units Requiring...powerful tool for performing comparative analyses if experimentaion is properly de- signed and conducted. 4. Specifics in the Measurement .f

  18. Measuring Drag Force in Newtonian Liquids

    ERIC Educational Resources Information Center

    Mawhinney, Matthew T.; O'Donnell, Mary Kate; Fingerut, Jonathan; Habdas, Piotr

    2012-01-01

    The experiments described in this paper have two goals. The first goal is to show how students can perform simple but fundamental measurements of objects moving through simple liquids (such as water, oil, or honey). In doing so, students can verify Stokes' law, which governs the motion of spheres through simple liquids, and see how it fails at…

  19. A force balance system for the measurement of skin friction drag force

    NASA Technical Reports Server (NTRS)

    Moore, J. W.; Mcvey, E. S.

    1971-01-01

    Research on force balance instrumentation to measure the skin friction of hypersonic vehicles at extreme temperatures, high altitudes and in a vibration field is discussed. A rough overall summary and operating instructions for the equipment are presented.

  20. Sensitivity of Force Specifications to the Errors in Measuring the Interface Force

    NASA Technical Reports Server (NTRS)

    Worth, Daniel

    1999-01-01

    Force-Limited Random Vibration Testing has been applied in the last several years at NASA/GSFC for various programs at the instrument and system level. Different techniques have been developed over the last few decades to estimate the dynamic forces that the test article under consideration will encounter in the operational environment. Some of these techniques are described in the handbook, NASA-HDBK-7004, and the monograph, NASA-RP-1403. A key element in the ability to perform force-limited testing is multi-component force gauges. This paper will show how some measurement and calibration errors in force gauges are compensated for w en tie force specification is calculated. The resulting notches in the acceleration spectrum, when a random vibration test is performed, are the same as the notches produced during an uncompensated test that has no measurement errors. The paper will also present the results of tests that were used to validate this compensation. Knowing that the force specification can compensate for some measurement errors allows tests to continue after force gauge failures or allows dummy gauges to be used in places that are inaccessible.

  1. Effect of nanobubbles on friction forces between hydrophobic surfaces in water.

    PubMed

    Hampton, Marc A; Donose, Bogdan C; Taran, Elena; Nguyen, Anh V

    2009-01-01

    The interaction between hydrophobic surfaces in aqueous solutions is particularly important because it is encountered in many industrial processes. Even though advances in surface science have been tremendous, the nature of the hydrophobic interaction remains one of the greatest challenges to the field. In this work an atomic force microscope (AFM) was used to measure the normal and lateral interactions between a silica bead and a smooth silica substrate hydrophobized by esterification with 1-octanol. The experiments were performed in water and in water after alcohol-water exchange, a method that has been shown to increase the occurrence and size of nanobubbles at the hydrophobic surface and in turn result in a longer range hydrophobic force due to capillary bridge formation. It was found that the alcohol-water exchange had a significant impact on the friction force due to the increased size of the capillary, which increased adhesion.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Imaging the condensation and evaporation of molecularly thin ethanol films with surface forces apparatus

    SciTech Connect

    Zhao, Gutian; Tan, Qiyan; Xiang, Li; Zhang, Di; Ni, Zhonghua E-mail: yunfeichen@seu.edu.cn; Yi, Hong; Chen, Yunfei E-mail: yunfeichen@seu.edu.cn

    2014-01-15

    A new method for imaging condensation and evaporation of molecularly thin ethanol films is reported. It is found that the first adsorbed layer of ethanol film on mica surface behaves as solid like structure that cannot flow freely. With the increase of exposure time, more ethanol molecules condense over the mica surface in the saturated ethanol vapor condition. The first layer of adsorbed ethanol film is about 3.8 Å thick measured from the surface forces apparatus, which is believed to be the average diameter of ethanol molecules while they are confined in between two atomically smooth mica surfaces.

  4. Measuring the complete force field of an optical trap.

    PubMed

    Jahnel, Marcus; Behrndt, Martin; Jannasch, Anita; Schäffer, Erik; Grill, Stephan W

    2011-04-01

    The use of optical traps to measure or apply forces on the molecular level requires a precise knowledge of the trapping force field. Close to the trap center, this field is typically approximated as linear in the displacement of the trapped microsphere. However, applications demanding high forces at low laser intensities can probe the light-microsphere interaction beyond the linear regime. Here, we measured the full nonlinear force and displacement response of an optical trap in two dimensions using a dual-beam optical trap setup with back-focal-plane photodetection. We observed a substantial stiffening of the trap beyond the linear regime that depends on microsphere size, in agreement with Mie theory calculations. Surprisingly, we found that the linear detection range for forces exceeds the one for displacement by far. Our approach allows for a complete calibration of an optical trap.

  5. Cutting force measurement of electrical jigsaw by strain gauges

    NASA Astrophysics Data System (ADS)

    Kazup, L.; Varadine Szarka, A.

    2016-11-01

    This paper describes a measuring method based on strain gauges for accurate specification of electric jigsaw's cutting force. The goal of the measurement is to provide an overall perspective about generated forces in a jigsaw's gearbox during a cutting period. The lifetime of the tool is affected by these forces primarily. This analysis is part of the research and development project aiming to develop a special linear magnetic brake for realizing automatic lifetime tests of electric jigsaws or similar handheld tools. The accurate specification of cutting force facilitates to define realistic test cycles during the automatic lifetime test. The accuracy and precision resulted by the well described cutting force characteristic and the possibility of automation provide new dimension for lifetime testing of the handheld tools with alternating movement.

  6. The measurement of surface gravity

    NASA Astrophysics Data System (ADS)

    Crossley, David; Hinderer, Jacques; Riccardi, Umberto

    2013-04-01

    This review covers basic theory and techniques behind the use of ground-based gravimetry at the Earth's surface. The orientation is toward modern instrumentation, data processing and interpretation for observing surface, land-based, time-variable changes to the geopotential. The instrumentation side is covered in some detail, with specifications and performance of the most widely used models of the three main types: the absolute gravimeters (FG5, A10 from Micro-g LaCoste), superconducting gravimeters (OSG, iGrav from GWR instruments), and the new generation of spring instruments (Micro-g LaCoste gPhone, Scintrex CG5 and Burris ZLS). A wide range of applications is covered, with selected examples from tides and ocean loading, atmospheric effects on gravity, local and global hydrology, seismology and normal modes, long period and tectonics, volcanology, exploration gravimetry, and some examples of gravimetry connected to fundamental physics. We show that there are only a modest number of very large signals, i.e. hundreds of µGal (10-8 m s-2), that are easy to see with all gravimeters (e.g. tides, volcanic eruptions, large earthquakes, seasonal hydrology). The majority of signals of interest are in the range 0.1-5.0 µGal and occur at a wide range of time scales (minutes to years) and spatial extent (a few meters to global). Here the competing effects require a careful combination of different gravimeter types and measurement strategies to efficiently characterize and distinguish the signals. Gravimeters are sophisticated instruments, with substantial up-front costs, and they place demands on the operators to maximize the results. Nevertheless their performance characteristics such as drift and precision have improved dramatically in recent years, and their data recording ability and ruggedness have seen similar advances. Many subtle signals are now routinely connected with known geophysical effects such as coseismic earthquake displacements, post-glacial rebound

  7. The measurement of surface gravity.

    PubMed

    Crossley, David; Hinderer, Jacques; Riccardi, Umberto

    2013-04-01

    This review covers basic theory and techniques behind the use of ground-based gravimetry at the Earth's surface. The orientation is toward modern instrumentation, data processing and interpretation for observing surface, land-based, time-variable changes to the geopotential. The instrumentation side is covered in some detail, with specifications and performance of the most widely used models of the three main types: the absolute gravimeters (FG5, A10 from Micro-g LaCoste), superconducting gravimeters (OSG, iGrav from GWR instruments), and the new generation of spring instruments (Micro-g LaCoste gPhone, Scintrex CG5 and Burris ZLS). A wide range of applications is covered, with selected examples from tides and ocean loading, atmospheric effects on gravity, local and global hydrology, seismology and normal modes, long period and tectonics, volcanology, exploration gravimetry, and some examples of gravimetry connected to fundamental physics. We show that there are only a modest number of very large signals, i.e. hundreds of µGal (10(-8) m s(-2)), that are easy to see with all gravimeters (e.g. tides, volcanic eruptions, large earthquakes, seasonal hydrology). The majority of signals of interest are in the range 0.1-5.0 µGal and occur at a wide range of time scales (minutes to years) and spatial extent (a few meters to global). Here the competing effects require a careful combination of different gravimeter types and measurement strategies to efficiently characterize and distinguish the signals. Gravimeters are sophisticated instruments, with substantial up-front costs, and they place demands on the operators to maximize the results. Nevertheless their performance characteristics such as drift and precision have improved dramatically in recent years, and their data recording ability and ruggedness have seen similar advances. Many subtle signals are now routinely connected with known geophysical effects such as coseismic earthquake displacements, post

  8. Fat-Line Towed-Array Force Measurement Apparatus

    DTIC Science & Technology

    2000-06-12

    No. 78872 n 3 FAT -LINE TOWED-ARRAY FORCE MEASUREMENT APPARATUS 4 5 STATEMENT OF GOVERNMENT INTEREST 6 The invention described herein may be...application. 16 17 BACKGROUND OF THE INVENTION 18 (1) Field of the Invention 19 The present invention relates generally to fat -line towed- 2 0 arrays, and...more particularly to an apparatus for measuring the 21 force applied to fat -line towed-arrays during flushing cycles. 22 (2) Description of the

  9. Icing Research Tunnel (IRT) Force Measurement System (FMS)

    NASA Technical Reports Server (NTRS)

    Roberts, Paul W.

    2012-01-01

    An Electronics Engineer at the Glenn Research Center (GRC), requested the NASA Engineering and Safety Center (NESC) provide technical support for an evaluation of the existing force measurement system (FMS) at the GRC's Icing Research Tunnel (IRT) with the intent of developing conceptual designs to improve the tunnel's force measurement capability in order to better meet test customer needs. This report contains the outcome of the NESC technical review.

  10. Flight of a Rufous Hummingbird Robotic Model-Force Measurements

    NASA Astrophysics Data System (ADS)

    Chavez Alarcon, Ramiro; Bocanegra Evans, Humberto; Ferreira de Sousa, Paulo; Tobalske, Bret; Allen, James

    2008-11-01

    Aerodynamic force data was measured on a 2-DOF scaled robotic hummingbird model for both hovering and translational flight. Experiments were conducted in a large water channel facility at New Mexico State University. Reynolds and Strouhal numbers for the experiment are in the range of 3600 and 0.97, respectively. Forces are directly measured using strain gages and compared with phase-locked PIV results.

  11. Acoustic force measurement in a dual-temperature resonant chamber

    NASA Technical Reports Server (NTRS)

    Robey, Judith L.; Trinh, Eugene H.; Wang, Taylor G.

    1987-01-01

    The acoustic radiation force was measured for a dual-temperature resonant chamber. This rectangular chamber has its long dimension approximately 8.5 times the square cross-sectional dimension, and the opposite ends are at widely different temperatures. Force profiles were obtained for two hot end temperatures of 520 C and 760 C, while the cool end remained at approximately room temperature. Force magnitudes as high as 17 dyn for a sample 1.2 cm in diameter at 760 C and at 162-dB input level were measured.

  12. Flight Force Measurements on a Spacecraft to Launch Vehicle Interface

    NASA Astrophysics Data System (ADS)

    Kaufman, Daniel S.; Gordon, Scott A.

    2012-07-01

    For several years we had wanted to measure interface forces between a launch vehicle and the Payload. Finally in July 2006 a proposal was made and funded to evaluate the use of flight force measurements (FFM) to improve the loads process of a Spacecraft in its design and test cycle. A NASA/Industry team was formed, the core Team consisted of 20 people. The proposal identified two questions that this assessment would attempt to address by obtaining the flight forces. These questions were: 1) Is flight correlation and reconstruction with acceleration methods sufficient? 2) How much can the loads and therefore the design and qualification be reduced by having force measurements? The objective was to predict the six interface driving forces between the Spacecraft and the Launch Vehicle throughout the boost phase. Then these forces would be compared with reconstructed loads analyses for evaluation in an attempt to answer them. The paper will present the development of a strain based force measurement system and also an acceleration method, actual flight results, post flight evaluations and lessons learned.

  13. MEMS-Based Flexible Force Sensor for Tri-Axial Catheter Contact Force Measurement.

    PubMed

    Pandya, Hardik J; Sheng, Jun; Desai, Jaydev P

    2017-02-01

    Atrial fibrillation (AFib) is a significant healthcare problem caused by the uneven and rapid discharge of electrical signals from pulmonary veins (PVs). The technique of radiofrequency (RF) ablation can block these abnormal electrical signals by ablating myocardial sleeves inside PVs. Catheter contact force measurement during RF ablation can reduce the rate of AFib recurrence, since it helps to determine effective contact of the catheter with the tissue, thereby resulting in effective power delivery for ablation. This paper presents the development of a three-dimensional (3D) force sensor to provide the real-time measurement of tri-axial catheter contact force. The 3D force sensor consists of a plastic cubic bead and five flexible force sensors. Each flexible force sensor was made of a PEDOT:PSS strain gauge and a PDMS bump on a flexible PDMS substrate. Calibration results show that the fabricated sensor has a linear response in the force range required for RF ablation. To evaluate its working performance, the fabricated sensor was pressed against gelatin tissue by a micromanipulator and also integrated on a catheter tip to test it within deionized water flow. Both experiments simulated the ventricular environment and proved the validity of applying the 3D force sensor in RF ablation.

  14. La force de Casimir et les plasmons de surface

    NASA Astrophysics Data System (ADS)

    Intravaia, F.; Lambrecht, A.; Reynaud, S.

    2004-11-01

    La présence de fluctuations irréductibles de champ dans le vide est une prédiction importante de la théorie quantique. Ces fluctuations ont de nombreux effets bien connus, dont l'archétype est la force de Casimir apparaîssant entre deux miroirs placés dans le vide par suite de la pression de radiation du vide. Elle a été récemment mesurée avec une précision de l'ordre du %. De nombreux travaux sont consacrés à l'évaluation théorique de cette force en visant une précision du même ordre. Ici nous étudions la force de Casimir dans la configuration de deux miroirs métalliques plans parallèles à température nulle. En supposant les miroirs décrits par un modèle plasma nous interprétons la force de Casimir comme le résultat de l'interaction entre les plasmons de surface des deux miroirs.

  15. Line contribution to the critical Casimir force between a homogeneous and a chemically stepped surface.

    PubMed

    Toldin, Francesco Parisen; Tröndle, Matthias; Dietrich, S

    2015-06-03

    Recent experimental realizations of the critical Casimir effect have been implemented by monitoring colloidal particles immersed in a binary liquid mixture near demixing and exposed to a chemically structured substrate. In particular, critical Casimir forces have been measured for surfaces consisting of stripes with periodically alternating adsorption preferences, forming chemical steps between them. Motivated by these experiments, we analyze the contribution of such chemical steps to the critical Casimir force for the film geometry and within the Ising universality class. By means of Monte Carlo simulations, mean-field theory and finite-size scaling analysis we determine the universal scaling function associated with the contribution to the critical Casimir force due to individual, isolated chemical steps facing a surface with homogeneous adsorption preference or with Dirichlet boundary condition. In line with previous findings, these results allow one to compute the critical Casimir force for the film geometry and in the presence of arbitrarily shaped, but wide stripes. In this latter limit the force decomposes into a sum of the contributions due to the two homogeneous parts of the surface and due to the chemical steps between the stripes. We assess this decomposition by comparing the resulting sum with actual simulation data for the critical Casimir force in the presence of a chemically striped substrate.

  16. Response of the surface tropical Atlantic Ocean to wind forcing

    NASA Astrophysics Data System (ADS)

    Castellanos, Paola; Pelegrí, Josep L.; Campos, Edmo J. D.; Rosell-Fieschi, Miquel; Gasser, Marc

    2015-05-01

    We use 10 years of satellite data (sea level pressure, surface winds and absolute dynamic topography [ADT]) together with Argo-inferred monthly-mean values of near-surface velocity and water transport, to examine how the tropical system of near-surface zonal currents responds to wind forcing. The data is analyzed using complex Hilbert empirical orthogonal functions, confirming that most of the variance has annual periodicity, with maximum amplitudes in the region spanned by the seasonal displacement of the Inter-Tropical Convergence Zone (ITCZ). The ADT mirrors the shape of the upper isopycnals, hence becoming a good indicator of the amount of water stored in the upper ocean. Within about 3° from the Equator, where the Coriolis force is small, there is year-long meridional Ekman-transport divergence that would lead to the eastward transport of the Equatorial Undercurrent and its northern and southern branches. Beyond 3° of latitude, and at least as far as 20°, the convergence of the Ekman transport generally causes a poleward positive ADT gradient, which sustains the westward South Equatorial Current (SEC). The sole exception occurs in summer, between 8°N and 12°N, when an Ekman-transport divergence develops and depletes de amount of surface water, resulting in an ADT ridge-valley system which reverses the ADT gradient and drives the eastward North Equatorial Countercurrent (NECC) at latitudes 4-9°N; in late fall, divergence ceases and the NECC drains the ADT ridge, so the ADT gradient again becomes positive and the SEC reappears. The seasonal evolution of a tilted ITCZ controls the surface water fluxes: the wind-induced transports set the surface divergence-convergence, which then drive the ADT and, through the ADT gradients, create the geostrophic jets that close the water balance.

  17. Quantitative measurements of force and displacement using an optical trap.

    PubMed Central

    Simmons, R M; Finer, J T; Chu, S; Spudich, J A

    1996-01-01

    We combined a single-beam gradient optical trap with a high-resolution photodiode position detector to show that an optical trap can be used to make quantitative measurements of nanometer displacements and piconewton forces with millisecond resolution. When an external force is applied to a micron-sized bead held by an optical trap, the bead is displaced from the center of the trap by an amount proportional to the applied force. When the applied force is changed rapidly, the rise time of the displacement is on the millisecond time scale, and thus a trapped bead can be used as a force transducer. The performance can be enhanced by a feedback circuit so that the position of the trap moves by means of acousto-optic modulators to exert a force equal and opposite to the external force applied to the bead. In this case the position of the trap can be used to measure the applied force. We consider parameters of the trapped bead such as stiffness and response time as a function of bead diameter and laser beam power and compare the results with recent ray-optic calculations. PMID:8785341

  18. Novel Low-Cost Sensor for Human Bite Force Measurement

    PubMed Central

    Fastier-Wooller, Jarred; Phan, Hoang-Phuong; Dinh, Toan; Nguyen, Tuan-Khoa; Cameron, Andrew; Öchsner, Andreas; Dao, Dzung Viet

    2016-01-01

    This paper presents the design and development of a low cost and reliable maximal voluntary bite force sensor which can be manufactured in-house by using an acrylic laser cutting machine. The sensor has been designed for ease of fabrication, assembly, calibration, and safe use. The sensor is capable of use within an hour of commencing production, allowing for rapid prototyping/modifications and practical implementation. The measured data shows a good linear relationship between the applied force and the electrical resistance of the sensor. The output signal has low drift, excellent repeatability, and a large measurable range of 0 to 700 N. A high signal-to-noise response to human bite forces was observed, indicating the high potential of the proposed sensor for human bite force measurement. PMID:27509496

  19. NASA ATP Force Measurement Technology Capability Strategic Plan

    NASA Technical Reports Server (NTRS)

    Rhew, Ray D.

    2008-01-01

    The Aeronautics Test Program (ATP) within the National Aeronautics and Space Administration (NASA) Aeronautics Research Mission Directorate (ARMD) initiated a strategic planning effort to re-vitalize the force measurement capability within NASA. The team responsible for developing the plan included members from three NASA Centers (Langley, Ames and Glenn) as well as members from the Air Force s Arnold Engineering and Development Center (AEDC). After visiting and discussing force measurement needs and current capabilities at each participating facility as well as selected force measurement companies, a strategic plan was developed to guide future NASA investments. This paper will provide the details of the strategic plan and include asset management, organization and technology research and development investment priorities as well as efforts to date.

  20. Rail supporting transducer posts for three-dimensional force measurement.

    PubMed

    Jin, Z; Kobetic, R

    1997-12-01

    Parallel bars supported on transducer posts were designed, instrumented and calibrated to measure three-dimensional (3-D) forces applied to the rails. These instrumented rails were designed for measuring forces applied by paraplegic patients during development and evaluation of functional electrical stimulation (FES) patterns for standing, side stepping, and ascending and descending stairs. The focus of this study was on the adaptation of the system for measuring support forces during stair climbing and descent. The specific problems with crosstalk among the three axes, nonlinearity, and hysteresis were investigated. In this design, the crosstalk between axes was less than 5%, nonlinearity was less than 2% of full scale, and force accuracy was better than 5%.

  1. Measuring electric fields from surface contaminants with neutral atoms

    SciTech Connect

    Obrecht, J. M.; Wild, R. J.; Cornell, E. A.

    2007-06-15

    In this paper we demonstrate a technique of utilizing magnetically trapped neutral {sup 87}Rb atoms to measure the magnitude and direction of stray electric fields emanating from surface contaminants. We apply an alternating external electric field that adds to (or subtracts from) the stray field in such a way as to resonantly drive the trapped atoms into a mechanical dipole oscillation. The growth rate of the oscillation's amplitude provides information about the magnitude and sign of the stray field gradient. Using this measurement technique, we are able to reconstruct the vector electric field produced by surface contaminants. In addition, we can accurately measure the electric fields generated from adsorbed atoms purposely placed onto the surface and account for their systematic effects, which can plague a precision surface-force measurement. We show that baking the substrate can reduce the electric fields emanating from adsorbate and that the mechanism for reduction is likely surface diffusion, not desorption.

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

    PubMed

    Schrader, Alex M; Cheng, Chi-Yuan; Israelachvili, Jacob N; Han, Songi

    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.

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

    NASA Astrophysics Data System (ADS)

    Schrader, Alex M.; Cheng, Chi-Yuan; Israelachvili, Jacob N.; Han, Songi

    2016-07-01

    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.

  4. Phoretic and Radiometric Force Measurements on Microparticles in Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Davis, E. James

    1996-01-01

    Thermophoretic, diffusiophoretic and radiometric forces on microparticles are being measured over a wide range of gas phase and particle conditions using electrodynamic levitation of single particles to simulate microgravity conditions. The thermophoretic force, which arises when a particle exists in a gas having a temperature gradient, is measured by levitating an electrically charged particle between heated and cooled plates mounted in a vacuum chamber. The diffusiophoretic force arising from a concentration gradient in the gas phase is measured in a similar manner except that the heat exchangers are coated with liquids to establish a vapor concentration gradient. These phoretic forces and the radiation pressure force acting on a particle are measured directly in terms of the change in the dc field required to levitate the particle with and without the force applied. The apparatus developed for the research and the experimental techniques are discussed, and results obtained by thermophoresis experiments are presented. The determination of the momentum and energy accommodation coefficients associated with molecular collisions between gases molecules and particles and the measurement of the interaction between electromagnetic radiation and small particles are of particular interest.

  5. Measurement of laterally induced optical forces at the nanoscale

    NASA Astrophysics Data System (ADS)

    Huang, Fei; Tamma, Venkata Ananth; Rajaei, Mohsen; Almajhadi, Mohammad; Kumar Wickramasinghe, H.

    2017-02-01

    We demonstrate the measurement of laterally induced optical forces using an Atomic Force Microscope (AFM). The lateral electric field distribution between a gold coated AFM probe and a single nano-aperture in a gold film is mapped by measuring the lateral optical force between the apex of the AFM probe and the nano-aperture. The fundamental torsional eigen-mode of an AFM cantilever probe was used to detect the laterally induced optical forces. We engineered the cantilever shape using focused ion beam milling to improve the detected signal to noise ratio. The measured distributions of lateral optical force agree well with electromagnetic simulations of the metal coated AFM probe interacting with the nano-aperture. This technique can be extended to simultaneously detect both lateral and longitudinal optical forces at the nanoscale by using an AFM cantilever as a multi-channel detector. This will enable simultaneous Photon Induced Force Microscopy detection of molecular responses with different incident field polarizations. The technique can be implemented on both cantilever and tuning fork based AFMs.

  6. Interaction of cationic hydrophobic surfactants at negatively charged surfaces investigated by atomic force microscopy.

    PubMed

    McNamee, Cathy E; Butt, Hans-Jürgen; Higashitani, Ko; Vakarelski, Ivan U; Kappl, Michael

    2009-10-06

    Atomic force microscopy was used to study the adsorption of the surfactant octadecyl trimethyl ammonium chloride (C18TAC) at a low concentration (0.03 mM) to negatively charged surfaces in water. Atomic force microscopy tips were functionalized with dimethyloctadecyl(3-tripropyl)ammonium chloride (C18TAC-si) or N-trimethoxysilylpropyl-N,N,N-trimethylammomium chloride (hydrophilpos-si) to facilitate imaging of the adsorbed surfactant without artifacts. Tapping mode images and force measurements revealed C18TAC patches, identified as partial surfactant bilayers or hemimicelles. The forces controlling the adsorption process of the C18TAC to a negatively charged surface were investigated by measuring the forces between a C18TAC-si or a hydrophilpos-si tip and a silica surface in the presence of varying concentrations of either NaCl or NaNO3. Screening of forces with an increasing NaCl concentration was observed for the C18TAC-si and hydrophilpos-si tips, proving an electrostatic contribution. Screening was also observed for the hydrophilpos-si tip in NaNO3, whereas a long-range attraction was observed for the C18TAC-si tip for all NaNO3 concentrations. These results indicate that screening of the forces for the C18TAC-si tip depended on the type and/or size of the anion, possibly due to a different probability of the anions to enter the silane layers. The interaction of C18TAC patches with C18TAC-si tips in the presence of NaCl and the interaction of the patches with hydrophilpos-si tips in either NaCl or NaNO3 were repulsive and independent of the number of force curves measured, indicating a stable, positively charged C18TAC patch. However, the forces measured between the patches and a C18TAC-si tip in NaNO3 depended on the number of force curves measured, indicating a change in patch structure induced by the first interaction.

  7. Direct measurements of controlled aerodynamic forces on a wire-suspended axisymmetric body

    NASA Astrophysics Data System (ADS)

    Abramson, Philip; Vukasinovic, Bojan; Glezer, Ari

    2011-06-01

    A novel in-line miniature force transducer is developed for direct measurements of the net aerodynamic forces and moments on a bluff body. The force transducers are integrated into each of the eight mounting wires that are utilized for suspension of an axisymmetric model in a wind tunnel having minimal wake interference. The aerodynamic forces and moments on the model are altered by induced active local attachment of the separated base flow. Fluidic control is effected by an array of four integrated aft-facing synthetic jet actuators that emanate from narrow, azimuthally segmented slots, equally distributed around the perimeter of the circular tail end. The jet orifices are embedded within a small backward-facing step that extends into a Coanda surface. The altered flow dynamics associated with both quasi-steady and transitory asymmetric activation of the flow control effect is characterized by direct force and PIV measurements.

  8. Predictability in France : atmospheric forcing or land surface initial conditions?

    NASA Astrophysics Data System (ADS)

    Singla, S.; Martin, E.; Céron, J.-P.; Regimbeau, F.

    2010-09-01

    A first study of a hydrological forecasting suite has already been done at seasonal time scales over France (Céron and al., 2010) in a context of adaptation for water resources management. The results showed the feasibility of hydrological seasonal forecasts by forcing the hydrometeorological model Safran-Isba-Modcou (SIM) with seasonal atmospheric forecasts from the DEMETER project. Scores were better for hydrological variables than for atmospheric variables for four river catchments for the spring season. The purpose of the present study is to quantify the sources of predictability of the hydrometeorological system. Two experiences were conducted in order to address this issue. The first experience consisted in testing the impact of the land surface initial conditions. We used realistic land surface initial state produced by the operational SIM model for the specific year and 9 random years of Safran atmospheric analyses (temperature and precipitation) from 1971 to 2001, in a consistent way with the previous study (Céron et al, 2010). The other atmospheric parameters (wind, specific humidity, long wave and short wave radiation and cloudiness) come from the SAFRAN climatology over the same period. The second experience was designed to evaluate the impact of the atmospheric forcing with 9 random years, chosen for the land surface initial state. The atmospheric forcing (temperature and precipitation) comes from the Safran analysis system for the corresponding year. Some results of this study will be presented on soil wetness index (SWI) forecasts and river flows forecasts for all stations in France. We will compare deterministic and probabilistic scores of the two experiences with those of the hydrological forecasting suite built with the seasonal forecasts from the DEMETER project. Perspectives for the downscaling of seasonal forecasts will be discussed in a last part. Céron J-P, Tanguy G, Franchistéguy L, Martin E, Regimbeau F and Vidal J-P, 2010. Hydrological

  9. Fiber optic micro sensor for the measurement of tendon forces.

    PubMed

    Behrmann, Gregory P; Hidler, Joseph; Mirotznik, Mark S

    2012-10-03

    A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces.The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements.

  10. Fiber optic micro sensor for the measurement of tendon forces

    PubMed Central

    2012-01-01

    A fiber optic sensor developed for the measurement of tendon forces was designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporated fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings were designed to convert radial forces applied to the housing into axial forces that could be sensed by the fiber Bragg grating. The metal housings were fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurements as well as for simultaneous resolution of multi-axis forces. The sensor was experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester was used to provide uniform pressures on the sensor in order to establish the linearity, repeatability, and accuracy characteristics of the sensor. The in vitro experiments were performed in excised tendon and in a dynamic gait simulator to simulate biological conditions. In both experimental conditions, the sensor was found to be a sensitive and reliable method for acquiring minimally invasive measurements of soft tissue forces. Our results suggest that this sensor will prove useful in a variety of biomechanical measurements. PMID:23033868

  11. Easy and direct method for calibrating atomic force microscopy lateral force measurements

    PubMed Central

    Liu, Wenhua; Bonin, Keith; Guthold, Martin

    2010-01-01

    We have designed and tested a new, inexpensive, easy-to-make and easy-to-use calibration standard for atomic force microscopy (AFM) lateral force measurements. This new standard simply consists of a small glass fiber of known dimensions and Young’s modulus, which is fixed at one end to a substrate and which can be bent laterally with the AFM tip at the other end. This standard has equal or less error than the commonly used method of using beam mechanics to determine a cantilever’s lateral force constant. It is transferable, thus providing a universal tool for comparing the calibrations of different instruments. It does not require knowledge of the cantilever dimensions and composition or its tip height. This standard also allows direct conversion of the photodiode signal to force and, thus, circumvents the requirement for a sensor response (sensitivity) measurement. PMID:17614616

  12. AFM study of forces between silicon oil and hydrophobic-hydrophilic surfaces in aqueous solutions.

    PubMed

    Zbik, Marek S; Frost, Ray L

    2010-09-15

    An investigation has been made of the interactions between silicone oil and various solid substrates immersed in aqueous solutions. Measurements were made using an atomic force microscope (AFM) using the colloid-probe method. The silicone oil drop is simulated by coating a small silica sphere with the oil, and measuring the force as this coated sphere is brought close to contact with a flat solid surface. It is found that the silicone oil surface is negatively charged, which causes a double-layer repulsion between the oil drop and another negatively charged surface such as mica. With hydrophilic solids, this repulsion is strong enough to prevent attachment of the drop to the solid. However, with hydrophobic surfaces there is an additional attractive force which overcomes the double-layer repulsion, and the silicone oil drop attaches to the solid. There is circumstantial evidence that linear and nonlinear effect take part in force results from compression of the silicone oil film coated on the glass sphere.

  13. Adhesion Forces between Lewis(X) Determinant Antigens as Measured by Atomic Force Microscopy.

    PubMed

    Tromas, C; Rojo, J; de la Fuente, J M; Barrientos, A G; García, R; Penadés, S

    2001-01-01

    The adhesion forces between individual molecules of Lewis(X) trisaccharide antigen (Le(X) ) have been measured in water and in calcium solution by using atomic force microscopy (AFM, see graph). These results demonstrate the self-recognition capability of this antigen, and reinforce the hypothesis that carbohydrate-carbohydrate interaction could be considered as the first step in the cell-adhesion process in nature.

  14. Atomic force microscopy: a tool for studying biophysical surface properties underpinning fungal interactions with plants and substrates.

    PubMed

    Adams, Elizabeth; Emerson, Danielle; Croker, Sean; Kim, Hye-Seon; Modla, Shannon; Kang, Seogchan; Czymmek, Kirk

    2012-01-01

    One of the primary roles of the cell surface is to provide an effective barrier to various external environmental factors. Specifically, the surface properties of organisms serve as a critical obstacle to pathogen attack. Since its inception, Atomic Force Microscopy (AFM) has enabled nanoscale imaging of cell surfaces in their native state. However AFM has yet to be systematically applied toward resolving surface features and the forces underpinning plant-fungal interactions. In an effort to understand the physical forces involved at the plant-microbe interface, we describe a method for the attachment of fungal spores to AFM tips and the subsequent measurement of unbinding forces between spores with a range of substrates and plant surfaces under physiologically relevant conditions. Investigations of binding events using AFM offer an unexplored, sensitive, and quantitative method for analyzing host-pathogen/microbe-surface interactions.

  15. Measuring and Plotting Surface-Contour Deviations

    NASA Technical Reports Server (NTRS)

    Aragon, Lino A.; Shuck, Thomas; Crockett, Leroy K.

    1987-01-01

    Hand-held device measures deviation of contour of surface from desired contour and provides output to x-y plotter. Carriage on device rolled along track representing desired contour, while spring-loaded stylus on device deflects perpendicularly to track to follow surface. Operator moves carriage of contour-measuring device on beamlike track. Stylus on carriage traces contour of surface above it. Carriage of measuring device holds transducer measuring cross-track displacement of surface from desired contour, and multiple-turn potentiometer measuring position along track.

  16. Topological and geometric measurements of force-chain structure

    NASA Astrophysics Data System (ADS)

    Giusti, Chad; Papadopoulos, Lia; Owens, Eli T.; Daniels, Karen E.; Bassett, Danielle S.

    2016-09-01

    Developing quantitative methods for characterizing structural properties of force chains in densely packed granular media is an important step toward understanding or predicting large-scale physical properties of a packing. A promising framework in which to develop such methods is network science, which can be used to translate particle locations and force contacts into a graph in which particles are represented by nodes and forces between particles are represented by weighted edges. Recent work applying network-based community-detection techniques to extract force chains opens the door to developing statistics of force-chain structure, with the goal of identifying geometric and topological differences across packings, and providing a foundation on which to build predictions of bulk material properties from mesoscale network features. Here we discuss a trio of related but fundamentally distinct measurements of the mesoscale structure of force chains in two-dimensional (2D) packings, including a statistic derived using tools from algebraic topology, which together provide a tool set for the analysis of force chain architecture. We demonstrate the utility of this tool set by detecting variations in force-chain architecture with pressure. Collectively, these techniques can be generalized to 3D packings, and to the assessment of continuous deformations of packings under stress or strain.

  17. Topological and geometric measurements of force-chain structure.

    PubMed

    Giusti, Chad; Papadopoulos, Lia; Owens, Eli T; Daniels, Karen E; Bassett, Danielle S

    2016-09-01

    Developing quantitative methods for characterizing structural properties of force chains in densely packed granular media is an important step toward understanding or predicting large-scale physical properties of a packing. A promising framework in which to develop such methods is network science, which can be used to translate particle locations and force contacts into a graph in which particles are represented by nodes and forces between particles are represented by weighted edges. Recent work applying network-based community-detection techniques to extract force chains opens the door to developing statistics of force-chain structure, with the goal of identifying geometric and topological differences across packings, and providing a foundation on which to build predictions of bulk material properties from mesoscale network features. Here we discuss a trio of related but fundamentally distinct measurements of the mesoscale structure of force chains in two-dimensional (2D) packings, including a statistic derived using tools from algebraic topology, which together provide a tool set for the analysis of force chain architecture. We demonstrate the utility of this tool set by detecting variations in force-chain architecture with pressure. Collectively, these techniques can be generalized to 3D packings, and to the assessment of continuous deformations of packings under stress or strain.

  18. Nanophotonic force microscopy: Characterizing particle–surface interactions using near-field photonics

    DOE PAGES

    Schein, Perry; Kang, Pilgyu; O’Dell, Dakota; ...

    2015-01-27

    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. In this paper, 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 scatteredmore » 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. Finally, 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.« less

  19. Nanophotonic force microscopy: Characterizing particle–surface interactions using near-field photonics

    SciTech Connect

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

    2015-01-27

    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. In this paper, 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. Finally, 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.

  20. Getting Physical with Your Chemistry: Mechanically Investigating Local Structure and Properties of Surfaces with the Atomic Force Microscope

    ERIC Educational Resources Information Center

    Heinz, William F.; Hoh, Jan H.

    2005-01-01

    Atomic force microscope (AFM) investigates mechanically the chemical properties of individual molecules, surfaces, and materials using suitably designed probes. The current state of the art of AFM in terms of imaging, force measurement, and sample manipulation and its application to physical chemistry is discussed.

  1. A scheme for solving the plane-plane challenge in force measurements at the nanoscale.

    PubMed

    Siria, Alessandro; Huant, Serge; Auvert, Geoffroy; Comin, Fabio; Chevrier, Joel

    2010-05-19

    Non-contact interaction between two parallel flat surfaces is a central paradigm in sciences. This situation is the starting point for a wealth of different models: the capacitor description in electrostatics, hydrodynamic flow, thermal exchange, the Casimir force, direct contact study, third body confinement such as liquids or films of soft condensed matter. The control of parallelism is so demanding that no versatile single force machine in this geometry has been proposed so far. Using a combination of nanopositioning based on inertial motors, of microcrystal shaping with a focused-ion beam (FIB) and of accurate in situ and real-time control of surface parallelism with X-ray diffraction, we propose here a "gedanken" surface-force machine that should enable one to measure interactions between movable surfaces separated by gaps in the micrometer and nanometer ranges.

  2. Mechanical Properties of Membrane Surface of Cultured Astrocyte Revealed by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Shiga, Hatsuki; Yamane, Yukako; Ito, Etsuro; Abe, Kazuhiro; Kawabata, Kazushige; Haga, Hisashi

    2000-06-01

    In order to examine the mechanical properties of the membrane surface of astrocytes, we observed living astrocytes by atomic force microscopy (AFM) both in contact mode and force-mapping mode. Ridge-like structures reflecting actin filaments were observed in the topographic images in contact mode, but not in force-mapping mode, using a zero-loading force. When we measured the elasticity of astrocytes, we observed that the cell membrane above the nucleus was soft and the cell membrane above the cytosol was stiff. In particular, the parts reflecting actin filaments were very stiff. This effect of actin filaments on the elasticity of astrocytes was confirmed by the loss of actin filaments after application of actin-polymerization inhibitor.

  3. Monitoring Coaxial-Probe Contact Force for Dielectric Properties Measurement

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A means is described for measuring and monitoring the contact force applied to a material sample with an open-ended coaxial-line probe for purposes of measuring the dielectric properties of semisolid material samples such as fruit, vegetable and animal tissues. The equipment consists of a stainless...

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

    SciTech Connect

    Pierce, Eric M

    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.

  5. Thermal desorption study of physical forces at the PTFE surface

    NASA Astrophysics Data System (ADS)

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

    Thermal desorption spectroscopy (TDS) of the polytetrafluoroethylene (PTFE) surface was successfully employed to study the possibile 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.

  6. Thermal desorption study of physical forces at the PTFE surface

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    Thermal desorption spectroscopy (TDS) of the polytetrafluoroethylene (PTFE) surface was successfully employed to study the possibile 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.

  7. Field measurement of basal forces generated by erosive debris flows

    USGS Publications Warehouse

    McCoy, S.W.; Tucker, G.E.; Kean, J.W.; Coe, J.A.

    2013-01-01

    It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‒flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‒flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‒flow events had a large‒magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‒averaged mean force), high‒frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‒averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ~ 20 times the median bed sediment grain size, no significant fluctuations about the time‒averaged mean force were measured, indicating that a thin layer of sediment (~ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‒grained granular surges and water‒rich, intersurge flow had very similar basal force distributions despite

  8. Reducing adhesion force by means of atomic layer deposition of ZnO films with nanoscale surface roughness.

    PubMed

    Chai, Zhimin; Liu, Yuhong; Lu, Xinchun; He, Dannong

    2014-03-12

    Adhesion is a big concern for the design of Si-based microelectromechanical devices. A ZnO film with nanoscale surface roughness is a promising candidate to decrease adhesion as the protective coating. In this study, the adhesion force of ZnO films prepared by atomic layer deposition (ALD) on a Si (100) substrate was studied. The root-mean-square (RMS) roughness of the ZnO films was in the range of 0.7-4.28 nm, and the contact angle of water was in the range of 85-88°. The adhesion force was measured by atomic force microscopy (AFM) at both low (12%) and high (60%) relative humidities. The results show that the adhesion force decreases as the surface roughness increases. A low adhesion force at high RMS roughness is attributed to the large asperities on the film, and a large adhesion force at high humidity is attributed to the large capillary force. The experimental adhesion force was compared to the force calculated using the Rabinovich model. Although the theoretical value underestimates the experimental value, the proportion of the two components of the adhesion force is clearly shown. At the low humidity, the van der Waals force component differs not greatly with the capillary force component, while at the high humidity, the capillary force component becomes dominant.

  9. Effect of contact angle hysteresis on the measurement of capillary forces.

    PubMed

    De Souza, E J; Gao, L; McCarthy, T J; Arzt, E; Crosby, A J

    2008-02-19

    We conduct experimental investigations of macroscopic capillary forces between two flat rigid substrates characterized by their advancing and receding contact angles with water. Our results exhibit excellent agreement with theoretical predictions obtained by the numerical solution of the capillary equation. On the basis of this comparison, we use the measurements of the capillary force to investigate the phenomenon of contact angle hysteresis. We present examples of force measurements for surfaces that display low, moderate, and high contact angle hysteresis and compare results for a larger variety of substrates. Finally, we show that for the case of water, the role of viscosity is insignificant within the range of force and velocity measured in the present work.

  10. Sensitivity of Force Specifications to the Errors in Measuring the Interface Force

    NASA Technical Reports Server (NTRS)

    Worth, Daniel

    2000-01-01

    Force-Limited Random Vibration Testing has been applied in the last several years at the NASA Goddard Space Flight Center (GSFC) and other NASA centers for various programs at the instrument and spacecraft level. Different techniques have been developed over the last few decades to estimate the dynamic forces that the test article under consideration will encounter in the flight environment. Some of these techniques are described in the handbook, NASA-HDBK-7004, and the monograph, NASA-RP-1403. This paper will show the effects of some measurement and calibration errors in force gauges. In some cases, the notches in the acceleration spectrum when a random vibration test is performed with measurement errors are the same as the notches produced during a test that has no measurement errors. The paper will also present the results Of tests that were used to validate this effect. Knowing the effect of measurement errors can allow tests to continue after force gauge failures or allow dummy gauges to be used in places that are inaccessible to a force gage.

  11. Atomic force microscopy measurements of bacterial adhesion and biofilm formation onto clay-sized particles

    PubMed Central

    Huang, Qiaoyun; Wu, Huayong; Cai, Peng; Fein, Jeremy B.; Chen, Wenli

    2015-01-01

    Bacterial adhesion onto mineral surfaces and subsequent biofilm formation play key roles in aggregate stability, mineral weathering, and the fate of contaminants in soils. However, the mechanisms of bacteria-mineral interactions are not fully understood. Atomic force microscopy (AFM) was used to determine the adhesion forces between bacteria and goethite in water and to gain insight into the nanoscale surface morphology of the bacteria-mineral aggregates and biofilms formed on clay-sized minerals. This study yields direct evidence of a range of different association mechanisms between bacteria and minerals. All strains studied adhered predominantly to the edge surfaces of kaolinite rather than to the basal surfaces. Bacteria rarely formed aggregates with montmorillonite, but were more tightly adsorbed onto goethite surfaces. This study reports the first measured interaction force between bacteria and a clay surface, and the approach curves exhibited jump-in events with attractive forces of 97 ± 34 pN between E. coli and goethite. Bond strengthening between them occurred within 4 s to the maximum adhesion forces and energies of −3.0 ± 0.4 nN and −330 ± 43 aJ (10−18 J), respectively. Under the conditions studied, bacteria tended to form more extensive biofilms on minerals under low rather than high nutrient conditions. PMID:26585552

  12. Atomic force microscopy measurements of bacterial adhesion and biofilm formation onto clay-sized particles

    NASA Astrophysics Data System (ADS)

    Huang, Qiaoyun; Wu, Huayong; Cai, Peng; Fein, Jeremy B.; Chen, Wenli

    2015-11-01

    Bacterial adhesion onto mineral surfaces and subsequent biofilm formation play key roles in aggregate stability, mineral weathering, and the fate of contaminants in soils. However, the mechanisms of bacteria-mineral interactions are not fully understood. Atomic force microscopy (AFM) was used to determine the adhesion forces between bacteria and goethite in water and to gain insight into the nanoscale surface morphology of the bacteria-mineral aggregates and biofilms formed on clay-sized minerals. This study yields direct evidence of a range of different association mechanisms between bacteria and minerals. All strains studied adhered predominantly to the edge surfaces of kaolinite rather than to the basal surfaces. Bacteria rarely formed aggregates with montmorillonite, but were more tightly adsorbed onto goethite surfaces. This study reports the first measured interaction force between bacteria and a clay surface, and the approach curves exhibited jump-in events with attractive forces of 97 ± 34 pN between E. coli and goethite. Bond strengthening between them occurred within 4 s to the maximum adhesion forces and energies of -3.0 ± 0.4 nN and -330 ± 43 aJ (10-18 J), respectively. Under the conditions studied, bacteria tended to form more extensive biofilms on minerals under low rather than high nutrient conditions.

  13. Mapping and control of atomic force on Si(1 1 1)square root(3) x square root(3)-Ag surface using noncontact atomic force microscope.

    PubMed

    Morita, S; Sugawara, Y

    2002-05-01

    We demonstrated the possibility of measuring the three-dimensional force-related map with true atomic resolution between an Si tip and Si(1 1 1)square root(3) x square root(3)-Ag sample surface by measuring the tip-sample distance dependence of noncontact atomic force microscope (NC-AFM) image, i.e. atomically resolved atomic force spectroscopy. Furthermore, we demonstrated the possibility of controlling the interaction force between the atom on the tip apex and a sample atom of Si(1 1 1)square root(3) x square root(3)-Ag surface on an atomic scale by placing an Ag atom on the Si tip apex instead of Si atom.

  14. Measurements of dispersion forces between colloidal latex particles with the atomic force microscope and comparison with Lifshitz theory

    SciTech Connect

    Elzbieciak-Wodka, Magdalena; Ruiz-Cabello, F. Javier Montes; Trefalt, Gregor; Maroni, Plinio; Borkovec, Michal; Popescu, Mihail N.

    2014-03-14

    Interaction forces between carboxylate colloidal latex particles of about 2 μm in diameter immersed in aqueous solutions of monovalent salts were measured with the colloidal probe technique, which is based on the atomic force microscope. We have systematically varied the ionic strength, the type of salt, and also the surface charge densities of the particles through changes in the solution pH. Based on these measurements, we have accurately measured the dispersion forces acting between the particles and estimated the apparent Hamaker constant to be (2.0 ± 0.5) × 10{sup −21} J at a separation distance of about 10 nm. This value is basically independent of the salt concentration and the type of salt. Good agreement with Lifshitz theory is found when roughness effects are taken into account. The combination of retardation and roughness effects reduces the value of the apparent Hamaker constant and its ionic strength dependence with respect to the case of ideally smooth surfaces.

  15. Measurements of dispersion forces between colloidal latex particles with the atomic force microscope and comparison with Lifshitz theory.

    PubMed

    Elzbieciak-Wodka, Magdalena; Popescu, Mihail N; Montes Ruiz-Cabello, F Javier; Trefalt, Gregor; Maroni, Plinio; Borkovec, Michal

    2014-03-14

    Interaction forces between carboxylate colloidal latex particles of about 2 μm in diameter immersed in aqueous solutions of monovalent salts were measured with the colloidal probe technique, which is based on the atomic force microscope. We have systematically varied the ionic strength, the type of salt, and also the surface charge densities of the particles through changes in the solution pH. Based on these measurements, we have accurately measured the dispersion forces acting between the particles and estimated the apparent Hamaker constant to be (2.0 ± 0.5) × 10(-21) J at a separation distance of about 10 nm. This value is basically independent of the salt concentration and the type of salt. Good agreement with Lifshitz theory is found when roughness effects are taken into account. The combination of retardation and roughness effects reduces the value of the apparent Hamaker constant and its ionic strength dependence with respect to the case of ideally smooth surfaces.

  16. DNA nanofilm thickness measurement on microarray in air and in liquid using an atomic force microscope.

    PubMed

    Legay, Guillaume; Finot, Eric; Meunier-Prest, Rita; Cherkaoui-Malki, Mustapha; Latruffe, Norbert; Dereux, Alain

    2005-10-15

    The measurement of the thickness of DNA films on microarray as a function of the medium (liquid, air) is gaining importance for understanding the signal response of biosensors. Thiol group has been used to attach DNA strands to gold micropads deposited on silicon surface. Atomic force microscopy (AFM) was employed in its height mode to measure the change in the pad thickness and in its force mode to measure the indentation depth of the nanofilm. A good coherence between the height and force modes is observed for the film thickness in air. The adhesion force was found to be an alternative way to measure the surface coverage of the biolayer at nanoscopic scale. However the force analysis (compression, steric and electrostatic) provides baseline information necessary to interpret the AFM height image in liquid. Analysis of the film thickness distribution shows that the height of the DNA strands depends on both the DNA strand length (15-35 base pairs) and the environment (air, liquid). In air, longer strands lay down onto gold surface whereas the charge reversal of gold in liquid causes a repulsion of longer strands, which stand up.

  17. Direct measurement of depletion and structural forces in a micellar system

    NASA Astrophysics Data System (ADS)

    Richetti, P.; Kékicheff, P.

    1992-03-01

    The force as a function of separation is measured between two mica surfaces coated with adsorbed bilayers of cetyltrimethylammonium bromide (CTAB) and immersed in aqueous ionic micellar solutions of CTAB. At low separations double-layer forces are observed and arise soley from the dissociated counterions and free CTA+. At large separations, the repulsion is reduced and a secondary minimum in the interaction potential deepens when the micellar concentration is increased. Finally, at higher concentrations, structural effects superimpose an oscillatory force profile at further separations.

  18. Forces applied by cilia measured on explants from mucociliary tissue.

    PubMed

    Teff, Zvi; Priel, Zvi; Gheber, Levi A

    2007-03-01

    Forces applied by intact mucus-propelling cilia were measured for the first time that we know of using a combined atomic force microscopy (AFM) and electrooptic system. The AFM probe was dipped into a field of beating cilia and its time-dependent deflection was recorded as it was struck by the cilia while the electrooptic system simultaneously and colocally measured the frequency to ensure that no perturbation was induced by the AFM probe. Using cilia from frog esophagus, we measured forces of approximately 0.21 nN per cilium during the effective stroke. This value, together with the known internal structure of these cilia, leads to the conclusion that most dynein arms along the length of the axoneme contribute to the effective stroke of these cilia.

  19. Note: Electrical resolution during conductive atomic force microscopy measurements under different environmental conditions and contact forces

    SciTech Connect

    Lanza, M.; Porti, M.; Nafria, M.; Aymerich, X.; Whittaker, E.; Hamilton, B.

    2010-10-15

    Conductive atomic force microscopy experiments on gate dielectrics in air, nitrogen, and UHV have been compared to evaluate the impact of the environment on topography and electrical measurements. In current images, an increase of the lateral resolution and a reduction of the conductivity were observed in N{sub 2} and, especially, in UHV (where current depends also on the contact force). Both effects were related to the reduction/elimination of the water layer between the tip and the sample in N{sub 2}/UHV. Therefore, since current measurements are very sensitive to environmental conditions, these factors must be taken into consideration when comparisons between several experiments are performed.

  20. Elasticity measurement of breast cancer cells by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Xu, Chaoxian; Wang, Yuhua; Jiang, Ningcheng; Yang, Hongqin; Lin, Juqiang; Xie, Shusen

    2014-09-01

    Mechanical properties of living cells play an important role in understanding various cells' function and state. Therefore cell biomechanics is expected to become a useful tool for cancer diagnosis. In this study, atomic force microscopy (AFM) using a square pyramid probe was performed to investigate cancerous (MCF-7) and benign (MCF-10A) human breast epithelial cells. The new QITM mode was used to acquire high-resolution topographic images and elasticity of living cells. Furthermore, individual force curves were recorded at maximum loads of 0.2, 0.5 and 1 nN, and the dependence of cell's elasticity with loading force was discussed. It was showed that the cancerous cells exhibited smaller elasticity modulus in comparison to non-cancerous counterparts. The elasticity modulus increased as the loading force increased from 0.2 nN to 1 nN. This observation indicates that loading force affects the cell's apparent elasticity and it is important to choose the appropriate force applied to cells in order to distinguish normal and cancer cells. The results reveal that the mechanical properties of living cells measured by atomic force microscopy may be a useful indicator of cell type and disease.

  1. Measuring colloidal forces with the magnetic chaining technique

    NASA Astrophysics Data System (ADS)

    Dreyfus, R.; Lacoste, D.; Bibette, J.; Baudry, J.

    2009-02-01

    In 1994 Leal Calderon et al. (Phys. Rev. Lett. 72, 2959 (1994)) introduced the magnetic chaining technique to directly probe the force-distance profile between colloidal particles. In this paper, we revisit this approach in two ways. First, we describe a new experimental design which allows us to utilize sample volumes as low as a few microliters, involving femtomoles of surface active macromolecules. Secondly, we extensively describe the characterization and preparation of the magnetic colloids, and we give a quantitative evaluation of performance and resolution of the technique in terms of force and interparticle separation.

  2. Asymmetric electrostatic and hydrophobic-hydrophilic interaction forces between mica surfaces and silicone polymer thin films.

    PubMed

    Donaldson, Stephen H; Das, Saurabh; Gebbie, Matthew A; Rapp, Michael; Jones, Louis C; Roiter, Yuri; Koenig, Peter H; Gizaw, Yonas; Israelachvili, Jacob N

    2013-11-26

    We have synthesized model hydrophobic silicone thin films on gold surfaces by a two-step covalent grafting procedure. An amino-functionalized gold surface reacts with monoepoxy-terminated polydimethylsiloxane (PDMS) via a click reaction, resulting in a covalently attached nanoscale thin film of PDMS, and the click chemistry synthesis route provides great selectivity, reproducibility, and stability in the resulting model hydrophobic silicone thin films. The asymmetric interaction forces between the PDMS thin films and mica surfaces were measured with the surface forces apparatus in aqueous sodium chloride solutions. At an acidic pH of 3, attractive interactions are measured, resulting in instabilities during both approach (jump-in) and separation (jump-out from adhesive contact). Quantitative analysis of the results indicates that the Derjaguin-Landau-Verwey-Overbeek theory alone, i.e., the combination of electrostatic repulsion and van der Waals attraction, cannot fully describe the measured forces and that the additional measured adhesion is likely due to hydrophobic interactions. The surface interactions are highly pH-dependent, and a basic pH of 10 results in fully repulsive interactions at all distances, due to repulsive electrostatic and steric-hydration interactions, indicating that the PDMS is negatively charged at high pH. We describe an interaction potential with a parameter, known as the Hydra parameter, that can account for the extra attraction (low pH) due to hydrophobicity as well as the extra repulsion (high pH) due to hydrophilic (steric-hydration) interactions. The interaction potential is general and provides a quantitative measure of interfacial hydrophobicity/hydrophilicity for any set of interacting surfaces in aqueous solution.

  3. General methodology for evaluating the adhesion force of drops and bubbles on solid surfaces.

    PubMed

    Antonini, C; Carmona, F J; Pierce, E; Marengo, M; Amirfazli, A

    2009-06-02

    The shortcomings of the current formulation for calculating the adhesion force for drops and bubbles with noncircular contact lines are discussed. A general formulation to evaluate the adhesion force due to surface forces is presented. Also, a novel methodology, that is, IBAFA, image based adhesion force analysis, was developed to allow implementation of the general formulation. IBAFA is based on the use of multiple profile images of a drop. The images are analyzed (1) to accurately reconstruct the contact line shape, which is analytically represented by a Fourier cosine series, and (2) to measure contact angles at multiple locations along the contact line and determine the contact angle distribution based on a linear piecewise interpolation routine. The contact line shape reconstruction procedure was validated with both actual experiments and simulated experiments. The procedure for the evaluation of the adhesion force was tested using simulated experiments with synthetic drops of known shapes. A comparison with current methods showed that simplifying assumptions (e.g., elliptical contact line or linear contact angle distribution) used in these methods result in errors up to 76% in the estimated adhesion force. However, the drop adhesion force evaluated using IBAFA results in small errors on the order of 1%.

  4. Aerosol Spectral Radiative Forcing Efficiency from Airborne Measurements During Multiple Field Missions

    NASA Astrophysics Data System (ADS)

    Schmidt, S.; Leblanc, S. E.; Pilewskie, P.; Redemann, J.; Hostetler, C. A.; Ferrare, R. A.; Hair, J. W.

    2012-12-01

    Measurements of shortwave spectral irradiance in conjunction with measurements of aerosol optical depth are used to determine the direct aerosol radiative forcing for various different regions and missions. To better compare cases with different air masses and solar geometry, we use the concept of top-of-layer and bottom-of-layer relative forcing efficiency. The aerosol layers were sampled from aircraft during several field campaigns, including the Megacity Initiative: Local and Global Research Observations (MILAGRO, Mexico, 2006); the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS, Alaska and Alberta, 2008), Research at the Nexus of Air Quality and Climate Change (CalNex, California, 2010); and the Deep Convective Clouds and Chemistry Experiment (DC3, central US, 2012). We show that the spectral shape of the relative forcing efficiency is similar for these aerosol layers regardless of the aerosol type. The spectral relative forcing efficiency at any one wavelength for the majority of the cases is constrained within a span of 20% per unit of midvisible aerosol optical depth. Single scattering albedo, asymmetry parameter, and surface albedo are secondary products for the various methods used to determine aerosol radiative forcing. Using these, we determine the diurnally averaged spectral and broadband top-of-atmosphere and surface radiative forcing efficiency for the various different aerosol types and surface conditions.

  5. Single-Molecule Force Spectroscopy of DNA-Based Reversible Polymer Bridges: Surface Robustness and Homogeneity

    PubMed Central

    Serpe, Michael J.; Whitehead, Jason R.; Rivera, Monica; Clark, Robert L.; Craig, Stephen L.

    2011-01-01

    Single-molecule force spectroscopy, as implemented in an atomic force microscope, provides a rarely-used method by which to monitor dynamic processes that occur near surfaces. Here, a methodology is presented and characterized that facilitates the study of polymer bridging across nanometer-sized gaps. The model system employed is that of DNA-based reversible polymers, and an automated procedure is introduced that allows the AFM tip-surface contact point to be automatically determined, and the distance d between opposing surfaces to be actively controlled. Using this methodology, the importance of several experimental parameters was systematically studied, e.g. the frequency of repeated tip/surface contacts, the area of the substrate surface sampled by the AFM, and the use of multiple AFM tips and substrates. Experiments revealed the surfaces to be robust throughout pulling experiments, so that multiple touches and pulls could be carried out on a single spot with no measurable affect on the results. Differences in observed bridging probabilities were observed, both on different spots on the same surface and, more dramatically, from one day to another. Data normalization via a reference measurement allows data from multiple days to be directly compared. PMID:21966095

  6. Measurement of transmitted blast force-time histories

    SciTech Connect

    Dr. Benjamin Langhorst; Corey Cook; James Schondel; Dr. Henry S. Chu

    2010-03-01

    A simple, reliable, and cost effective method is presented for the measurement of transmitted force behind a panel subjected to blast loads. Sensors were designed for a specific blast environment and successfully used to measure transmitted blast force behind solid polyethylene plates of thickness 0.125 and 0.25 inches. Experimental data was collected and examined to reveal consistent differences in the response of different thicknesses of otherwise identical panels. Finally, recommendations are made for future design, construction and use of similar sensors.

  7. Numerical study of the hydrodynamic drag force in atomic force microscopy measurements undertaken in fluids.

    PubMed

    Méndez-Méndez, J V; Alonso-Rasgado, M T; Faria, E Correia; Flores-Johnson, E A; Snook, R D

    2014-11-01

    When atomic force microscopy (AFM) is employed for in vivo study of immersed biological samples, the fluid medium presents additional complexities, not least of which is the hydrodynamic drag force due to viscous friction of the cantilever with the liquid. This force should be considered when interpreting experimental results and any calculated material properties. In this paper, a numerical model is presented to study the influence of the drag force on experimental data obtained from AFM measurements using computational fluid dynamics (CFD) simulation. The model provides quantification of the drag force in AFM measurements of soft specimens in fluids. The numerical predictions were compared with experimental data obtained using AFM with a V-shaped cantilever fitted with a pyramidal tip. Tip velocities ranging from 1.05 to 105 μm/s were employed in water, polyethylene glycol and glycerol with the platform approaching from a distance of 6000 nm. The model was also compared with an existing analytical model. Good agreement was observed between numerical results, experiments and analytical predictions. Accurate predictions were obtained without the need for extrapolation of experimental data. In addition, the model can be employed over the range of tip geometries and velocities typically utilized in AFM measurements.

  8. Instrumentation for Surface Flux Measurements

    DTIC Science & Technology

    2012-05-10

    National Park , she used the sonic and a Li-Cor C02-H20 analyzer at a height of 3 m to measure the vertical turbulent flux of C02 downwind of...SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) U. S. Army Research Office P.O. Box 12211 Research Triangle Park , NC 27709-2211 3. REPORT TYPE...and subgrid-scale array measurements In summer 2000 we lent 7 of the CSAT3 sonics to the National Center for Atmo- spheric Research (NCAR) for use in

  9. The Analog Atomic Force Microscope: Measuring, Modeling, and Graphing for Middle School

    ERIC Educational Resources Information Center

    Goss, Valerie; Brandt, Sharon; Lieberman, Marya

    2013-01-01

    using an analog atomic force microscope (A-AFM) made from a cardboard box and mailing tubes. Varying numbers of ping pong balls inside the tubes mimic atoms on a surface. Students use a dowel to make macroscale measurements similar to those of a nanoscale AFM tip as it…

  10. Systematic review of ground reaction force measurements in cats.

    PubMed

    Schnabl, E; Bockstahler, B

    2015-10-01

    Although orthopaedic abnormalities in cats are frequently observed radiographically, they remain clinically underdiagnosed, and kinetic motion analysis, a fundamental aspect of orthopaedic research in dogs and horses, is not commonly performed. More information obtained with non-invasive measurement techniques to assess normal and abnormal gait in cats would provide a greater insight into their locomotion and biomechanics and improve the objective measurement of disease alterations and treatment modalities. In this systematic review, 12 previously performed studies that investigated ground reaction force measurements in cats during locomotion were evaluated. The aims of these studies, the measurement methods and equipment used, and the outcomes of parameters used to assess both sound and diseased cats are summarised and discussed. All reviewed studies used pressure sensitive walkways to gain data and all provided an acclimatisation period as a prerequisite for measurements. In sound cats during walking, the forelimb peak vertical force was greater than in the hindlimb and the peak vertical force in the hindlimb was greater in cats than in dogs. This review confirms that ground reaction forces can be used to evaluate lameness and treatment effects in the cat.

  11. Colored polydimethylsiloxane micropillar arrays for high throughput measurements of forces applied by genetic model organisms

    PubMed Central

    Khare, Siddharth M.; Awasthi, Anjali; Venkataraman, V.; Koushika, Sandhya P.

    2015-01-01

    Measuring forces applied by multi-cellular organisms is valuable in investigating biomechanics of their locomotion. Several technologies have been developed to measure such forces, for example, strain gauges, micro-machined sensors, and calibrated cantilevers. We introduce an innovative combination of techniques as a high throughput screening tool to assess forces applied by multiple genetic model organisms. First, we fabricated colored Polydimethylsiloxane (PDMS) micropillars where the color enhances contrast making it easier to detect and track pillar displacement driven by the organism. Second, we developed a semi-automated graphical user interface to analyze the images for pillar displacement, thus reducing the analysis time for each animal to minutes. The addition of color reduced the Young's modulus of PDMS. Therefore, the dye-PDMS composite was characterized using Yeoh's hyperelastic model and the pillars were calibrated using a silicon based force sensor. We used our device to measure forces exerted by wild type and mutant Caenorhabditis elegans moving on an agarose surface. Wild type C. elegans exert an average force of ∼1 μN on an individual pillar and a total average force of ∼7.68 μN. We show that the middle of C. elegans exerts more force than its extremities. We find that C. elegans mutants with defective body wall muscles apply significantly lower force on individual pillars, while mutants defective in sensing externally applied mechanical forces still apply the same average force per pillar compared to wild type animals. Average forces applied per pillar are independent of the length, diameter, or cuticle stiffness of the animal. We also used the device to measure, for the first time, forces applied by Drosophila melanogaster larvae. Peristaltic waves occurred at 0.4 Hz applying an average force of ∼1.58 μN on a single pillar. Our colored microfluidic device along with its displacement tracking software allows us to measure forces

  12. Atomic force microscope imaging and force measurements at electrified and actively corroding interfaces: Challenges and novel cell design

    NASA Astrophysics Data System (ADS)

    Valtiner, Markus; Ankah, Genesis Ngwa; Bashir, Asif; Renner, Frank Uwe

    2011-02-01

    We report the design of an improved electrochemical cell for atomic force microscope measurements in corrosive electrochemical environments. Our design improvements are guided by experimental requirements for studying corrosive reactions such as selective dissolution, dealloying, pitting corrosion, and/or surface and interface forces at electrified interfaces. Our aim is to examine some of the limitations of typical electrochemical scanning probe microscopy (SPM) experiments and in particular to outline precautions and cell-design elements, which must necessarily be taken into account in order to obtain reliable experimental results. In particular, we discuss electrochemical requirements for typical electrochemical SPM experiments and introduce novel design features to avoid common issues such as crevice formations; we discuss the choice of electrodes and contaminations from ions of reference electrodes. We optimize the cell geometry and introduce standard samples for electrochemical AFM experiments. We have tested the novel design by performing force-distance spectroscopy as a function of the applied electrochemical potential between a bare gold electrode surface and a SAM-coated AFM tip. Topography imaging was tested by studying the well-known dealloying process of a Cu3Au(111) surface up to the critical potential. Our design improvements should be equally applicable to in situ electrochemical scanning tunneling microscope cells.

  13. Dynamics of a disturbed sessile drop measured by atomic force microscopy (AFM).

    PubMed

    McGuiggan, Patricia M; Grave, Daniel A; Wallace, Jay S; Cheng, Shengfeng; Prosperetti, Andrea; Robbins, Mark O

    2011-10-04

    A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r ∼ 20-30 μm) is brought into contact with a small sessile water drop resting on a polytetrafluoroethylene (PTFE) surface. When the microsphere touches the liquid surface, the meniscus rises onto it because of capillary forces. Although the microsphere volume is 6 orders of magnitude smaller than the drop, it excites the normal resonance modes of the liquid interface. The sphere is pinned at the interface, whose small (<100 nm) oscillations are readily measured with AFM. Resonance oscillation frequencies were measured for drop volumes between 5 and 200 μL. The results for the two lowest normal modes are quantitatively consistent with continuum calculations for the natural frequency of hemispherical drops with no adjustable parameters. The method may enable sensitive measurements of volume, surface tension, and viscosity of small drops.

  14. Parameters affecting the adhesion strength between a living cell and a colloid probe when measured by the atomic force microscope.

    PubMed

    McNamee, Cathy E; Pyo, Nayoung; Tanaka, Saaya; Vakarelski, Ivan U; Kanda, Yoichi; Higashitani, Ko

    2006-03-15

    In this study, we used the colloid probe atomic force microscopy (AFM) technique to investigate the adhesion force between a living cell and a silica colloid particle in a Leibovitz's L-15 medium (L-15). The L-15 liquid maintained the pharmaceutical conditions necessary to keep the cells alive in the outside environment during the AFM experiment. The force curves in such a system showed a steric repulsion in the compression force curve, due to the compression of the cells by the colloid probe, and an adhesion force in the decompression force curve, due to binding events between the cell and the probe. We also investigated for the first time how the position on the cell surface, the strength of the pushing force, and the residence time of the probe at the cell surface individually affected the adhesion force between a living cell and a 6.84 microm diameter silica colloid particle in L-15. The position of measuring the force on the cell surface was seen not to affect the value of the maximum adhesion force. The loading force was also seen not to notably affect the value of the maximum adhesion force, if it was small enough not to pierce and damage the cell. The residence time of the probe at the cell surface, however, clearly affected the adhesion force, where a longer residence time gave a larger maximum force. From these results, we could conclude that the AFM force measurements should be made using a loading force small enough not to damage the cell and a fixed residence time, when comparing results of different systems.

  15. Slip-length measurement of confined air flow using dynamic atomic force microscopy.

    PubMed

    Maali, Abdelhamid; Bhushan, Bharat

    2008-08-01

    We present an experimental measurement of the slip length of air flow close to solid surfaces using an atomic force microscope (AFM) in dynamic mode. The air was confined between a glass surface and a spherical glass particle glued to an AFM cantilever. The Knudsen number was varied continuously over three decades by varying the distance between the two surfaces. Our results show that the effect of confining the air is purely dissipative. The data are described by an isothermal Maxwell slip-boundary condition, and the measured slip-length value was 118 nm .

  16. Kinesin force generation measured using a centrifuge microscope sperm-gliding motility assay.

    PubMed Central

    Hall, K; Cole, D; Yeh, Y; Baskin, R J

    1996-01-01

    To measure force generation and characterize the relationship between force and velocity in kinesin-driven motility we have developed a centrifuge microscope sperm-gliding motility assay. The average (extrapolated) value of maximum isometric force at low kinesin density was 0.90 +/- 0.14 pN. Furthermore, in the experiments at low kinesin density, sperm pulled off before stall at forces between 0.40 and 0.75 pN. To further characterize our kinesin-demembranated sperm assay we estimated maximum isometric force using a laser trap-based assay. At low kinesin density, 4.34 +/- 1.5 pN was the maximum force. Using values of axoneme stiffness available from other studies, we concluded that, in our centrifuge microscope-based assay, a sperm axoneme functions as a lever arm, magnifying the centrifugal force and leading to pull-off before stall. In addition, drag of the distal portion of the axoneme is increased by the centrifugal force (because the axoneme is rotated into closer proximity to the glass surface) and represents an additional force that the kinesin motor must overcome. Images FIGURE 1 FIGURE 9 FIGURE 10 PMID:8968616

  17. Measurement of cell adhesion force by vertical forcible detachment using an arrowhead nanoneedle and atomic force microscopy

    SciTech Connect

    Ryu, Seunghwan; Hashizume, Yui; Mishima, Mari; Kawamura, Ryuzo; Tamura, Masato; Matsui, Hirofumi; Matsusaki, Michiya; Akashi, Mitsuru; Nakamura, Chikashi

    2014-08-15

    Graphical abstract: - Highlights: • We developed a method to measure cell adhesion force by detaching cell using an arrowhead nanoneedle and AFM. • A nanofilm consisting of fibronectin and gelatin was formed on cell surface to reinforce the cell cortex. • By the nanofilm lamination, detachment efficiencies of strongly adherent cell lines were improved markedly. - Abstract: The properties of substrates and extracellular matrices (ECM) are important factors governing the functions and fates of mammalian adherent cells. For example, substrate stiffness often affects cell differentiation. At focal adhesions, clustered–integrin bindings link cells mechanically to the ECM. In order to quantitate the affinity between cell and substrate, the cell adhesion force must be measured for single cells. In this study, forcible detachment of a single cell in the vertical direction using AFM was carried out, allowing breakage of the integrin–substrate bindings. An AFM tip was fabricated into an arrowhead shape to detach the cell from the substrate. Peak force observed in the recorded force curve during probe retraction was defined as the adhesion force, and was analyzed for various types of cells. Some of the cell types adhered so strongly that they could not be picked up because of plasma membrane breakage by the arrowhead probe. To address this problem, a technique to reinforce the cellular membrane with layer-by-layer nanofilms composed of fibronectin and gelatin helped to improve insertion efficiency and to prevent cell membrane rupture during the detachment process, allowing successful detachment of the cells. This method for detaching cells, involving cellular membrane reinforcement, may be beneficial for evaluating true cell adhesion forces in various cell types.

  18. Dynamic contact angle measurements on superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  19. Force-Velocity Measurements of a Few Growing Actin Filaments

    PubMed Central

    Brangbour, Coraline; du Roure, Olivia; Helfer, Emmanuèle; Démoulin, Damien; Mazurier, Alexis; Fermigier, Marc; Carlier, Marie-France; Bibette, Jérôme; Baudry, Jean

    2011-01-01

    The polymerization of actin in filaments generates forces that play a pivotal role in many cellular processes. We introduce a novel technique to determine the force-velocity relation when a few independent anchored filaments grow between magnetic colloidal particles. When a magnetic field is applied, the colloidal particles assemble into chains under controlled loading or spacing. As the filaments elongate, the beads separate, allowing the force-velocity curve to be precisely measured. In the widely accepted Brownian ratchet model, the transduced force is associated with the slowing down of the on-rate polymerization. Unexpectedly, in our experiments, filaments are shown to grow at the same rate as when they are free in solution. However, as they elongate, filaments are more confined in the interspace between beads. Higher repulsive forces result from this higher confinement, which is associated with a lower entropy. In this mechanism, the production of force is not controlled by the polymerization rate, but is a consequence of the restriction of filaments' orientational fluctuations at their attachment point. PMID:21541364

  20. Measurement of impact force, simulation of fall and hip fracture.

    PubMed

    Gardner, T N; Simpson, A H; Booth, C; Sprukkelhorst, P; Evans, M; Kenwright, J; Evans, J G

    1998-01-01

    It has been shown that the incidence of hip fracture in the elderly may be influenced by the type of floor covering commonly used in homes for the elderly. This study describes the development of a method for modelling a fall during a hip fracture event, to examine the influence of different floors on impact force. An impact transducer is dropped in free fall through a smooth plastic tube. The impactor nose of the transducer models the curvature of the greater trochanter, and a steel spring is used to simulate the compliance of the skeletal structure. A weight, which corresponds to one-sixteenth of average body mass, compresses the spring and applies force to the impactor nose on striking the floor. The temporal variation in the force of impact with the floor is measured by the transducer to within 0.41 percent (SD = 0.63%, n = 10). Five common floor coverings were tested over a concrete floor slab (vinyl, loop carpet and pile carpet--both with and without underpad). ANOVA analysis showed that the differences between mean forces for each floor covering were highly significant (p > 0.001), with the thicker coverings producing 7 percent lower forces. The transducer may be used to examine the correlation between impact force and fracture incidence for a variety of different floors in homes for the elderly.

  1. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  2. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  3. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  4. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  5. 21 CFR 890.1575 - Force-measuring platform.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Force-measuring platform. 890.1575 Section 890.1575 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) MEDICAL DEVICES PHYSICAL MEDICINE DEVICES Physical Medicine Diagnostic Devices § 890.1575...

  6. Force Exertion Capacity Measurements in Haptic Virtual Environments

    ERIC Educational Resources Information Center

    Munih, Marko; Bardorfer, Ales; Ceru, Bojan; Bajd, Tadej; Zupan, Anton

    2010-01-01

    An objective test for evaluating functional status of the upper limbs (ULs) in patients with muscular distrophy (MD) is presented. The method allows for quantitative assessment of the UL functional state with an emphasis on force exertion capacity. The experimental measurement setup and the methodology for the assessment of maximal exertable force…

  7. A measuring system for surface roughness parameters

    NASA Astrophysics Data System (ADS)

    Han, Jinhong; Wang, Yunkai; Zhang, Xianfeng

    2006-11-01

    We designed a measurement and control system which can measure the surface roughness parameters with a Single Chip Micyoco (SCM) as its kernel. It uses an inductive transducer to pick up the data. The instrumental structure and the working principle are also introduced in this paper. The integrated hardware and software systems have been designed and improved. The prototype model was calibrated and the instrumental precision was analysed according to the measured data. In this system the surface roughness parameters can automatically be measured and controlled, such as data processing, determination of the reference line, disposal of the surface profile informations, display and print of the results etc.

  8. Harnessing bifurcations in tapping-mode atomic force microscopy to calibrate time-varying tip-sample force measurements.

    PubMed

    Sahin, Ozgur

    2007-10-01

    Torsional harmonic cantilevers allow measurement of time-varying tip-sample forces in tapping-mode atomic force microscopy. Accuracy of these force measurements is important for quantitative nanomechanical measurements. Here we demonstrate a method to convert the torsional deflection signals into a calibrated force wave form with the use of nonlinear dynamical response of the tapping cantilever. Specifically the transitions between steady oscillation regimes are used to calibrate the torsional deflection signals.

  9. Noncontact intraoral measurement of force-related tooth mobility.

    PubMed

    Göllner, Matthias; Holst, Alexandra; Berthold, Christine; Schmitt, Johannes; Wichmann, Manfred; Holst, Stefan

    2010-10-01

    The aim of this pilot study was to measure force-related tooth mobility. Vertical and horizontal anterior tooth mobility in 31 healthy periodontal subjects was measured by a noncontact optical measurement technique. The subjects continuously increased the force on each tooth by biting on a load cell. An automated software program recorded tooth displacement at 9-N intervals. Vertical and horizontal displacements were subsequently measured. The vector of tooth mobility in the buccal direction was calculated using the Pythagorean theorem. The average displacements over all subjects for each tooth were determined. Global differences were assessed with the Wilcoxon test. There were no significant differences between contralateral teeth overall load stages. There were no significant differences in tooth mobility between the central and lateral incisors except for in the horizontal direction. However, there were significant differences between central incisor and canine and lateral incisor and canine teeth.

  10. Enclosed electronic system for force measurements in knee implants.

    PubMed

    Forchelet, David; Simoncini, Matteo; Arami, Arash; Bertsch, Arnaud; Meurville, Eric; Aminian, Kamiar; Ryser, Peter; Renaud, Philippe

    2014-08-14

    Total knee arthroplasty is a widely performed surgical technique. Soft tissue force balancing during the operation relies strongly on the experience of the surgeon in equilibrating tension in the collateral ligaments. Little information on the forces in the implanted prosthesis is available during surgery and post-operative treatment. This paper presents the design, fabrication and testing of an instrumented insert performing force measurements in a knee prosthesis. The insert contains a closed structure composed of printed circuit boards and incorporates a microfabricated polyimide thin-film piezoresistive strain sensor for each condylar compartment. The sensor is tested in a mechanical knee simulator that mimics in-vivo conditions. For characterization purposes, static and dynamic load patterns are applied to the instrumented insert. Results show that the sensors are able to measure forces up to 1.5 times body weight with a sensitivity fitting the requirements for the proposed use. Dynamic testing of the insert shows a good tracking of slow and fast changing forces in the knee prosthesis by the sensors.

  11. Enclosed Electronic System for Force Measurements in Knee Implants

    PubMed Central

    Forchelet, David; Simoncini, Matteo; Arami, Arash; Bertsch, Arnaud; Meurville, Eric; Aminian, Kamiar; Ryser, Peter; Renaud, Philippe

    2014-01-01

    Total knee arthroplasty is a widely performed surgical technique. Soft tissue force balancing during the operation relies strongly on the experience of the surgeon in equilibrating tension in the collateral ligaments. Little information on the forces in the implanted prosthesis is available during surgery and post-operative treatment. This paper presents the design, fabrication and testing of an instrumented insert performing force measurements in a knee prosthesis. The insert contains a closed structure composed of printed circuit boards and incorporates a microfabricated polyimide thin-film piezoresistive strain sensor for each condylar compartment. The sensor is tested in a mechanical knee simulator that mimics in-vivo conditions. For characterization purposes, static and dynamic load patterns are applied to the instrumented insert. Results show that the sensors are able to measure forces up to 1.5 times body weight with a sensitivity fitting the requirements for the proposed use. Dynamic testing of the insert shows a good tracking of slow and fast changing forces in the knee prosthesis by the sensors. PMID:25196007

  12. Model Engine Performance Measurement From Force Balance Instrumentation

    NASA Technical Reports Server (NTRS)

    Jeracki, Robert J.

    1998-01-01

    A large scale model representative of a low-noise, high bypass ratio turbofan engine was tested for acoustics and performance in the NASA Lewis 9- by 15-Foot Low-Speed Wind Tunnel. This test was part of NASA's continuing Advanced Subsonic Technology Noise Reduction Program. The low tip speed fan, nacelle, and an un-powered core passage (with core inlet guide vanes) were simulated. The fan blades and hub are mounted on a rotating thrust and torque balance. The nacelle, bypass duct stators, and core passage are attached to a six component force balance. The two balance forces, when corrected for internal pressure tares, measure the total thrust-minus-drag of the engine simulator. Corrected for scaling and other effects, it is basically the same force that the engine supports would feel, operating at similar conditions. A control volume is shown and discussed, identifying the various force components of the engine simulator thrust and definitions of net thrust. Several wind tunnel runs with nearly the same hardware installed are compared, to identify the repeatability of the measured thrust-minus-drag. Other wind tunnel runs, with hardware changes that affected fan performance, are compared to the baseline configuration, and the thrust and torque effects are shown. Finally, a thrust comparison between the force balance and nozzle gross thrust methods is shown, and both yield very similar results.

  13. Measuring and Understanding Forces on Atomic Length Scales with the Atomic Force Microscope

    NASA Astrophysics Data System (ADS)

    Cleveland, Jason Paul

    Most microscopes can be used with little understanding of how they work--much can be learned looking through a light microscope without ever knowing what a photon is or who Maxwell was--and the Atomic Force Microscope (AFM) is no exception. Many AFM images don't look much different from a mountainous landscape, and much is learned interpreting them as such; however, to really push a microscope to its limits means understanding the interactions creating the contrast in the picture. For a Scanning Electron Microscope, this means understanding how electrons interact with matter, for an AFM it means understanding forces. The focus of this thesis is understanding the forces acting (especially in liquids) between tip and sample in AFM and a better understanding the instrument itself. Chapters I, II and VI involve better characterizing and improving the most important part of the AFM, the tiny cantilever used to measure forces. Chapter I describes a solution to one of the most basic problems that must be solved before forces can be accurately measured--measuring the stiffness of these cantilevers. Many limitations in AFM are set by physical characteristics of the cantilever itself, such as resonance frequency, spring constant, and quality factor. If an external force can be applied to the cantilever, feedback can be used to improve these characteristics. Chapter II shows how to do this using a magnetically applied external force, which has the advantage of working in liquids. These physical characteristics also change drastically when the cantilever is immersed in fluid. The resonance frequency of common cantilevers drops by as much as a factor of six in going from air to water. Chapter VI studies these changes and shows how further miniaturization of cantilevers can improve imaging speeds and signal-to-noise ratio. Early in its career, the AFM was heralded as having atomic resolution, but as the field matured researchers realized that the contact area between tip and

  14. Optimized Model Surfaces for Advanced Atomic Force Microscopy Studies of Surface Nanobubbles.

    PubMed

    Song, Bo; Zhou, Yi; Schönherr, Holger

    2016-11-01

    The formation of self-assembled monolayers (SAMs) of binary mixtures of 16-mercaptohexadecanoic acid (MHDA) and 1-octadecanethiol (ODT) on ultraflat template-stripped gold (TSG) surfaces was systematically investigated to clarify the assembly behavior, composition, and degree of possible phase segregation in light of atomic force microscopy (AFM) studies of surface nanobubbles on these substrates. The data for SAMs on TSG were compared to those obtained by adsorption on rough evaporated gold, as reported in a previous study. Quartz crystal microbalance and surface plasmon resonance data acquired in situ on TSG indicate that similar to SAM formation on conventional evaporated gold substrates ODT and MHDA form monolayers and bilayers, respectively. The second layer on MHDA, whose formation is attributed to hydrogen bonding, can be easily removed by adequate rinsing with water. The favorable agreement of the grazing incidence reflection Fourier transform infrared (GIR FTIR) spectroscopy and contact angle data analyzed with the Israelachvili-Gee model suggests that the binary SAMs do not segregate laterally. This conclusion is fully validated by high-resolution friction force AFM observations down to a length scale of 8-10 nm, which is much smaller than the typical observed surface nanobubble radii. Finally, correspondingly functionalized TSG substrates are shown to be valuable supports for studying surface nanobubbles by AFM in water and for addressing the relation between surface functionality and nanobubble formation and properties.

  15. Probing the contribution of different intermolecular forces to the adsorption of spheroproteins onto hydrophilic surfaces.

    PubMed

    Borges, João; Campiña, José M; Silva, A Fernando

    2013-12-27

    Protein adsorption is a delicate process, which results from the balance between the properties of proteins and their solid supports. Although the relevance of some of these parameters has been already unveiled, the precise involvement of electrostatics and other weaker intermolecular forces requires further comprehension. Aiming to contribute to this task, this work explores the attachment, rearrangement, and surface aggregation of a model spheroprotein, such as bovine β-lactoglobulin (β-LG), onto hydrophilic substrates prefunctionalized with different alkylthiol films. Thereby, a variety of electrostatic scenarios for the adsorption of β-LG could be recreated through the variation of the pH and the functional chemistry of the surfaces. The changes in surface mass density (plus associated water) and film flexibility were followed in situ with quartz crystal microbalance with dissipation monitoring. Film packing and aggregation were assessed by faradaic electrochemical measurements and ex situ atomic force microscopy and field effect scanning electron microscopy. In contrast to previous hypotheses arguing that electrostatic interactions between charged substrates and proteins would be the only driving force, a complex interplay between Coulombic and non-Coulombic intermolecular forces (which would depend upon the experimental conditions) has been suggested to explain the results.

  16. Effect of permanent-magnet irregularities in levitation force measurements

    NASA Astrophysics Data System (ADS)

    Hull, John R.

    2000-06-01

    In the measurement of the levitation force between a vertically magnetized permanent magnet (PM) and a bulk high-temperature superconductor (HTS), PM domains with horizontal components of magnetization are shown to produce a non-negligible contribution to the levitation force in most systems. Such domains are typically found in all PMs, even in those that exhibit zero net horizontal magnetic moment. Extension of this analysis leads to an HTS analogue of Earnshaw's theorem, in which the vertical stiffness is equal to the sum of the horizontal stiffness at the field-cooling position, independent of the angular distribution of magnetic moments within the PM.

  17. Effect of permanent-magnet irregularities in levitation force measurements.

    SciTech Connect

    Hull, J. R.

    1999-10-14

    In the measurement of the levitation force between a vertically magnetized permanent magnet (PM) and a bulk high-temperature superconductor (HTS), PM domains with horizontal components of magnetization are shown to produce a nonnegligible contribution to the levitation force in most systems. Such domains are typically found in all PMs, even in those that exhibit zero net horizontal magnetic moment. Extension of this analysis leads to an HTS analog of Earnshaw's theorem, in which at the field-cooling position the vertical stiffness is equal to the sum of the horizontal stiffnesses, independent of angular distribution of magnetic moments within the PM.

  18. Surface texture measurement for dental wear applications

    NASA Astrophysics Data System (ADS)

    Austin, R. S.; Mullen, F.; Bartlett, D. W.

    2015-06-01

    The application of surface topography measurement and characterization within dental materials science is highly active and rapidly developing, in line with many modern industries. Surface measurement and structuring is used extensively within oral and dental science to optimize the optical, tribological and biological performance of natural and biomimetic dental materials. Although there has historically been little standardization in the use and reporting of surface metrology instrumentation and software, the dental industry is beginning to adopt modern areal measurement and characterization techniques, especially as the dental industry is increasingly adopting digital impressioning techniques in order to leverage CAD/CAM technologies for the design and construction of dental restorations. As dental treatment becomes increasingly digitized and reliant on advanced technologies such as dental implants, wider adoption of standardized surface topography and characterization techniques will become evermore essential. The dental research community welcomes the advances that are being made in surface topography measurement science towards realizing this ultimate goal.

  19. Thirty-Five Year Record of Shortwave TOA radiative cloud forcing from SBUV Measurements

    NASA Astrophysics Data System (ADS)

    Weaver, C. J.; Herman, J. R.; Labow, G. J.

    2015-12-01

    A thirty-five year record (1980-2014) of Shortwave TOA radiative cloud forcing is derived from UV Lambertian-Equivalent (LER) reflectivity data constructed using measured upwelling radiances from Nimbus-7 SBUV and seven NOAA SBUV/2 polar orbiting instruments. The approach is to scale the dimensionless UV LER data to match the CERES Shortwave Cloud radiative forcing when they are concurrent (2000-2014). The derived scaling factors are then used to produces a CERES-proxy of SW cloud forcing back to 1980. The good agreement between trends and anomalies of the CERES-proxy and CERES Shortwave Cloud forcing records during the overlapping data period supports using this new data set for extended climate studies.During 1980-2000 period of globally warming surface temperatures, our record of shortwave cloud forcing shows a widespread global increase in forcing from reduced cloudiness. However, during the more recent pause in global warming 2000-2012, our record shows a reduction in SW cloud forcing from increased cloudiness.Historical CMIP5 AMIP simulations from eight models do not capture the 1980-2000 reduction in cloudiness. Twenty-year segments of future RCP45 long-term runs with comparable surface temperature warming to that observed from 1980-2000, also do not simulate our observed reduction in cloud amount. This suggests that the climate sensitivity in the tested CMIP5 models is too low.

  20. Surface microstructure of bitumen characterized by atomic force microscopy.

    PubMed

    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

  1. Intracellular forces during guided cell growth on micropatterns using FRET measurement

    PubMed Central

    Suffoletto, Kevin; Ye, Nannan; Meng, Fanjie; Verma, Deepika; Hua, Susan Z.

    2015-01-01

    Interaction of cells with extracellular matrix (ECM) regulates cell shape, differentiation and polarity. This effect has been widely observed in cells grown on substrates with various patterned features, stiffness and surface chemistry. It has been postulated that mechanical confinement of cells by the substrate causes a redistribution of tension in cytoskeletal proteins resulting in cytoskeletal reorganization through force sensitive pathways. However, the mechanisms for force transduction during reorganization remain unclear. In this study, using FRET based force sensors we have measured tension in an actin cross-linking protein, α-actinin, and followed reorganization of actin cytoskeleton in real time in HEK cells grown on patterned substrates. We show that the patterned substrates cause a redistribution of tension in α-actinin that coincides with cytoskeleton reorganization. Higher tension was observed in portions of cells where they form bridges across inhibited regions of the patterned substrates; the attachment to the substrate is found to release tension. Real time measurements of α-actinin tension and F-actin arrangement show that an increase in tension coincides with formation of F-actin bundles at the cell periphery during cell-spreading across inhibited regions, suggesting that mechanical forces stimulate cytoskeleton enhancement. Rho-ROCK inhibitor (Y27632) causes reduction in actinin tension followed by retraction of bridged regions. Our results demonstrate that changes in cell shape and expansion over patterned surfaces is a force sensitive process that requires actomyosin contractile force involving Rho-ROCK pathway. PMID:25596631

  2. Chapter 16: Magnetic manipulation for force measurements in cell biology.

    PubMed

    Tim O'Brien, E; Cribb, Jeremy; Marshburn, David; Taylor, Russell M; Superfine, Richard

    2008-01-01

    Life is a mechanical process. Cells, tissues, and bodies must act within their environments to grow, divide, move, communicate, and defend themselves. The stiffness and viscosity of cells and biologic materials will vary depending upon a wide variety of variables including for example environmental conditions, activation of signaling pathways, stage of development, gene expression. By pushing and pulling cells or materials such as mucus or extracellular matrix, one can learn about their mechanical properties. By varying the conditions, signaling pathways or genetic background, one can also assess how the response of the cell or material is modulated by that pathway. Magnetic particles are available commercially in many useful sizes, magnetic contents, and surface chemistries. The variety of surface chemistries allow forces to be applied to a specimen through specific linkages such as receptors or particular proteins, allowing the biologist to ask fundamental questions about the role of those linkages in the transduction of force or motion. In this chapter, we discuss the use of a magnetic system designed to apply a wide range of forces and force patterns fully integrated into a high numerical aperture inverted fluorescence microscope. Fine, thin and flat magnetic poles allow the use of high magnification microscope objectives, and flexible software to control the direction and pattern of applied forces supports a variety of experimental situations. The system can be coupled with simple video acquisition for medium-bandwidth, two-dimensional particle tracking. Alternatively, the system can be coupled with a laser tracking and position feedback system for higher resolution, high bandwidth, three-dimensional tracking.

  3. Hole-to-surface resistivity measurements.

    USGS Publications Warehouse

    Daniels, J.J.

    1983-01-01

    Hole-to-surface resistivity measurements over a layered volcanic tuff sequence illustrate procedures for gathering, reducing, and interpreting hole-to-surface resistivity data. The magnitude and direction of the total surface electric field resulting from a buried current source is calculated from orthogonal potential difference measurements for a grid of closely spaced stations. A contour map of these data provides a detailed map of the distribution of the electric field away from the drill hole. Resistivity anomalies can be enhanced by calculating the difference between apparent resistivities calculated from the total surface electric field and apparent resistivities for a layered earth model.-from Author

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

    SciTech Connect

    Wang, R.; Williams, C. C.

    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.

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

    PubMed

    Wang, R; Williams, C C

    2015-09-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Wang, R.; Williams, C. C.

    2015-09-01

    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.

  7. In situ ion gun cleaning of surface adsorbates and its effect on electrostatic forces

    NASA Astrophysics Data System (ADS)

    Schafer, Robert; Xu, Jun; Mohideen, Umar

    2016-01-01

    To obtain precise measurements of the Casimir force, it is crucial to take into account the electrostatic interactions that exist between the two boundaries. Two otherwise grounded conductors will continue to have residual electrostatic effects from patch potentials existing on the surfaces. In this paper, we look at the effect of in situ cleaning of adsorbate patches, and the resultant effect on the net electrostatic potential difference between two surfaces. We find a significant reduction in the residual potential due to in situ Ar+ cleaning for the samples used.

  8. Photothermally excited force modulation microscopy for broadband nanomechanical property measurements

    SciTech Connect

    Wagner, Ryan Killgore, Jason P.

    2015-11-16

    We demonstrate photothermally excited force modulation microscopy (PTE FMM) for mechanical property characterization across a broad frequency range with an atomic force microscope (AFM). Photothermal excitation allows for an AFM cantilever driving force that varies smoothly as a function of drive frequency, thus avoiding the problem of spurious resonant vibrations that hinder piezoelectric excitation schemes. A complication of PTE FMM is that the sub-resonance cantilever vibration shape is fundamentally different compared to piezoelectric excitation. By directly measuring the vibrational shape of the cantilever, we show that PTE FMM is an accurate nanomechanical characterization method. PTE FMM is a pathway towards the characterization of frequency sensitive specimens such as polymers and biomaterials with frequency range limited only by the resonance frequency of the cantilever and the low frequency limit of the AFM.

  9. Measurement of the Casimir force between dissimilar metals.

    PubMed

    Decca, R S; López, D; Fischbach, E; Krause, D E

    2003-08-01

    The first precise measurement of the Casimir force between dissimilar metals is reported. The attractive force, between a Cu layer evaporated on a microelectromechanical torsional oscillator and an Au layer deposited on an Al2O3 sphere, was measured dynamically with a noise level of 6 fN/sqrt[Hz]. Measurements were performed for separations in the 0.2-2 micro m range. The results agree to better than 1% in the 0.2-0.5 micro m range with a theoretical model that takes into account the finite conductivity and roughness of the two metals. The observed discrepancies, which are much larger than the experimental precision, can be attributed to a lack of a complete characterization of the optical properties of the specific samples used in the experiment.

  10. Surface roughness contribution to the adhesion force distribution of salmeterol xinafoate on lactose carriers by atomic force microscopy.

    PubMed

    Islam, Nazrul; Stewart, Peter; Larson, Ian; Hartley, Patrick

    2005-07-01

    Adhesion force distributions of silica spheres (5 and 20 microm) and salmeterol xinafoate (4 microm) particles with inhalation grade lactose surfaces and spin coated lactose films were determined by atomic force microscopy (AFM) to investigate the influence of surface roughness on the force distributions. The roughness of lactose particles and films was determined by both AFM and confocal microscopy (CM); the lactose particles showed RMS R(q) values between 0.93 and 2.2 microm. The adhesion force distributions for silica and SX probes were significantly different for the different lactose carriers and broad, e.g., the adhesion force distribution between a 5 microm silica sphere and lactose particles ranged from 5 to 105 nN. This contrasted with distributions on smooth spin coated lactose films (RMS R(q) of 0.28 nm) which were not significantly different and were narrow, e.g., the adhesion force distribution between a 5 microm silica sphere and spin coated lactose films was between 42 and 68 nN. In addition, no significant difference in adhesion force distribution occurred with silica probe size on the lactose carrier surface. The use of X-ray photoelectron spectroscopic analysis confirmed that the lactose surfaces were free of impurities that might contribute to variation in adhesion. Although the almost atomically flat films showed some adhesion variability, the surface roughness of the lactose particles was a major contributing factor to the broad distributions seen in this study.

  11. Seasonal variation of surface and atmospheric cloud radiative forcing over the globe derived from satellite data

    NASA Technical Reports Server (NTRS)

    Gupta, Shashi K.; Staylor, W. Frank; Darnell, Wayne L.; Wilber, Anne C.; Ritchey, Nancy A.

    1993-01-01

    Global distributions of surface and atmospheric cloud radiative forcing parameters have been derived using parameterized radiation models with satellite meteorological data from the International Satellite Cloud Climatology Project, and directly measured top-of-atmosphere radiative fluxes from the Earth Radiation Budget Experiment. Specifically, shortwave, longwave, and total cloud forcing at the surface, and column-averaged values of longwave cloud forcing of the atmosphere were derived for the midseasonal months of April, July, and October 1985 and January 1986, covering a complete annual cycle. Seasonal variability is illustrated by comparing the results for July 1985 and January 1986, which represent the seasonal extremes. Surface shortwave cloud forcing is always negative, representing a cooling of the surface, with strongest cooling (-120 to -180 W/sq m) occurring over midlatitude storm tracks of the summer hemisphere. Surface longwave cloud forcing is always positive, representing a warming of the surface, with strongest warming (60 to 75 W/sq m) occurring over storm tracks of the winter hemisphere. Zonal averages show the entire summer hemisphere dominated by shortwave cooling, the middle and high latitudes of the winter hemisphere dominated by longwave warming, and a broad zone of transition in between. The globally averaged total cloud forcing amounts to a cooling throughout the year, ranging from a low of about -12 W/sq m for July 1985 to a high of about -25 W/sq m for January 1986. The longwave cloud forcing of the atmosphere shows a strong warming over deep convective regions in the tropics and a moderate cooling outside the tropics, amounting to a weak cooling (-2 to -5 W/sq m) in the global average. Comparisons of the results with general circulation model simulations show broad qualitative agreement regarding the locations of prominent warming and cooling regions. Quantitative comparisons, on the other hand, show significant differences between the

  12. Heart cell contractions measured using a micromachined polysilicon force transducer

    NASA Astrophysics Data System (ADS)

    Lin, Gisela; Pister, Kristofer S. J.; Roos, Kenneth P.

    1995-09-01

    A microelectromechanical systems (MEMS) force transducer, with a volume less than one cubic millimeter, is being developed to measure forces generated by living, isolated cardiac muscle cells in order to resolve the complex mechanisms of muscle contraction. The force transducer consists of two movable clamps facing each other. Each clamp contains two vertical, parallel hinged polysilicon plates attached to a moveable shuttle, and the entire structure is suspended 2 micrometers above the substrate via support beams attached to the substrate at one end. Each end of a living rat heart cell is glued between a pair of vertical plates. Calcium is then introduced into the cell's nutrient bath and stimulates the cell to contract. Upon contraction the support beams bend, and the amount of deflection is translated to force via the known spring constant in the beams. Typcially the 70 micrometers long central portion of a 120 micrometers long cell will contract approximately 6-7 micrometers in full activating solution, resulting in forces up to 16 (mu) N. The average value obtained for Fmax per cross-sectional area was 21.8mN/mm2 which is comparable to the value found in other laboratories using standard transducer technology.

  13. Measurement of the Temperature Dependence of the Casimir-Polder Force

    SciTech Connect

    Obrecht, J. M.; Wild, R. J.; Cornell, E. A.; Antezza, M.; Stringari, S.; Pitaevskii, L. P.

    2007-02-09

    We report on the first measurement of a temperature dependence of the Casimir-Polder force. This measurement was obtained by positioning a nearly pure {sup 87}Rb Bose-Einstein condensate a few microns from a dielectric substrate and exciting its dipole oscillation. Changes in the collective oscillation frequency of the magnetically trapped atoms result from spatial variations in the surface-atom force. In our experiment, the dielectric substrate is heated up to 605 K, while the surrounding environment is kept near room temperature (310 K). The effect of the Casimir-Polder force is measured to be nearly 3 times larger for a 605 K substrate than for a room-temperature substrate, showing a clear temperature dependence in agreement with theory.

  14. Measurement of forces applied during Macintosh direct laryngoscopy compared with GlideScope® videolaryngoscopy.

    PubMed

    Russell, T; Khan, S; Elman, J; Katznelson, R; Cooper, R M

    2012-06-01

    Laryngoscopy can induce stress responses that may be harmful in susceptible patients. We directly measured the force applied to the base of the tongue as a surrogate for the stress response. Force measurements were obtained using three FlexiForce Sensors(®) (Tekscan Inc, Boston, MA, USA) attached along the concave surface of each laryngoscope blade. Twenty-four 24 adult patients of ASA physical status 1-2 were studied. After induction of anaesthesia and neuromuscular blockade, laryngoscopy and tracheal intubation was performed using either a Macintosh or a GlideScope(®) (Verathon, Bothell, WA, USA) laryngoscope. Complete data were available for 23 patients. Compared with the Macintosh, we observed lower median (IQR [range]) peak force (9 (5-13 [3-25]) N vs 20 (14-28 [4-41]) N; p = 0.0001), average force (5 (3-7 [2-19]) N vs 11 (6-16 [1-24]) N; p = 0.0003) and impulse force (98 (42-151 [26-444]) Ns vs 150 (93-207 [17-509]) Ns; p = 0.017) with the GlideScope. Our study shows that the peak lifting force on the base of the tongue during laryngoscopy is less with the GlideScope videolaryngoscope compared with the Macintosh laryngoscope.

  15. MD simulations of chain molecules in the Surface Force Apparatus.

    NASA Astrophysics Data System (ADS)

    Batista, Adriano A.; Carlson, Jean M.

    1998-03-01

    We performed MD simulations of chain molecules confined between two smooth flat crystalline plates in which we drove the top plate in two ways. In a constant shear rate in which we saw that the chains tend to align along the shear flow. We also measured the time scale associated with this alignment. In the second way we dragged the top confining plate with an elastic spring which was pulled at a constant speed. The stick-slip oscillations were overdamped. We studied the transition from stick-slip to steady-sliding and noticed that unlike the underdamped regime, this transition depends also on the elastic constant of the pulling spring. Finally we also perfomed stop-start like experiments and observed a sharp time scale for the onset of the stiction spikes in the spring force as in the experiments performed by J. Israelachvili et al.

  16. Sea Surface Temperature Forcing of the Late Indian Summer Monsoon

    NASA Astrophysics Data System (ADS)

    Terray, P.; Delecluse, P.; Labattu, S.; Terray, L.; Cassou, C.

    2002-12-01

    This paper uses recent historical data and Atmospheric General Circulation Model (AGCM) simulations in order to assess the relationships between interannual variability of the Indian Summer Monsoon (ISM) and Sea Surface Temperature (SST) anomaly patterns over the Indian and Pacific oceans. The focus is on the predictability of ISM rainfall and circulation, and its links to local (Indian Ocean) and remote (Pacific Ocean) SST forcing. Interannual variability of ISM rainfall and dynamical indices for the traditional summer monsoon season (June-September) are strongly influenced by rainfall and circulation anomalies observed during August and September, or the Late Indian Summer Monsoon (LISM). Anomalous monsoons are linked to well-defined LISM rainfall and large-scale circulation anomalies. The whole three-dimensional monsoon circulation, i.e., the east-west Walker and local Hadley circulations, fluctuates during the LISM of anomalous ISM years. LISM circulation is weakened and shifted eastward during weak ISM years. Therefore, we focus on the predictability of the LISM in this study. It is found that southern Indian Ocean SST acts as a major boundary forcing for the LISM system. Strong (weak) LISMs are preceded by significant positive (negative) SST anomalies in the southeastern subtropical Indian Ocean, off Australia. These SST anomalies are highly persistent and affect the northwestward translation of the Mascarene high from austral to boreal summer. The southeastward (northwestward) shift of this subtropical high associated with cold (warm) SST anomalies off Australia causes a weakening (strengthening) of the whole monsoon circulation through a modulation of the local Hadley cell during the LISM. Furthermore, it is suggested that the Mascarene high interacts with the underlying SST anomalies through a positive dynamical feedback mechanism, maintaining its anomalous position during the LISM. Southeastern Indian Ocean SST anomalies during boreal winter are mainly

  17. Techniques for Measuring Surface Potentials in Space

    NASA Technical Reports Server (NTRS)

    Minow, Joseph I.; Parker, Linda Neergaard

    2015-01-01

    Materials exposed to the space plasma environment charge to a net potential relative to the ambient plasma. The charging process is due to differential currents to the material surface that results in a net surface charge density. While this process is termed "spacecraft surface charging" when applied to aerospace hardware, it also applies to the surfaces of astronomical objects in direct contact with the space plasma environment including a number of planetary bodies, asteroids, and dust particles. The ability to measure surface potentials is important to many techniques used in conducting fundamental heliospheric science, spacecraft engineering operations, and space technology development activities. This presentation provides a survey of current technologies used to measure surface potentials of spacecraft and planetary bodies with examples of their application to space science and technology programs.

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

    SciTech Connect

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

    2011-07-21

    This paper focuses on three interconnected topics: (1) quantitative relationship between surface shortwave cloud radiative forcing, cloud fraction, and cloud albedo; (2) surface-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 fraction, and cloud albedo. The analytical expression is then used to deduce a new approach for inferring cloud albedo from concurrent surface-based measurements of downwelling surface shortwave radiation and cloud fraction. High-resolution decade-long data on cloud albedos are obtained by use of this surface-based approach over the US Department of Energy's Atmospheric Radiaton Measurement (ARM) Program at the Great Southern Plains (SGP) site. The surface-based cloud albedos are further compared against those derived from the coincident GOES satellite measurements. The three long-term (1997-2009) sets of hourly data on shortwave cloud radiative forcing, cloud fraction and cloud albedo collected over the SGP site are analyzed to explore the multiscale (diurnal, annual and inter-annual) variations and covariations. The analytical formulation is useful for diagnosing deficiencies of cloud-radiation parameterizations in climate models.

  19. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    SciTech Connect

    Bietti, Sergio Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano; Fedorov, Alexey

    2014-09-21

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano–disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E{sub A}=1.31±0.15 eV, a diffusivity prefactor of D₀=0.53(×2.1±1) cm² s⁻¹ that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad–atoms on III–V crystal surfaces and the fabrication of designable nanostructures.

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

    NASA Technical Reports Server (NTRS)

    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.

  1. A Portable, High Resolution, Surface Measurement Device

    NASA Technical Reports Server (NTRS)

    Ihlefeld, Curtis M.; Burns, Bradley M.; Youngquist, Robert C.

    2012-01-01

    A high resolution, portable, surface measurement device has been demonstrated to provide micron-resolution topographical plots. This device was specifically developed to allow in-situ measurements of defects on the Space Shuttle Orbiter windows, but is versatile enough to be used on a wide variety of surfaces. This paper discusses the choice of an optical sensor and then the decisions required to convert a lab bench optical measurement device into an ergonomic portable system. The necessary trade-offs between performance and portability are presented along with a description of the device developed to measure Orbiter window defects.

  2. Numerical study on the adhesion and reentrainment of nondeformable particles on surfaces: the role of surface roughness and electrostatic forces.

    PubMed

    Henry, Christophe; Minier, Jean-Pierre; Lefèvre, Grégory

    2012-01-10

    In this paper, the reentrainment of nanosized and microsized particles from rough walls under various electrostatic conditions and various hydrodynamic conditions (either in air or aqueous media) is numerically investigated. This issue arises in the general context of particulate fouling in industrial applications, which involves (among other phenomena) particle deposition and particle reentrainment. The deposition phenomenon has been studied previously and, in the present work, we focus our attention on resuspension. Once particles are deposited on a surface, the balance between hydrodynamic forces (which tend to move particles away from the surface) and adhesion forces (which maintain particles on the surface) can lead to particle removal. Adhesion forces are generally described using van der Waals attractive forces, but the limit of these models is that any dependence of adhesion forces on electrostatic forces (due to variations in pH or ionic strength) cannot be reproduced numerically. For this purpose, we develop a model of adhesion forces that is based on the DLVO (Derjaguin and Landau, Verwey and Overbeek) theory and which includes also the effect of surface roughness through the use of hemispherical asperities on the surface. We first highlight the effect of the curvature radius on adhesion forces. Then some numerical predictions of adhesion forces or adhesion energies are compared to experimental data. Finally, the overall effects of surface roughness and electrostatic forces are demonstrated with some applications of the complete reentrainment model in some simple test cases.

  3. Measurement of interactions between protein layers adsorbed on silica by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Valle-Delgado, J. J.; Molina-Bolívar, J. A.; Galisteo-González, F.; Gálvez-Ruiz, M. J.; Feiler, A.; Rutland, M. W.

    2004-07-01

    The present work, using an atomic force microscope and the colloid probe technique, investigates the interaction forces between bovine serum albumin (BSA) layers and between apoferritin layers adsorbed on silica surfaces. The measurements have been carried out in an aqueous medium at different pH values and NaCl concentrations. Similar behaviours have been found with both proteins. Electrostatic and steric forces dominate the interactions between the protein layers at low NaCl concentrations. However, a very strange behaviour is found as a function of pH at high NaCl concentrations. The results obtained under these conditions could be explained if the presence of hydration forces in these systems is assumed.

  4. ForceFit: a code to fit classical force fields to ab-initio potential energy surfaces

    SciTech Connect

    Henson, Neil Jon; Waldher, Benjamin; Kuta, Jadwiga; Clark, Aurora; Clark, Aurora E

    2009-01-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under Unix and is written in C++, is an easy to use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program.

  5. Harmonic force microscope: A new tool for biomolecular identification and material characterization based on nanomechanical measurements

    NASA Astrophysics Data System (ADS)

    Sahin, Ozgur

    At the molecular level, physical and chemical properties of materials are tightly coupled to the mechanical properties. The potential of mechanics for interacting with matter at the nanoscale has been largely unexplored due to lack of instruments capable of performing mechanical measurements at nanometer length scales. This thesis describes nanomechanical sensing techniques and applications based on time-resolved tip-sample force measurements in tapping-mode atomic force microscopy. Tapping mode is the most successful operation mode of atomic force microscopes. Theoretical calculations presented in the first part of this thesis show that time variations of the tip-sample forces in the tapping-mode depend on the physical and chemical properties of the sample and therefore, have the potential to be used for nanomechanical measurements. Unfortunately, the force-sensing probe of the tapping-mode atomic force microscope, the vibrating cantilever, is limited in its response to the variations of forces in time within a period of oscillations. We are describing two types of special micromachined cantilevers that enable measurements of time variations of tip-sample forces: the harmonic cantilever and the coupled torsional cantilever. These special cantilevers allow sensitive mechanical measurements at the nanoscale and single molecular level. The operation of these cantilevers does not require any modifications to the existing atomic force microscopy systems. With the nanomechanical sensing techniques we have developed, we investigated phase transformations of sub-micron domains of composite polymers and observed their glass transitions for the first time. Conventional measurements on bulk properties of these samples do not provide information on the physical changes at the nanoscale. Studies on nucleic acids attached to a surface, a configuration commonly used in DNA microarray technology, showed that the hybridized DNA molecules can be detected at the single molecule

  6. Evaluation of the sensing block method for dynamic force measurement

    NASA Astrophysics Data System (ADS)

    Zhang, Qinghui; Chen, Hao; Li, Wenzhao; Song, Li

    2017-01-01

    Sensing block method was proposed for the dynamic force measurement by Tanimura et al. in 1994. Comparing with the Split Hopkinson pressure bar (SHPB) technique, it can provide a much longer measuring time for the dynamic properties test of materials. However, the signals recorded by sensing block are always accompanied with additional oscillations. Tanimura et al. discussed the effect of force rising edge on the test results, whereas more research is still needed. In this paper, some more dominant factors have been extracted through dimensional analysis. The finite element simulation has been performed to assess these factors. Base on the analysis and simulation, some valuable results are obtained and some criterions proposed in this paper can be applied in design or selection of the sensing block.

  7. Measurement of Multiple Blade Rate Unsteady Propeller Forces

    DTIC Science & Technology

    1990-05-01

    Report I 0 Measurement of Multiple Blade Rate Unsteady Propeller Forces _ by Stuart D. Jessup DTIC SELECTE JUN07 1990 00 U,);i -,,I-ll lll ll mml~ CODE...blade rat and multiple axia wake inflow harmonics. The axial wake distributions weret meaured using a Piot tube. Unsteady propeller bearing thrust and...diameter EAR Propeller expanded area ratio f Maximum camber of section J Advance coefficient, Vvm/nD K Integer multiple of blade number KT Thrust

  8. Dynamic Forces in Spur Gears - Measurement, Prediction, and Code Validation

    NASA Technical Reports Server (NTRS)

    Oswald, Fred B.; Townsend, Dennis P.; Rebbechi, Brian; Lin, Hsiang Hsi

    1996-01-01

    Measured and computed values for dynamic loads in spur gears were compared to validate a new version of the NASA gear dynamics code DANST-PC. Strain gage data from six gear sets with different tooth profiles were processed to determine the dynamic forces acting between the gear teeth. Results demonstrate that the analysis code successfully simulates the dynamic behavior of the gears. Differences between analysis and experiment were less than 10 percent under most conditions.

  9. Coefficients of variation of ground reaction force measurement in cats

    PubMed Central

    Tichy, Alexander

    2017-01-01

    Gait analysis has been extensively performed in dogs and horses; however, very little is known about feline biomechanics. It was, therefore, the aim of this study to determine the coefficient of variation (CV) among three ground reaction force (GRF) measurements taken for 15 client-owned European shorthaired cats without a training period and a short acclimatisation time. Gait was measured as each cat walked across a pressure-sensitive walkway, and measurements were made three times over a multi-week period (range: 2 to 17 weeks). The parameters evaluated were peak vertical force (PFz), vertical impulse (IFz), stance phase duration (SPD), step length (SL), paw contact area (PCA) and symmetry index (SI%) of the front and hind limbs. After averaging each of the values from the three measurements, the CV and 95% confidence interval (CI) were calculated for all parameters. PFz showed the lowest CV (~ 3%), while IFz showed the highest CV (~11%) when normalised to body mass. When the GRFs were normalised to total force, the CV of PFz dropped to ~2% and that of IFz dropped to ~3%. The CV of SL and PCA were lower (~6% respectively ~5%) compared to the CV for SPD (~10%). The SI% for both PFz and IFz were comparable to the values reported in the gait analysis literature for dogs. Results of the current study indicate that gait analysis of cats using pressure-sensitive walkways produces reliable data and is a promising approach for evaluation of lameness. The results also suggest that PFz may be a more reliable parameter than IFz and that normalisation to percent of total force may aid in interpretation of the evaluated data. PMID:28355209

  10. Lateral forces on circularly polarizable particles near a surface

    PubMed Central

    Rodríguez-Fortuño, Francisco J.; Engheta, Nader; Martínez, Alejandro; Zayats, Anatoly V.

    2015-01-01

    Optical forces allow manipulation of small particles and control of nanophotonic structures with light beams. While some techniques rely on structured light to move particles using field intensity gradients, acting locally, other optical forces can ‘push' particles on a wide area of illumination but only in the direction of light propagation. Here we show that spin–orbit coupling, when the spin of the incident circularly polarized light is converted into lateral electromagnetic momentum, leads to a lateral optical force acting on particles placed above a substrate, associated with a recoil mechanical force. This counterintuitive force acts in a direction in which the illumination has neither a field gradient nor propagation. The force direction is switchable with the polarization of uniform, plane wave illumination, and its magnitude is comparable to other optical forces. PMID:26581479

  11. Lateral forces on circularly polarizable particles near a surface.

    PubMed

    Rodríguez-Fortuño, Francisco J; Engheta, Nader; Martínez, Alejandro; Zayats, Anatoly V

    2015-11-19

    Optical forces allow manipulation of small particles and control of nanophotonic structures with light beams. While some techniques rely on structured light to move particles using field intensity gradients, acting locally, other optical forces can 'push' particles on a wide area of illumination but only in the direction of light propagation. Here we show that spin-orbit coupling, when the spin of the incident circularly polarized light is converted into lateral electromagnetic momentum, leads to a lateral optical force acting on particles placed above a substrate, associated with a recoil mechanical force. This counterintuitive force acts in a direction in which the illumination has neither a field gradient nor propagation. The force direction is switchable with the polarization of uniform, plane wave illumination, and its magnitude is comparable to other optical forces.

  12. Coherent methods for measuring ophthalmic surfaces

    NASA Astrophysics Data System (ADS)

    Rottenkolber, Matthias; Podbielska, Halina

    1996-01-01

    Topographic analysis of the ophthalmic surfaces is an important task. Especially recently, when a laser assisted refractive surgery becomes more and more popular in a daily clinical praxis. Ophthalmologists need to know exact corneal parameters as a basis for proper operational approach, as well as for monitoring of the post-operative process. The fitting of the contact lenses can be more accurate when topography of both, cornea and contacts, can be precisely measured. We develop new coherent methods for measuring of the topography of curved optical surfaces. One of the proposed techniques is based on interferometry with a special distance measurement unit and spatial phase shifting interferogram evaluation. The other one uses deflectometry with spatial carrier frequency. The sensitivity of this method is adjustable and thus it closes the gap between the white light and interferometric measuring methods. The techniques proposed here can be suitable for measurement of the contact lenses or corneal surface.

  13. Development of Field Excavator with Embedded Force Measurement

    NASA Technical Reports Server (NTRS)

    Johnson, K.; Creager, C.; Izadnegahdar, A.; Bauman, S.; Gallo, C.; Abel, P.

    2012-01-01

    A semi-intelligent excavation mechanism was developed for use with the NASA-built Centaur 2 rover prototype. The excavator features a continuously rotatable large bucket supported between two parallel arms, both of which share a single pivot axis near the excavator base attached to the rover. The excavator is designed to simulate the collection of regolith, such as on the Moon, and to dump the collected soil into a hopper up to one meter tall for processing to extract oxygen. Because the vehicle can be autonomous and the terrain is generally unknown, there is risk of damaging equipment or using excessive power when attempting to extract soil from dense or rocky terrain. To minimize these risks, it is critical for the rover to sense the digging forces and adjust accordingly. It is also important to understand the digging capabilities and limitations of the excavator. This paper discusses the implementation of multiple strain gages as an embedded force measurement system in the excavator's arms. These strain gages can accurately measure and resolve multi-axial forces on the excavator. In order to validate these sensors and characterize the load capabilities, a series of controlled excavation tests were performed at Glenn Research Center with the excavator at various depths and cut angles while supported by a six axis load cell. The results of these tests are both compared to a force estimation model and used for calibration of the embedded strain gages. In addition, excavation forces generated using two different types of bucket edge (straight vs. with teeth) were compared.

  14. Measurements of stiff-material compliance on the nanoscale using ultrasonic force microscopy

    NASA Astrophysics Data System (ADS)

    Dinelli, F.; Biswas, S. K.; Briggs, G. A. D.; Kolosov, O. V.

    2000-05-01

    Ultrasonic force microscopy (UFM) was introduced to probe nanoscale mechanical properties of stiff materials. This was achieved by vibrating the sample far above the first resonance of the probing atomic force microscope cantilever where the cantilever becomes dynamically rigid. By operating UFM at different set force values, it is possible to directly measure the absolute values of the tip-surface contact stiffness. From this an evaluation of surface elastic properties can be carried out assuming a suitable solid-solid contact model. In this paper we present curves of stiffness as a function of the normal load in the range of 0-300 nN. The dependence of stiffness on the relative humidity has also been investigated. Materials with different elastic constants (such as sapphire lithium fluoride, and silicon) have been successfully differentiated. Continuum mechanics models cannot however explain the dependence of stiffness on the normal force and on the relative humidity. In this high-frequency regime, it is likely that viscous forces might play an important role modifying the tip-surface interaction. Plastic deformation might also occur due to the high strain rates applied when ultrasonically vibrating the sample. Another possible cause of these discrepancies might be the presence of water in between the two bodies in contact organizing in a solidlike way and partially sustaining the load.

  15. Contact angle measurement on rough surfaces.

    PubMed

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

    2004-06-15

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

  16. Effect of Surface Omniphobicity on Drying by Forced Convection (Briefing Charts)

    DTIC Science & Technology

    2015-08-01

    Charts 3. DATES COVERED (From - To) July 2015-August 2015 4. TITLE AND SUBTITLE Effect of Surface Omniphobicity on Drying by Forced Convection ...Forced Convection Madani Khan The City College of New York STAR Program August, 2015 2DISTRIBUTION A: Approved for public release; distribution...to enhance the drying rate of liquids removed from the surface by forced convection . We control surface roughness by substrate abrasion and by the

  17. Constant tip-surface distance with atomic force microscopy via quality factor feedback

    NASA Astrophysics Data System (ADS)

    Fan, Lin; Potter, Daniel; Sulchek, Todd

    2012-02-01

    The atomic force microscope (AFM) is a powerful and widely used instrument to image topography and measure forces at the micrometer and nanometer length scale. Because of the high degree of operating accuracy required of the instrument, small thermal and mechanical drifts of the cantilever and piezoactuator systems hamper measurements as the AFM tip drifts spatially relative to the sample surface. To compensate for the drift, we control the tip-surface distance by monitoring the cantilever quality factor (Q) in a closed loop. Brownian thermal fluctuations provide sufficient actuation to accurately determine cantilever Q by fitting the thermal noise spectrum to a Lorentzian function. We show that the cantilever damping is sufficiently affected by the tip-surface distance so that the tip position of soft cantilevers can be maintained within 40 nm of a setpoint in air and within 3 nm in water with 95% reliability. Utilizing this method to hover the tip above a sample surface, we have the capability to study sensitive interactions at the nanometer length scale over long periods of time.

  18. Direct measurement of cortical force generation and polarization in a living parasite.

    PubMed

    Stadler, Rachel V; White, Lauren A; Hu, Ke; Helmke, Brian P; Guilford, William H

    2017-02-16

    Apicomplexa is a large phylum of intracellular parasites that are notable for the diseases they cause, including toxoplasmosis, malaria and cryptosporidiosis. A conserved motile system is critical to their lifecycles as it drives directional gliding motility between cells, as well as invasion of and egress from host cells. However, our understanding of this system is limited by a lack of measurements of the forces driving parasite motion. We used a laser trap to measure the function of the motility apparatus of living Toxoplasma gondii by adhering a microsphere to the surface of an immobilized parasite. Motion of the microsphere reflected underlying forces exerted by the motile apparatus. We found that force generated at the parasite surface begins with no preferential directionality, but becomes directed toward the rear of the cell after a period of time. The transition from non-directional to directional force generation occurs on spatial intervals consistent with the lateral periodicity of structures associated with the membrane pellicle, and is influenced by the kinetics of actin filament polymerization and cytoplasmic calcium. A lysine methyltransferase regulates both the magnitude and polarization of the force. Our work provides a novel means to dissect the motile mechanisms of these pathogens.

  19. Use of piezoelectric multicomponent force measuring devices in fluid mechanics

    NASA Technical Reports Server (NTRS)

    Richter, A.; Stefan, K.

    1979-01-01

    The characterisitics of piezoelectric multicomponent transducers are discussed, giving attention to the advantages of quartz over other materials. The main advantage of piezoelectric devices in aerodynamic studies is their ability to indicate rapid changes in the values of physical parameters. Problems in the accuracy of measurments by piezoelectric devices can be overcome by suitable design approaches. A practical example is given of how such can be utilized to measure rapid fluctuations of fluid forces exerted on a circular cylinder mounted in a water channel.

  20. Instrumented Bolts Would Measure Shear Forces In Joints

    NASA Technical Reports Server (NTRS)

    Sawyer, James Wayne; Mcwithey, Robert R.

    1994-01-01

    Bolts instrumented with strain gauges used to measure shear forces. Bolts installed in multiple-bolt lap joints to obtain data on distribution of stresses and deformations in and around joints. Strain gauges indicate share of applied load borne by each individual bolt. In original application, bolted panels made of advanced refractory composite materials designed to withstand use at temperatures up to 4,000 degrees F. Also applicable to other joint materials and measurement of shear loads in other connections such as, shear loads on shafts in pulleys or gears.

  1. Characterization of CaF2 surfaces using Adsorption-Desorption Isotherms and Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Wadleigh, L. R.; Luhman, D. R.; Bumcrot, P. G.

    2012-02-01

    We are interested in using rough CaF2 films to study the superfluid transition in two-dimensional helium systems. These experiments require quantitative information regarding the topography of the CaF2 surfaces. The surface roughness of CaF2 films is known to increase with film thickness as has been shown with previous atomic force microscopy (AFM) measurements [1]. We have fabricated a series of CaF2 samples of different film thicknesses and thus different surface roughnesses. These surfaces were studied using AFM and adsorption-desorption isotherm measurements with liquid nitrogen at T=77 K. The isotherm measurements allow us to determine the pore size distribution of each CaF2 film thickness. We find the emergence of hysteretic capillary condensation due to deep pores in the CaF2 as the film thickness increases. The development of these deep pores is also seen in our AFM measurements. Our combined results provide a detailed description of CaF2 surface roughness which can be utilized in the planned superfluid experiment. [1] D.R. Luhman and R.B. Hallock, Phys Rev. E 70, 051606 (2004).

  2. Surface roughness measurement with laser triangulation

    NASA Astrophysics Data System (ADS)

    Bai, Fuzhong; Zhang, Xiaoyan; Tian, Chaoping

    2016-09-01

    A surface roughness measurement method is introduced in the paper, which is based on laser triangulation and digital image processing technique. In the measuring system, we use the line-structured light as light source, microscope lens and high-accuracy CCD sensor as displacement sensor as well. In addition, the working angle corresponding to the optimal sensitivity is considered in the optical structure design to improve the measuring accuracy. Through necessary image processing operation for the light strip image, such as center-line extraction with the barycenter algorithm, Gaussian filtering, the value of roughness is calculated. A standard planing surface is measured experimentally with the proposed method and the stylus method (Mitutoyo SJ-410) respectively. The profilograms of surface appearance are greatly similar in the shape and the amplitude to two methods. Also, the roughness statistics values are close. The results indicate that the laser triangulation with the line-structured light can be applied to measure the surface roughness with the advantages of rapid measurement and visualized display of surface roughness profile.

  3. A noncontact force sensor based on a fiber Bragg grating and its application for corrosion measurement.

    PubMed

    Pacheco, Clara J; Bruno, Antonio C

    2013-08-29

    A simple noncontact force sensor based on an optical fiber Bragg grating attached to a small magnet has been proposed and built. The sensor measures the force between the magnet and any ferromagnetic material placed within a few millimeters of the sensor. Maintaining the sensor at a constant standoff distance, material loss due to corrosion increases the distance between the magnet and the corroded surface, which decreases the magnetic force. This will decrease the strain in the optical fiber shifting the reflected Bragg wavelength. The measured shift for the optical fiber used was 1.36 nm per Newton. Models were developed to optimize the magnet geometry for a specific sensor standoff distance and for particular corrosion pit depths. The sensor was able to detect corrosion pits on a fuel storage tank bottom with depths in the sub-millimeter range.

  4. A Noncontact Force Sensor Based on a Fiber Bragg Grating and Its Application for Corrosion Measurement

    PubMed Central

    Pacheco, Clara J.; Bruno, Antonio C.

    2013-01-01

    A simple noncontact force sensor based on an optical fiber Bragg grating attached to a small magnet has been proposed and built. The sensor measures the force between the magnet and any ferromagnetic material placed within a few millimeters of the sensor. Maintaining the sensor at a constant standoff distance, material loss due to corrosion increases the distance between the magnet and the corroded surface, which decreases the magnetic force. This will decrease the strain in the optical fiber shifting the reflected Bragg wavelength. The measured shift for the optical fiber used was 1.36 nm per Newton. Models were developed to optimize the magnet geometry for a specific sensor standoff distance and for particular corrosion pit depths. The sensor was able to detect corrosion pits on a fuel storage tank bottom with depths in the sub-millimeter range. PMID:23995095

  5. Silica nano-particle super-hydrophobic surfaces: the effects of surface morphology and trapped air pockets on hydrodynamic drainage forces.

    PubMed

    Chan, Derek Y C; Uddin, Md Hemayet; Cho, Kwun L; Liaw, Irving I; Lamb, Robert N; Stevens, Geoffrey W; Grieser, Franz; Dagastine, Raymond R

    2009-01-01

    We used atomic force microscopy to study dynamic forces between a rigid silica sphere (radius approximately 45 microm) and a silica nano-particle super-hydrophobic surface (SNP-SHS) in aqueous electrolyte, in the presence and absence of surfactant. Characterization of the SNP-SHS surface in air showed a surface roughness of up to two microns. When in contact with an aqueous phase, the SNP-SHS traps large, soft and stable air pockets in the surface interstices. The inherent roughness of the SNP-SHS together with the trapped air pockets are responsible for the superior hydrophobic properties of SNP-SHS such as high equilibrium contact angle (> 140 degrees) of water sessile drops on these surfaces and low hydrodynamic friction as observed in force measurements. We also observed that added surfactants adsorbed at the surface of air pockets magnified hydrodynamic interactions involving the SNP-SHS. The dynamic forces between the same silica sphere and a laterally smooth mica surface showed that the fitted Navier slip lengths using the Reynolds lubrication model were an order of magnitude larger than the length scale of the sphere surface roughness. The surface roughness and the lateral heterogeneity of the SNP-SHS hindered attempts to characterize the dynamic response using the Reynolds lubrication model even when augmented with a Navier slip boundary.

  6. Surface instability of an imperfectly bonded thin elastic film under surface van der Waals forces

    NASA Astrophysics Data System (ADS)

    Wang, Xu; Jing, Rong

    2017-02-01

    This paper studies surface instability of a thin elastic film imperfectly bonded to a rigid substrate interacting with a rigid contactor through van der Waals forces under plane strain conditions. The film-substrate interface is modeled as a linear spring with vanishing thickness described in terms of the normal and tangential interface parameters. Depending on the ratio of the two imperfect interface parameters, the critical value of the Poisson's ratio for the occurrence of surface wrinkling in the absence of surface energy can be greater than, equal to, or smaller than 0.25, which is the critical Poisson's ratio for a perfect film-substrate interface. The critical surface energy for the inhibition of the surface wrinkling is also obtained. Finally, we propose a very simple and effective method to study the surface instability of a multilayered elastic film with imperfect interfaces interacting with a rigid contactor or with another multilayered elastic film (or a multilayered simply supported plate) with imperfect interfaces.

  7. Real time drift measurement for colloidal probe atomic force microscope: a visual sensing approach

    SciTech Connect

    Wang, Yuliang Bi, Shusheng; Wang, Huimin

    2014-05-15

    Drift has long been an issue in atomic force microscope (AFM) systems and limits their ability to make long time period measurements. In this study, a new method is proposed to directly measure and compensate for the drift between AFM cantilevers and sample surfaces in AFM systems. This was achieved by simultaneously measuring z positions for beads at the end of an AFM colloidal probe and on sample surface through an off-focus image processing based visual sensing method. The working principle and system configuration are presented. Experiments were conducted to validate the real time drift measurement and compensation. The implication of the proposed method for regular AFM measurements is discussed. We believe that this technique provides a practical and efficient approach for AFM experiments requiring long time period measurement.

  8. Precise displacement measurement for a local surface.

    PubMed

    Yeh, Sheng Lih; Lin, Shyh Tsong; Chang, Yu Hsin

    2009-11-01

    An optical measurement method to get the in-plane and out-of-plane displacements of a local surface using a laser is proposed. The proposed method simultaneously derives the in-plane and out-of-plane displacements by measuring the shift of interference fringes formed by scattered beams. The average errors of the in-plane and out-of-plane displacement measurements are significantly smaller than 10 nm. Moreover, the proposed method uses only low-cost optical elements.

  9. An Electromotive Force Measurement System for Alloy Fuels

    SciTech Connect

    Changhu Xing; Colby Jensen; Heng Ban; Robert Mariani; J. Rory Kennedy

    2010-11-01

    The development of advanced nuclear fuels requires a better understanding of the transmutation and micro-structural evolution of the materials. Alloy fuels have the advantage of high thermal conductivity and improved characteristics in fuel-cladding chemical reaction. However, information on thermodynamic and thermophysical properties is limited. The objective of this project is to design and build an experimental system to measure the thermodynamic properties of solid materials from which the understanding of their phase change can be determined. The apparatus was used to measure the electromotive force (EMF) of several materials in order to calibrate and test the system. The EMF of chromel was measured from 100°C to 800°C and compared with theoretical values. Additionally, the EMF measurement of Ni-Fe alloy was performed and compared with the Ni-Fe phase diagram. The prototype system is to be modified eventually and used in a radioactive hot-cell in the future.

  10. Forces of Interaction between Surfaces Bearing Looped Polymer Brushes in Good Solvent.

    SciTech Connect

    Alonzo, Jose; Mays, Jimmy; Kilbey, II, S Michael

    2009-01-01

    In a previous publication we suggested [Huang et al., Macromolecules, 2008, 41, 1745-1752] that looped polymer brushes formed by tethering chains by both ends to a surface may exhibit a polydispersity-like effect due to a distribution of distances between tethering points, leading to segment density profiles dominated by a long and diffuse exponentially-decaying tail. To study this issue in more detail, the force profiles (forces of interaction as a function of separation distance) of a series of looped polymer brushes made by preferential adsorption of poly(2-vinylpyridine)-polystyrene-poly(2-vinylpyridine) (PVP-b-PS-b-PVP) triblock copolymers of varying molecular weight and asymmetry ratio are measured using the surface forces apparatus. The force profiles are analyzed using an equivalent diblock model, which considers the triblock copolymer brushes as being comprised of two diblock copolymers of half the PS molecular weight. While scaling the dependencies of the interaction energy and distance on molecular weight, the tethering density and segment size coalesce the measured force profiles to the universal profile, it is necessary to include polydispersity in the description of the equilibrium structure. This is done using the self-consistent field model of Milner et al. [Macromolecules, 1988, 21, 2610-2619]. For looped brushes formed from the symmetric and moderately symmetric triblock copolymers we find that the polydispersity due to molecular weight distribution effectively accounts for the observed force profiles. On the other hand, agreement between the measured and predicted force profiles of looped brushes formed from highly asymmetric copolymers at low degrees-of-compression is achieved only if a much smaller value of the polydispersity index is used in the fitting. The implication of these results is that the shape of the segment density profiles is not due to the previously proposed anchor-induced polydispersity arising due to loop formation; however in

  11. Sensitivity of soil surface temperature in a force-restore equation to heat fluxes and deep soil temperature

    NASA Astrophysics Data System (ADS)

    Mihailovi, Dragutin T.; Kallos, George; Arseni, Ilija D.; Lali, Branislava; Rajkovi, Borivoj; Papadopoulos, Atanasios

    1999-11-01

    The force-restore approach is commonly used in order to calculate the surface temperature in atmospheric models. A critical point in this method is how to calculate the deep soil temperature which appears in the restore term of the force-restore equation. If the prognostic equation for calculating the deep soil temperature is used, some errors in surface temperature calculation and consequently in partitioning the surface energy and land surface water can be introduced. Usually, these errors should appear as a result of incorrect parameterization of surface energy terms in the prognostic equation based on force-restore approach.In this paper, the sensitivity of the force-restore model for surface temperature to the: (a) changes of soil heat flux; (b) variations of deep soil temperature and (c) changes in soil water evaporation is examined. In addition, the impact of the deep soil temperature variations on partitioning the surface energy and land surface water is discussed. Finally, a new procedure for calculating the deep soil temperature based, on climatological data of soil temperature and its exponential attenuation in the deep soil layers is suggested. All numerical experiments with the LAPS land surface scheme were performed using two data sets, obtained from the micrometeorological measurements over a bare soil at Rimski ančevi (Yugoslavia), RS, and Caumont (France), HAPEX.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  13. The Measurement of Surface Rheological and Surface Adhesive Properties using Nanosphere Embedment

    NASA Astrophysics Data System (ADS)

    Hutcheson, Stephen; McKenna, Gregory

    2008-03-01

    In previous work, we determined the actual rheological behavior at the surface of a polystyrene film with nanometer scale resolution by applying a viscoelastic contact mechanics model to experimental data in the literature. The goal of our current research is to build upon this analysis and use nanosphere embedment experiments to probe the nanorheological behavior of polymer surfaces near the glass transition, in the melt state and in the solid rubbery state. An atomic force microscope (AFM) is used to measure the embedment depth as nanoparticles are pulled into the surface by the thermodynamic work of adhesion. The results show that, with properly designed experiments, both the surface adhesion properties and the surface rheological properties can be extracted from nanosphere embedment rates. We include work on a phase separated copolymer and a commercially available polydimethylsiloxane (PDMS) rubber.

  14. Ion Beam Analysis Of Silicon-Based Surfaces And Correlation With Surface Energy Measurements

    SciTech Connect

    Xing Qian; Herbots, N.; Hart, M.; Bradley, J. D.; Wilkens, B. J.; Sell, D. A.; Culbertson, R. J.; Whaley, S. D.; Sell, Clive H.; Kwong, Henry Mark Jr.

    2011-06-01

    The water affinity of Si-based surfaces is quantified by contact angle measurement and surface free energy to explain hydrophobic or hydrophilic behavior of silicone, silicates, and silicon surfaces. Surface defects such as dangling bonds, surface free energy including Lewis acid-base and Lifshitz-van der Waals components are discussed. Water nucleation and condensation is further explained by surface topography. Tapping mode atomic force microscopy (TMAFM) provides statistical analysis of the topography of these Si-based surfaces. The correlation of the above two characteristics describes the behavior of water condensation at Si-based surfaces. Surface root mean square roughness increasing from several A ring to several nm is found to provide nucleation sites that expedite water condensation visibly for silica and silicone. Hydrophilic surfaces have a condensation pattern that forms puddles of water while hydrophobic surfaces form water beads. Polymer adsorption on these surfaces alters the water affinity as well as the surface topography, and therefore controls condensation on Si-based surfaces including silicone intraocular lens (IOL). The polymer film is characterized by Rutherford backscattering spectrometry (RBS) in conjunction with 4.265 MeV {sup 12}C({alpha}, {alpha}){sup 12}C, 3.045 MeV {sup 16}O({alpha},{alpha}){sup 16}O nuclear resonance scattering (NRS), and 2.8 MeV elastic recoil detection (ERD) of hydrogen for high resolution composition and areal density measurements. The areal density of hydroxypropyl methylcellulose (HPMC) film ranges from 10{sup 18} atom/cm{sup 2} to 10{sup 19} atom/cm{sup 2} gives the silica or silicone surface a roughness of several A ring and a wavelength of 0.16{+-}0.02 {mu}m, and prevents fogging by forming a complete wetting layer during water condensation.

  15. Measurement of lateral adhesion forces at the interface between a liquid drop and a substrate.

    PubMed

    Tadmor, Rafael; Bahadur, Prashant; Leh, Aisha; N'guessan, Hartmann E; Jaini, Rajiv; Dang, Lan

    2009-12-31

    A novel instrument allows for the first time measurements of the lateral adhesion forces at a solid-liquid interface, f(parallel), in a way that is decoupled from the normal forces, f(perpendicular). We use it to measure how f(parallel) between a drop and a surface is influenced by different f(perpendicular) and different histories of drop resting periods on the surface prior to sliding, t(rest). The variation of f(parallel) with t(rest) is similar for different f(perpendicular) and always plateaus as t(rest)-->infinity. We show that the f(parallel) plateau value is higher when f(perpendicular) is lower. This seemingly counterintuitive result is in agreement with recent theories.

  16. Possibility of measuring thermal effects in the Casimir force

    SciTech Connect

    Geyer, B.; Klimchitskaya, G. L.; Mostepanenko, V. M.

    2010-09-15

    We analyze the possibility of measuring small thermal effects in the Casimir force between metal test bodies in configurations of a sphere above a plate and two parallel plates. For the sphere-plate geometry used in many experiments, we investigate the applicability of the proximity force approximation (PFA) to calculation of thermal effects in the Casimir force and its gradient. It is shown that for real metals the two formulations of the PFA used in the literature lead to relative differences in the results obtained being less than a small parameter equal to the ratio of separation distance to sphere radius. For ideal metals, PFA results for the thermal correction are obtained and compared with available exact results. It is emphasized that in the experimental region in the zeroth order of the small parameter already mentioned, the thermal Casimir force and its gradient calculated using the PFA (and thermal corrections in their own right) coincide with the respective exact results. For real metals, available exact results are outside the application region of the PFA. However, the exact results are shown to converge with the PFA results when the small parameter goes down to experimental values. We arrive at the conclusion that the large thermal effects predicted by the Drude-model approach, if they exist, could be measured in both static and dynamic experiments in sphere-plate and plate-plate configurations. As for the small thermal effects predicted by the plasma-model approach, the static experiment in the configuration of two parallel plates is found to be the best for their observation.

  17. Sahel Precipitation Variability and Global Sea Surface Temperature Forcing

    NASA Astrophysics Data System (ADS)

    Bach, D. E.; Kushnir, Y.; Seager, R.; Goddard, L.; Giannini, A.

    2003-12-01

    In the last 50 years or so, the Sahel region in sub-Saharan Africa has experienced two multi-decadal wet and dry periods separated by a relatively sharp transition. The onset of the dry episode in the Sahel is associated with the start of a significant warming trend in Southern Hemisphere sea surface temperatures (SST) that persisted well into the late 1990's. It has been stipulated, based on general circulation model (GCM) experiments, that the SST rise in the southern ocean basins is the predominant driver of rainfall patterns over the Sahel. Here we support this notion by comparing the observed rate of change in Southern Hemisphere SST with that of Sahel summertime rainfall. We examine the variations in each ocean basin separately and find that the drought pattern is most prominently associated with SST changes in the Indian Ocean, which display maximum warming rates simultaneously with the wet to dry shift in the Sahel. We provide further support to the role of the Indian Ocean using results from GCM integrations forced with observed Indian Ocean SST values and climatological values elsewhere, which effectively recreate the dry Sahel rainfall pattern. While the variations in equatorial Pacific SST associated with El Ni¤o have been found to have an effect on Sahel rainfall during the summer months, their influence does not appear to be significantly connected with the prolonged drought episode. The dry period was accentuated by two severe droughts in the early 1970's and 1980s, which generated very different repercussions for the Sahelian people. The first drought resulted in widespread famine and death while the second more severe drought in 1983-84 generated very few casualties. The political and socioeconomic assessment of these episodes suggests that the extensive loss of life was due to inefficient transportation of supplies to the starving populations. International aid organizations initiated famine protection programs following the 1970's drought that

  18. Transformation of body force localized near the surface of a half-space into equivalent surface stresses.

    PubMed

    Rouge, Clémence; Lhémery, Alain; Ségur, Damien

    2013-10-01

    An electromagnetic acoustic transducer (EMAT) or a laser used to generate elastic waves in a component is often described as a source of body force confined in a layer close to the surface. On the other hand, models for elastic wave radiation more efficiently handle sources described as distributions of surface stresses. Equivalent surface stresses can be obtained by integrating the body force with respect to depth. They are assumed to generate the same field as the one that would be generated by the body force. Such an integration scheme can be applied to Lorentz force for conventional EMAT configuration. When applied to magnetostrictive force generated by an EMAT in a ferromagnetic material, the same scheme fails, predicting a null stress. Transforming body force into equivalent surface stresses therefore, requires taking into account higher order terms of the force moments, the zeroth order being the simple force integration over the depth. In this paper, such a transformation is derived up to the second order, assuming that body forces are localized at depths shorter than the ultrasonic wavelength. Two formulations are obtained, each having some advantages depending on the application sought. They apply regardless of the nature of the force considered.

  19. Measurement of dynamic surface tension by mechanically vibrated sessile droplets.

    PubMed

    Iwata, Shuichi; Yamauchi, Satoko; Yoshitake, Yumiko; Nagumo, Ryo; Mori, Hideki; Kajiya, Tadashi

    2016-04-01

    We developed a novel method for measuring the dynamic surface tension of liquids using mechanically vibrated sessile droplets. Under continuous mechanical vibration, the shape of the deformed droplet was fitted by numerical analysis, taking into account the force balance at the drop surface and the momentum equation. The surface tension was determined by optimizing four parameters: the surface tension, the droplet's height, the radius of the droplet-substrate contact area, and the horizontal symmetrical position of the droplet. The accuracy and repeatability of the proposed method were confirmed using drops of distilled water as well as viscous aqueous glycerol solutions. The vibration frequency had no influence on surface tension in the case of pure liquids. However, for water-soluble surfactant solutions, the dynamic surface tension gradually increased with vibration frequency, which was particularly notable for low surfactant concentrations slightly below the critical micelle concentration. This frequency dependence resulted from the competition of two mechanisms at the drop surface: local surface deformation and surfactant transport towards the newly generated surface.

  20. Measurement of dynamic surface tension by mechanically vibrated sessile droplets

    NASA Astrophysics Data System (ADS)

    Iwata, Shuichi; Yamauchi, Satoko; Yoshitake, Yumiko; Nagumo, Ryo; Mori, Hideki; Kajiya, Tadashi

    2016-04-01

    We developed a novel method for measuring the dynamic surface tension of liquids using mechanically vibrated sessile droplets. Under continuous mechanical vibration, the shape of the deformed droplet was fitted by numerical analysis, taking into account the force balance at the drop surface and the momentum equation. The surface tension was determined by optimizing four parameters: the surface tension, the droplet's height, the radius of the droplet-substrate contact area, and the horizontal symmetrical position of the droplet. The accuracy and repeatability of the proposed method were confirmed using drops of distilled water as well as viscous aqueous glycerol solutions. The vibration frequency had no influence on surface tension in the case of pure liquids. However, for water-soluble surfactant solutions, the dynamic surface tension gradually increased with vibration frequency, which was particularly notable for low surfactant concentrations slightly below the critical micelle concentration. This frequency dependence resulted from the competition of two mechanisms at the drop surface: local surface deformation and surfactant transport towards the newly generated surface.

  1. Lubrication forces in air and accommodation coefficient measured by a thermal damping method using an atomic force microscope

    NASA Astrophysics Data System (ADS)

    Honig, Christopher D. F.; Sader, John E.; Mulvaney, Paul; Ducker, William A.

    2010-05-01

    By analysis of the thermally driven oscillation of an atomic force microscope (AFM) cantilever, we have measured both the damping and static forces acting on a sphere near a flat plate immersed in gas. By varying the proximity of the sphere to the plate, we can continuously vary the Knudsen number (Kn) at constant pressure, thereby accessing the slip flow, transition, and molecular regimes at a single pressure. We use measurements in the slip-flow regime to determine the combined slip length (on both sphere and plate) and the tangential momentum accommodation coefficient, σ . For ambient air at 1 atm between two methylated glass solids, the inverse damping is linear with separation and the combined slip length on both surfaces is 250nm±100nm , which corresponds to σ=0.77±0.24 . At small separations (Kn>0.4) the measured inverse damping is no longer linear with separation, and is observed to exhibit reasonable agreement with the Vinogradova formula.

  2. Apparatus for measuring surface particulate contamination

    DOEpatents

    Woodmansee, Donald E.

    2002-01-01

    An apparatus for measuring surface particulate contamination includes a tool for collecting a contamination sample from a target surface, a mask having an opening of known area formed therein for defining the target surface, and a flexible connector connecting the tool to the mask. The tool includes a body portion having a large diameter section defining a surface and a small diameter section extending from the large diameter section. A particulate collector is removably mounted on the surface of the large diameter section for collecting the contaminants. The tool further includes a spindle extending from the small diameter section and a spool slidingly mounted on the spindle. A spring is disposed between the small diameter section and the spool for biasing the spool away from the small diameter section. An indicator is provided on the spindle so as to be revealed when the spool is pressed downward to compress the spring.

  3. The height of biomolecules measured with the atomic force microscope depends on electrostatic interactions.

    PubMed Central

    Müller, D J; Engel, A

    1997-01-01

    In biological applications of atomic force microscopy, the different surface properties of the biological sample and its support become apparent. Observed height differences between the biomolecule and its supporting surface are thus not only of structural origin, but also depend on the different sample-tip and support-tip interactions. This can result in negative or positive contributions to the measured height, effects that are described by the DLVO (Derjaguin, Landau, Verwey, Overbeek) theory. Experimental verification shows that the electrostatic interactions between tip and sample can strongly influence the result obtained. To overcome this problem, pH and electrolyte concentration of the buffer solution have to be adjusted to screen out electrostatic forces. Under these conditions, the tip comes into direct contact with the surface of support and biological system, even when low forces required to prevent sample deformation are applied. In this case, the measured height can be related to the thickness of the native biological structure. The observed height dependence of the macromolecules on electrolyte concentration makes it possible to estimate surface charge densities. Images FIGURE 1 FIGURE 2 FIGURE 8 FIGURE 10 FIGURE 11 PMID:9284330

  4. Proximity effect on hydrodynamic interaction between a sphere and a plane measured by force feedback microscopy at different frequencies

    NASA Astrophysics Data System (ADS)

    Carpentier, Simon; Rodrigues, Mario S.; Charlaix, Elisabeth; Chevrier, Joël

    2015-07-01

    In this article, we measure the viscous damping G″, and the associated stiffness G', of a liquid flow in sphere-plane geometry over a large frequency range. In this regime, the lubrication approximation is expected to dominate. We first measure the static force applied to the tip. This is made possible thanks to a force feedback method. Adding a sub-nanometer oscillation of the tip, we obtain the dynamic part of the interaction with solely the knowledge of the lever properties in the experimental context using a linear transformation of the amplitude and phase change. Using a Force Feedback Microscope (FFM), we are then able to measure simultaneously the static force, the stiffness, and the dissipative part of the interaction in a broad frequency range using a single AFM probe. Similar measurements have been performed by the Surface Force Apparatus (SFA) with a probe radius hundred times bigger. In this context, the FFM can be called nano-SFA.

  5. Measurement of Gas-Surface Accommodation

    NASA Astrophysics Data System (ADS)

    Trott, W. M.; Rader, D. J.; Castañeda, J. N.; Torczynski, J. R.; Gallis, M. A.

    2008-12-01

    Thermal accommodation coefficients have been determined for a variety of gas-surface combinations using an experimental apparatus developed to measure both the pressure dependence of the conductive heat flux and the variation of gas density between parallel plates separated by a gas-filled gap. Effects of gas composition, surface roughness and surface contamination have been examined with this system, and the behavior of gas mixtures has also been explored. Results are discussed in comparison with previous parallel-plate experimental studies as well as numerical simulations.

  6. Complex Squeezing and Force Measurement Beyond the Standard Quantum Limit

    NASA Astrophysics Data System (ADS)

    Buchmann, L. F.; Schreppler, S.; Kohler, J.; Spethmann, N.; Stamper-Kurn, D. M.

    2016-07-01

    A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme called synodyne detection, which reveals complex squeezing and allows the accounting of measurement backaction. Even with the optomechanical system subject to continuous measurement, such detection allows the measurement of one component of an external force with sensitivity only limited by the mechanical oscillator's thermal occupation.

  7. Measurement of solution viscosity by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ahmed, Nabil; Nino, Diego F.; Moy, Vincent T.

    2001-06-01

    We report on studies aimed at employing the atomic force microscope (AFM) to measure the viscosity of aqueous solutions. At ambient temperature, the AFM cantilever undergoes thermal fluctuations that are highly sensitive to the local environment. Here, we present measurements of the cantilever's resonant frequency in aqueous solutions of glycerol, sucrose, ethanol, sodium chloride, polyethylene glycol, and bovine plasma albumin. The measurements revealed that variations in the resonant frequency of the cantilever in the different solutions are largely dependent on the viscosity of the medium. An application of this technique is to monitor the progression of a chemical reaction where a change in viscosity is expected to occur. An example is demonstrated through monitoring of the hydrolysis of double stranded deoxyribonucleic acid by DNase I.

  8. Complex Squeezing and Force Measurement Beyond the Standard Quantum Limit.

    PubMed

    Buchmann, L F; Schreppler, S; Kohler, J; Spethmann, N; Stamper-Kurn, D M

    2016-07-15

    A continuous quantum field, such as a propagating beam of light, may be characterized by a squeezing spectrum that is inhomogeneous in frequency. We point out that homodyne detectors, which are commonly employed to detect quantum squeezing, are blind to squeezing spectra in which the correlation between amplitude and phase fluctuations is complex. We find theoretically that such complex squeezing is a component of ponderomotive squeezing of light through cavity optomechanics. We propose a detection scheme called synodyne detection, which reveals complex squeezing and allows the accounting of measurement backaction. Even with the optomechanical system subject to continuous measurement, such detection allows the measurement of one component of an external force with sensitivity only limited by the mechanical oscillator's thermal occupation.

  9. A force measuring treadmill in clinical gait analysis.

    PubMed

    Dierick, Frédéric; Penta, Massimo; Renaut, David; Detrembleur, Christine

    2004-12-01

    This preliminary study presents the development and testing of an instrumented treadmill device measuring the ground reaction forces (GRFs) and the feasibility of using this force measuring treadmill (FMT) in clinical gait analysis. A commercially available treadmill was modified and fitted out with three-dimensional strain-gauge force transducers. Tests of linearity, centre of pressure position (CoP), cross talk, natural frequency, background noises, and belt speed were undertaken in order to assess the performance of the FMT. In addition, the GRFs and segmental kinematics were recorded while healthy subjects and patients walked on the FMT, in order to compute the net ankle joint moments and the body centre of mass (CMb) kinematics and mechanics. The preliminary results of technical tests were satisfactory with an error less than 10% and dynamic tests in healthy subjects corresponded to the literature. The results of patients were clearly disturbed, demonstrating the ability of the FMT to discriminate pathological gaits from normal ones. We concluded that the GRFs measurements obtained from the FMT seem valid and the clinical assessment of net joint moments and CMb kinematics and mechanics seem feasible. The FMT could be useful device for clinical research and routine gait analysis since it allows gaining some extra room and quickly collecting the GRFs during a large number of successive gait cycles and over a wide range of steady-state gait speeds. However, more work is needed in this area in order to confirm the present results, collect reference data and validate the methodology across pathologies.

  10. Contractile force measured in unskinned isolated adult rat heart fibres.

    PubMed

    Brady, A J; Tan, S T; Ricchiuti, N V

    1979-12-13

    A number of investigators have succeeded in preparing isolated cardiac cells by enzymatic digestion which tolerate external [Ca2+] in the millimolar range. However, a persistent problem with these preparations is that, unlike in situ adult ventricular fibres, the isolated fibres usually beat spontaneously. This spontaneity suggests persistent ionic leakage not present in situ. A preferable preparation for mechanical and electrical studies would be one which is quiescent but excitable in response to electrical stimulation and which does not undergo contracture with repeated stimulation. We report here a modified method of cardiac fibre isolation and perfusion which leaves the fibre membrane electrically excitable and moderately resistant to mechanical stress so that the attachment of suction micropipettes to the fibre is possible for force measurement and length control. Force generation in single isolated adult rat heart fibres is consistent with in situ contractile force. The negative staircase effect (treppe) characteristic of adult not heart tissue is present with increased frequency of stimulation. Isometric developed tension increases with fibre length as in in situ ventricular tissue.

  11. Measurement of Metal Cutting Forces at High Speeds

    NASA Astrophysics Data System (ADS)

    Princehouse, David W.

    1996-03-01

    Proposed numerically-controlled milling machines will cut aluminum alloys with cutter tip speeds of up to 130 m/s (300 MPH). There are a variety of challenging technical problems to be solved--high power density motors, inverters, cutter/machine dynamics, servo control systems--and compelling reasons to do so. We measured time-varying cutting forces at these tip speeds with a 25.4-cm (10-in) diameter cutter turning at rates up to 167 Hz (10,000 RPM.) We took special care to measure and compensate for the dynamic response of the force transducer (a three-axis quartz-crystal milling dynamometer), extending the useful bandwidth of the measurements well into the mechanical resonances of the dynamometer. We instrumented a production milling machine on the factory floor and processed megabytes of data, obtaining results minutes after a cut was made. This case study shows how a physicist's background in mechanics, instrumentation, signal processing, and computing hardware and software can help advance the state of the art in aerospace manufacturing.

  12. Development of a surface panel measurement system

    NASA Technical Reports Server (NTRS)

    Jones, D. L.

    1981-01-01

    Reflector measurement systems are studied in support of the reshaping of the 34 meter antenna at Goldstone. The requirements for measurement systems are presented. A survey is made of the surface errors of existing antennas. Reflector measurement systems are divided into three categories and representative examples of each category are illustrated and discussed. Parametric error analyses are made of selected optical systems. The existing measurement method using a theodolite at the vertex is retained. A method using a theodolite on the RF cone is a possible variant.

  13. Self-Calibrating Surface Measuring Machine

    NASA Astrophysics Data System (ADS)

    Greenleaf, Allen H.

    1983-04-01

    A new kind of surface-measuring machine has been developed under government contract at Itek Optical Systems, a Division of Itek Corporation, to assist in the fabrication of large, highly aspheric optical elements. The machine uses four steerable distance-measuring interferometers at the corners of a tetrahedron to measure the positions of a retroreflective target placed at various locations against the surface being measured. Using four interferometers gives redundant information so that, from a set of measurement data, the dimensions of the machine as well as the coordinates of the measurement points can be determined. The machine is, therefore, self-calibrating and does not require a structure made to high accuracy. A wood-structured prototype of this machine was made whose key components are a simple form of air bearing steering mirror, a wide-angle cat's eye retroreflector used as the movable target, and tracking sensors and servos to provide automatic tracking of the cat's eye by the four laser beams. The data are taken and analyzed by computer. The output is given in terms of error relative to an equation of the desired surface. In tests of this machine, measurements of a 0.7 m diameter mirror blank have been made with an accuracy on the order of 0.2µm rms.

  14. Roll Damping Derivatives from Generalized Lifting-Surface Theory and Wind Tunnel Forced-Oscillation Tests

    NASA Technical Reports Server (NTRS)

    Pototzky, Anthony S; Murphy, Patrick C.

    2014-01-01

    Improving aerodynamic models for adverse loss-of-control conditions in flight is an area being researched under the NASA Aviation Safety Program. Aerodynamic models appropriate for loss of control conditions require a more general mathematical representation to predict nonlinear unsteady behaviors. As more general aerodynamic models are studied that include nonlinear higher order effects, the possibility of measurements that confound aerodynamic and structural responses are probable. In this study an initial step is taken to look at including structural flexibility in analysis of rigid-body forced-oscillation testing that accounts for dynamic rig, sting and balance flexibility. Because of the significant testing required and associated costs in a general study, it makes sense to capitalize on low cost analytical methods where possible, especially where structural flexibility can be accounted for by a low cost method. This paper provides an initial look at using linear lifting surface theory applied to rigid-body aircraft roll forced-oscillation tests.

  15. Measurement of high viscosity with laser induced surface deformation technique

    SciTech Connect

    Yoshitake, Y.; Mitani, S.; Sakai, K.; Takagi, K.

    2005-01-15

    A technique for viscosity measurement was developed based on the principle of laser-induced surface deformation. Light incident into liquids increases its momentum due to the difference in refractive index and gives the surface an upward force as a reaction. The plane surface thus swells up and deforms, and the shape is determined so that the force is balanced with the surface tension and the gravity. On sudden laser irradiation, the deformation inevitably accompanies a viscous flow and exhibits a relaxational behavior with a delay time, which gives the viscosity. Theoretical prediction of the step-response function was given that takes surface tension waves excited by the laser into consideration. Nd-yttritium-aluminum-garnet laser with 0.6 W output was focused to {approx}200 {mu}m beam waist and used for the pumping. The deformation process was observed sensitively with another probe laser illuminating the activated area. This system was tested with the standard liquids for viscosity ranging from 1 to 10{sup 6} cSt. The results demonstrated the validity of this technique, though a correction for the inertia effect was needed in the range lower than 10 cSt. Further, effect of the thermal expansion by a slight optical absorption was discussed. This technique is especially useful at high viscosities since the measurement takes only a few seconds even in the specimen with 10{sup 6} cSt. Besides the rapidity, it has a great advantage of a noncontact feature and is appropriate for measuring the liquids that strongly dislike contamination. It has also potential applications in industries, measurement of liquids isolated in a production line, for instance.

  16. Surface forces in model oil-in-water emulsions stabilized by proteins.

    PubMed

    Dimitrova, Tatiana D; Leal-Calderon, Fernando; Gurkov, Theodor D; Campbell, Bruce

    2004-05-20

    We have employed two complementary techniques, namely, the magnetic chaining technique (MCT) and a variant of the Mysels cell to obtain data concerning the repulsive interaction profiles between protein layers formed at liquid-liquid interfaces. For BSA-stabilized systems, a long-ranged repulsion is operative. It is not of an electrostatic origin, but originates most probably from the formation of multiple protein layers at the interface. The interactions between beta-casein layers formed at the water/oil interface are governed by electrostatic repulsion. Due to the relatively large final thickness of approximately 20 nm, the van der Waals contribution to the total disjoining pressure is inferior. The oscillatory component is also negligible for the studied protein concentration of 0.1 wt.%. For both proteins, the extracted information describes the situation where the protein-covered surfaces are approached/manipulated in a quasi-static manner. We observe a very good agreement between the data obtained from MCT and Mysels cell. The comparison of our results with literature data from surface force apparatus (SFA) experiments reveals a substantial difference in the force laws existing between protein-stabilized liquid droplets and mica surfaces covered by proteins. We explain this discrepancy in terms of the different protein absorption on solid and liquid interfaces. We also measured the threshold force necessary to induce irreversible flocculation in beta-casein and beta-lactoglobulin (BLG) stabilized emulsions. Under similar conditions, the threshold flocculation force is higher for beta-casein than for BLG stabilized droplets. The flocs formed from BLG covered droplets are tight and remain without visible change for at least 48 h. We speculate that the flocculation is due to formation of protein aggregates between the approaching droplets.

  17. Effect of contact force on breast tissue optical property measurements using a broadband diffuse optical spectroscopy handheld probe

    PubMed Central

    Cerussi, Albert; Siavoshi, Sarah; Durkin, Amanda; Chen, Cynthia; Tanamai, Wendy; Hsiang, David; Tromberg, Bruce J.

    2010-01-01

    We investigated the effects of operator-applied force on diffuse optical spectroscopy (DOS) by integrating a force transducer into the handheld probe. Over the typical range of contact forces measured in the breasts of eight patients, absorption and reduced scattering coefficients (650 to 1000 nm) variance was 3.1 ± 1.0% and 1.0 ± 0.4%. For trained operators, we observed <5% variation in hemoglobin and <2% variation in water and lipids. Contact force is not a significant source of variation, most likely because of a relatively wide probe surface area and the stability of the DOS method for calculating tissue optical properties. PMID:19623242

  18. Measurement of surface scratches on aircraft structures

    NASA Astrophysics Data System (ADS)

    Sarr, Dennis P.

    1996-01-01

    In assuring the quality of aircraft, the skin quality must be free of surface imperfections. Surface imperfections such as scratches are unacceptable for cosmetic and structural reasons. Scratches beyond a certain depth are not repairable, resulting in costly replacement of an aircraft's part. Measurements of aircraft exterior surfaces require a ladder or cherry picker for positioning the inspector. Commercially-available computer vision systems are not portable, easy to use, or ergonomic. The machine vision system must be designed with these criteria in mind. The scratch measurement system (SMS) uses computer vision, digital signal processing, and automated inspection methods. The system is portable and battery powered. It is certified for measuring the depth and width of the anomaly. The SMS provides a comprehensive, analytical, and accurate reading. A hardcopy output provides a permanent record of the analysis. The graphical data shows the surface profile and provides substantial information of the surface anomaly. The factory and flight line use the SMS at different stages of aircraft production. Six systems have been built for use within Boeing. A patent was issued for the SMS in February 1994.

  19. Surface radiation budget and cloud radiative forcing from pan-Arctic Baseline Surface Radiation Network (BSRN) stations

    NASA Astrophysics Data System (ADS)

    Cox, C. J.; Long, C. N.; Crepinsek, S.; Maturilli, M.; McComiskey, A. C.; Miller, N.; Konopleva-Akish, E.; Kustov, V. Y.; Shupe, M.; Steffen, K.; Stanitski, D.; Starkweather, S.; Stone, R. S.; Uttal, T.; Walden, V. P.

    2015-12-01

    Monitoring and forecasting of the seasonal melt of snow and ice in the Arctic is a priority need as Arctic climate changes and the number of stakeholders increases. Seasonal snow and ice melt represent the largest annual perturbation to the surface net radiation budget. Radiative interactions between clouds, the surface and the atmosphere play an important role on scales of minutes to decades, but models insufficiently represent cloud properties. Furthermore, the surface radiation budget is not directly observed from satellite platforms. Direct observations from the surface must therefore be used to document the physical and correlative relationships between variables, and to provide a baseline target for data sets with more comprehensive spatial representation. High-quality, continuous, long-term observations of radiative fluxes are collected from land stations surrounding the Arctic Basin as part of the Baseline Surface Radiation Network (BSRN). The International Arctic Systems for Observing the Atmosphere (IASOA) facilitates international collaboration amongst station scientists and other topic experts for the purposes of streamlining pan-Arctic synthesis studies. The IASOA Radiation Working Group is currently analyzing the data acquired from Barrow, Alaska (1993-2015), Alert, Canada (2004-2014), Ny-Ålesund, Svalbard (1993-2015), Eureka, Canada (2007-2015), and Tiksi, Russia (2011-2015). The measurements include upwelling and downwelling longwave and shortwave fluxes, as well as direct and diffuse shortwave flux components, and surface meteorology. The observations are post-processed using the Radiative Flux Analysis (RFA) method, which, in addition to basic quality control, provides value-added metrics such as cloud radiative forcing (CRF), optical depth, and fractional sky cover. Here, we present a spatial and temporal analysis of the surface radiation budget and calculated variables from the pan-Arctic BSRN stations. Particular attention is given to inter

  20. Surface conformations of anti-ricin aptamer and its affinity to ricin determined by atomic force microscopy and surface plasmon resonance

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The specific interactions between ricin and anti-ricin aptamer were measured with atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectrometry and the results were compared. In AFM, a single-molecule experiment with ricin functionalized AFM tip was used for scanning the aptamer mol...

  1. Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces

    PubMed Central

    Endlein, Thomas; Ji, Aihong; Samuel, Diana; Yao, Ning; Wang, Zhongyuan; Barnes, W. Jon P.; Federle, Walter; Kappl, Michael; Dai, Zhendong

    2013-01-01

    To live and clamber about in an arboreal habitat, tree frogs have evolved adhesive pads on their toes. In addition, they often have long and slender legs to facilitate not only long jumps, but also to bridge gaps between leaves when climbing. Both adhesive pads and long limbs are used in conjunction, as we will show in this study. Previous research has shown that tree frogs change from a crouched posture (where the limbs are close to the body) to a sprawled posture with extended limbs when clinging on to steeper inclines such as vertical or overhanging slopes. We investigated this change in posture in White's tree frogs (Litoria caerulea) by challenging the frogs to cling onto a tiltable platform. The platform consisted of an array of 24 three-dimensional force transducers, which allowed us to measure the ground reaction forces of the frogs during a tilt. Starting from a crouched resting position, the normal forces on the forelimbs changed sign and became increasingly negative with increasing slope angle of the platform. At about 106°±12°, tilt of the platform the frogs reacted by extending one or two of their limbs outwards. At a steeper angle (131°±11°), the frogs spread out all their limbs sideways, with the hindlimbs stretched out to their maximum reach. Although the extension was strongest in the lateral direction, limbs were significantly extended in the fore–aft direction as well. With the extension of the limbs, the lateral forces increased relative to the normal forces. The large contribution of the in-plane forces helped to keep the angle between the force vector and the platform small. The Kendall theory for the peeling of adhesive tape predicts that smaller peel angles lead to higher attachment forces. We compare our data with the predictions of the Kendall model and discuss possible implications of the sliding of the pads on the surface. The forces were indeed much larger for smaller angles and thus can be explained by peeling theory. PMID

  2. Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces.

    PubMed

    Endlein, Thomas; Ji, Aihong; Samuel, Diana; Yao, Ning; Wang, Zhongyuan; Barnes, W Jon P; Federle, Walter; Kappl, Michael; Dai, Zhendong

    2013-03-06

    To live and clamber about in an arboreal habitat, tree frogs have evolved adhesive pads on their toes. In addition, they often have long and slender legs to facilitate not only long jumps, but also to bridge gaps between leaves when climbing. Both adhesive pads and long limbs are used in conjunction, as we will show in this study. Previous research has shown that tree frogs change from a crouched posture (where the limbs are close to the body) to a sprawled posture with extended limbs when clinging on to steeper inclines such as vertical or overhanging slopes. We investigated this change in posture in White's tree frogs (Litoria caerulea) by challenging the frogs to cling onto a tiltable platform. The platform consisted of an array of 24 three-dimensional force transducers, which allowed us to measure the ground reaction forces of the frogs during a tilt. Starting from a crouched resting position, the normal forces on the forelimbs changed sign and became increasingly negative with increasing slope angle of the platform. At about 106° ± 12°, tilt of the platform the frogs reacted by extending one or two of their limbs outwards. At a steeper angle (131° ± 11°), the frogs spread out all their limbs sideways, with the hindlimbs stretched out to their maximum reach. Although the extension was strongest in the lateral direction, limbs were significantly extended in the fore-aft direction as well. With the extension of the limbs, the lateral forces increased relative to the normal forces. The large contribution of the in-plane forces helped to keep the angle between the force vector and the platform small. The Kendall theory for the peeling of adhesive tape predicts that smaller peel angles lead to higher attachment forces. We compare our data with the predictions of the Kendall model and discuss possible implications of the sliding of the pads on the surface. The forces were indeed much larger for smaller angles and thus can be explained by peeling theory.

  3. Measuring the Mechanical Properties of Living Cells Using Atomic Force Microscopy

    PubMed Central

    Thomas, Gawain; Burnham, Nancy A.; Camesano, Terri Anne; Wen, Qi

    2013-01-01

    Mechanical properties of cells and extracellular matrix (ECM) play important roles in many biological processes including stem cell differentiation, tumor formation, and wound healing. Changes in stiffness of cells and ECM are often signs of changes in cell physiology or diseases in tissues. Hence, cell stiffness is an index to evaluate the status of cell cultures. Among the multitude of methods applied to measure the stiffness of cells and tissues, micro-indentation using an Atomic Force Microscope (AFM) provides a way to reliably measure the stiffness of living cells. This method has been widely applied to characterize the micro-scale stiffness for a variety of materials ranging from metal surfaces to soft biological tissues and cells. The basic principle of this method is to indent a cell with an AFM tip of selected geometry and measure the applied force from the bending of the AFM cantilever. Fitting the force-indentation curve to the Hertz model for the corresponding tip geometry can give quantitative measurements of material stiffness. This paper demonstrates the procedure to characterize the stiffness of living cells using AFM. Key steps including the process of AFM calibration, force-curve acquisition, and data analysis using a MATLAB routine are demonstrated. Limitations of this method are also discussed. PMID:23851674

  4. Measurement of surface deformation of soft tissue.

    PubMed

    Stokes, I; Greenapple, D M

    1985-01-01

    A method is described for measuring the surface shape and deformations of soft tissue in three dimensions. The method uses close range stereophotogrammetry to record the three-dimensional locations of miniature optical targets applied to the tissue surface. This has been applied to study of human lumbar intervertebral disc. Measurements of the strain along surface annular fibers have been made under varying loads. In this case the maximum expected errors are about 0.15 mm, which corresponds to a strain of less than 1%. Preliminary findings have differed from predictions made in published mathematical models for the disc in that they show very little strain of the annulus in compression loading, but confirm axial torsional loading as liable to produce mechanical disruption of the disc annulus.

  5. Operation Argus. Surface measurements - project midas

    SciTech Connect

    Newman, P.; Chernosky, E.; Markham, T.; McCabe, L.; Peterson, A.

    1984-08-31

    The objective was to make surface measurements of the electromagnetic and optical effects in the detonation area (South Atlantic) and in the area geomagnetically conjugate (Azores) during the Argus experiment. The project participated in three events - Argus I, II, and III.

  6. Optical Roughness Measurements Of Industrial Surfaces

    NASA Astrophysics Data System (ADS)

    Gilsinn, David; Vorburger, Theodore; Cao, Lin-Xiang; Giauque, Charles; Scire, Fredric; Teague, E. Clayton

    1986-10-01

    This paper reviews our efforts to develop the theory and instrumentation needed to measure surface roughness of manufactured surfaces by optical scattering methods. We are addressing three key problems: developing a valid and sufficient optical scattering theory for this roughness range, applying appropriate mathematical inversion techniques so that practical roughness parameters can be calculated from scattering distributions, and finally evaluating a compact commercial instrument for a wide variety of problems. Recent results from our group suggest that the simple phase screen approximation model of optical scattering validly describes light scattering from machined metal surfaces with a predominant surface lay in the 0.01 pm R to 3.0 pm R range. A model for scattering in the entire farr-field hemisphere and obsera vations on our r approach to the inverse problem is given.

  7. Multi-dimensional modelling of electrostatic force distance curve over dielectric surface: Influence of tip geometry and correlation with experiment

    SciTech Connect

    Boularas, A. Baudoin, F.; Villeneuve-Faure, C.; Clain, S.; Teyssedre, G.

    2014-08-28

    Electric Force-Distance Curves (EFDC) is one of the ways whereby electrical charges trapped at the surface of dielectric materials can be probed. To reach a quantitative analysis of stored charge quantities, measurements using an Atomic Force Microscope (AFM) must go with an appropriate simulation of electrostatic forces at play in the method. This is the objective of this work, where simulation results for the electrostatic force between an AFM sensor and the dielectric surface are presented for different bias voltages on the tip. The aim is to analyse force-distance curves modification induced by electrostatic charges. The sensor is composed by a cantilever supporting a pyramidal tip terminated by a spherical apex. The contribution to force from cantilever is neglected here. A model of force curve has been developed using the Finite Volume Method. The scheme is based on the Polynomial Reconstruction Operator—PRO-scheme. First results of the computation of electrostatic force for different tip–sample distances (from 0 to 600 nm) and for different DC voltages applied to the tip (6 to 20 V) are shown and compared with experimental data in order to validate our approach.

  8. Influence of rough track surfaces on components of vertical forces in cantering thoroughbred horses.

    PubMed

    Kai, M; Takahashi, T; Aoki, O; Oki, H

    1999-07-01

    No kinetic data are available to indicate the influence of a rough track surface and the resultant loss of footing on the components of hoof vertical forces. The aim of the present study was to evaluate the influence of rough track surfaces on the components of hoof vertical forces. Seven clinically sound 2-year-old Thoroughbred horses had instrumented shoes attached to both of the fore hooves to obtain the magnitudes of consecutive forces exerted in the hoof. All horses were cantered at approximately 10 m/s on straight tracks of smooth and rough surfaces of woodchip and dirt. The instrumented shoe indicated in real time 4 component forces acting on the hoof via 4 transducers positioned on the lateral and medial sides of the toe (LT, MT) and the heel (LH, MH). The peak vertical component forces of the heel were about twice that of the toe. The variances of the 4 components of peak vertical forces significantly increased on the rough track surface of both the woodchip (Leading: LH, MH and MT; Trailing: MH and LT) and dirt (Leading: LH and LT; Trailing: MH and MT) tracks. The trajectories of the position of the resultant force acting on the hoof also tended to increase the variance on rough track surfaces. Therefore, running on a rough track changes the vertical hoof forces and the balance of the resultant hoof forces. These results suggest a mechanism by which the rough track surfaces may influence the soundness of the horse.

  9. Surface field of forces and protein adsorption behavior of poly(hydroxyethylmethacrylate) films deposited from plasma.

    PubMed

    Morra, M; Cassinelli, C

    1995-01-01

    Polymeric films were deposited from hydroxyethylmethacrylate (HEMA) plasma on non-woven poly(butyleneterephtalate) (PBT) filter materials. To test the effect of deposition conditions on surface properties, film were deposited using a constant monomer flow rate and a discharge power ranging from 40-100 W. Surface composition and surface energetics were evaluated by Electron Spectroscopy for Chemical Analysis (ESCA) and contact angle measurement, respectively. Albumin (Alb) and fibrinogen (Fg) adsorption from single protein solutions to the plasma-coated filters was measured. Results illustrate the marked effects of the deposition condition on the surface composition, the surface field of forces, and the protein adsorption behavior. The latter is modeled by the application of the Good-van Oss-Chaudhury theory of Lewis acid-base contribution to interfacial energetics. Materials endowed with widely different properties are obtained from the same monomer and different deposition conditions, a result that must be taken into account both in the production step, to assure constant quality, and in the development of specifically tailored materials.

  10. Sea-surface salinity: the missing measurement

    NASA Astrophysics Data System (ADS)

    Stocker, Erich F.; Koblinsky, Chester

    2003-04-01

    Even the youngest child knows that the sea is salty. Yet, routine, global information about the degree of saltiness and the distribution of the salinity is not available. Indeed, the sea surface salinity measurement is a key missing measurement in global change research. Salinity influences circulation and links the ocean to global change and the water-cycle. Space-based remote sensing of important global change ocean parameters such as sea-surface temperature and water-cycle parameters such as precipitation have been available to the research community but a space-based global sensing of salinity has been missing. In July 2002, the National Aeronautical and Space Administration (NASA) announced that the Aquarius mission, focused on the global measurement of sea surface salinity, is one of the missions approved under its ESSP-3 program. Aquarius will begin a risk-reduction phase during 2003. Aquarius will carry a multi-beam 1.4 GHz (L-band) radiometer used for retrieving salinity. It also will carry a 1.2 GHz (L-band) scatterometer used for measuring surface roughness. Aquarius is tentatively scheduled for a 2006 launch into an 8-day Sun-synchronous orbit. Aquarius key science data product will be a monthly, global surface salinity map at 100 km resolution with an accuracy of 0.2 practical salinity units. Aquarius will have a 3 year operational period. Among other things, global salinity data will permit estimates of sea surface density, or buoyancy, that drives the ocean's three-dimensional circulation.

  11. Investigation and experimental measurement of scissor blade cutting forces using fiber Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Callaghan, D. J.; Rajan, G.; McGrath, M. M.; Coyle, E.; Semenova, Y.; Farrell, G.

    2011-10-01

    This paper reports on unique and scalable sensorized medical scissor blades for application in minimally invasive robotic surgery. The blades exploit the strain sensing capabilities of a single fiber Bragg grating (FBG) sensor bonded to the blade surface. This smart sensing structure allows detection of friction and material fracture forces during cutting and subsequently enables accurate estimation of the blade kinetic friction coefficient and fracture toughness values of the material being cut. We present theory on the determination of strain variation along the blade length during combined direct and lateral loading of the blade element during operation. Demonstration of the sensorized instrument is realized on an application specific experimental test-bed employing a commercial interrogation system for signal demodulation. Friction and cutting forces measured using the FBG are validated against load cell force data from the test-bed. Characterization tests showed that the sensorized blade has an unfiltered force sensing resolution of 0.5 N over a 30 N load range. This work demonstrates that a single optical fiber placed onto cutting instrument blades can, in an unobtrusive manner, reliably measure friction forces and material fracture properties during surgical cutting.