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Sample records for adhesive potential electrostatic

  1. Innovative Electrostatic Adhesion Technologies

    NASA Technical Reports Server (NTRS)

    Bryan, Tom; Macleod, Todd; Gagliano, Larry; Williams, Scott; McCoy, Brian

    2015-01-01

    Developing specialized Electro-Static grippers (commercially used in Semiconductor Manufacturing and in package handling) will allow gentle and secure Capture, Soft Docking, and Handling of a wide variety of materials and shapes (such as upper-stages, satellites, arrays, and possibly asteroids) without requiring physical features or cavities for a pincher or probe or using harpoons or nets. Combined with new rigid boom mechanisms or small agile chaser vehicles, flexible, high speed Electro-Static Grippers can enable compliant capture of spinning objects starting from a safe stand-off distance. Electroadhesion (EA) can enable lightweight, ultra-low-power, compliant attachment in space by using an electrostatic force to adhere similar and dissimilar surfaces. A typical EA enabled device is composed of compliant space-rated materials, such as copper-clad polyimide encapsulated by polymers. Attachment is induced by strong electrostatic forces between any substrate material, such as an exterior satellite panel and a compliant EA gripper pad surface. When alternate positive and negative charges are induced in adjacent planar electrodes in an EA surface, the electric fields set up opposite charges on the substrate and cause an electrostatic adhesion between the electrodes and the induced charges on the substrate. Since the electrodes and the polymer are compliant and can conform to uneven or rough surfaces, the electrodes can remain intimately close to the entire surface, enabling high clamping pressures. Clamping pressures of more than 3 N/cm2 in shear can be achieved on a variety of substrates with ultra-low holding power consumption (measured values are less than 20 microW/Newton weight held). A single EA surface geometry can be used to clamp both dielectric and conductive substrates, with slightly different physical mechanisms. Furthermore EA clamping requires no normal force be placed on the substrate, as conventional docking requires. Internally funded research and

  2. Innovative Electrostatic Adhesion Technologies

    NASA Astrophysics Data System (ADS)

    Gagliano, L.; Bryan, T.; Williams, S.; McCoy, B.; MacLeod, T.

    Developing specialized Electro-Static grippers (commercially used in Semiconductor Manufacturing and in package handling) will allow gentle and secure Capture, Soft Docking, and Handling of a wide variety of materials and shapes (such as upper-stages, satellites, arrays, and possibly asteroids) without requiring physical features or cavities for a pincher or probe or using harpoons or nets. Combined with new rigid boom mechanisms or small agile chaser vehicles, flexible, high speed Electro-Static Grippers can enable compliant capture of spinning objects starting from a safe stand-off distance. Electroadhesion (EA) can enable lightweight, ultra-low-power, compliant attachment in space by using an electrostatic force to adhere similar and dissimilar surfaces. A typical EA enabled device is composed of compliant space-rated materials, such as copper-clad polyimide encapsulated by polymers. Attachment is induced by strong electrostatic forces between any substrate material, such as an exterior satellite panel and a compliant EA surface. When alternate positive and negative charges are induced in adjacent planar electrodes in an EA surface, the electric fields set up opposite charges on the substrate and cause an electrostatic adhesion between the electrodes and the induced charges on the substrate. Since the electrodes and the polymer are compliant and can conform to uneven or rough surfaces, the electrodes can remain intimately close to the entire surface, enabling high clamping pressures. Clamping pressures of more than 3 N/cm2 in shear can be achieved on a variety of substrates with ultra-low holding power consumption (measured values are less than 20 microW/Newton weight held). A single EA surface geometry can be used to clamp both dielectric and conductive substrates, with slightly different physical mechanisms. Furthermore EA clamping requires no normal force be placed on the substrate, as conventional docking requires. Internally funded research and development

  3. Optimization and experimental validation of electrostatic adhesive geometry

    NASA Astrophysics Data System (ADS)

    Ruffatto, D.; Shah, J.; Spenko, M.

    This paper introduces a method to optimize the electrode geometry of electrostatic adhesives for robotic gripping, attachment, and manipulation applications. Electrostatic adhesion is achieved by applying a high voltage potential, on the order of kV, to a set of electrodes, which generates an electric field. The electric field polarizes the substrate material and creates an adhesion force. Previous attempts at creating electro-static adhesives have shown them to be effective, but researchers have made no effort to optimize the electrode configuration and geometry. We have shown that by optimizing the geometry of the electrode configuration, the electric field strength, and therefore the adhesion force, is enhanced. To accomplish this, Comsol Multiphysics was utilized to evaluate the average electric field generated by a given electrode geometry. Several electrode patterns were evaluated, including parallel conductors, concentric circles, Hilbert curves (a fractal geometry) and spirals. The arrangement of the electrodes in concentric circles with varying electrode widths proved to be the most effective. The most effective sizing was to use the smallest gap spacing allowable coupled with a variable electrode width. These results were experimentally validated on several different surfaces including drywall, wood, tile, glass, and steel. A new manufacturing process allowing for the fabrication of thin, conformal electro-static adhesive pads was utilized. By combining the optimized electrode geometry with the new fabrication process we are able to demonstrate a marked improvement of up to 500% in shear pressure when compared to previously published values.

  4. Integrating electrostatic adhesion to composite structures

    NASA Astrophysics Data System (ADS)

    Heath, Callum J. C.; Bond, Ian P.; Potter, Kevin D.

    2015-04-01

    Additional functionality within load bearing components holds potential for adding value to a structure, design or product. We consider the adaptation of an established technology, electrostatic adhesion or electroadhesion, for application in glass fibre reinforced polymer (GFRP) composite materials. Electroadhesion uses high potential difference (~2-3 kV) between co-planar electrodes to generate temporary holding forces to both electrically conductive and nonconductive contact surfaces. Using a combination of established fabrication techniques, electroadhesive elements are co-cured within a composite host structure during manufacture. This provides an almost symbiotic relationship between the electroadhesive and the composite structure, with the electroadhesive providing an additional functionality, whilst the epoxy matrix material of the composite acts as a dielectric for the high voltage electrodes of the device. Silicone rubber coated devices have been shown to offer high shear load (85kPa) capability for GFRP components held together using this technique. Through careful control of the connection interface, we consider the incorporation of these devices within complete composite structures for additional functionality. The ability to vary the internal connectivity of structural elements could allow for incremental changes in connectivity between discrete sub-structures, potentially introducing variable stiffness to the global structure.

  5. The Role of the Electrostatic Force in Spore Adhesion

    SciTech Connect

    Chung, Eunhyea; Yiacoumi, Sotira; Lee, Ida; Tsouris, Costas

    2010-01-01

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

  6. Electrostatic adhesion for added functionality of composite structures

    NASA Astrophysics Data System (ADS)

    Heath, Callum J. C.; Bond, Ian P.; Potter, Kevin D.

    2016-02-01

    Electrostatic adhesion can be used as a means of reversible attachment. The incorporation of electrostatic adhesion into fibre reinforced polymer (FRP) composite structures could provide significant value added functionality. Imparting large potential differences (∼2 kV) across electrodes generates an attractive force, thus providing a means of attachment. This could be used as a reversible latching mechanism or as a means of controllable internal connectivity. Varying the connectivity for discrete elements of a substructure of a given design allows for control of internal load paths and moment of area of the cross section. This could facilitate variable stiffness (both in bending and torsion). Using a combination of existing fabrication techniques, functional electrodes have been integrated within a FRP. Copper polyimide thin film laminate material has been both co-cured with carbon fibre reinforced epoxy and bonded to PVC closed cell foam core material to provide a range of structural configurations with integrated electrodes. The ability of such integrated devices to confer variations in global bending stiffness of basic beam structures is investigated. Through the application of 4 kV across integrated electrostatic adhesive devices, a 112% increase in flexural stiffness has been demonstrated for a composite sandwich structure.

  7. Role of contact electrification and electrostatic interactions in gecko adhesion.

    PubMed

    Izadi, Hadi; Stewart, Katherine M E; Penlidis, Alexander

    2014-09-01

    Geckos, which are capable of walking on walls and hanging from ceilings with the help of micro-/nano-scale hierarchical fibrils (setae) on their toe pads, have become the main prototype in the design and fabrication of fibrillar dry adhesives. As the unique fibrillar feature of the toe pads of geckos allows them to develop an intimate contact with the substrate the animal is walking on or clinging to, it is expected that the toe setae exchange significant numbers of electric charges with the contacted substrate via the contact electrification (CE) phenomenon. Even so, the possibility of the occurrence of CE and the contribution of the resulting electrostatic interactions to the dry adhesion of geckos have been overlooked for several decades. In this study, by measuring the magnitude of the electric charges, together with the adhesion forces, that gecko foot pads develop in contact with different materials, we have clarified for the first time that CE does contribute effectively to gecko adhesion. More importantly, we have demonstrated that it is the CE-driven electrostatic interactions which dictate the strength of gecko adhesion, and not the van der Waals or capillary forces which are conventionally considered as the main source of gecko adhesion. PMID:25008078

  8. Electrostatic adhesion of multiple non-uniformly charged dielectric particles

    NASA Astrophysics Data System (ADS)

    Kemp, B. A.; Whitney, J. G.

    2013-01-01

    Charged particle adhesion measurements can be as much as one order of magnitude higher than theoretical calculations. This discrepancy has ignited a debate as to the nature of the physics occurring with microscopic particle adhesion. Attempts to bring calculations closer to measured results have produced models that include multiple particle interactions, dielectric polarization, and non-uniform charge. Individually, each of these models can only produce a 2× to 5× enhancement in predicted adhesion force over simple Coulombic attraction. In this correspondence, an analytical model of electrostatic particle forces is developed, which allows for independent assignment of dielectric constant and non-uniform surface charge distribution to an arbitrary number of particles. Because the model can include an image plane, it is ideal for electrostatic adhesion calculations. Application to a monolayer of printed toner particles predicts nearly an order of magnitude increase in adhesion force over Coulombic attraction. These results are the first analytical results to place predictions of charged particle adhesion on the same order of magnitude with measurements.

  9. Epithelial Microvilli Establish an Electrostatic Barrier to Microbial Adhesion

    PubMed Central

    Bennett, Kaila M.; Walker, Sharon L.

    2014-01-01

    Microvilli are membrane extensions on the apical surface of polarized epithelia, such as intestinal enterocytes and tubule and duct epithelia. One notable exception in mucosal epithelia is M cells, which are specialized for capturing luminal microbial particles; M cells display a unique apical membrane lacking microvilli. Based on studies of M cell uptake under different ionic conditions, we hypothesized that microvilli may augment the mucosal barrier by providing an increased surface charge density from the increased membrane surface and associated glycoproteins. Thus, electrostatic charges may repel microbes from epithelial cells bearing microvilli, while M cells are more susceptible to microbial adhesion. To test the role of microvilli in bacterial adhesion and uptake, we developed polarized intestinal epithelial cells with reduced microvilli (“microvillus-minus,” or MVM) but retaining normal tight junctions. When tested for interactions with microbial particles in suspension, MVM cells showed greatly enhanced adhesion and uptake of particles compared to microvillus-positive cells. This preference showed a linear relationship to bacterial surface charge, suggesting that microvilli resist binding of microbes by using electrostatic repulsion. Moreover, this predicts that pathogen modification of electrostatic forces may contribute directly to virulence. Accordingly, the effacement effector protein Tir from enterohemorrhagic Escherichia coli O157:H7 expressed in epithelial cells induced a loss of microvilli with consequent enhanced microbial binding. These results provide a new context for microvillus function in the host-pathogen relationship, based on electrostatic interactions. PMID:24778113

  10. Improving controllable adhesion on both rough and smooth surfaces with a hybrid electrostatic/gecko-like adhesive.

    PubMed

    Ruffatto, Donald; Parness, Aaron; Spenko, Matthew

    2014-04-01

    This paper describes a novel, controllable adhesive that combines the benefits of electrostatic adhesives with gecko-like directional dry adhesives. When working in combination, the two technologies create a positive feedback cycle whose adhesion, depending on the surface type, is often greater than the sum of its parts. The directional dry adhesive brings the electrostatic adhesive closer to the surface, increasing its effect. Similarly, the electrostatic adhesion helps engage more of the directional dry adhesive fibrillar structures, particularly on rough surfaces. This paper presents the new hybrid adhesive's manufacturing process and compares its performance to three other adhesive technologies manufactured using a similar process: reinforced PDMS, electrostatic and directional dry adhesion. Tests were performed on a set of ceramic tiles with varying roughness to quantify its effect on shear adhesive force. The relative effectiveness of the hybrid adhesive increases as the surface roughness is increased. Experimental data are also presented for different substrate materials to demonstrate the enhanced performance achieved with the hybrid adhesive. Results show that the hybrid adhesive provides up to 5.1× greater adhesion than the electrostatic adhesive or directional dry adhesive technologies alone. PMID:24451392

  11. Improving controllable adhesion on both rough and smooth surfaces with a hybrid electrostatic/gecko-like adhesive

    PubMed Central

    Ruffatto, Donald; Parness, Aaron; Spenko, Matthew

    2014-01-01

    This paper describes a novel, controllable adhesive that combines the benefits of electrostatic adhesives with gecko-like directional dry adhesives. When working in combination, the two technologies create a positive feedback cycle whose adhesion, depending on the surface type, is often greater than the sum of its parts. The directional dry adhesive brings the electrostatic adhesive closer to the surface, increasing its effect. Similarly, the electrostatic adhesion helps engage more of the directional dry adhesive fibrillar structures, particularly on rough surfaces. This paper presents the new hybrid adhesive's manufacturing process and compares its performance to three other adhesive technologies manufactured using a similar process: reinforced PDMS, electrostatic and directional dry adhesion. Tests were performed on a set of ceramic tiles with varying roughness to quantify its effect on shear adhesive force. The relative effectiveness of the hybrid adhesive increases as the surface roughness is increased. Experimental data are also presented for different substrate materials to demonstrate the enhanced performance achieved with the hybrid adhesive. Results show that the hybrid adhesive provides up to 5.1× greater adhesion than the electrostatic adhesive or directional dry adhesive technologies alone. PMID:24451392

  12. Electrostatic potential map modelling with COSY Infinity

    NASA Astrophysics Data System (ADS)

    Maloney, J. A.; Baartman, R.; Planche, T.; Saminathan, S.

    2016-06-01

    COSY Infinity (Makino and Berz, 2005) is a differential-algebra based simulation code which allows accurate calculation of transfer maps to arbitrary order. COSY's existing internal procedures were modified to allow electrostatic elements to be specified using an array of field potential data from the midplane. Additionally, a new procedure was created allowing electrostatic elements and their fringe fields to be specified by an analytic function. This allows greater flexibility in accurately modelling electrostatic elements and their fringe fields. Applied examples of these new procedures are presented including the modelling of a shunted electrostatic multipole designed with OPERA, a spherical electrostatic bender, and the effects of different shaped apertures in an electrostatic beam line.

  13. Electrostatic potential fluctuations in a Maxwellian plasma

    SciTech Connect

    Hazeltine, R.D.; Lowrey, J.D.

    2006-01-15

    The spatial correlation function of a Maxwellian plasma with perturbations arising in the electrostatic potential due to random ion density fluctuations is examined. The entropy is found from the one-particle distribution function using the Shannon formula and then, using the Einstein method, the probability distribution for the electrostatic potential fluctuation is determined. This straightforward procedure is demonstrated to be a powerful tool in studying plasma correlation functions when the system entropy can be computed.

  14. The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

    SciTech Connect

    Kweon, Hyojin; Yiacoumi, Sotira Z.; Tsouris, Costas

    2015-06-19

    In this study, the influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorption on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.

  15. The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

    DOE PAGESBeta

    Kweon, Hyojin; Yiacoumi, Sotira Z.; Tsouris, Costas

    2015-06-19

    In this study, the influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorptionmore » on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.« less

  16. 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.

  17. Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular Materials

    NASA Technical Reports Server (NTRS)

    Marshall, J.; Weislogel, M.; Jacobson, T.

    1999-01-01

    , are pervasive and probably affect, at some level, everything from astrophysical-scale granular systems such as interstellar nebulae, protoplanetary dust and debris disks, planetary-scale systems such as debris palls from meteorite impact, volcanic eruptions, and aeolian dust storms, all the way to industrial-scale systems in mining, powder and grain processing, pharmaceuticals, and smoke-stack technologies. NASA must concern itself with the electrostatic behavior of dust and sand on Mars because of its potentially critical importance to human exploration. The motion and adhesion of martian surface materials will affect the design and performance of spacesuits, habitats, processing plants, solar panels, and any externally exposed equipment such as surface rovers or communication and weather stations. Additionally, the adhesion of dust and sand could greatly enhance contact with the potentially toxic components of the martian soil.

  18. Molecular Electrostatic Potentials from Invariom Point Charges.

    PubMed

    Wandtke, Claudia M; Lübben, Jens; Dittrich, Birger

    2016-07-18

    A set of look-up point charges for generating molecular electrostatic potentials is provided. The set relies on atom classification of the invariom database, which has already been applied to assign aspherical scattering factors in single-crystal X-ray diffraction. The focus of the investigation is on improving the accuracy of electrostatic potentials calculated by using tabulated point charges. In this respect, the performance of invariom point charges is compared with 1) those from a restrained fit to the electrostatic potential directly following quantum-chemical DFT computations, 2) semi-empirical AM1-bcc charges, and 3) conceptually similar TPACM4 look-up charges. Invariom classification gives charges that perform better than those from TPACM4, although tabulated charges remain inferior to those from molecule-specific computations. Point-charge electrostatic potentials also agree favorably with those from charge-density studies on the basis of X-ray experiments, without requiring the considerable effort of the latter. PMID:26999276

  19. Molecular electrostatic potentials by systematic molecular fragmentation

    SciTech Connect

    Reid, David M.; Collins, Michael A.

    2013-11-14

    A simple method is presented for estimating the molecular electrostatic potential in and around molecules using systematic molecular fragmentation. This approach estimates the potential directly from the electron density. The accuracy of the method is established for a set of organic molecules and ions. The utility of the approach is demonstrated by estimating the binding energy of a water molecule in an internal cavity in the protein ubiquitin.

  20. A finite element technique for accurate determination of interfacial adhesion force in MEMS using electrostatic actuation

    NASA Astrophysics Data System (ADS)

    Shavezipur, M.; Li, G. H.; Laboriante, I.; Gou, W. J.; Carraro, C.; Maboudian, R.

    2011-11-01

    This paper reports on accurate analysis of adhesion force between polysilicon-polysilicon surfaces in micro-/nanoelectromechanical systems (M/NEMS). The measurement is carried out using double-clamped beams. Electrostatic actuation and structural restoring force are exploited to respectively initiate and terminate the contact between the two surfaces under investigation. The adhesion force is obtained by balancing the electrostatic and mechanical forces acting on the beam just before the separation of the two surfaces. Different finite element models are developed to simulate the coupled-field multiphysics problem. The effects of fringing field in the electrostatic domain and geometric nonlinearity and residual stress in the structural domain are taken into consideration. Moreover, the beam stiffness is directly obtained for the case of combined loading (electrostatic and adhesion). Therefore, the overall electrostatic and structural forces used to extract the actual adhesion force from measured data are determined with high accuracy leading to accurate values for the adhesion force. The finite element simulations presented in this paper are not limited to adhesion force measurement and can be used to design or characterize electrostatically actuated devices such as MEM tunable capacitors and micromirrors, RF switches and M/NEM relays.

  1. Electrostatic Potential of Specific Mineral Faces

    SciTech Connect

    Zarzycki, Piotr P.; Chatman, Shawn ME; Preocanin, Tajana; Rosso, Kevin M.

    2011-07-05

    Reaction rates of environmental processes occurring at hydrated mineral surfaces are primarily controlled by the electrostatic potential that develops at the interface. This potential depends on the structure of exposed crystal faces, as well as the pH and the type of ions and their interactions with these faces. Despite its importance, experimental methods for determining fundamental electrostatic properties of specific crystal faces such as the point of zero charge are few. Here we show that this information may be obtained from simple, cyclic potentiometric titration using a well characterized single-crystal electrode exposing the face of interest. The method exploits the presence of a hysteresis loop in the titration measurements that allows extraction of key electrostatic descriptors using the Maxwell construction. The approach is demonstrated for hematite (α-Fe2O3) (001), and a thermodynamic proof is provided for the resulting estimate of its point of zero charge. Insight gained from this method will aid in predicting the fate of migrating contaminants, mineral growth/dissolution processes, mineral-microbiological interactions, and in testing surface complexation theories.

  2. Modeling and analysis of electrostatic adhesion force for climbing robot on dielectric wall materials

    NASA Astrophysics Data System (ADS)

    Mao, Jiu-Bing; Qin, Lan; Zhang, Wan-Xiong; Xie, Li; Wang, Yong

    2015-01-01

    In recent years, electrostatic adhesion technology on the wall climbing robots has attracted many researchers interest for its outstanding characteristics. In this paper, a theoretical analytical model is derived from the electrostatic adhesion field between the dielectric wall and a coplanar array of parallel strip electrodes called inter-digital electrodes (IDE). Due to the polarization on the different dielectric being complicated, the field is divided into four layers in order to obtain corresponding boundaries. Besides, the roughness of the wall surface, alternately polarities applied voltages and different dielectric parameter with different layer, all of which are also taken into account in the model since they have a significant influence on the electrostatic adhesion field. Based on this model, the electrostatic adhesion force (EAF) is calculated utilizing the Maxwell stress tensor (MST) formulation. As we all known, EAF is vital to the climbing robot design. Specially, it is possible for us to optimize the load to weight ratio in next step. Through comparing the finite element method (FEM) simulation with theoretical computation, the simulation and calculated data show that our proposed scheme can achieve desired results. Moreover, experiments of electrostatic adhesion performance for the adhesive on some different dielectric materials are also implemented.

  3. Electrostatic adhesion of polymer particles to a foil electrode

    NASA Astrophysics Data System (ADS)

    Ziteng, Li; Praeger, Matthew; Smallwood, Jeremy; Lewin, Paul

    2015-10-01

    The SPABRINK EU project requires temporary adhesion of coloured solid “ink” particles to a surface, for later recovery and reuse. This is achieved through the use of dielectrophoretic force under the control of a voltage applied to an interdigitated electrode pattern on the polymer foil. One concern is the ability to hold particles under vibration conditions. In this paper we present an experimental study of the adhesion of 50-300 μm polymer particles to an experimental interdigitated electrode structure on flexible polymer foil. Powder loss as a function of calibrated displacement and applied voltage to the electrodes are presented. This is compared with theoretical results obtained by modelling adhesion using Pohl's equation in terms of an “adhesion factor”. Some difficulties in directly comparing experimental and modelling results are discussed.

  4. Electrostatic Potential Across Supercritical Collisionless Shock

    NASA Astrophysics Data System (ADS)

    Khotyaintsev, Y. V.; Vaivads, A.; Krasnoselskikh, V.

    2013-12-01

    Using multi-spacecraft Cluster observations of the Earth's bow shock we estimate the electrostatic potential across a supercritical quasi-perpendicular collisionless shock. We find the potential values of the order of several kV, which correspond roughly to the kinetic energy of the inflowing solar wind. It is expected that the plasma flow in the de Hoffmann-Teller frame is field-aligned, and thus the potential computed in this frame is the parallel potential experienced by both ions and electrons. Contrary to this expectation, we show that most of the potential computed in the de Hoffmann-Teller frame is contributed by sub-proton scale Hall electric field, E~JxB/ne, which exists due to decoupling of electron and ion motions at such small scales (ions are demagnetized, and electrons are still well magnetized), and therefore the electron motion in such field is perpendicular to B. In order to calculate the parallel potential drop experienced by electrons, one needs to go to the 'electron' Hoffmann-Teller frame at small scales, in which the JxB/ne field is zero. In this 'electron' frame we find much smaller values of the potential drop across the shock of the order of 100 eV, which is comparable to the change of electron temperature across the shock, and is in agreement with theoretical estimates.

  5. Electrostatic Potentials from Self-Consistent Hirshfeld Atomic Charges.

    PubMed

    Van Damme, Sofie; Bultinck, Patrick; Fias, Stijn

    2009-02-10

    It is shown that molecular electrostatic potentials obtained from iterative or self-consistent Hirshfeld atomic point charges agree remarkably well with the ab initio computed electrostatic potentials. The iterative Hirshfeld scheme performs nearly as well as electrostatic potential derived atomic charges, having the advantage of allowing the definition of the atom in the molecule, rather than just yielding charges. The quality of the iterative Hirshfeld charges for computing electrostatic potentials is examined for a large set of molecules and compared to other commonly used techniques for population analysis. PMID:26610109

  6. A review of factors affecting electrostatic charging of pharmaceuticals and adhesive mixtures for inhalation.

    PubMed

    Kaialy, Waseem

    2016-04-30

    Pharmaceutical powders are typically insulators consisting of relatively small particles and thus they usually exhibit significant electrostatic charging behaviours. In the inhalation field, the measurement of electrostatic charge is an imperative stage during pharmaceutical formulation development. The electrostatic charge is affected by the interplay of many factors. This article reviews the factors affecting the electrostatic charging of pharmaceutical powders with a focus on dry powder inhalations. The influences of particle resistivity, size distribution, shape distribution, surface roughness, polymorphic form and hygroscopicity, as well as the effects of moisture uptake, environmental conditions, pharmaceutical processing (i.e., milling, sieving, spray drying and blending), and storage on the electrostatic charge behaviours of pharmaceuticals, with focus on inhalation powders, were reviewed. The influence of electrostatic charge on the performance of dry powder inhaler formulations in terms of drug content homogeneity, the passage of drug through the inhaler device, drug-carrier adhesion/detachment, and drug deposition on the respiratory airways were discussed. The understanding gained is crucial to improving the safety, quality, and efficiency of the pharmaceutical inhalation products. PMID:26836710

  7. Effect of hydrogen ion concentration and electrostatic polarity on food powder coating transfer efficiency and adhesion.

    PubMed

    Setyo, D; Barringer, S

    2007-08-01

    Two kinds of soy protein isolate, rice protein, whey protein isolate, albumen, bovine collagen hydrolysate, NaCl, and corn starch were used in this study. Solutions were prepared by mixing the powder and distilled water (1:8 ratio) and either H(2)SO(4) or NH(4)OH to obtain pH 3, 5, 7, 9, and 11. The solutions were dried to produce powders with different hydrogen ion concentrations and the powders were ground. Powders were coated nonelectrostatically and using negative and positive polarity corona electrostatically. There was no solution pH effect on transfer efficiency or adhesion for most powders. However, transfer efficiency and density of both of the soy protein isolates and corn starch changed with solution pH. Solution pH may have affected the density, which affected the transfer efficiency for these powders. Adhesion and cohesiveness of one of the soy protein isolates and corn starch also changed with solution pH. Solution pH may have affected the cohesiveness, which affected the adhesion for these powders. Negative and positive coronas produced the same results for most powders, with no solution pH effect, except for one of the soy protein isolates, rice protein, and corn starch. These powders accumulated on the electrode wires during negative corona electrostatic coating, reducing transfer efficiency and adhesion. This polarity effect was intermittent, implying it is due to tribocharging. PMID:17995680

  8. The Calculation of the Electrostatic Potential of Infinite Charge Distributions

    ERIC Educational Resources Information Center

    Redzic, Dragan V.

    2012-01-01

    We discuss some interesting aspects in the calculation of the electrostatic potential of charge distributions extending to infinity. The presentation is suitable for the advanced undergraduate level. (Contains 3 footnotes.)

  9. Scanning Surface Potential Microscopy of Spore Adhesion on Surfaces

    SciTech Connect

    Lee, Ida; Chung, Eunhyea; Kweon, Hyojin; Yiacoumi, Sotira; Tsouris, Costas

    2012-01-01

    The adhesion of spores of Bacillus anthracis - the cause of anthrax and a likely biological threat - to solid surfaces is an important consideration in cleanup after an accidental or deliberate release. However, because of safety concerns, directly studying B. anthracis spores with advanced instrumentation is problematic. As a first step, we are examining the electrostatic potential of Bacillus thuringiensis (Bt), which is a closely related species that is often used as a simulant to study B. anthracis. Scanning surface potential microscopy (SSPM), also known as Kelvin probe force microscopy (KPFM), was used to investigate the influence of relative humidity (RH) on the surface electrostatic potential of Bt that had adhered to silica, mica, or gold substrates. AFM/SSPM side-by-side images were obtained separately in air, at various values of RH, after an aqueous droplet with spores was applied on each surface and allowed to dry before measurements. In the SSPM images, a negative potential on the surface of the spores was observed compared with that of the substrates. The surface potential decreased as the humidity increased. Spores were unable to adhere to a surface with an extremely negative potential, such as mica.

  10. Hyaluronan-based pericellular matrix: substrate electrostatic charges and early cell adhesion events.

    PubMed

    Fotia, Caterina; Messina, Grazia M L; Marletta, Giovanni; Baldini, Nicola; Ciapetti, Gabriela

    2013-01-01

    Cells are surrounded by a hyaluronan-rich coat called 'pericellular matrix' (PCM), mainly constituted by hyaluronan, a long-chain linear polysaccharide which is secreted and resorbed by the cell, depending on its activity. Cell attachment to a surface is mediated by PCM before integrins and focal adhesions are involved. As hyaluronan is known to bear a negative charge at physiological pH, the relevance of its electrical properties in driving the early cell adhesion steps has been studied, exploring how PCM mediates cell adhesion to charged surfaces, such as polyelectrolyte multilayer (PEM) films. Poly(ethylene imine) (PEI) and poly(sodium 4-styrene sulphonate) (PSS), assembled as PEI/PSS and PEI/PSS/PEI layers, were used. The nanoscale morphology of such layers was analysed by atomic force microscopy, and the detailed surface structure was analysed by X-ray photoemission spectroscopy. PCM-coated and PCM-depleted MG63 osteoblast-like cells were used, and cell density, morphology and adhesive structures were analysed during early steps of cell attachment to the PEM surfaces (1-6 h). The present study demonstrates that the pericellular matrix is involved in cell adhesion to material surfaces, and its arrangement depends on the cell interaction with the surface. Moreover, the PCM/surface interaction is not simply driven by electrostatic effects, as the cell response may be affected by specific chemical groups at the material surface. In the development of biomimetic surfaces promoting cell adhesion and function, the role of this unrecognised outer cell structure has to be taken into account. PMID:24052426

  11. 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. PMID:22107171

  12. Realistic electrostatic potentials in a neutron star crust

    NASA Astrophysics Data System (ADS)

    Ebel, Claudio; Mishustin, Igor; Greiner, Walter

    2015-10-01

    We study the electrostatic properties of inhomogeneous nuclear matter which can be formed in the crusts of neutron stars or in supernova explosions. Such matter is represented by Wigner-Seitz cells of different geometries (spherical, cylindrical, cartesian), which contain nuclei, free neutrons and electrons under the conditions of electrical neutrality. Using the Thomas-Fermi approximation, we have solved the Poisson equation for the electrostatic potential and calculated the corresponding electron density distributions in individual cells. The calculations are done for different shapes and sizes of the cells and different average baryon densities. The electron-to-baryon fraction was fixed at 0.3. Using realistic electron distributions leads to a significant reduction in electrostatic energy and electron chemical potential.

  13. Potential Polymeric Sphere Construction Materials for a Spacecraft Electrostatic Shield

    NASA Technical Reports Server (NTRS)

    Smith, Joseph G., Jr.; Smith, Trent; Williams, Martha; Youngquist, Robert; Mendell, Wendell

    2006-01-01

    An electrostatic shielding concept for spacecraft radiation protection under NASA s Exploration Systems Research and Technology Program was evaluated for its effectiveness and feasibility. The proposed shield design is reminiscent of a classic quadrupole with positively and negatively charged spheres surrounding the spacecraft. The project addressed materials, shield configuration, power supply, and compared its effectiveness to that of a passive shield. The report herein concerns the identification of commercially available materials that could be used in sphere fabrication. It was found that several materials were needed to potentially construct the spheres for an electrostatic shield operating at 300 MV.

  14. Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular Materials

    NASA Technical Reports Server (NTRS)

    Marshall, J.; Weislogel, M.; Jacobson, T.

    1999-01-01

    The bulk behavior of dispersed, fluidized, or undispersed stationary granular systems cannot be fully understood in terms of adhesive/cohesive properties without understanding the role of electrostatic forces acting at the level of the grains themselves. When grains adhere to a surface, or come in contact with one another in a stationary bulk mass, it is difficult to measure the forces acting on the grains, and the forces themselves that induced the cohesion and adhesion are changed. Even if a single grain were to be scrutinized in the laboratory, it might be difficult, perhaps impossible, to define the distribution and character of surface charging and the three-dimensional relationship that charges (electrons, holes) have to one another. The hypothesis that we propose to test in microgravity (for dielectric materials) is that adhesion and cohesion of granular matter are mediated primarily by dipole forces that do not require the presence of a net charge; in fact, nominally electrically neutral materials should express adhesive and cohesive behavior when the neutrality results from a balance of positive and negative charge carriers. Moreover, the use of net charge alone as a measure of the electrical nature of grain-to-grain relationships within a granular mass may be misleading. We believe that the dipole forces arise from the presence of randomly-distributed positive and negative fixed charge carriers on grains that give rise to a resultant dipole moment. These dipole forces have long-range attraction. Random charges are created whenever there is triboelectrical activity of a granular mass, that is, whenever the grains experience contact/separation sequences or friction.

  15. Pulse voltage determination for electrostatic micro manipulation considering surface conductivity and adhesion of glass particle

    NASA Astrophysics Data System (ADS)

    Fujiwara, Ryo; Hemthavy, Pasomphone; Takahashi, Kunio; Saito, Shigeki

    2015-05-01

    A model with surface conductivity and adhesional force is proposed to investigate the mechanism for electrostatic micro manipulation of a dielectric object using a single probe. The manipulation system consists of three elements: a conductive probe as a manipulator, a conductive plate as a substrate, and a dielectric particle as the target object for manipulation. The particle can be successfully picked up/placed if a rectangular pulse voltage is applied between the probe and the plate. The reliability of the picking up/placing operation is improved by applying a pulse voltage that is determined by a theoretical model considering surface conductivity and adhesion. To verify the theoretical prediction, manipulation experiment is conducted using soda-lime glass particles with radii of 20 μm and 40 μm.

  16. Electrostatics

    NASA Astrophysics Data System (ADS)

    Wallace, John P.; Wallace, Michael J.

    2015-12-01

    Quantum mechanics should be able to generate the basic properties of a particle. One of the most basic properties are charge and the associated electrostatic electric field. Electrostatic force is a fundamental characteristics of a charged fermion and should have its nature described by the fermion's structure. To produce the particle properties require two spaces that define both their dynamics and their base structure. Relativity and the conservation of energy dictate how these two separate spaces are connected and the differential equations that describe behavior within these two spaces. The main static characteristic of an elementary fermion are mass and charge. Mass represents a scale measure of the fermion and it appears that charge results from the detailed structure of the fermion, which must merge into the electric field description of Maxwell. Coulomb's law is a good approximation for large distances, but it is a poor approximation at dimension on the order of a particle's Compton wavelength. The relativistic description of the fermion in its own frame of reference contains the information required for producing the electrostatic field over all space without a singularity as a source. With this description it is possible to understand the first order correction to the ionization energy of hydrogen. The role of nuclear effects on ionization energies can now be better defined for nuclei heavier than hydrogen.

  17. Electrostatics

    SciTech Connect

    Wallace, John P.; Wallace, Michael J.

    2015-12-04

    Quantum mechanics should be able to generate the basic properties of a particle. One of the most basic properties are charge and the associated electrostatic electric field. Electrostatic force is a fundamental characteristics of a charged fermion and should have its nature described by the fermion’s structure. To produce the particle properties require two spaces that define both their dynamics and their base structure. Relativity and the conservation of energy dictate how these two separate spaces are connected and the differential equations that describe behavior within these two spaces. The main static characteristic of an elementary fermion are mass and charge. Mass represents a scale measure of the fermion and it appears that charge results from the detailed structure of the fermion, which must merge into the electric field description of Maxwell. Coulomb’s law is a good approximation for large distances, but it is a poor approximation at dimension on the order of a particle’s Compton wavelength. The relativistic description of the fermion in its own frame of reference contains the information required for producing the electrostatic field over all space without a singularity as a source. With this description it is possible to understand the first order correction to the ionization energy of hydrogen. The role of nuclear effects on ionization energies can now be better defined for nuclei heavier than hydrogen.

  18. Analytic model of aurorally coupled magnetospheric and ionospheric electrostatic potentials

    NASA Astrophysics Data System (ADS)

    Cornwall, John M.

    1993-09-01

    This paper describes modest but significant improvements on earlier studies of electrostatic potential structure in the auroral region, using the adiabatic auroral arc model. With certain simplifying assumptions, new analytic nonlinear solutions fully exhibiting the parametric dependence of potentials on magnetospheric (e.g., cross-tail potential) and ionospheric (e.g., recombination rate) parameters are found. No purely phenomenological parameters are introduced. The results are in reasonable agreement with observed average auroral potential drops, inverted-V scale sizes, and dissipation rates. The dissipation rate is quite comparable to tail energization and transport rates and should have a major effect on tail and magnetospheric dynamics. Various relations between the cross-tail potential and auroral parameters (e.g., total parallel currents and potential drops) are given which can be studied with existing data sets.

  19. Analytic model of aurorally coupled magnetospheric and ionospheric electrostatic potentials

    NASA Technical Reports Server (NTRS)

    Cornwall, John M.

    1993-01-01

    This paper describes modest but significant improvements on earlier studies of electrostatic potential structure in the auroral region, using the adiabatic auroral arc model. With certain simplifying assumptions, new analytic nonlinear solutions fully exhibiting the parametric dependence of potentials on magnetospheric (e.g., cross-tail potential) and ionospheric (e.g., recombination rate) parameters are found. No purely phenomenological parameters are introduced. The results are in reasonable agreement with observed average auroral potential drops, inverted-V scale sizes, and dissipation rates. The dissipation rate is quite comparable to tail energization and transport rates and should have a major effect on tail and magnetospheric dynamics. Various relations between the cross-tail potential and auroral parameters (e.g., total parallel currents and potential drops) are given which can be studied with existing data sets.

  20. Multilevel Summation of Electrostatic Potentials Using Graphics Processing Units*

    PubMed Central

    Hardy, David J.; Stone, John E.; Schulten, Klaus

    2009-01-01

    Physical and engineering practicalities involved in microprocessor design have resulted in flat performance growth for traditional single-core microprocessors. The urgent need for continuing increases in the performance of scientific applications requires the use of many-core processors and accelerators such as graphics processing units (GPUs). This paper discusses GPU acceleration of the multilevel summation method for computing electrostatic potentials and forces for a system of charged atoms, which is a problem of paramount importance in biomolecular modeling applications. We present and test a new GPU algorithm for the long-range part of the potentials that computes a cutoff pair potential between lattice points, essentially convolving a fixed 3-D lattice of “weights” over all sub-cubes of a much larger lattice. The implementation exploits the different memory subsystems provided on the GPU to stream optimally sized data sets through the multiprocessors. We demonstrate for the full multilevel summation calculation speedups of up to 26 using a single GPU and 46 using multiple GPUs, enabling the computation of a high-resolution map of the electrostatic potential for a system of 1.5 million atoms in under 12 seconds. PMID:20161132

  1. Coarse-graining the electrostatic potential via distributed multipole expansions

    PubMed Central

    Gramada, Apostol; Bourne, Philip E.

    2011-01-01

    Multipole expansions offer a natural path to coarse-graining the electrostatic potential. However, the validity of the expansion is restricted to regions outside a spherical enclosure of the distribution of charge and, therefore, not suitable for most applications that demand accurate representation at arbitrary positions around the molecule. We propose and demonstrate a distributed multipole expansion approach that resolves this limitation. We also provide a practical algorithm for the computational implementation of this approach. The method allows the partitioning of the charge distribution into subsystems so that the multipole expansion of each component of the partition, and therefore of their superposition, is valid outside an enclosing surface of the molecule of arbitrary shape. The complexity of the resulting coarse-grained model of electrostatic potential is dictated by the area of the molecular surface and therefore, for a typical three-dimensional molecule, it scale as N2/3 with N, the number of charges in the system. This makes the method especially useful for coarse-grained studies of biological systems consisting of many large macromolecules provided that the configuration of the individual molecules can be approximated as fixed. PMID:21572587

  2. The Charge Density and Electrostatic Potential of Three Dinitramide Salts

    NASA Astrophysics Data System (ADS)

    Martin, Anthony

    The aim of this dissertation was to obtain information about the redistribution of electrons due to effects such as chemical bonding using X-ray diffraction. There is a great deal of current interest in the production of new energetic materials. A new class of the salts based on the dinitramide anion, N(NO _2)_sp{2}{-}, DN has attracted some interest. Three dinitramide salts (ammonium, monoprotonated and diprotonated biguanidinium) have been selected for charge density analyses on the basis of the observed variation of the dinitramide anion in the room temperature structures and the potential applications of these compounds. However, while a good deal of work has gone into the methodology of charge density studies, relatively little has been done to improve the presentation of the results. As a result the quality of presentation has remained essentially unchanged for twenty years. While this may sound like a triviality, it is visualization of data that produces information. Existing programs have been modified to produce output suitable for improved visualization, in particular using color and 3D computer graphics. From a chemist's viewpoint there were two aims for this project. The first was to see if the difference in the geometries of the dinitramide ion is reflected in the size and shape of the bonding electron density using experimental methods. The second aim was to obtain the electrostatic potential of the materials based on the experimentally determined electron density distribution in order to obtain some insight into the reactivity of the dinitramide ion. The different geometries produce observable differences in the deformation density. The electrostatic potential derived from the experimental electron density also shows variations with respect to the geometry and environment. These potentials have different minima and are also different from potentials produced from gas phase semi-empirical and ab-initio calculations. Whether the reactivity can be

  3. The theory of Langmuir probes in strong electrostatic potential structures

    NASA Technical Reports Server (NTRS)

    Borovsky, J. E.

    1986-01-01

    The operation of collecting and emitting Langmuir probes and double probes within time-stationary strong electrostatic potential structures is analyzed. The cross sections of spherical and cylindrical probes to charged particles within the structures are presented and used to obtain the current-voltage characteristics of idealized probes. The acquisition of plasma parameters from these characteristics is outlined, and the operation of idealized floating double-probe systems is analyzed. Probe surface effects are added to the idealized theory, and some surface effects pertinent to spacecraft probes are quantified. Magnetic field effects on idealized probes are examined, and the time required for floating probes to change their potentials by collecting charge and by emitting photoelectrons is discussed. Calculations on the space-charge effects of probe-perturbed beams and on the space-charge limiting of electron emission are given in an appendix.

  4. Analytic model of aurorally coupled magnetospheric and ionospheric electrostatic potentials

    NASA Technical Reports Server (NTRS)

    Cornwall, J. M.

    1994-01-01

    This paper describes modest but significant improvements on earlier studies of electrostatic potential structure in the auroral region using the adiabatic auroral arc model. This model has crucial nonlinearities (connected, for example. with aurorally produced ionization) which have hampered analysis; earlier work has either been linear, which I will show is a poor approximation or, if nonlinear, either numerical or too specialized to study parametric dependencies. With certain simplifying assumptions I find new analytic nonlinear solutions fully exhibiting the parametric dependence of potentials on magnetospheric (e.g.. cross-tail potential) and ionospheric (e.g., recombination rate) parameters. No purely phenomenological parameters are introduced. The results are in reasonable agreement with observed average auroral potential drops, inverted-V scale sizes, and dissipation rates. The dissipation rate is quite comparable to tail energization and transport rates and should have a major effect on tail and magnetospheric dynamics. This paper gives various relations between the cross-tail potential and auroral parameters (e.g., total parallel currents and potential drops) which can be studied with existing data sets.

  5. Determination of the electrostatic potential difference between DNA and the solution containing it: A kinetic approach

    NASA Astrophysics Data System (ADS)

    Carrasco, Mario; Coca, Raquel; Cruz, Isabel; Daza, Silvia; Espina, Manuela; Garcia-Fernandez, Emilio; Guerra, Francisco J.; León, Rafael; Marchena, María J.; Pérez, Inmaculada; Puente, Manuel; Suárez, Esteban; Valencia, Inmaculada; Villalba, Inmaculada; Jiménez, Rafael

    2007-06-01

    A kinetic approach to determine the electrostatic potential difference in soft interfaces, when classical methods fail, is presented. The method is based on electrostatic and non-electrostatic separation of the binding constant of one reactant to one of the phases. Here the method is applied to the DNA/water interface. Reliable results are obtained using as probes the reactions [Ru(NH)5pz]+SO82- and [Co(NH 3) 5pz] 3+ + [Fe(CN) 6] 4-.

  6. Molecular dynamics study of electrostatic potential along lipid bilayer with gramicidin A

    NASA Astrophysics Data System (ADS)

    Saito, Hiroaki; Nishimura, Megumi; Takagi, Hiroyuki; Miyakawa, Takeshi; Kawaguchi, Kazutomo; Nagao, Hidemi

    2013-02-01

    The structure and electrostatic potential profile of the DMPC lipid bilayers with a gramicidin A (GA) were studied by molecular dynamics (MD) simulation. The MD simulation reproduced the effect of GA on the membrane structure; the area per lipid decreases and membrane thickness increases, and the observed membrane structures correspond to the experimental data. The polar headgroup of lipid was found to orient toward the membrane normal as the lipid approaches the GA. The observed electrostatic potential map showed that the electrostatic potential around the region of GA gate was lower than the others at the same level of the membrane normal and the values of electrostatic potential in the pore region of GA were negative. These results indicate that a cation in the aqueous region of membrane can be electrostatically led to the GA entrance and penetrate the GA channel following the gradient of ion concentration.

  7. Structural origins of redox potentials in Fe-S proteins: electrostatic potentials of crystal structures.

    PubMed Central

    Swartz, P D; Beck, B W; Ichiye, T

    1996-01-01

    Redox potentials often differ dramatically for homologous proteins that have identical redox centers. For two types of iron-sulfur proteins, the rubredoxins and the high-potential iron-sulfur proteins (HiPIPs), no structural explanations for these differences have been found. We calculated the classical electrostatic potential at the redox site using static crystal structures of four rubredoxins and four HiPIPs to identify important structural determinants of their redox potentials. The contributions from just the backbone and polar side chains are shown to explain major features of the experimental redox potentials. For instance, in the rubredoxins, the presence of Val 44 versus Ala 44 causes a backbone shift that explains a approximately 50 mV lower redox potential in one of the four rubredoxins. This result is consistent with experimental redox potentials of five additional rubredoxins with known sequence. Also, we attribute the unusually lower redox potentials of two of the HiPIPs studied to a less positive electrostatic environment around their redox sites. Finally, molecular dynamics simulations of solvent around static rubredoxin crystal structures indicate that water alone is a major factor in dampening the contribution of charged side chains, in accord with experiments showing that mutations of surface charges produce relatively little effect on redox potentials. Images FIGURE 1 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 PMID:8968568

  8. Noncontact measurement of electrostatic fields: Verification of modeled potentials within ion mobility spectrometer drift tube designs

    SciTech Connect

    Scott, Jill R.; Tremblay, Paul L.

    2007-03-15

    The heart of an ion mobility spectrometer is the drift region where ion separation occurs. While the electrostatic potentials within a drift tube design can be modeled, no method for independently validating the electrostatic field has previously been reported. Two basic drift tube designs were modeled using SIMION 7.0 to reveal the expected electrostatic fields: (1) A traditional alternating set of electrodes and insulators and (2) a truly linear drift tube. One version of the alternating electrode/insulator drift tube and two versions of linear drift tubes were then fabricated. The stacked alternating electrodes/insulators were connected through a resistor network to generate the electrostatic gradient in the drift tube. The two linear drift tube designs consisted of two types of resistive drift tubes with one tube consisting of a resistive coating within an insulating tube and the other tube composed of resistive ferrites. The electrostatic fields within each type of drift tube were then evaluated by a noncontact method using a Kelvin-Zisman type electrostatic voltmeter and probe (results for alternative measurement methods provided in supplementary material). The experimental results were then compared with the electrostatic fields predicted by SIMION. Both the modeling and experimental measurements reveal that the electrostatic fields within a stacked ion mobility spectrometer drift tube are only pseudo-linear, while the electrostatic fields within a resistive drift tube approach perfect linearity.

  9. Adhesion of dry and wet electrostatic capture silk of uloborid spider.

    PubMed

    Elettro, Hervé; Neukirch, Sébastien; Antkowiak, Arnaud; Vollrath, Fritz

    2015-08-01

    We demonstrate the impressive adhesive qualities of uloborid spider orb-web capture when dry, which are lost when the nano-filament threads are wetted. A force sensor with a 50 nN-1 mN detection sensitively allowed us to measure quantitatively the stress-strain characteristics of native silk threads in both the original dry state and after wetting by controlled application of water mist with droplet sizes ranging between 3 and 5 μm and densities ranging between 10(4) and 10(5) per mm(3). Stress forces of between 1 and 5 μN/μm(2) in the native, dry multifilament thread puffs were reduced to between 0.1 and 0.5 μN/μm(2) in the wetted collapsed state, with strain displacements reducing from between 2 and 5 mm in the dry to 0.10-0.12 mm in the wetted states. We conclude that wetting cribellate threads reduce their van der Waals adhesion with implications on the thread's adhesive strength under tension. This should be considered when discussing the evolutionary transitions of capture silks from the ancestral dry-state nano-filaments of the cribellate spider taxa to the wet-state glue-droplets of the ecribellate taxa. PMID:26148900

  10. Adhesion of dry and wet electrostatic capture silk of uloborid spider

    NASA Astrophysics Data System (ADS)

    Elettro, Hervé; Neukirch, Sébastien; Antkowiak, Arnaud; Vollrath, Fritz

    2015-08-01

    We demonstrate the impressive adhesive qualities of uloborid spider orb-web capture when dry, which are lost when the nano-filament threads are wetted. A force sensor with a 50 nN-1 mN detection sensitively allowed us to measure quantitatively the stress-strain characteristics of native silk threads in both the original dry state and after wetting by controlled application of water mist with droplet sizes ranging between 3 and 5 μm and densities ranging between 104 and 105 per mm3. Stress forces of between 1 and 5 μN/μm2 in the native, dry multifilament thread puffs were reduced to between 0.1 and 0.5 μN/μm2 in the wetted collapsed state, with strain displacements reducing from between 2 and 5 mm in the dry to 0.10-0.12 mm in the wetted states. We conclude that wetting cribellate threads reduce their van der Waals adhesion with implications on the thread's adhesive strength under tension. This should be considered when discussing the evolutionary transitions of capture silks from the ancestral dry-state nano-filaments of the cribellate spider taxa to the wet-state glue-droplets of the ecribellate taxa.

  11. Coarse Point Charge Models For Proteins From Smoothed Molecular Electrostatic Potentials.

    PubMed

    Leherte, Laurence; Vercauteren, Daniel P

    2009-12-01

    To generate coarse electrostatic models of proteins, we developed an original approach to hierarchically locate maxima and minima in smoothed molecular electrostatic potentials. A charge-fitting program was used to assign charges to the so-obtained reduced representations. Templates are defined to easily generate coarse point charge models for protein structures, in the particular cases of the Amber99 and Gromos43A1 force fields. Applications to four small peptides and to the ion channel KcsA are presented. Electrostatic potential values generated by the reduced models are compared with the corresponding values obtained using the original sets of atomic charges. PMID:26602509

  12. MULTIPOLE EXPANSION TECHNIQUES FOR THE CALCULATION AND CHARACTERIZATION OF MOLECULAR ELECTROSTATIC POTENTIALS

    EPA Science Inventory

    The electrostatic interaction between a chemical and its site of biological action is often important in determining biological activity. In order to include this interaction in methods to assess the potential biological activity of large molecules, rapid and reliable techniques ...

  13. QUANTITATIVE COMPARISON OF MOLECULAR ELECTROSTATIC POTENTIALS FOR STRUCTURE-ACTIVITY STUDIES

    EPA Science Inventory

    Further development of an approach for representing, efficiently calculating and comparing discreet 3-dimensional molecular electrostatic potentials using a quantitative similarity index (MEP-SI) based on the Carbo formalism is presented. adial-type (MACRA) grid representation is...

  14. Electrostatic potential of ferroelectric PbTiO{sub 3}: Visualized electron polarization of Pb ion

    SciTech Connect

    Tanaka, Hiroshi; Kuroiwa, Yoshihiro; Takata, Masaki

    2006-11-01

    A different method is proposed to evaluate the electrostatic potential and electric field from x-ray diffraction data by using maximum entropy method. The efficiency of the method is revealed in the application to a ferroelectric material PbTiO{sub 3}. Visualized electrostatic potential and electric field on the charge density distribution give a direct evidence for the dipolar polarization of the Pb ion. They show close agreement with results by ab initio calculations.

  15. Topological properties of the electrostatic potential in weak and moderate N...H hydrogen bonds.

    PubMed

    Mata, Ignasi; Molins, Elies; Alkorta, Ibon; Espinosa, Enrique

    2007-07-19

    The topological analyses of the electrostatic potential phi(r) and the electron density distribution rho(r) have been performed for a set of 20 neutral complexes with weak and moderate N...H bonds. In all cases, a zero flux surface of the electrostatic potential containing a saddle point analogous to the bond critical point of the electron density distribution is observed. These surfaces define an equivalent of the atomic basin of rho(r) for the electrostatic potential, which exhibits zero net charge and can be regarded as an electrostatically isolated region if its volume is finite. The phi(r) and rho(r) zero flux surfaces divide the hydrogen-bonding region in three parts, being the central one related to the electrostatic interaction between donor and acceptor. This central region exhibits a relative size of approximately 13-14% of the N...H distance dNH, it belongs to the outermost shell of the nitrogen and is mainly associated with its lone pair. Topological properties of both rho(r) and phi(r), as well as the electron kinetic (G) and potential (V) energy densities, show similar dependences with dNH at both bond critical points (phi-BCP and rho-BCP). Phenomenological proportionalities between the rho(r) curvatures and G and V are also found at the electrostatic potential critical point. The curvatures of the electrostatic potential, which are interpreted in terms of the electrostatic forces in the bonding region, present the same exponential dependency as the electron density distribution, to which they are related by Poisson's equation. PMID:17583329

  16. Molecular electrostatic potential at the atomic sites in the effective core potential approximation.

    PubMed

    Lesiuk, Michał; Zachara, Janusz

    2013-02-21

    Considering calculations of the molecular electrostatic potential at the atomic sites (MEP@AS) in the presence of effective core potentials (ECP), we found that the consequent use of the definition of MEP@AS based on the energy derivative with respect to nuclear charge leads to a formula that differs by one term from the result of simple application of Coulomb's law. We have developed a general method to analytically treat derivatives of ECP with respect to nuclear charge. Benchmarking calculations performed on a set of simple molecules show that our formula leads to a systematic decrease in the error connected with the introduction of ECP when compared to all-electron results. Because of a straightforward implementation and relatively low costs of the developed procedure we suggest to use it by default. PMID:23444997

  17. Molecular electrostatic potential at the atomic sites in the effective core potential approximation

    NASA Astrophysics Data System (ADS)

    Lesiuk, Michał; Zachara, Janusz

    2013-02-01

    Considering calculations of the molecular electrostatic potential at the atomic sites (MEP@AS) in the presence of effective core potentials (ECP), we found that the consequent use of the definition of MEP@AS based on the energy derivative with respect to nuclear charge leads to a formula that differs by one term from the result of simple application of Coulomb's law. We have developed a general method to analytically treat derivatives of ECP with respect to nuclear charge. Benchmarking calculations performed on a set of simple molecules show that our formula leads to a systematic decrease in the error connected with the introduction of ECP when compared to all-electron results. Because of a straightforward implementation and relatively low costs of the developed procedure we suggest to use it by default.

  18. The effect of surface conductivity and adhesivity on the electrostatic manipulation condition for dielectric microparticles using a single probe

    NASA Astrophysics Data System (ADS)

    Fujiwara, Ryo; Hemthavy, Pasomphone; Takahashi, Kunio; Saito, Shigeki

    2016-05-01

    By clarifying the effect of surface conductivity and adhesivity on the electrostatic manipulation condition, a dielectric particle made of any material can be manipulated with surface conductivity. The manipulation system consists of three elements: a conductive probe as a manipulator, a conductive plate as a substrate, and a dielectric particle as the target object for manipulation. The particle can be successfully picked up/placed if a rectangular pulse voltage is applied between the probe and the plate. Four kinds of particle materials are used in the experiment: silica, soda-lime glass, polymethyl methacrylate coated by conductive polymer, and polystyrene coated by surfactant. The radius of each particle is 15 μm. A first-order resistor-capacitor (RC) circuit model is adopted to describe the effect of surface conductivity and adhesivity on the manipulation condition. The manipulation system is modeled as a series circuit consisting of a resistor and a capacitor by considering the surface conductivity. A detachment voltage is defined as the capacitance voltage to detach the particle adhered to the plate or probe. Parameters of the RC model, surface resistance, surface capacitance and detachment voltage are identified by a simulation and measurements. To verify the RC model, the particle’s behavior is observed by a high-speed camera, and the electrical current is measured by an electrometer. A manipulation experiment is demonstrated to show the effectiveness of the model. The particle reaction is observed for each duration and magnitude of the pulse voltage for the manipulation. The optimum pulse voltage for successful manipulation is determined by the parameters of the RC model as the standard. This knowledge is expected to expand the possibility of micro-fabrication technology.

  19. Electrostatic Forces: Formulas for the First Derivatives of a Polarizable, Anisotropic Electrostatic Potential Energy Function Based on Machine Learning.

    PubMed

    Mills, Matthew J L; Popelier, Paul L A

    2014-09-01

    Explicit formulas are derived analytically for the first derivatives of a (i) polarizable, (ii) high-rank multipolar electrostatic potential energy function for (iii) flexible molecules. The potential energy function uses a machine learning method called Kriging to predict the local-frame multipole moments of atoms defined via the Quantum Chemical Topology (QCT) approach. These atomic multipole moments then interact via an interaction tensor based on spherical harmonics. Atom-centered local coordinate frames are used, constructed from the internal geometry of the molecular system. The forces involve derivatives of both this geometric dependence and of the trained kriging models. In the near future, these analytical forces will enable molecular dynamics and geometry optimization calculations as part of the QCT force field. PMID:26588529

  20. Adhesion

    MedlinePlus

    ... adhesions Ovarian cyst References Munireddy S, Kavalukas SL, Barbul A. Intra-abdominal healing: gastrointestinal tract and adhesions. Surg Clin N Am Kulaylat MN, Dayton, MT. Surgical complications. In: Townsend CM Jr, Beauchamp RD, Evers BM, Mattox KL, ...

  1. Modeling the Electrostatic Potential of Asymmetric Lipopolysaccharide Membranes: The MEMPOT Algorithm Implemented in DelPhi

    PubMed Central

    Soares, Thereza A.; Alexov, Emil

    2014-01-01

    Four chemotypes of the Rough lipopolysaccharides (LPS) membrane from Pseudomonas aeruginosa were investigated by a combined approach of explicit water molecular dynamics (MD) simulations and Poisson-Boltzmann continuum electrostatics with the goal to deliver the distribution of the electrostatic potential across the membrane. For the purpose of this investigation, a new tool for modeling the electrostatic potential profile along the axis normal to the membrane, MEMPOT, was developed and implemented in DelPhi. Applying MEMPOT on the snapshots obtained by MD simulations, two observations were made: (a) the average electrostatic potential has a complex profile, but is mostly positive inside the membrane due to the presence of Ca2+ ions which overcompensate for the negative potential created by lipid phosphate groups; and (b) correct modeling of the electrostatic potential profile across the membrane requires taking into account the water phase, while neglecting it (vacuum calculations) results in dramatic changes including a reversal of the sign of the potential inside the membrane. Furthermore, using DelPhi to assign different dielectric constants for different regions of the LPS membranes, it was investigated whether a single frame structure before MD simulations with appropriate dielectric constants for the lipid tails, inner, and the external leaflet regions, can deliver the same average electrostatic potential distribution as obtained from the MD-generated ensemble of structures. Indeed, this can be attained by using smaller dielectric constant for the tail and inner leaflet regions (mostly hydrophobic) than for the external leaflet region (hydrophilic) and the optimal dielectric constant values are chemotype-specific. PMID:24799021

  2. Confusing Aspects in the Calculation of the Electrostatic Potential of an Infinite Line of Charge

    ERIC Educational Resources Information Center

    Jimenez, J. L.; Campos, I.; Roa-Neri, J. A. E.

    2012-01-01

    In this work we discuss the trick of eliminating infinite potential of reference arguing that it corresponds to a constant of integration, in the problem of determining the electrostatic potential of an infinite line of charge with uniform density, and show how the problem must be tackled properly. The usual procedure is confusing for most…

  3. FINITE EXPANSION METHOD FOR THE CALCULATION AND INTERPRETATION OF MOLECULAR ELECTROSTATIC POTENTIALS

    EPA Science Inventory

    Because it is useful to have the molecular electrostatic potential as an element in a complex scheme to assess the toxicity of large molecules, efficient and reliable methods are needed for the calculation and characterization of these potentials. A multicenter multipole expansio...

  4. ELECTROSTATIC POTENTIALS OF SOME DIBENZO-P-DIOXINS IN RELATION TO THEIR BIOLOGICAL ACTIVITIES (JOURNAL VERSION)

    EPA Science Inventory

    A computational analysis of the electrostatic potentials of eight halogenated dibenzo-p-dioxins has been carried out at the ab initio SCF STO-5G level. It focuses upon the relationships between these potentials and the biological activities of the molecules, including toxicity, a...

  5. Determination of auroral electrostatic potentials using high- and low-altitude particle distributions

    NASA Technical Reports Server (NTRS)

    Reiff, P. H.; Collin, H. L.; Craven, J. D.; Burch, J. L.; Winningham, J. D.

    1988-01-01

    The auroral electrostatic potential differences were determined from the particle distribution functions obtained nearly simultaneously above and below the auroral acceleration region by DE-1 at altitudes 9000-15,000 km and DE-2 at 400-800 km. Three independent techniques were used: (1) the peak energies of precipitating electrons observed by DE-2, (2) the widening of loss cones for upward traveling electrons observed by DE-1, and (3) the energies of upgoing ions observed by DE-1. The assumed parallel electrostatic potential difference calculated by the three methods was nearly the same. The results confirmed the hypothesis that parallel electrostatic fields of 1-10 kV potential drop at 1-2 earth radii altitude are an important source for auroral particle acceleration.

  6. On stochastic heating of electrons by intense laser radiation in the presence of electrostatic potential well

    SciTech Connect

    Krasheninnikov, S. I.

    2014-10-15

    A simple model developed by Paradkar et al. [Phys. Plasmas 19, 060703 (2012)] for the study of synergistic effects of electrostatic potential well and laser radiation is extended for the case where electric field of the well is accelerating electrons moving in the direction of the laser field propagation. It was found that in these cases, the rate of stochastic heating of energetic electrons remains virtually the same as in Paradkar et al. [Phys. Plasmas 19, 060703 (2012)], where electric field in electrostatic potential was slowing down electrons moving in the direction of the laser field propagation. However, the heating of electrons with relatively low energy can be sensitive to the orientation of the electrostatic potential well with respect to the direction of the laser radiation propagation.

  7. Space and Time Evolution of the Electrostatic Potential During the Activation of a Visual Pigment.

    PubMed

    Melaccio, Federico; Calimet, Nicolas; Schapiro, Igor; Valentini, Alessio; Cecchini, Marco; Olivucci, Massimo

    2016-07-01

    Animal and microbial retinal proteins employ the Schiff base of retinal as their chromophore. Here, the possible consequences of the charge translocation associated with the light-induced dynamics of the chromophore of a visual opsin are investigated along a representative semiclassical trajectory. We show that the evolution of the electrostatic potential projected by the chromophore onto the surrounding protein displays intense but topographically localized sudden variations in proximity of the decay region. pKa calculations carried out on selected snapshots used as probes, indicate that the only residue which may be sensitive to the electrostatic potential shift is Glu181. Accordingly, our results suggest that the frail Tyr191/268-Glu181-Wat2-Ser186 hydrogen bond network may be perturbed by the transient variations of the electrostatic potential. PMID:27322155

  8. Split-illumination electron holography for improved evaluation of electrostatic potential associated with electrophotography

    SciTech Connect

    Tanigaki, Toshiaki Aizawa, Shinji; Soon Park, Hyun; Sato, Kuniaki; Akase, Zentaro; Matsuda, Tsuyoshi; Murakami, Yasukazu; Shindo, Daisuke; Kawase, Hiromitsu

    2014-03-31

    Precise evaluation of the electrostatic potential distributions of and around samples with multiple charges using electron holography has long been a problem due to unknown perturbation of the reference wave. Here, we report the first practical application of split-illumination electron holography (SIEH) to tackle this problem. This method enables the use of a non-perturbed reference wave distant from the sample. SIEH revealed the electrostatic potential distributions at interfaces of the charged particles used for development in electrophotography and should lead to dramatic improvements in electrophotography.

  9. Scanning quantum dot microscopy: A quantitative method to measure local electrostatic potential near surfaces

    NASA Astrophysics Data System (ADS)

    Green, Matthew F. B.; Wagner, Christian; Leinen, Philipp; Deilmann, Thorsten; Krüger, Peter; Rohlfing, Michael; Tautz, F. Stefan; Temirov, Ruslan

    2016-08-01

    In this paper we review a recently introduced microscopy technique, scanning quantum dot microscopy (SQDM), which delivers quantitative maps of local electrostatic potential near surfaces in three dimensions. The key to achieving SQDM imaging is the functionalization of a scanning probe microscope tip with a π-conjugated molecule that acts as a gateable QD. Mapping of electrostatic potential with SQDM is performed by gating the QD by the bias voltage applied to the scanning probe microscope junction and registering changes of the QD charge state with frequency-modulated atomic force microscopy.

  10. On the structures and mapping of auroral electrostatic potentials

    NASA Technical Reports Server (NTRS)

    Chiu, Y. T.; Newman, A. L.; Cornwall, J. M.

    1981-01-01

    The mapping of magnetospheric and ionospheric electric fields in a kinetic model of magnetospheric-ionospheric electrodynamic coupling proposed for the aurora is examined. One feature is the generalization of the kinetic current-potential relationship to the return current region (identified as a region where the parallel drop from magnetosphere to ionosphere is positive); such a return current always exists unless the ionosphere is electrically charged to grossly unphysical values. A coherent phenomenological picture of both the low energy return current and the high energy precipitation of an inverted-V is given. The mapping between magnetospheric and ionospheric electric fields is phrased in terms of a Green's function which acts as a filter, emphasizing magnetospheric latitudinal spatial scales of order (when mapped to the ionosphere) 50 to 150 km. This same length, when multiplied by electric fields just above the ionosphere, sets the scale for potential drops between the ionosphere and equatorial magnetosphere.

  11. Mapping electrostatic potentials from the ionosphere to the magnetosphere

    NASA Technical Reports Server (NTRS)

    Sojka, J. J.; Foster, J. C.; Banks, P. M.; Doupnik, J. R.

    1983-01-01

    Techniques for mapping observed ionospheric-potential distributions into the magnetosphere are discussed and illustrated using published Millstone Hill and Chatanika incoherent-scatter-radar data. It is shown that the mapping of a given field line to the equator is subject to strong diurnal and seasonal variations (attributed to the combination of internal and tail-current magnetic-field sources at auroral latitudes and the diurnal variation of solar declination in dipole coordinates) and longitude-dependent differences in ionospheric geometry. A mapping based on the tilt-dependent model of Olson and Pfitzer (1977) and using an empirical ionospheric-potential distribution derived from Chatanika plasma-drift measurements produces a relativity uniform magnetospheric electric field in the tail region. The field at 12 earth radii (Re) is found to be between 1 and 2 kV/Re; at the dawn-dusk meridian beyond the plasmasphere it is as high as 5 kV/Re. The plasmasphere is shown to have a dusk bulge in its equipotential structure and to be almost symmetric about the dawn-dusk meridian.

  12. Mapping electrostatic potentials from the ionosphere to the magnetosphere

    NASA Astrophysics Data System (ADS)

    Sojka, J. J.; Foster, J. C.; Banks, P. M.; Doupnik, J. R.

    1983-11-01

    Techniques for mapping observed ionospheric-potential distributions into the magnetosphere are discussed and illustrated using published Millstone Hill and Chatanika incoherent-scatter-radar data. It is shown that the mapping of a given field line to the equator is subject to strong diurnal and seasonal variations (attributed to the combination of internal and tail-current magnetic-field sources at auroral latitudes and the diurnal variation of solar declination in dipole coordinates) and longitude-dependent differences in ionospheric geometry. A mapping based on the tilt-dependent model of Olson and Pfitzer (1977) and using an empirical ionospheric-potential distribution derived from Chatanika plasma-drift measurements produces a relativity uniform magnetospheric electric field in the tail region. The field at 12 earth radii (Re) is found to be between 1 and 2 kV/Re; at the dawn-dusk meridian beyond the plasmasphere it is as high as 5 kV/Re. The plasmasphere is shown to have a dusk bulge in its equipotential structure and to be almost symmetric about the dawn-dusk meridian.

  13. Textbook Treatments of Electrostatic Potential Maps in General and Organic Chemistry

    ERIC Educational Resources Information Center

    Hinze, Scott R.; Williamson, Vickie M.; Deslongchamps, Ghislain; Shultz, Mary Jane; Williamson, Kenneth C.; Rapp, David N.

    2013-01-01

    Electrostatic potential maps (EPMs) allow for representation of key molecular-level information in a relatively simple and inexpensive format. As these visualizations become more prevalent in instruction, it is important to determine how students are exposed to them and supported in their use. A systematic review of current general and organic…

  14. Student Reasoning about Electrostatic and Gravitational Potential Energy: An Exploratory Study with Interdisciplinary Consequences

    ERIC Educational Resources Information Center

    Lindsey, Beth A.

    2014-01-01

    This paper describes an investigation into student reasoning about potential energy in the context of introductory electrostatics. Similar incorrect reasoning patterns emerged both in written questions administered after relevant instruction and in one-on-one interviews. These reasoning patterns are also prevalent in responses to questions posed…

  15. Determination of electrostatic potentials at biological interfaces using electron-electron double resonance.

    PubMed Central

    Shin, Y K; Hubbell, W L

    1992-01-01

    A new general method for the determination of electrostatic potentials at biological surfaces is presented. The approach is based on measurement of the collision frequency of a charged nitroxide in solution with a nitroxide fixed to the surface at the point of interest. The collision frequency is determined with 14N:15N double label electron-electron double resonance (ELDOR). As a test, the method is shown to give values for phospholipid bilayer surface potentials consistent with the Gouy-Chapman theory, a simple model shown by many independent tests to accurately describe charged, planar surfaces. In addition, the method is applied to determine the electrostatic potential near the surface of DNA. The results indicate that the potential is significantly smaller than that predicted from Poisson-Boltzmann analysis, but is in qualitative agreement with that predicted by Manning's theory of counter ion condensation. The method is readily extended to measurement of surface potentials of proteins. PMID:1319760

  16. Measurement of electrostatic potentials above oriented single photosynthetic reaction centers

    SciTech Connect

    Lee, I.; Lee, J.W.; Stubna, A.; Greenbaum, E.

    2000-03-23

    Photosystem 1 (PS 1) reaction centers are nanometer-size robust supramolecular structures that can be isolated and purified from green plants. Using the technique of Kelvin force probe microscopy, the authors report here the first measurement of exogenous photovoltages generated from single PS 1 reaction centers in a heterostructure composed of PS 1, organosulfur molecules, and atomically flat gold. Illumination of the reaction centers was achieved with a diode laser at {lambda} = 670 nm. Data sets consisting of 22 individual PS 1s measured entirely in darkness, and four PS 1s in which the light-dark transition occurred in midscan of a single PS 1 were obtained. The average values of the light minus dark voltages relative to the substrate for the four PS 1s were {minus}1.13 {+-} 0.14 and {minus}1.20 {+-} 0.19 V at diametrical peripheries and {minus}0.97 {+-} 0.04 V at the center. Under illumination, the potentials of the central region of the PS 1s were typically more positive than the periphery by 6--9 kT, where kT is the Boltzmann energy at room temperature. These energies suggest a possible mechanism whereby negatively charged ferredoxin, the soluble electron carrier from PS 1 to the Calvin-Benson cycle, is anchored and positioned at the reducing end of PS 1 for electron transfer. The results are placed in context with the prior experimental literature on the structure of the reducing end of PS 1.

  17. Visualizing the Positive-Negative Interface of Molecular Electrostatic Potentials as an Educational Tool for Assigning Chemical Polarity

    ERIC Educational Resources Information Center

    Schonborn, Konrad; Host, Gunnar; Palmerius, Karljohan

    2010-01-01

    To help in interpreting the polarity of a molecule, charge separation can be visualized by mapping the electrostatic potential at the van der Waals surface using a color gradient or by indicating positive and negative regions of the electrostatic potential using different colored isosurfaces. Although these visualizations capture the molecular…

  18. Theory, experiment and computer simulation of the electrostatic potential at crystal/electrolyte interfaces

    SciTech Connect

    Zarzycki, Piotr P.; Rosso, Kevin M.; Chatman, Shawn ME; Preocanin, Tajana; Kallay, Nikola; Piasecki, Wojciech

    2010-10-01

    In this feature article we discuss recent advances and challenges in measuring, analyzing and interpreting the electrostatic potential development at crystal/electrolyte interfaces. We highlight progress toward fundamental understanding of historically difficult aspects, including point of zero potential estimation for single faces of single crystals, the non-equilibrium pH titration hysteresis loop, and the origin of nonlinearities in the titration response. It has been already reported that the electrostatic potential is strongly affected by many second order type phenomena such as: surface heterogeneity, (sub)surface transformations, charge transfer reactions, and additional potential jumps at crystal face edges and/or Schottky barriers. Single-crystal electrode potentials seem particularly sensitive to these phenomena, which makes interpretation of experimental observations complicated. We hope that recent theory developments in our research group including an analytical model of titration hysteresis, a perturbative surface potential expansion, and a new surface complexation model that incorporates charge transfer processes will help experimental data analysis, and provide unique insights into the electrostatic response of nonpolarizable single-crystal electrodes.

  19. The electrostatic potential generated by topological atoms. II. Inverse multipole moments.

    PubMed

    Rafat, M; Popelier, P L A

    2005-11-22

    Quantum chemical topology defines finite atoms, whose bounded electron density generates a well-defined electrostatic potential. A multipole expansion based on spherical tensors provides a potential that is formally convergent outside the divergence sphere. Part I of this series [P. L. A. Popelier and M. Rafat, Chem. Phys. Lett.376, 148 (2003)] showed that a continuous multipole expansion expands the convergence region, thereby allowing the electrostatic potential to be evaluated at short range. Here, we propose a different method, based on "inverse" multipole moments, enabling an expansion that converges everywhere. These moments are defined by inverse (i.e., negative) powers of the magnitude of the position vector describing the electron density inside the atom. We illustrate this technique on nitrogen in N(2), oxygen in H(2)O, and oxygen in the phenolic group of the amino acid tyrosine. The proposed method constitutes a considerable advance over the method presented in Part I. PMID:16351236

  20. Stigmatellin Probes the Electrostatic Potential in the QB Site of the Photosynthetic Reaction Center

    PubMed Central

    Gerencsér, László; Boros, Bogáta; Derrien, Valerie; Hanson, Deborah K.; Wraight, Colin A.; Sebban, Pierre; Maróti, Péter

    2015-01-01

    The electrostatic potential in the secondary quinone (QB) binding site of the reaction center (RC) of the photosynthetic bacterium Rhodobacter sphaeroides determines the rate and free energy change (driving force) of electron transfer to QB. It is controlled by the ionization states of residues in a strongly interacting cluster around the QB site. Reduction of the QB induces change of the ionization states of residues and binding of protons from the bulk. Stigmatellin, an inhibitor of the mitochondrial and photosynthetic respiratory chain, has been proven to be a unique voltage probe of the QB binding pocket. It binds to the QB site with high affinity, and the pK value of its phenolic group monitors the local electrostatic potential with high sensitivity. Investigations with different types of detergent as a model system of isolated RC revealed that the pK of stigmatellin was controlled overwhelmingly by electrostatic and slightly by hydrophobic interactions. Measurements showed a high pK value (>11) of stigmatellin in the QB pocket of the dark-state wild-type RC, indicating substantial negative potential. When the local electrostatics of the QB site was modulated by a single mutation, L213Asp→Ala, or double mutations, L213Asp-L212Glu→Ala-Ala (AA), the pK of stigmatellin dropped to 7.5 and 7.4, respectively, which corresponds to a >210 mV increase in the electrostatic potential relative to the wild-type RC. This significant pK drop (ΔpK > 3.5) decreased dramatically to (ΔpK > 0.75) in the RC of the compensatory mutant (AA+M44Asn→AA+M44Asp). Our results indicate that the L213Asp is the most important actor in the control of the electrostatic potential in the QB site of the dark-state wild-type RC, in good accordance with conclusions of former studies using theoretical calculations or light-induced charge recombination assay. PMID:25606686

  1. Electrostatic potentials of some dibenzo-p-dioxins in relation to their biological activities (journal version)

    SciTech Connect

    Murray, J.S.; Politzer, P.

    1987-01-01

    A computational analysis of the electrostatic potentials of eight halogenated dibenzo-p-dioxins was carried out at the ab initio SCF STO-5G level. It focuses upon the relationships between these potentials and the biological activities of the molecules, including toxicity, aryl hydrocarbon hydroxylase induction and receptor binding. In general, regions of negative potential are found to be associated with the oxygens and with the halogen substituents. Biological activity appears to be related to the presence of an optimum range of negative potentials above the lateral portions of the molecules in conjunction with a weakening of those near the oxygens.

  2. Charged patchy particle models in explicit salt: Ion distributions, electrostatic potentials, and effective interactions

    SciTech Connect

    Yigit, Cemil; Dzubiella, Joachim; Heyda, Jan

    2015-08-14

    We introduce a set of charged patchy particle models (CPPMs) in order to systematically study the influence of electrostatic charge patchiness and multipolarity on macromolecular interactions by means of implicit-solvent, explicit-ion Langevin dynamics simulations employing the Gromacs software. We consider well-defined zero-, one-, and two-patched spherical globules each of the same net charge and (nanometer) size which are composed of discrete atoms. The studied mono- and multipole moments of the CPPMs are comparable to those of globular proteins with similar size. We first characterize ion distributions and electrostatic potentials around a single CPPM. Although angle-resolved radial distribution functions reveal the expected local accumulation and depletion of counter- and co-ions around the patches, respectively, the orientation-averaged electrostatic potential shows only a small variation among the various CPPMs due to space charge cancellations. Furthermore, we study the orientation-averaged potential of mean force (PMF), the number of accumulated ions on the patches, as well as the CPPM orientations along the center-to-center distance of a pair of CPPMs. We compare the PMFs to the classical Derjaguin-Verwey-Landau-Overbeek theory and previously introduced orientation-averaged Debye-Hückel pair potentials including dipolar interactions. Our simulations confirm the adequacy of the theories in their respective regimes of validity, while low salt concentrations and large multipolar interactions remain a challenge for tractable theoretical descriptions.

  3. Charged patchy particle models in explicit salt: Ion distributions, electrostatic potentials, and effective interactions.

    PubMed

    Yigit, Cemil; Heyda, Jan; Dzubiella, Joachim

    2015-08-14

    We introduce a set of charged patchy particle models (CPPMs) in order to systematically study the influence of electrostatic charge patchiness and multipolarity on macromolecular interactions by means of implicit-solvent, explicit-ion Langevin dynamics simulations employing the Gromacs software. We consider well-defined zero-, one-, and two-patched spherical globules each of the same net charge and (nanometer) size which are composed of discrete atoms. The studied mono- and multipole moments of the CPPMs are comparable to those of globular proteins with similar size. We first characterize ion distributions and electrostatic potentials around a single CPPM. Although angle-resolved radial distribution functions reveal the expected local accumulation and depletion of counter- and co-ions around the patches, respectively, the orientation-averaged electrostatic potential shows only a small variation among the various CPPMs due to space charge cancellations. Furthermore, we study the orientation-averaged potential of mean force (PMF), the number of accumulated ions on the patches, as well as the CPPM orientations along the center-to-center distance of a pair of CPPMs. We compare the PMFs to the classical Derjaguin-Verwey-Landau-Overbeek theory and previously introduced orientation-averaged Debye-Hückel pair potentials including dipolar interactions. Our simulations confirm the adequacy of the theories in their respective regimes of validity, while low salt concentrations and large multipolar interactions remain a challenge for tractable theoretical descriptions. PMID:26277163

  4. Charged patchy particle models in explicit salt: Ion distributions, electrostatic potentials, and effective interactions

    NASA Astrophysics Data System (ADS)

    Yigit, Cemil; Heyda, Jan; Dzubiella, Joachim

    2015-08-01

    We introduce a set of charged patchy particle models (CPPMs) in order to systematically study the influence of electrostatic charge patchiness and multipolarity on macromolecular interactions by means of implicit-solvent, explicit-ion Langevin dynamics simulations employing the Gromacs software. We consider well-defined zero-, one-, and two-patched spherical globules each of the same net charge and (nanometer) size which are composed of discrete atoms. The studied mono- and multipole moments of the CPPMs are comparable to those of globular proteins with similar size. We first characterize ion distributions and electrostatic potentials around a single CPPM. Although angle-resolved radial distribution functions reveal the expected local accumulation and depletion of counter- and co-ions around the patches, respectively, the orientation-averaged electrostatic potential shows only a small variation among the various CPPMs due to space charge cancellations. Furthermore, we study the orientation-averaged potential of mean force (PMF), the number of accumulated ions on the patches, as well as the CPPM orientations along the center-to-center distance of a pair of CPPMs. We compare the PMFs to the classical Derjaguin-Verwey-Landau-Overbeek theory and previously introduced orientation-averaged Debye-Hückel pair potentials including dipolar interactions. Our simulations confirm the adequacy of the theories in their respective regimes of validity, while low salt concentrations and large multipolar interactions remain a challenge for tractable theoretical descriptions.

  5. Hydrogen Bonding between Metal-Ion Complexes and Noncoordinated Water: Electrostatic Potentials and Interaction Energies.

    PubMed

    Andrić, Jelena M; Misini-Ignjatović, Majda Z; Murray, Jane S; Politzer, Peter; Zarić, Snežana D

    2016-07-01

    The hydrogen bonding of noncoordinated water molecules to each other and to water molecules that are coordinated to metal-ion complexes has been investigated by means of a search of the Cambridge Structural Database (CSD) and through quantum chemical calculations. Tetrahedral and octahedral complexes that were both charged and neutral were studied. A general conclusion is that hydrogen bonds between noncoordinated water and coordinated water are much stronger than those between noncoordinated waters, whereas hydrogen bonds of water molecule in tetrahedral complexes are stronger than in octahedral complexes. We examined the possibility of correlating the computed interaction energies with the most positive electrostatic potentials on the interacting hydrogen atoms prior to interaction and obtained very good correlation. This study illustrates the fact that electrostatic potentials computed for ground-state molecules, prior to interaction, can provide considerable insight into the interactions. PMID:26989883

  6. Theoretical and experimental electrostatic potential around the m-nitrophenol molecule.

    PubMed

    Drissi, Mokhtaria; Benhalima, Nadia; Megrouss, Youcef; Rachida, Rahmani; Chouaih, Abdelkader; Hamzaoui, Fodil

    2015-01-01

    This work concerns a comparison of experimental and theoretical results of the electron charge density distribution and the electrostatic potential around the m-nitrophenol molecule (m-NPH) known for its interesting physical characteristics. The molecular experimental results have been obtained from a high-resolution X-ray diffraction study. Theoretical investigations were performed using the Density Functional Theory at B3LYP level of theory at 6-31G* in the Gaussian program. The multipolar model of Hansen and Coppens was used for the experimental electron charge density distribution around the molecule, while we used the DFT methods for the theoretical calculations. The electron charge density obtained in both methods allowed us to find out different molecular properties such us the electrostatic potential and the dipole moment, which were finally subject to a comparison leading to a good match obtained between both methods. The intramolecular charge transfer has also been confirmed by an HOMO-LUMO analysis. PMID:25741898

  7. Electrostatic-Force-Assisted Dispensing Printing to Construct High-Aspect-Ratio of 0.79 Electrodes on a Textured Surface with Improved Adhesion and Contact Resistivity

    PubMed Central

    Shin, Dong-Youn; Yoo, Sung-Soo; Song, Hee-eun; Tak, Hyowon; Byun, Doyoung

    2015-01-01

    As a novel route to construct fine and abnormally high-aspect-ratio electrodes with excellent adhesion and reduced contact resistivity on a textured surface, an electrostatic-force-assisted dispensing printing technique is reported and compared with conventional dispensing and electrohydrodynamic jet printing techniques. The electrostatic force applied between a silver paste and the textured surface of a crystalline silicon solar cell wafer significantly improves the physical adhesion of the electrodes, whereas those fabricated using a conventional dispensing printing technique peel off with a silver paste containing 2 wt% of a fluorosurfactant. Moreover, the contact resistivity and dimensionless deviation of total resistance are significantly reduced from 2.19 ± 1.53 mΩ·cm2 to 0.98 ± 0.92 mΩ·cm2 and from 0.10 to 0.03, respectively. By utilizing electrodes with an abnormally high-aspect-ratio of 0.79 (the measured thickness and width are 30.4 μm and 38.3 μm, respectively), the cell efficiency is 17.2% on a polycrystalline silicon solar cell with an emitter sheet resistance of 60 Ω/sq. This cell efficiency is considerably higher than previously reported values obtained using a conventional electrohydrodynamic jet printing technique, by +0.48–3.5%p. PMID:26576857

  8. Gay-Berne and electrostatic multipole based coarse-grain potential in implicit solvent

    NASA Astrophysics Data System (ADS)

    Wu, Johnny; Zhen, Xia; Shen, Hujun; Li, Guohui; Ren, Pengyu

    2011-10-01

    A general, transferable coarse-grain (CG) framework based on the Gay-Berne potential and electrostatic point multipole expansion is presented for polypeptide simulations. The solvent effect is described by the Generalized Kirkwood theory. The CG model is calibrated using the results of all-atom simulations of model compounds in solution. Instead of matching the overall effective forces produced by atomic models, the fundamental intermolecular forces such as electrostatic, repulsion-dispersion, and solvation are represented explicitly at a CG level. We demonstrate that the CG alanine dipeptide model is able to reproduce quantitatively the conformational energy of all-atom force fields in both gas and solution phases, including the electrostatic and solvation components. Replica exchange molecular dynamics and microsecond dynamic simulations of polyalanine of 5 and 12 residues reveal that the CG polyalanines fold into "alpha helix" and "beta sheet" structures. The 5-residue polyalanine displays a substantial increase in the "beta strand" fraction relative to the 12-residue polyalanine. The detailed conformational distribution is compared with those reported from recent all-atom simulations and experiments. The results suggest that the new coarse-graining approach presented in this study has the potential to offer both accuracy and efficiency for biomolecular modeling.

  9. Determining polarizable force fields with electrostatic potentials from quantum mechanical linear response theory.

    PubMed

    Wang, Hao; Yang, Weitao

    2016-06-14

    We developed a new method to calculate the atomic polarizabilities by fitting to the electrostatic potentials (ESPs) obtained from quantum mechanical (QM) calculations within the linear response theory. This parallels the conventional approach of fitting atomic charges based on electrostatic potentials from the electron density. Our ESP fitting is combined with the induced dipole model under the perturbation of uniform external electric fields of all orientations. QM calculations for the linear response to the external electric fields are used as input, fully consistent with the induced dipole model, which itself is a linear response model. The orientation of the uniform external electric fields is integrated in all directions. The integration of orientation and QM linear response calculations together makes the fitting results independent of the orientations and magnitudes of the uniform external electric fields applied. Another advantage of our method is that QM calculation is only needed once, in contrast to the conventional approach, where many QM calculations are needed for many different applied electric fields. The molecular polarizabilities obtained from our method show comparable accuracy with those from fitting directly to the experimental or theoretical molecular polarizabilities. Since ESP is directly fitted, atomic polarizabilities obtained from our method are expected to reproduce the electrostatic interactions better. Our method was used to calculate both transferable atomic polarizabilities for polarizable molecular mechanics' force fields and nontransferable molecule-specific atomic polarizabilities. PMID:27305996

  10. Charge density distributions derived from smoothed electrostatic potential functions: design of protein reduced point charge models.

    PubMed

    Leherte, Laurence; Vercauteren, Daniel P

    2011-10-01

    To generate reduced point charge models of proteins, we developed an original approach to hierarchically locate extrema in charge density distribution functions built from the Poisson equation applied to smoothed molecular electrostatic potential (MEP) functions. A charge fitting program was used to assign charge values to the so-obtained reduced representations. In continuation to a previous work, the Amber99 force field was selected. To easily generate reduced point charge models for protein structures, a library of amino acid templates was designed. Applications to four small peptides, a set of 53 protein structures, and four KcsA ion channel models, are presented. Electrostatic potential and solvation free energy values generated by the reduced models are compared with the corresponding values obtained using the original set of atomic charges. Results are in closer agreement with the original all-atom electrostatic properties than those obtained with a previous reduced model that was directly built from the smoothed MEP functions [Leherte and Vercauteren in J Chem Theory Comput 5:3279-3298, 2009]. PMID:21915750

  11. Gay-Berne and electrostatic multipole based coarse-grain potential in implicit solvent

    PubMed Central

    Wu, Johnny; Zhen, Xia; Shen, Hujun; Li, Guohui; Ren, Pengyu

    2011-01-01

    A general, transferable coarse-grain (CG) framework based on the Gay-Berne potential and electrostatic point multipole expansion is presented for polypeptide simulations. The solvent effect is described by the Generalized Kirkwood theory. The CG model is calibrated using the results of all-atom simulations of model compounds in solution. Instead of matching the overall effective forces produced by atomic models, the fundamental intermolecular forces such as electrostatic, repulsion-dispersion, and solvation are represented explicitly at a CG level. We demonstrate that the CG alanine dipeptide model is able to reproduce quantitatively the conformational energy of all-atom force fields in both gas and solution phases, including the electrostatic and solvation components. Replica exchange molecular dynamics and microsecond dynamic simulations of polyalanine of 5 and 12 residues reveal that the CG polyalanines fold into “alpha helix” and “beta sheet” structures. The 5-residue polyalanine displays a substantial increase in the “beta strand” fraction relative to the 12-residue polyalanine. The detailed conformational distribution is compared with those reported from recent all-atom simulations and experiments. The results suggest that the new coarse-graining approach presented in this study has the potential to offer both accuracy and efficiency for biomolecular modeling. PMID:22029338

  12. Gay-Berne and electrostatic multipole based coarse-grain potential in implicit solvent.

    PubMed

    Wu, Johnny; Zhen, Xia; Shen, Hujun; Li, Guohui; Ren, Pengyu

    2011-10-21

    A general, transferable coarse-grain (CG) framework based on the Gay-Berne potential and electrostatic point multipole expansion is presented for polypeptide simulations. The solvent effect is described by the Generalized Kirkwood theory. The CG model is calibrated using the results of all-atom simulations of model compounds in solution. Instead of matching the overall effective forces produced by atomic models, the fundamental intermolecular forces such as electrostatic, repulsion-dispersion, and solvation are represented explicitly at a CG level. We demonstrate that the CG alanine dipeptide model is able to reproduce quantitatively the conformational energy of all-atom force fields in both gas and solution phases, including the electrostatic and solvation components. Replica exchange molecular dynamics and microsecond dynamic simulations of polyalanine of 5 and 12 residues reveal that the CG polyalanines fold into "alpha helix" and "beta sheet" structures. The 5-residue polyalanine displays a substantial increase in the "beta strand" fraction relative to the 12-residue polyalanine. The detailed conformational distribution is compared with those reported from recent all-atom simulations and experiments. The results suggest that the new coarse-graining approach presented in this study has the potential to offer both accuracy and efficiency for biomolecular modeling. PMID:22029338

  13. Non-contact Measurement of Electrostatic Fields: Verification of Modeled Potentials within Ion Mobility Spectrometer Drift Tube Designs

    SciTech Connect

    Jill R. Scott; Paul L. Tremblay

    2007-03-01

    The heart of an ion mobility spectrometer is the drift region where the ion separation occurs. While the electrostatic potentials within a drift tube design can be modeled, no method for validating the electrostatic field has previously been reported. Two basic drift tube designs were modeled using SIMION 7.0 to reveal the expected electrostatic fields: 1) a traditional “stacked” alternating electrodes and insulators and 2) a truly linear drift tube. One version of the stacked electrode/insulator drift tube and two versions of linear drift tubes were then fabricated. The stacked alternating electrodes/insulators were connected through a resistor network to generate the electrostatic gradient in the drift tube. The two linear drift tube designs consisted of two types of resistive drift tubes with one tube consisting of a resistive coating within an insulating tube and the other tube composed of semiconducting ferrites. The electrostatic fields within each type of drift tube were then evaluated using a non-contact method using a Kelvin-Zisman type electrostatic voltmeter and probe. The experimental results were then compared with the electrostatic fields predicted by SIMION. Both the modeling and experimental measurements reveal that the electrostatic fields within a stacked IMS drift tube are only pseudo-linear, while the electrostatic fields within a resistive drift tube can approach perfect linearity.

  14. Electrostatic potential generated during extracorporeal pump prime circulation before cardiopulmonary bypass initiation.

    PubMed

    Newton, Haley S; Niles, Scott D; Ploessl, James; Richenbacher, Wayne

    2007-03-01

    The development of electrostatic potentials generated during cardiopulmonary bypass (CPB) procedures using polyvinylchloride (PVC) tubing in conjunction with roller pumps has been previously documented. The resulting damage from the electrostatic discharge (ESD) has been reported to affect gas transfer devices, but details of potential damage to electronic components commonly used during extracorporeal circulation have not been similarly described. The purpose of this study was to measure the ability of a triboelectric potential to be generated from a primed, circulating, adult CPB pump before the initiation of CPB. Two identical adult CPB circuits were assembled: one incorporating a roller pump and the second incorporating a centrifugal pump mechanism. Primed pumps were circulated (1-6 LPM), and evidence of generated triboelectric potentials was evaluated using a digital multimeter (Fluke 8062 A). The ESD generated from an adult CPB circuit using a roller head configuration elicited a charge in excess of 600 DC V. An identical circuit constructed with a centrifugal pump mechanism did not produce any measurable charge. Sensitive electrical components in the CPB hardware platform may be damaged by ESD potential spikes of this magnitude. Preventative measures, such as circuit charge dissipation, may reduce the potential for such damage when using PVC tubing. PMID:17486872

  15. Intriguing Electrostatic Potential of CO: Negative Bond-ends and Positive Bond-cylindrical-surface.

    PubMed

    Kim, Hahn; Doan, Van Dung; Cho, Woo Jong; Valero, Rosendo; Aliakbar Tehrani, Zahra; Madridejos, Jenica Marie L; Kim, Kwang S

    2015-01-01

    The strong electronegativity of O dictates that the ground state of singlet CO has positively charged C and negatively charged O, in agreement with ab initio charge analysis, but in disagreement with the dipole direction. Though this unusual phenomenon has been fairly studied, the study of electrostatic potential (EP) for noncovalent interactions of CO is essential for better understanding. Here we illustrate that both C and O atom-ends show negative EP (where the C end gives more negative EP), favoring positively charged species, whereas the cylindrical surface of the CO bond shows positive EP, favoring negatively charged ones. This is demonstrated from the interactions of CO with Na(+), Cl(-), H2O, CO and benzene. It can be explained by the quadrupole driven electrostatic nature of CO (like N2) with very weak dipole moment. The EP is properly described by the tripole model taking into account the electrostatic multipole moments, which has a large negative charge at a certain distance protruded from C, a large positive charge on C, and a small negative charge on O. We also discuss the EP of the first excited triplet CO. PMID:26542890

  16. Intriguing Electrostatic Potential of CO: Negative Bond-ends and Positive Bond-cylindrical-surface

    PubMed Central

    Kim, Hahn; Doan, Van Dung; Cho, Woo Jong; Valero, Rosendo; Aliakbar Tehrani, Zahra; Madridejos, Jenica Marie L.; Kim, Kwang S.

    2015-01-01

    The strong electronegativity of O dictates that the ground state of singlet CO has positively charged C and negatively charged O, in agreement with ab initio charge analysis, but in disagreement with the dipole direction. Though this unusual phenomenon has been fairly studied, the study of electrostatic potential (EP) for noncovalent interactions of CO is essential for better understanding. Here we illustrate that both C and O atom-ends show negative EP (where the C end gives more negative EP), favoring positively charged species, whereas the cylindrical surface of the CO bond shows positive EP, favoring negatively charged ones. This is demonstrated from the interactions of CO with Na+, Cl–, H2O, CO and benzene. It can be explained by the quadrupole driven electrostatic nature of CO (like N2) with very weak dipole moment. The EP is properly described by the tripole model taking into account the electrostatic multipole moments, which has a large negative charge at a certain distance protruded from C, a large positive charge on C, and a small negative charge on O. We also discuss the EP of the first excited triplet CO. PMID:26542890

  17. Intriguing Electrostatic Potential of CO: Negative Bond-ends and Positive Bond-cylindrical-surface

    NASA Astrophysics Data System (ADS)

    Kim, Hahn; Doan, Van Dung; Cho, Woo Jong; Valero, Rosendo; Aliakbar Tehrani, Zahra; Madridejos, Jenica Marie L.; Kim, Kwang S.

    2015-11-01

    The strong electronegativity of O dictates that the ground state of singlet CO has positively charged C and negatively charged O, in agreement with ab initio charge analysis, but in disagreement with the dipole direction. Though this unusual phenomenon has been fairly studied, the study of electrostatic potential (EP) for noncovalent interactions of CO is essential for better understanding. Here we illustrate that both C and O atom-ends show negative EP (where the C end gives more negative EP), favoring positively charged species, whereas the cylindrical surface of the CO bond shows positive EP, favoring negatively charged ones. This is demonstrated from the interactions of CO with Na+, Cl-, H2O, CO and benzene. It can be explained by the quadrupole driven electrostatic nature of CO (like N2) with very weak dipole moment. The EP is properly described by the tripole model taking into account the electrostatic multipole moments, which has a large negative charge at a certain distance protruded from C, a large positive charge on C, and a small negative charge on O. We also discuss the EP of the first excited triplet CO.

  18. An analytical approach to computing biomolecular electrostatic potential. II. Validation and applications.

    PubMed

    Gordon, John C; Fenley, Andrew T; Onufriev, Alexey

    2008-08-21

    An ability to efficiently compute the electrostatic potential produced by molecular charge distributions under realistic solvation conditions is essential for a variety of applications. Here, the simple closed-form analytical approximation to the Poisson equation rigorously derived in Part I for idealized spherical geometry is tested on realistic shapes. The effects of mobile ions are included at the Debye-Huckel level. The accuracy of the resulting closed-form expressions for electrostatic potential is assessed through comparisons with numerical Poisson-Boltzmann (NPB) reference solutions on a test set of 580 representative biomolecular structures under typical conditions of aqueous solvation. For each structure, the deviation from the reference is computed for a large number of test points placed near the dielectric boundary (molecular surface). The accuracy of the approximation, averaged over all test points in each structure, is within 0.6 kcal/mol/mid R:emid R: approximately kT per unit charge for all structures in the test set. For 91.5% of the individual test points, the deviation from the NPB potential is within 0.6 kcal/mol/mid R:emid R:. The deviations from the reference decrease with increasing distance from the dielectric boundary: The approximation is asymptotically exact far away from the source charges. Deviation of the overall shape of a structure from ideal spherical does not, by itself, appear to necessitate decreased accuracy of the approximation. The largest deviations from the NPB reference are found inside very deep and narrow indentations that occur on the dielectric boundaries of some structures. The dimensions of these pockets of locally highly negative curvature are comparable to the size of a water molecule; the applicability of a continuum dielectric models in these regions is discussed. The maximum deviations from the NPB are reduced substantially when the boundary is smoothed by using a larger probe radius (3 A) to generate the

  19. An analytical approach to computing biomolecular electrostatic potential. II. Validation and applications

    NASA Astrophysics Data System (ADS)

    Gordon, John C.; Fenley, Andrew T.; Onufriev, Alexey

    2008-08-01

    An ability to efficiently compute the electrostatic potential produced by molecular charge distributions under realistic solvation conditions is essential for a variety of applications. Here, the simple closed-form analytical approximation to the Poisson equation rigorously derived in Part I for idealized spherical geometry is tested on realistic shapes. The effects of mobile ions are included at the Debye-Hückel level. The accuracy of the resulting closed-form expressions for electrostatic potential is assessed through comparisons with numerical Poisson-Boltzmann (NPB) reference solutions on a test set of 580 representative biomolecular structures under typical conditions of aqueous solvation. For each structure, the deviation from the reference is computed for a large number of test points placed near the dielectric boundary (molecular surface). The accuracy of the approximation, averaged over all test points in each structure, is within 0.6 kcal/mol/|e|~kT per unit charge for all structures in the test set. For 91.5% of the individual test points, the deviation from the NPB potential is within 0.6 kcal/mol/|e|. The deviations from the reference decrease with increasing distance from the dielectric boundary: The approximation is asymptotically exact far away from the source charges. Deviation of the overall shape of a structure from ideal spherical does not, by itself, appear to necessitate decreased accuracy of the approximation. The largest deviations from the NPB reference are found inside very deep and narrow indentations that occur on the dielectric boundaries of some structures. The dimensions of these pockets of locally highly negative curvature are comparable to the size of a water molecule; the applicability of a continuum dielectric models in these regions is discussed. The maximum deviations from the NPB are reduced substantially when the boundary is smoothed by using a larger probe radius (3 A˚) to generate the molecular surface. A detailed accuracy

  20. Radial control of the electrostatic potential in a tandem mirror with quadrupole end cells

    SciTech Connect

    Severn, G.D.; Hershkowitz, N. )

    1992-10-01

    It is demonstrated that the radial electrostatic potential in the Phaedrus tandem mirror ({ital Plasma} {ital Physics} {ital and} {ital Controlled} {ital Fusion} {ital Research}, 1984 (International Atomic Energy Agency, Vienna, 1985), Vol. 2, p. 265) can be altered using plasma potential control rings (PPC rings) situated at each end of the device. With the PPC rings grounded, the radial electric field in the central cell was directed outward and peaked near the plasma edge. By externally controlling the potentials of the PPC rings, the peak value of the radial electric field was varied by over a factor of 2, obtaining plasmas with a maximum value of the radial electric field {bold E}({ital r}){le}15 V/cm. A simple calculation to model the change in the central cell potential due to a bias voltage applied to the PPC rings is presented.

  1. The role of the exchange in the embedding electrostatic potential for the fragment molecular orbital method.

    PubMed

    Fedorov, Dmitri G; Kitaura, Kazuo

    2009-11-01

    We have examined the role of the exchange in describing the electrostatic potential in the fragment molecular orbital method and showed that it should be included in the total Fock matrix to obtain an accurate one-electron spectrum; however, adding it to the Fock matrices of individual fragments and pairs leads to very large errors. For the error analysis we have used the virial theorem; numerical tests have been performed for solvated phenol at the Hartree-Fock level with the 6-31G( *) and 6-311G( * *) basis sets. PMID:19894991

  2. Intrinsic Electrostatic Potential in the BK Channel Pore: Role in Determining Single Channel Conductance and Block

    PubMed Central

    Carvacho, Ingrid; Gonzalez, Wendy; Torres, Yolima P.; Brauchi, Sebastian; Alvarez, Osvaldo; Gonzalez-Nilo, Fernando D.; Latorre, Ramon

    2008-01-01

    The internal vestibule of large-conductance Ca2+ voltage-activated K+ (BK) channels contains a ring of eight negative charges not present in K+ channels of lower conductance (Glu386 and Glu389 in hSlo) that modulates channel conductance through an electrostatic mechanism (Brelidze, T.I., X. Niu, and K.L. Magleby. 2003. Proc. Natl. Acad. Sci. USA. 100:9017–9022). In BK channels there are also two acidic amino acid residues in an extracellular loop (Asp326 and Glu329 in hSlo). To determine the electrostatic influence of these charges on channel conductance, we expressed wild-type BK channels and mutants E386N/E389N, D326N, E329Q, and D326N/E329Q channels on Xenopus laevis oocytes, and measured the expressed currents under patch clamp. Contribution of E329 to the conductance is negligible and single channel conductance of D326N/E329Q channels measured at 0 mV in symmetrical 110 mM K+ was 18% lower than the control. Current–voltage curves displayed weak outward rectification for D326N and the double mutant. The conductance differences between the mutants and wild-type BK were caused by an electrostatic effect since they were enhanced at low K+ (30 mM) and vanished at high K+ (1 M K+). We determine the electrostatic potential change, Δφ, caused by the charge neutralization using TEA+ block for the extracellular charges and Ba2+ for intracellular charges. We measured 13 ± 2 mV for Δφ at the TEA+ site when turning off the extracellular charges, and 17 ± 2 mV for the Δφ at the Ba2+ site when the intracellular charges were turned off. To understand the electrostatic effect of charge neutralizations, we determined Δφ using a BK channel molecular model embedded in a lipid bilayer and solving the Poisson-Boltzmann equation. The model explains the experimental results adequately and, in particular, gives an economical explanation to the differential effect on the conductance of the neutralization of charges D326 and E329. PMID:18227273

  3. Electrostatic forces for personnel restraints

    NASA Technical Reports Server (NTRS)

    Ashby, N.; Ciciora, J.; Gardner, R.; Porter, K.

    1977-01-01

    The feasibility of utilizing electrostatic forces for personnel retention devices on exterior spacecraft surfaces was analyzed. The investigation covered: (1) determination of the state of the art; (2) analysis of potential adhesion surfaces; (3) safety considerations for personnel; (4) electromagnetic force field determination and its effect on spacecraft instrumentation; and (5) proposed advances to current technology based on documentation review, analyses, and experimental test data.

  4. Biobriefcase electrostatic aerosol collector

    DOEpatents

    Bell, Perry M.; Christian, Allen T.; Bailey, Christopher G.; Willis, Ladona; Masquelier, Donald A.; Nasarabadi, Shanavaz L.

    2009-03-17

    A system for sampling air and collecting particles entrained in the air comprising a receiving surface, a liquid input that directs liquid to the receiving surface and produces a liquid surface, an air input that directs the air so that the air with particles entrained in the air impact the liquid surface, and an electrostatic contact connected to the liquid that imparts an electric charge to the liquid. The particles potentially including bioagents become captured in the liquid by the air with particles entrained in the air impacting the liquid surface. Collection efficiency is improved by the electrostatic contact electrically charging the liquid. The effects of impaction and adhesion due to electrically charging the liquid allows a unique combination in a particle capture medium that has a low fluid consumption rate while maintaining high efficiency.

  5. An analytical approach to computing biomolecular electrostatic potential. I. Derivation and analysis.

    PubMed

    Fenley, Andrew T; Gordon, John C; Onufriev, Alexey

    2008-08-21

    Analytical approximations to fundamental equations of continuum electrostatics on simple shapes can lead to computationally inexpensive prescriptions for calculating electrostatic properties of realistic molecules. Here, we derive a closed-form analytical approximation to the Poisson equation for an arbitrary distribution of point charges and a spherical dielectric boundary. The simple, parameter-free formula defines continuous electrostatic potential everywhere in space and is obtained from the exact infinite-series (Kirkwood) solution by an approximate summation method that avoids truncating the infinite series. We show that keeping all the terms proves critical for the accuracy of this approximation, which is fully controllable for the sphere. The accuracy is assessed by comparisons with the exact solution for two unit charges placed inside a spherical boundary separating the solute of dielectric 1 and the solvent of dielectric 80. The largest errors occur when the source charges are closest to the dielectric boundary and the test charge is closest to either of the sources. For the source charges placed within 2 A from the boundary, and the test surface located on the boundary, the root-mean-square error of the approximate potential is less than 0.1 kcal/mol/mid R:emid R: (per unit test charge). The maximum error is 0.4 kcal/mol/mid R:emid R:. These results correspond to the simplest first-order formula. A strategy for adopting the proposed method for realistic biomolecular shapes is detailed. An extensive testing and performance analysis on real molecular structures are described in Part II that immediately follows this work as a separate publication. Part II also contains an application example. PMID:19044802

  6. Orbits of magnetized charged particles in parabolic and inverse electrostatic potentials

    NASA Astrophysics Data System (ADS)

    Bellan, P. M.

    2016-02-01

    Analytic solutions are presented for the orbit of a charged particle in the combination of a uniform axial magnetic field and parabolic electrostatic potential. These trajectories are shown to correspond to the sum of two individually rotating vectors with one vector rotating at a constant fast frequency and the other rotating in the same sense but with a constant slow frequency. These solutions are related to Penning trap orbits and to stochastic orbits. If the lengths of the two rotating vectors are identical, the particle has zero canonical angular momentum in which case the particle orbit will traverse the origin. If the potential has an inverse dependence on distance from the source of the potential, the particle can impact the source. Axis-encircling orbits are where the length of the vector associated with the fast frequency is longer than the vector associated with the slow frequency. Non-axis-encircling orbits are the other way around.

  7. Potential structure of discharge plasma inside liquid directly measured by an electrostatic probe

    SciTech Connect

    Chen, Qiang; Hatakeyama, Rikizo; Kaneko, Toshiro

    2013-06-17

    Potential structures of a discharge plasma inside a liquid are investigated by an electrostatic probe measurement. The time evolution of radial profiles of the floating potential for the plasma inside liquid reveals that the dominant negative charges in the plasma are the negative ion species such as OH{sup -} and O{sub 2}{sup -} rather than electrons. In addition, a positive potential gradient exists at the plasma-liquid interface due to the presence of an electrical double layer which is caused by the separation of low-mass positive ion of H{sup +} and high-mass negative ions of OH{sup -} and O{sub 2}{sup -} near the plasma-liquid interface.

  8. Ion tracking in an electrostatic potential distribution. Ph.D. Thesis; [photomultiplier tubes

    NASA Technical Reports Server (NTRS)

    Ross, D. P.

    1978-01-01

    An ion tracking system utilizing a single detector was designed to resolve two dimensional potential distributions in a vacuum. The ion detector consisted of a continuous dynode electron multiplier tube mounted behind a series of aperture plates. The detector was located on a track below a wedge shaped structure used to produce the desired potential distribution. A 150 volt electron beam aimed at selected regions, ionized the residual gas in the chamber. The ions were ejected from their source points by electrostatic forces causing them to drift downward toward the detector. Measurements of particle energy, detector position, and entry angle of the incoming particle flux were used to initialize a computer trajectory-tracing program. The program assumes a known theoretically calculated potential distribution near the wedge for computation of particle trajectories, providing a basis for evaluating the data. Special attention was given to characterization of the ion detector.

  9. A linear-scaling spectral-element method for computing electrostatic potentials.

    PubMed

    Watson, Mark A; Hirao, Kimihiko

    2008-11-14

    A new linear-scaling method is presented for the fast numerical evaluation of the electronic Coulomb potential. Our approach uses a simple real-space partitioning of the system into cubic cells and a spectral-element representation of the density in a tensorial basis of high-order Chebyshev polynomials. Electrostatic interactions between non-neighboring cells are described using the fast multipole method. The remaining near-field interactions are computed in the tensorial basis as a sum of differential contributions by exploiting the numerical low-rank separability of the Coulomb operator. The method is applicable to arbitrary charge densities, avoids the Poisson equation, and does not involve the solution of any systems of linear equations. Above all, an adaptive resolution of the Chebyshev basis in each cell facilitates the accurate and efficient treatment of molecular systems. We demonstrate the performance of our implementation for quantum chemistry with benchmark calculations on the noble gas atoms, long-chain alkanes, and diamond fragments. We conclude that the spectral-element method can be a competitive tool for the accurate computation of electrostatic potentials in large-scale molecular systems. PMID:19045386

  10. Relationships between bond dissociation energies, electron density minima and electrostatic potential minima

    NASA Astrophysics Data System (ADS)

    Wiener, John J. M.; Murray, Jane S.; Grice, M. Edward; Politzer, Peter

    The experimental dissociation energies of a group of homonuclear diatomic molecules are found to correlate with computed electron densities pho(r) and electrostatic potentials V (r) at the bond midpoints, supporting an earlier prediction based on density functional arguments (N. H. March, P. M. Kozlowski and F. Perrot 1990, J. molec. Struct. Theochem, 209, 433). The relationships are generalized to 45 molecules of various types, focusing upon the minima of pho(r) and V (r) along internuclear axes. Dissociation energies are shown to be related distinctly more closely to the minimum values of V (r) than to those of pho(r). This complements previous findings for negative monatomic ions as well as the recent observation that the V (r) minima provide the more realistic boundary points between bonded atoms (relative to literature values of covalent radii), and thus further establishes the significance of electrostatic potential axial minima with respect to covalent bonding. In the present work, all calculations were carried out by a density functional procedure (Becke exchange, Lee, Yang and Parr correlation, 6-31G** basis sets).

  11. Potential of the adhesion of bacteria isolated from drinking water to materials.

    PubMed

    Simões, Lúcia Chaves; Simões, Manuel; Oliveira, Rosário; Vieira, Maria João

    2007-04-01

    Heterotrophic bacteria (11 genera, 14 species, 25 putative strains) were isolated from drinking water, identified either biochemically or by partial 16s rDNA gene sequencing and their adherence characteristics were determined by two methods: i. thermodynamic prediction of adhesion potential by measuring hydrophobicity (contact angle measurements) and ii. by measuring adherence to eight different substrata (ASI 304 and 316 stainless steel, copper, polyvinyl chloride, polypropylene, polyethylene, silicone and glass). All the test organisms were hydrophilic and inter-species variation in hydrophobicity occurred only for Comamonas acidovorans. Stainless steel 304 (SS 304), copper, polypropylene (PP), polyethylene (PE) and silicone thermodynamically favoured adhesion for the majority of test strains (>18/25), whilst adhesion was generally less thermodynamically favorable for stainless steel 316 (SS 316), polyvinyl chloride (PVC) and glass. The predictability of thermodynamic adhesion test methods was validated by comparison with 24-well microtiter plate assays using nine reference strains and three adhesion surfaces (SS 316, PVC and PE). Results for Acinetobacter calcoaceticus, Burkolderia cepacia and Stenotrophomonas maltophilia sp. 2 were congruent between both methods whilst they differed for the other bacteria to at least one material. Only A. calcoaceticus had strongly adherent properties to the three tested surfaces. Strain variation in adhesion ability was detected only for Sphingomonas capsulata. Analysis of adhesion demonstrated that in addition to physicochemical surface properties of bacterium and substratum, biological factors are involved in early adhesion processes, suggesting that reliance on thermodynamic approaches alone may not accurately predict adhesion capacity. PMID:17440920

  12. Gyrokinetic determination of the electrostatic potential of rotating magnetic islands in tokamaks

    SciTech Connect

    Siccinio, M.; Poli, E.; Casson, F. J.; Hornsby, W. A.; Peeters, A. G.

    2011-12-15

    The electrostatic potential related to a magnetic island structure with imposed width and rotation frequency is studied by means of gyrokinetic simulations, which allow its self-consistent determination via the Poisson equation. An adiabatic response of the trapped ions at the island separatrix leads to a significant smoothing of the potential with respect to analytic calculations based on a complete flattening of the pressure profile inside the island. As a consequence, the magnitude of the polarization current is drastically reduced. When the island size is comparable to the ion banana width, the adiabatic response covers the whole island region, leading to a reduced density flattening for islands rotating in the electron diamagnetic direction. This confirms previous results based on drift-kinetic simulations.

  13. Effects of electron exchange-correlation potential on electrostatic oscillations in single-walled carbon nanotubes

    SciTech Connect

    Khan, S. A. Hassan, Sunia

    2014-05-28

    Using macroscopic quantum hydrodynamic formulation, we study the dispersion properties of electrostatic electron plasma oscillations in single-walled carbon nanotubes. The electrons and ions are considered uniformly distributed over the cylindrical surface of a nanotube thus forming a two-component (electron-ion) quantum plasma system. Electron degeneracy via Fermi-Dirac statistics as well as electron exchange and correlation effects is taken into account. It is found that the quantum (Bohm) potential arising due to fermionic nature of electrons and exchange-correlations effects has significant impact on the wave. The frequency of wave is influenced by variation in azimuthal index and radius of the nanotube. The results are analyzed numerically for typical systems for relatively longer wavelength waves and possible consequences are discussed. The results can be important in general understanding of the role of exchange-correlation potential in quantum hydrodynamic treatment of charge-carriers in nanotubes.

  14. Design of [2]rotaxane through image threshold segmentation of electrostatic potential image.

    PubMed

    Liu, Pingying; Chen, Qiufeng; Ma, Jing

    2016-09-15

    An electrostatic potential (ESP)-based image segmentation method has been used to estimate the ability of proton donation and acceptance involved in ring-rod recognition. The relative binding strength of [2]rotaxane has also been further estimated from the difference of the characteristic image-segmentation derived ESP between proton donor and proton acceptor. The size and electrostatic compatibility criteria are introduced to guide the design of interlocked [2]rotaxane. A library of 75 thermodynamically stable [2]rotaxane candidates has been generated, including 16 experimentally known systems. The theoretical results for 16 experimentally known [2]rotaxanes are in good agreement with both the experimental association constants and density functional theory-calculated binding energies. Our ESP-based image segmentation model is also applicable to the tristable [2]rotaxane molecular shuttle as well as [1]rotaxane with self-inclusion function, indicating this simple method is generic in the field of constructing other supramolecular architectures formed with donor/acceptor molecular recognition. © 2016 Wiley Periodicals, Inc. PMID:27439676

  15. Mapping the electrostatic potential of Au nanoparticles using hybrid electron holography.

    PubMed

    Ozsoy-Keskinbora, Cigdem; Boothroyd, Chris B; Dunin-Borkowski, Rafal E; van Aken, Peter A; Koch, Christoph T

    2016-06-01

    Electron holography is a powerful technique for characterizing electrostatic potentials, charge distributions, electric and magnetic fields, strain distributions and semiconductor dopant distributions with sub-nm spatial resolution. Mapping internal electrostatic and magnetic fields within nanoparticles and other low-dimensional materials by TEM requires both high spatial resolution and high phase sensitivity. Carrying out such an analysis fully quantitatively is even more challenging, since artefacts such as dynamical electron scattering may strongly affect the measurement. In-line electron holography, one of the variants of electron holography, features high phase sensitivity at high spatial frequencies, but suffers from inefficient phase recovery at low spatial frequencies. Off-axis electron holography, in contrast, can recover low spatial frequency phase information much more reliably, but is less effective in retrieving phase information at high spatial frequencies when compared to in-line holography. We investigate gold nanoparticles using hybrid electron holography at both atomic-resolution and intermediate magnification. Hybrid electron holography is a novel technique that synergistically combines off-axis and in-line electron holography, allowing the measurement of the complex wave function describing the scattered electrons with excellent signal-to-noise properties at both high and low spatial frequencies. The effect of dynamical electron scattering is minimized by beam tilt averaging. PMID:27043767

  16. Physical model of granule adhesion to the belt-electrodes of a tribo-aero-electrostatic separator

    NASA Astrophysics Data System (ADS)

    Li, Jia; Dascalescu, Lucian; Miloudi, Mohamed; Bilici, Mihai; Xu, Zhenming

    2013-03-01

    Recent studies have demonstrated the effectiveness of tribo-aero-electrostatic separation technologies, which consist in the selective sorting of mixed granular insulating materials in a fluidized bed affected by an electric field orthogonally oriented to the direction of the fluidization air. The aim of the present paper is to put the theoretical bases for the optimization of this process, i. e. maximize the total mass of the granules collected at the two electrodes that generate the electric field. The various forces that drive a granule of given mass and electric charge through the electric field and make it stick to an electrode are expressed as functions of the several input variables and parameters of the process, such as the applied high-voltage or the surface roughness, the size and the position of the electrodes. The concepts of "critical electrostatic field" and "virtual climbing distance" are introduced. The prediction of the theoretical model are confirmed by the results of three sets of experiments, carried out on samples of a granular mixture consisting of 50% Acrylonitrile Butadiene Styrene (ABS) and 50% High Impact Polystyrene (HIPS), originating from the recycling of waste electric and electronic equipment. Higher separation efficiency was obtained when the electric field in the active zone was intensified by the use of an additional electrode connected to the ground and when the collecting electrodes were covered by a thin insulating layer.

  17. Visualization of the electrostatic potential distribution in both polar ionospheres using multiple satellite measurements

    NASA Technical Reports Server (NTRS)

    Hairston, Marc R.; Heelis, Roderick A.; Rich, Frederick J.

    1995-01-01

    During the time from December 1991 through March 1992, there were four operational DMSP satellites in polar orbit. All four satellites carried the Special Sensor-Ions, Electrons, Scintillation (SSIES) plasma package which included an ion drift meter. Data from the drift meter, combined with the magnetic field data, allowed the calculation of the electrostatic potential in the ionosphere along the satellite's path. Simultaneous polar coverage by four satellites was unprecedented, providing researchers with almost continuous monitoring of the potential distribution in both hemispheres for the four month period. Combining the magnitude and location of the potential data from each of the four satellites in order to examine the varying potential distribution pattern in both hemispheres presented a major challenge in data visualization. The problem was solved by developing a three-dimensional presentation of the data where the potentials are color coded and represented by the vertical dimension. This paper presents examples from a computer animation of several days of data demonstrating evolution of the size and shape of the potential distribution, along with how these changes correspond to variations in other geophysical parameters, such as the IMF orientation and the K(sub p) index.

  18. Visualization of the electrostatic potential distribution in both polar ionospheres using multiple satellite measurements

    SciTech Connect

    Hairston, M.R.; Heelis, R.A.; Rich, F.J.

    1995-01-01

    During the time from December 1991 through March 1992, there were four operational DMSP satellites in polar orbit. All four satellites carried the Special Sensor-Ions, Electrons, Scintillation (SSIES) plasma package which included an ion drift meter. Data from the drift meter, combined with the magnetic field data, allowed the calculation of the electrostatic potential in the ionosphere along the satellite`s path. Simultaneous polar coverage by four satellites was unprecedented, providing researchers with almost continuous monitoring of the potential distribution in both hemispheres for the four month period. Combining the magnitude and location of the potential data from each of the four satellites in order to examine the varying potential distribution pattern in both hemispheres presented a major challenge in data visualization. The problem was solved by developing a three-dimensional presentation of the data where the potentials are color coded and represented by the vertical dimension. This paper presents examples from a computer animation of several days of data demonstrating evolution of the size and shape of the potential distribution, along with how these changes correspond to variations in other geophysical parameters, such as the IMF orientation and the K{sub p} index.

  19. Evaluation of an electrostatic dust removal system with potential application in next-step fusion devices

    SciTech Connect

    Friesen, F. Q. L.; John, B.; Skinner, C. H.; Roquemore, A. L.; Calle, C. I.

    2011-05-15

    The ability to manage inventories of carbon, tritium, and high-Z elements in fusion plasmas depends on means for effective dust removal. A dust conveyor, based on a moving electrostatic potential well, was tested with particles of tungsten, carbon, glass, and sand. A digital microscope imaged a representative portion of the conveyor, and dust particle size and volume distributions were derived before and after operation. About 10 mm{sup 3} volume of carbon and tungsten particles were moved in under 5 s. The highest driving amplitude tested of 3 kV was the most effective. The optimal driving frequency was 210 Hz (maximum tested) for tungsten particles, decreasing to below 60 Hz for the larger sand particles. Measurements of particle size and volume distributions after 10 and 100 cycles show the breaking apart of agglomerated carbon and the change in particle distribution over short timescales (<1 s).

  20. Evaluation of an Electrostatic Dust Removal System with Potential Application in Next-Step Fusion Devices

    SciTech Connect

    Friesen, F. QL.

    2011-01-20

    The ability to manage inventories of carbon, tritium, and high-Z elements in fusion plasmas depends on means for effective dust removal. A dust conveyor, based on a moving electrostatic potential well, was tested with particles of tungsten, carbon, glass and sand. A digital microscope imaged a representative portion of the conveyor, and dust particle size and volume distributions were derived before and after operation. About 10 mm3 volume of carbon and tungsten particles were moved in under 5 seconds. The highest driving amplitude tested of 3 kV was the most effective. The optimal driving frequency was 210 Hz (maximum tested) for tungsten particles, decreasing to below 60 Hz for the larger sand particles. Measurements of particle size and volume distributions after 10 and 100 cycles show the breaking apart of agglomerated carbon, and the change in particle distribution over short timescales (<1 s).

  1. An appraisal of Poincaré-Hopf relation and application to topography of molecular electrostatic potentials.

    PubMed

    Roy, D; Balanarayan, P; Gadre, Shridhar R

    2008-11-01

    The Poincaré-Hopf relation is studied for molecular electrostatic potentials (MESPs) of a few test systems such as cyclopropane, cyclobutane, pyridine, and benzene. Appropriate spheres centered at various points, including the center of mass of the system under study, are constructed and the MESP gradient is evaluated on the corresponding spherical grid. The change in directional nature of MESP gradient on the surface of these spheres gives indication of the critical points of the function. This is used for developing a method for locating the critical points of MESP. The strategy also enables a general definition of the Euler characteristic (EC) of the molecule, independent of any region or space. Further, the effect of basis set and level of theory on the EC is discussed. PMID:19045329

  2. An appraisal of Poincaré-Hopf relation and application to topography of molecular electrostatic potentials

    NASA Astrophysics Data System (ADS)

    Roy, D.; Balanarayan, P.; Gadre, Shridhar R.

    2008-11-01

    The Poincaré-Hopf relation is studied for molecular electrostatic potentials (MESPs) of a few test systems such as cyclopropane, cyclobutane, pyridine, and benzene. Appropriate spheres centered at various points, including the center of mass of the system under study, are constructed and the MESP gradient is evaluated on the corresponding spherical grid. The change in directional nature of MESP gradient on the surface of these spheres gives indication of the critical points of the function. This is used for developing a method for locating the critical points of MESP. The strategy also enables a general definition of the Euler characteristic (EC) of the molecule, independent of any region or space. Further, the effect of basis set and level of theory on the EC is discussed.

  3. Evaluation of an Electrostatic Dust Removal System with Potential Application in Next-Step Fusion Devices

    NASA Technical Reports Server (NTRS)

    Friesen, F. Q. L.; John, B.; Skinner, C. H.; Roquemore, A. L.; Calle, C. I.

    2011-01-01

    The ability to manage inventories of carbon, tritium, and high-Z elements in fusion plasmas depends on means for effective dust removal. A dust conveyor, based on a moving electrostatic potential well, was tested with particles of tungsten, carbon, glass and sand. A digital microscope imaged a representative portion of the conveyor, and dust particle size and volume distributions were derived before and after operation. About 10 cu mm volume of carbon and tungsten particles were moved in under 5 seconds. The highest driving amplitude tested of 3 kV was the most effective. The optimal driving frequency was 210 Hz (maximum tested) for tungsten particles, decreasing to below 60 Hz for the larger sand particles. Measurements of particle size and volume distributions after 10 and 100 cycles show the breaking apart of agglomerated carbon, and the change in particle distribution over short timescales 1 s).

  4. Grid-based lattice summation of electrostatic potentials by assembled rank-structured tensor approximation

    NASA Astrophysics Data System (ADS)

    Khoromskaia, Venera; Khoromskij, Boris N.

    2014-12-01

    Our recent method for low-rank tensor representation of sums of the arbitrarily positioned electrostatic potentials discretized on a 3D Cartesian grid reduces the 3D tensor summation to operations involving only 1D vectors however retaining the linear complexity scaling in the number of potentials. Here, we introduce and study a novel tensor approach for fast and accurate assembled summation of a large number of lattice-allocated potentials represented on 3D N×N×N grid with the computational requirements only weakly dependent on the number of summed potentials. It is based on the assembled low-rank canonical tensor representations of the collected potentials using pointwise sums of shifted canonical vectors representing the single generating function, say the Newton kernel. For a sum of electrostatic potentials over L×L×L lattice embedded in a box the required storage scales linearly in the 1D grid-size, O(N), while the numerical cost is estimated by O(NL). For periodic boundary conditions, the storage demand remains proportional to the 1D grid-size of a unit cell, n=N/L, while the numerical cost reduces to O(N), that outperforms the FFT-based Ewald-type summation algorithms of complexity O(N3logN). The complexity in the grid parameter N can be reduced even to the logarithmic scale O(logN) by using data-sparse representation of canonical N-vectors via the quantics tensor approximation. For justification, we prove an upper bound on the quantics ranks for the canonical vectors in the overall lattice sum. The presented approach is beneficial in applications which require further functional calculus with the lattice potential, say, scalar product with a function, integration or differentiation, which can be performed easily in tensor arithmetics on large 3D grids with 1D cost. Numerical tests illustrate the performance of the tensor summation method and confirm the estimated bounds on the tensor ranks.

  5. Expanding the applicability of electrostatic potentials to the realm of transition states.

    PubMed

    Bhasi, Priya; Nhlabatsi, Zanele P; Sitha, Sanyasi

    2016-05-14

    Central to any reaction mechanism study, and sometimes a challenging job, is tracing a transition state in a reaction path. For the first time, electrostatic potentials (ESP) of the reactants were used as guiding tactics to predict whether there is a possibility of any transition state in a reaction surface. The main motive behind this strategy is to see whether the directionality nature of the transition state has something to do with the anisotropic natures of the ESP with their embedded directionalities. Strategically, some atmospherically important, but simple, reactions have been chosen for this study, which heretofore were believed to be barrierless. By carefully analysing the ESP maps of the reactants, regions of possible interactions were located. Using the bilinear interpolation of the 2D grids of the ESP surfaces, search co-ordinates were fine-tuned for a local gradient based approach for the search of a transition state. Out of the three reactions studied in this work, we were able to successfully locate transition states, for the first time, in two cases and the third one still proved to be barrierless. This gives a clear indication that though ESP maps can qualitatively predict the possibility of a transition state; it is not always true that there should definitely be a transition state, as some of the reaction surfaces may genuinely be barrierless. But, nevertheless this strategy definitely has credential to be tested for many more reactions, either new or already established, and may be applied to create the initial search co-ordinates for any well-established transition state search method. Moreover, we have observed that the analysis of the ESP maps of the reactants were very much useful in explaining the nature of interactions existing in those observed transition states and we hope the same can also be extended to any transition state in an electrostatically driven reaction potential energy surface. PMID:27108668

  6. Electronic structure, molecular electrostatic potential and hydrogen bonding in DMSO-X complexes (X = ethanol, methanol and water)

    NASA Astrophysics Data System (ADS)

    Dhumal, Nilesh R.

    2011-08-01

    In the present work, we have studied the electronic structure, molecular electrostatic potential (MEP) and hydrogen bonding in DMSO-ethanol, DMSO-methanol and DMSO-water complexes by employing the MP2 method. Different conformers were simulated on the basis of possible binding sites guided by molecular electrostatic potential topology. The stronger hydrogen bonded interaction lowers the energy of the conformer. Molecular electron density topology and natural bond orbital analysis were used to explain the strength of interactions. Experimental vibrations are also compared with the calculated normal vibrations. Blue shift is predicted for SC vibration in experimental and theoretical spectra as well. Molecular electrostatic potential and topology are used to understand the interaction strength of the conformer.

  7. Exploring the Gradient Paths and Zero Flux Surfaces of Molecular Electrostatic Potential.

    PubMed

    Kumar, Anmol; Gadre, Shridhar R

    2016-04-12

    The gradient vector field of molecular electrostatic potential, ∇V(r), has remained relatively unexplored in molecular quantum mechanics. The present article explores the conceptual as well as practical aspects of this vector field. A three-dimensional atomic partition of molecular space has been achieved on the basis of zero flux surfaces (ZFSs) of ∇V(r). Such ZFSs may completely enclose some of the atoms in the molecule, unlike what is observed in density-based atomic partitioning. The demonstration of this phenomenon is elucidated through typical examples, e.g., N2, CO, H2O, H2CO, OF(•), :CH2, and NH3BF3, where the electronegative atoms or group of atoms (group electronegativity) exhibits a closed ZFS of ∇V(r) around them. The present article determines an explicit reason for this phenomenon and also provides a necessary and sufficient condition for such a closed ZFS of ∇V(r) to exist. It also describes how the potential-based picture of atoms in molecules differs from its electron density-based analogue. This work further illustrates the manifestation of anisotropy in the gradient paths of MESP of some molecular systems, with respect to CO, (•)OH, H2O, and H2CO, and points to its potential in understanding the reactivity patterns of the interacting molecules. PMID:26881455

  8. Electrostatic Potential-Based Method of Balancing Charge Transfer Across ONIOM QM:QM Boundaries.

    PubMed

    Jovan Jose, K V; Raghavachari, Krishnan

    2014-10-14

    The inability to describe charge redistribution effects between different regions in a large molecule can be a source of error in an ONIOM hybrid calculation. We propose a new and an inexpensive method for describing such charge-transfer effects and for improving reaction energies obtained with the ONIOM method. Our method is based on matching the electrostatic potential (ESP) between the model system and the real system. The ESP difference arising due to charge redistribution is overcome by placing an optimum one electron potential at a defined buffer region. In our current implementation, the link atom nuclear charge is optimized iteratively to produce a model low ESP distribution equal to that in the real low calculation. These optimum charges are relatively small in magnitude and corroborate physical intuition. This new ESP-ONIOM-CT method is independent of any arbitrary definition of charges, is defined on the basis of a physical observable, and is less basis set dependent than previous approaches. The method is easily extended for studying reactions involving multiple link atoms. We present a thorough benchmark of this method on test sets consisting of one- and two-link atom reactions. Using reaction energies of four different test sets each with four different combinations of high:low levels of theory, the accuracy of ESP-ONIOM-CT improved by 40-60% over the ONIOM method. PMID:26588132

  9. Role of electrostatic potential in the in silico prediction of molecular bioactivation and mutagenesis.

    PubMed

    Ford, Kevin A

    2013-04-01

    Electrostatic potential (ESP) is a useful physicochemical property of a molecule that provides insights into inter- and intramolecular associations, as well as prediction of likely sites of electrophilic and nucleophilic metabolic attack. Knowledge of sites of metabolic attack is of paramount importance in DMPK research since drugs frequently fail in clinical trials due to the formation of bioactivated metabolites which are often difficult to measure experimentally due to their reactive nature and relatively short half-lives. Computational chemistry methods have proven invaluable in recent years as a means to predict and study bioactivated metabolites without the need for chemical syntheses, or testing on experimental animals. Additional molecular properties (heat of formation, heat of solvation and E(LUMO) - E(HOMO)) are discussed in this paper as complementary indicators of the behavior of metabolites in vivo. Five diverse examples are presented (acetaminophen, aniline/phenylamines, imidacloprid, nefazodone and vinyl chloride) which illustrate the utility of this multidimensional approach in predicting bioactivation, and in each case the predicted data agreed with experimental data described in the scientific literature. A further example of the usefulness of calculating ESP, in combination with the molecular properties mentioned above, is provided by an examination of the use of these parameters in providing an explanation for the sites of nucleophilic attack of the nucleic acid cytosine. Exploration of sites of nucleophilic attack of nucleic acids is important as adducts of DNA have the potential to result in mutagenesis. PMID:23323940

  10. Role of surface layer collagen binding protein from indigenous Lactobacillus plantarum 91 in adhesion and its anti-adhesion potential against gut pathogen.

    PubMed

    Yadav, Ashok Kumar; Tyagi, Ashish; Kaushik, Jai Kumar; Saklani, Asha Chandola; Grover, Sunita; Batish, Virender Kumar

    2013-12-14

    Human feacal isolates were ascertain as genus Lactobacillus using specific primer LbLMA1/R16-1 and further identified as Lactobacillus plantarum with species specific primers Lpl-3/Lpl-2. 25 L. plantarum strains were further assessed for hydrophobicity following the microbial adhesion to hydrocarbons (MATH) method and colonization potentials based on their adherence to immobilized human collagen type-1. Surface proteins were isolated from selected L. plantarum 91(Lp91) strain. The purified collagen binding protein (Cbp) protein was assessed for its anti-adhesion activity against enteric Escherichia coli 0157:H7 pathogen on immobilized collagen. Four L. plantarum strains displayed high degree of hydrophobicity and significant adhesion to collagen. A 72 kDa protein was purified which reduced 59.71% adhesion of E. coli 0157:H7 on immobilized collagen as compared to control well during adhesion assay. Cbp protein is the major influencing factor in inhibition of E. coli 0157:H7 adhesion with extracellular matrix (ECM) components. Hydrophobicity and adhesion potential are closely linked attributes precipitating in better colonization potential of the lactobacillus strains. Cbp is substantiated as a crucial surface protein contributing in adhesion of lactobacillus strains. The study can very well be the platform for commercialization of indigenous probiotic strain once their functional attributes are clinically explored. PMID:23890721

  11. ELECTROSTATIC POTENTIAL ANALYSIS OF DIBENZO-P-DIOXINS AND STRUCTURALLY SIMILAR SYSTEMS IN RELATION TO THEIR BIOLOGICAL ACTIVITIES

    EPA Science Inventory

    The electrostatic potential V(r) that is created in the space around a molecule by its nuclei and electrons is a rigorously defined property that is useful in (a) analyzing and predicting the reactive behavior of molecules, and (b) the study of biological recognition processes, s...

  12. Identifying Student Use of Ball-and-Stick Images versus Electrostatic Potential Map Images via Eye Tracking

    ERIC Educational Resources Information Center

    Williamson, Vickie M.; Hegarty, Mary; Deslongchamps, Ghislain; Williamson, Kenneth C., III

    2013-01-01

    This pilot study examined students' use of ball-and-stick images versus electrostatic potential maps when asked questions about electron density, positive charge, proton attack, and hydroxide attack with six different molecules (two alcohols, two carboxylic acids, and two hydroxycarboxylic acids). Students' viewing of these dual images…

  13. Correlation and Prediction of Redox Potentials of Hydrogen Evolution Mononuclear Cobalt Catalysts via Molecular Electrostatic Potential: A DFT Study.

    PubMed

    Anjali, Bai Amutha; Sayyed, Fareed Bhasha; Suresh, Cherumuttathu H

    2016-02-25

    Reduction potentials (E(0)) of six mononuclear cobalt catalysts (1-6) for hydrogen evolution reaction and electron donating/withdrawing effect of nine X-substituents on their macrocyclic ligand are reported at solvation effect-included B3P86/6-311+G** level of density functional theory. The electrostatic potential at the Co nucleus (VCo) is found to be a powerful descriptor of the electronic effect experienced by Co from the ligand environment. The VCo values vary substantially with respect to the nature of macrocycle, type of apical ligands, nature of substituent and oxidation state of the metal center. Most importantly, VCo values of both the oxidized and reduced states of all the six complexes show strong linear correlation with E(0). The correlation plots between VCo and E(0) provide an easy-to-interpret graphical interpretation and quantification of the effect of ligand environment on the reduction potential. Further, on the basis of a correlation between the relative VCo and relative E(0) values of a catalyst with respect to the CF3-substituted reference system, the E(0) of any X-substituted 1-6 complexes is predicted. PMID:26836251

  14. Quantitative imaging of the electrostatic field and potential generated by a transmembrane protein pore at subnanometer resolution.

    PubMed

    Pfreundschuh, Moritz; Hensen, Ulf; Müller, Daniel J

    2013-01-01

    Elucidating the mechanisms by which proteins translocate small molecules and ions through transmembrane pores and channels is of great interest in biology, medicine, and nanotechnology. However, the characterization of pore forming proteins in their native state lacks suitable methods that are capable of high-resolution imaging (~1 nm) while simultaneously mapping physical and chemical properties. Here we report how force-distance (FD) curve-based atomic force microscopy (AFM) imaging can be applied to image the native pore forming outer membrane protein F (OmpF) at subnanometer resolution and to quantify the electrostatic field and potential generated by the transmembrane pore. We further observe the electrostatic field and potential of the OmpF pore switching "on" and "off" in dependence of the electrolyte concentration. Because electrostatic field and potential select for charged molecules and ions and guide them to the transmembrane pore the insights are of fundamental importance to understand the pore function. These experimental results establish FD-based AFM as a unique tool to image biological systems to subnanometer resolution and to quantify their electrostatic properties. PMID:24079830

  15. Prediction of physicochemical properties of organic molecules using van der Waals surface electrostatic potentials.

    PubMed

    Kim, Chan Kyung; Lee, Kyung A; Hyun, Kwan Hoon; Park, Heung Jin; Kwack, In Young; Kim, Chang Kon; Lee, Hai Whang; Lee, Bon-Su

    2004-12-01

    The generalized interaction properties function (GIPF) methodology developed by Politzer and coworkers, which calculated molecular surface electrostatic potential (MSESP) on a density envelope surface, was modified by calculating the MSESP on a much simpler van der Waals (vdW) surface of a molecule. In this work, vdW molecular surfaces were obtained from the fully optimized structures confirmed by frequency calculations at B3LYP/6-31G(d) level of theory. Multiple linear regressions for normal boiling point, heats of vaporization, heats of sublimation, heats of fusion, liquid density, and solid density were performed using GIPF variables from vdW model surface. Results from our model are compared with those from Politzer and coworkers. The surface-dependent beta (and gamma) values are dependent on the surface models but the surface-independent alpha and regression coefficients (r) are constant when vdW surface and density surface with 0.001 a.u. contour value are compared. This interesting phenomenon is explained by linear dependencies of GIPF variables. PMID:15484184

  16. Electronic coupling calculations with transition charges, dipoles, and quadrupoles derived from electrostatic potential fitting.

    PubMed

    Fujimoto, Kazuhiro J

    2014-12-01

    A transition charge, dipole, and quadrupole from electrostatic potential (TrESP-CDQ) method for electronic coupling calculations is proposed. The TrESP method is based on the classical description of electronic Coulomb interaction between transition densities for individual molecules. In the original TrESP method, only the transition charge interactions were considered as the electronic coupling. In the present study, the TrESP method is extended to include the contributions from the transition dipoles and quadrupoles as well as the transition charges. Hence, the self-consistent transition density is employed in the ESP fitting procedure. To check the accuracy of the present approach, several test calculations are performed to a helium dimer, a methane dimer, and an ethylene dimer. As a result, the TrESP-CDQ method gives a much improved description of the electronic coupling, compared with the original TrESP method. The calculated results also show that the self-consistent treatment to the transition densities contributes significantly to the accuracy of the electronic coupling calculations. Based on the successful description of the electronic coupling, the contributions to the electronic coupling are also analyzed. This analysis clearly shows a negligible contribution of the transition charge interaction to the electronic coupling. Hence, the distribution of the transition density is found to strongly influence the magnitudes of the transition charges, dipoles, and quadrupoles. The present approach is useful for analyzing and understanding the mechanism of excitation-energy transfer. PMID:25481127

  17. A molecular electrostatic potential analysis of hydrogen, halogen, and dihydrogen bonds.

    PubMed

    Mohan, Neetha; Suresh, Cherumuttathu H

    2014-03-01

    Hydrogen, halogen, and dihydrogen bonds in weak, medium and strong regimes (<1 to ∼ 60 kcal/mol) have been investigated for several intermolecular donor-acceptor (D-A) complexes at ab initio MP4//MP2 method coupled with atoms-in-molecules and molecular electrostatic potential (MESP) approaches. Electron density ρ at bond critical point correlates well with interaction energy (Enb) for each homogeneous sample of complexes, but its applicability to the entire set of complexes is not satisfactory. Analysis of MESP minimum (V(min)) and MESP at the nuclei (Vn) shows that in all D-A complexes, MESP of A becomes more negative and that of D becomes less negative suggesting donation of electrons from D to A leading to electron donor-acceptor (eDA) interaction between A and D. MESP based parameter ΔΔVn measures donor-acceptor strength of the eDA interactions as it shows a good linear correlation with Enb for all D-A complexes (R(2) = 0.976) except the strongly bound bridged structures. The bridged structures are classified as donor-acceptor-donor complexes. MESP provides a clear evidence for hydrogen, halogen, and dihydrogen bond formation and defines them as eDA interactions in which hydrogen acts as electron acceptor in hydrogen and dihydrogen bonds while halogen acts as electron acceptor in halogen bonds. PMID:24506527

  18. Quantification and classification of substituent effects in organic chemistry: a theoretical molecular electrostatic potential study.

    PubMed

    Remya, Geetha S; Suresh, Cherumuttathu H

    2016-07-27

    Substituent effects in organic chemistry are generally described in terms of experimentally derived Hammett parameters whereas a convenient theoretical tool to study these effects in π-conjugated molecular systems is molecular electrostatic potential (MESP) analysis. The present study shows that the difference between MESP at the nucleus of the para carbon of substituted benzene and a carbon atom in benzene, designated as ΔVC, is very useful to quantify and classify substituent effects. On the basis of positive and negative ΔVC values, a broad classification of around 381 substituents into electron withdrawing and donating categories is made. Each category is again sorted based on the magnitude of ΔVC into subcategories such as very strong, strong, medium, and weak electron donating/withdrawing. Furthermore, the data are used to show the transferability and additivity of substituent effects in π-conjugated organic molecules such as condensed aromatic, olefinic, acetylenic, and heterocyclic systems. The transferability properties hold good for ΔVC in all these molecular systems. The additive properties of substituent effects are strongly reflected on ΔVC and the predictive power of the data to assign the total substituent effects of multi-substituted systems is verified. The ΔVC data and the present classification of substituents are very useful to design π-conjugated organic molecular systems with desired electron rich/poor character. PMID:27412764

  19. Measurement of electrostatic potential variations between 2D materials using low-energy electron microscopy

    NASA Astrophysics Data System (ADS)

    de La Barrera, Sergio; Mende, Patrick; Li, Jun; Feenstra, Randall; Lin, Yu-Chuan; Robinson, Joshua; Vishwanath, Suresh; Xing, Huili

    Among the many properties that evolve as isolated 2D materials are brought together to form a heterostructure, rearrangement of charges between layers due to unintentional doping results in dipole fields at the interface, which critically affect the electronic properties of the structure. Here we report a method for directly measuring work function differences, and hence electrostatic potential variations, across the surface of 2D materials and heterostructures thereof using low energy electron microscopy (LEEM). Study of MoSe2 grown by molecular beam epitaxy on epitaxial graphene on SiC with LEEM reveals a large work function difference between the MoSe2 and the graphene, indicating charge transfer between the layers and a subsequent dipole layer. In addition to quantifying dipole effects between transition metal dichalcogenides and graphene, direct imaging of the surface, diffraction information, and the spectroscopic dependence of electron reflectivity will be discussed. This work was supported in part by the Center for Low Energy Systems Technology (LEAST), one of the six SRC STARnet Centers, sponsored by MARCO and DARPA.

  20. Electronic coupling calculations with transition charges, dipoles, and quadrupoles derived from electrostatic potential fitting

    SciTech Connect

    Fujimoto, Kazuhiro J.

    2014-12-07

    A transition charge, dipole, and quadrupole from electrostatic potential (TrESP-CDQ) method for electronic coupling calculations is proposed. The TrESP method is based on the classical description of electronic Coulomb interaction between transition densities for individual molecules. In the original TrESP method, only the transition charge interactions were considered as the electronic coupling. In the present study, the TrESP method is extended to include the contributions from the transition dipoles and quadrupoles as well as the transition charges. Hence, the self-consistent transition density is employed in the ESP fitting procedure. To check the accuracy of the present approach, several test calculations are performed to a helium dimer, a methane dimer, and an ethylene dimer. As a result, the TrESP-CDQ method gives a much improved description of the electronic coupling, compared with the original TrESP method. The calculated results also show that the self-consistent treatment to the transition densities contributes significantly to the accuracy of the electronic coupling calculations. Based on the successful description of the electronic coupling, the contributions to the electronic coupling are also analyzed. This analysis clearly shows a negligible contribution of the transition charge interaction to the electronic coupling. Hence, the distribution of the transition density is found to strongly influence the magnitudes of the transition charges, dipoles, and quadrupoles. The present approach is useful for analyzing and understanding the mechanism of excitation-energy transfer.

  1. Estimation of Molecular Acidity via Electrostatic Potential at the Nucleus and Valence Natural Atomic Orbitals

    PubMed Central

    Liu, Shubin; Pedersen, Lee G.

    2009-01-01

    An effective approach of estimating molecular pKa values from simple density functional calculations is proposed in this work. Both the molecular electrostatic potential (MEP) at the nucleus of the acidic atom and the sum of valence natural atomic orbitals are employed for three categories of compounds, amines and anilines, carbonyl acids and alcohols, and sulfonic acids and thiols. A strong correlation between experimental pKa values and each of these two quantities for each of the three categories has been discovered. Moreover, if the MEP is subtracted by the isolated atomic MEP for each category of compounds, we observe a single unique linear relationship between the resultant MEP difference and experimental pKa data of amines, anilines, carbonyl acids, alcohols, sulfonic acids, thiols, and their substituents. These results can generally be utilized to simultaneously estimate pKa values at multiple sites with a single calculation for either relatively small molecules in drug design or amino acids in proteins and macromolecules. PMID:19317439

  2. Effect of surface potential on epithelial cell adhesion, proliferation and morphology.

    PubMed

    Chang, Hsun-Yun; Kao, Wei-Lun; You, Yun-Wen; Chu, Yi-Hsuan; Chu, Kuo-Jui; Chen, Peng-Jen; Wu, Chen-Yi; Lee, Yu-Hsuan; Shyue, Jing-Jong

    2016-05-01

    Cell adhesion is the basis of individual cell survival, division and motility. Hence, understanding the effects that the surface properties have on cell adhesion, proliferation and morphology are crucial. In particular, surface charge/potential has been identified as an important factor that affects cell behavior. However, how cells respond to incremental changes in surface potential remains unclear. By using binary self-assembled monolayer (SAM) modified Au surfaces that are similar in mechanical/chemical properties and provide a series of surface potentials, the effect of surface potential on the behavior of cells can be studied. In this work, the effect of surface potential on epithelial cells, including human embryonic kidney (HEK293T) and human hepatocellular carcinoma (HepG2), were examined. The results showed that the adhesion density of epithelial cells increased with increasing surface potential, which is similar to but varied more significantly compared with fibroblasts. The proliferation rate is found to be independent of surface potential in both cell types. Furthermore, epithelial cells show no morphological change with respect to surface potential, whereas the morphology of the fibroblasts clearly changed with the surface potential. These differences between the cell types were rationalized by considering the difference in extracellular matrix composition. Laminin-dominant epithelial cells showed higher adhesion density and less morphological change than did fibronectin-dominant fibroblasts because the more significant adsorption of positively charged laminin on the surface enhanced the adhesion of epithelial cells. In contrast, due to the dominance of negatively charged fibronectin that adsorbed weakly on the surface, fibroblasts had to change their morphology to fit the inhomogeneous fibronectin-adsorbed area. PMID:26852101

  3. Semi-continuum electrostatic calculations of redox potentials in photosystem I.

    PubMed

    Ptushenko, Vasily V; Cherepanov, Dmitry A; Krishtalik, Lev I; Semenov, Alexey Yu

    2008-07-01

    The midpoint redox potentials (E(m)) of all cofactors in photosystem I from Synechococcus elongatus as well as of the iron-sulfur (Fe(4)S(4)) clusters in two soluble ferredoxins from Azotobacter vinelandii and Clostridium acidiurici were calculated within the framework of a semi-continuum dielectric approach. The widely used treatment of proteins as uniform media with single dielectric permittivity is oversimplified, particularly, because permanent charges are considered both as a source for intraprotein electric field and as a part of dielectric polarizability. Our approach overcomes this inconsistency by using two dielectric constants: optical epsilon(o)=2.5 for permanent charges pre-existing in crystal structure, and static epsilon(s) for newly formed charges. We also take into account a substantial dielectric heterogeneity of photosystem I revealed by photoelectric measurements and a liquid junction potential correction for E(m) values of relevant redox cofactors measured in aprotic solvents. We show that calculations based on a single permittivity have the discrepancy with experimental data larger than 0.7 V, whereas E(m) values calculated within our approach fall in the range of experimental estimates. The electrostatic analysis combined with quantum chemistry calculations shows that (i) the energy decrease upon chlorophyll dimerization is essential for the downhill mode of primary charge separation between the special pair P(700) and the primary acceptor A(0); (ii) the primary donor is apparently P(700) but not a pair of accessory chlorophylls; (iii) the electron transfer from the A branch quinone Q(A) to the iron-sulfur cluster F(X) is most probably downhill, whereas that from the B branch quinone Q(B) to F(X) is essentially downhill. PMID:18483776

  4. Through-Space Effects of Substituents Dominate Molecular Electrostatic Potentials of Substituted Arenes

    PubMed Central

    Wheeler, Steven E.; Houk, K. N.

    2009-01-01

    Model systems have been studied using density functional theory to assess the contributions of π-resonance and through-space effects on electrostatic potentials of substituted arenes. The results contradict the widespread assumption that changes in molecular ESPs reflect only local changes in the electron density. Substituent effects on the ESP above the molecular plane are commonly attributed to changes in the aryl π-system. We show that ESP changes for a collection of substituted benzenes and more complex aromatic systems can be accounted for mostly by through-space effects, with no change in the aryl π-electron density. Only when π-resonance effects are substantial do they influence changes in the ESP above the aromatic ring to any extent. Examples of substituted arenes studied here are taken from the fields of drug design, host-guest chemistry, and crystal engineering. These findings emphasize the potential pitfalls of assuming ESP changes reflect changes in the local electron density. Since ESP changes are frequently used to rationalize and predict intermolecular interactions, these findings have profound implications for our understanding of substituent effects in countless areas of chemistry and molecular biology. Specifically, in many non-covalent interactions there are significant, often neglected, through-space interactions with the substituents. Finally, the present results explain the perhaps unexpectedly good performance of many molecular mechanics force-fields applied to supramolecular assembly phenomena and π-π interactions in biological systems despite the neglect of the polarization of the aryl π-system by substituents. PMID:20161573

  5. Inverted xerographic depletion discharge mechanism for the dark decay of electrostatic surface potential on amorphous semiconductors

    SciTech Connect

    Kasap, S.O.

    1988-07-01

    Recently, the xerographic depletion discharge (XDD) model has been applied extensively to chemically modified a-Se, a-Se/sub 1/..sqrt../sub x/Te/sub x/ alloys, and a-As/sub 2/Se/sub 3/ as well as to a-Si:H films to study the nature of charge carrier generation from deep mobility gap states which control the dark decay of the electrostatic surface potential on a corona charged amorphous semiconductor. In the normal XDD model, the dark discharge involves bulk thermal generation of a mobile carrier of the same sign as the surface charge and its subsequent sweep out from the sample leaving behind an ionized center of opposite charge. It is shown that an ''inverted depletion discharge'' mechanism, which involves the thermal generation of a mobile charge carrier of the opposite sign to the surface charge and its subsequent drift to the surface and the resulting surface charge neutralization there, results in a dark discharge rate which has identical features as the normal XDD mechanism. In the normal XDD mechanism, the neutral region develops after the depletion time from the grounded electrode, whereas in the inverted XDD mechanism the neutral region grows from the surface. Furthermore, during inverted depletion discharge the surface charge is actually dissipated by neutralization, whereas in the normal depletion discharge model there is no such requirement over the time scale of the experiment. It is concluded that xerographic dark decay experiments alone cannot determine the sign of the thermally generated mobile carrier and that of the bulk space charge. Chemically modified amorphous selenium case is discussed as an example of surface potential decay resulting from bulk space-charge buildup.

  6. Dependence of electrostatic potential distribution of Al2O3/Ge structure on Al2O3 thickness

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolei; Xiang, Jinjuan; Wang, Wenwu; Zhao, Chao; Zhang, Jing

    2016-09-01

    Electrostatic potential distribution of Al2O3/Ge structure is investigated vs. Al2O3 thickness by X-ray photoelectron spectroscopy (XPS). The electrostatic potential distribution is found to be Al2O3 thickness dependent. This interesting phenomenon is attributed to the appearance of gap states on Al2O3 surface (GSAl2O3) and its higher charge neutrality level (CNL) compared with the CNL of gap states at Al2O3/Ge interface (GSAl2O3/Ge), leading to electron transfer from GSAl2O3 to GSAl2O3/Ge. In the case of thicker Al2O3, fewer electrons transfer from GSAl2O3 to GSAl2O3/Ge, resulting in a larger potential drop across Al2O3 and XPS results.

  7. Electrostatic potential of mean force between two curved surfaces in the presence of counterion connectivity

    NASA Astrophysics Data System (ADS)

    Zhou, Shiqi

    2015-11-01

    In this paper, we investigate effects of counterion connectivity (i.e., association of the counterions into a chain molecule) on the electrostatic potential of mean force (EPMF) between two similarly charged cylinder rods in a primitive model electrolyte solution by solving a classical density functional theory. The main findings include the following: (i) The counterion connectivity helps in inducing a like-charge-attractionlike (LCA-like) phenomenology even in a monovalent counterion solution wherein the LCA-like observation generally does not occur without the counterion connectivity. (ii) For divalent counterion solutions, the counterion connectivity can reinforce or weaken the LCA-like observation depending on the chain length N , and simply increases the equilibrium nearest surface separation of the rods corresponding to the minimum EPMF to nearly three times the counterion site diameter, whether N is large or small. (iii) If N is large enough, the LCA-like strength tends to be negatively correlated with the electrolyte concentration c over the entire range of the rod surface charge magnitude | σ*| considered; whereas if N drops, the correlation tends to become positive with decrease of the | σ*| value, and particularly for modest | σ*| values, the correlation relationship exhibits an extreme value phenomenon. (iv) In the case of a 1:1 electrolyte, the EPMF effects of the diameters of counterion and coion sites are similar in both situations with and without the counterion connectivity. All of these findings can be explained self-consistently by a recently proposed hydrogen-bonding style mechanism reinforced by one additional concept: flexibility of the counterion chain and the factors affecting it, like N and counterion site valence.

  8. Protein Recovery from Secondary Paper Sludge and Its Potential Use as Wood Adhesive

    NASA Astrophysics Data System (ADS)

    Pervaiz, Muhammad

    cross-linking, the synergy of adhesive blends was evaluated through classical rule-of-mixture. The findings of this study warrants further investigation concerning other potential uses of recovered sludge protein, especially as food supplements and economic implications.

  9. A novel method for screening of potential probiotics for high adhesion capability.

    PubMed

    Wang, Xin; Wu, Qinglong; Deng, Kan; Wei, Qiang; Hu, Ping; He, Jingjing; Liu, Huan; Zheng, Yong; Wei, Hua; Shah, Nagendra P; Chen, Tingtao

    2015-07-01

    To screen for potential probiotics with high adhesion capability, a chemostat model-based cultured human feces and denaturing gradient gel electrophoresis methods were applied, and the adhesion capability of the isolates was evaluated in vitro and in vivo. Lactobacillus plantarum (HM218749), Lactobacillus reuteri (EU547310), and Enterococcus faecalis (HM218543) were isolated from the slime on the chemostat wall, as these organisms could grow better at 37°C in an anaerobic environment and could resist harsh conditions (pH 1.5 and 0.30% bile salt). Lactobacillus plantarum, L. reuteri, and E. faecalis could adhere to HT-29 cells and reduce the adhesion of Shigella dysenteriae 2457, Staphylococcus aureus Cowan1, Enterobacter sakazakii 45401, and Escherichia coli 44102 to HT-29 cells. Moreover, the animal experiment showed that L. plantarum could adhere to mice intestine, increasing the number of lactobacilli and decreasing the number of enterococci. PMID:25912863

  10. Adhesion Potential of Intestinal Microbes Predicted by Physico-Chemical Characterization Methods

    PubMed Central

    Niederberger, Tobias; Fischer, Peter; Rühs, Patrick Alberto

    2015-01-01

    Bacterial adhesion to epithelial surfaces affects retention time in the human gastro-intestinal tract and therefore significantly contributes to interactions between bacteria and their hosts. Bacterial adhesion among other factors is strongly influenced by physico-chemical factors. The accurate quantification of these physico-chemical factors in adhesion is however limited by the available measuring techniques. We evaluated surface charge, interfacial rheology and tensiometry (interfacial tension) as novel approaches to quantify these interactions and evaluated their biological significance via an adhesion assay using intestinal epithelial surface molecules (IESM) for a set of model organisms present in the human gastrointestinal tract. Strain pairs of Lactobacillus plantarum WCFS1 with its sortase knockout mutant Lb. plantarum NZ7114 and Lb. rhamnosus GG with Lb. rhamnosus DSM 20021T were used with Enterococcus faecalis JH2-2 as control organism. Intra-species comparison revealed significantly higher abilities for Lb. plantarum WCSF1 and Lb. rhamnosus GG vs. Lb. plantarum NZ7114 and Lb. rhamnosus DSM 20021T to dynamically increase interfacial elasticity (10−2 vs. 10−3 Pa*m) and reduce interfacial tension (32 vs. 38 mN/m). This further correlated for Lb. plantarum WCSF1 and Lb. rhamnosus GG vs. Lb. plantarum NZ7114 and Lb. rhamnosus DSM 20021T with the decrease of relative hydrophobicity (80–85% vs. 57–63%), Zeta potential (-2.9 to -4.5 mV vs. -8.0 to -13.8 mV) and higher relative adhesion capacity to IESM (3.0–5.0 vs 1.5–2.2). Highest adhesion to the IESM collagen I and fibronectin was found for Lb. plantarum WCFS1 (5.0) and E. faecalis JH2-2 (4.2) whereas Lb. rhamnosus GG showed highest adhesion to type II mucus (3.8). Significantly reduced adhesion (2 fold) to the tested IESM was observed for Lb. plantarum NZ7114 and Lb. rhamnosus DSM 20021T corresponding with lower relative hydrophobicity, Zeta potential and abilities to modify interfacial

  11. Hybrid QTAIM and electrostatic potential-based quantum topology phase diagrams for water clusters.

    PubMed

    Kumar, Anmol; Gadre, Shridhar R; Chenxia, Xiao; Tianlv, Xu; Kirk, Steven Robert; Jenkins, Samantha

    2015-06-21

    The topological diversity of sets of isomers of water clusters (W = H2O)n, 7 ≤ n ≤ 10, is analyzed employing the scalar fields of total electronic charge density ρ(r) and the molecular electrostatic potential (MESP). The features uncovered by the MESP are shown to be complementary to those revealed by the theory of atoms in molecules (QTAIM) analysis. The MESP is known to exhibit the electron localizations such as lone pairs that are central to water cluster behavior. Therefore, a 'hybrid' QTAIM and MESP quantum topology phase diagram (QTPD) for Wn, 7 ≤ n ≤ 10, is introduced in addition to the QTPD. The 'spanning' QTPD with upper and lower bounds is constructed from the solutions of the Poincaré-Hopf relation involving the non-degenerate critical points. The changing subtle balance between the planar and three dimensional character of the growing water clusters Wn, 4 ≤ n ≤ 10, is revealed. Characterization of the structure of the QTPDs, possible with new tools, demonstrated the migration of the position of the global minimum on the spanning QTPD from the lower bound to upper bound as the Wn, 4 ≤ n ≤ 10, cluster grows in size. Differences in the structure of the QTPD are found between the clusters containing even versus odd monomers for Wn, n = 7-10. The energetic stability of the clusters which possess even number of monomers viz. n = 8, 10 is higher than that of the n = 7, 9 clusters due to relatively higher numbers of hydrogen-bond BCPs in the n = 8, 10 clusters, in agreement with energetic results reported in the literature. A 'hybrid' QTPD is created from a new chemical relation bHB + l ≥ 2n for Wn that relates the number of hydrogen-bond bond critical points (bHB) with the number of oxygen lone pairs exclusively specified by the negative valued MESP (3,+3) critical points (l). The topologies of the subset bHB + l = 2n for Wn, point the way to the discovery of unknown 'missing' lower energy isomers. A discussion of the relative merits and

  12. Study of electrostatic potential surface distribution of wild-type plastocyanin Synechocystis solution structure determined by homonuclear NMR.

    PubMed

    Monleón, Daniel; Celda, Bernardo

    2003-10-01

    Plastocyanin is a small (approximately 10 kDa), type I blue copper protein that works as an electron donor to photosystem I from cytochrome f in both chloroplast systems and in some strains of cyanobacteria. Comparative studies of the kinetic mechanisms of plastocyanins in different organisms show that the electron transfer from photosystem I happens by simple collision in cyanobacteria but through a intermediate transition complex in green algae and superior plants. Previous work has proved that this effect cannot be explained by structural variations across the different plastocyanins but it can be explained by differences in the electrostatic potential distribution at the protein surface. In that case, minor conformational errors at the amino acid side chain level may imply an important effect in the electrostatic potential distribution calculation. In this work we present a high resolution study of side chain conformation by homonuclear NMR for the reduced wild-type plastocyanin Synechocystis using intensity ratios for 2D-NOESY and 2D-H,H-TOCSY cross peaks at different mixing times. We also present the corresponding comparison with different plastocyanin structures and the effect in the electrostatic potential distribution at the protein surface. We discuss the importance of indirect J-coupling information from TOCSY-type experiments as complement for intraresidue distances derived from NOESY experiments in the determination of side chain orientation and stereo-specific assignments. PMID:14517909

  13. Loss of Cell Adhesion Increases Tumorigenic Potential of Polarity Deficient Scribble Mutant Cells

    PubMed Central

    Waghmare, Indrayani

    2016-01-01

    Epithelial polarity genes are important for maintaining tissue architecture, and regulating growth. The Drosophila neoplastic tumor suppressor gene scribble (scrib) belongs to the basolateral polarity complex. Loss of scrib results in disruption of its growth regulatory functions, and downregulation or mislocalization of Scrib is correlated to tumor growth. Somatic scribble mutant cells (scrib-) surrounded by wild-type cells undergo apoptosis, which can be prevented by introduction of secondary mutations that provide a growth advantage. Using genetic tools in Drosophila, we analyzed the phenotypic effects of loss of scrib in different growth promoting backgrounds. We investigated if a central mechanism that regulates cell adhesion governs the growth and invasive potential of scrib mutant cells. Here we show that increased proliferation, and survival abilities of scrib- cells in different genetic backgrounds affect their differentiation, and intercellular adhesion. Further, loss of scrib is sufficient to cause reduced cell survival, activation of the JNK pathway and a mild reduction of cell adhesion. Our data show that for scrib cells to induce aggressive tumor growth characterized by loss of differentiation, cell adhesion, increased proliferation and invasion, cooperative interactions that derail signaling pathways play an essential role in the mechanisms leading to tumorigenesis. Thus, our study provides new insights on the effects of loss of scrib and the modification of these effects via cooperative interactions that enhance the overall tumorigenic potential of scrib deficient cells. PMID:27327956

  14. Electrostatic forces involved in orienting Anabaena ferredoxin during binding to Anabaena ferredoxin:NADP+ reductase: site-specific mutagenesis, transient kinetic measurements, and electrostatic surface potentials.

    PubMed Central

    Hurley, J. K.; Hazzard, J. T.; Martínez-Júlvez, M.; Medina, M.; Gómez-Moreno, C.; Tollin, G.

    1999-01-01

    Transient absorbance measurements following laser flash photolysis have been used to measure the rate constants for electron transfer (et) from reduced Anabaena ferredoxin (Fd) to wild-type and seven site-specific charge-reversal mutants of Anabaena ferredoxin:NADP+ reductase (FNR). These mutations have been designed to probe the importance of specific positively charged amino acid residues on the surface of the FNR molecule near the exposed edge of the FAD cofactor in the protein-protein interaction during et with Fd. The mutant proteins fall into two groups: overall, the K75E, R16E, and K72E mutants are most severely impaired in et, and the K138E, R264E, K290E, and K294E mutants are impaired to a lesser extent, although the degree of impairment varies with ionic strength. Binding constants for complex formation between the oxidized proteins and for the transient et complexes show that the severity of the alterations in et kinetics for the mutants correlate with decreased stabilities of the protein-protein complexes. Those mutated residues, which show the largest effects, are located in a region of the protein in which positive charge predominates, and charge reversals have large effects on the calculated local surface electrostatic potential. In contrast, K138, R264, K290, and K294 are located within or close to regions of intense negative potential, and therefore the introduction of additional negative charges have considerably smaller effects on the calculated surface potential. We attribute the relative changes in et kinetics and complex binding constants for these mutants to these characteristics of the surface charge distribution in FNR and conclude that the positively charged region of the FNR surface located in the vicinity of K75, R16, and K72 is especially important in the binding and orientation of Fd during electron transfer. PMID:10452605

  15. Cation-pi interactions in aromatics of biological and medicinal interest: electrostatic potential surfaces as a useful qualitative guide.

    PubMed Central

    Mecozzi, S; West, A P; Dougherty, D A

    1996-01-01

    The cation-pi interaction is an important, general force for molecular recognition in biological receptors. Through the sidechains of aromatic amino acids, novel binding sites for cationic ligands such as acetylcholine can be constructed. We report here a number of calculations on prototypical cation-pi systems, emphasizing structures of relevance to biological receptors and prototypical heterocycles of the type often of importance in medicinal chemistry. Trends in the data can be rationalized using a relatively simple model that emphasizes the electrostatic component of the cation-pi interaction. In particular, plots of the electrostatic potential surfaces of the relevant aromatics provide useful guidelines for predicting cation-pi interactions in new systems. Images Fig. 2 Fig. 3 Fig. 4 PMID:8855218

  16. Electrostatic Charge on Flying Hummingbirds and Its Potential Role in Pollination

    PubMed Central

    von Rabenau, Lisa; Smiley, Ashley; Dudley, Robert

    2015-01-01

    Electrostatic phenomena are known to enhance both wind- and insect-mediated pollination, but have not yet been described for nectar-feeding vertebrates. Here we demonstrate that wild Anna's Hummingbirds (Calypte anna) can carry positive charges up to 800 pC while in flight (mean ± s.d.: 66 ± 129 pC). Triboelectric charging obtained by rubbing an isolated hummingbird wing against various plant structures generated charges up to 700 pC. A metal hummingbird model charged to 400 pC induced bending of floral stamens in four plants (Nicotiana, Hemerocallis, Penstemon, and Aloe spp.), and also attracted falling Lycopodium spores at distances of < 2 mm. Electrostatic forces may therefore influence pollen transfer onto nectar-feeding birds. PMID:26421845

  17. Electrostatic potential wells for on-demand drop manipulation in microchannels.

    PubMed

    de Ruiter, Riëlle; Pit, Arjen M; de Oliveira, Vitor Martins; Duits, Michèl H G; van den Ende, Dirk; Mugele, Frieder

    2014-03-01

    Precise control and manipulation of individual drops are crucial in many lab-on-a-chip applications. We present a novel hybrid concept for channel-based discrete microfluidics with integrated electrowetting functionality by incorporating co-planar electrodes (separated by a narrow gap) in one of the microchannel walls. By combining the high throughput of channel-based microfluidics with the individual drop control achieved using electrical actuation, we acquire the strengths of both worlds. The tunable strength of the electrostatic forces enables a wide range of drop manipulations, such as on-demand trapping and release, guiding, and sorting of drops in the microchannel. In each of these scenarios, the retaining electrostatic force competes with the hydrodynamic drag force. The conditions for trapping can be predicted using a simple model that balances these forces. PMID:24394887

  18. Electrostatic Charge on Flying Hummingbirds and Its Potential Role in Pollination.

    PubMed

    Badger, Marc; Ortega-Jimenez, Victor Manuel; von Rabenau, Lisa; Smiley, Ashley; Dudley, Robert

    2015-01-01

    Electrostatic phenomena are known to enhance both wind- and insect-mediated pollination, but have not yet been described for nectar-feeding vertebrates. Here we demonstrate that wild Anna's Hummingbirds (Calypte anna) can carry positive charges up to 800 pC while in flight (mean ± s.d.: 66 ± 129 pC). Triboelectric charging obtained by rubbing an isolated hummingbird wing against various plant structures generated charges up to 700 pC. A metal hummingbird model charged to 400 pC induced bending of floral stamens in four plants (Nicotiana, Hemerocallis, Penstemon, and Aloe spp.), and also attracted falling Lycopodium spores at distances of < 2 mm. Electrostatic forces may therefore influence pollen transfer onto nectar-feeding birds. PMID:26421845

  19. Electron holographic tomography for mapping the three-dimensional distribution of electrostatic potential in III-V semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Wolf, D.; Lichte, H.; Pozzi, G.; Prete, P.; Lovergine, N.

    2011-06-01

    Electron holographic tomography (EHT), the combination of off-axis electron holography with electron tomography, is a technique, which can be applied to the quantitative 3-dimensional (3D) mapping of electrostatic potential at the nanoscale. Here, we show the results obtained in the EHT investigation of GaAs and GaAs-AlGaAs core-shell nanowires grown by Au-catalysed metalorganic vapor phase epitaxy. The unique ability of EHT of disentangling the materials mean inner potential (MIP) from the specimen projected thickness allows reconstruction of the nanowire 3D morphology and inner compositional structure as well as the measurement of the MIP.

  20. Electron holographic tomography for mapping the three-dimensional distribution of electrostatic potential in III-V semiconductor nanowires

    SciTech Connect

    Wolf, D.; Lichte, H.; Pozzi, G.; Lovergine, N.

    2011-06-27

    Electron holographic tomography (EHT), the combination of off-axis electron holography with electron tomography, is a technique, which can be applied to the quantitative 3-dimensional (3D) mapping of electrostatic potential at the nanoscale. Here, we show the results obtained in the EHT investigation of GaAs and GaAs-AlGaAs core-shell nanowires grown by Au-catalysed metalorganic vapor phase epitaxy. The unique ability of EHT of disentangling the materials mean inner potential (MIP) from the specimen projected thickness allows reconstruction of the nanowire 3D morphology and inner compositional structure as well as the measurement of the MIP.

  1. The potential of sarcospan in adhesion complex replacement therapeutics for the treatment of muscular dystrophy.

    PubMed

    Marshall, Jamie L; Kwok, Yukwah; McMorran, Brian J; Baum, Linda G; Crosbie-Watson, Rachelle H

    2013-09-01

    Three adhesion complexes span the sarcolemma and facilitate critical connections between the extracellular matrix and the actin cytoskeleton: the dystrophin- and utrophin-glycoprotein complexes and α7β1 integrin. Loss of individual protein components results in a loss of the entire protein complex and muscular dystrophy. Muscular dystrophy is a progressive, lethal wasting disease characterized by repetitive cycles of myofiber degeneration and regeneration. Protein-replacement therapy offers a promising approach for the treatment of muscular dystrophy. Recently, we demonstrated that sarcospan facilitates protein-protein interactions amongst the adhesion complexes and is an important potential therapeutic target. Here, we review current protein-replacement strategies, discuss the potential benefits of sarcospan expression, and identify important experiments that must be addressed for sarcospan to move to the clinic. PMID:23601082

  2. Auto-Adhesion Potential of Extraocular Aqp0 during Teleost Development.

    PubMed

    Chauvigné, François; Fjelldal, Per Gunnar; Cerdà, Joan; Finn, Roderick Nigel

    2016-01-01

    AQP0 water channels are the most abundant proteins expressed in the mammalian lens fiber membranes where they are essential for lens development and transparency. Unlike other aquaporin paralogs, mammalian AQP0 has a low intrinsic water permeability, but can form cell-to-cell junctions between the lens fibers. It is not known whether the adhesive properties of AQP0 is a derived feature found only in mammals, or exists as a conserved ancestral trait in non-mammalian vertebrates. Here we show that a tetraploid teleost, the Atlantic salmon, expresses four Aqp0 paralogs in the developing lens, but also expresses significant levels of aqp0 mRNAs and proteins in the epithelia of the pronephros, presumptive enterocytes, gill filament and epidermis. Quantitative PCR reveals that aqp0 mRNA titres increase by three orders of magnitude between the onset of somitogenesis and pigmentation of the eye. Using in situ hybridization and specific antisera, we show that at least two of the channels (Aqp0a1, -0b1 and/or -0b2) are localized in the extraocular basolateral and apical membranes, while Aqp0a2 is lens-specific. Heterologous expression of the Aqp0 paralogs in adhesion-deficient mouse fibolast L-cells reveals that, as for human AQP0, each intact salmon channel retains cell-to-cell adhesive properties. The strongest Aqp0 interactions are auto-adhesion, suggesting that homo-octamers likely form the intercellular junctions of the developing lens and epithelial tissues. The present data are thus the first to show the adhesion potential of Aqp0 channels in a non-mammalian vertebrate, and further uncover a novel extraocular role of the channels during vertebrate development. PMID:27153052

  3. Auto-Adhesion Potential of Extraocular Aqp0 during Teleost Development

    PubMed Central

    Chauvigné, François; Fjelldal, Per Gunnar; Cerdà, Joan; Finn, Roderick Nigel

    2016-01-01

    AQP0 water channels are the most abundant proteins expressed in the mammalian lens fiber membranes where they are essential for lens development and transparency. Unlike other aquaporin paralogs, mammalian AQP0 has a low intrinsic water permeability, but can form cell-to-cell junctions between the lens fibers. It is not known whether the adhesive properties of AQP0 is a derived feature found only in mammals, or exists as a conserved ancestral trait in non-mammalian vertebrates. Here we show that a tetraploid teleost, the Atlantic salmon, expresses four Aqp0 paralogs in the developing lens, but also expresses significant levels of aqp0 mRNAs and proteins in the epithelia of the pronephros, presumptive enterocytes, gill filament and epidermis. Quantitative PCR reveals that aqp0 mRNA titres increase by three orders of magnitude between the onset of somitogenesis and pigmentation of the eye. Using in situ hybridization and specific antisera, we show that at least two of the channels (Aqp0a1, -0b1 and/or -0b2) are localized in the extraocular basolateral and apical membranes, while Aqp0a2 is lens-specific. Heterologous expression of the Aqp0 paralogs in adhesion-deficient mouse fibolast L-cells reveals that, as for human AQP0, each intact salmon channel retains cell-to-cell adhesive properties. The strongest Aqp0 interactions are auto-adhesion, suggesting that homo-octamers likely form the intercellular junctions of the developing lens and epithelial tissues. The present data are thus the first to show the adhesion potential of Aqp0 channels in a non-mammalian vertebrate, and further uncover a novel extraocular role of the channels during vertebrate development. PMID:27153052

  4. Origins of electrostatic potential wells at dislocations in polycrystalline Cu(In,Ga)Se{sub 2} thin films

    SciTech Connect

    Dietrich, J.; Abou-Ras, D. Schmidt, S. S.; Rissom, T.; Unold, T.; Cojocaru-Mirédin, O.; Niermann, T.; Lehmann, M.; Koch, C. T.; Boit, C.

    2014-03-14

    Thin-film solar cells based on Cu(In,Ga)Se{sub 2} (CIGSe) reach high power-conversion efficiencies in spite of large dislocation densities of up to 10{sup 10}–10{sup 11} cm{sup −2}. The present work gives insight into the structural and compositional properties of dislocations in CIGSe thin films, which are embedded in a complete solar cell stack. These properties are related to the average electrical potential distributions obtained by means of inline electron holography. At a part of the dislocations studied, the average electrostatic potential shows local minima, all with depths of about −1.4 V. The measured average electrostatic potential distributions were modeled in order to reveal possible influences from strain fields, excess charge, and also compositional changes at the dislocation core. Cu depletion around the dislocation core, as evidenced by atom-probe tomography, explains best the measured potential wells. Their influences of the strain field around the dislocation core and of excess charge at the dislocation core are small. A structural model of dislocations in CIGSe thin films is provided which includes a Cu-depleted region around the dislocation core and gives a possible explanation for why decent photovoltaic performances are possible in the presence of rather large dislocation densities.

  5. Photogenerated charges and surface potential variations investigated on single Si nanorods by electrostatic force microscopy combined with laser irradiation

    PubMed Central

    2014-01-01

    Photogenerated charging properties of single Si nanorods (Si NRs) are investigated by electrostatic force microscopy (EFM) combined with laser irradiation. Under laser irradiation, Si NRs are positively charged. The amount of the charges trapped in single NRs as well as the contact potential difference between the tip and NRs' surface is achieved from an analytical fitting of the phase shift - voltage curve. Both of them significantly vary with the laser intensity and the NR's size and construction. The photogenerated charging and decharging rates are obtained at a timescale of seconds or slower, indicating that the Si NRs are promising candidates in photovoltaic applications. PMID:24940176

  6. The potential of sarcospan in adhesion complex replacement therapeutics for the treatment of muscular dystrophy

    PubMed Central

    Marshall, Jamie L.; Kwok, Yukwah; McMorran, Brian; Baum, Linda G.; Crosbie-Watson, Rachelle H.

    2013-01-01

    Three adhesion complexes span the sarcolemma and facilitate critical connections between the extracellular matrix and the actin cytoskeleton: the dystrophin- and utrophin-glycoprotein complexes and α7β1 integrin. Loss of individual protein components results in a loss of the entire protein complex and muscular dystrophy. Muscular dystrophy is a progressive, lethal wasting disease characterized by repetitive cycles of myofiber degeneration and regeneration. Protein replacement therapy offers a promising approach for the treatment of muscular dystrophy. Recently, we demonstrated that sarcospan facilitates protein-protein interactions amongst the adhesion complexes and is an important therapeutic target. Here, we review current protein replacement strategies, discuss the potential benefits of sarcospan expression, and identify important experiments that must be addressed for sarcospan to move to the clinic. PMID:23601082

  7. Radial scan of the molecular electrostatic potential of RNA double helices: an application to the enzyme-tRNA recognition.

    PubMed

    Marín, Ray M; Agudelo, William A; Daza C, Edgar E

    2008-10-01

    We introduced a method to characterize quantitatively the molecular electrostatic potential (MEP) of the minor and major grooves of base pairs located at nucleic acid double helices. By means of a radial MEP scan, we obtained a n-tuple of potential values corresponding to each groove, which can be analyzed by plotting the MEP values as a function of the angle in the radial scan. We studied base pairs of two different tRNAs, relevant in the recognition process with their cognate aminoacyl tRNA synthetases (aaRSs), in order to correlate their electrostatic behavior with the corresponding aminoacylation activity. We analyzed the first three base pairs of the Escherichia coli tRNA(Ala) acceptor stem, finding several cases where the MEP profiles obtained from the plots are in agreement with the reported aminoacylation activities. Additionally, a non-hierarchical clustering performed over the MEP n-tuples resulted in meaningful classifications that correlate with the activity and with the predicted stereochemistry of the reaction. We also studied the first two base pairs of the E. coli tRNA(Thr) acceptor stem but constraining the analysis to the angle intervals that seem relevant for the binding sites of the enzyme. These intervals were deduced from the ThrRS-tRNA(Thr) complex crystal structure. In this case, we also found a good agreement between the MEP profiles and the activity, supporting the idea that the tRNA identity elements function is to allow an optimal electrostatic complementarity between the aminoacyl-tRNA synthetase and the tRNA. PMID:18586541

  8. Sweating the small stuff: Glycoproteins in human sweat and their unexplored potential for microbial adhesion.

    PubMed

    Peterson, Robyn A; Gueniche, Audrey; Adam de Beaumais, Ségolène; Breton, Lionel; Dalko-Csiba, Maria; Packer, Nicolle H

    2016-03-01

    There is increasing evidence that secretory fluids such as tears, saliva and milk play an important role in protecting the human body from infection via a washing mechanism involving glycan-mediated adhesion of potential pathogens to secretory glycoproteins. Interaction of sweat with bacteria is well established as the cause of sweat-associated malodor. However, the role of sweat glycoproteins in microbial attachment has received little, if any, research interest in the past. In this review, we demonstrate how recent published studies involving high-throughput proteomic analysis have inadvertently, and fortuitously, exposed an abundance of glycoproteins in sweat, many of which have also been identified in other secretory fluids. We bring together research demonstrating microbial adhesion to these secretory glycoproteins in tears, saliva and milk and suggest a similar role of the sweat glycoproteins in mediating microbial attachment to sweat and/or skin. The contribution of glycan-mediated microbial adhesion to sweat glycoproteins, and the associated impact on sweat derived malodor and pathogenic skin infections are unchartered new research areas that we are beginning to explore. PMID:26582610

  9. Accuracy and efficiency in computing electrostatic potential for an ion channel model in layered dielectric/electrolyte media

    NASA Astrophysics Data System (ADS)

    Lin, Huimin; Tang, Huazhong; Cai, Wei

    2014-02-01

    This paper will investigate the numerical accuracy and efficiency in computing the electrostatic potential for a finite-height cylinder, used in an explicit/implicit hybrid solvation model for ion channel and embedded in a layered dielectric/electrolyte medium representing a biological membrane and ionic solvents. A charge locating inside the cylinder cavity, where ion channel proteins and ions are given explicit atomistic representations, will be influenced by the polarization field of the surrounding implicit dielectric/electrolyte medium. Two numerical techniques, a specially designed boundary integral equation method and an image charge method, will be investigated and compared in terms of accuracy and efficiency for computing the electrostatic potential. The boundary integral equation method based on the three-dimensional layered Green's functions provides a highly accurate solution suitable for producing a benchmark reference solution, while the image charge method is found to give reasonable accuracy and highly efficient and viable to use the fast multipole method for interactions of a large number of charges in the atomistic region of the hybrid solvation model.

  10. Accuracy and efficiency in computing electrostatic potential for an ion channel model in layered dielectric/electrolyte media

    SciTech Connect

    Lin, Huimin; Tang, Huazhong; Cai, Wei

    2014-02-15

    This paper will investigate the numerical accuracy and efficiency in computing the electrostatic potential for a finite-height cylinder, used in an explicit/implicit hybrid solvation model for ion channel and embedded in a layered dielectric/electrolyte medium representing a biological membrane and ionic solvents. A charge locating inside the cylinder cavity, where ion channel proteins and ions are given explicit atomistic representations, will be influenced by the polarization field of the surrounding implicit dielectric/electrolyte medium. Two numerical techniques, a specially designed boundary integral equation method and an image charge method, will be investigated and compared in terms of accuracy and efficiency for computing the electrostatic potential. The boundary integral equation method based on the three-dimensional layered Green's functions provides a highly accurate solution suitable for producing a benchmark reference solution, while the image charge method is found to give reasonable accuracy and highly efficient and viable to use the fast multipole method for interactions of a large number of charges in the atomistic region of the hybrid solvation model.

  11. Cell adhesion antagonists: therapeutic potential in asthma and chronic obstructive pulmonary disease.

    PubMed

    Woodside, Darren G; Vanderslice, Peter

    2008-01-01

    Chronic obstructive pulmonary disease (COPD) and asthma are inflammatory diseases of the lung where a hallmark feature is excessive leukocyte infiltration that leads to tissue injury. Cell adhesion molecules (e.g. selectins and integrins) play a key role in cell trafficking, and in the lung they regulate leukocyte extravasation, migration within the interstitium, cellular activation, and tissue retention. All selectin family members (including L-selectin, P-selectin, and E-selectin) and many of the beta1 and beta2 integrins appear to be important therapeutic targets, as numerous animal studies have demonstrated essential roles for these cell adhesion molecules in lung inflammation. Not surprisingly, these families of adhesion molecules have been under intense investigation by the pharmaceutical industry for the development of novel therapeutics. Integrins are validated drug targets, as drugs that antagonize integrin alphaIIbbeta3 (e.g. abciximab), integrin alphaLbeta2 (efalizumab), and integrin alpha4beta1 (natalizumab) are currently US FDA-approved for acute coronary syndromes, psoriasis, and multiple sclerosis, respectively. However, none has been approved for indications related to asthma or COPD. Here, we provide an overview of roles played by selectins and integrins in lung inflammation. We also describe recent clinical results (both failures and successes) in developing adhesion molecule antagonists, with specific emphasis on those targets that may have potential benefit in asthma and COPD. Early clinical trials using selectin and integrin antagonists have met with limited success. However, recent positive phase II clinical trials with a small-molecule selectin antagonist (bimosiamose) and a small-molecule integrin alpha4beta1 antagonist (valategrast [R411]), have generated enthusiastic anticipation that novel strategies to treat asthma and COPD may be forthcoming. PMID:18345706

  12. An improved fast multipole method for electrostatic potential calculations in a class of coarse-grained molecular simulations

    SciTech Connect

    Poursina, Mohammad; Anderson, Kurt S.

    2014-08-01

    This paper presents a novel algorithm to approximate the long-range electrostatic potential field in the Cartesian coordinates applicable to 3D coarse-grained simulations of biopolymers. In such models, coarse-grained clusters are formed via treating groups of atoms as rigid and/or flexible bodies connected together via kinematic joints. Therefore, multibody dynamic techniques are used to form and solve the equations of motion of such coarse-grained systems. In this article, the approximations for the potential fields due to the interaction between a highly negatively/positively charged pseudo-atom and charged particles, as well as the interaction between clusters of charged particles, are presented. These approximations are expressed in terms of physical and geometrical properties of the bodies such as the entire charge, the location of the center of charge, and the pseudo-inertia tensor about the center of charge of the clusters. Further, a novel substructuring scheme is introduced to implement the presented far-field potential evaluations in a binary tree framework as opposed to the existing quadtree and octree strategies of implementing fast multipole method. Using the presented Lagrangian grids, the electrostatic potential is recursively calculated via sweeping two passes: assembly and disassembly. In the assembly pass, adjacent charged bodies are combined together to form new clusters. Then, the potential field of each cluster due to its interaction with faraway resulting clusters is recursively calculated in the disassembly pass. The method is highly compatible with multibody dynamic schemes to model coarse-grained biopolymers. Since the proposed method takes advantage of constant physical and geometrical properties of rigid clusters, improvement in the overall computational cost is observed comparing to the tradition application of fast multipole method.

  13. High-resolution, three-dimensional modeling of human leukocyte antigen class I structure and surface electrostatic potential reveals the molecular basis for alloantibody binding epitopes.

    PubMed

    Kosmoliaptsis, Vasilis; Dafforn, Timothy R; Chaudhry, Afzal N; Halsall, David J; Bradley, J Andrew; Taylor, Craig J

    2011-11-01

    The potential of human leukocyte antigens (HLA) to stimulate humoral alloimmunity depends on the orientation, accessibility and physiochemical properties of polymorphic amino acids. We have generated high-resolution structural and physiochemical models of all common HLA class I alleles and analyzed the impact of amino acid polymorphisms on surface electrostatic potential. Atomic resolution three-dimensional structural models of HLA class I molecules were generated using the MODELLER computer algorithm. The molecular surface electrostatic potential was calculated using the DelPhi program. To confirm that electrostatic surface topography reflects known HLA B cell epitopes, we examined Bw4 and Bw6 and ascertained the impact of amino acid polymorphisms on their tertiary and physiochemical composition. The HLA protein structures generated performed well when subjected to stereochemical and energy-based testing for structural integrity. The electrostatic pattern and conformation of Bw4 and Bw6 epitopes are maintained among HLA molecules even when expressed in a different structural context. Importantly, variation in epitope amino acid composition does not always translate into a different electrostatic motif, providing an explanation for serologic cross-reactivity. Mutations of critical amino acids that abrogate antibody binding also induce distinct changes in epitope electrostatic properties. In conclusion, high-resolution structural modeling provides a physiochemical explanation for serologic patterns of antibody binding and provides novel insights into HLA immunogenicity. PMID:21840357

  14. Reduced Zeta potential through use of cationic adhesion promoter for improved resist process performance and minimizing material consumption

    NASA Astrophysics Data System (ADS)

    Hodgson, Lorna; Thompson, Andrew

    2012-03-01

    This paper presents the results of a non-HMDS (non-silane) adhesion promoter that was used to reduce the zeta potential for very thin (proprietary) polymer on silicon. By reducing the zeta potential, as measured by the minimum sample required to fully coat a wafer, the amount of polymer required to coat silicon substrates was significantly reduced in the manufacture of X-ray windows used for high transmission of low-energy X-rays. Moreover, this approach used aqueous based adhesion promoter described as a cationic surface active agent that has been shown to improve adhesion of photoresists (positive, negative, epoxy [SU8], e-beam and dry film). As well as reducing the amount of polymer required to coat substrates, this aqueous adhesion promoter is nonhazardous, and contains non-volatile solvents.

  15. Effects of natural antimicrobials on bacterial cell hydrophobicity, adhesion, and zeta potential / Vpliv naravnih protimikrobnih snovi na bakterijsko hidrofobnost, adhezijo in zeta potencial.

    PubMed

    Kurinčič, Marija; Jeršek, Barbara; Klančnik, Anja; Možina, Sonja Smole; Fink, Rok; Dražić, Goran; Raspor, Peter; Bohinc, Klemen

    2016-03-01

    Interactions between bacterial cells and contact materials play an important role in food safety and technology. As bacterial strains become ever more resistant to antibiotics, the aim of this study was to analyse adhesion of selected foodborne bacterial strains on polystyrene surface and to evaluate the effects of natural antimicrobials on bacterial cell hydrophobicity, adhesion, and zeta potential as strategies of adhesion prevention. The results showed strain-specific adhesion rate on polystyrene. The lowest and the highest adhesion were found for two B. cereus lines. Natural antimicrobials ferulic and rosmarinic acid substantially decreased adhesion, whereas the effect of epigallocatechin gallate was neglectful. Similar results were found for the zeta potential, indicating that natural antimicrobials reduce bacterial adhesion. Targeting bacterial adhesion using natural extracts we can eliminate potential infection at an early stage. Future experimental studies should focus on situations that are as close to industrial conditions as possible. PMID:27092638

  16. Fabrication and Characterization of Nano/Micro Textured Electret to Avoid Electrostatic Stiction and Enhance Its Surface Potential

    NASA Astrophysics Data System (ADS)

    Suzuki, M.; Shimokizaki, M.; Takahashi, T.; Yoshikawa, Y.; Aoyagi, S.

    2015-12-01

    An SiO2 electret with nano/micro scaled texture was developed to enhance generation power of our previously developed electrostatic vibration energy harvester. The texture on SiO2 was formed by lithography and wet etching process. The width /pitch of the each texture is 0.2 μm/0.6 μm or 1.0 μm/2.0 μm, respectively. Both initial value and stability of surface potential of textured electret was better than that of control sample. It was also found that the smaller texture enhance these properties. On the other hand, the stiction force using textured electret was smaller than that using control electret.

  17. On the origin of the electrostatic potential difference at a liquid-vacuum interface

    PubMed Central

    Harder, Edward; Roux, Benoît

    2008-01-01

    The microscopic origin of the interface potential calculated from computer simulations is elucidated by considering a simple model of molecules near an interface. The model posits that molecules are isotropically oriented and their charge density is Gaussian distributed. Molecules that have a charge density that is more negative toward their interior tend to give rise to a negative interface potential relative to the gaseous phase, while charge densities more positive toward their interior give rise to a positive interface potential. The interface potential for the model is compared to the interface potential computed from molecular dynamics simulations of the nonpolar vacuum-methane system and the polar vacuum-water interface system. The computed vacuum-methane interface potential from a molecular dynamics simulation (−220 mV) is captured with quantitative precision by the model. For the vacuum-water interface system, the model predicts a potential of −400 mV compared to −510 mV, calculated from a molecular dynamics simulation. The physical implications of this isotropic contribution to the interface potential is examined using the example of ion solvation in liquid methane. PMID:19102551

  18. Involvement of flocculin in negative potential-applied ITO electrode adhesion of yeast cells.

    PubMed

    Koyama, Sumihiro; Tsubouchi, Taishi; Usui, Keiko; Uematsu, Katsuyuki; Tame, Akihiro; Nogi, Yuichi; Ohta, Yukari; Hatada, Yuji; Kato, Chiaki; Miwa, Tetsuya; Toyofuku, Takashi; Nagahama, Takehiko; Konishi, Masaaki; Nagano, Yuriko; Abe, Fumiyoshi

    2015-09-01

    The purpose of this study was to develop novel methods for attachment and cultivation of specifically positioned single yeast cells on a microelectrode surface with the application of a weak electrical potential. Saccharomyces cerevisiae diploid strains attached to an indium tin oxide/glass (ITO) electrode to which a negative potential between -0.2 and -0.4 V vs. Ag/AgCl was applied, while they did not adhere to a gallium-doped zinc oxide/glass electrode surface. The yeast cells attached to the negative potential-applied ITO electrodes showed normal cell proliferation. We found that the flocculin FLO10 gene-disrupted diploid BY4743 mutant strain (flo10Δ /flo10Δ) almost completely lost the ability to adhere to the negative potential-applied ITO electrode. Our results indicate that the mechanisms of diploid BY4743 S. cerevisiae adhesion involve interaction between the negative potential-applied ITO electrode and the Flo10 protein on the cell wall surface. A combination of micropatterning techniques of living single yeast cell on the ITO electrode and omics technologies holds potential of novel, highly parallelized, microchip-based single-cell analysis that will contribute to new screening concepts and applications. PMID:26187908

  19. Involvement of flocculin in negative potential-applied ITO electrode adhesion of yeast cells

    PubMed Central

    Koyama, Sumihiro; Tsubouchi, Taishi; Usui, Keiko; Uematsu, Katsuyuki; Tame, Akihiro; Nogi, Yuichi; Ohta, Yukari; Hatada, Yuji; Kato, Chiaki; Miwa, Tetsuya; Toyofuku, Takashi; Nagahama, Takehiko; Konishi, Masaaki; Nagano, Yuriko; Abe, Fumiyoshi

    2015-01-01

    The purpose of this study was to develop novel methods for attachment and cultivation of specifically positioned single yeast cells on a microelectrode surface with the application of a weak electrical potential. Saccharomyces cerevisiae diploid strains attached to an indium tin oxide/glass (ITO) electrode to which a negative potential between −0.2 and −0.4 V vs. Ag/AgCl was applied, while they did not adhere to a gallium-doped zinc oxide/glass electrode surface. The yeast cells attached to the negative potential-applied ITO electrodes showed normal cell proliferation. We found that the flocculin FLO10 gene-disrupted diploid BY4743 mutant strain (flo10Δ /flo10Δ) almost completely lost the ability to adhere to the negative potential-applied ITO electrode. Our results indicate that the mechanisms of diploid BY4743 S. cerevisiae adhesion involve interaction between the negative potential-applied ITO electrode and the Flo10 protein on the cell wall surface. A combination of micropatterning techniques of living single yeast cell on the ITO electrode and omics technologies holds potential of novel, highly parallelized, microchip-based single-cell analysis that will contribute to new screening concepts and applications. PMID:26187908

  20. Evaluation of Serum Vascular Adhesion Protein-1 as a Potential Biomarker in Thyroid Cancer

    PubMed Central

    Zhao, Pengxin; Zhang, Kaili

    2016-01-01

    Vascular adhesion protein-1 (VAP-1) is a glycoprotein that mediates tissue-selective lymphocyte adhesion. The prognostic value of VAP-1 has been determined in gastric cancer. The aim of this study was to evaluate the changes and the predictive value of serum VAP-1 in patients with thyroid cancer. A total of 126 patients with thyroid nodules and 53 healthy controls participated in this study. The patients were further divided into subgroup 1 (69 cases with benign thyroid nodules) and subgroup 2 (57 cases with thyroid cancer). Serum VAP-1 was measured by time-resolved immunofluorometric assay. Diagnostic value of presurgical VAP-1 for thyroid cancer was conducted by receiver operating characteristic (ROC) curves. Serum levels of VAP-1 were significantly lower in thyroid cancer group than in healthy control and benign thyroid nodule groups. VAP-1 concentrations negatively correlated with serum thyroglobulin (Tg) levels in thyroid cancer patients (r = −0.81; p < 0.001). The optimum cut-off value of VAP-1 was 456.6 ng/mL with a 77.4% specificity and 66.7% sensitivity for thyroid cancer diagnosis. Serum VAP-1 decreased in thyroid cancer patients and VAP-1 could be a potential useful adjunct biomarker in the diagnosis of thyroid cancer. PMID:27446209

  1. Helical modulation of the electrostatic plasma potential due to edge magnetic islands induced by resonant magnetic perturbation fields at TEXTOR

    SciTech Connect

    Ciaccio, G. Spizzo, G.; Schmitz, O. Frerichs, H.; Abdullaev, S. S.; Evans, T. E.; White, R. B.

    2015-10-15

    The electrostatic response of the edge plasma to a magnetic island induced by resonant magnetic perturbations to the plasma edge of the circular limiter tokamak TEXTOR is analyzed. Measurements of plasma potential are interpreted by simulations with the Hamiltonian guiding center code ORBIT. We find a strong correlation between the magnetic field topology and the poloidal modulation of the measured plasma potential. The ion and electron drifts yield a predominantly electron driven radial diffusion when approaching the island X-point while ion diffusivities are generally an order of magnitude smaller. This causes a strong radial electric field structure pointing outward from the island O-point. The good agreement found between measured and modeled plasma potential connected to the enhanced radial particle diffusivities supports that a magnetic island in the edge of a tokamak plasma can act as convective cell. We show in detail that the particular, non-ambipolar drifts of electrons and ions in a 3D magnetic topology account for these effects. An analytical model for the plasma potential is implemented in the code ORBIT, and analyses of ion and electron radial diffusion show that both ion- and electron-dominated transport regimes can exist, which are known as ion and electron root solutions in stellarators. This finding and comparison with reversed field pinch studies and stellarator literature suggest that the role of magnetic islands as convective cells and hence as major radial particle transport drivers could be a generic mechanism in 3D plasma boundary layers.

  2. Analytical Debye-Huckel model for electrostatic potentials around dissolved DNA.

    PubMed Central

    Wagner, K; Keyes, E; Kephart, T W; Edwards, G

    1997-01-01

    We present an analytical, Green-function-based model for the electric potential of DNA in solution, treating the surrounding solvent with the Debye-Huckel approximation. The partial charge of each atom is accounted for by modeling DNA as linear distributions of atoms on concentric cylindrical surfaces. The condensed ions of the solvent are treated with the Debye-Huckel approximation. The resultant leading term of the potential is that of a continuous shielded line charge, and the higher order terms account for the helical structure. Within several angstroms of the surface there is sufficient information in the electric potential to distinguish features and symmetries of DNA. Plots of the potential and equipotential surfaces, dominated by the phosphate charges, reflect the structural differences between the A, B, and Z conformations and, to a smaller extent, the difference between base sequences. As the distances from the helices increase, the magnitudes of the potentials decrease. However, the bases and sugars account for a larger fraction of the double helix potential with increasing distance. We have found that when the solvent is treated with the Debye-Huckel approximation, the potential decays more rapidly in every direction from the surface than it did in the concentric dielectric cylinder approximation. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 7 PMID:9199767

  3. Electrostatic potentials and energy loss due to a projectile propagating through a non-Maxwellian dusty plasma

    SciTech Connect

    Deeba, F.; Ahmad, Zahoor; Murtaza, G.

    2006-08-15

    The electrostatic potentials (Debye and wake) and energy loss due to a charged projectile propagating through an unmagnetized collisionless dusty plasma are derived employing kappa and generalized (r,q) velocity distributions for the dust acoustic wave. It is found that these quantities in general differ from their Maxwellian counterparts and are sensitive to the values of spectral index, {kappa} in the case of kappa distribution and to r, q in the case of generalized (r,q) distribution. The amplitudes of these quantities are less for small values of the spectral index ({kappa}, r=0, q) but approach the Maxwellian in the limit {kappa}{yields}{infinity} (for kappa distribution) and for r=0, q{yields}{infinity} [for generalized (r,q) distribution]. For any nonzero value of r, the potential and the energy loss grow beyond the Maxwellian results. The effect of kappa and generalized (r,q) distributions on potential and energy loss is also studied numerically and the results are compared with those of the Maxwellian distribution.

  4. Measuring electrostatic potential profiles across amorphous intergranular films by electron diffraction.

    PubMed

    Koch, Christoph T; Bhattacharyya, Somnath; Rühle, Manfred; Satet, Raphaëlle L; Hoffmann, Michael J

    2006-04-01

    Amorphous 1-2-nm-wide intergranular films in ceramics dictate many of their properties. The detailed investigation of structure and chemistry of these films pushes the limits of today's transmission electron microscopy. We report on the reconstruction of the one-dimensional potential profile across the film from an experimentally acquired tilt series of energy-filtered electron diffraction patterns. Along with the potential profile, the specimen thickness, film orientation with respect to the grain lattice and specimen surface, and the absolute specimen orientation with respect to the laboratory frame of reference are retrieved. PMID:17481353

  5. Relative contribution of combined kinetic and exchange energy terms vs the electronic component of molecular electrostatic potential in hardness potential derivatives.

    PubMed

    Bhattacharjee, Rituparna; Roy, Ram Kinkar

    2013-11-14

    The relative contribution of the sum of kinetic [(10/9)CFρ(r)2/3] and exchange energy [(4/9)CXρ(r)1/3] terms to that of the electronic part of the molecular electrostatic potential [Vel(r)] in the variants of hardness potential is investigated to assess the proposed definition of Δ+h(k) = −[VelN+1(k) – VelN(k)] and Δ–h(k) = −[VelN(k) – VelN–1(k)] (Saha; et al. J. Comput. Chem. 2013, 34, 662). Some substituted benzenes and polycyclic aromatic hydrocarbons (PAHs) (undergoing electrophilic aromatic substitution), carboxylic acids, and their derivatives are chosen to carry out the theoretical investigation as stated above. Intra- and intermolecular reactivity trends generated by Δ+h(k) and Δ–h(k) are found to be satisfactory and are correlated reasonably well with experimental results. PMID:24083374

  6. Characterisation of a novel light activated adhesive scaffold: Potential for device attachment.

    PubMed

    Ark, Morris; Boughton, Philip; Lauto, Antonio; Tran, Giang T; Chen, Yongjuan; Cosman, Peter H; Dunstan, Colin R

    2016-09-01

    The most common methods for attaching a device to the internal tissues of the human body are via sutures, clips or staples. These attachment techniques require penetration and manipulation of the tissue. Tears and leaks can often be a complication post-attachment, and scarring usually occurs around the attachment sites. To resolve these issues, it is proposed to develop a soft tissue scaffold impregnated with Rose Bengal/Chitosan solution (RBC-scaffold, 0.01% w/v Rose Bengal, 1.7% w/v Medium Molecular Weight Chitosan). This scaffold will initially attach to the tissue via a light activation method. The light activates the dye in the scaffold which causes cross-links to form between the scaffold and tissue, thus adhering them together. This is done without mechanically manipulating the surrounding tissue, thus avoiding the issues associated with current techniques. Eventually, the scaffold will be resorbed and tissue will integrate for long-term attachment. A variety of tests were performed to characterise the RBC-scaffold. Porosity, interconnectivity, and mechanical strength were measured. Light activation was performed with a broad spectrum (380-780nm) 10W LED lamp exposed to various time lengths (2-15min, Fluence range 0.4-3J/cm(2) ). Adhesive strength of the light-activated bond was measured with lap-shear tests performed on porcine stomach tissue. Cell culture viability was also assessed to confirm tissue integration potential. These properties were compared to Variotis™, an aliphatic polyester soft tissue scaffold which has proven to be viable for soft tissue regeneration. The RBC-scaffolds were found to have high porosity (86.46±2.95%) and connectivity, showing rapid fluid movement. The elastic modulus of the RBC-scaffolds (3.55±1.28MPa) was found to be significantly higher than the controls (0.15±0.058MPa, p<0.01) and approached reported values for human gastrointestinal tissue (2.3MPa). The maximum adhesion strength achieved of the RBC-scaffolds was 8

  7. HEATING OF SIMPLE SOLUTIONS AND EMULSIONS EXPOSED TO HIGH FREQUENCY HIGH POTENTIAL ELECTROSTATIC FIELDS

    PubMed Central

    Marshall, W. H.

    1930-01-01

    1. It is shown that the absorption in liquid dielectrics is a function of potential gradient (field intensity) as well as frequency and that for values of potential gradient above, at least 70 volts per millimeter, the rate of rise of temperature-frequency curve increases rapidly with frequency. 2. The presence of ions in measurable quantity considerably changes the absorption characteristics and apparently causes the values to remain constant, whereas the values for water drop about 40 per cent, during exposure. The absorption also changes rapidly with the concentration of the electrolyte. 3. Very high absorption values are found for an emulsion of cotton-seed oil in 1 per cent sodium oleate. It is shown that the absorption is due to the colloidal structure (with the possibility that the energy is dissipated at the phase boundaries). PMID:19872553

  8. Confinement effects on excitation energies and regioselectivity as probed by the Fukui function and the molecular electrostatic potential

    NASA Astrophysics Data System (ADS)

    Borgoo, Alex; Tozer, David; Geerlings, Paul; de Proft, Frank

    2009-03-01

    When a molecule is placed as a guest inside a zeolite pore, its electronic structure will be altered, among others by the effect of the so-called ``confinement". It has been established that the compression of the molecular orbitals influences a system's reactivity. In this work we use a simple potential barrier method to quantify the importance of confinement effects on chemical reactivity. In the first part, excitation energies and molecular orbital energy gaps are evaluated for molecules placed in cavities of different sizes. Our results for ethylene and formaldehyde reveal an increase in excitation energy and the gap between the occupied and the unoccupied levels. In the case of the larger molecules naphthalene and anthracene, the HOMO-LUMO gap shows very little sensitivity to the confinement. To investigate the role of confinement effects on local aspects of chemical reactivity and on regioselectivity, we evaluated its effect on the Fukui function and the molecular electrostatic potential, reactivity indices that are central in the description of orbital and charge controlled reactions. The results indicate that confinement can influence the regioselectivity and that the reactivity of anions is expected to change, due to the artificial binding of the exess electron.

  9. Zero-flux surfaces of the electrostatic potential: the border of influence zones of nucleophilic and electrophilic sites in crystalline environment.

    PubMed

    Mata, Ignasi; Molins, Elies; Espinosa, Enrique

    2007-10-01

    The topology of the electrostatic potential varphi(r) has been studied for single molecules using geometries and electron distributions rho(r) determined from high-resolution single-crystal X-ray diffraction data. The electrostatic potential gradient nablavarphi(r), which is the negative of the electric field E = -nablavarphi, has been represented, revealing the position of zero-flux surfaces and critical points. Local maxima and minima of the electrostatic potential are interpreted in terms of electrophilic and nucleophilic sites, which present influence zones delimited by zero-flux surfaces containing saddle points. The influence zones of the nucleophilic and electrophilic sites define two alternative partitions of the space in disjoint volumes, the completeness of these partitions depending on either the neutral or ionic character of the molecule. The results obtained by using this methodology are useful for the interpretation of the saddle points of the electrostatic potential, which are related to the limits of the influence zones and reveal the path for preferred attack on reactive sites with finite influence zones. PMID:17727276

  10. EVALUATION OF A FINITE MULTIPOLE EXPANSION TECHNIQUE FOR THE COMPUTATION OF ELECTROSTATIC POTENTIALS OF DIBENZO-P-DIOXINS AND RELATED SYSTEMS

    EPA Science Inventory

    The electrostatic potential V(r) that the nuclei and electrons of a molecule create in the surrounding space is well established as a guide in the study of molecular reactivity, and particularly, of biological recognition processes. ts rigorous computation is, however, very deman...

  11. COMPARATIVE ANALYSIS OF THE ELECTROSTATIC POTENTIALS OF SOME STRUCTURAL ANALOGUES OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN AND OF RELATED AROMATIC SYSTEMS

    EPA Science Inventory

    We have carried out an ab initio STO-5G computational analysis of the electrostatic potential of four structural analogues of the highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and four related aromatic systems: benzo[a]pyrene, benz[a]anthracene and two isomeric benzofla...

  12. Electrical potential-assisted DNA hybridization. How to mitigate electrostatics for surface DNA hybridization.

    PubMed

    Tymoczko, Jakub; Schuhmann, Wolfgang; Gebala, Magdalena

    2014-12-24

    Surface-confined DNA hybridization reactions are sensitive to the number and identity of DNA capture probes and experimental conditions such as the nature and the ionic strength of the electrolyte solution. When the surface probe density is high or the concentration of bulk ions is much lower than the concentration of ions within the DNA layer, hybridization is significantly slowed down or does not proceed at all. However, high-density DNA monolayers are attractive for designing high-sensitivity DNA sensors. Thus, circumventing sluggish DNA hybridization on such interfaces allows a high surface concentration of target DNA and improved signal/noise ratio. We present potential-assisted hybridization as a strategy in which an external voltage is applied to the ssDNA-modified interface during the hybridization process. Results show that a significant enhancement of hybridization can be achieved using this approach. PMID:25102381

  13. Sterically stabilized liposomes. Reduction in electrophoretic mobility but not electrostatic surface potential.

    PubMed Central

    Woodle, M C; Collins, L R; Sponsler, E; Kossovsky, N; Papahadjopoulos, D; Martin, F J

    1992-01-01

    The electrophoretic mobility of liposomes containing a negatively charged derivative of phosphatidylethanolamine with a large headgroup composed of the hydrophilic polymer polyethylene glycol (PEG-PE) was determined by Doppler electrophoretic light scattering. The results show that this method is improved by the use of measurements at multiple angles to eliminate artifacts and that very small mobilities can be measured. The electrophoretic mobility of liposomes with 5 to 10 mol% PEG-PE is approximately -0.5 mu ms-1/Vcm-1 regardless of PEG-PE content compared with approximately -2 mu ms-1/Vcm-1 for similar liposomes but containing 7.5% phosphatidylglycerol (PG) instead of PEG-PE. Measurements of surface potential by distribution of an anionic fluorescent probe show that the PEG-PE imparts a negative charge identical to that by PG, consistent with the expectation of similar locations of the ionized phosphate responsible for the charge. The reduced mobility imparted by the surface bound PEG is attributed to a mechanism similar to that described for colloidal steric stabilization: hydrodynamic drag moves the hydrodynamic plane of shear, or the hydrodynamic radius, away from the charge-bearing plane, that of the phosphate moities. An extended length of approximately 50 A for the 2,000 molecular weight PEG is estimated from the reduction in electrophoretic mobility. PMID:1581503

  14. La3+-induced fusion of phosphatidylserine liposomes. Close approach, intermembrane intermediates, and the electrostatic surface potential.

    PubMed Central

    Bentz, J; Alford, D; Cohen, J; Düzgüneş, N

    1988-01-01

    The fusion of large unilamellar phosphatidylserine liposomes (PS LUV) induced by La3+ has been monitored using the 1-aminoapthalene-3,6,8-trisulfonic acid/p-xylenebis(pyridinium bromide) (ANTS/DPX) fluorescence assay for the mixing of aqueous contents. The fusion event is extensive and nonleaky, with up to 95% mixing of contents in the fused liposomes. However, addition of excess EDTA leads to disruption of the fusion products in a way that implies the existence of metastable intermembrane contact sites. The maximal fusion activity occurs between 10 and 100 microM La3+ and fusion can be terminated rapidly, without loss of contents, by the addition of excess La3+, e.g., 1 mM La3+ at pH 7.4. This observation is explained by the very large intrinsic binding constant (approximately 10(5) M-1) of La3+ to the PS headgroup, as measured by microelectrophoresis. Addition of 1 mM La3+ causes charge reversal of the membrane and a large positive surface potential. La3+ binding to PS causes the release of a proton. These data can be explained if La3+ can chelate to PS at two sites, with one of the sites being the primary amino group. This binding model successfully predicts that at pH 4.5 fusion occurs up to 2 mM La3+, due to reduced La3+ binding at low pH. We conclude that the general mechanism of membrane fusion includes three kinetic steps. In addition to (a) aggregation, there is (b) the close approach of the surfaces, or thinning of the hydration layer, and (c) the formation of intermembrane intermediates which determine the extent to which membrane destabilization leads to fusion (mixing of aqueous contents), as opposed to lysis. The lifetime of these intermembrane intermediates appears to depend upon La3+ binding to both PS sites. PMID:3382713

  15. Kirkwood-Buff Integrals for Aqueous Urea Solutions Based upon the Quantum Chemical Electrostatic Potential and Interaction Energies.

    PubMed

    Chiba, Shuntaro; Furuta, Tadaomi; Shimizu, Seishi

    2016-08-11

    Cosolvents, such as urea, affect protein folding and binding, and the solubility of solutes. The modeling of cosolvents has been facilitated significantly by the rigorous Kirkwood-Buff (KB) theory of solutions, which can describe structural thermodynamics over the entire composition range of aqueous cosolvent mixtures based only on the solution density and the KB integrals (KBIs), i.e., the net excess radial distribution functions from the bulk. Using KBIs to describe solution thermodynamics has given rise to a clear guideline that an accurate prediction of KBIs is equivalent to accurate modeling of cosolvents. Taking urea as an example, here we demonstrate that an improvement in the prediction of KBIs comes from an improved reproduction of high-level quantum chemical (QC) electrostatic potential and molecular pairwise interaction energies. This rational approach to the improvement of the KBI prediction stems from a comparison of existing force fields, AMOEBA, and the generalized AMBER force field, as well as the further optimization of the former to enable better agreement with QC interaction energies. Such improvements would pave the way toward a rational and systematic determination of the transferable force field parameters for a number of important small molecule cosolvents. PMID:27434200

  16. CFTR: A Cysteine at Position 338 in TM6 Senses a Positive Electrostatic Potential in the Pore

    PubMed Central

    Liu, Xuehong; Zhang, Zhi-Ren; Fuller, Matthew D.; Billingsley, Joshua; McCarty, Nael A.; Dawson, David C.

    2004-01-01

    We investigated the accessibility to protons and thiol-directed reagents of a cysteine substituted at position 338 in transmembrane segment 6 (TM6) of CFTR to test the hypothesis that T338 resides in the pore. Xenopus oocytes expressing T338C CFTR exhibited pH-dependent changes in gCl and I-V shape that were specific to the substituted cysteine. The apparent pKa of T338C CFTR was more acidic than that expected for a cysteine or similar simple thiols in aqueous solution. The pKa was shifted toward alkaline values when a nearby positive charge (R334) was substituted with neutral or negatively charged residues, consistent with the predicted influence of the positive charge of R334, and perhaps other residues, on the titration of a cysteine at 338. The relative rates of chemical modification of T338C CFTR by MTSET+ and MTSES− were also altered by the charge at 334. These observations support a model for CFTR that places T338 within the anion conduction path. The apparent pKa of a cysteine substituted at 338 and the relative rates of reaction of charged thiol-directed reagents provide a crude measure of a positive electrostatic potential that may be due to R334 and other residues near this position in the pore. PMID:15361410

  17. CFTR: a cysteine at position 338 in TM6 senses a positive electrostatic potential in the pore.

    PubMed

    Liu, Xuehong; Zhang, Zhi-Ren; Fuller, Matthew D; Billingsley, Joshua; McCarty, Nael A; Dawson, David C

    2004-12-01

    We investigated the accessibility to protons and thiol-directed reagents of a cysteine substituted at position 338 in transmembrane segment 6 (TM6) of CFTR to test the hypothesis that T338 resides in the pore. Xenopus oocytes expressing T338C CFTR exhibited pH-dependent changes in gCl and I-V shape that were specific to the substituted cysteine. The apparent pKa of T338C CFTR was more acidic than that expected for a cysteine or similar simple thiols in aqueous solution. The pKa was shifted toward alkaline values when a nearby positive charge (R334) was substituted with neutral or negatively charged residues, consistent with the predicted influence of the positive charge of R334, and perhaps other residues, on the titration of a cysteine at 338. The relative rates of chemical modification of T338C CFTR by MTSET+ and MTSES- were also altered by the charge at 334. These observations support a model for CFTR that places T338 within the anion conduction path. The apparent pKa of a cysteine substituted at 338 and the relative rates of reaction of charged thiol-directed reagents provide a crude measure of a positive electrostatic potential that may be due to R334 and other residues near this position in the pore. PMID:15361410

  18. Inverted cucurbit[n]urils: density functional investigations on the electronic structure, electrostatic potential, and NMR chemical shifts.

    PubMed

    Pinjari, Rahul V; Gejji, Shridhar P

    2009-02-19

    Inverted cucurbit[n]uril (i(x)CB[n], x = 1, 2; n = 6-8), the enantiomers of cucurbit[n]uril (CB[n]) comprising one or more inverted glycouril units, show distinct selectivity in recognition toward the guest by the virtue of shape and dimensions of its cavity. The iCB[n] (x = 1 and n = 6, 7) are isolated as intermediates during the synthesis of CB[n]. In this work, density functional theory using the hybrid B3LYP functional has been employed to derive the electronic structure and the NMR chemical shifts in the i(x)CB[n] hosts. The present calculations have shown that the inversion of the glycouril unit of CB[6] and CB[7] engenders a destabilization by 4.2 and 5.7 kJ mol(-1), respectively, and, as opposed to this, the iCB[8] is favored by 18.6 kJ mol(-1) over the corresponding CB[8] host. Likewise, i2CB[7] possessing two inverted glycourils are highly destabilized over CB[7]. A large separation of the inverted glycouril units reduces the repulsion between methine protons inside the cavity, rendering the 1,4-i2CB[n] (n = 7 or 8) to be of lowest energy. Stabilization energies from the self-consistent reaction field (SCRF) theory are calculated with water, ethanol, and tetrahydrofuran (THF) as solvents. Unlike in gas phase and other solvents, the stabilization hierarchy iCB[6] < iCB[7] < iCB[8] has been predicted in THF. Molecular electrostatic potential (MESP) was used to gauge the cavity shape of these hosts. Consequently the iCB[6] reveals a half-sprocket-like cavity; an additional tooth for each glycouril in the succeeding iCB[n] homologue was noticed. In the case of the 1,5-i2CB[8] enantiomer, the cavity turns out to be rectangular. The deeper MESP minima near the ureido oxygens suggest strong electrostatic interactions with the guest at the iCB[6] portals. The electron-rich region within the cavity explains the large affinity of CB[n] toward the electron deficient guests. The electronic distribution and shape and size of the cavity thus derived provide insights

  19. Electrostatic Field Invisibility Cloak.

    PubMed

    Lan, Chuwen; Yang, Yuping; Geng, Zhaoxin; Li, Bo; Zhou, Ji

    2015-01-01

    The invisibility cloak has been drawing much attention due to its new concept for manipulating many physical fields, from oscillating wave fields (electromagnetic, acoustic and elastic) to static magnetic fields, dc electric fields, and diffusive fields. Here, an electrostatic field invisibility cloak has been theoretically investigated and experimentally demonstrated to perfectly hide two dimensional objects without disturbing their external electrostatic fields. The desired cloaking effect has been achieved via both cancelling technology and transformation optics (TO). This study demonstrates a novel way for manipulating electrostatic fields, which shows promise for a wide range of potential applications. PMID:26552343

  20. Electrostatic Field Invisibility Cloak

    PubMed Central

    Lan, Chuwen; Yang, Yuping; Geng, Zhaoxin; Li, Bo; Zhou, Ji

    2015-01-01

    The invisibility cloak has been drawing much attention due to its new concept for manipulating many physical fields, from oscillating wave fields (electromagnetic, acoustic and elastic) to static magnetic fields, dc electric fields, and diffusive fields. Here, an electrostatic field invisibility cloak has been theoretically investigated and experimentally demonstrated to perfectly hide two dimensional objects without disturbing their external electrostatic fields. The desired cloaking effect has been achieved via both cancelling technology and transformation optics (TO). This study demonstrates a novel way for manipulating electrostatic fields, which shows promise for a wide range of potential applications. PMID:26552343

  1. Electrostatic Field Invisibility Cloak

    NASA Astrophysics Data System (ADS)

    Lan, Chuwen; Yang, Yuping; Geng, Zhaoxin; Li, Bo; Zhou, Ji

    2015-11-01

    The invisibility cloak has been drawing much attention due to its new concept for manipulating many physical fields, from oscillating wave fields (electromagnetic, acoustic and elastic) to static magnetic fields, dc electric fields, and diffusive fields. Here, an electrostatic field invisibility cloak has been theoretically investigated and experimentally demonstrated to perfectly hide two dimensional objects without disturbing their external electrostatic fields. The desired cloaking effect has been achieved via both cancelling technology and transformation optics (TO). This study demonstrates a novel way for manipulating electrostatic fields, which shows promise for a wide range of potential applications.

  2. Numerically bridging lamellipodial and filopodial activity during cell spreading reveals a potentially novel trigger of focal adhesion maturation.

    PubMed

    Loosli, Y; Vianay, B; Luginbuehl, R; Snedeker, J G

    2012-05-01

    We present a novel approach to modeling cell spreading, and use it to reveal a potentially central mechanism regulating focal adhesion maturation in various cell phenotypes. Actin bundles that span neighboring focal complexes at the lamellipodium-lamellum interface were assumed to be loaded by intracellular forces in proportion to bundle length. We hypothesized that the length of an actin bundle (with the corresponding accumulated force at its adhesions) may thus regulate adhesion maturation to ensure cell mechanical stability and morphological integrity. We developed a model to test this hypothesis, implementing a "top-down" approach to simplify certain cellular processes while explicitly incorporating complexity of other key subcellular mechanisms. Filopodial and lamellipodial activities were treated as modular processes with functional spatiotemporal interactions coordinated by rules regarding focal adhesion turnover and actin bundle dynamics. This theoretical framework was able to robustly predict temporal evolution of cell area and cytoskeletal organization as reported from a wide range of cell spreading experiments using micropatterned substrates. We conclude that a geometric/temporal modeling framework can capture the key functional aspects of the rapid spreading phase and resultant cytoskeletal complexity. Hence the model is used to reveal mechanistic insight into basic cell behavior essential for spreading. It demonstrates that actin bundles spanning nascent focal adhesions such that they are aligned to the leading edge may accumulate centripetal endogenous forces along their length, and could thus trigger focal adhesion maturation in a force-length dependent fashion. We suggest that this mechanism could be a central "integrating" factor that effectively coordinates force-mediated adhesion maturation at the lamellipodium-lamellum interface. PMID:22453759

  3. Surface Electrostatic Potential and Water Orientation in the presence of Sodium Octanoate Dilute Monolayers Studied by Means of Molecular Dynamics Simulations.

    PubMed

    Bernardino, Kalil; de Moura, André F

    2015-10-13

    A series of atomistic molecular dynamics simulations were performed in the present investigation to assess the spontaneous formation of surfactant monolayers of sodium octanoate at the water-vacuum interface. The surfactant surface coverage increased until a saturation threshold was achieved, after which any further surfactant addition led to the formation of micellar aggregates within the solution. The saturated films were not densely packed, as might be expected for short-chained surfactants, and all films regardless of the surface coverage presented surfactant molecules with the same ordering pattern, namely, with the ionic heads toward the aqueous solution and the tails lying nearly parallel to the interface. The major contributions to the electrostatic surface potential came from the charged heads and the counterion distribution, which nearly canceled out each other. The balance between the oppositely charged ions rendered the electrostatic contributions from water meaningful, amounting to ca. 10% of the contributions arising from the ionic species. And even the aliphatic tails, whose atoms bear relatively small partial atomic charges as compared to the polar molecules and molecular fragments, contributed with ca. 20% of the total electrostatic surface potential of the systems under investigation. Although the aliphatic tails were not so orderly arranged as in a compact film, the C-H bonds assumed a preferential orientation, leading to an increased contribution to the electrostatic properties of the interface. The most prominent feature arising from the partitioning of the electrostatic potential into individual contributions was the long-range ordering of the water molecules. This ordering of the water molecules produced a repulsive dipole-dipole interaction between the two interfaces, which increased with the surface coverage. Only for a water layer wider than 10 nm was true bulk behavior observed, and the repulsive dipole-dipole interaction faded away. PMID

  4. Electrostatic Explorations.

    ERIC Educational Resources Information Center

    Gallai, Ditta; Stewart, Gay

    1998-01-01

    Presents a set of hands-on electrostatics experiments in the form of an activity guide and worksheet through which students discover the different types of electric charge, Coulomb's Law, induced charge separation, and grounding. (DDR)

  5. Effects of electronic coupling and electrostatic potential on charge transport in carbon-based molecular electronic junctions.

    PubMed

    McCreery, Richard L

    2016-01-01

    Molecular junctions consisting of 2-20 nm thick layers of organic oligomers oriented between a conducting carbon substrate and a carbon/gold top contact have proven to be reproducible and reliable, and will soon enter commercial production in audio processing circuits. The covalent, conjugated bond between one or both sp(2)-hybridized carbon contacts and an aromatic molecular layer is distinct from the more common metal/molecule or silicon/molecule structures in many reported molecular junctions. Theoretical observations based on density functional theory are presented here, which model carbon-based molecular junctions as single molecules and oligomers between fragments of graphene. Electronic coupling between the molecules and the contacts is demonstrated by the formation of hybrid orbitals in the model structure, which have significant electron density on both the graphene and the molecule. The energies of such hybrid orbitals correlate with tunneling barriers determined experimentally, and electronic coupling between the two graphene fragments in the model correlates with experimentally observed attenuation of transport with molecular layer thickness. Electronic coupling is affected significantly by the dihedral angle between the planes of the graphene and the molecular π-systems, but is absent only when the two planes are orthogonal. Coupling also results in partial charge transfer between the graphene contacts and the molecular layer, which results in a shift in electrostatic potential which affects the observed tunneling barrier. Although the degree of partial charge transfer is difficult to calculate accurately, it does provide a basis for the "vacuum level shift" observed in many experiments, including transport and ultraviolet photoelectron spectroscopy of molecular layers on conductors. PMID:26925350

  6. A self-consistent, microenvironment modulated screened coulomb potential approximation to calculate pH-dependent electrostatic effects in proteins.

    PubMed

    Mehler, E L; Guarnieri, F

    1999-07-01

    An improved approach is presented for calculating pH-dependent electrostatic effects in proteins using sigmoidally screened Coulomb potentials (SCP). It is hypothesized that a key determinant of seemingly aberrant behavior in pKa shifts is due to the properties of the unique microenvironment around each residue. To help demonstrate this proposal, an approach is developed to characterize the microenvironments using the local hydrophobicity/hydrophilicity around each residue of the protein. The quantitative characterization of the microenvironments shows that the protein is a complex mosaic of differing dielectric regions that provides a physical basis for modifying the dielectric screening functions: in more hydrophobic microenvironments the screening decreases whereas the converse applies to more hydrophilic regions. The approach was applied to seven proteins providing more than 100 measured pKa values and yielded a root mean square deviation of 0.5 between calculated and experimental values. The incorporation of the local hydrophobicity characteristics into the algorithm allowed the resolution of some of the more intractable problems in the calculation of pKa. Thus, the divergent shifts of the pKa of Glu-35 and Asp-66 in hen egg white lysozyme, which are both about 90% buried, was correctly predicted. Mechanistically, the divergence occurs because Glu-35 is in a hydrophobic microenvironment, while Asp-66 is in a hydrophilic microenvironment. Furthermore, because the calculation of the microenvironmental effects takes very little CPU time, the computational speed of the SCP formulation is conserved. Finally, results from different crystal structures of a given protein were compared, and it is shown that the reliability of the calculated pKa values is sufficient to allow identification of conformations that may be more relevant for the solution structure. PMID:10388736

  7. Effects of electronic coupling and electrostatic potential on charge transport in carbon-based molecular electronic junctions

    PubMed Central

    2016-01-01

    Summary Molecular junctions consisting of 2–20 nm thick layers of organic oligomers oriented between a conducting carbon substrate and a carbon/gold top contact have proven to be reproducible and reliable, and will soon enter commercial production in audio processing circuits. The covalent, conjugated bond between one or both sp2-hybridized carbon contacts and an aromatic molecular layer is distinct from the more common metal/molecule or silicon/molecule structures in many reported molecular junctions. Theoretical observations based on density functional theory are presented here, which model carbon-based molecular junctions as single molecules and oligomers between fragments of graphene. Electronic coupling between the molecules and the contacts is demonstrated by the formation of hybrid orbitals in the model structure, which have significant electron density on both the graphene and the molecule. The energies of such hybrid orbitals correlate with tunneling barriers determined experimentally, and electronic coupling between the two graphene fragments in the model correlates with experimentally observed attenuation of transport with molecular layer thickness. Electronic coupling is affected significantly by the dihedral angle between the planes of the graphene and the molecular π-systems, but is absent only when the two planes are orthogonal. Coupling also results in partial charge transfer between the graphene contacts and the molecular layer, which results in a shift in electrostatic potential which affects the observed tunneling barrier. Although the degree of partial charge transfer is difficult to calculate accurately, it does provide a basis for the “vacuum level shift” observed in many experiments, including transport and ultraviolet photoelectron spectroscopy of molecular layers on conductors. PMID:26925350

  8. Complex coacervates as a foundation for synthetic underwater adhesives

    PubMed Central

    Stewart, Russell J.; Wang, Ching Shuen; Shao, Hui

    2011-01-01

    Complex coacervation was proposed to play a role in the formation of the underwater bioadhesive of the Sandcastle worm (Phragmatopoma californica) based on the polyacidic and polybasic nature of the glue proteins and the balance of opposite charges at physiological pH. Morphological studies of the secretory system suggested the natural process does not involve complex coacervation as commonly defined. The distinction may not be important because electrostatic interactions likely play an important role in formation of the sandcastle glue. Complex coacervation has also been invoked in the formation of adhesive underwater silk fibers of caddisfly larvae and the adhesive plaques of mussels. A process similar to complex coacervation, that is, condensation and dehydration of biopolyelectrolytes through electrostatic associations, seems plausible for the caddisfly silk. This much is clear, the sandcastle glue complex coacervation model provided a valuable blueprint for the synthesis of a biomimetic, waterborne, underwater adhesive with demonstrated potential for repair of wet tissue. PMID:21081223

  9. The atomic structure, band gap, and electrostatic potential at the (112)[11{sup ¯}0] twin grain boundary of CuInSe{sub 2}

    SciTech Connect

    Yamaguchi, Hiroyuki; Mizoguchi, Teruyasu; Hiramatsu, Hidenori; Hosono, Hideo

    2014-04-14

    To develop a higher efficiency thin-film compound photovoltaic (PV) cell, it is crucial to understand not only the key factors determining the stability of the grain boundary (GB) but also the band gap and band bending at the GB in the photoabsorption layer. In this study, we investigate the atomic structure, band gap, and electrostatic potential at the (112)[11{sup ¯}0] twin GB of CuInSe{sub 2} (CIS), which is typically used in the photoabsorption layer in thin-film compound PV cells. We utilize aberration-corrected scanning transmission electron microscopy and first-principles hybrid-functional calculations. We find that the formation energies of the twin GB in CIS are very small: 0.03–0.15 J/m{sup 2}. The local coordination of the Se at the GB is a primary factor modulating the GB energy, band gap, and the electrostatic potential at the GB.

  10. The atomic structure, band gap, and electrostatic potential at the (112)[11¯0] twin grain boundary of CuInSe2

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Hiroyuki; Hiramatsu, Hidenori; Hosono, Hideo; Mizoguchi, Teruyasu

    2014-04-01

    To develop a higher efficiency thin-film compound photovoltaic (PV) cell, it is crucial to understand not only the key factors determining the stability of the grain boundary (GB) but also the band gap and band bending at the GB in the photoabsorption layer. In this study, we investigate the atomic structure, band gap, and electrostatic potential at the (112)[11¯0] twin GB of CuInSe2 (CIS), which is typically used in the photoabsorption layer in thin-film compound PV cells. We utilize aberration-corrected scanning transmission electron microscopy and first-principles hybrid-functional calculations. We find that the formation energies of the twin GB in CIS are very small: 0.03-0.15 J/m2. The local coordination of the Se at the GB is a primary factor modulating the GB energy, band gap, and the electrostatic potential at the GB.

  11. Ab initio study of the electrostatic multipole nature of torsional potentials in CH3SSCH3, CH3SSH, and HOOH

    NASA Technical Reports Server (NTRS)

    Sokalski, W. A.; Lai, J.; Luo, N.; Sun, S.; Shibata, M.; Ornstein, R.; Rein, R.

    1991-01-01

    The origin of torsional potentials in H3CSSCH3, H3CSSH, and HOOH and the anisotropy of the local charge distribution has been analyzed in terms of atomic multipoles calculated from the ab initio LCAO-MO-SCF wave function in the 6-31G* basis set. The results indicate that for longer -S-S-bonds the major contribution to these torsional barriers are electrostatic interactions of the atomic multipoles located on two atoms forming the rotated bond. This finding demonstrates the important role of electrostatic 1-2 interatomic interactions, usually neglected in conformational studies. It also opens the possibility to derive directly from accurate ab initio wave functions a simple nonempirical torsional potential involving atomic multipoles of two bonded atoms defining the torsional angle. For shorter -O-O- bonds, use of more precise models and inclusion of 1-3 interactions seems to be necessary.

  12. Ab initio study of the electrostatic multipole nature of torsional potentials in CH3SSCH3, CH3SSH, and HOOH.

    PubMed

    Sokalski, W A; Lai, J; Luo, N; Sun, S; Shibata, M; Ornstein, R; Rein, R

    1991-01-01

    The origin of torsional potentials in H3CSSCH3, H3CSSH, and HOOH and the anisotropy of the local charge distribution has been analyzed in terms of atomic multipoles calculated from the ab initio LCAO-MO-SCF wave function in the 6-31G* basis set. The results indicate that for longer -S-S-bonds the major contribution to these torsional barriers are electrostatic interactions of the atomic multipoles located on two atoms forming the rotated bond. This finding demonstrates the important role of electrostatic 1-2 interatomic interactions, usually neglected in conformational studies. It also opens the possibility to derive directly from accurate ab initio wave functions a simple nonempirical torsional potential involving atomic multipoles of two bonded atoms defining the torsional angle. For shorter -O-O- bonds, use of more precise models and inclusion of 1-3 interactions seems to be necessary. PMID:11538107

  13. Study by electron holography on the distribution of the electrostatic potential and charge at heterostructures and dislocations

    NASA Astrophysics Data System (ADS)

    Cai, Juan

    2003-03-01

    Electron holography is able to record the phase of an electron wave passing through the specimens by producing an interference pattern between the sampling electron beam and a reference beam traveling through vacuum. The electrostatic potential in the specimen can be derived from the recorded phase information, and the charge density can be determined by use of Poisson's equation. We have applied electron holography to analyze the potential and charge distribution across InGaN single quantum wells; and in threading dislocations in GaN film with different doping conditions. In_xGa_1-xN quantum wells are often used in the active region of short wavelength light emitting diodes and laser diodes. Strong internal electric fields (in the order of MV/cm) influence the electronic properties and the light emission process of InGaN quantum wells. We have used electron holography to directly profile the potential and charge distribution across a GaN/In_0.18Ga_0.82N/GaN quantum well structure. The potential profiles show a drop of 0.6 0.2 V across, and an internal electric field of 2.2 0.6 MV/cm in the quantum well. An analysis based on Poisson's equation suggests that the field is caused by electronic charges with a peak density of 8 x 10^20 cm-3, corresponding to a sheet charge density of 0.027 C/m^2. Free electrons and holes in the order of 10^20 cm-3 are confined separately in the quantum well. These free carriers screen only part of the electric field due to the polarization effect. High density of threading dislocations in GaN may degrade the optical and electrical performance of devices. The electronic properties of the threading dislocations in GaN with different doping conditions have been studied using electron holography. Potential profiles across dislocations in undoped GaN show that all dislocations are negatively charged. The line charge density at the dislocation core, defined as the number of electrons per period along the dislocation line, is found to be ˜ 0

  14. Antibacterial and Cell-adhesive Polypeptide and Poly(ethylene glycol) Hydrogel as a Potential Scaffold for Wound Healing

    PubMed Central

    Song, Airong; Rane, Aboli A.; Christman, Karen L.

    2011-01-01

    The ideal wound healing scaffold should provide the appropriate physical and mechanical properties to prevent secondary infection, as well as an excellent physiological environment to facilitate cell adhesion, proliferation and/or differentiation. Therefore, we developed a synthetic cell-adhesive polypeptide hydrogel with inherent antibacterial activity. A series of polypeptides, poly(Lys)x(Ala)y (x+y=100) with varied hydrophobicity via metal-free ring-opening polymerization of NCA-Lys(Boc) and NCA-Ala monomers (NCA = N-carboxylic anhydride) mediated by hexamethyldisilazane (HMDS) were synthesized. These polypeptides were cross-linked with 6-arm PEG-amide succinimidyl glutarate (ASG) (Mw = 10K) to form hydrogels with a gelation time of five minutes and a storage modulus (G') of 1400–3000 Pa as characterized by rheometry. The hydrogel formed by cross-linking of poly(Lys)60(Ala)40 (5 wt%) and 6-arm PEG-ASG (16 wt%) (Gel-III) exhibited cell adhesion and cell proliferation activities superior to other polypeptide hydrogels. In addition, Gel-III displays significant antibacterial activity against E. coli JM109 and S. aureus ATCC25923. Thus, we have developed a novel, cell-adhesive hydrogel with inherent antibacterial activity as a potential scaffold for cutaneous wound healing. PMID:22023748

  15. Focal adhesion molecules as potential target of lead toxicity in NRK-52E cell line.

    PubMed

    Giuliani, Roberta; Bettoni, Francesca; Leali, Daria; Morandini, Fausta; Apostoli, Pietro; Grigolato, Piergiovanni; Cesana, Bruno Mario; Aleo, Maria Francesca

    2005-11-01

    In this study, we investigated the influence of inorganic lead (Pb(II)), an environmental pollutant having nephrotoxic action, on the focal adhesion (FA) organization of a rat kidney epithelial cell line (NRK-52E). In particular, we evaluated the effects of the metal on the recruitment of paxillin, focal adhesion kinase, vinculin and cytoskeleton proteins at the FAs complexes. We provided evidences that, in proliferating NRK-52E cell cultures, low concentrations of Pb(II) affect the cell adhesive ability and stimulate the disassembly of FAs, thus inhibiting the integrin-activated signalling. These effects appeared to be strictly associated to the Pb-induced arrest of cell cycle at G0/G1 phase also proved in this cell line. PMID:16253243

  16. Synthesis of the RGO/Al2O3 core-shell nanocomposite flakes and characterization of their unique electrostatic properties using zeta potential measurements

    NASA Astrophysics Data System (ADS)

    Jastrzębska, A. M.; Karcz, J.; Letmanowski, R.; Zabost, D.; Ciecierska, E.; Zdunek, J.; Karwowska, E.; Siekierski, M.; Olszyna, A.; Kunicki, A.

    2016-01-01

    The aim of this study was to describe the influence of the modification of electrostatic properties of RGO/Al2O3 core-shell nanocomposite flakes. The amount of crystalline form of aluminum oxide was very small. It existed mostly in amorphous phase in the form of covalently bonded to GO surface. The morphological, structural and physicochemical investigations results showed that spherical Al2O3 nanoparticles (ca. 41 nm) in gamma phase completely covered the surface of curly-shaped RGO flakes and acted as a spreader between individual flakes. The high BET specific surface area of the analyzed composite (119.71 m2/g) together with very low open porosity (0.479 cm3/g) indicated that RGO/Al2O3 nanocomposite flakes showed low tendency to agglomeration. The zeta potential curves obtained for RGO/Al2O3 core-shell nanocomposite flakes were differing from curves obtained for GO and Al2O3 suspensions in distilled water and neutral environment. The specific electrostatic properties of the core-shell system of RGO/Al2O3 flakes had an influence on its surface charge (zeta potential) which was measured by applying an external electric field. The FTIR and Raman investigations results also confirmed that the Cdbnd O species were not taking part in the surface amphoteric reactions resulting in the formation of electrostatic surface charge.

  17. Exendin-4 induces cell adhesion and differentiation and counteracts the invasive potential of human neuroblastoma cells.

    PubMed

    Luciani, Paola; Deledda, Cristiana; Benvenuti, Susanna; Squecco, Roberta; Cellai, Ilaria; Fibbi, Benedetta; Marone, Ilaria Maddalena; Giuliani, Corinna; Modi, Giulia; Francini, Fabio; Vannelli, Gabriella Barbara; Peri, Alessandro

    2013-01-01

    Exendin-4 is a molecule currently used, in its synthetic form exenatide, for the treatment of type 2 diabetes mellitus. Exendin-4 binds and activates the Glucagon-Like Peptide-1 Receptor (GLP-1R), thus inducing insulin release. More recently, additional biological properties have been associated to molecules that belong to the GLP-1 family. For instance, Peptide YY and Vasoactive Intestinal Peptide have been found to affect cell adhesion and migration and our previous data have shown a considerable actin cytoskeleton rearrangement after exendin-4 treatment. However, no data are currently available on the effects of exendin-4 on tumor cell motility. The aim of this study was to investigate the effects of this molecule on cell adhesion, differentiation and migration in two neuroblastoma cell lines, SH-SY5Y and SK-N-AS. We first demonstrated, by Extra Cellular Matrix cell adhesion arrays, that exendin-4 increased cell adhesion, in particular on a vitronectin substrate. Subsequently, we found that this molecule induced a more differentiated phenotype, as assessed by i) the evaluation of neurite-like protrusions in 3D cell cultures, ii) the analysis of the expression of neuronal markers and iii) electrophysiological studies. Furthermore, we demonstrated that exendin-4 reduced cell migration and counteracted anchorage-independent growth in neuroblastoma cells. Overall, these data indicate for the first time that exendin-4 may have anti-tumoral properties. PMID:23990978

  18. Nanofluidization electrostatics

    NASA Astrophysics Data System (ADS)

    Valverde, J. M.; Quintanilla, M. A. S.; Espin, M. J.; Castellanos, A.

    2008-03-01

    Electrostatic charging of powders is a relevant phenomenon for a number of industrial applications. The design of new processes and the use of high resistivity materials and ultrafine powders may lead to higher charging rates and to higher levels of charge accumulation that can become a serious problem. In this work we investigate experimentally electrostatic charging in nanofluidization. The behavior of a fluidized bed of silica nanoparticles under the influence of an electrostatic field is studied. The electric field is applied in the horizontal direction and perpendicular to the gas flow. On one hand, we observe the influence of the electric field on the bulk behavior of the fluidized bed, which suffers a collapse when the electric field is turned on. For strong electric fields the stationary state of the fluidized bed reminds one of that of a spouted bed, with a solid layer adhered to the wall and a low density core region of local high gas velocity. On the other hand, and in order to gain additional insight, we look at the trajectories of nanoparticle agglomerates as affected by the electric field. This images analysis reveals that these agglomerates are horizontally deflected towards the wall as a consequence of being charged. From the analysis of agglomerate trajectories the charge per agglomerate is estimated. Using these measurements the electrostatic forces between agglomerates are calculated and compared to van der Waals attractive forces.

  19. Nanofluidization electrostatics.

    PubMed

    Valverde, J M; Quintanilla, M A S; Espin, M J; Castellanos, A

    2008-03-01

    Electrostatic charging of powders is a relevant phenomenon for a number of industrial applications. The design of new processes and the use of high resistivity materials and ultrafine powders may lead to higher charging rates and to higher levels of charge accumulation that can become a serious problem. In this work we investigate experimentally electrostatic charging in nanofluidization. The behavior of a fluidized bed of silica nanoparticles under the influence of an electrostatic field is studied. The electric field is applied in the horizontal direction and perpendicular to the gas flow. On one hand, we observe the influence of the electric field on the bulk behavior of the fluidized bed, which suffers a collapse when the electric field is turned on. For strong electric fields the stationary state of the fluidized bed reminds one of that of a spouted bed, with a solid layer adhered to the wall and a low density core region of local high gas velocity. On the other hand, and in order to gain additional insight, we look at the trajectories of nanoparticle agglomerates as affected by the electric field. This images analysis reveals that these agglomerates are horizontally deflected towards the wall as a consequence of being charged. From the analysis of agglomerate trajectories the charge per agglomerate is estimated. Using these measurements the electrostatic forces between agglomerates are calculated and compared to van der Waals attractive forces. PMID:18517364

  20. Dual and self-curing potential of self-adhesive resin cements as thin films.

    PubMed

    Moraes, R R; Boscato, N; Jardim, P S; Schneider, L F J

    2011-01-01

    In this study, the dual- and self-curing potential of self-adhesive resin cements (SARCs) as thin, clinically-relevant cement films was investigated. The SARCs tested were: BisCem (BSC; Bisco), Maxcem Elite (MXE; Kerr), RelyX Unicem clicker (UNI; 3M ESPE), seT capsule (SET; SDI), and SmartCem 2 (SC2; Dentsply Caulk). The conventional cement RelyX ARC (3M ESPE) was tested as a reference. The degree of conversion (DC) as a function of time was evaluated by real-time Fourier transform infrared spectroscopy with an attenuated total reflectance (ATR) device. The cements were either photoactivated for 40 seconds (dual-cure mode) or not photoactivated (self-cure mode). The cement film thickness was 50 ± 10 μm. The DC (%) was evaluated 1, 5, 10, 15, 20, 25, and 30 minutes after placing the cement on the ATR cell. Data for DC as a function of time were analyzed by two-way repeated measures analysis of variance (ANOVA). DC values at 30 minutes for the self- and dual-cure modes were submitted to one-way ANOVA. Post hoc comparisons were performed using the Student-Newman-Keuls test (p<0.05). The rate and the extent of conversion were lower for the SARCs compared with the conventional cement. Means ± standard deviations (SD) for the dual-cure mode at 30 minutes were: 75 ± 5 (ARC)a, 73 ± 8 (SET)a, 61 ± 4 (MXE)b, 51 ± 9 (BSC)c, 51 ± 4 (UNI)c, and 48 ± 3 (SC2)c, while in the self-cure mode means and SD were 62 ± 6 (ARC)a, 54 ± 3 (MXE)b, 40 ± 6 (SC2)c, 35 ± 2 (UNI)c, 35 ± 3 (SET)c, and 11 ± 3 (BSC)d. The DC for the dual-cure mode was generally higher than the self-cure, irrespective of the time. Discrepancies in DC between the dual- and self-cure modes from 11% to 79% were observed. In conclusion, SARCs may present slower rate of polymerization and lower final DC than conventional resin cements, in either the dual- or self-cure mode. PMID:21864125

  1. A Simple Apparatus for Electrostatic Force Measurement.

    ERIC Educational Resources Information Center

    Hale, D. P.

    1981-01-01

    Describes the construction of an apparatus that demonstrates that electrostatic forces can be large and also gives some idea of dependence of electrostatic forces between charged parallel discs on potential differences and separation. (CS)

  2. Possible involvement of the transient receptor potential vanilloid type 1 channel in postoperative adhesive obstruction and its prevention by a kampo (traditional Japanese) medicine, daikenchuto.

    PubMed

    Tokita, Yohei; Yamamoto, Masahiro; Satoh, Kazuko; Nishiyama, Mitsue; Iizuka, Seiichi; Imamura, Sachiko; Kase, Yoshio

    2011-01-01

    This study focused on the localization of transient receptor potential vanilloid type 1 (TRPV1) in the intestines in postoperative adhesion model rats and investigated the underlying mechanism for the anti-adhesion action of daikenchuto (DKT), especially in relation to TRPV1. Postoperative intestinal adhesion was induced by sprinkling talc in the small intestine. The expression of TRPV1 mRNA was examined by in situ hybridization and real-time RT-PCR. The effects of DKT and its major ingredient, hydroxy sanshool, with or without ruthenium red, a TRP-channel antagonist, on talc-induced intestinal adhesions were evaluated. The level of TRPV1 mRNA was higher in the adhesion regions of talc-treated rats than in normal small intestine of sham-operated rats. Localization of TRPV1 mRNA expression was identified in the submucosal plexus of both sham-operated and talc-treated rats; and in talc-treated rats, it was observed also in the myenteric plexus and regions of adhesion. Capsaicin, DKT, and hydroxy sanshool significantly prevented formation of intestinal adhesions. The effects of DKT and hydroxy sanshool were abrogated by subcutaneous injection of ruthenium red. These results suggest that pharmacological modulation of TRPV1 might be a possible therapeutic option in postoperative intestinal adhesion, which might be relevant to the prevention of postoperative adhesive obstruction by DKT. PMID:21186335

  3. Spectroscopic and DFT Studies of Second Sphere Variants of the Type 1 Copper Site in Azurin: Covalent and Non-Local Electrostatic Contributions to Reduction Potentials

    PubMed Central

    Hadt, Ryan G.; Sun, Ning; Marshall, Nicholas M.; Hodgson, Keith O.; Hedman, Britt; Lu, Yi; Solomon, Edward I.

    2012-01-01

    The reduction potentials (E0) of type 1 (T1) or blue copper (BC) sites in proteins and enzymes with identical first coordination spheres around the redox active copper ion can vary by ~400 mV. Here, we use a combination of low temperature electronic absorption and magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and S K-edge X-ray absorption spectroscopies to investigate a series of second sphere variants—F114P, N47S, and F114N in Pseudomonas aeruginosa azurin (Az)—which modulate hydrogen bonding to and protein derived dipoles nearby the Cu-S(Cys) bond. Density functional theory (DFT) calculations correlated to the experimental data allow for the fractionation of the contributions to tuning E0 into covalent and non-local electrostatic components. These are found to be significant, comparable in magnitude, and additive for active H-bonds, while passive H-bonds are mostly non-local electrostatic in nature. For dipoles, these terms can be additive to or oppose one another. This study provides a methodology for uncoupling covalency from non-local electrostatics, which, when coupled to X-ray crystallographic data, distinguishes specific local interactions from more long range protein/active interactions, while affording further insight into the second sphere mechanisms available to the protein to tune the E0 of electron transfer sites in biology. PMID:22985400

  4. Electrostatic potential distribution of the gene V protein from Ff phage facilitates cooperative DNA binding: a model of the GVP-ssDNA complex.

    PubMed Central

    Guan, Y.; Zhang, H.; Wang, A. H.

    1995-01-01

    The crystal structure of the gene V protein (GVP) from the Ff filamentous phages (M13, fl, fd) has been solved for the wild-type and two mutant (Y41F and Y41H) proteins at high resolution. The Y41H mutant crystal structure revealed crystal packing interactions, which suggested a plausible scheme for constructing the polymeric protein shell of the GVP-single-stranded DNA (ssDNA) complex (Guan Y, et al., 1994, Biochemistry 33:7768-7778). The electrostatic potentials of the isolated and the cooperatively formed protein shell have been calculated using the program GRASP and they revealed a highly asymmetric pattern of the electrostatic charge distribution. The inner surface of the putative DNA-binding channel is positively charged, whereas the opposite outer surface is nearly neutral. The electrostatic calculation further demonstrated that the formation of the helical protein shell enhanced the asymmetry of the electrostatic distribution. A model of the GVP-ssDNA complex with the n = 4 DNA-binding mode could be built with only minor conformational perturbation to the GVP protein shell. The model is consistent with existing biochemical and biophysical data and provides clues to the properties of GVP, including the high cooperatively of the protein binding to ssDNA. The two antiparallel ssDNA strands form a helical ribbon with the sugar-phosphate backbones at the middle and the bases pointing away from each other. The bases are stacked and the Phe 73 residue is intercalated between two bases. The optimum binding to a tetranucleotide unit requires the participation of four GVP dimers, which may explain the cooperativity of the GVP binding to DNA. PMID:7757008

  5. GENIPIN-CROSSLINKED FIBRIN HYDROGELS AS A POTENTIAL ADHESIVE TO AUGMENT INTERVERTEBRAL DISC ANNULUS REPAIR

    PubMed Central

    Schek, R.M.; Michalek, A.J.; Iatridis, J.C.

    2011-01-01

    Treatment of damaged intervertebral discs is a significant clinical problem and, despite advances in the repair and replacement of the nucleus pulposus, there are few effective strategies to restore defects in the annulus fibrosus. An annular repair material should meet three specifications: have a modulus similar to the native annulus tissue, support the growth of disc cells, and maintain adhesion to tissue under physiological strain levels. We hypothesized that a genipin crosslinked fibrin gel could meet these requirements. Our mechanical results showed that genipin crosslinked fibrin gels could be created with a modulus in the range of native annular tissue. We also demonstrated that this material is compatible with the in vitro growth of human disc cells, when genipin:fibrin ratios were 0.25:1 or less, although cell proliferation was slower and cell morphology more rounded than for fibrin alone. Finally, lap tests were performed to evaluate adhesion between fibrin gels and pieces of annular tissue. Specimens created without genipin had poor handling properties and readily delaminated, while genipin crosslinked fibrin gels remained adhered to the tissue pieces at strains exceeding physiological levels and failed at 15–30%. This study demonstrated that genipin crosslinked fibrin gels show promise as a gap-filling adhesive biomaterial with tunable material properties, yet the slow cell proliferation suggests this biomaterial may be best suited as a sealant for small annulus fibrosus defects or as an adhesive to augment large annulus repairs. Future studies will evaluate degradation rate, fatigue behaviors, and long-term biocompatibility. PMID:21503869

  6. On the potential for fibronectin/phosphorylcholine coatings on PTFE substrates to jointly modulate endothelial cell adhesion and hemocompatibility properties

    PubMed Central

    Montaño-Machado, Vanessa; Chevallier, Pascale; Mantovani, Diego; Pauthe, Emmanuel

    2015-01-01

    The use of biomolecules as coatings on biomaterials is recognized to constitute a promising approach to modulate the biological response of the host. In this work, we propose a coating composed by 2 biomolecules susceptible to provide complementary properties for cardiovascular applications: fibronectin (FN) to enhance endothelialization, and phosphorylcholine (PRC) for its non thrombogenic properties. Polytetrafluoroethylene (PTFE) was selected as model substrate mainly because it is largely used in cardiovascular applications. Two approaches were investigated: 1) a sequential adsorption of the 2 biomolecules and 2) an adsorption of the protein followed by the grafting of phosphorylcholine via chemical activation. All coatings were characterized by immunofluorescence staining, X-Ray Photoelectron Spectroscopy and Scanning Electron Microscopy analyses. Assays with endothelial cells showed improvement on cell adhesion, spreading and metabolic activity on FN-PRC coatings compared with the uncoated PTFE. Platelets adhesion and activation were both reduced on the coated surfaces when compared with uncoated PTFE. Moreover, clotting time tests exhibited better hemocompatibility properties of the surfaces after a sequential adsorption of FN and PRC. In conclusion, FN-PRC coating improves cell adhesion and non-thrombogenic properties, thus revealing a certain potential for the development of this combined deposition strategy in cardiovascular applications. PMID:25785369

  7. Adhesion of perfume-filled microcapsules to model fabric surfaces.

    PubMed

    He, Yanping; Bowen, James; Andrews, James W; Liu, Min; Smets, Johan; Zhang, Zhibing

    2014-01-01

    The retention and adhesion of melamine formaldehyde (MF) microcapsules on a model fabric surface in aqueous solution were investigated using a customised flow chamber technique and atomic force microscopy (AFM). A cellulose film was employed as a model fabric surface. Modification of the cellulose with chitosan was found to increase the retention and adhesion of microcapsules on the model fabric surface. The AFM force-displacement data reveal that bridging forces resulting from the extension of cellulose chains dominate the adhesion between the microcapsule and the unmodified cellulose film, whereas electrostatic attraction helps the microcapsules adhere to the chitosan-modified cellulose film. The correlation between results obtained using these two complementary techniques suggests that the flow chamber device can be potentially used for rapid screening of the effect of chemical modification on the adhesion of microparticles to surfaces, reducing the time required to achieve an optimal formulation. PMID:24697187

  8. Evaluation of a finite multipole expansion technique for the computation of electrostatic potentials of dibenzo-p-dioxins and related systems

    SciTech Connect

    Murray, J.S.; Grice, M.E.; Politzer, P.; Rabinowitz, J.R.

    1990-01-01

    The electrostatic potential V(r) that the nuclei and electrons of a molecule create in the surrounding space is well established as a guide in the study of molecular reactivity, and particularly, of biological recognition processes. Its rigorous computation is, however, very demanding of computer time for large molecules, such as those of interest in recognition interactions. The authors have accordingly investigated the use of an approximate finite multicenter multipole expansion technique to determine its applicability for producing reliable electrostatic potentials of dibenzo-p-dioxins and related molecules, with significantly reduced amounts of computer time, at distances of interest in recognition studies. A comparative analysis of the potentials of three dibenzo-q-dioxins and a substituted naphthalene molecule computed using both the multipole expansion technique and GAUSSIAN 82 at the STO-5G level has been carried out. Overall they found that regions of negative and positive V(r) at 1.75 A above the molecular plane are very well reproduced by the multipole expansion technique, with up to a twenty-fold improvement in computer time.

  9. Electrostatic monitoring

    DOEpatents

    Orr, Christopher Henry; Luff, Craig Janson; Dockray, Thomas; Macarthur, Duncan Whittemore

    2001-01-01

    The apparatus and method provide a technique for more simply measuring alpha and/or beta emissions arising from items or locations. The technique uses indirect monitoring of the emissions by detecting ions generated by the emissions, the ions being attracted electrostatically to electrodes for discharge of collection. The apparatus and method employ a chamber which is sealed around the item or location during monitoring with no air being drawn into or expelled from the chamber during the monitoring process. A simplified structure and operations arises as a result, but without impairing the efficiency and accuracy of the detection technique.

  10. A theoretical prediction of the relationships between the impact sensitivity and electrostatic potential in strained cyclic explosive and application to H-bonded complex of nitrocyclohydrocarbon.

    PubMed

    Ren, Fu-de; Cao, Duan-lin; Shi, Wen-jing; Gao, Hong-fei

    2016-04-01

    Seven models that related the features of molecular surface electrostatic potentials (ESPs) above the bond midpoints and rings, statistical parameters of ESPs to the experimental impact sensitivities h 50 of eight strained cyclic explosives with the C-NO2 bonds were theoretically predicted at the DFT-B3LYP/6-311++G** level. One of the models was used to investigate the changes of h 50 for the nitrocyclohydrocarbon frameworks in the H-bonded complexes of HF with nitrocyclopropane, nitrocyclobutane, nitrocyclopentane, and nitrocyclohexane. The results show that the correlation coefficients of the obtained models are small. When adding the effect of ring strain, the value of correlation coefficient is increased. According to the calculated h 50, the sensitivities in the frameworks are increased after hydrogen bonding. As a global feature of molecules, surface electrostatic potential is more available to judge the sensitivity change than the trigger bond dissociation energy or ring strain energy in H-bonded complex. PMID:27029622

  11. Modelling liquid crystal elastomers and potential application as a reversibly switchable adhesive

    NASA Astrophysics Data System (ADS)

    Adams, James

    2013-03-01

    Liquid crystal elastomers (LCEs) are rubbery materials that composed of liquid crystalline polymers (LCPs) crosslinked into a network. The rod-like mesogens incorporated into the LCPs are have random orientations in the high temperature isotropic phase, but can adopt the canonical liquid crystalline phases as the temperature is lowered. Smectic liquid crystal elastomers have highly anisotropic mechanical behaviour. This arises in side chain smectic-A systems because the smectic layers behave as if they are embedded in the rubber matrix. The macroscopic mechanical behaviour of these solids is sensitive to the buckling of the layers, so is a multiscale problem. A coarse grained free energy that includes the fine-scale buckling of the layers has been developed, which enables continuum modelling of these systems. In the first part of this talk I present a model of the mechanical behaviour of side chain smectic elastomers. The properties of nematic LCEs, such as their high loss tangent, and mechanical strain hardening, might enable them to be used as reversibly switchable pressure sensitive adhesive (PSA). PSAs are typically made from viscoelastic polymers. The quality of their adhesion can be measured by the tack energy, which is the work required to separate two bodies. To obtain a high tack energy a PSA should be capable of a large strain. It should strain soften at low strain to produce crack blunting, and then strain harden at high strain to stiffen the fibrils formed late in the debonding process. I will present a model of the tack energy of weakly crosslinked nematic polymers. To describe the constitutive properties of this system the nematic dumbbell model of Maffettone et al. was used. This constutitive model was then combined with the block model of Yamaguchi et al. describing PSAs. It was found that the parallel orientation of the nematic has a higher tack energy than both the isotropic and the perpendicular director orientation. This work is supported by

  12. α6-integrin is required for the adhesion and vasculogenic potential of hemangioma stem cells

    PubMed Central

    Smadja, David M.; Guerin, Coralie L.; Boscolo, Elisa; Bieche, Ivan; Mulliken, John B.; Bischoff, Joyce

    2013-01-01

    Background Infantile hemangioma (IH) is the most common tumor of infancy. Hemangioma stem cells (HemSC) are a mesenchymal subpopulation isolated from IH CD133+ cells. HemSC can differentiate into endothelial and pericyte/smooth muscle cells and form vascular networks when injected in immune-deficient mice. α6-Integrin subunit has been implicated in the tumorgenicity of glioblastoma stem cells and the homing properties of hematopoietic, endothelial and mesenchymal progenitor cells. Therefore, we investigated the possible function(s) of α6-integrin in HemSC. Methods/Results We documented α6-integrin expression in IH tumor specimens and HemSC by RT-qPCR and flow cytometry. We examined the effect of blocking or silencing α6-integrin on the adhesive and proliferative properties of HemSCin vitro and the vasculogenic and homing properties of HemSCin vivo. Targeting α6-integrin in cultured HemSC inhibited adhesion to laminin but had no effect on proliferation. Vessel-forming ability in Matrigel implants and hepatic homing after intravenous delivery were significantly decreased in α6-integrin siRNA transfected HemSC. Conclusion α6-Integrin is required for HemSC adherence to laminin, vessel formation in vivo and for homing to the liver. Thus, we uncovered an important role for α6 integrin in the vasculogenic properties of HemSC. Our results suggest that α6-integrin expression on HemSC could be a new target for anti-hemangioma therapy. PMID:24022922

  13. Effect of the electrostatic surface potential on the oligomerization of full-length human recombinant prion protein at single-molecule level.

    PubMed

    Wang, Bin; Lou, Zhichao; Zhang, Haiqian; Xu, Bingqian

    2016-03-21

    The electrostatic surface potential (ESP) of prion oligomers has critical influences on the aggregating processes of the prion molecules. The atomic force microscopy (AFM) and structural simulation were combined to investigate the molecular basis of the full-length human recombinant prion oligomerization on mica surfaces. The high resolution non-intrusive AFM images showed that the prion oligomers formed different patterns on mica surfaces at different buffer pH values. The basic binding units for the large oligomers were determined to be prion momoners (Ms), dimers (Ds), and trimers (Ts). The forming of the D and T units happened through the binding of hydrophobic β-sheets of the M units. In contrast, the α-helices of these M, D, and T units were the binding areas for the formation of large oligomers. At pH 4.5, the binding units M, D, and T showed clear polarized ESP distributions on the surface domains, while at pH 7.0, they showed more evenly distributed ESPs. Based on the conformations of oligomers observed from AFM images, the D and T units were more abundantly on mica surface at pH 4.5 because the ESP re-distribution of M units helped to stabilize these larger oligomers. The amino acid side chains involved in the binding interfaces were stabilized by hydrogen bonds and electrostatic interactions. The detailed analysis of the charged side chains at pH 4.5 indicated that the polarized ESPs induced the aggregations among M, D, and T to form larger oligomers. Therefore, the hydrogen bonds and electrostatic interactions worked together to form the stabilized prion oligomers. PMID:27004887

  14. Effect of the electrostatic surface potential on the oligomerization of full-length human recombinant prion protein at single-molecule level

    NASA Astrophysics Data System (ADS)

    Wang, Bin; Lou, Zhichao; Zhang, Haiqian; Xu, Bingqian

    2016-03-01

    The electrostatic surface potential (ESP) of prion oligomers has critical influences on the aggregating processes of the prion molecules. The atomic force microscopy (AFM) and structural simulation were combined to investigate the molecular basis of the full-length human recombinant prion oligomerization on mica surfaces. The high resolution non-intrusive AFM images showed that the prion oligomers formed different patterns on mica surfaces at different buffer pH values. The basic binding units for the large oligomers were determined to be prion momoners (Ms), dimers (Ds), and trimers (Ts). The forming of the D and T units happened through the binding of hydrophobic β-sheets of the M units. In contrast, the α-helices of these M, D, and T units were the binding areas for the formation of large oligomers. At pH 4.5, the binding units M, D, and T showed clear polarized ESP distributions on the surface domains, while at pH 7.0, they showed more evenly distributed ESPs. Based on the conformations of oligomers observed from AFM images, the D and T units were more abundantly on mica surface at pH 4.5 because the ESP re-distribution of M units helped to stabilize these larger oligomers. The amino acid side chains involved in the binding interfaces were stabilized by hydrogen bonds and electrostatic interactions. The detailed analysis of the charged side chains at pH 4.5 indicated that the polarized ESPs induced the aggregations among M, D, and T to form larger oligomers. Therefore, the hydrogen bonds and electrostatic interactions worked together to form the stabilized prion oligomers.

  15. Micromachined silicon electrostatic chuck

    SciTech Connect

    Anderson, R.A.; Seager, C.H.

    1994-12-31

    In the field of microelectronics, and in particular the fabrication of microelectronics during plasma etching processes, electrostatic chucks have been used to hold silicon wafers during the plasma etching process. Current electrostatic chucks that operate by the {open_quotes}Johnson-Rahbek Effect{close_quotes} consist of a metallic base plate that is typically coated with a thick layer of slightly conductive dielectric material. A silicon wafer of approximately the same size as the chuck is placed on top of the chuck and a potential difference of several hundred volts is applied between the silicon and the base plate of the electrostatic chuck. This causes an electrostatic attraction proportional to the square of the electric field in the gap between the silicon wafer and the chuck face. When the chuck is used in a plasma filled chamber the electric potential of the wafer tends to be fixed by the effective potential of the plasma. The purpose of the dielectric layer on the chuck is to prevent the silicon wafer from coming into direct electrical contact with the metallic part of the chuck and shorting out the potential difference. On the other hand, a small amount of conductivity appears to be desirable in the dielectric coating so that much of its free surface between points of contact with the silicon wafer is maintained near the potential of the metallic base plate; otherwise, a much larger potential difference would be needed to produce a sufficiently large electric field in the vacuum gap between the wafer and chuck. Typically, the face of the chuck has a pattern of grooves in which about 10 torr pressure of helium gas is maintained. This gas provides cooling (thermal contact) between the wafer and the chuck. A pressure of 10 torr is equivalent to about 0.2 psi.

  16. Electrostatic forces in planetary rings

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.; Shan, Linhua; Havnes, O.

    1988-01-01

    The average charge on a particle in a particle-plasma cloud, the plasma potential inside the cloud, and the Coulomb force acting on the particle are calculated. The net repulsive electrostatic force on a particle depends on the plasma density, temperature, density of particles, particle size, and the gradient of the particle density. In a uniformly dense ring the electrostatic repulsion is zero. It is also shown that the electrostatic force acts like a pressure force, that even a collisionless ring can be stable against gravitational collapse, and that a finite ring thickness does not necessarily imply a finite velocity dispersion. A simple criterion for the importance of electrostatic forces in planetary rings is derived which involves the calculation of the vertical ring thickness which would result if only electrostatic repulsion were responsible for the finite ring thickness. Electrostatic forces are entirely negligible in the main rings of Saturn and the E and G rings. They may also be negligible in the F ring. However, the Uranian rings and Jupiter's ring seem to be very much influenced by electrostatic repulsion. In fact, electrostatic forces could support a Jovian ring which is an order of magnitude more dense than observed.

  17. Determination of the electrostatic potential distribution in Pt/Fe:SrTiO3/Nb:SrTiO3 thin-film structures by electron holography

    PubMed Central

    Marchewka, Astrid; Cooper, David; Lenser, Christian; Menzel, Stephan; Du, Hongchu; Dittmann, Regina; Dunin-Borkowski, Rafal E.; Waser, Rainer

    2014-01-01

    We determined the electrostatic potential distribution in pristine Pt/Fe:SrTiO3/Nb:SrTiO3 structures by electron holography experiments, revealing the existence of a depletion layer extending into the Nb-doped bottom electrode. Simulations of potential profiles in metal-insulator-metal structures were conducted assuming different types and distributions of dopants. It is found that the presence of acceptor-type dopant concentrations at the Fe:SrTiO3/Nb:SrTiO3 interface with a donor-doped insulating layer provides a good match to the measured profile. Such acceptor-type interface concentrations may be associated with Sr vacancies on the Nb:SrTiO3 side of the bottom interface. PMID:25381733

  18. Nanowell-Trapped Charged Ligand-Bearing Nanoparticle Surfaces – A Novel Method of Enhancing Flow-Resistant Cell Adhesion

    PubMed Central

    Tran, Phat L.; Gamboa, Jessica R.; McCracken, Katherine E.; Riley, Mark R.

    2014-01-01

    Assuring cell adhesion to an underlying biomaterial surface is vital in implant device design and tissue engineering, particularly under circumstances where cells are subjected to potential detachment from overriding fluid flow. Cell-substrate adhesion is a highly regulated process involving the interplay of mechanical properties, surface topographic features, electrostatic charge, and biochemical mechanisms. At the nanoscale level the physical properties of the underlying substrate are of particular importance in cell adhesion. Conventionally, natural, pro-adhesive, and often thrombogenic, protein biomaterials are frequently utilized to facilitate adhesion. In the present study nanofabrication techniques are utilized to enhance the biological functionality of a synthetic polymer surface, polymethymethacrylate, with respect to cell adhesion. Specifically we examine the effect on cell adhesion of combining: 1. optimized surface texturing, 2. electrostatic charge and 3. cell adhesive ligands, uniquely assembled on the substrata surface, as an ensemble of nanoparticles trapped in nanowells. Our results reveal that the ensemble strategy leads to enhanced, more than simply additive, endothelial cell adhesion under both static and flow conditions. This strategy may be of particular utility for enhancing flow-resistant endothelialization of blood-contacting surfaces of cardiovascular devices subjected to flow-mediated shear. PMID:23225491

  19. Variable stiffness sandwich panels using electrostatic interlocking core

    NASA Astrophysics Data System (ADS)

    Heath, Callum J. C.; Bond, Ian P.; Potter, Kevin D.

    2016-04-01

    Structural topology has a large impact on the flexural stiffness of a beam structure. Reversible attachment between discrete substructures allows for control of shear stress transfer between structural elements, thus stiffness modulation. Electrostatic adhesion has shown promise for providing a reversible latching mechanism for controllable internal connectivity. Building on previous research, a thin film copper polyimide laminate has been used to incorporate high voltage electrodes to Fibre Reinforced Polymer (FRP) sandwich structures. The level of electrostatic holding force across the electrode interface is key to the achievable level of stiffness modulation. The use of non-flat interlocking core structures can allow for a significant increase in electrode contact area for a given core geometry, thus a greater electrostatic holding force. Interlocking core geometries based on cosine waves can be Computer Numerical Control (CNC) machined from Rohacell IGF 110 Foam core. These Interlocking Core structures could allow for enhanced variable stiffness functionality compared to basic planar electrodes. This novel concept could open up potential new applications for electrostatically induced variable stiffness structures.

  20. Development of Electrostatically Clean Solar Array Panels

    NASA Technical Reports Server (NTRS)

    Stern, Theodore G.

    2000-01-01

    Certain missions require Electrostatically Clean Solar Array (ECSA) panels to establish a favorable environment for the operation of sensitive scientific instruments. The objective of this program was to demonstrate the feasibility of an ECSA panel that minimizes panel surface potential below 100mV in LEO and GEO charged particle environments, prevents exposure of solar cell voltage and panel insulating surfaces to the ambient environment, and provides an equipotential, grounded structure surrounding the entire panel. An ECSA panel design was developed that uses a Front Side Aperture-Shield (FSA) that covers all inter-cell areas with a single graphite composite laminate, composite edge clips for connecting the FSA to the panel substrate, and built-in tabs that interconnect the FSA to conductive coated coverglasses using a conductive adhesive. Analysis indicated the ability of the design to meet the ECSA requirements. Qualification coupons and a 0.5m x 0.5m prototype panel were fabricated and tested for photovoltaic performance and electrical grounding before and after exposure to acoustic and thermal cycling environments. The results show the feasibility of achieving electrostatic cleanliness with a small penalty in mass, photovoltaic performance and cost, with a design is structurally robust and compatible with a wide range of current solar panel technologies.

  1. Some molecular/crystalline factors that affect the sensitivities of energetic materials: molecular surface electrostatic potentials, lattice free space and maximum heat of detonation per unit volume.

    PubMed

    Politzer, Peter; Murray, Jane S

    2015-02-01

    We discuss three molecular/crystalline properties that we believe to be among the factors that influence the impact/shock sensitivities of energetic materials (i.e., their vulnerabilities to unintended detonation due to impact or shock). These properties are (a) the anomalously strong positive electrostatic potentials in the central regions of their molecular surfaces, (b) the free space per molecule in their crystal lattices, and (c) their maximum heats of detonation per unit volume. Overall, sensitivity tends to become greater as these properties increase; however these are general trends, not correlations. Nitramines are exceptions in that their sensitivities show little or no variation with free space in the lattice and heat of detonation per unit volume. We outline some of the events involved in detonation initiation and show how the three properties are related to different ones of these events. PMID:25631919

  2. InfiniCharges: A tool for generating partial charges via the simultaneous fit of multiframe electrostatic potential (ESP) and total dipole fluctuations (TDF)

    NASA Astrophysics Data System (ADS)

    Sant, Marco; Gabrieli, Andrea; Demontis, Pierfranco; Suffritti, Giuseppe B.

    2016-03-01

    The InfiniCharges computer program, for generating reliable partial charges for molecular simulations in periodic systems, is here presented. This tool is an efficient implementation of the recently developed DM-REPEAT method, where the stability of the resulting charges, over a large set of fitting regions, is obtained through the simultaneous fit of multiple electrostatic potential (ESP) configurations together with the total dipole fluctuations (TDF). Besides DM-REPEAT, the program can also perform standard REPEAT fit and its multiframe extension (M-REPEAT), with the possibility to restrain the charges to an arbitrary value. Finally, the code is employed to generate partial charges for ZIF-90, a microporous material of the metal organic frameworks (MOFs) family, and an extensive analysis of the results is carried out.

  3. Electrostatic Enhancement of Coagulation in Protoplanetary Nebulae

    NASA Technical Reports Server (NTRS)

    Marshall, J.; Cuzzi, J.

    2001-01-01

    Microgravity experiments suggest that electrostatic forces (overwhelmed by normal Earth gravity) could greatly enhance cohesive strength of preplanetary aggregates. Cohesive forces may be 103 times larger than those for van der Waals adhesion. Additional information is contained in the original extended abstract.

  4. Comparative analysis of the electrostatic potentials of some structural analogues of 2,3,7,8-tetrachlorodibenzo-p-dioxin and of related aromatic systems

    SciTech Connect

    Murray, J.S.; Evans, P.; Politzer, P.

    1990-01-01

    An ab initio STO-5G computational analysis of the electrostatic potentials of four structural analogs of the highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and four related aromatic systems (benzo(a)pyrene, benz(a)anthracene and two isomeric benzoflavones) was carried out. The systems, to varying degrees, induce aryl hydrocarbon hydroxylase activity and are believed to interact with the same cytosolic receptor in initiating their biochemical responses. It was found that a high degree of activity appears to require negative potentials that are non-overlapping above all or most of the lateral regions, with an observed optimum range of magnitudes. In systems with central oxygens, it is required that the negative oxygen potentials be small and weak; however, oxygen negative regions in the molecule are not necessary for high activity. The observed differences between the potential patterns of the four aromatic systems and those of TCDD and its active analogs may reflect an inherent dissimilarity in the nature of their interactions with the cytosolic receptor.

  5. microRNA-146a targets the L1 cell adhesion molecule and suppresses the metastatic potential of gastric cancer.

    PubMed

    Hou, Zhibo; Yin, Haitao; Chen, Cong; Dai, Xinzheng; Li, Xiaolin; Liu, Baorui; Fang, Xuefeng

    2012-09-01

    Recent studies have shown that microRNA-146a (miR-146a) is associated with cancer metastasis. However, the mechanisms underlying this process remain poorly understood. In this study, we aimed to investigate the potential role of miR-146a in gastric cancer metastasis. A wound-healing assay and a Transwell assay were used to investigate the impact of miR-146a on the migratory and invasive abilities of MKN-45 cells in vitro. MKN-45 cells stably expressing miR-146a or the negative control were transplanted into nude mice through the lateral tail vein to explore the effect of miR-146a on tumor metastasis in vivo. A luciferase reporter assay and western blot analysis were used to identify the potential target genes. Our results show that the overexpression of miR-146a inhibits the invasion and metastasis of MKN-45 cells in vitro and in vivo. Furthermore, the L1 cell adhesion molecule (L1CAM) was identified as a novel target of miR‑146a in gastric cancer. Taken together, our results provide evidence that miR-146a suppresses gastric cancer cell invasion and metastasis in vitro and in vivo, which may be in part due to the downregulation of L1CAM. miR-146a may have the therapeutic potential to suppress gastric cancer metastasis. PMID:22711166

  6. Electrostatic Return of Contaminants

    NASA Technical Reports Server (NTRS)

    Rantanen, R.; Gordon, T.

    2003-01-01

    A Model has been developed capable of calculating the electrostatic return of spacecraft-emitted molecules that are ionized and attracted back to the spacecraft by the spacecraft electric potential on its surfaces. The return of ionized contaminant molecules to charged spacecraft surfaces is very important to all altitudes. It is especially important at geosynchronous and interplanetary environments, since it may be the only mechanism by which contaminants can degrade a surface. This model is applicable to all altitudes and spacecraft geometries. In addition to results of the model will be completed to cover a wide range of potential space systems.

  7. Electrostatic interaction of neutral semi-permeable membranes

    NASA Astrophysics Data System (ADS)

    Vinogradova, Olga I.; Bocquet, Lyderic; Bogdanov, Artem N.; Tsekov, Roumen; Lobaskin, Vladimir

    2012-01-01

    We consider an osmotic equilibrium between bulk solutions of polyelectrolyte bounded by semi-permeable membranes and separated by a thin film of salt-free liquid. Although the membranes are neutral, the counter-ions of the polyelectrolyte molecules permeate into the gap and lead to a steric charge separation. This gives rise to a distance-dependent membrane potential, which translates into a repulsive electrostatic disjoining pressure. From the solution of the nonlinear Poisson-Boltzmann equation, we obtain the distribution of the potential and of ions. We then derive an explicit formula for the pressure exerted on the membranes and show that it deviates from the classical van't Hoff expression for the osmotic pressure. This difference is interpreted in terms of a repulsive electrostatic disjoining pressure originating from the overlap of counterion clouds inside the gap. We also develop a simplified theory based on a linearized Poisson-Boltzmann approach. A comparison with simulation of a primitive model for the electrolyte is provided and does confirm the validity of the theoretical predictions. Beyond the fundamental result that the neutral surfaces can repel, this mechanism not only helps to control the adhesion and long-range interactions of living cells, bacteria, and vesicles, but also allows us to argue that electrostatic interactions should play enormous role in determining behavior and functions of systems bounded by semi-permeable membranes.

  8. Electrostatic modulation of periodic potentials in a two-dimensional electron gas: From antidot lattice to quantum dot lattice

    SciTech Connect

    Goswami, Srijit; Aamir, Mohammed Ali; Shamim, Saquib; Ghosh, Arindam; Siegert, Christoph; Farrer, Ian; Ritchie, David A.; Pepper, Michael

    2013-12-04

    We use a dual gated device structure to introduce a gate-tuneable periodic potential in a GaAs/AlGaAs two dimensional electron gas (2DEG). Using only a suitable choice of gate voltages we can controllably alter the potential landscape of the bare 2DEG, inducing either a periodic array of antidots or quantum dots. Antidots are artificial scattering centers, and therefore allow for a study of electron dynamics. In particular, we show that the thermovoltage of an antidot lattice is particularly sensitive to the relative positions of the Fermi level and the antidot potential. A quantum dot lattice, on the other hand, provides the opportunity to study correlated electron physics. We find that its current-voltage characteristics display a voltage threshold, as well as a power law scaling, indicative of collective Coulomb blockade in a disordered background.

  9. Electrostatic modulation of periodic potentials in a two-dimensional electron gas: From antidot lattice to quantum dot lattice

    NASA Astrophysics Data System (ADS)

    Goswami, Srijit; Aamir, Mohammed Ali; Shamim, Saquib; Siegert, Christoph; Pepper, Michael; Farrer, Ian; Ritchie, David A.; Ghosh, Arindam

    2013-12-01

    We use a dual gated device structure to introduce a gate-tuneable periodic potential in a GaAs/AlGaAs two dimensional electron gas (2DEG). Using only a suitable choice of gate voltages we can controllably alter the potential landscape of the bare 2DEG, inducing either a periodic array of antidots or quantum dots. Antidots are artificial scattering centers, and therefore allow for a study of electron dynamics. In particular, we show that the thermovoltage of an antidot lattice is particularly sensitive to the relative positions of the Fermi level and the antidot potential. A quantum dot lattice, on the other hand, provides the opportunity to study correlated electron physics. We find that its current-voltage characteristics display a voltage threshold, as well as a power law scaling, indicative of collective Coulomb blockade in a disordered background.

  10. Molecular structure, spectroscopy (FT-IR, FT-Raman), thermodynamic parameters, molecular electrostatic potential and HOMO-LUMO analysis of 2, 6-dichlorobenzamide

    NASA Astrophysics Data System (ADS)

    Tao, Yaping; Han, Ligang; Li, Xiaofeng; Han, Yunxia; Liu, Zhaojun

    2016-03-01

    2, 6-dichlorobenzamide is the degradation product of 2, 6-dichlorobenzonitrile, which is often used as herbicide and can cause groundwater pollution. The FT-IR and FT-Raman spectra of 2, 6-dichlorobenzamide at room temperature were recorded and analyzed in the range 4000-400 and 3700-100 cm-1, respectively. In order to obtain the most stable structure, a potential energy surface (PES) scan for internal rotations was carried out at the B3LYP/6-31G(d) level. The optimized geometry, structural parameters energies, theoretical IR and Raman spectra for the title compound have been obtained by employing B3LYP exchange-correlation functional with high-quality aug-cc-pVTZ basis-set. Detailed vibrational assignments of vibrational spectra have been made on the basis of the potential energy distributions (PED) analysis. In addition, the HOMO-LUMO gap and molecular electrostatic potential (MEP) were studied theoretically. Finally, the thermodynamic functions (heat capacity, entropy, enthalpy, and Gibbs free energy) of 2, 6-dichlorobenzamide were obtained in the range of 100-1000 K.

  11. Nonlinear response of the surface electrostatic potential formed at metal oxide/electrolyte interfaces. A Monte Carlo simulation study

    SciTech Connect

    Zarzycki, Piotr P.; Rosso, Kevin M.

    2010-01-01

    An analysis of surface potential nonlinearity at metal oxide/electrolyte interfaces is presented. By using Grand Canonical Monte Carlo simulations of a simple lattice model of an interface, we show a correlation exists between ionic strength as well as surface site densities and the non-Nernstian response of a metal oxide electrode. We propose two approaches to deal with the 0-nonlinearity: one based on perturbative expansion of the Gibbs free energy and another based on assumption of the pH-dependence of surface potential slope. The theoretical anal ysis based on our new potential form gives excellent performance at extreme pH regions, where classical formulae based on the Poisson-Boltzmann equation fail. The new formula is general and independent of any underlying assumptions. For this reason, it can be directly applied to experimental surface potential measurements, including those for individual surfaces of single crystals, as we present for data reported by Kallay and Preocanin [Kallay, Preocanin J. Colloid and Interface20 Sci. 318 (2008) 290].

  12. Electrostatic modulation of periodic potentials in a two-dimensional electron gas: from antidot lattice to quantum dot lattice

    NASA Astrophysics Data System (ADS)

    Goswami, Srijit; Aamir, Mohammad Ali; Shamim, Saquib; Siegert, Christoph; Pepper, Michael; Farrer, Ian; Ritchie, David; Ghosh, Arindam

    2012-02-01

    We use a dual gated device structure to introduce a gate-tunable periodic potential in a GaAs/AlGaAs two dimensional electron gas (2DEG). Using a suitable choice of gate voltages we can controllably alter the potential landscape in the 2DEG, thereby inducing either a periodic array of antidots or quantum dots. Antidots are artificial scattering centers, and therefore allow for a study of electron dynamics. On the other hand, a quantum dot lattice provides the opportunity to study correlated electron physics. We use a variety of electrical measurements such as magneto-resistance, thermo-voltage and current-voltage characteristics to probe these two contrasting regimes.

  13. Computer-generated formulas for three-center nuclear-attraction integrals (electrostatic potential) for Slater-type orbitals

    NASA Technical Reports Server (NTRS)

    Jones, H. W.

    1984-01-01

    The computer-assisted C-matrix, Loewdin-alpha-function, single-center expansion method in spherical harmonics has been applied to the three-center nuclear-attraction integral (potential due to the product of separated Slater-type orbitals). Exact formulas are produced for 13 terms of an infinite series that permits evaluation to ten decimal digits of an example using 1s orbitals.

  14. PREFACE: Electrostatics 2015

    NASA Astrophysics Data System (ADS)

    Matthews, James

    2015-10-01

    Electrostatics 2015, supported by the Institute of Physics, was held in the Sir James Matthews building at Southampton Solent University, UK between 12th and 16th April 2015. Southampton is a historic city on the South Coast of England with a strong military and maritime history. Southampton is home to two Universities: Solent University, which hosted the conference, and the University of Southampton, where much work is undertaken related to electrostatics. 37 oral and 44 poster presentations were accepted for the conference, and 60 papers were submitted and accepted for the proceedings. The Bill Bright Memorial Lecture was delivered this year by Professor Mark Horenstein from Boston University who was, until recently, Editor-in-Chief of the Journal of Electrostatics. He spoke on The contribution of surface potential to diverse problems in electrostatics and his thorough knowledge of the subject of electrostatics was evident in the presentation. The first session was chaired by the Conference Chair, Dr Keith Davies, whose experience in the field showed through his frequent contributions to the discussions throughout the conference. Hazards and Electrostatic Discharge have formed a strong core to Electrostatics conferences for many years, and this conference contained sessions on both Hazards and on ESD, including an invited talk from Dr Jeremy Smallwood on ESD in Industry - Present and Future. Another strong theme to emerge from this year's programme was Non-Thermal Plasmas, which was covered in two sessions. There were two invited talks on this subject: Professor Masaaki Okubo gave a talk on Development of super-clean diesel engine and combustor using nonthermal plasma hybrid after treatment and Dr David Go presented a talk on Atmospheric-pressure ionization processes: New approaches and applications for plasmas in contact with liquids. A new innovation to the conference this year was the opportunity for conference sponsors to present to the delegates a technical

  15. Search for Effects of an Electrostatic Potential on Clocks in the Frame of Reference of a Charged Particle

    NASA Technical Reports Server (NTRS)

    Ringermacher, Harry I.; Conradi, Mark S.; Cassenti, Brice

    2005-01-01

    Results of experiments to confirm a theory that links classical electromagnetism with the geometry of spacetime are described. The theory, based on the introduction of a Torsion tensor into Einstein s equations and following the approach of Schroedinger, predicts effects on clocks attached to charged particles, subject to intense electric fields, analogous to the effects on clocks in a gravitational field. We show that in order to interpret this theory, one must re-interpret all clock changes, both gravitational and electromagnetic, as arising from changes in potential energy and not merely potential. The clock is provided naturally by proton spins in hydrogen atoms subject to Nuclear Magnetic Resonance trials. No frequency change of clocks was observed to a resolution of 6310(exp -9). A new "Clock Principle" was postulated to explain the null result. There are two possible implications of the experiments: (a) The Clock Principle is invalid and, in fact, no metric theory incorporating electromagnetism is possible; (b) The Clock Principle is valid and it follows that a negative rest mass cannot exist.

  16. Adhesion to Carbon Nanotube Conductive Scaffolds Forces Action-Potential Appearance in Immature Rat Spinal Neurons

    PubMed Central

    Toma, Francesca Maria; Calura, Enrica; Rizzetto, Lisa; Carrieri, Claudia; Roncaglia, Paola; Martinelli, Valentina; Scaini, Denis; Masten, Lara; Turco, Antonio; Gustincich, Stefano; Prato, Maurizio; Ballerini, Laura

    2013-01-01

    In the last decade, carbon nanotube growth substrates have been used to investigate neurons and neuronal networks formation in vitro when guided by artificial nano-scaled cues. Besides, nanotube-based interfaces are being developed, such as prosthesis for monitoring brain activity. We recently described how carbon nanotube substrates alter the electrophysiological and synaptic responses of hippocampal neurons in culture. This observation highlighted the exceptional ability of this material in interfering with nerve tissue growth. Here we test the hypothesis that carbon nanotube scaffolds promote the development of immature neurons isolated from the neonatal rat spinal cord, and maintained in vitro. To address this issue we performed electrophysiological studies associated to gene expression analysis. Our results indicate that spinal neurons plated on electro-conductive carbon nanotubes show a facilitated development. Spinal neurons anticipate the expression of functional markers of maturation, such as the generation of voltage dependent currents or action potentials. These changes are accompanied by a selective modulation of gene expression, involving neuronal and non-neuronal components. Our microarray experiments suggest that carbon nanotube platforms trigger reparative activities involving microglia, in the absence of reactive gliosis. Hence, future tissue scaffolds blended with conductive nanotubes may be exploited to promote cell differentiation and reparative pathways in neural regeneration strategies. PMID:23951361

  17. Particle adhesion in powder coating

    SciTech Connect

    Mazumder, M.K.; Wankum, D.L.; Knutson, M.; Williams, S.; Banerjee, S.

    1996-12-31

    Electrostatic powder coating is a widely used industrial painting process. It has three major advantages: (1) it provides high quality durable finish, (2) the process is environmentally friendly and does not require the use of organic solvents, and (3) it is economically competitive. The adhesion of electrostatically deposited polymer paint particles on the grounded conducting substrate depends upon many parameters: (a) particle size and shape distributions, (b) electrostatic charge distributions, (c) electrical resistivity, (d) dielectric strength of the particles, (e) thickness of the powder film, (f) presence and severity of the back corona, and (g) the conductivity and surface properties of the substrate. The authors present a model on the forces of deposition and adhesion of corona charged particles on conducting substrates.

  18. Differences in Electrostatic Potential Around DNA Fragments Containing Adenine and 8-oxo-Adenine. An Analysis Based on Regular Cylindrical Projection

    SciTech Connect

    Haranczyk, Maciej; Miller, John H; Gutowski, Maciej S

    2007-07-01

    Changes of electrostatic potential (EP) around the DNA molecule resulting from chemical modifications of nucleotides may play a role in enzymatic recognition of damaged sites. Effects of chemical modifications of nucleotides on the structure of DNA have been characterized through large scale density functional theory computations. Quantum mechanical structural optimizations of DNA fragments with three pairs of nucleotides and accompanying counteractions were performed with a B3LYP exchange-correlation functional and 6-31G** basis sets. The “intact” DNA fragment contained adenine in the middle layer, while the “damaged” fragment had the adenine replaced with 8-oxo-adenine. The electrostatic potential around these DNA fragments was projected on a cylindrical surface around the double helix. The two-dimensional maps of EP of the intact and damaged DNA fragments were analyzed to identify these modifications of EP that result from the occurrence of 8-oxo-adenine (8oA). It was found that distortions of a phosphate group neighboring 8oA and displacements of the accompanying countercation are clearly reflected in the EP maps. Helpful discussions Michel Dupuis are gratefully acknowledged. Authors wish to thank Marcel Swart for directing us to a compilation of van der Waals radii. This work was supported by the: (i) US DOE Office of Biological and Environmental Research, Low Dose Radiation Research Program (M.G. and M.H.), (ii) the Office of Science (BER), U. S. Department of Energy, Grant No. DE-FG03-02ER63470 (JHM), (iii) Polish State Committee for Scientific Research (KBN) Grant DS/8221-4-0140-6 (MG), (iv) European Social Funds (EFS) ZPORR/2.22/II/2.6/ARP/U/2/05 (M.H.). M.H. holds the Foundation for Polish Science (FNP) award for young scientists. The calculations were performed at the Academic Computer Center in Gdansk (TASK) and at the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a national

  19. Inhibition of cell adhesion by anti–P-selectin aptamer: a new potential therapeutic agent for sickle cell disease

    PubMed Central

    Gutsaeva, Diana R.; Parkerson, James B.; Yerigenahally, Shobha D.; Kurz, Jeffrey C.; Schaub, Robert G.; Ikuta, Tohru

    2011-01-01

    Adhesive interactions between circulating sickle red blood cells (RBCs), leukocytes, and endothelial cells are major pathophysiologic events in sickle cell disease (SCD). To develop new therapeutics that efficiently inhibit adhesive interactions, we generated an anti–P-selectin aptamer and examined its effects on cell adhesion using knockout-transgenic SCD model mice. Aptamers, single-stranded oligonucleotides that bind molecular targets with high affinity and specificity, are emerging as new therapeutics for cardiovascular and hematologic disorders. In vitro studies found that the anti–P-selectin aptamer exhibits high specificity to mouse P-selectin but not other selectins. SCD mice were injected with the anti–P-selectin aptamer, and cell adhesion was observed under hypoxia. The anti–P-selectin aptamer inhibited the adhesion of sickle RBCs and leukocytes to endothelial cells by 90% and 80%, respectively. The anti–P-selectin aptamer also increased microvascular flow velocities and reduced the leukocyte rolling flux. SCD mice treated with the anti–P-selectin aptamer demonstrated a reduced mortality rate associated with the experimental procedures compared with control mice. These results demonstrate that anti–P-selectin aptamer efficiently inhibits the adhesion of both sickle RBCs and leukocytes to endothelial cells in SCD model mice, suggesting a critical role for P-selectin in cell adhesion. Anti–P-selectin aptamer may be useful as a novel therapeutic agent for SCD. PMID:20926770

  20. pH-dependent cross-linking of catechols through oxidation via Fe(3+) and potential implications for mussel adhesion.

    PubMed

    Fullenkamp, Dominic E; Barrett, Devin G; Miller, Dusty R; Kurutz, Josh W; Messersmith, Phillip B

    2014-01-01

    The mussel byssus is a remarkable attachment structure that is formed by injection molding and rapid in-situ hardening of concentrated solutions of proteins enriched in the catecholic amino acid 3,4-dihydroxy-L-phenylalanine (DOPA). Fe(3+), found in high concentrations in the byssus, has been speculated to participate in redox reactions with DOPA that lead to protein polymerization, however direct evidence to support this hypothesis has been lacking. Using small molecule catechols, DOPA-containing peptides, and native mussel foot proteins, we report the first direct observation of catechol oxidation and polymerization accompanied by reduction of Fe(3+) to Fe(2+). In the case of the small molecule catechol, we identified two dominant dimer species and characterized their connectivities by nuclear magnetic resonance (NMR), with the C6-C6 and C5-C6 linked species as the major and minor products, respectively. For the DOPA-containing peptide, we studied the pH dependence of the reaction and demonstrated that catechol polymerization occurs readily at low pH, but is increasingly diminished in favor of metal-catechol coordination interactions at higher pH. Finally, we demonstrate that Fe(3+) can induce cross-links in native byssal mussel proteins mefp-1 and mcfp-1 at acidic pH. Based on these findings, we discuss the potential implications to the chemistry of mussel adhesion. PMID:25243062

  1. pH-dependent cross-linking of catechols through oxidation via Fe3+ and potential implications for mussel adhesion

    PubMed Central

    Fullenkamp, Dominic E.; Barrett, Devin G.; Miller, Dusty R.; Kurutz, Josh W.; Messersmith, Phillip B.

    2014-01-01

    The mussel byssus is a remarkable attachment structure that is formed by injection molding and rapid in-situ hardening of concentrated solutions of proteins enriched in the catecholic amino acid 3,4-dihydroxy-L-phenylalanine (DOPA). Fe3+, found in high concentrations in the byssus, has been speculated to participate in redox reactions with DOPA that lead to protein polymerization, however direct evidence to support this hypothesis has been lacking. Using small molecule catechols, DOPA-containing peptides, and native mussel foot proteins, we report the first direct observation of catechol oxidation and polymerization accompanied by reduction of Fe3+ to Fe2+. In the case of the small molecule catechol, we identified two dominant dimer species and characterized their connectivities by nuclear magnetic resonance (NMR), with the C6-C6 and C5-C6 linked species as the major and minor products, respectively. For the DOPA-containing peptide, we studied the pH dependence of the reaction and demonstrated that catechol polymerization occurs readily at low pH, but is increasingly diminished in favor of metal-catechol coordination interactions at higher pH. Finally, we demonstrate that Fe3+ can induce cross-links in native byssal mussel proteins mefp-1 and mcfp-1 at acidic pH. Based on these findings, we discuss the potential implications to the chemistry of mussel adhesion. PMID:25243062

  2. Electrostatics in protein–protein docking

    PubMed Central

    Heifetz, Alexander; Katchalski-Katzir, Ephraim; Eisenstein, Miriam

    2002-01-01

    A novel geometric-electrostatic docking algorithm is presented, which tests and quantifies the electrostatic complementarity of the molecular surfaces together with the shape complementarity. We represent each molecule to be docked as a grid of complex numbers, storing information regarding the shape of the molecule in the real part and information regarding the electrostatic character of the molecule in the imaginary part. The electrostatic descriptors are derived from the electrostatic potential of the molecule. Thus, the electrostatic character of the molecule is represented as patches of positive, neutral, or negative values. The potential for each molecule is calculated only once and stored as potential spheres adequate for exhaustive rotation/translation scans. The geometric-electrostatic docking algorithm is applied to 17 systems, starting form the structures of the unbound molecules. The results—in terms of the complementarity scores of the nearly correct solutions, their ranking in the lists of sorted solutions, and their statistical uniqueness—are compared with those of geometric docking, showing that the inclusion of electrostatic complementarity in docking is very important, in particular in docking of unbound structures. Based on our results, we formulate several "good electrostatic docking rules": The geometric-electrostatic docking procedure is more successful than geometric docking when the potential patches are large and when the potential extends away from the molecular surface and protrudes into the solvent. In contrast, geometric docking is recommended when the electrostatic potential around the molecules to be docked appears homogenous, that is, with a similar sign all around the molecule. PMID:11847280

  3. Change of electrostatic potential of mean force between two curved surfaces due to different salt composition, ion valence and size under certain ionic strength

    NASA Astrophysics Data System (ADS)

    Zhou, Shiqi

    2016-02-01

    Change of an electrostatic potential of mean force (EPMF) between two cylindrical rod surfaces with salt composition, ion valence, and ion size at a constant ionic strength of 0.3 M is studied by a classical density functional theory (CDFT) in a primitive model electrolyte solution. Several novel observations are made: (i) strength of a so-called like charge attraction (LCA) reduces in an invariable manner with the salt solution changing from single 2:1 electrolyte to mixture of 2:1 and 1:1 type electrolytes of varying concentration ratios; the change is even over entire range of the composition variation under low surface charge strength, and tends to be insensitive to the composition variation in the presence of the divalent counter-ion, and more and more drastic at a critical point the divalent counter-ion disappears, respectively, as the surface charge strength becomes big enough. (ii) Both monovalent counter-ion and co-ion diameters have only a marginal effect on both the LCA strength and equilibrium distance, and the former "abnormally" affects less than the latter. (iii) Depending on the surface charge strength considered, the divalent counter-ion diameter influences the LCA strength in solution comprised of 2:1 type and 1:1 type electrolytes, monotonously or non-monotonously. All of these findings provide forceful support for a recently proposed hydrogen-bonding style mechanism explaining the LCA.

  4. Vibrational spectroscopic (FT-IR and FT-Raman) studies, natural bond orbital analysis and molecular electrostatic potential surface of 3-hydroxy-6-methyl-2-nitropyridine

    NASA Astrophysics Data System (ADS)

    Karnan, M.; Balachandran, V.; Murugan, M.

    2012-10-01

    The optimized molecular structure and corresponding vibrational assignments of 3-hydroxy-6-methyl-2-nitropyridine have been investigated using density functional theory (DFT) B3LYP method with 6-311++G(d,p), 6-311++G(2d,2p) and 6-311++G(3d,3p) basis sets. Investigation of the relative orientation of the hydroxyl group with respect to the nitro group has shown that two conformers (O-cis) and (O-trans) exist. The vibrational analysis of the stable conformer of the title compound is performed by means of infrared absorption and Raman spectroscopy in combination with theoretical simulations. The molecular stability and bond strength were investigated by applying the natural bond orbital (NBO) analysis. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with electrostatic potential (ESP). The isotropic chemical shift computed by 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the HMNP calculated using the gauge invariant atomic orbital (GIAO) method also shows good agreement with experimental observations.

  5. Electrostatically screened, voltage-controlled electrostatic chuck

    DOEpatents

    Klebanoff, Leonard Elliott

    2001-01-01

    Employing an electrostatically screened, voltage-controlled electrostatic chuck particularly suited for holding wafers and masks in sub-atmospheric operations will significantly reduce the likelihood of contaminant deposition on the substrates. The electrostatic chuck includes (1) an insulator block having a outer perimeter and a planar surface adapted to support the substrate and comprising at least one electrode (typically a pair of electrodes that are embedded in the insulator block), (2) a source of voltage that is connected to the at least one electrode, (3) a support base to which the insulator block is attached, and (4) a primary electrostatic shield ring member that is positioned around the outer perimeter of the insulator block. The electrostatic chuck permits control of the voltage of the lithographic substrate; in addition, it provides electrostatic shielding of the stray electric fields issuing from the sides of the electrostatic chuck. The shielding effectively prevents electric fields from wrapping around to the upper or front surface of the substrate, thereby eliminating electrostatic particle deposition.

  6. Capture of soft particles on electrostatically heterogeneous collectors: brushy particles.

    PubMed

    Wen, Yicun; Guo, Xuhong; Kalasin, Surachate; Santore, Maria M

    2014-03-01

    This work investigated how particle softness can influence the initial adhesive capture of submicrometer colloidal particles from flow onto collecting surfaces. The study focused on the case dominated by potential attractions at the particle periphery (rather than, for instance, steric stabilization, requiring entropically costly deformations to access shorter-range van der Waals attractions.) The particles, "spherical polyelectrolyte brushes" with diameters in the range of 150-200 nm depending on the ionic strength, consisted of a polystyrene core and a corona of grafted poly(acrylic acid) chains, producing a relatively thick (20-40 nm) negative brushy layer. The adhesion of these particles was studied on electrostatically heterogeneous collecting surfaces: negatively charged substrates carrying flat polycationic patches made by irreversibly adsorbing the poly-l-lysine (PLL) polyelectrolyte. Variation in the amount of adsorbed PLL changed the net collector charge from completely negatively charged (repulsive) to positively charged (attractive). Adjustments in ionic strength varied the range of the electrostatic interactions. Comparing capture kinetics of soft brushy particles to those of similarly sized and similarly charged silica particles revealed nearly identical particle capture kinetics over the full range of collecting surface compositions at high ionic strengths. Even though the brushy particles contained an average of 5 vol % PAA in the brushy shell, with the rest being water under these conditions, their capture was indistinguishable from that of similarly charged rigid spheres. The brushy particles were, however, considerably less adherent at low ionic strengths where the brush was more extended, suggesting an influence of particle deformability or reduced interfacial charge. These findings, that the short time adhesion of brushy particles can resemble that of rigid particles, suggest that for bacteria and cell capture, modeling the cells as rigid

  7. Using Programmable Calculators to Solve Electrostatics Problems.

    ERIC Educational Resources Information Center

    Yerian, Stephen C.; Denker, Dennis A.

    1985-01-01

    Provides a simple routine which allows first-year physics students to use programmable calculators to solve otherwise complex electrostatic problems. These problems involve finding electrostatic potential and electric field on the axis of a uniformly charged ring. Modest programing skills are required of students. (DH)

  8. Double layers and electrostatic shocks

    NASA Technical Reports Server (NTRS)

    Hershkowitz, N.

    1981-01-01

    It is shown that it is useful to define double layers and shocks so that the ion phase spaces of double layers are the mirror image (about zero ion velocity) of the ion phase spaces for laminar electrostatic shocks. The distinguishing feature is the direction of the free ion velocity. It is also shown that double layers can exist without the presence of trapped ions. The Bohm condition for double layers, that the ion drift velocity on the high potential side must be greater than the ion sound velocity, is shown to be related to a requirement of a lower limit on the Mach number of laminar electrostatic shocks

  9. Potentially probiotic and bioprotective lactic acid bacteria starter cultures antagonise the Listeria monocytogenes adhesion to HT29 colonocyte-like cells.

    PubMed

    Garriga, M; Rubio, R; Aymerich, T; Ruas-Madiedo, P

    2015-01-01

    The capability of five lactic acid bacteria (LAB) to counteract the adhesion of Listeria monocytogenes to the epithelial intestinal cell line HT29 was studied. The highest adhesion ability to HT29 was achieved by the intestinal strain Lactobacillus rhamnosus CTC1679, followed by the meat-derived strains Lactobacillus sakei CTC494 and Enterococcus faecium CTC8005. Surprisingly, the meat strains showed significantly better adhesion to HT29 than two faecal isolates of Lactobacillus casei and even significantly higher than the reference strain L. rhamnosus GG. Additionally, the anti-listerial, bacteriocin-producer starter culture L. sakei CTC494 was able to significantly reduce the adhesion of L. monocytogenes to HT29 in experiments of exclusion, competition and inhibition. The performance was better than the faecal isolate L. rhamnosus CTC1679. Our results reinforce the fact that the ability of LAB to interact with a host epithelium model, as well as to antagonise with foodborne pathogens, is a strain-specific characteristic. Additionally, it is underlined that this trait is not dependent on the origin of the bacterium, since some food LAB behave better than intestinal ones. Therefore, the search for novel strains in food niches is a suitable approach to find those with potential health benefits. These strains are likely pre-adapted to the food environment, which would make their inclusion in the formulation of probiotic foods more feasible. PMID:25488261

  10. Application of a collagen-based membrane and chondroitin sulfate-based hydrogel adhesive for the potential repair of severe ocular surface injuries.

    PubMed

    Chae, Jemin J; Mulreany, Daniel G; Guo, Qiongyu; Lu, Qiaozhi; Choi, Joseph S; Strehin, Iossif; Espinoza, Freddy A; Schein, Oliver; Trexler, Morgana M; Bower, Kraig S; Elisseeff, Jennifer H

    2014-06-01

    This study was performed to evaluate the potential of a chondroitin sulfate-polyethylene glycol (CS-PEG) adhesive and collagen-based membrane (collagen vitrigel, CV) combination as a method to treat penetrating ocular injuries on the battlefield and to improve this method with two technologies: an antibiotic releasing CS-PEG adhesive and a corneal shaped CV. Burst testing using porcine cadaveric eyes, high-performance liquid chromatography, the Kirby-Bauer bacterial inhibition test, and CV implantations on the live and cadaveric rabbit eyes were performed. The ocular burst test showed CS-PEG adhesive could successfully repair 5-mm to 6-mm length wounds in the corneal and corneoscleral regions but would require CS-PEG + CV to treat larger wounds similar to those seen on the battlefield. In addition, high performance liquid chromatography and the Kirby-Bauer bacterial inhibition test presented evidence suggesting the vancomycin incorporated CS-PEG could inhibit Staphylococcus infection for 9 days. Furthermore, the curved CV showed an advantage by matching the corneal contour without any wrinkle formation. Although this pilot study showed a limited range of possible applications, we demonstrated that the combination of CS-PEG adhesive + CV is a promising method and the 2 technologies improve their applicability to the special demands of the battlefield. PMID:24902138

  11. Abdominal Adhesions

    MedlinePlus

    ... Abdominal Adhesions 1 Ward BC, Panitch A. Abdominal adhesions: current and novel therapies. Journal of Surgical Research. 2011;165(1):91– ... are abdominal adhesions and intestinal obstructions ... generally do not require treatment. Surgery is the only way to treat abdominal ...

  12. Modeling electrostatic effects in proteins.

    PubMed

    Warshel, Arieh; Sharma, Pankaz K; Kato, Mitsunori; Parson, William W

    2006-11-01

    Electrostatic energies provide what is perhaps the most effective tool for structure-function correlation of biological molecules. This review considers the current state of simulations of electrostatic energies in macromolecules as well as the early developments of this field. We focus on the relationship between microscopic and macroscopic models, considering the convergence problems of the microscopic models and the fact that the dielectric 'constants' in semimacroscopic models depend on the definition and the specific treatment. The advances and the challenges in the field are illustrated considering a wide range of functional properties including pK(a)'s, redox potentials, ion and proton channels, enzyme catalysis, ligand binding and protein stability. We conclude by pointing out that, despite the current problems and the significant misunderstandings in the field, there is an overall progress that should lead eventually to quantitative descriptions of electrostatic effects in proteins and thus to quantitative descriptions of the function of proteins. PMID:17049320

  13. Prolonged E-selectin induction by monocytes potentiates the adhesion of flowing neutrophils to cultured endothelial cells.

    PubMed

    Rainger, G E; Wautier, M P; Nash, G B; Wautier, J L

    1996-01-01

    We investigated the hypothesis that the infiltration of monocytes into inflamed tissue or damaged vessels would induce a secondary accumulation of neutrophils. Confluent human umbilical vein endothelial cells (HUVEC) and blood monocytes (0.5 or 0.05 monocytes/endothelial cell) were co-incubated for 4 or 24 h. The adhesion of neutrophils flowing over HUVEC was then analysed by video microscopy. Co-incubation caused up to a 40-fold increase in neutrophil adhesion, dependent upon monocyte/HUVEC ratio and duration of incubation. At the lower monocyte/HUVEC ratio, rolling adhesion alone was induced after 4 h co-incubation; however, the full repertoire of rolling, immobilization and migration of neutrophils was observed at all other combinations of co-culture ratio and exposure time. After maximal stimulation by monocytes, antibody blockade of the neutrophil integrin CD18 inhibited neutrophil arrest and migration and revealed underlying rolling adhesion. Rolling was supported by endothelial E-selectin as demonstrated by the almost total abolition of adhesion by a blocking antibody. In a direct comparison, monocytes, tumour necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) were assessed for their ability to induce endothelial expression of E-selectin. E selectin was significantly increased by all agents at 4 h, but monocytes alone were able to maintain high levels of E-selectin expression for 24 h. We conclude that monocytes can induce prolonged neutrophil adhesion and migration by activating endothelial cells and causing expression of E-selectin. PMID:8562395

  14. Modeling biophysical and biological properties from the characteristics of the molecular electron density, electron localization and delocalization matrices, and the electrostatic potential.

    PubMed

    Matta, Chérif F

    2014-06-15

    The electron density and the electrostatic potential are fundamentally related to the molecular hamiltonian, and hence are the ultimate source of all properties in the ground- and excited-states. The advantages of using molecular descriptors derived from these fundamental scalar fields, both accessible from theory and from experiment, in the formulation of quantitative structure-to-activity and structure-to-property relationships, collectively abbreviated as QSAR, are discussed. A few such descriptors encode for a wide variety of properties including, for example, electronic transition energies, pK(a)'s, rates of ester hydrolysis, NMR chemical shifts, DNA dimers binding energies, π-stacking energies, toxicological indices, cytotoxicities, hepatotoxicities, carcinogenicities, partial molar volumes, partition coefficients (log P), hydrogen bond donor capacities, enzyme-substrate complementarities, bioisosterism, and regularities in the genetic code. Electronic fingerprinting from the topological analysis of the electron density is shown to be comparable and possibly superior to Hammett constants and can be used in conjunction with traditional bulk and liposolubility descriptors to accurately predict biological activities. A new class of descriptors obtained from the quantum theory of atoms in molecules' (QTAIM) localization and delocalization indices and bond properties, cast in matrix format, is shown to quantify transferability and molecular similarity meaningfully. Properties such as "interacting quantum atoms (IQA)" energies which are expressible into an interaction matrix of two body terms (and diagonal one body "self" terms, as IQA energies) can be used in the same manner. The proposed QSAR-type studies based on similarity distances derived from such matrix representatives of molecular structure necessitate extensive investigation before their utility is unequivocally established. PMID:24777743

  15. Alteration of Electrostatic Surface Potential Enhances Affinity and Tumor Killing Properties of Anti-ganglioside GD2 Monoclonal Antibody hu3F8*

    PubMed Central

    Zhao, Qi; Ahmed, Mahiuddin; Guo, Hong-fen; Cheung, Irene Y.; Cheung, Nai-Kong V.

    2015-01-01

    Ganglioside GD2 is highly expressed on neuroectodermal tumors and an attractive therapeutic target for antibodies that have already shown some clinical efficacy. To further improve the current antibodies, which have modest affinity, we sought to improve affinity by using a combined method of random mutagenesis and in silico assisted design to affinity-mature the anti-GD2 monoclonal antibody hu3F8. Using yeast display, mutants in the Fv with enhanced binding over the parental clone were FACS-sorted and cloned. In silico modeling identified the minimal key interacting residues involved in the important charged interactions with the sialic acid groups of GD2. Two mutations, D32H (L-CDR1) and E1K (L-FR1) altered the electrostatic surface potential of the antigen binding site, allowing for an increase in positive charge to enhance the interaction with the negatively charged GD2-pentasaccharide headgroup. Purified scFv and IgG mutant forms were then tested for antigen specificity by ELISA, for tissue specificity by immunohistochemistry, for affinity by BIACORE, for antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-mediated cytotoxicity in vitro, and for anti-tumor efficacy in xenografted humanized mice. The nearly 7-fold improvement in affinity of hu3F8 with a single D32H (L-CDR1) mutation translated into a ∼12-fold improvement in NK92MI-transfected CD16-mediated ADCC, a 6-fold improvement in CD32-mediated ADCC, and a 2.5-fold improvement in complement-mediated cytotoxicity while maintaining restricted normal tissue cross-reactivity and achieving substantial improvement in tumor ablation in vivo. Despite increasing GD2 affinity, the double mutation D32H (L-CDR1) and E1K (L-FR1) did not further improve anti-tumor efficacy. PMID:25851904

  16. Modeling Biophysical and Biological Properties From the Characteristics of the Molecular Electron Density, Electron Localization and Delocalization Matrices, and the Electrostatic Potential

    PubMed Central

    Matta*, Chérif F

    2014-01-01

    The electron density and the electrostatic potential are fundamentally related to the molecular hamiltonian, and hence are the ultimate source of all properties in the ground- and excited-states. The advantages of using molecular descriptors derived from these fundamental scalar fields, both accessible from theory and from experiment, in the formulation of quantitative structure-to-activity and structure-to-property relationships, collectively abbreviated as QSAR, are discussed. A few such descriptors encode for a wide variety of properties including, for example, electronic transition energies, pKa's, rates of ester hydrolysis, NMR chemical shifts, DNA dimers binding energies, π-stacking energies, toxicological indices, cytotoxicities, hepatotoxicities, carcinogenicities, partial molar volumes, partition coefficients (log P), hydrogen bond donor capacities, enzyme–substrate complementarities, bioisosterism, and regularities in the genetic code. Electronic fingerprinting from the topological analysis of the electron density is shown to be comparable and possibly superior to Hammett constants and can be used in conjunction with traditional bulk and liposolubility descriptors to accurately predict biological activities. A new class of descriptors obtained from the quantum theory of atoms in molecules' (QTAIM) localization and delocalization indices and bond properties, cast in matrix format, is shown to quantify transferability and molecular similarity meaningfully. Properties such as “interacting quantum atoms (IQA)” energies which are expressible into an interaction matrix of two body terms (and diagonal one body “self” terms, as IQA energies) can be used in the same manner. The proposed QSAR-type studies based on similarity distances derived from such matrix representatives of molecular structure necessitate extensive investigation before their utility is unequivocally established. © 2014 The Author and the Journal of Computational Chemistry Published

  17. Vibrational spectroscopic (FT-IR and FT-Raman) studies, natural bond orbital analysis and molecular electrostatic potential surface of Isoxanthopterin

    NASA Astrophysics Data System (ADS)

    Prabavathi, N.; Nilufer, A.; Krishnakumar, V.

    2013-10-01

    The FTIR and FT-Raman spectra of Isoxanthopterin have been recorded in the region 4000-450 and 4000-100 cm-1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of Isoxanthopterin were obtained by the density functional theory (DFT) using 6-311++G(d,p) basis set. The harmonic vibrational frequencies were scaled and compared with experimental values. The observed and the calculated frequencies are found to be in good agreement. The 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The UV-visible spectrum was also recorded and compared with the theoretical values. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (β0), related properties (β, α0 and Δα) and the Mulliken charges of the molecule were also computed using DFT calculations. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and π* antibonding orbitals and second order delocalization energies (E2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. Information about the charge density distribution of the molecule and its chemical reactivity has been obtained by mapping molecular electrostatic potential surface. In addition, the non-linear optical properties were discussed from the dipole moment values and excitation wavelength in the UV-visible region.

  18. Vibrational spectroscopic (FT-IR and FT-Raman) studies, natural bond orbital analysis and molecular electrostatic potential surface of Isoxanthopterin.

    PubMed

    Prabavathi, N; Nilufer, A; Krishnakumar, V

    2013-10-01

    The FTIR and FT-Raman spectra of Isoxanthopterin have been recorded in the region 4000-450 and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of Isoxanthopterin were obtained by the density functional theory (DFT) using 6-311++G(d,p) basis set. The harmonic vibrational frequencies were scaled and compared with experimental values. The observed and the calculated frequencies are found to be in good agreement. The (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. The UV-visible spectrum was also recorded and compared with the theoretical values. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (β0), related properties (β, α0 and Δα) and the Mulliken charges of the molecule were also computed using DFT calculations. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in the σ* and π* antibonding orbitals and second order delocalization energies (E2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. Information about the charge density distribution of the molecule and its chemical reactivity has been obtained by mapping molecular electrostatic potential surface. In addition, the non-linear optical properties were discussed from the dipole moment values and excitation wavelength in the UV-visible region. PMID:23751224

  19. Electronic structure, molecular electrostatic potential and spectral characteristics of pillar[6]arene hosts and their complexes with n-octyltriethylammonium ions.

    PubMed

    Peerannawar, Swarada R; Gejji, Shridhar P

    2012-06-28

    Electronic structure, charge distribution and (1)H NMR in pillar[6]arene (P6) conformers, their diisobutoxy derivatives and their host-guest complexes have been investigated by employing the density functional theory. It has been shown that a P6 conformer obtained by flipping of alternate hydroquinone units turns out to be of lowest energy, owing to the hydrogen bonded network at both rims of the host. As opposed to this, a conformer void of hydrogen bonding interactions has largely been destabilized. The O-HO interactions are analyzed using molecular electrostatic potential topography as a tool. Modification of a P6 host by substituting a diisobutoxy group at reactive phenols (DIBP6) renders rigid pillar-shape architecture to the host in which electron-rich regions are localized within the cavity and near portals. Complexation of n-octyltriethylammonium ions (n-OTEA) with P6 and DIBP6 reveals qualitatively different binding patterns. It has been shown that the conformer in which n-OTEA penetrates from the lower rim of the host and partially encapsulates within the P6 cavity turns out to be 1.4 kJ mol(-1) lower in energy than the complex showing complete guest encapsulation. Host-guest binding patterns, viz. encapsulation or portal interactions, can be distinguished from (1)H NMR chemical shifts. The shielding of ethyl and n-octyl chain protons in an n-OTEA⊂DIBP6 complex points to encapsulation of the guest which has been rationalized from natural bond orbital analyses. These inferences are in consonance with (1)H NMR experiments. PMID:22596047

  20. Alteration of Electrostatic Surface Potential Enhances Affinity and Tumor Killing Properties of Anti-ganglioside GD2 Monoclonal Antibody hu3F8.

    PubMed

    Zhao, Qi; Ahmed, Mahiuddin; Guo, Hong-fen; Cheung, Irene Y; Cheung, Nai-Kong V

    2015-05-22

    Ganglioside GD2 is highly expressed on neuroectodermal tumors and an attractive therapeutic target for antibodies that have already shown some clinical efficacy. To further improve the current antibodies, which have modest affinity, we sought to improve affinity by using a combined method of random mutagenesis and in silico assisted design to affinity-mature the anti-GD2 monoclonal antibody hu3F8. Using yeast display, mutants in the Fv with enhanced binding over the parental clone were FACS-sorted and cloned. In silico modeling identified the minimal key interacting residues involved in the important charged interactions with the sialic acid groups of GD2. Two mutations, D32H (L-CDR1) and E1K (L-FR1) altered the electrostatic surface potential of the antigen binding site, allowing for an increase in positive charge to enhance the interaction with the negatively charged GD2-pentasaccharide headgroup. Purified scFv and IgG mutant forms were then tested for antigen specificity by ELISA, for tissue specificity by immunohistochemistry, for affinity by BIACORE, for antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-mediated cytotoxicity in vitro, and for anti-tumor efficacy in xenografted humanized mice. The nearly 7-fold improvement in affinity of hu3F8 with a single D32H (L-CDR1) mutation translated into a ∼12-fold improvement in NK92MI-transfected CD16-mediated ADCC, a 6-fold improvement in CD32-mediated ADCC, and a 2.5-fold improvement in complement-mediated cytotoxicity while maintaining restricted normal tissue cross-reactivity and achieving substantial improvement in tumor ablation in vivo. Despite increasing GD2 affinity, the double mutation D32H (L-CDR1) and E1K (L-FR1) did not further improve anti-tumor efficacy. PMID:25851904

  1. Compact electrostatic comb actuator

    DOEpatents

    Rodgers, M. Steven; Burg, Michael S.; Jensen, Brian D.; Miller, Samuel L.; Barnes, Stephen M.

    2000-01-01

    A compact electrostatic comb actuator is disclosed for microelectromechanical (MEM) applications. The actuator is based upon a plurality of meshed electrostatic combs, some of which are stationary and others of which are moveable. One or more restoring springs are fabricated within an outline of the electrostatic combs (i.e. superposed with the moveable electrostatic combs) to considerably reduce the space required for the actuator. Additionally, a truss structure is provided to support the moveable electrostatic combs and prevent bending or distortion of these combs due to unbalanced electrostatic forces or external loading. The truss structure formed about the moveable electrostatic combs allows the spacing between the interdigitated fingers of the combs to be reduced to about one micron or less, thereby substantially increasing the number of active fingers which can be provided in a given area. Finally, electrostatic shields can be used in the actuator to substantially reduce unwanted electrostatic fields to further improve performance of the device. As a result, the compact electrostatic comb actuator of the present invention occupies only a fraction of the space required for conventional electrostatic comb actuators, while providing a substantial increase in the available drive force (up to one-hundred times).

  2. The effect of split gate dimensions on the electrostatic potential and 0.7 anomaly within one-dimensional quantum wires on a modulation doped GaAs/AlGaAs heterostructure

    NASA Astrophysics Data System (ADS)

    Smith, L. W.; Al-Taie, H.; Lesage, A. A. J.; Thomas, K. J.; Sfigakis, F.; See, P.; Griffiths, J. P.; Farrer, I.; Jones, G. A. C.; Ritchie, D. A.; Kelly, M. J.; Smith, C. G.

    We use a multiplexing scheme to measure the conductance properties of 95 split gates of 7 different gate dimensions fabricated on a GaAs/AlGaAs chip, in a single cool down. The number of devices for which conductance is accurately quantized reduces as the gate length increases. However, even the devices for which conductance is accurately quantized in units of 2e2 / h show no correlation between the length of electrostatic potential barrier in the channel and the gate length, using a saddle point model to estimate the barrier length. Further, the strength of coupling between the gates and the 1D channel does not increase with gate length beyond 0.7 μm. The background electrostatic profile appears as significant as the gate dimension in determining device behavior. We find a clear correlation between the curvature of the electrostatic barrier along the channel and the strength of the ``0.7 anomaly'' which identifies the electrostatic length of the channel as the principal factor governing the conductance of the 0.7 anomaly. Present address: Wisconsin Institute for Quantum Information, University of Wisconsin-Madison, Madison, WI.

  3. PREFACE: Electrostatics 2015

    NASA Astrophysics Data System (ADS)

    Matthews, James

    2015-10-01

    Electrostatics 2015, supported by the Institute of Physics, was held in the Sir James Matthews building at Southampton Solent University, UK between 12th and 16th April 2015. Southampton is a historic city on the South Coast of England with a strong military and maritime history. Southampton is home to two Universities: Solent University, which hosted the conference, and the University of Southampton, where much work is undertaken related to electrostatics. 37 oral and 44 poster presentations were accepted for the conference, and 60 papers were submitted and accepted for the proceedings. The Bill Bright Memorial Lecture was delivered this year by Professor Mark Horenstein from Boston University who was, until recently, Editor-in-Chief of the Journal of Electrostatics. He spoke on The contribution of surface potential to diverse problems in electrostatics and his thorough knowledge of the subject of electrostatics was evident in the presentation. The first session was chaired by the Conference Chair, Dr Keith Davies, whose experience in the field showed through his frequent contributions to the discussions throughout the conference. Hazards and Electrostatic Discharge have formed a strong core to Electrostatics conferences for many years, and this conference contained sessions on both Hazards and on ESD, including an invited talk from Dr Jeremy Smallwood on ESD in Industry - Present and Future. Another strong theme to emerge from this year's programme was Non-Thermal Plasmas, which was covered in two sessions. There were two invited talks on this subject: Professor Masaaki Okubo gave a talk on Development of super-clean diesel engine and combustor using nonthermal plasma hybrid after treatment and Dr David Go presented a talk on Atmospheric-pressure ionization processes: New approaches and applications for plasmas in contact with liquids. A new innovation to the conference this year was the opportunity for conference sponsors to present to the delegates a technical

  4. N-methylformamide induces changes on adhesive properties and lung-colonizing potential of M14 melanoma cells.

    PubMed Central

    Del Bufalo, D.; Leonetti, C.; Bucci, B.; Amedeo, C.; Falcioni, R.; Biroccio, A.; Zupi, G.

    1998-01-01

    We have studied whether N-methylformamide can affect the expression pattern of adhesion molecules and the attachment behaviour of M14 human melanoma cells. The role of N-methylformamide on experimental and spontaneous pulmonary metastases from M14 cells in nude mice was also investigated. We demonstrate that N-methylformamide in vitro pretreatment of M14 cells, although inducing a significant increase in the expression of alpha2beta1, alpha6beta1 and alpha(v)beta3 integrin receptors, slightly modifies alpha5beta1 heterodimer and beta1 subunit expression. After this modulation, enhancement of cell adhesion to laminin, collagen I, vitronectin and fibrinogen, which is blocked by specific anti-integrin antibodies, also occurs. No changes in binding to fibronectin are observed. In vitro N-methylformamide pretreatment also results in an increased number of experimental nodules and in a decrease in spontaneous metastases. Moreover, in vivo treatment with N-methylformamide significantly reduces the number of spontaneous metastases. Collectively, these data show that N-methylformamide modulates the expression of some adhesion receptors, cell adhesion to laminin, collagen I, vitronectin and fibrinogen as well as the metastatic behaviour of M14 cells. Our data also suggest that the effect of N-methylformamide might be evaluated in combination with antineoplastic agents for the treatment of human melanoma. PMID:9460990

  5. Electrostatic ion thruster optics calculations

    NASA Technical Reports Server (NTRS)

    Whealton, John H.; Kirkman, David A.; Raridon, R. J.

    1992-01-01

    Calculations have been performed which encompass both a self-consistent ion source extraction plasma sheath and the primary ion optics including sheath and electrode-induced aberrations. Particular attention is given to the effects of beam space charge, accelerator geometry, and properties of the downstream plasma sheath on the position of the electrostatic potential saddle point near the extractor electrode. The electron blocking potential blocking is described as a function of electrode thickness and secondary plasma processes.

  6. Effect of Split Gate Size on the Electrostatic Potential and 0.7 Anomaly within Quantum Wires on a Modulation-Doped GaAs /AlGaAs Heterostructure

    NASA Astrophysics Data System (ADS)

    Smith, L. W.; Al-Taie, H.; Lesage, A. A. J.; Thomas, K. J.; Sfigakis, F.; See, P.; Griffiths, J. P.; Farrer, I.; Jones, G. A. C.; Ritchie, D. A.; Kelly, M. J.; Smith, C. G.

    2016-04-01

    We study 95 split gates of different size on a single chip using a multiplexing technique. Each split gate defines a one-dimensional channel on a modulation-doped GaAs /AlGaAs heterostructure, through which the conductance is quantized. The yield of devices showing good quantization decreases rapidly as the length of the split gates increases. However, for the subset of devices showing good quantization, there is no correlation between the electrostatic length of the one-dimensional channel (estimated using a saddle-point model) and the gate length. The variation in electrostatic length and the one-dimensional subband spacing for devices of the same gate length exceeds the variation in the average values between devices of different lengths. There is a clear correlation between the curvature of the potential barrier in the transport direction and the strength of the "0.7 anomaly": the conductance value of the 0.7 anomaly reduces as the barrier curvature becomes shallower. These results highlight the key role of the electrostatic environment in one-dimensional systems. Even in devices with clean conductance plateaus, random fluctuations in the background potential are crucial in determining the potential landscape in the active device area such that nominally identical gate structures have different characteristics.

  7. Intrinsic electrostatic effects in nanostructured ceramics

    SciTech Connect

    Uberuaga, Blas Pedro; Stanek, Chris R; Nerikar, Pankaj V

    2009-01-01

    Using empirical potentials, we have found that electrostatic dipoles can be created at grain boundaries formed from non-polar surfaces of fluorite-structured materials. In particular, the {Sigma}5(310)/[001] symmetric tilt grain boundary reconstructs to break the symmetry in the atomic structure at the boundary, forming the dipole. This dipole results in an abrupt change in electrostatic potential across the boundary. In multilayered ceramics composed of stacks of grain boundaries, the change in electrostatic potential at the boundary results in profound electrostatic effects within the crystalline layers, the nature of which depends on the electrostatic boundary conditions. For open-circuit boundary conditions, layers with either high or low electrostatic potential are formed. By contrast, for short-circuit boundary conditions, electric fields can be created within each layer, the strength of which then depends on the thickness of the layers. These electrostatic effects may have important consequences for the behavior of defects and dopants within these materials and offer the possibility of interesting technological applications.

  8. Natural Green Coating Inhibits Adhesion of Clinically Important Bacteria

    PubMed Central

    Trentin, Danielle S.; Silva, Denise B.; Frasson, Amanda P.; Rzhepishevska, Olena; da Silva, Márcia V.; de L. Pulcini, Elinor; James, Garth; Soares, Gabriel V.; Tasca, Tiana; Ramstedt, Madeleine; Giordani, Raquel B.; Lopes, Norberto P.; Macedo, Alexandre J.

    2015-01-01

    Despite many advances, biomaterial-associated infections continue to be a major clinical problem. In order to minimize bacterial adhesion, material surface modifications are currently being investigated and natural products possess large potential for the design of innovative surface coatings. We report the bioguided phytochemical investigation of Pityrocarpa moniliformis and the characterization of tannins by mass spectrometry. It was demonstrated that B-type linked proanthocyanidins-coated surfaces, here termed Green coatings, reduced Gram-positive bacterial adhesion and supported mammalian cell spreading. The proposed mechanism of bacterial attachment inhibition is based on electrostatic repulsion, high hydrophilicity and the steric hindrance provided by the coating that blocks bacterium-substratum interactions. This work shows the applicability of a prototype Green-coated surface that aims to promote necessary mammalian tissue compatibility, while reducing bacterial colonization. PMID:25655943

  9. Electrostatic disruption of a charged conducting spheroid

    NASA Technical Reports Server (NTRS)

    Hill, J. R.; Mendis, D. A.

    1981-01-01

    Electrostatic disruption of elongated parent grains following sudden charging to high electrostatic potentials is proposed as a specific mechanism for the appearance of striae or pseudosynchronic bands which have been observed in several comets. The polar and equatorial electrostatic tension for axis ratios between 0.01 and 1000 are calculated, and the polar pressure is found to be larger than the equatorial pressure for prolate spheroids. The electrostatic polar pressure profile along the polar axis for prolate spheroids is calculated, and the pressure is found to increase monotonically from a minimum at the center to a maxima at the ends. This indicates that as a prolate spheroid of uniform tensile strength is charged up, it will continue to chip off at the ends when the electrostatic pressure there exceeds the uniform tensile strength of the grain. The result can be a prolate grain or a grain which continues chipping until it explodes.

  10. High potential of adhesion to biotic and abiotic surfaces by opportunistic Staphylococcus aureus strains isolated from orthodontic appliances.

    PubMed

    Merghni, Abderrahmen; Ben Nejma, Mouna; Dallel, Ines; Tobji, Samir; Ben Amor, Adel; Janel, Sébastien; Lafont, Frank; Aouni, Mahjoub; Mastouri, Maha

    2016-02-01

    Orthodontic and other oral appliances act as reservoir of opportunistic pathogens that can easily become resistant to antibiotics and cause systemic infections. The aim of this study was to investigate the ability of Staphylococcus aureus strains isolated from healthy patients with orthodontic appliances, to adhere to biotic (HeLa cells) and abiotic surfaces (polystyrene and dental alloy). Adhesive ability to polystyrene was tested by crystal violet staining and quantitative biofilm production on dental alloy surfaces was evaluated by MTT reduction assay. In addition, the presence of icaA and icaD genes was achieved by polymerase chain reaction (PCR). Qualitative biofilm production revealed that 70.6% of strains were slime producers. The metabolic activity of S. aureus biofilms on dental alloy surfaces was high and did not differ between tested strains. Moreover, all the isolates were adhesive to HeLa cells and 94% of them harbor icaA and icaD genes. Considerable adhesion and internalization capacity to the epithelial HeLa cells and strong biofilm production abilities together, with a high genotypic expression of icaA/icaD genes are an important equipment of S. aureus to colonize orthodontic appliances and eventually to disseminate towards other body areas. PMID:26620082

  11. Adhesion of Escherichia coli to nano-Fe/Al oxides and its effect on the surface chemical properties of Fe/Al oxides.

    PubMed

    Liu, Zhao-Dong; Li, Jiu-Yu; Jiang, Jun; Hong, Zhi-Neng; Xu, Ren-Kou

    2013-10-01

    We investigated the adhesion of Escherichia coli to α-Fe2O3 and γ-Al2O3 and the effects of adhesion on the surface properties of the oxides in batch experiments, where we conducted potentiometric titration, zeta potential measurements, and FTIR spectroscopy. The adhesion isotherms fitted a Langmuir equation well. γ-Al2O3 had a higher adhesion capacity than α-Fe2O3 because of the higher positive charge on γ-Al2O3. The adhesion of E. coli to Fe/Al oxides decreased with increasing pH. Adhesion increased with increasing NaCl concentration, reaching its maximum at 0.05M for α-Fe2O3 and at 0.1M for γ-Al2O3, after which it decreased with further increases in NaCl concentration. Therefore, the electrostatic force plays an important role in the adhesion of E. coli to Fe/Al oxides. The zeta potential-pH curves of the binary-system fell between that for bacteria and those for Fe/Al oxides. Thus, overlapping of the diffuse layers of the electric double layers on the negatively-charged E. coli and positively-charged Fe/Al oxides reduced the effective surface charge density of the minerals and bacteria. E. coli adhesion decreased the point of zero salt effect and the isoelectric point of the Fe/Al oxides. The FTIR spectra indicated that non-electrostatic force also contributed to the interaction between E. coli and Fe/Al oxides, in addition to the electrostatic force between them. PMID:23732807

  12. Ectopic expression of polysialylated neural cell adhesion molecule in adult macaque Schwann cells promotes their migration and remyelination potential in the central nervous system

    PubMed Central

    Bachelin, C.; Zujovic, V.; Buchet, D.; Mallet, J.

    2010-01-01

    Recent findings suggested that inducing neural cell adhesion molecule polysialylation in rodents is a promising strategy for promoting tissue repair in the injured central nervous system. Since autologous grafting of Schwann cells is one potential strategy to promote central nervous system remyelination, it is essential to show that such a strategy can be translated to adult primate Schwann cells and is of interest for myelin diseases. Adult macaque Schwann cells were transduced with a lentiviral vector encoding sialyltransferase, an enzyme responsible for neural cell adhesion molecule polysialylation. In vitro, we found that ectopic expression of polysialylate promoted adult macaque Schwann cell migration and improved their integration among astrocytes in vitro without modifying their antigenic properties as either non-myelinating or pro-myelinating. In addition, forced expression of polysialylate in adult macaque Schwann cells decreased their adhesion with sister cells. To investigate the ability of adult macaque Schwann cells to integrate and migrate in vivo, focally induced demyelination was targeted to the spinal cord dorsal funiculus of nude mice, and both control and sialyltransferase expressing Schwann cells overexpressing green fluorescein protein were grafted remotely from the lesion site. Analysis of the spatio-temporal distribution of the grafted Schwann cells performed in toto and in situ, showed that in both groups, Schwann cells migrated towards the lesion site. However, migration of sialyltransferase expressing Schwann cells was more efficient than that of control Schwann cells, leading to their accelerated recruitment by the lesion. Moreover, ectopic expression of polysialylated neural cell adhesion molecule promoted adult macaque Schwann cell interaction with reactive astrocytes when exiting the graft, and their ‘chain-like’ migration along the dorsal midline. The accelerated migration of sialyltransferase expressing Schwann cells to the

  13. High temperature adhesives

    NASA Technical Reports Server (NTRS)

    St.clair, Terry L.

    1991-01-01

    The aerospace and electronics industries have an ever increasing need for higher performance materials. In recent years, linear aromatic polyimides have been proven to be a superior class of materials for various applications in these industries. The use of this class of polymers as adhesives is continuing to increase. Several NASA Langley developed polyimides show considerable promise as adhesives because of their high glass transition temperatures, thermal stability, resistance to solvents/water, and their potential for cost effective manufacture.

  14. Abdominal Adhesions

    MedlinePlus

    ... Adhesions 1 Ward BC, Panitch A. Abdominal adhesions: current and novel therapies. Journal of Surgical Research. 2011;165(1):91–111. Seek Help for ... and how to participate, visit the NIH Clinical Research Trials and You website ... Foundation for Functional Gastrointestinal Disorders 700 West Virginia ...

  15. Edutainment Science: Electrostatics

    ERIC Educational Resources Information Center

    Ahlers, Carl

    2009-01-01

    Electrostatics should find a special place in all primary school science curricula. It is a great learning area that reinforces the basics that underpin electricity and atomic structure. Furthermore, it has many well documented hands-on activities. Unfortunately, the "traditional" electrostatics equipment such as PVC rods, woollen cloths, rabbit…

  16. Electrostatic Levitator (ESL)

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Dr. Rulison of Space System LORAl working with the Electrostatic Levitation (ESL) prior to the donation. Space System/LORAL donated the electrostatic containerless processing system to NASA's Marshall Space Flight Center (MSFC). The official hand over took place in July 1998.

  17. Electrostatic Levitator (ESL) Facility

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The Electrostatic Levitator (ESL) Facility established at Marshall Space Flight Center (MSFC) supports NASA's Microgravity Materials Science Research Program. NASA materials science investigations include ground-based, flight definition and flight projects. Flight definition projects, with demanding science concept review schedules, receive highest priority for scheduling experiment time in the Electrostatic Levitator (ESL) Facility.

  18. Novel secreted isoform of adhesion molecule ICAM-4: Potential regulator of membrane-associated ICAM-4 interactions

    SciTech Connect

    Lee, Gloria; Spring, Frances A.; Parons, Stephen F.; Mankelow, Tosti J.; Peters, Luanne L.; Koury, Mark J.; Mohandas, Narla; Anstee, David J.; Chasis, Joel Anne

    2003-02-18

    ICAM-4, a newly characterized adhesion molecule, is expressed early in human erythropoiesis and functions as a ligand for binding a4b1 and aV integrin-expressing cells. Within the bone marrow, erythroblasts surround central macrophages forming erythroblastic islands. Evidence suggests that these islands are highly specialized subcompartments where cell adhesion events, in concert with cytokines, play critical roles in regulating erythropoiesis and apoptosis. Since erythroblasts express a4b1 and ICAM-4 and macrophages exhibit aV, ICAM-4 is an attractive candidate for mediating cellular interactions within erythroblastic islands. To determine whether ICAM-4 binding properties are conserved across species, we first cloned and sequenced the murine homologue. The translated amino acid sequence showed 68 percent overall identity with human ICAM-4. Using recombinant murine ICAM-4 extracellular domains, we discovered that hematopoietic a4b1-expressing HEL cells and non-hematopoietic aV-expressing FLY cells adhered to mouse ICAM-4. Cell adhesion studies showed that FLY and HEL cells bound to mouse and human proteins with similar avidity. These data strongly suggest conservation of integrin-binding properties across species. Importantly, we characterized a novel second splice cDNA that would be predicted to encode an ICAM-4 isoform, lacking the membrane-spanning domain. Erythroblasts express both isoforms of ICAM-4. COS-7 cells transfected with GFP constructs of prototypic or novel ICAM-4 cDNA showed different cellular localization patterns. Moreover, analysis of tissue culture medium revealed that the novel ICAM-4 cDNA encodes a secreted protein. We postulate that secretion of this newly described isoform, ICAM-4S, may modulate binding of membrane-associated ICAM-4 and could thus play a critical regulatory role in erythroblast molecular attachments.

  19. Self-etching zinc-doped adhesives improve the potential of caries-affected dentin to be functionally remineralized.

    PubMed

    Toledano, Manuel; Aguilera, Fátima S; Osorio, Estrella; Cabello, Inmaculada; Toledano-Osorio, Manuel; Osorio, Raquel

    2015-01-01

    The aim of this study was to evaluate if mechanical cycling influences bioactivity at the resin-carious dentin interface after bonding with Zn-doped self-etching adhesives. Caries-affected dentin surfaces were bonded with: Clearfil SE bond (SEB), and 10 wt. % ZnO nanoparticles or 2 wt. % ZnCl2 were added into the SEB primer or bonding components. Bonded interfaces were stored during 24 h and then tested or submitted to mechanical loading. Microtensile bond strength was assessed. Debonded dentin surfaces were studied by field emission scanning electron microscopy. Remineralization of the bonded interfaces was evaluated through nanohardness (Hi) and Young's modulus (Ei), Raman spectroscopy/cluster analysis, and Masson's trichrome staining technique. New precipitation of minerals composed of zinc-base salts and multiple Zn-rich phosphate deposits was observed in samples infiltrated with the Zn-doped adhesives. At the hybrid layer, specimens treated with ZnO incorporated in the primer (SEB·P-ZnO), after load cycling, attained the highest Ei and Hi. Load cycling increased Ei at the bottom of the hybrid layer when both, SEB undoped and SEB with ZnCl2 included in the bonding (SEB·Bd-ZnCl2), were used. ZnO incorporated in the primer promoted an increase in height of the phosphate and carbonate peaks, crystallinity, relative mineral concentration, and lower collagen crosslinking. ZnCl2 included in the bonding attained similar results, but relative mineral concentration decreased, associated to higher crosslinking and restricted collagen maturation. In general, a substantial restoration of the mechanical properties of caries-affected dentin substrata occurred when SEB-Zn doped adhesives were used and load cycled was applied, leading to functional and biochemical remineralization. PMID:26178264

  20. Electrostatic electrochemistry at insulators.

    PubMed

    Liu, Chongyang; Bard, Allen J

    2008-06-01

    The identity of charges generated by contact electrification on dielectrics has remained unknown for centuries and the precise determination of the charge density is also a long-standing challenge. Here, electrostatic charges on Teflon (polytetrafluoroethylene) produced by rubbing with Lucite (polymethylmethacrylate) were directly identified as electrons rather than ions by electrochemical (redox) experiments with charged Teflon used as a single electrode in solution causing various chemical reactions: pH increases; hydrogen formation; metal deposition; Fe(CN)(6)(3-) reduction; and chemiluminescence in the system of Teflon(-)/Ru(bpy)(3)(2+)/S(2)O(8)(2-) (analogous to electrogenerated chemiluminescence). Moreover, copper deposition could be amplified by depositing Pd first in a predetermined pattern, followed by electroless deposition to produce Cu lines. This process could be potentially important for microelectronic and other applications because Teflon has desirable properties including a low dielectric constant and good thermal stability. Charge density was determined using Faraday's law and the significance of electron transfer processes on charged polymers and potentially other insulators have been demonstrated. PMID:18362908

  1. Electrostatic and electromagnetic instabilities associated with electrostatic shocks: Two-dimensional particle-in-cell simulation

    SciTech Connect

    Kato, Tsunehiko N.; Takabe, Hideaki

    2010-03-15

    A two-dimensional electromagnetic particle-in-cell simulation with the realistic ion-to-electron mass ratio of 1836 is carried out to investigate the electrostatic collisionless shocks in relatively high-speed (approx3000 km s{sup -1}) plasma flows and also the influence of both electrostatic and electromagnetic instabilities, which can develop around the shocks, on the shock dynamics. It is shown that the electrostatic ion-ion instability can develop in front of the shocks, where the plasma is under counterstreaming condition, with highly oblique wave vectors as was shown previously. The electrostatic potential generated by the electrostatic ion-ion instability propagating obliquely to the shock surface becomes comparable with the shock potential and finally the shock structure is destroyed. It is also shown that in front of the shock the beam-Weibel instability gradually grows as well, consequently suggesting that the magnetic field generated by the beam-Weibel instability becomes important in long-term evolution of the shock and the Weibel-mediated shock forms long after the electrostatic shock vanished. It is also observed that the secondary electrostatic shock forms in the reflected ions in front of the primary electrostatic shock.

  2. A nontransferring dry adhesive with hierarchical polymer nanohairs

    PubMed Central

    Jeong, Hoon Eui; Lee, Jin-Kwan; Kim, Hong Nam; Moon, Sang Heup; Suh, Kahp Y.

    2009-01-01

    We present a simple yet robust method for fabricating angled, hierarchically patterned high-aspect-ratio polymer nanohairs to generate directionally sensitive dry adhesives. The slanted polymeric nanostructures were molded from an etched polySi substrate containing slanted nanoholes. An angled etching technique was developed to fabricate slanted nanoholes with flat tips by inserting an etch-stop layer of silicon dioxide. This unique etching method was equipped with a Faraday cage system to control the ion-incident angles in the conventional plasma etching system. The polymeric nanohairs were fabricated with tailored leaning angles, sizes, tip shapes, and hierarchical structures. As a result of controlled leaning angle and bulged flat top of the nanohairs, the replicated, slanted nanohairs showed excellent directional adhesion, exhibiting strong shear attachment (≈26 N/cm2 in maximum) in the angled direction and easy detachment (≈2.2 N/cm2) in the opposite direction, with a hysteresis value of ≈10. In addition to single scale nanohairs, monolithic, micro-nanoscale combined hierarchical hairs were also fabricated by using a 2-step UV-assisted molding technique. These hierarchical nanoscale patterns maintained their adhesive force even on a rough surface (roughness <20 μm) because of an increase in the contact area by the enhanced height of hierarchy, whereas simple nanohairs lost their adhesion strength. To demonstrate the potential applications of the adhesive patch, the dry adhesive was used to transport a large-area glass (47.5 × 37.5 cm2, second-generation TFT-LCD glass), which could replace the current electrostatic transport/holding system with further optimization. PMID:19304801

  3. Effect of viscous macromolecules on peritoneal plasminogen activator activity: a potential mechanism for their ability to reduce postoperative adhesion formation.

    PubMed

    Mayer, M; Yedgar, S; Hurwitz, A; Palti, Z; Finzi, Z; Milwidsky, A

    1988-10-01

    Activity of peritoneal plasminogen activator and its regulation by dextran and other macromolecules that clinically suppress postoperative adhesions was studied. Plasminogen activator activity was assayed by a two-stage globinolytic assay that monitors formation of plasmin, as well as by cleavage of a chromogenic peptide substrate (S-2444) in the presence of aprotinin (Trasylol). Plasminogen activator activity was located on the outer surface of human peritoneum. Incubation of peritoneal tissue with buffer in vitro (conditioning) prompted release of plasminogen activator into the conditioning medium. The released plasminogen activator formed a single band on sodium dodecyl sulfate-gel electrophoresis at an apparent molecular weight of 174,000 and was markedly suppressed by antiserum raised against human melanoma tissue-type plasminogen activator. Nonspecific proteolytic activity did not accumulate in the medium during conditioning. The presence of dextran 80 during conditioning of peritoneum reversibly suppressed tissue-bound plasminogen activator activity and reduced plasminogen activator activity in the spent medium. A similar inhibition of peritoneal plasminogen activator was induced by dextran 500, methyl cellulose, and polyvinylpyrrolidone. Dextran, when added to the medium after conditioning, had no direct inhibitory effect on plasminogen activator activity. Dextran did not induce peritoneal production of inhibitor(s) of trypsin, chymotrypsin, or urokinase. On the basis of these findings, two possible mechanisms for the effect of viscous polymers in the reduction of adhesion formation are proposed. These mechanisms consider the importance of peritoneal tissue-type plasminogen activator for removal of fibrin clots and suggest that polymer coating either prevents the shedding of plasminogen activator into the abdominal cavity or reduces the access of fibrin clots to the serosal surfaces. PMID:2459968

  4. Studying Electrostatic Levitator Specimen

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Kevin Croat of Washington University in St. Louis, MO, examines samples processed in NASA/Marshall Space Flight Center's (MSFC)Electrostatic Levitator Facility. Croat is working with Prof. Kerneth Kelton in investigating undercooling of polytetrahedral phase-forming liquids.

  5. More Electrostatic Explorations.

    ERIC Educational Resources Information Center

    Stewart, Gay; Gallai, Ditta

    1998-01-01

    Presents worksheet activities that enable students to explore the concept of electrostatic induction and learn the meaning of grounding. Students build two classic devices, the electrophorus and the leaf electroscope. (DDR)

  6. Micromachined electrostatic vertical actuator

    DOEpatents

    Lee, Abraham P.; Sommargren, Gary E.; McConaghy, Charles F.; Krulevitch, Peter A.

    1999-10-19

    A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion` micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.

  7. Electrostatic discharge test apparatus

    NASA Technical Reports Server (NTRS)

    Smith, William Conrad (Inventor)

    1988-01-01

    Electrostatic discharge properties of materials are quantitatively measured and ranked. Samples are rotated on a turntable beneath selectable, co-available electrostatic chargers, one being a corona charging element and the other a sample-engaging triboelectric charging element. Samples then pass under a voltage meter to measure the amount of residual charge on the samples. After charging is discontinued, measurements are continued to record the charge decay history over time.

  8. Electrostatic discharge test apparatus

    NASA Technical Reports Server (NTRS)

    Smith, William C. (Inventor)

    1989-01-01

    Electrostatic discharge properties of materials are quantitatively measured and ranked. Samples (20) are rotated on a turntable (15) beneath selectable, co-available electrostatic chargers (30/40), one being a corona charging element (30) and the other a sample-engaging triboelectric charging element (40). They then pass under a voltage meter (25) to measure the amount of residual charge on the samples (20). After charging is discontinued, measurements are continued to record the charge decay history over time.

  9. Electrostatic Levitator Electrode Layout

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Schematic of Electrostatic Levitator (ESL) electrodes and controls system. The ESL uses static electricity to suspend an object (about 2-3 mm in diameter) inside a vacuum chamber while a laser heats the sample until it melts. This lets scientists record a wide range of physical properties without the sample contacting the container or any instruments, conditions that would alter the readings. The Electrostatic Levitator is one of several tools used in NASA's microgravity materials science program.

  10. Graphene Electrostatic Microphone

    NASA Astrophysics Data System (ADS)

    Zhou, Qin; Onishi, Seita; Zettl, A.

    2015-03-01

    We demonstrate a wideband electrostatic graphene microphone displaying flat frequency response over the entire human audible region as well as into the ultrasonic regime. Using the microphone, low-level ultrasonic bat calls are successfully recorded. The microphone can be paired with a similarly constructed electrostatic graphene loudspeaker to create a wideband ultrasonic radio. Materials Sciences Division, Lawrence Berkeley National Laboratory Kavli Energy NanoSciences Institute at the University of California - Berkeley.

  11. Electrostatic particle collection in vacuum

    NASA Astrophysics Data System (ADS)

    Afshar-Mohajer, Nima; Damit, Brian; Wu, Chang-Yu; Sorloaica-Hickman, Nicoleta

    2011-09-01

    Lunar grains accumulate charges due to solar-based ionizing radiations, and the repelling action of like-charged particles causes the levitation of lunar dust. The lunar dust deposit on sensitive and costly surfaces of investigative equipment is a serious concern in lunar explorations. Inspired by electrostatic precipitators (ESPs), the Electrostatic Lunar Dust Collector (ELDC) was proposed for collecting already charged lunar dust particles to prevent the lunar dust threat. As the conditions for terrestrial counterparts are not valid in the lunar environment, equations developed for terrestrial devices yield incorrect predictions in lunar application. Hence, a mathematical model was developed for the ELDC operating in vacuum to determine its collection efficiency. The ratios of electrical energy over potential energy, kinetic energy over potential energy and the ratio of ELDC dimensions were identified to be the key dimensionless parameters. Sensitivity analyses of the relevant parameters showed that depending on ELDC orientation, smaller particles would be collected more easily at vertical orientation, whereas larger particles were easier to collect in a horizontal ELDC configuration. In the worst case scenario, the electrostatic field needed to be 10 times stronger in the vertical mode in order to adequately collect larger particles. The collection efficiency was very sensitive to surface potential of lunar dust and it reached the maximum when surface potential was between 30 and 120 V. Except for regions of the lunar day side with surface potential close to zero, providing 1 kV ( E = 20 kV m -1) with the ELDC was more than enough for collecting all the particles in the most critical orientation. The needed field strength was about 4000 times less than that for repelling 1-μm size particles already settled on the surfaces. The analysis shows that the ELDC offers a viable solution for lunar dust control due to its effectiveness, ease of cleaning and low voltage

  12. Adhesion hysteresis of silane coated microcantilevers

    SciTech Connect

    DE BOER,MAARTEN P.; KNAPP,JAMES A.; MICHALSKE,TERRY A.; SRINIVASAN,U.; MABOUDIAN,R.

    2000-04-17

    The authors have developed a new experimental approach for measuring hysteresis in the adhesion between micromachined surfaces. By accurately modeling the deformations in cantilever beams that are subject to combined interfacial adhesion and applied electrostatic forces, they determine adhesion energies for advancing and receding contacts. They draw on this new method to examine adhesion hysteresis for silane coated micromachined structures and found significant hysteresis for surfaces that were exposed to high relative humidity (RH) conditions. Atomic force microscopy studies of these surfaces showed spontaneous formation of agglomerates that they interpreted as silages that have irreversibly transformed from uniform surface layers at low RH to isolated vesicles at high RH. They used contact deformation models to show that the compliance of these vesicles could reasonably account for the adhesion hysteresis that develops at high RH as the surfaces are forced into contact by an externally applied load.

  13. Altering the Electrostatic Potential in the Major Groove: Thermodynamic and Structural Characterization of 7-Deaza-2′-deoxyadenosine:dT Base Pairing in DNA

    PubMed Central

    2011-01-01

    As part of an ongoing effort to explore the effect of major groove electrostatics on the thermodynamic stability and structure of DNA, a 7-deaza-2′-deoxyadenosine:dT (7-deaza-dA:dT) base pair in the Dickerson–Drew dodecamer (DDD) was studied. The removal of the electronegative N7 atom on dA and the replacement with an electropositive C–H in the major groove was expected to have a significant effect on major groove electrostatics. The structure of the 7-deaza-dA:dT base pair was determined at 1.1 Å resolution in the presence of Mg2+. The 7-deaza-dA, which is isosteric for dA, had minimal effect on the base pairing geometry and the conformation of the DDD in the crystalline state. There was no major groove cation association with the 7-deaza-dA heterocycle. In solution, circular dichroism showed a positive Cotton effect centered at 280 nm and a negative Cotton effect centered at 250 nm that were characteristic of a right-handed helix in the B-conformation. However, temperature-dependent NMR studies showed increased exchange between the thymine N3 imino proton of the 7-deaza-dA:dT base pair and water, suggesting reduced stacking interactions and an increased rate of base pair opening. This correlated with the observed thermodynamic destabilization of the 7-deaza-dA modified duplex relative to the DDD. A combination of UV melting and differential scanning calorimetry experiments were conducted to evaluate the relative contributions of enthalpy and entropy in the thermodynamic destabilization of the DDD. The most significant contribution arose from an unfavorable enthalpy term, which probably results from less favorable stacking interactions in the modified duplex, which was accompanied by a significant reduction in the release of water and cations from the 7-deaza-dA modified DNA. PMID:22059929

  14. Altering the Electrostatic Potential in the Major Groove: Thermodynamic and Structural Characterization of 7-Deaza-2;#8242;-deoxyadenosine:dT Base Pairing in DNA

    SciTech Connect

    Kowal, Ewa A.; Ganguly, Manjori; Pallan, Pradeep S.; Marky, Luis A.; Gold, Barry; Egli, Martin; Stone, Michael P.

    2012-02-15

    As part of an ongoing effort to explore the effect of major groove electrostatics on the thermodynamic stability and structure of DNA, a 7-deaza-2'-deoxyadenosine:dT (7-deaza-dA:dT) base pair in the Dickerson-Drew dodecamer (DDD) was studied. The removal of the electronegative N7 atom on dA and the replacement with an electropositive C-H in the major groove was expected to have a significant effect on major groove electrostatics. The structure of the 7-deaza-dA:dT base pair was determined at 1.1 {angstrom} resolution in the presence of Mg{sup 2+}. The 7-deaza-dA, which is isosteric for dA, had minimal effect on the base pairing geometry and the conformation of the DDD in the crystalline state. There was no major groove cation association with the 7-deaza-dA heterocycle. In solution, circular dichroism showed a positive Cotton effect centered at 280 nm and a negative Cotton effect centered at 250 nm that were characteristic of a right-handed helix in the B-conformation. However, temperature-dependent NMR studies showed increased exchange between the thymine N3 imino proton of the 7-deaza-dA:dT base pair and water, suggesting reduced stacking interactions and an increased rate of base pair opening. This correlated with the observed thermodynamic destabilization of the 7-deaza-dA modified duplex relative to the DDD. A combination of UV melting and differential scanning calorimetry experiments were conducted to evaluate the relative contributions of enthalpy and entropy in the thermodynamic destabilization of the DDD. The most significant contribution arose from an unfavorable enthalpy term, which probably results from less favorable stacking interactions in the modified duplex, which was accompanied by a significant reduction in the release of water and cations from the 7-deaza-dA modified DNA.

  15. Electrostatic coupling of ion pumps.

    PubMed Central

    Nieto-Frausto, J; Lüger, P; Apell, H J

    1992-01-01

    In this paper the electrostatic interactions between membrane-embedded ion-pumps and their consequences for the kinetics of pump-mediated transport processes have been examined. We show that the time course of an intrinsically monomolecular transport reaction can become distinctly nonexponential, if the reaction is associated with charge translocation and takes place in an aggregate of pump molecules. First we consider the electrostatic coupling of a single dimer of ion-pumps embedded in the membrane. Then we apply the treatment to the kinetic analysis of light-driven proton transport by bacteriorhodopsin which forms two-dimensional hexagonal lattices. Finally, for the case of nonordered molecules, we also consider a model in which the pumps are randomly distributed over the nodes of a lattice. Here the average distance is equal to that deduced experimentally and the elemental size of the lattice is the effective diameter of one single pump. This latter model is applied to an aggregate of membrane-embedded Na, K- and Ca-pumps. In all these cases the electrostatic potential considered is the exact solution calculated from the method of electrical images for a plane membrane of finite thickness immersed in an infinite aqueous solution environment. The distributions of charges (ions or charged binding sites) are considered homogeneous or discrete in the membrane and/or in the external solution. In the case of discrete distributions we compare the results from a mean field approximation and a stochastic simulation. PMID:1371705

  16. Prognostic microRNAs modulate the RHO adhesion pathway: A potential therapeutic target in undifferentiated pleomorphic sarcomas

    PubMed Central

    Wong, Philip; Hui, Angela; Su, Jie; Yue, Shijun; Haibe-Kains, Benjamin; Gokgoz, Nalan; Xu, Wei; Bruce, Jeff; Williams, Justin; Catton, Charles; Wunder, Jay S.; Andrulis, Irene L.; Gladdy, Rebecca; Dickson, Brendan; O'Sullivan, Brian; Liu, Fei-Fei

    2015-01-01

    A common and aggressive subtype of soft-tissue sarcoma, undifferentiated pleomorphic sarcoma (UPS) was examined to determine the role of micro-RNAs (miRNAs) in modulating distant metastasis. Following histopathologic review, 110 fresh frozen clinically annotated UPS samples were divided into two independent cohorts for Training (42 patients), and Validation (68 patients) analyses. Global miRNA profiling on the Training Set and functional analysis in vitro suggested that miRNA-138 and its downstream RHO-ROCK cell adhesion pathway was a convergent target of miRNAs associated with the development of metastasis. A six-miRNA signature set prognostic of distant metastasis-free survival (DMFS) was developed from Training Set miRNA expression values. Using the six-miRNA signature, patients were successfully categorized into high- and low-risk groups for DMFS in an independent Validation Set, with a hazard ratio (HR) of 2.25 (p = 0.048). After adjusting for other known prognostic variables such as age, gender, tumor grade, size, depth, and treatment with radiotherapy, the six-miRNA signature retained prognostic value with a HR of 3.46 (p < 0.001). A prognostic miRNA biomarker for clinical validation was thus identified along with a functional pathway that modulates UPS metastatic phenotype. PMID:25970788

  17. Prognostic microRNAs modulate the RHO adhesion pathway: A potential therapeutic target in undifferentiated pleomorphic sarcomas.

    PubMed

    Wong, Philip; Hui, Angela; Su, Jie; Yue, Shijun; Haibe-Kains, Benjamin; Gokgoz, Nalan; Xu, Wei; Bruce, Jeff; Williams, Justin; Catton, Charles; Wunder, Jay S; Andrulis, Irene L; Gladdy, Rebecca; Dickson, Brendan; O'Sullivan, Brian; Liu, Fei-Fei

    2015-11-17

    A common and aggressive subtype of soft-tissue sarcoma, undifferentiated pleomorphic sarcoma (UPS) was examined to determine the role of micro-RNAs (miRNAs) in modulating distant metastasis. Following histopathologic review, 110 fresh frozen clinically annotated UPS samples were divided into two independent cohorts for Training (42 patients), and Validation (68 patients) analyses. Global miRNA profiling on the Training Set and functional analysis in vitro suggested that miRNA-138 and its downstream RHO-ROCK cell adhesion pathway was a convergent target of miRNAs associated with the development of metastasis. A six-miRNA signature set prognostic of distant metastasis-free survival (DMFS) was developed from Training Set miRNA expression values. Using the six-miRNA signature, patients were successfully categorized into high- and low-risk groups for DMFS in an independent Validation Set, with a hazard ratio (HR) of 2.25 (p = 0.048). After adjusting for other known prognostic variables such as age, gender, tumor grade, size, depth, and treatment with radiotherapy, the six-miRNA signature retained prognostic value with a HR of 3.46 (p < 0.001). A prognostic miRNA biomarker for clinical validation was thus identified along with a functional pathway that modulates UPS metastatic phenotype. PMID:25970788

  18. Investigation of electrostatic discharge phenomena on conductive and non-conductive solar reflectors

    NASA Technical Reports Server (NTRS)

    Bosma, S. J.; Minier, C. F.; Levy, L.

    1979-01-01

    A sample composed of non conductive optical solar reflectors (OSR) was irradiated with low energy electrons at the DERTS facility to study the effects of charge build up on thermal control coating materials. The degration effects on this panel due to electrostatic discharges were investigated to find possible alternatives to limit the amount of damage. The following systems are evaluated: (1) non conductive OSR (non conductive adhesive) (2) non conductive OSR (conductive adhesive); and conductive OSR (conductive adhesive).

  19. Sundew adhesive: a naturally occurring hydrogel

    PubMed Central

    Huang, Yujian; Wang, Yongzhong; Sun, Leming; Agrawal, Richa; Zhang, Mingjun

    2015-01-01

    Bioadhesives have drawn increasing interest in recent years, owing to their eco-friendly, biocompatible and biodegradable nature. As a typical bioadhesive, sticky exudate observed on the stalked glands of sundew plants aids in the capture of insects and this viscoelastic adhesive has triggered extensive interests in revealing the implied adhesion mechanisms. Despite the significant progress that has been made, the structural traits of the sundew adhesive, especially the morphological characteristics in nanoscale, which may give rise to the viscous and elastic properties of this mucilage, remain unclear. Here, we show that the sundew adhesive is a naturally occurring hydrogel, consisting of nano-network architectures assembled with polysaccharides. The assembly process of the polysaccharides in this hydrogel is proposed to be driven by electrostatic interactions mediated with divalent cations. Negatively charged nanoparticles, with an average diameter of 231.9 ± 14.8 nm, are also obtained from this hydrogel and these nanoparticles are presumed to exert vital roles in the assembly of the nano-networks. Further characterization via atomic force microscopy indicates that the stretching deformation of the sundew adhesive is associated with the flexibility of its fibrous architectures. It is also observed that the adhesion strength of the sundew adhesive is susceptible to low temperatures. Both elasticity and adhesion strength of the sundew adhesive reduce in response to lowering the ambient temperature. The feasibility of applying sundew adhesive for tissue engineering is subsequently explored in this study. Results show that the fibrous scaffolds obtained from sundew adhesive are capable of increasing the adhesion of multiple types of cells, including fibroblast cells and smooth muscle cells, a property that results from the enhanced adsorption of serum proteins. In addition, in light of the weak cytotoxic activity exhibited by these scaffolds towards a variety of

  20. Sundew adhesive: a naturally occurring hydrogel.

    PubMed

    Huang, Yujian; Wang, Yongzhong; Sun, Leming; Agrawal, Richa; Zhang, Mingjun

    2015-06-01

    Bioadhesives have drawn increasing interest in recent years, owing to their eco-friendly, biocompatible and biodegradable nature. As a typical bioadhesive, sticky exudate observed on the stalked glands of sundew plants aids in the capture of insects and this viscoelastic adhesive has triggered extensive interests in revealing the implied adhesion mechanisms. Despite the significant progress that has been made, the structural traits of the sundew adhesive, especially the morphological characteristics in nanoscale, which may give rise to the viscous and elastic properties of this mucilage, remain unclear. Here, we show that the sundew adhesive is a naturally occurring hydrogel, consisting of nano-network architectures assembled with polysaccharides. The assembly process of the polysaccharides in this hydrogel is proposed to be driven by electrostatic interactions mediated with divalent cations. Negatively charged nanoparticles, with an average diameter of 231.9 ± 14.8 nm, are also obtained from this hydrogel and these nanoparticles are presumed to exert vital roles in the assembly of the nano-networks. Further characterization via atomic force microscopy indicates that the stretching deformation of the sundew adhesive is associated with the flexibility of its fibrous architectures. It is also observed that the adhesion strength of the sundew adhesive is susceptible to low temperatures. Both elasticity and adhesion strength of the sundew adhesive reduce in response to lowering the ambient temperature. The feasibility of applying sundew adhesive for tissue engineering is subsequently explored in this study. Results show that the fibrous scaffolds obtained from sundew adhesive are capable of increasing the adhesion of multiple types of cells, including fibroblast cells and smooth muscle cells, a property that results from the enhanced adsorption of serum proteins. In addition, in light of the weak cytotoxic activity exhibited by these scaffolds towards a variety of

  1. Polyimide adhesives

    NASA Technical Reports Server (NTRS)

    Progar, D. J.; Bell, V. L.; Saintclair, T. L. (Inventor)

    1974-01-01

    A process of preparing aromatic polyamide-acids for use as adhesives is described. An equimolar quantity of an aromatic dianhydride is added to a stirred solution of an aromatic diamine in a water or alcohol-miscible ether solvent to obtain a viscous polymer solution. The polymeric-acid intermediate polymer does not become insoluble but directly forms a smooth viscous polymer solution. These polyamic-acid polymers are converted, by heating in the range of 200-300 C and with pressure, to form polyimides with excellent adhesive properties.

  2. Electrostatics of a Family of Conducting Toroids

    ERIC Educational Resources Information Center

    Lekner, John

    2009-01-01

    An exact solution is found for the electrostatic potential of a family of conducting charged toroids. The toroids are characterized by two lengths "a" and "b", with "a" greater than or equal to "2b". They are closed, with no hole in the "doughnut". The results are obtained by considering the potential of two equal charges, displaced from the…

  3. Oxygen vacancy formation in CeO2 and Ce(1-x)Zr(x)O2 solid solutions: electron localization, electrostatic potential and structural relaxation.

    PubMed

    Wang, Hai-Feng; Li, Hui-Ying; Gong, Xue-Qing; Guo, Yang-Long; Lu, Guan-Zhong; Hu, P

    2012-12-28

    Ceria (CeO(2)) and ceria-based composite materials, especially Ce(1-x)Zr(x)O(2) solid solutions, possess a wide range of applications in many important catalytic processes, such as three-way catalysts, owing to their excellent oxygen storage capacity (OSC) through the oxygen vacancy formation and refilling. Much of this activity has focused on the understanding of the electronic and structural properties of defective CeO(2) with and without doping, and comprehending the determining factor for oxygen vacancy formation and the rule to tune the formation energy by doping has constituted a central issue in material chemistry related to ceria. However, the calculation on electronic structures and the corresponding relaxation patterns in defective CeO(2-x) oxides remains at present a challenge in the DFT framework. A pragmatic approach based on density functional theory with the inclusion of on-site Coulomb correction, i.e. the so-called DFT + U technique, has been extensively applied in the majority of recent theoretical investigations. Firstly, we review briefly the latest electronic structure calculations of defective CeO(2)(111), focusing on the phenomenon of multiple configurations of the localized 4f electrons, as well as the discussions of its formation mechanism and the catalytic role in activating the O(2) molecule. Secondly, aiming at shedding light on the doping effect on tuning the oxygen vacancy formation in ceria-based solid solutions, we summarize the recent theoretical results of Ce(1-x)Zr(x)O(2) solid solutions in terms of the effect of dopant concentrations and crystal phases. A general model on O vacancy formation is also discussed; it consists of electrostatic and structural relaxation terms, and the vital role of the later is emphasized. Particularly, we discuss the crucial role of the localized structural relaxation patterns in determining the superb oxygen storage capacity in kappa-phase Ce(1-x)Zr(1-x)O(2). Thirdly, we briefly discuss some

  4. On the electrostatic properties of homodimeric proteins

    PubMed Central

    Campbell, Brandon; Petukh, Marharyta; Alexov, Emil

    2014-01-01

    A large fraction of proteins function as homodimers, but it is not always clear why the dimerization is important for functionality since frequently each monomer possesses a distinctive active site. Recent work (PLoS Computational Biology, 9(2), e1002924) indicates that homodimerization may be important for forming an electrostatic funnel in the spermine synthase homodimer which guides changed substrates toward the active centers. This prompted us to investigate the electrostatic properties of a large set of homodimeric proteins and resulted in an observation that in a vast majority of the cases the dimerization indeed results in specific electrostatic features, although not necessarily in an electrostatic funnel. It is demonstrated that the electrostatic dipole moment of the dimer is predominantly perpendicular to the axis connecting the centers of the mass of the monomers. In addition, the surface points with highest potential are located in the proximity of the interfacial plane of the homodimeric complexes. These findings indicate that frequently homodimerization provides specific electrostatic features needed for the function of proteins. PMID:25419028

  5. Yukawa multipole electrostatics and nontrivial coupling between electrostatic and dispersion interactions in electrolytes

    NASA Astrophysics Data System (ADS)

    Kjellander, Roland; Ramirez, Rosa

    2008-12-01

    An exact treatment of screened electrostatics in electrolyte solutions is presented. In electrolytes the anisotropy of the exponentially decaying electrostatic potential from a molecule extends to the far field region. The full directional dependence of the electrostatic potential from a charged or uncharged molecule remains in the longest range tail (i.e. from all multipole moments). In particular, the range of the potential from an ion and that from an electroneutral polar particle is generally exactly the same. This is in contrast to the case in vacuum or pure polar liquids, where the potential from a single charge is longer ranged than that from a dipole, which is, itself, longer ranged than the one from a quadrupole etc. The orientational dependence of the exponentially screened electrostatic interaction between two molecules in electrolytes is therefore rather complex even at long distances. These facts are formalized in Yukawa multipole expansions of the electrostatic potential and the pair interaction free energy based on the Yukawa function family exp(-κr)/rm, where r is the distance, κ is a decay parameter and m is a positive integer. The expansion is formally exact for electrolytes with molecular solvent and in the primitive model, provided the non-Coulombic interactions between the particles are sufficiently short ranged. The results can also be applied in the Poisson-Boltzmann approximation. Differences and similarities to the ordinary multipole expansion of electrostatics are pointed out. On the other hand, when the non-Coulombic interactions between the constituent particles of the electrolyte solution contain a dispersion 1/r6 potential, the electrostatic potential from a molecule decays like a power law for long distances rather than as a Yukawa function. This is due to nontrivial coupling between the electrostatic and dispersion interactions. There remains an exponentially decaying component in the electrostatic potential, but it becomes

  6. Lone pairs: an electrostatic viewpoint.

    PubMed

    Kumar, Anmol; Gadre, Shridhar R; Mohan, Neetha; Suresh, Cherumuttathu H

    2014-01-16

    A clear-cut definition of lone pairs has been offered in terms of characteristics of minima in molecular electrostatic potential (MESP). The largest eigenvalue and corresponding eigenvector of the Hessian at the minima are shown to distinguish lone pair regions from the other types of electron localization (such as π bonds). A comparative study of lone pairs as depicted by various other scalar fields such as the Laplacian of electron density and electron localization function is made. Further, an attempt has been made to generalize the definition of lone pairs to the case of cations. PMID:24372481

  7. Screened Electrostatic Interactions in Molecular Mechanics.

    PubMed

    Wang, Bo; Truhlar, Donald G

    2014-10-14

    In a typical application of molecular mechanics (MM), the electrostatic interactions are calculated from parametrized partial atomic charges treated as point charges interacting by radial Coulomb potentials. This does not usually yield accurate electrostatic interactions at van der Waals distances, but this is compensated by additional parametrized terms, for example Lennard-Jones potentials. In the present work, we present a scheme involving radial screened Coulomb potentials that reproduces the accurate electrostatics much more accurately. The screening accounts for charge penetration of one subsystem's charge cloud into that of another subsystem, and it is incorporated into the interaction potential in a way similar to what we proposed in a previous article (J. Chem. Theory Comput. 2010, 6, 3330) for combined quantum mechanical and molecular mechanical (QM/MM) simulations, but the screening parameters are reoptimized for MM. The optimization is carried out with electrostatic-potential-fitted partial atomic charges, but the optimized parameters should be useful with any realistic charge model. In the model we employ, the charge density of an atom is approximated as the sum of a point charge representing the nucleus and inner electrons and a smeared charge representing the outermost electrons; in particular, for all atoms except hydrogens, the smeared charge represents the two outermost electrons in the present model. We find that the charge penetration effect can cause very significant deviations from the popular point-charge model, and by comparison to electrostatic interactions calculated by symmetry-adapted perturbation theory, we find that the present results are considerably more accurate than point-charge electrostatic interactions. The mean unsigned error in electrostatics for a large and diverse data set (192 interaction energies) decreases from 9.2 to 3.3 kcal/mol, and the error in the electrostatics for 10 water dimers decreases from 1.7 to 0.5 kcal

  8. Electrostatic graphene loudspeaker

    NASA Astrophysics Data System (ADS)

    Zhou, Qin; Zettl, A.

    2013-06-01

    Graphene has extremely low mass density and high mechanical strength, and key qualities for efficient wide-frequency-response electrostatic audio speaker design. Low mass ensures good high frequency response, while high strength allows for relatively large free-standing diaphragms necessary for effective low frequency response. Here, we report on construction and testing of a miniaturized graphene-based electrostatic audio transducer. The speaker/earphone is straightforward in design and operation and has excellent frequency response across the entire audio frequency range (20 Hz-20 kHz), with performance matching or surpassing commercially available audio earphones.

  9. Flexibilized copolyimide adhesives

    NASA Technical Reports Server (NTRS)

    Progar, Donald J.; St.clair, Terry L.

    1988-01-01

    Two copolyimides, LARC-STPI and STPI-LARC-2, with flexible backbones were processed and characterized as adhesives. The processability and adhesive properties were compared to those of a commercially available form of LARC-TPI. Lap shear specimens were fabricated using adhesive tape prepared from each of the three polymers. Lap shear tests were performed at room temperature, 177 C, and 204 C before and after exposure to water-boil and to thermal aging at 204 C for up to 1000 hours. The three adhesive systems possess exceptional lap shear strengths at room temperature and elevated temperatures both before and after thermal exposure. LARC-STPI, because of its high glass transition temperature provided high lap shear strengths up to 260 C. After water-boil, LARC-TPI exhibited the highest lap shear strengths at room temperature and 177 C, whereas the LARC-STPI retained a higher percentage of its original strength when tested at 204 C. These flexible thermoplastic copolyimides show considerable potential as adhesives based on this study and because of the ease of preparation with low cost, commercially available materials.

  10. Theoretical insight into the binding energy and detonation performance of ε-, γ-, β-CL-20 cocrystals with β-HMX, FOX-7, and DMF in different molar ratios, as well as electrostatic potential.

    PubMed

    Feng, Rui-Zhi; Zhang, Shu-Hai; Ren, Fu-de; Gou, Rui-Jun; Gao, Li

    2016-06-01

    Molecular dynamics method was employed to study the binding energies on the selected crystal planes of the ε-, γ-, β-conformation 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (ε-, γ-, β-CL-20) cocrystal explosives with 1,1-diamino-2,2-dinitroethylene (FOX-7), 1,3,5,7-tetranitro- 1,3,5,7-tetrazacyclooctane with β-conformation (β-HMX) and N,N-dimethylformamide (DMF) in different molar ratios. The oxygen balance, density, detonation velocity, detonation pressure, and surface electrostatic potential were analyzed. The results indicate that the binding energies E b (*) and stabilities are in the order of 1:1 > 2:1 > 3:1 > 5:1 > 8:1 (CL-20:FOX-7/β-HMX/DMF). The values of E b (*) and stabilities of the energetic-nonenergetic CL-20/DMF cocrystals are far larger than those of the energetic-energetic CL-20/FOX-7 and CL-20/β-HMX, and those of CL-20/β-HMX are the smallest. For CL-20/FOX-7 and CL-20/β-HMX, the largest E b (*) appears in the cocrystals with the 1:1, 1:2 or 1:3 molar ratio, and the stabilities of the cocrystals with the excess ratio of CL-20 are weaker than those in the cocrystals with the excess ratio of FOX-7 or β-HMX. In CL-20/FOX-7, CL-20 prefers adopting the γ-form, and ε-CL-20 is the preference in CL-20/β-HMX, and ε-CL-20 and β-CL-20 can be found in CL-20/DMF. The CL-20/FOX-7 and CL-20/β-HMX cocrystals with low molar ratios can meet the requirements of low sensitive high energetic materials. Surface electrostatic potential reveals the nature of the sensitivity change upon the cocrystal formation. Graphical Abstract MD method was employed to study the binding energies on the selected crystal planes in the ε-, γ-, β-CL-20 cocrystals with FOX-7, β-HMX and DMF in different molar ratios. Surface electrostatic potential reveals the nature of the sensitivity change in cocrystals. PMID:27168198

  11. Electrostatically Enhanced Vortex Separator

    NASA Technical Reports Server (NTRS)

    Collins, Earl R.

    1993-01-01

    Proposed device removes fine particles from high-pressure exhaust gas of chemical reactor. Negatively charged sectors on rotating disks in vortex generator attracts positively charged particles from main stream of exhaust gas. Electrostatic charge enhances particle-separating action of vortex. Gas without particles released to atmosphere.

  12. An asymmetry in electrostatics

    NASA Astrophysics Data System (ADS)

    Ganci, Salvatore

    2013-11-01

    This paper outlines a misuse of the electrostatic induction concept. A non-symmetrical behaviour was observed in a charge by the induction of an insulated hollow metallic conductor (the Faraday ice pail experiment). The major consequence of this experiment is a quick demonstration that the Earth must have a net negative charge.

  13. Magnetosheath electrostatic turbulence

    NASA Technical Reports Server (NTRS)

    Rodriquez, P.

    1977-01-01

    The spectrum of electrostatic plasma waves in the terrestrial magnetosheath was studied using the plasma wave experiment on the IMP-6 satellite. Electrostatic plasma wave turbulence is almost continuously present throughout the magnetosheath with broadband (20 Hz- 70 kHz) r.m.s. field intensities typically 0.01 - 1.0 millivolts/m. Peak intensities of about 1.0 millivolts/m near the electron plasma frequency (30 - 60 kHz) were detected occasionally. The components usually identified in the spectrum of magnetosheath electrostatic turbulence include a high frequency ( or = 30 kHz) component peaking at the electron plasma frequency f sub pe, a low frequency component with a broad intensity maximum below the nominal ion plasma frequency f sub pi (approximately f sub pe/43), and a less well defined intermediate component in the range f sub pi f f sub pe. The intensity distribution of magnetosheath electrostatic turbulence clearly shows that the low frequency component is associated with the bow shock, suggesting that the ion heating begun at the shock continues into the downstream magnetosheath.

  14. Studying Electrostatic Levitator Specimen

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Prof. Kerneth Kelton of Washington University in St. Lous, MO, (L) and Dr. Michael Robinson of NASA's Marshall Space Flight Center (MSFC) examine a titanium-iron silicate (TiFeSiO)sample processed in MSFC's Electrostatic Levitator (ESL) Facility (background). Kelton is investigating undercooling of polytetrahedral phase-forming liquids.

  15. Electrostatic heat flux instabilities

    NASA Technical Reports Server (NTRS)

    Morrison, P. J.; Ionson, J. A.

    1980-01-01

    The electrostatic cyclotron and ion acoustic instabilities in a plasma driven by a combined heat flux and current were investigated. The minimum critical heat conduction speed (above which the plasma is unstable) is given as a function of the ratio of electron to ion temperatures.

  16. Nanoscale Electrostatics in Mitosis

    NASA Astrophysics Data System (ADS)

    Gagliardi, L. John; West, Patrick Michael

    2001-04-01

    Primitive biological cells had to divide with very little biology. This work simulates a physicochemical mechanism, based upon nanoscale electrostatics, which explains the anaphase A poleward motion of chromosomes. In the cytoplasmic medium that exists in biological cells, electrostatic fields are subject to strong attenuation by Debye screening, and therefore decrease rapidly over a distance equal to several Debye lengths. However, the existence of microtubules within cells changes the situation completely. Microtubule dimer subunits are electric dipolar structures, and can act as intermediaries that extend the reach of the electrostatic interaction over cellular distances. Experimental studies have shown that intracellular pH rises to a peak at mitosis, and decreases through cytokinesis. This result, in conjunction with the electric dipole nature of microtubule subunits and the Debye screened electrostatic force is sufficient to explain and unify the basic events during mitosis and cytokinesis: (1) assembly of asters, (2) motion of the asters to poles, (3) poleward motion of chromosomes (anaphase A), (4) cell elongation, and (5) cytokinesis. This paper will focus on a simulation of the dynamics if anaphase A motion based on this comprehensive model. The physicochemical mechanisms utilized by primitive cells could provide important clues regarding our understanding of cell division in modern eukaryotic cells.

  17. Electrostatics of Rigid Polyelectrolytes

    SciTech Connect

    Wong, G.C.L.

    2009-06-04

    The organization of rigid biological polyelectrolytes by multivalent ions and macroions are important for many fundamental problems in biology and biomedicine, such as cytoskeletal regulation and antimicrobial sequestration in cystic fibrosis. These polyelectrolytes have been used as model systems for understanding electrostatics in complex fluids. Here, we review some recent results in theory, simulations, and experiments.

  18. Alterations in cell adhesion proteins and cardiomyopathy

    PubMed Central

    Li, Jifen

    2014-01-01

    Cell adhesive junction is specialized intercellular structure composed of cell adhesion proteins. They are essential to connect adjacent heart muscle cell and make heart contraction effectively and properly. Clinical and genetic studies have revealed close relationship between cell adhesive proteins and the occurrence of various cardiomyopathies. Here we will review recent development on the disease phenotype, potential cellular and molecular mechanism related to cell adhesion molecules, with particular disease pathogenesis learned from genetic manipulated murine models. PMID:24944760

  19. Modeling and simulation of electrostatically gated nanochannels.

    PubMed

    Pardon, G; van der Wijngaart, W

    2013-11-01

    Today, despite the growing interest in nanofluidics, the descriptions of the many complex physical phenomena occurring at this scale remain scattered in the literature. Due to the additional complexity encountered when considering electrostatic nanofluidic gating, it is important to regroup several relevant theories and discuss them with regard to this application. In this work, we present a theoretical study of electrostatically gated phenomena and propose a model for the electrostatic gating of ion and molecular transport in nanochannels. In addition to the classical electrokinetic equations, that are reviewed in this work, several relevant phenomena are considered and combined to describe gating effects on nanofluidic properties more accurately. Dynamic surface charging is accounted for and is shown to be an essential element for electrostatic gating. The autoprotolysis of water is also considered to allow for accurate computing of the surface charge. Modifications of the Nernst-Planck equations are considered for more accurate computing of the concentration profiles at higher surface potentials by accounting for ion crowding near charge walls. The sensitivity of several parameters to the electric field and ion crowding is also studied. Each of these models is described separately before their implementation in a finite element model. The model is verified against previous experimental work. Finally, the model is used to simulate the tuning of the ionic current through the nanochannel via electrostatic gating. The influence of the additional models on these results is discussed. Guidelines for potentially better gating efficiencies are finally proposed. PMID:23915526

  20. Molecular Adhesion between Cartilage Extracellular Matrix Macromolecules

    PubMed Central

    2015-01-01

    In this study, we investigated the molecular adhesion between the major constituents of cartilage extracellular matrix, namely, the highly negatively charged proteoglycan aggrecan and the type II/IX/XI fibrillar collagen network, in simulated physiological conditions. Colloidal force spectroscopy was applied to measure the maximum adhesion force and total adhesion energy between aggrecan end-attached spherical tips (end radius R ≈ 2.5 μm) and trypsin-treated cartilage disks with undamaged collagen networks. Studies were carried out in various aqueous solutions to reveal the physical factors that govern aggrecan–collagen adhesion. Increasing both ionic strength and [Ca2+] significantly increased adhesion, highlighting the importance of electrostatic repulsion and Ca2+-mediated ion bridging effects. In addition, we probed how partial enzymatic degradation of the collagen network, which simulates osteoarthritic conditions, affects the aggrecan–collagen interactions. Interestingly, we found a significant increase in aggrecan–collagen adhesion even when there were no detectable changes at the macro- or microscales. It is hypothesized that the aggrecan–collagen adhesion, together with aggrecan–aggrecan self-adhesion, works synergistically to determine the local molecular deformability and energy dissipation of the cartilage matrix, in turn, affecting its macroscopic tissue properties. PMID:24491174

  1. High-performance mussel-inspired adhesives of reduced complexity

    PubMed Central

    Ahn, B. Kollbe; Das, Saurabh; Linstadt, Roscoe; Kaufman, Yair; Martinez-Rodriguez, Nadine R.; Mirshafian, Razieh; Kesselman, Ellina; Talmon, Yeshayahu; Lipshutz, Bruce H.; Israelachvili, Jacob N.; Waite, J. Herbert

    2015-01-01

    Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remains limited or non-existent for diverse applications. Translation of mussel-inspired wet adhesion typically entails catechol functionalization of polymers and/or polyelectrolytes, and solution processing of many complex components and steps that require optimization and stabilization. Here we reduced the complexity of a wet adhesive primer to synthetic low-molecular-weight catecholic zwitterionic surfactants that show very strong adhesion (∼50 mJ m−2) and retain the ability to coacervate. This catecholic zwitterion adheres to diverse surfaces and self-assembles into a molecularly smooth, thin (<4 nm) and strong glue layer. The catecholic zwitterion holds particular promise as an adhesive for nanofabrication. This study significantly simplifies bio-inspired themes for wet adhesion by combining catechol with hydrophobic and electrostatic functional groups in a small molecule. PMID:26478273

  2. High-performance mussel-inspired adhesives of reduced complexity

    NASA Astrophysics Data System (ADS)

    Ahn, B. Kollbe; Das, Saurabh; Linstadt, Roscoe; Kaufman, Yair; Martinez-Rodriguez, Nadine R.; Mirshafian, Razieh; Kesselman, Ellina; Talmon, Yeshayahu; Lipshutz, Bruce H.; Israelachvili, Jacob N.; Waite, J. Herbert

    2015-10-01

    Despite the recent progress in and demand for wet adhesives, practical underwater adhesion remains limited or non-existent for diverse applications. Translation of mussel-inspired wet adhesion typically entails catechol functionalization of polymers and/or polyelectrolytes, and solution processing of many complex components and steps that require optimization and stabilization. Here we reduced the complexity of a wet adhesive primer to synthetic low-molecular-weight catecholic zwitterionic surfactants that show very strong adhesion (~50 mJ m-2) and retain the ability to coacervate. This catecholic zwitterion adheres to diverse surfaces and self-assembles into a molecularly smooth, thin (<4 nm) and strong glue layer. The catecholic zwitterion holds particular promise as an adhesive for nanofabrication. This study significantly simplifies bio-inspired themes for wet adhesion by combining catechol with hydrophobic and electrostatic functional groups in a small molecule.

  3. Electrostatic chuck consisting of polymeric electrostatic inductive fibers for handling of objects with rough surfaces

    NASA Astrophysics Data System (ADS)

    Dhelika, Radon; Sawai, Kenji; Takahashi, Kunio; Takarada, Wataru; Kikutani, Takeshi; Saito, Shigeki

    2013-09-01

    An electrostatic chuck (ESC) is a type of reversible dry adhesive which clamps objects by means of electrostatic force. Currently an ESC is used only for objects having flat surfaces because the attractive force is reduced for rough surfaces. An ESC that can handle objects with rough surfaces will expand its applications to MEMS (micro electro mechanical system) or optical parts handling. An ESC consisting of compliant electrostatic inductive fibers which conform to the profile of the surface has been proposed for such use. This paper aims at furthering previous research by observing the attractive force/pressure generated, both theoretically and experimentally, through step-by-step fabrication and analysis. Additionally, how the proposed fiber ESC behaves toward rough surfaces is also observed. The attractive force/pressure of the fiber ESC is theoretically investigated using a robust mechano-electrostatic model. Subsequently, a prototype of the fiber ESC consisting of ten fibers arranged at an angle is employed to experimentally observe its attractive force/pressure for objects with rough surfaces. The attractive force of the surface which is modeled as a sinusoidal wave with various amplitudes is observed, through which the feasibility of a fiber ESC is justified.

  4. Electrostatics of Deformable Lipid Membranes

    PubMed Central

    Vorobyov, Igor; Bekker, Borislava; Allen, Toby W.

    2010-01-01

    Abstract It was recently demonstrated that significant local deformations of biological membranes take place due to the fields of charged peptides and ions, challenging the standard model of membrane electrostatics. The ability of ions to retain their immediate hydration environment, combined with the lack of sensitivity of permeability to ion type or even ion pairs, led us to question the extent to which hydration energetics and electrostatics control membrane ion permeation. Using the arginine analog methyl-guanidinium as a test case, we find that although hydrocarbon electronic polarizability causes dramatic changes in ion solvation free energy, as well as a significant change (∼0.4 V) in the membrane dipole potential, little change in membrane permeation energetics occurs. We attribute this to compensation of solvation terms from polar and polarizable nonpolar components within the membrane, and explain why the dipole potential is not fully sensed in terms of the locally deformed bilayer interface. Our descriptions provide a deeper understanding of the translocation process and allow predictions for poly-ions, ion pairs, charged lipids, and lipid flip-flop. We also report simulations of large hydrophobic-ion-like membrane defects and the ionophore valinomycin, which exhibit little membrane deformation, as well as hydrophilic defects and the ion channel gramicidin A, to provide parallels to membranes deformed by unassisted ion permeation. PMID:20550903

  5. Electrostatic particle trap for ion beam sputter deposition

    DOEpatents

    Vernon, Stephen P.; Burkhart, Scott C.

    2002-01-01

    A method and apparatus for the interception and trapping of or reflection of charged particulate matter generated in ion beam sputter deposition. The apparatus involves an electrostatic particle trap which generates electrostatic fields in the vicinity of the substrate on which target material is being deposited. The electrostatic particle trap consists of an array of electrode surfaces, each maintained at an electrostatic potential, and with their surfaces parallel or perpendicular to the surface of the substrate. The method involves interception and trapping of or reflection of charged particles achieved by generating electrostatic fields in the vicinity of the substrate, and configuring the fields to force the charged particulate material away from the substrate. The electrostatic charged particle trap enables prevention of charged particles from being deposited on the substrate thereby enabling the deposition of extremely low defect density films, such as required for reflective masks of an extreme ultraviolet lithography (EUVL) system.

  6. Electrostatics in sandstorms and earthquakes

    NASA Astrophysics Data System (ADS)

    Shinbrot, Troy; Thyagu, Nirmal; Paehtz, Thomas; Herrmann, Hans

    2010-11-01

    We present new data demonstrating (1) that electrostatic charging in sandstorms is a necessary outcome in a class of rapid collisional flows, and (2) that electrostatic precursors to slip events - long reported in earthquakes - can be reproduced in the laboratory.

  7. A theoretical investigation into the cooperativity effect between the H∙∙∙O and H∙∙∙F⁻ interactions and electrostatic potential upon 1:2 (F⁻:N-(Hydroxymethyl)acetamide) ternary-system formation.

    PubMed

    Tian, Qing-Ping; Wang, Yan-Hong; Shi, Wen-Jing; Song, Shu-Qin; Tang, Hai-Fei

    2013-12-01

    The cooperativity effects between the O/N-H∙∙∙F(-) anionic hydrogen-bonding and O/N-H∙∙∙O hydrogen-bonding interactions and electrostatic potentials in the 1:2 (F(-):N-(Hydroxymethyl)acetamide (signed as "ha")) ternary systems are investigated at the B3LYP/6-311++G** and MP2/6-311++G** levels. A comparison of the cooperativity effect in the "F(-)∙∙∙ha∙∙∙ha" and "FH∙∙∙ha(-)∙∙∙ha" systems is also carried out. The result shows that the increase of the H∙∙∙O interaction energy in the O-H∙∙∙O-H, N-H∙∙∙O-H or N-H∙∙∙O = C link is more notable than that in the O-H∙∙∙O = C contact upon ternary-system formation. The cooperativity effect is found in the complex formed by the O/N-H∙∙∙F(-) and O/N-H∙∙∙O interactions, while the anti-cooperativity effect is present in the system with only the O/N-H∙∙∙F(-) H-bond or the "FH∙∙∙ha(-)∙∙∙ha" complex by the N(-)∙∙∙H-F contact. Atoms in molecules (AIM) analysis and shift of electron density confirm the existence of cooperativity. The most negative surface electrostatic potential (V(S,min)) correlates well with the interaction energy E' int.(ha∙∙∙F-) and synergetic energy E(syn.), respectively. The relationship between the change of V(S,min) (i.e., ΔV(S,min)) and E(syn.) is also found. PMID:24114326

  8. Hydrophobic and Electrostatic Cell Surface Properties of Thermophilic Dairy Streptococci

    PubMed Central

    van der Mei, H. C.; de Vries, J.; Busscher, H. J.

    1993-01-01

    Microbial adhesion to hydrocarbons (MATH) and microelectrophoresis were done in 10 mM potassium phosphate solutions to characterize the surfaces of thermophilic dairy streptococci, isolated from pasteurizers. Regardless of whether they were grown (in M17 broth) with lactose, sucrose, or glucose added, strains were relatively hydrophilic (showing low initial removal rates by hexadecane) and slightly negatively charged. A tendency exists for cells grown with sucrose added to be more hydrophilic than cells grown with glucose or lactose added. Also, the lowest isoelectric points, i.e., the pH values for which the zeta potentials are zero, were measured for strains with glucose added to the growth medium. The isoelectric points for the strains were all rather high, between pH 3 and 5, indicative of protein-rich surfaces, although X-ray photoelectron spectroscopy did not measure excessively large amounts of nitrogen on the cell surfaces. Both MATH and microelectrophoresis were done as a function of pH. Maxima in hydrophobicity were observed at certain pH values. Usually these pH values were in the range of the isoelectric points of the cells. Thus it appears that MATH measures an interplay of hydrophobicity and electrostatic interactions. MATH measures solely hydrophobicity only when electrostatic interactions are absent, i.e., close to the isoelectric points of the cells. Considering that these thermophilic streptococci are all rather hydrophilic, a possible pathway to prevent fouling in the pasteurization process might be to render the heat exchanger plates of the pasteurizer more hydrophobic. PMID:16349127

  9. Electrostatic supersolitons in three-species plasmas

    SciTech Connect

    Verheest, Frank; Hellberg, Manfred A.; Kourakis, Ioannis

    2013-01-15

    Superficially, electrostatic potential profiles of supersolitons look like those of traditional solitons. However, their electric field profiles are markedly different, having additional extrema on the wings of the standard bipolar structure. This new concept was recently pointed out in the literature for a plasma model with five species. Here, it is shown that electrostatic supersolitons are not an artefact of exotic, complicated plasma models, but can exist even in three-species plasmas and are likely to occur in space plasmas. Further, a methodology is given to delineate their existence domains in a systematic fashion by determining the specific limiting factors.

  10. Electrostatically clean solar array

    NASA Technical Reports Server (NTRS)

    Stern, Theodore Garry (Inventor); Krumweide, Duane Eric (Inventor)

    2004-01-01

    Provided are methods of manufacturing an electrostatically clean solar array panel and the products resulting from the practice of these methods. The preferred method uses an array of solar cells, each with a coverglass where the method includes machining apertures into a flat, electrically conductive sheet so that each aperture is aligned with and undersized with respect to its matched coverglass sheet and thereby fashion a front side shield with apertures (FSA). The undersized portion about each aperture of the bottom side of the FSA shield is bonded to the topside portions nearest the edges of each aperture's matched coverglass. Edge clips are attached to the front side aperture shield edges with the edge clips electrically and mechanically connecting the tops of the coverglasses to the solar panel substrate. The FSA shield, edge clips and substrate edges are bonded so as to produce a conductively grounded electrostatically clean solar array panel.

  11. Automated Electrostatics Environmental Chamber

    NASA Technical Reports Server (NTRS)

    Calle, Carlos; Lewis, Dean C.; Buchanan, Randy K.; Buchanan, Aubri

    2005-01-01

    The Mars Electrostatics Chamber (MEC) is an environmental chamber designed primarily to create atmospheric conditions like those at the surface of Mars to support experiments on electrostatic effects in the Martian environment. The chamber is equipped with a vacuum system, a cryogenic cooling system, an atmospheric-gas replenishing and analysis system, and a computerized control system that can be programmed by the user and that provides both automation and options for manual control. The control system can be set to maintain steady Mars-like conditions or to impose temperature and pressure variations of a Mars diurnal cycle at any given season and latitude. In addition, the MEC can be used in other areas of research because it can create steady or varying atmospheric conditions anywhere within the wide temperature, pressure, and composition ranges between the extremes of Mars-like and Earth-like conditions.

  12. Electrostatic membrane deformable mirror characterization and applications

    NASA Astrophysics Data System (ADS)

    Bush, Keith; Marrs, Anthony; Schoen, Michael

    2005-08-01

    Electrostatic Membrane Deformable Mirror (MDM) technology developed using silicon bulk micro-machining techniques offers the potential of providing low-cost, compact wavefront control systems for diverse optical system applications. Electrostatic mirror construction using bulk micro-machining allows for custom designs to satisfy wavefront control requirements for most optical systems. An electrostatic MDM consists of a thin membrane, generally with a thin metal or multi-layer high-reflectivity coating, suspended over an actuator pad array that is connected to a high-voltage driver. Voltages applied to the array elements deflect the membrane to provide an optical surface capable of correcting for measured optical aberrations in a given system. Electrostatic membrane DM designs are derived from well-known principles of membrane mechanics and electrostatics, the desired optical wavefront control requirements, and the current limitations of mirror fabrication and actuator drive electronics. MDM performance is strongly dependent on mirror diameter and air damping in meeting desired spatial and temporal frequency requirements. In this paper, we discuss characterization measurements and modeling of MDM spatial and temporal performance for different mirror designs and present application results illustrating the diverse uses of MDM technology in optical wavefront compensation systems.

  13. Electrostatic effects on hyaluronic acid configuration

    NASA Astrophysics Data System (ADS)

    Berezney, John; Saleh, Omar

    2015-03-01

    In systems of polyelectrolytes, such as solutions of charged biopolymers, the electrostatic repulsion between charged monomers plays a dominant role in determining the molecular conformation. Altering the ionic strength of the solvent thus affects the structure of such a polymer. Capturing this electrostatically-driven structural dependence is important for understanding many biological systems. Here, we use single molecule manipulation experiments to collect force-extension behavior on hyaluronic acid (HA), a polyanion which is a major component of the extracellular matrix in all vertebrates. By measuring HA elasticity in a variety of salt conditions, we are able to directly assess the contribution of electrostatics to the chain's self-avoidance and local stiffness. Similar to recent results from our group on single-stranded nucleic acids, our data indicate that HA behaves as a swollen chain of electrostatic blobs, with blob size proportional to the solution Debye length. Our data indicate that the chain structure within the blob is not worm-like, likely due to long-range electrostatic interactions. We discuss potential models of this effect.

  14. Electrostatic curtain studies

    SciTech Connect

    Meyer, L C

    1992-05-01

    This report presents the results of experiments using electrostatic curtains (ESCS) as a transuranic (TRU) contamination control technique. The TRU contaminants included small (micrometer to sub micrometer) particles of plutonium and americium compounds associated with defense-related waste. Three series of experiments were conducted. The first was with uncontaminated Idaho National Engineering Laboratory (INEL) soil, the second used contaminated soil containing plutonium-239 (from a mixture of Rocky Flats Plant contaminated soil and INEL uncontaminated soil), and the third was uncontaminated INEL soil spiked with plutonium-239. All experiments with contaminated soil were conducted inside a glove box containing a dust generator, low volume cascade impactor (LVCI), electrostatic separator, and electrostatic materials. The data for these experiments consisted of the mass of dust collected on the various material coupons, plates, and filters; radiochemical analysis of selected samples; and photographs, as well as computer printouts giving particle size distributions and dimensions from the scanning electron microscope (SEM). The following results were found: (a) plutonium content (pCi/g) was found to increase with smaller soil particle sizes and (b) the electrostatic field had a stronger influence on smaller particle sizes compared to larger particle sizes. The SEM analysis indicated that the particle size of the tracer Pu239 used in the spiked soil experiments was below the detectable size limit (0.5 {mu}m) of the SEM and, thus, may not be representative of plutonium particles found in defense-related waste. The use of radiochemical analysis indicated that plutonium could be found on separator plates of both polarities, as well as passing through the electric field and collecting on LVCI filters.

  15. Spherical electrostatic electron spectrometer

    NASA Astrophysics Data System (ADS)

    Yang, T.-S.; Kolk, B.; Kachnowski, T.; Trooster, J.; Benczer-Koller, N.

    1982-06-01

    A high transmission, low energy spherical electrostatic electron spectrometer particularly suited to the geometry required for Mössbauer-conversion electron spectroscopy was built. A transmission of 13% at an energy resolution of 2% was obtained with an 0.5 cm diameter source of 13.6 keV electrons. Applications to the study of hyperfine interactions of surfaces and interfaces are discussed.

  16. Electrostatic Plasma Accelerator (EPA)

    NASA Technical Reports Server (NTRS)

    Brophy, John R.; Aston, Graeme

    1989-01-01

    The Electrostatic Plasma Accelerator (EPA) is a thruster concept which promises specific impulse levels between low power arcjets and those of the ion engine while retaining the relative simplicity of the arcjet. The EPA thruster produces thrust through the electrostatic acceleration of a moderately dense plasma. No accelerating electrodes are used and the specific impulse is a direct function of the applied discharge voltage and the propellant atomic mass. The goal of the present program is to demonstrate feasibility of the EPA thruster concept through experimental and theoretical investigations of the EPA acceleration mechanism and discharge chamber performance. Experimental investigations will include operating the test bed ion (TBI) engine as an EPA thruster and parametrically varying the thruster geometry and operating conditions to quantify the electrostatic plasma acceleration effect. The theoretical investigations will include the development of a discharge chamber model which describes the relationships between the engine size, plasma properties, and overall performance. For the EPA thruster to be a viable propulsion concept, overall thruster efficiencies approaching 30% with specific impulses approaching 1000 s must be achieved.

  17. Electrostatic modeling for LISA

    NASA Astrophysics Data System (ADS)

    Shaul, Diana N.; Sumner, Timothy J.

    2003-03-01

    LISA employs a capacitive sensing and positioning system to maintain the drag free environment of the test masses acting as interferometer mirror elements. The need for detailed electrostatic modelling of the test mass environment arises because any electric field gradient or variation associated with test mass motion can couple the test mass to its housing, and ultimately the spacecraft. Cross-couplings between components in the system can introduce direct couplings between sensing signals, sensing axes and the drive signal. A variation in cross-couplings or asymmetry in the system can introduce capacitance gradients and second derivatives, giving rise to unwanted forces and spring constant modifications. These effects will vary dependent on the precise geometry of the system and will also tend to increase the sensitivity to accumulated charge on the test-mass. Presented are the results of a systematic study of the effect of the principal geometry elements (e.g. machining imperfections, the caging mechanism) on the test mass electrostatic environment, using the finite element code ANSYS. This work is part of an ongoing ESA study into drag-free control for LISA and the LTP on SMART 2 and ultimately aims to eliminate geometries that introduce too large a disturbance and optimise the electrostatic design.

  18. Electrostatics of Granular Materials

    NASA Technical Reports Server (NTRS)

    Marshall, John

    2004-01-01

    The purpose of the research was to continue developing an understanding of electrostatic phenomena in preparation for any future flight opportunities of the EGM experiment, originally slated for a 2004 Space Station deployment. Work would be based on theoretical assessments, ground-based lab experiments, and reduced-gravity experiments. The ability to examine dipoles in the lab proved to be elusive, and thus, effort was concentrated on monopoles -how materials become charged, the fate of the charge, the role of material type, and so forth. Several significant milestones were achieved in this regard. In regard of the dipoles, experiments were designed in collaboration with the University of Chicago school district who had access to reduced gravity on the KC-135 aircraft. Two experiments were slated to fly last year but were cancelled after the Columbia accident. One of the experiments has been given a second life and will fly sometime in 2005 if the Shuttle flights resume. There remains active interest in the question of electrostatic dipoles within the educational community, and experiments using magnetic dipoles as a substitute are to be examined. The KC-135 experiments will also examine dispersion methods for particles as a verification of possible future techniques in microgravity. Both laboratory and theoretical work established a number of breakthroughs in our understanding of electrostatic phenomena. These breakthroughs are listed in this paper.

  19. Electrostatic and potential cation-pi forces may guide the interaction of extracellular loop III with Na+ and bile acids for human apical Na+-dependent bile acid transporter.

    PubMed

    Banerjee, Antara; Hussainzada, Naissan; Khandelwal, Akash; Swaan, Peter W

    2008-03-01

    The hASBT (human apical Na(+)-dependent bile acid transporter) constitutes a key target of anti-hypercholesterolaemic therapies and pro-drug approaches; physiologically, hASBT actively reclaims bile acids along the terminal ileum via Na(+) co-transport. Previously, TM (transmembrane segment) 7 was identified as part of the putative substrate permeation pathway using SCAM (substitute cysteine accessibility mutagenesis). In the present study, SCAM was extended through EL3 (extracellular loop 3; residues Arg(254)-Val(286)) that leads into TM7 from the exofacial matrix. Activity of most EL3 mutants was significantly hampered upon cysteine substitution, whereas ten (out of 31) were functionally inactive (<10% activity). Since only E282C lacked plasma membrane expression, EL3 amino acids predominantly fulfill critical functional roles during transport. Oppositely charged membrane-impermeant MTS (methanethiosulfonate) reagents {MTSET [(2-trimethylammonium) ethyl MTS] and MTSES [(2-sulfonatoethyl) MTS]} produced mostly similar inhibition profiles wherein only middle and descending loop segments (residues Thr(267)-Val(286)) displayed significant MTS sensitivity. The presence of bile acid substrate significantly reduced the rates of MTS modification for all MTS-sensitive mutants, suggesting a functional association between EL3 residues and bile acids. Activity assessments at equilibrative [Na(+)] revealed numerous Na(+)-sensitive residues, possibly performing auxiliary functions during transport such as transduction of protein conformational changes during translocation. Integration of these data suggests ligand interaction points along EL3 via electrostatic interactions with Arg(256), Glu(261) and probably Glu(282) and a potential cation-pi interaction with Phe(278). We conclude that EL3 amino acids are essential for hASBT activity, probably as primary substrate interaction points using long-range electrostatic attractive forces. PMID:18028035

  20. Adhesion effects in contact interaction of solids

    NASA Astrophysics Data System (ADS)

    Goryacheva, Irina; Makhovskaya, Yulya

    2008-01-01

    An approach to solving problems of the interaction of axisymmetric elastic bodies in the presence of adhesion is developed. The different natures of adhesion, i.e. capillary adhesion, or molecular adhesion described by the Lennard-Jones potential are examined. The effect of additional loading of the interacting bodies outside the contact zone is also investigated. The approach is based on the representation of the pressure outside the contact zone arising from adhesion by a step function. The analytical solution is obtained and is used to analyze the influence of the form of the adhesion interaction potential, of the surface energy of interacting bodies or the films covering the bodies, their shapes (parabolic, higher power exponential function), volume of liquid in the meniscus, density of contact spots, of elastic modulus and the Poisson ratio on the characteristics of the interaction of the bodies in the presence of adhesion. To cite this article: I. Goryacheva, Y. Makhovskaya, C. R. Mecanique 336 (2008).

  1. Antagonistic properties of a natural product - Bicuculline with the gamma-aminobutyric acid receptor: Studied through electrostatic potential mapping, electronic and vibrational spectra using ab initio and density functional theory

    NASA Astrophysics Data System (ADS)

    Srivastava, Anubha; Tandon, Poonam; Jain, Sudha; Asthana, B. P.

    2011-12-01

    (+)-Bicuculline (hereinafter referred to as bicuculline), a phthalide isoquinoline alkaloid is of current interest as an antagonist of gamma-aminobutyric acid (GABA). Its inhibitor properties have been studied through molecular electrostatic potential (MEP) mapping of this molecule and GABA receptor. The hot site on the potential surface of bicuculline, which is also isosteric with GABA receptor, has been used to interpret the inhibitor property. A systematic quantum chemical study of the possible conformations, their relative stabilities, FT-Raman, FT-IR and UV-vis spectroscopic analysis of bicuculline has been reported. The optimized geometries, wavenumber and intensity of the vibrational bands of all the conformers of bicuculline have been calculated using ab initio Hartree-Fock (HF) and density functional theory (DFT) employing B3LYP functional and 6-311G(d,p) basis set. Mulliken atomic charges, HOMO-LUMO gap Δ E, ionization potential, dipole moments and total energy have also been obtained for the optimized geometries of both the molecules. TD-DFT method is used to calculate the electronic absorption parameters in gas phase as well as in solvent environment using integral equation formalism-polarizable continuum model (IEF-PCM) employing 6-31G basis set and the results thus obtained are compared with the UV absorption spectra. The combination of experimental and calculated results provides an insight into the structural and vibrational spectroscopic properties of bicuculline.

  2. Valorization of solid wastes from chestnut industry processing: Extraction and optimization of polyphenols, tannins and ellagitannins and its potential for adhesives, cosmetic and pharmaceutical industry.

    PubMed

    Aires, Alfredo; Carvalho, Rosa; Saavedra, Maria José

    2016-02-01

    The aim of the current study was to evaluate the potential of chestnut peels to produce pomaces enhanced with tannins to be used in the formulations of wood adhesives, leather tanning or as natural antioxidants in food, cosmetic and pharmaceutical industry. An analytical procedure was planned as 2 factorial design to analyze the influence of solvent (water, Na2SO3 and NaOH at different concentrations of 1, 2, 4, and 8% in water) and extraction time (30, 60, and 120, 240, 480 and 960min) on extraction yield, pH, Stiasny index, and tannins. HPLC-diode array detector equipped with an ionization mass spectrophotometer was used to assess the polyphenol composition. Our results showed that both extraction properties and phytochemicals were significantly affected (P<0.001) by all independent factors. The main tannins identified were the hydrolyzable gallic acid, vescalagin castalagin and ellagic acid, and the condensed epigallocatechin, catechin and epicatechin. The solvent 1% Na2SO3 was more effective to extract the condensed tannins whilst hydrolyzable tannins were extracted efficiently by 1% NaOH. The multivariable analysis and the Pearson's correlation coefficients showed a direct association between Stiasny number and the average levels of condensed tannins. PMID:26626811

  3. Notch-Mediated Cell Adhesion.

    PubMed

    Murata, Akihiko; Hayashi, Shin-Ichi

    2016-01-01

    Notch family members are generally recognized as signaling molecules that control various cellular responses in metazoan organisms. Early fly studies and our mammalian studies demonstrated that Notch family members are also cell adhesion molecules; however, information on the physiological roles of this function and its origin is limited. In this review, we discuss the potential present and ancestral roles of Notch-mediated cell adhesion in order to explore its origin and the initial roles of Notch family members dating back to metazoan evolution. We hypothesize that Notch family members may have initially emerged as cell adhesion molecules in order to mediate multicellularity in the last common ancestor of metazoan organisms. PMID:26784245

  4. Notch-Mediated Cell Adhesion

    PubMed Central

    Murata, Akihiko; Hayashi, Shin-Ichi

    2016-01-01

    Notch family members are generally recognized as signaling molecules that control various cellular responses in metazoan organisms. Early fly studies and our mammalian studies demonstrated that Notch family members are also cell adhesion molecules; however, information on the physiological roles of this function and its origin is limited. In this review, we discuss the potential present and ancestral roles of Notch-mediated cell adhesion in order to explore its origin and the initial roles of Notch family members dating back to metazoan evolution. We hypothesize that Notch family members may have initially emerged as cell adhesion molecules in order to mediate multicellularity in the last common ancestor of metazoan organisms. PMID:26784245

  5. Adhesives for the composite wood panel industry

    SciTech Connect

    Koch, G.S.; Klareich, F.; Exstrum, B.

    1987-01-01

    This book presents a market and technology analysis of current fossil-fuel-based adhesives for the composite wood panel industry. It is also a study of the potential for, and technology of, less-energy-intensive biomass-derived adhesives for use in the industry. Adhesives manufacturer and production account for a significant portion of overall wood panel industry energy use as well as overall production costs, and the wood panel industry consumes about 25% of the total U.S. adhesives production. Significant savings might be realized if current fossil-fuel-based resins could be replaced with alternative biomass-derived adhesives.

  6. A review of high-temperature adhesives

    NASA Technical Reports Server (NTRS)

    St.clair, A. K.; St.clair, T. L.

    1981-01-01

    The development of high temperature adhesives and polyphenylquinoxalines (PPQ) is reported. Thermoplastic polyimides and linear PPQ adhesive are shown to have potential for bonding both metals and composite structures. A nadic terminated addition polyimide adhesive, LARC-13, and an acetylene terminated phenylquinoxaline (ATPQ) were developed. Both of the addition type adhesives are shown to be more readily processable than linear materials but less thermooxidatively stable and more brittle. It is found that the addition type adhesives are able to perform, at elevated temperatures up to 595 C where linear systems fail thermoplastically.

  7. Electrostatic disruption of lunar dust particles

    NASA Technical Reports Server (NTRS)

    Rhee, J. W.

    1976-01-01

    The possibility that dust particles might explode catastrophically on the lunar surface due to electrostatic charging is examined. For the dark side along the terminator zone, dust balls and compact stony particles of micron and submicron sizes will be blown up if their surface potential is as low as a kilovolt negative. This mechanism does not operate on the sunlit side because the surface potential is only 3.5-20 volts positive.

  8. Internal Electrostatic Discharge Monitor - IESDM

    NASA Technical Reports Server (NTRS)

    Kim, Wousik; Goebel, Dan M.; Jun, Insoo; Garrett, Henry B.

    2011-01-01

    A document discusses an innovation designed to effectively monitor dielectric charging in spacecraft components to measure the potential for discharge in order to prevent damage from internal electrostatic discharge (IESD). High-energy electrons penetrate the structural materials and shielding of a spacecraft and then stop inside dielectrics and keep accumulating. Those deposited charges generate an electric field. If the electric field becomes higher than the breakdown threshold (approx. =2 x 10(exp 5) V/cm), discharge occurs. This monitor measures potentials as a function of dielectric depth. Differentiation of potential with respect to the depth yields electric field. Direct measurement of the depth profile of the potential in a dielectric makes real-time electronic field evaluation possible without simulations. The IESDM has been designed to emulate a multi-layer circuit board, to insert very thin metallic layers between the dielectric layers. The conductors serve as diagnostic monitoring locations to measure the deposited electron-charge and the charge dynamics. Measurement of the time-dependent potential of the metal layers provides information on the amount of charge deposited in the dielectrics and the movement of that charge with time (dynamics).

  9. Spacecraft Electrostatic Radiation Shielding

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This project analyzed the feasibility of placing an electrostatic field around a spacecraft to provide a shield against radiation. The concept was originally proposed in the 1960s and tested on a spacecraft by the Soviet Union in the 1970s. Such tests and analyses showed that this concept is not only feasible but operational. The problem though is that most of this work was aimed at protection from 10- to 100-MeV radiation. We now appreciate that the real problem is 1- to 2-GeV radiation. So, the question is one of scaling, in both energy and size. Can electrostatic shielding be made to work at these high energy levels and can it protect an entire vehicle? After significant analysis and consideration, an electrostatic shield configuration was proposed. The selected architecture was a torus, charged to a high negative voltage, surrounding the vehicle, and a set of positively charged spheres. Van de Graaff generators were proposed as the mechanism to move charge from the vehicle to the torus to generate the fields necessary to protect the spacecraft. This design minimized complexity, residual charge, and structural forces and resolved several concerns raised during the internal critical review. But, it still is not clear if such a system is costeffective or feasible, even though several studies have indicated usefulness for radiation protection at energies lower than that of the galactic cosmic rays. Constructing such a system will require power supplies that can generate voltages 10 times that of the state of the art. Of more concern is the difficulty of maintaining the proper net charge on the entire structure and ensuring that its interaction with solar wind will not cause rapid discharge. Yet, if these concerns can be resolved, such a scheme may provide significant radiation shielding to future vehicles, without the excessive weight or complexity of other active shielding techniques.

  10. Study on plasma parameters and dust charging in an electrostatically plugged multicusp plasma device

    SciTech Connect

    Kakati, B.; Kausik, S. S.; Saikia, B. K.; Bandyopadhyay, M.

    2011-06-15

    The effect of the electrostatic confinement potential on the charging of dust grains and its relationship with the plasma parameters has been studied in an electrostatically plugged multicusp dusty plasma device. Electrostatic plugging is implemented by biasing the electrically isolated magnetic multicusp channel walls. The experimental results show that voltage applied to the channel walls can be a controlling parameter for dust charging.

  11. Neuregulin-1 Regulates Cell Adhesion via an ErbB2/Phosphoinositide-3 Kinase/Akt-Dependent Pathway: Potential Implications for Schizophrenia and Cancer

    PubMed Central

    Kanakry, Christopher G.; Li, Zhen; Nakai, Yoko; Sei, Yoshitatsu; Weinberger, Daniel R.

    2007-01-01

    Background Neuregulin-1 (NRG1) is a putative schizophrenia susceptibility gene involved extensively in central nervous system development as well as cancer invasion and metastasis. Using a B lymphoblast cell model, we previously demonstrated impairment in NRG1α-mediated migration in cells derived from patients with schizophrenia as well as effects of risk alleles in NRG1 and catechol-O-methyltransferase (COMT), a second gene implicated both in schizophrenia susceptibility and in cancer. Methodology/Principal Findings Here, we examine cell adhesion, an essential component process of cell motility, using an integrin-mediated cell adhesion assay based on an interaction between ICAM-1 and the CD11a/CD18 integrin heterodimer expressed on lymphoblasts. In our assay, NRG1α induces lymphoblasts to assume varying levels of adhesion characterized by time-dependent fluctuations in the firmness of attachment. The maximum range of variation in adhesion over sixty minutes correlates strongly with NRG1α-induced migration (r2 = 0.61). NRG1α-induced adhesion variation is blocked by erbB2, PI3K, and Akt inhibitors, but not by PLC, ROCK, MLCK, or MEK inhibitors, implicating the erbB2/PI3K/Akt1 signaling pathway in NRG1-stimulated, integrin-mediated cell adhesion. In cell lines from 20 patients with schizophrenia and 20 normal controls, cells from patients show a significant deficiency in the range of NRG1α-induced adhesion (p = 0.0002). In contrast, the response of patient-derived cells to phorbol myristate acetate is unimpaired. The COMT Val108/158Met genotype demonstrates a strong trend towards predicting the range of the NRG1α-induced adhesion response with risk homozygotes having decreased variation in cell adhesion even in normal subjects (p = 0.063). Conclusion/Significance Our findings suggest that a mechanism of the NRG1 genetic association with schizophrenia may involve the molecular biology of cell adhesion. PMID:18159252

  12. An electrostatic suspension method for determining photoionization energies of solids.

    NASA Technical Reports Server (NTRS)

    George, A.

    1973-01-01

    A sample is suspended on a quartz fibre in an electrostatic condenser and the onset of ionization with photon energy is determined through the potential required to restore zero deflection. Results for a few organic semiconductors are given.

  13. Applications of electrostatic accelerators

    SciTech Connect

    Norton, G.A.; Klody, G.M.

    1995-10-01

    Most applications of electrostatic accelerators fit into two main groups, materials analysis and materials modification. Materials analysis includes routine use of Rutherford Backscattering for quality control applications in the semiconductor field. Particle induced x-ray emission (PDCE) is used in fields from art history through environmental sciences. X-ray imaging using 5 MeV DC electron beams and fast pulsed neutron analysis (PFNA) for plastic explosive and drug detection provide promise in the area of security. Accelerator based mass spectrometry (AMS) is having a profound effect in a wide variety of fields which rely on counting extremely rare isotopes in small samples. Materials modification provides a very significant economic impact in the field of semiconductors. Virtually all semiconductor devices now rely on ion implantation with ion beam energies ranging from a few kilovolts to several MeV. With some mention of electron beams, this talk will concentrate primarily on the applications of MeV ion beams from electrostatic accelerators.

  14. Electrostatic Beneficiation of Coal

    SciTech Connect

    D. Lindquist; K. B. Tennal; M. K. Mazumder

    1998-10-29

    It was suggested in the proposal that small particles, due to low inertia, may not impact on the surfaces of the tribocharger. They would, thus, not receive charge and would not be beneficiated in the electrostatic separation. A milling process was proposed in which the small particles are stirred together with larger carrier beads producing the desired contact charge exchange. A force is necessary for removing the coal particles from the carrier beads. In copying machines electrostatic force is used to pull toner particles away horn iron carrier particles which are held back by magnetic force. Aerodynamic force is used in test instruments for measuring the charge to mass ratio on toners. A similar system of milling and removal is desired for use with the small coal particles. The carrier beads need to be made of copper rather than iron. This complicates the separation process since copper is non-magnetic. We are working on coating of iron beads with a layer of copper. Dr. Robert Engleken of Arkansas State University has supplied us with several test batches of copper-coated iron in the size range of -40 +70 mesh. ` We are currently testing whether the milling process used with the copper coated iron beads produces the desired charge on the coal particles.

  15. Undamped electrostatic plasma waves

    SciTech Connect

    Valentini, F.; Perrone, D.; Veltri, P.; Califano, F.; Pegoraro, F.; Morrison, P. J.; O'Neil, T. M.

    2012-09-15

    Electrostatic waves in a collision-free unmagnetized plasma of electrons with fixed ions are investigated for electron equilibrium velocity distribution functions that deviate slightly from Maxwellian. Of interest are undamped waves that are the small amplitude limit of nonlinear excitations, such as electron acoustic waves (EAWs). A deviation consisting of a small plateau, a region with zero velocity derivative over a width that is a very small fraction of the electron thermal speed, is shown to give rise to new undamped modes, which here are named corner modes. The presence of the plateau turns off Landau damping and allows oscillations with phase speeds within the plateau. These undamped waves are obtained in a wide region of the (k,{omega}{sub R}) plane ({omega}{sub R} being the real part of the wave frequency and k the wavenumber), away from the well-known 'thumb curve' for Langmuir waves and EAWs based on the Maxwellian. Results of nonlinear Vlasov-Poisson simulations that corroborate the existence of these modes are described. It is also shown that deviations caused by fattening the tail of the distribution shift roots off of the thumb curve toward lower k-values and chopping the tail shifts them toward higher k-values. In addition, a rule of thumb is obtained for assessing how the existence of a plateau shifts roots off of the thumb curve. Suggestions are made for interpreting experimental observations of electrostatic waves, such as recent ones in nonneutral plasmas.

  16. Electrostatic Plasma Accelerator (EPA)

    NASA Technical Reports Server (NTRS)

    Brophy, John R.; Aston, Graeme

    1995-01-01

    The application of electric propulsion to communications satellites, however, has been limited to the use of hydrazine thrusters with electric heaters for thrust and specific impulse augmentation. These electrothermal thrusters operate at specific impulse levels of approximately 300 s with heater powers of about 500 W. Low power arcjets (1-3 kW) are currently being investigated as a way to increase specific impulse levels to approximately 500 s. Ion propulsion systems can easily produce specific impulses of 3000 s or greater, but have yet to be applied to communications satellites. The reasons most often given for not using ion propulsion systems are their high level of overall complexity, low thrust with long burn times, and the difficulty of integrating the propulsion system into existing commercial spacecraft busses. The Electrostatic Plasma Accelerator (EPA) is a thruster concept which promises specific impulse levels between low power arcjets and those of the ion engine while retaining the relative simplicity of the arcjet. The EPA thruster produces thrust through the electrostatic acceleration of a moderately dense plasma. No accelerating electrodes are used and the specific impulse is a direct function of the applied discharge voltage and the propellant atomic mass.

  17. Photoswitched Cell Adhesion on Azobenzene-Containing Self-Assembled Films.

    PubMed

    Bian, Qing; Wang, Wenshuo; Han, Guoxiang; Chen, Yupeng; Wang, Shutao; Wang, Guojie

    2016-08-18

    Stimuli-responsive surfaces that can regulate and control cell adhesion have attracted much attention for their great potential in diverse biomedical applications. Unlike for pH- and temperature-responsive surfaces, the process of photoswitching requires no additional input of chemicals or thermal energy. In this work, two different photoresponsive azobenzene films are synthesized by chemisorption and electrostatic layer-by-layer (LbL) assembly techniques. The LbL film exhibits a relatively loose packing of azobenzene chromophores compared with the chemisorbed film. The changes in trans/cis isomer ratio of the azobenzene moiety and the corresponding wettability of the LbL films are larger than those of the chemisorbed films under UV light irradiation. The tendency for cell adhesion on the LbL films decreases markedly after UV light irradiation, whereas adhesion on the chemisorbed films decreases only slightly, because the azobenzene chromophores stay densely packed. Interestingly, the tendency for cell adhesion can be considerably increased on rough substrates, the roughness being introduced by use of photolithography and inductively coupled plasma deep etching techniques. For the chemisorbed films on rough substrates, the amount of cells that adhere also changes slightly after UV light irradiation, whereas, the amount of cells that adhere to LbL films on rough substrates decreases significantly. PMID:27146320

  18. Spectroscopic (FTIR, FT-Raman, 13C and 1H NMR) investigation, molecular electrostatic potential, polarizability and first-order hyperpolarizability, FMO and NBO analysis of 1-methyl-2-imidazolethiol.

    PubMed

    Xavier, R John; Dinesh, P

    2014-01-24

    In this work, experimental and theoretical study on the molecular structure and vibrational spectra of 1-methyl-2-imidazolethiol (MIME) were presented. The vibrational frequencies of the title compound were obtained theoretically by ab initio HF and DFT (B3LYP/LSDA) employing 6-311G (d,p) and 6-311++G(d,p) basis sets and compared with experimental spectral bands (FTIR and FT-Raman). The thermodynamic properties of the studied compound have been computed at different temperatures. The atomic charges and charge delocalization of the molecule have been analyzed by natural bond orbital (NBO) analysis. The reactivity sites are identified by mapping the molecular electrostatic potential (MESP) surface. Electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Besides, (13)C and (1)H nuclear magnetic resonance (NMR) chemical shifts of the molecule in chloroform solvent calculated using the Gauge-Independent Atomic Orbital (GIAO) method are found to be in good agreement with experimental values. PMID:24184581

  19. Synthetic Studies on Centromere-Associated Protein-E (CENP-E) Inhibitors: 2. Application of Electrostatic Potential Map (EPM) and Structure-Based Modeling to Imidazo[1,2-a]pyridine Derivatives as Anti-Tumor Agents.

    PubMed

    Hirayama, Takaharu; Okaniwa, Masanori; Banno, Hiroshi; Kakei, Hiroyuki; Ohashi, Akihiro; Iwai, Kenichi; Ohori, Momoko; Mori, Kouji; Gotou, Mika; Kawamoto, Tomohiro; Yokota, Akihiro; Ishikawa, Tomoyasu

    2015-10-22

    To develop centromere-associated protein-E (CENP-E) inhibitors for use as anticancer therapeutics, we designed novel imidazo[1,2-a]pyridines, utilizing previously discovered 5-bromo derivative 1a. By site-directed mutagenesis analysis, we confirmed the ligand binding site. A docking model revealed the structurally important molecular features for effective interaction with CENP-E and could explain the superiority of the inhibitor (S)-isomer in CENP-E inhibition vs the (R)-isomer based on the ligand conformation in the L5 loop region. Additionally, electrostatic potential map (EPM) analysis was employed as a ligand-based approach to optimize functional groups on the imidazo[1,2-a]pyridine scaffold. These efforts led to the identification of the 5-methoxy imidazo[1,2-a]pyridine derivative (+)-(S)-12, which showed potent CENP-E inhibition (IC50: 3.6 nM), cellular phosphorylated histone H3 (p-HH3) elevation (EC50: 180 nM), and growth inhibition (GI50: 130 nM) in HeLa cells. Furthermore, (+)-(S)-12 demonstrated antitumor activity (T/C: 40%, at 75 mg/kg) in a human colorectal cancer Colo205 xenograft model in mice. PMID:26372373

  20. Gecko adhesion pad: a smart surface?

    NASA Astrophysics Data System (ADS)

    Pesika, Noshir S.; Zeng, Hongbo; Kristiansen, Kai; Zhao, Boxin; Tian, Yu; Autumn, Kellar; Israelachvili, Jacob

    2009-11-01

    Recently, it has been shown that humidity can increase the adhesion of the spatula pads that form the outermost (adhesive) surface of the tokay gecko feet by 50% relative to the main adhesion mechanism (i.e. van der Waals adhesive forces), although the mechanism by which the enhancement is realized is still not well understood. A change in the surface hydrophobicity of a gecko setal array is observed when the array, which supports the spatulae, is exposed to a water drop for more than 20 min, suggesting a change in the hydrophilic-lyophilic balance (HLB), and therefore of the conformation of the surface proteins. A surface force apparatus (SFA) was used to quantify these changes, i.e. in the adhesion and friction forces, while shearing the setal array against a silica surface under (i) dry conditions, (ii) 100% humidity and (iii) when fully immersed in water. The adhesion increased in the humid environment but greatly diminished in water. Although the adhesion forces changed significantly, the friction forces remained unaffected, indicating that the friction between these highly textured surfaces is 'load-controlled' rather than 'adhesion-controlled'. These results demonstrate that the gecko adhesive pads have the ability to exploit environmental conditions to maximize their adhesion and stabilize their friction forces. Future designs of synthetic dry adhesives inspired by the gecko can potentially include similar 'smart' surfaces that adapt to their environment.

  1. Electrostatic sampling of trace DNA from clothing.

    PubMed

    Zieger, Martin; Defaux, Priscille Merciani; Utz, Silvia

    2016-05-01

    During acts of physical aggression, offenders frequently come into contact with clothes of the victim, thereby leaving traces of DNA-bearing biological material on the garments. Since tape-lifting and swabbing, the currently established methods for non-destructive trace DNA sampling from clothing, both have their shortcomings in collection efficiency and handling, we thought about a new collection method for these challenging samples. Testing two readily available electrostatic devices for their potential to sample biological material from garments made of different fabrics, we found one of them, the electrostatic dust print lifter (DPL), to perform comparable to well-established sampling with wet cotton swabs. In simulated aggression scenarios, we had the same success rate for the establishment of single aggressor profiles, suitable for database submission, with both the DPL and wet swabbing. However, we lost a substantial amount of information with electrostatic sampling, since almost no mixed aggressor-victim profiles suitable for database entry could be established, compared to conventional swabbing. This study serves as a proof of principle for electrostatic DNA sampling from items of clothing. The technique still requires optimization before it might be used in real casework. But we are confident that in the future it could be an efficient and convenient contribution to the toolbox of forensic practitioners. PMID:26753871

  2. Proteomic dataset of the sea urchin Paracentrotus lividus adhesive organs and secreted adhesive.

    PubMed

    Lebesgue, Nicolas; da Costa, Gonçalo; Ribeiro, Raquel Mesquita; Ribeiro-Silva, Cristina; Martins, Gabriel G; Matranga, Valeria; Scholten, Arjen; Cordeiro, Carlos; Heck, Albert J R; Santos, Romana

    2016-06-01

    Sea urchins have specialized adhesive organs called tube feet, which mediate strong but reversible adhesion. Tube feet are composed by a disc, producing adhesive and de-adhesive secretions for substratum attachment, and a stem for movement. After detachment the secreted adhesive remains bound to the substratum as a footprint. Recently, a label-free quantitative proteomic approach coupled with the latest mass-spectrometry technology was used to analyze the differential proteome of Paracentrotus lividus adhesive organ, comparing protein expression levels in the tube feet adhesive part (the disc) versus the non-adhesive part (the stem), and also to profile the proteome of the secreted adhesive (glue). This data article contains complementary figures and results related to the research article "Deciphering the molecular mechanisms underlying sea urchin reversible adhesion: a quantitative proteomics approach" (Lebesgue et al., 2016) [1]. Here we provide a dataset of 1384 non-redundant proteins, their fragmented peptides and expression levels, resultant from the analysis of the tube feet differential proteome. Of these, 163 highly over-expressed tube feet disc proteins (>3-fold), likely representing the most relevant proteins for sea urchin reversible adhesion, were further annotated in order to determine the potential functions. In addition, we provide a dataset of 611 non-redundant proteins identified in the secreted adhesive proteome, as well as their functional annotation and grouping in 5 major protein groups related with adhesive exocytosis, and microbial protection. This list was further analyzed to identify the most abundant protein groups and pinpoint putative adhesive proteins, such as Nectin, the most abundant adhesive protein in sea urchin glue. The obtained data uncover the key proteins involved in sea urchins reversible adhesion, representing a step forward to the development of new wet-effective bio-inspired adhesives. PMID:27182547

  3. Proteomic dataset of the sea urchin Paracentrotus lividus adhesive organs and secreted adhesive

    PubMed Central

    Lebesgue, Nicolas; da Costa, Gonçalo; Ribeiro, Raquel Mesquita; Ribeiro-Silva, Cristina; Martins, Gabriel G.; Matranga, Valeria; Scholten, Arjen; Cordeiro, Carlos; Heck, Albert J.R.; Santos, Romana

    2016-01-01

    Sea urchins have specialized adhesive organs called tube feet, which mediate strong but reversible adhesion. Tube feet are composed by a disc, producing adhesive and de-adhesive secretions for substratum attachment, and a stem for movement. After detachment the secreted adhesive remains bound to the substratum as a footprint. Recently, a label-free quantitative proteomic approach coupled with the latest mass-spectrometry technology was used to analyze the differential proteome of Paracentrotus lividus adhesive organ, comparing protein expression levels in the tube feet adhesive part (the disc) versus the non-adhesive part (the stem), and also to profile the proteome of the secreted adhesive (glue). This data article contains complementary figures and results related to the research article “Deciphering the molecular mechanisms underlying sea urchin reversible adhesion: a quantitative proteomics approach” (Lebesgue et al., 2016) [1]. Here we provide a dataset of 1384 non-redundant proteins, their fragmented peptides and expression levels, resultant from the analysis of the tube feet differential proteome. Of these, 163 highly over-expressed tube feet disc proteins (>3-fold), likely representing the most relevant proteins for sea urchin reversible adhesion, were further annotated in order to determine the potential functions. In addition, we provide a dataset of 611 non-redundant proteins identified in the secreted adhesive proteome, as well as their functional annotation and grouping in 5 major protein groups related with adhesive exocytosis, and microbial protection. This list was further analyzed to identify the most abundant protein groups and pinpoint putative adhesive proteins, such as Nectin, the most abundant adhesive protein in sea urchin glue. The obtained data uncover the key proteins involved in sea urchins reversible adhesion, representing a step forward to the development of new wet-effective bio-inspired adhesives. PMID:27182547

  4. Electrostatically Guided Rydberg Positronium.

    PubMed

    Deller, A; Alonso, A M; Cooper, B S; Hogan, S D; Cassidy, D B

    2016-08-12

    We report experiments in which positronium (Ps) atoms were guided using inhomogeneous electric fields. Ps atoms in Rydberg-Stark states with principal quantum number n=10 and electric dipole moments up to 610 D were prepared via two-color two-photon optical excitation in the presence of a 670  V cm^{-1} electric field. The Ps atoms were created at the entrance of a 0.4 m long electrostatic quadrupole guide, and were detected at the end of the guide via annihilation gamma radiation. When the lasers were tuned to excite low-field-seeking Stark states, a fivefold increase in the number of atoms reaching the end of the guide was observed, whereas no signal was detected when high-field-seeking states were produced. The data are consistent with the calculated geometrical guide acceptance. PMID:27563960

  5. ELECTROSTATIC MEMORY SYSTEM

    DOEpatents

    Chu, J.C.

    1958-09-23

    An improved electrostatic memory system is de scribed fer a digital computer wherein a plarality of storage tubes are adapted to operate in either of two possible modes. According to the present irvention, duplicate storage tubes are provided fur each denominational order of the several binary digits. A single discriminator system is provided between corresponding duplicate tubes to determine the character of the infurmation stored in each. If either tube produces the selected type signal, corresponding to binazy "1" in the preferred embodiment, a "1" is regenerated in both tubes. In one mode of operation each bit of information is stored in two corresponding tubes, while in the other mode of operation each bit is stored in only one tube in the conventional manner.

  6. Electrostatically Guided Rydberg Positronium

    NASA Astrophysics Data System (ADS)

    Deller, A.; Alonso, A. M.; Cooper, B. S.; Hogan, S. D.; Cassidy, D. B.

    2016-08-01

    We report experiments in which positronium (Ps) atoms were guided using inhomogeneous electric fields. Ps atoms in Rydberg-Stark states with principal quantum number n =10 and electric dipole moments up to 610 D were prepared via two-color two-photon optical excitation in the presence of a 670 V cm-1 electric field. The Ps atoms were created at the entrance of a 0.4 m long electrostatic quadrupole guide, and were detected at the end of the guide via annihilation gamma radiation. When the lasers were tuned to excite low-field-seeking Stark states, a fivefold increase in the number of atoms reaching the end of the guide was observed, whereas no signal was detected when high-field-seeking states were produced. The data are consistent with the calculated geometrical guide acceptance.

  7. Control of vascular permeability by adhesion molecules.

    PubMed

    Sarelius, Ingrid H; Glading, Angela J

    2015-01-01

    Vascular permeability is a vital function of the circulatory system that is regulated in large part by the limited flux of solutes, water, and cells through the endothelial cell layer. One major pathway through this barrier is via the inter-endothelial junction, which is driven by the regulation of cadherin-based adhesions. The endothelium also forms attachments with surrounding proteins and cells via 2 classes of adhesion molecules, the integrins and IgCAMs. Integrins and IgCAMs propagate activation of multiple downstream signals that potentially impact cadherin adhesion. Here we discuss the known contributions of integrin and IgCAM signaling to the regulation of cadherin adhesion stability, endothelial barrier function, and vascular permeability. Emphasis is placed on known and prospective crosstalk signaling mechanisms between integrins, the IgCAMs- ICAM-1 and PECAM-1, and inter-endothelial cadherin adhesions, as potential strategic signaling nodes for multipartite regulation of cadherin adhesion. PMID:25838987

  8. High-Temperature Electrostatic Levitator

    NASA Technical Reports Server (NTRS)

    Rhim, Won-Kyu; Chung, Sang K.

    1994-01-01

    High-temperature electrostatic levitator provides independent control of levitation and heating of sample in vacuum. Does not cause electromagnetic stirring in molten sample (such stirring causes early nucleation in undercooling). Maintenance of levitating force entails control of electrostatic field and electrical charge on sample.

  9. Teaching Electrostatics in University Courses

    ERIC Educational Resources Information Center

    Hughes, J. F.

    1974-01-01

    Describes an optional course on applied electrostatics that was offered to electrical engineers in their final year. Topics included the determination of electric fields, nature of the charging process, static electricity in liquids, solid state processes, charged particle applications, and electrostatic ignition. (GS)

  10. Colloid adhesive parameters for chemical heterogeneous porous media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A simple modeling approach was developed to calculate colloid adhesive parameters for chemically heterogeneous porous media. The area of the zone of electrostatic influence between a colloid and solid-water interface (Az) was discretized into a number of equally sized grid cells to capture chemical...

  11. Conservation and Role of Electrostatics in Thymidylate Synthase

    NASA Astrophysics Data System (ADS)

    Garg, Divita; Skouloubris, Stephane; Briffotaux, Julien; Myllykallio, Hannu; Wade, Rebecca C.

    2015-11-01

    Conservation of function across families of orthologous enzymes is generally accompanied by conservation of their active site electrostatic potentials. To study the electrostatic conservation in the highly conserved essential enzyme, thymidylate synthase (TS), we conducted a systematic species-based comparison of the electrostatic potential in the vicinity of its active site. Whereas the electrostatics of the active site of TS are generally well conserved, the TSs from minimal organisms do not conform to the overall trend. Since the genomes of minimal organisms have a high thymidine content compared to other organisms, the observation of non-conserved electrostatics was surprising. Analysis of the symbiotic relationship between minimal organisms and their hosts, and the genetic completeness of the thymidine synthesis pathway suggested that TS from the minimal organism Wigglesworthia glossinidia (W.g.b.) must be active. Four residues in the vicinity of the active site of Escherichia coli TS were mutated individually and simultaneously to mimic the electrostatics of W.g.b TS. The measured activities of the E. coli TS mutants imply that conservation of electrostatics in the region of the active site is important for the activity of TS, and suggest that the W.g.b. TS has the minimal activity necessary to support replication of its reduced genome.

  12. Conservation and Role of Electrostatics in Thymidylate Synthase

    PubMed Central

    Garg, Divita; Skouloubris, Stephane; Briffotaux, Julien; Myllykallio, Hannu; Wade, Rebecca C.

    2015-01-01

    Conservation of function across families of orthologous enzymes is generally accompanied by conservation of their active site electrostatic potentials. To study the electrostatic conservation in the highly conserved essential enzyme, thymidylate synthase (TS), we conducted a systematic species-based comparison of the electrostatic potential in the vicinity of its active site. Whereas the electrostatics of the active site of TS are generally well conserved, the TSs from minimal organisms do not conform to the overall trend. Since the genomes of minimal organisms have a high thymidine content compared to other organisms, the observation of non-conserved electrostatics was surprising. Analysis of the symbiotic relationship between minimal organisms and their hosts, and the genetic completeness of the thymidine synthesis pathway suggested that TS from the minimal organism Wigglesworthia glossinidia (W.g.b.) must be active. Four residues in the vicinity of the active site of Escherichia coli TS were mutated individually and simultaneously to mimic the electrostatics of W.g.b TS. The measured activities of the E. coli TS mutants imply that conservation of electrostatics in the region of the active site is important for the activity of TS, and suggest that the W.g.b. TS has the minimal activity necessary to support replication of its reduced genome. PMID:26612036

  13. ELECTROSTATICALLY ENHANCED BARRIER FILTER COLLECTION

    SciTech Connect

    John Erjavec; Michael D. Mann; Ryan Z. Knutson; Michael L. Swanson; Michael E. Collings

    2003-06-01

    This work was performed through the University of North Dakota (UND) Chemical Engineering Department with assistance from UND's Energy & Environmental Research Center. This research was undertaken in response to the U.S. Department of Energy Federal Technology Center Program Solicitation No. DE-PS26-99FT40479, Support of Advanced Coal Research at U.S. Universities and Colleges. Specifically, this research was in support of the UCR Core Program and addressees Topic 1, Improved Hot-Gas Contaminant and Particulate Removal Techniques, introducing an advanced design for particulate removal. Integrated gasification combined cycle (IGCC) offers the potential for very high efficiency and clean electric generation. In IGCC, the product gas from the gasifier needs to be cleaned of particulate matter to avoid erosion and high-temperature corrosion difficulties arising with the turbine blades. Current methods involve cooling the gases to {approx}100 C to condense alkalis and remove sulfur and particulates using conventional scrubber technology. This ''cool'' gas is then directed to a turbine for electric generation. While IGCC has the potential to reach efficiencies of over 50%, the current need to cool the product gas for cleaning prior to firing it in a turbine is keeping IGCC from reaching its full potential. The objective of the current project was to develop a highly reliable particulate collector system that can meet the most stringent turbine requirements and emission standards, can operate at temperatures above 1500 F, is applicable for use with all U.S. coals, is compatible with various sorbent injection schemes for sulfur and alkali control, can be integrated into a variety of configurations for both pressurized gasification and combustion, increases allowable face velocity to reduce filter system capital cost, and is cost-competitive with existing technologies. The collector being developed is a new concept in particulate control called electrostatically enhanced

  14. Evaluation of a lipopeptide biosurfactant from Bacillus natto TK-1 as a potential source of anti-adhesive, antimicrobial and antitumor activities

    PubMed Central

    Cao, Xiao-Hong; Liao, Zhen-Yu; Wang, Chun-Ling; Yang, Wen-Yan; Lu, Mei-Fang

    2009-01-01

    A lipopeptide biosurfactant produced by Bacillus natto TK-1 has a strong surface activity. The biosurfactant was found to be an anti-adhesive agent against several bacterial strains, and also showed a broad spectrum of antimicrobial activity. The biosurfactant induced a significant reduction in tumor cells viability in a dose-dependent manner. PMID:24031375

  15. Electrostatic Interactions in Aminoglycoside-RNA Complexes

    PubMed Central

    Kulik, Marta; Goral, Anna M.; Jasiński, Maciej; Dominiak, Paulina M.; Trylska, Joanna

    2015-01-01

    Electrostatic interactions often play key roles in the recognition of small molecules by nucleic acids. An example is aminoglycoside antibiotics, which by binding to ribosomal RNA (rRNA) affect bacterial protein synthesis. These antibiotics remain one of the few valid treatments against hospital-acquired infections by Gram-negative bacteria. It is necessary to understand the amplitude of electrostatic interactions between aminoglycosides and their rRNA targets to introduce aminoglycoside modifications that would enhance their binding or to design new scaffolds. Here, we calculated the electrostatic energy of interactions and its per-ring contributions between aminoglycosides and their primary rRNA binding site. We applied either the methodology based on the exact potential multipole moment (EPMM) or classical molecular mechanics force field single-point partial charges with Coulomb formula. For EPMM, we first reconstructed the aspherical electron density of 12 aminoglycoside-RNA complexes from the atomic parameters deposited in the University at Buffalo Databank. The University at Buffalo Databank concept assumes transferability of electron density between atoms in chemically equivalent vicinities and allows reconstruction of the electron densities from experimental structural data. From the electron density, we then calculated the electrostatic energy of interaction using EPMM. Finally, we compared the two approaches. The calculated electrostatic interaction energies between various aminoglycosides and their binding sites correlate with experimentally obtained binding free energies. Based on the calculated energetic contributions of water molecules mediating the interactions between the antibiotic and rRNA, we suggest possible modifications that could enhance aminoglycoside binding affinity. PMID:25650932

  16. Plasticizers Increase Adhesion of the Deteriogenic Fungus Aureobasidium pullulans to Polyvinyl Chloride

    PubMed Central

    Webb, Jeremy S.; Van der Mei, Henny C.; Nixon, Marianne; Eastwood, Ian M.; Greenhalgh, Malcolm; Read, Simon J.; Robson, Geoffrey D.; Handley, Pauline S.

    1999-01-01

    Initial adhesion of fungi to plasticized polyvinyl chloride (pPVC) may determine subsequent colonization and biodeterioration processes. The deteriogenic fungus Aureobasidium pullulans was used to investigate the physicochemical nature of adhesion to both unplasticized PVC (uPVC) and pPVC containing the plasticizers dioctyl phthalate (DOP) and dioctyl adipate (DOA). A quantitative adhesion assay using image analysis identified fundamental differences in the mechanism of adhesion of A. pullulans blastospores to these substrata. Adhesion to pPVC was greater than that to uPVC by a maximum of 280% after a 4-h incubation with 108 blastospores ml−1. That plasticizers enhance adhesion to PVC was confirmed by incorporating a dispersion of both DOA and DOP into the blastospore suspension. Adhesion to uPVC was increased by up to 308% in the presence of the dispersed plasticizers. Hydrophobic interactions were found to dominate adhesion to uPVC because (i) a strong positive correlation was observed between substratum hydrophobicity (measured by using a dynamic contact angle analyzer) and adhesion to a range of unplasticized polymers including uPVC, and (ii) neither the pH nor the electrolyte concentration of the suspension buffer, both of which influence electrostatic interactions, affected adhesion to uPVC. In contrast, adhesion to pPVC is principally controlled by electrostatic interactions. Enhanced adhesion to pPVC occurred despite a relative reduction of 13° in the water contact angle of pPVC compared to that of uPVC. Furthermore, adhesion to pPVC was strongly dependent on both the pH and electrolyte concentration of the suspension medium, reaching maximum levels at pH 8 and with an electrolyte concentration of 10 mM NaCl. Plasticization with DOP and DOA therefore increases adhesion of A. pullulans blastospores to pPVC through an interaction mediated by electrostatic forces. PMID:10427051

  17. Electrostatics of photosynthetic reaction centers in membranes.

    PubMed

    Pennisi, Cristian P; Greenbaum, Elias; Yoshida, Ken

    2006-01-01

    Photosynthetic reaction centers are integral membrane complexes. They have potential application as molecular photovoltaic structures and have been used in diverse technological applications. A three-dimensional electrostatic model of the photosystem I reaction center (PSI) embedded in a lipid membrane is presented. The potential is obtained by solving the Poisson-Boltzmann equation with the finite element method (FEM). Simulations showing the potential distribution in a vesicle containing PSI reaction centers under different conditions are presented. The results of the simulations are compared with previous findings and a possible application of PSI to provide light activation of voltage-gated ion channels is discussed. PMID:17946611

  18. Thermal Characterization of Adhesive

    NASA Technical Reports Server (NTRS)

    Spomer, Ken A.

    1999-01-01

    The current Space Shuttle Reusable Solid Rocket Motor (RSRM) nozzle adhesive bond system is being replaced due to obsolescence. Down-selection and performance testing of the structural adhesives resulted in the selection of two candidate replacement adhesives, Resin Technology Group's Tiga 321 and 3M's EC2615XLW. This paper describes rocket motor testing of these two adhesives. Four forty-pound charge motors were fabricated in configurations that would allow side by side comparison testing of the candidate replacement adhesives and the current RSRM adhesives. The motors provided an environment where the thermal performance of adhesives in flame surface bondlines was compared. Results of the FPC testing show that: 1) The phenolic char depths on radial bond lines is approximately the same and vary depending on the position in the blast tube regardless of which adhesive was used; 2) The adhesive char depth of the candidate replacement adhesives is less than the char depth of the current adhesives; 3) The heat-affected depth of the candidate replacement adhesives is less than the heat-affected depth of the current adhesives; and 4) The ablation rates for both replacement adhesives are slower than that of the current adhesives.

  19. Electrostatic Dust Control on Planetary Surfaces

    NASA Astrophysics Data System (ADS)

    Clark, P. E.; Calle, C. I.; Curtis, S. A.; Keller, J. F.; Minetto, F.; Mantovani, J. G.

    2007-01-01

    Successful operation for exploration of planetary regoliths will depend on the capability to keep surfaces free of dust which could compromise performance and to collect dust for characterization. Such study is essential in order to resolve issues in dealing with regolith fines identified during the Apollo missions where dust behaved like abrasive Velcro before returning to the Moon. During Moon landings, locally-induced stirring of the regolith caused dust to be suspended long enough to come into contact with conducting surfaces. Lunar fines, because of their electrostatic charging, were difficult to collect and sparsely sampled: bag seals were broken, samples contaminated and lost. Our objectives here are to describe a multi-faceted electrostatically-based approach and methodology for addressing this issue, as well as to present our preliminary results which confirm the view that the successful strategy will deal with dust dynamics resulting from interaction between mechanical and electrostatic forces. Our device concept combines electron or ion beams, acting as a plasma dust sweeper to control the flow of dust by systematic scanning of the surface with an electrostatically controlled potential. A plate of the opposite potential used to induce dust migration in the presence of an electrical field. Our goal is a compact device of < 5 kg mass and using <5 watts of power to be operational in <5 years with heritage from ionic sweepers for active spacecraft potential control (e.g., on POLAR). Rovers, human or robotic, wheeled, legged, or tetrahedral, could be fitted with devices that could harness the removal of dust for sampling as part of the extended exploration process on extensive areas of exposed impact-generated regolith, on Mercury, Mars, asteroids or outer solar system satellites, as well as the Moon.

  20. The development of aerospace polyimide adhesives

    NASA Technical Reports Server (NTRS)

    St.clair, A. K.; St.clair, T. L.

    1983-01-01

    Few materials are available which can be used as aerospace adhesives at temperatures in the range of 300 C. The Materials Division at NASA-Langley Research Center developed several high temperature polyimide adhesives to fulfill the stringent needs of current aerospace programs. These adhesives are the result of a decade of basic research studies on the structure property relationships of both linear and addition aromatic polyimides. The development of both in house and commercially available polyimides is reviewed with regards to their potential for use as aerospace adhesives.

  1. Micromachined silicon electrostatic chuck

    DOEpatents

    Anderson, Robert A.; Seager, Carleton H.

    1996-01-01

    An electrostatic chuck is faced with a patterned silicon plate 11, created y micromachining a silicon wafer, which is attached to a metallic base plate 13. Direct electrical contact between the chuck face 15 (patterned silicon plate's surface) and the silicon wafer 17 it is intended to hold is prevented by a pattern of flat-topped silicon dioxide islands 19 that protrude less than 5 micrometers from the otherwise flat surface of the chuck face 15. The islands 19 may be formed in any shape. Islands may be about 10 micrometers in diameter or width and spaced about 100 micrometers apart. One or more concentric rings formed around the periphery of the area between the chuck face 15 and wafer 17 contain a low-pressure helium thermal-contact gas used to assist heat removal during plasma etching of a silicon wafer held by the chuck. The islands 19 are tall enough and close enough together to prevent silicon-to-silicon electrical contact in the space between the islands, and the islands occupy only a small fraction of the total area of the chuck face 15, typically 0.5 to 5 percent. The pattern of the islands 19, together with at least one hole 12 bored through the silicon veneer into the base plate, will provide sufficient gas-flow space to allow the distribution of the helium thermal-contact gas.

  2. Micromachined silicon electrostatic chuck

    DOEpatents

    Anderson, R.A.; Seager, C.H.

    1996-12-10

    An electrostatic chuck is faced with a patterned silicon plate, created by micromachining a silicon wafer, which is attached to a metallic base plate. Direct electrical contact between the chuck face (patterned silicon plate`s surface) and the silicon wafer it is intended to hold is prevented by a pattern of flat-topped silicon dioxide islands that protrude less than 5 micrometers from the otherwise flat surface of the chuck face. The islands may be formed in any shape. Islands may be about 10 micrometers in diameter or width and spaced about 100 micrometers apart. One or more concentric rings formed around the periphery of the area between the chuck face and wafer contain a low-pressure helium thermal-contact gas used to assist heat removal during plasma etching of a silicon wafer held by the chuck. The islands are tall enough and close enough together to prevent silicon-to-silicon electrical contact in the space between the islands, and the islands occupy only a small fraction of the total area of the chuck face, typically 0.5 to 5 percent. The pattern of the islands, together with at least one hole bored through the silicon veneer into the base plate, will provide sufficient gas-flow space to allow the distribution of the helium thermal-contact gas. 6 figs.

  3. Functionally Graded Adhesives for Composite Joints

    NASA Technical Reports Server (NTRS)

    Stapleton, Scott E.; Waas, Anthony M.; Arnold, Steven M.

    2012-01-01

    Adhesives with functionally graded material properties are being considered for use in adhesively bonded joints to reduce the peel stress concentrations located near adherend discontinuities. Several practical concerns impede the actual use of such adhesives. These include increased manufacturing complications, alterations to the grading due to adhesive flow during manufacturing, and whether changing the loading conditions significantly impact the effectiveness of the grading. An analytical study is conducted to address these three concerns. An enhanced joint finite element, which uses an analytical formulation to obtain exact shape functions, is used to model the joint. Furthermore, proof of concept testing is conducted to show the potential advantages of functionally graded adhesives. In this study, grading is achieved by strategically placing glass beads within the adhesive layer at different densities along the joint.

  4. Understanding Marine Mussel Adhesion

    SciTech Connect

    H. G. Silverman; F. F. Roberto

    2007-12-01

    In addition to identifying the proteins that have a role in underwater adhesion by marine mussels, research efforts have focused on identifying the genes responsible for the adhesive proteins, environmental factors that may influence protein production, and strategies for producing natural adhesives similar to the native mussel adhesive proteins. The production-scale availability of recombinant mussel adhesive proteins will enable researchers to formulate adhesives that are waterimpervious and ecologically safe and can bind materials ranging from glass, plastics, metals, and wood to materials, such as bone or teeth, biological organisms, and other chemicals or molecules. Unfortunately, as of yet scientists have been unable to duplicate the processes that marine mussels use to create adhesive structures. This study provides a background on adhesive proteins identified in the blue mussel, Mytilus edulis, and introduces our research interests and discusses the future for continued research related to mussel adhesion.

  5. Understanding marine mussel adhesion.

    PubMed

    Silverman, Heather G; Roberto, Francisco F

    2007-01-01

    In addition to identifying the proteins that have a role in underwater adhesion by marine mussels, research efforts have focused on identifying the genes responsible for the adhesive proteins, environmental factors that may influence protein production, and strategies for producing natural adhesives similar to the native mussel adhesive proteins. The production-scale availability of recombinant mussel adhesive proteins will enable researchers to formulate adhesives that are water-impervious and ecologically safe and can bind materials ranging from glass, plastics, metals, and wood to materials, such as bone or teeth, biological organisms, and other chemicals or molecules. Unfortunately, as of yet scientists have been unable to duplicate the processes that marine mussels use to create adhesive structures. This study provides a background on adhesive proteins identified in the blue mussel, Mytilus edulis, and introduces our research interests and discusses the future for continued research related to mussel adhesion. PMID:17990038

  6. Understanding Marine Mussel Adhesion

    PubMed Central

    Roberto, Francisco F.

    2007-01-01

    In addition to identifying the proteins that have a role in underwater adhesion by marine mussels, research efforts have focused on identifying the genes responsible for the adhesive proteins, environmental factors that may influence protein production, and strategies for producing natural adhesives similar to the native mussel adhesive proteins. The production-scale availability of recombinant mussel adhesive proteins will enable researchers to formulate adhesives that are water-impervious and ecologically safe and can bind materials ranging from glass, plastics, metals, and wood to materials, such as bone or teeth, biological organisms, and other chemicals or molecules. Unfortunately, as of yet scientists have been unable to duplicate the processes that marine mussels use to create adhesive structures. This study provides a background on adhesive proteins identified in the blue mussel, Mytilus edulis, and introduces our research interests and discusses the future for continued research related to mussel adhesion. PMID:17990038

  7. Stability, Nonlinearity and Reliability of Electrostatically Actuated MEMS Devices

    PubMed Central

    Zhang, Wen-Ming; Meng, Guang; Chen, Di

    2007-01-01

    Electrostatic micro-electro-mechanical system (MEMS) is a special branch with a wide range of applications in sensing and actuating devices in MEMS. This paper provides a survey and analysis of the electrostatic force of importance in MEMS, its physical model, scaling effect, stability, nonlinearity and reliability in detail. It is necessary to understand the effects of electrostatic forces in MEMS and then many phenomena of practical importance, such as pull-in instability and the effects of effective stiffness, dielectric charging, stress gradient, temperature on the pull-in voltage, nonlinear dynamic effects and reliability due to electrostatic forces occurred in MEMS can be explained scientifically, and consequently the great potential of MEMS technology could be explored effectively and utilized optimally. A simplified parallel-plate capacitor model is proposed to investigate the resonance response, inherent nonlinearity, stiffness softened effect and coupled nonlinear effect of the typical electrostatically actuated MEMS devices. Many failure modes and mechanisms and various methods and techniques, including materials selection, reasonable design and extending the controllable travel range used to analyze and reduce the failures are discussed in the electrostatically actuated MEMS devices. Numerical simulations and discussions indicate that the effects of instability, nonlinear characteristics and reliability subjected to electrostatic forces cannot be ignored and are in need of further investigation.

  8. Jumping-droplet electrostatic energy harvesting

    NASA Astrophysics Data System (ADS)

    Miljkovic, Nenad; Preston, Daniel J.; Enright, Ryan; Wang, Evelyn N.

    2014-07-01

    Micro- and nanoscale wetting phenomena have been an active area of research due to its potential for improving engineered system performance involving phase change. With the recent advancements in micro/nanofabrication techniques, structured surfaces can now be designed to allow condensing coalesced droplets to spontaneously jump off the surface due to the conversion of excess surface energy into kinetic energy. In addition to being removed at micrometric length scales (˜10 μm), jumping water droplets also attain a positive electrostatic charge (˜10-100 fC) from the hydrophobic coating/condensate interaction. In this work, we take advantage of this droplet charging to demonstrate jumping-droplet electrostatic energy harvesting. The charged droplets jump between superhydrophobic copper oxide and hydrophilic copper surfaces to create an electrostatic potential and generate power during formation of atmospheric dew. We demonstrated power densities of ˜15 pW/cm2, which, in the near term, can be improved to ˜1 μW/cm2. This work demonstrates a surface engineered platform that promises to be low cost and scalable for atmospheric energy harvesting and electric power generation.

  9. Studies on biodegradable and crosslinkable poly(castor oil fumarate)/poly(propylene fumarate) composite adhesive as a potential injectable biomaterial.

    PubMed

    Mitha, M K; Jayabalan, M

    2009-12-01

    Biodegradable hydroxyl terminated-poly(castor oil fumarate) (HT-PCF) and poly(propylene fumarate) (HT-PPF) resins were synthesized as an injectable and in situ-cross linkable polyester resins for orthopedic applications. An injectable adhesive formulation containing this resin blend, N-vinyl pyrrolidone (NVP), hydroxy apatite, free radical initiator and accelerator was developed. The Composite adhesives containing the ratio of resin blend and NVP, 2.1:1.5, 2.1:1.2 and 2.1:1.0 set fast with tolerable exothermic temperature as a three dimensionally cross linked toughened material. Crosslink density and mechanical properties of the crosslinked composite increase with increase of NVP. The present crosslinked composite has hydrophilic character and cytocompatibility with L929 fibroblast cells. PMID:18592346

  10. Singular electrostatic energy of nanoparticle clusters

    NASA Astrophysics Data System (ADS)

    Qin, Jian; Krapf, Nathan W.; Witten, Thomas A.

    2016-02-01

    The binding of clusters of metal nanoparticles is partly electrostatic. We address difficulties in calculating the electrostatic energy when high charging energies limit the total charge to a single quantum, entailing unequal potentials on the particles. We show that the energy at small separation h has a singular logarithmic dependence on h . We derive a general form for this energy in terms of the singular capacitance of two spheres in near contact c (h ) , together with nonsingular geometric features of the cluster. Using this form, we determine the energies of various clusters, finding that more compact clusters are more stable. These energies are proposed to be significant for metal-semiconductor binary nanoparticle lattices found experimentally. We sketch how these effects should dictate the relative abundances of metal nanoparticle clusters in nonpolar solvents.

  11. Test progress on the electrostatic membrane reflector

    NASA Technical Reports Server (NTRS)

    Mihora, D. J.

    1981-01-01

    An extemely lightweight type of precision reflector antenna, being developed for potential deployment from the space shuttle, uses electrostatic forces to tension a thin membrane and form it into a concave reflector surface. The typical shuttle-deployed antenna would have a diameter of 100 meters and an RMS surface smoothness of 10 to 1 mm for operation at 1 to 10 GHz. NASA Langley Research Center built and is currently testing a subscale (16 foot diameter) model of the membrane reflector portion of such an antenna. Preliminary test results and principal factors affecting surface quality are addressed. Factors included are the effect of the perimeter boundary, splicing of the membrane, the long-scale smoothness of commercial membranes, and the spatial controllability of the membrane using voltage adjustments to alter the electrostatic pressure. Only readily available commercial membranes are considered.

  12. Reliable aluminum contact formation by electrostatic bonding

    NASA Astrophysics Data System (ADS)

    Kárpáti, T.; Pap, A. E.; Radnóczi, Gy; Beke, B.; Bársony, I.; Fürjes, P.

    2015-07-01

    The paper presents a detailed study of a reliable method developed for aluminum fusion wafer bonding assisted by the electrostatic force evolving during the anodic bonding process. The IC-compatible procedure described allows the parallel formation of electrical and mechanical contacts, facilitating a reliable packaging of electromechanical systems with backside electrical contacts. This fusion bonding method supports the fabrication of complex microelectromechanical systems (MEMS) and micro-opto-electromechanical systems (MOEMS) structures with enhanced temperature stability, which is crucial in mechanical sensor applications such as pressure or force sensors. Due to the applied electrical potential of  -1000 V the Al metal layers are compressed by electrostatic force, and at the bonding temperature of 450 °C intermetallic diffusion causes aluminum ions to migrate between metal layers.

  13. A simple apparatus for electrostatic force measurement

    NASA Astrophysics Data System (ADS)

    Hale, D. P.

    1981-01-01

    Electrostatic attraction can explain as a first approximation the binding of ionic solids. One of the two reasons for constructing the apparatus described was to demonstrate that electrostatic forces can be large, thus giving at least some plausibility to the theory of ionic solids. Secondly, it is an attempt to create a cheap and simple apparatus for measuring these forces and relating them to other physical quantities. An apparatus giving similar results of some precision has already been described (Hale 1978a). That was constructed by skilled instrument makers for undergraduate teaching, cost several hundred pounds and needed a considerable amount of time to iron out the problems encountered. The present apparatus was made in a few hours largely from scrap and using only ordinary hand tools. Although it is somewhat crude, quite acceptable results can be obtained from it. It could be used to advantage in courses dealing with fields and potential for example Nuffield advanced physics, unit 3.

  14. Analysis of the effect of LRP-1 silencing on the invasive potential of cancer cells by nanomechanical probing and adhesion force measurements using atomic force microscopy.

    PubMed

    Le Cigne, A; Chièze, L; Beaussart, A; El-Kirat-Chatel, S; Dufrêne, Y F; Dedieu, S; Schneider, C; Martiny, L; Devy, J; Molinari, M

    2016-04-01

    Low-density lipoprotein receptor-related protein 1 (LRP-1) can internalize proteases involved in cancer progression and is thus considered a promising therapeutic target. However, it has been demonstrated that LRP-1 is also able to regulate the endocytosis of membrane-anchored proteins. Thus, strategies that target LRP-1 to modulate proteolysis could also affect adhesion and cytoskeleton dynamics. Here, we investigated the effect of LRP-1 silencing on parameters reflecting cancer cells' invasiveness by atomic force microscopy (AFM). The results show that LRP-1 silencing induces changes in the cells' adhesion behavior, particularly the dynamics of cell attachment. Clear alterations in morphology, such as more pronounced stress fibers and increased spreading, leading to increased area and circularity, were also observed. The determination of the cells' mechanical properties by AFM showed that these differences are correlated with an increase in Young's modulus. Moreover, the measurements show an overall decrease in cell motility and modifications of directional persistence. An overall increase in the adhesion force between the LRP-1-silenced cells and a gelatin-coated bead was also observed. Ultimately, our AFM-based force spectroscopy data, recorded using an antibody directed against the β1 integrin subunit, provide evidence that LRP-1 silencing modifies the rupture force distribution. Together, our results show that techniques traditionally used for the investigation of cancer cells can be coupled with AFM to gain access to complementary phenotypic parameters that can help discriminate between specific phenotypes associated with different degrees of invasiveness. PMID:26965453

  15. Drosophila homologue of Diaphanous 1 (DIAPH1) controls the metastatic potential of colon cancer cells by regulating microtubule-dependent adhesion.

    PubMed

    Lin, Yuan-Na; Bhuwania, Ridhirama; Gromova, Kira; Failla, Antonio Virgilio; Lange, Tobias; Riecken, Kristoffer; Linder, Stefan; Kneussel, Matthias; Izbicki, Jakob R; Windhorst, Sabine

    2015-07-30

    Drosophila homologue of Diaphanous 1 (DIAPH1) regulates actin polymerization and microtubule (MT) stabilization upon stimulation with lysophosphatidic acid (LPA). Recently, we showed strongly reduced lung metastasis of DIAPH1-depleted colon cancer cells but we found accumulations of DIAPH1-depleted cells in bone marrow. Here, we analyzed possible organ- or tissue-specific metastasis of DIAPH1-depleted HCT-116 cells. Our data confirmed that depletion of DIAPH1 strongly inhibited lung metastasis and revealed that, in contrast to control cells, DIAPH1-depleted cells did not form metastases in further organs. Detailed mechanistic analysis on cells that were not stimulated with LPA to activate the cytoskeleton-modulating activity of DIAPH1, revealed that even under basal conditions DIAPH1 was essential for cellular adhesion to collagen. In non-stimulated cells DIAPH1 did not control actin dynamics but, interestingly, was essential for stabilization of microtubules (MTs). Additionally, DIAPH1 controlled directed vesicle trafficking and with this, local clustering of the adhesion protein integrin-β1 at the plasma membrane. Therefore, we conclude that under non-stimulating conditions DIAPH1 controls cellular adhesion by stabilizing MTs required for local clustering of integrin-β1 at the plasma membrane. Thus, blockade of DIAPH1-tubulin interaction may be a promising approach to inhibit one of the earliest steps in the metastatic cascade of colon cancer. PMID:26124177

  16. Intermolecular electrostatic energies using density fitting

    PubMed Central

    Cisneros, G. Andrés; Piquemal, Jean-Philip; Darden, Thomas A.

    2009-01-01

    A method is presented to calculate the electron-electron and nuclear-electron intermolecular Coulomb interaction energy between two molecules by separately fitting the unperturbed molecular electron density of each monomer. This method is based on the variational Coulomb fitting method which relies on the expansion of the ab initio molecular electron density in site-centered auxiliary basis sets. By expanding the electron density of each monomer in this way the integral expressions for the intermolecular electrostatic calculations are simplified, lowering the operation count as well as the memory usage. Furthermore, this method allows the calculation of intermolecular Coulomb interactions with any level of theory from which a one-electron density matrix can be obtained. Our implementation is initially tested by calculating molecular properties with the density fitting method using three different auxiliary basis sets and comparing them to results obtained from ab initio calculations. These properties include dipoles for a series of molecules, as well as the molecular electrostatic potential and electric field for water. Subsequently, the intermolecular electrostatic energy is tested by calculating ten stationary points on the water dimer potential-energy surface. Results are presented for electron densities obtained at four different levels of theory using two different basis sets, fitted with three auxiliary basis sets. Additionally, a one-dimensional electrostatic energy surface scan is performed for four different systems (H2O dimer, Mg2+–H2O, Cu+–H2O, and n-methyl-formamide dimer). Our results show a very good agreement with ab initio calculations for all properties as well as interaction energies. PMID:16095348

  17. Denture Adhesives

    MedlinePlus

    ... bone and give temporary relief from loosening dentures. Zinc and Potential Risk Zinc is a mineral that is an essential ingredient for good health. ... in some dietary supplements. However, an excess of zinc in the body can lead to health problems ...

  18. The Electrostatic Environments of Mars and the Moon

    NASA Technical Reports Server (NTRS)

    Calle, Carlos I.

    2011-01-01

    The electrical activity present in the environment near the surfaces of Mars and the moon has very different origins and presents a challenge to manned and robotic planetary exploration missions. Mars is covered with a layer of dust that has been redistributed throughout the entire planet by global dust storms. Dust, levitated by these storms as well as by the frequent dust devils, is expected to be electrostatically charged due to the multiple grain collisions in the dust-laden atmosphere. Dust covering the surface of the moon is expected to be electrostatically charged due to the solar wind, cosmic rays, and the solar radiation itself through the photoelectric effect. Electrostatically charged dust has a large tendency to adhere to surfaces. NASA's Mars exploration rovers have shown that atmospheric dust falling on solar panels can decrease their efficiency to the point of rendering the rover unusable. And as the Apollo missions to the moon showed, lunar dust adhesion can hinder manned and unmanned lunar exploration activities. Taking advantage of the electrical activity on both planetary system bodies, dust removal technologies are now being developed that use electrostatic and dielectrophoretic forces to produce controlled dust motion. This paper presents a short review of the theoretical and semiempirical models that have been developed for the lunar and Martian electrical environments.

  19. Electrostatic Characterization of Lunar Dust

    NASA Technical Reports Server (NTRS)

    2008-01-01

    To ensure the safety and success of future lunar exploration missions, it is important to measure the toxicity of the lunar dust and its electrostatic properties. The electrostatic properties of lunar dust govern its behavior, from how the dust is deposited in an astronaut s lungs to how it contaminates equipment surfaces. NASA has identified the threat caused by lunar dust as one of the top two problems that need to be solved before returning to the Moon. To understand the electrostatic nature of lunar dust, NASA must answer the following questions: (1) how much charge can accumulate on the dust? (2) how long will the charge remain? and (3) can the dust be removed? These questions can be answered by measuring the electrostatic properties of the dust: its volume resistivity, charge decay, charge-to-mass ratio or chargeability, and dielectric properties.

  20. Electrostatic prepregging of thermoplastic matrices

    NASA Technical Reports Server (NTRS)

    Muzzy, John D.; Varughese, Babu; Thammongkol, Vivan; Tincher, Wayne

    1989-01-01

    Thermoplastic towpregs of PEEK/AS-4, PEEK/S-2 glass and LaRC-TPI/AS-4, produced by electrostatic deposition of charged and fluidized polymer powders on spread continuous fiber tows, are described. Processing parameters for combining PEEK 150 powder with unsized 3k AS-4 carbon fiber are presented. The experimental results for PEEK 150/AS-4 reveal that electrostatic fluidized bed coating may be an economically attractive process for producing towpreg.

  1. Fluorescence Reveals Contamination From Adhesives

    NASA Technical Reports Server (NTRS)

    Nikolia, William

    1992-01-01

    Contamination of nearby surfaces from ingredients in some adhesive materials detected by ultraviolet illumination and observation of resulting fluorescence. Identification of contaminants via telltale fluorescence not new; rather, significance lies in method of implementation and potential extension to wider variety of materials and applications.

  2. Polyurethane adhesive ingestion.

    PubMed

    Fitzgerald, Kevin T; Bronstein, Alvin C

    2013-02-01

    Polyurethane adhesives are found in a large number of household products in the United States and are used for a variety of purposes. Several brands of these expanding wood glues (those containing diphenylmethane diisocyanate [MDI]) have the potential to form gastrointestinal (GI) foreign bodies if ingested. The ingested adhesive forms an expanding ball of glue in the esophagus and gastric lumen. This expansion is caused by a polymerization reaction using the heat, water, and gastric acids of the stomach. A firm mass is created that can be 4-8 times its original volume. As little as 2 oz of glue have been reported to develop gastric foreign bodies. The obstructive mass is reported to form within minutes of ingestion of the adhesive. The foreign body can lead to esophageal impaction and obstruction, airway obstruction, gastric outflow obstruction, mucosal hemorrhage, ulceration, laceration, perforation of the esophageal and gastric linings, and death. Clinical signs following ingestion include anorexia, lethargy, vomiting, tachypnea, and abdominal distention and pain, and typically develop within 12 hours. Clinical signs may depend upon the size of the mass. If left untreated, perforation and rupture of the esophagus or stomach can occur. The glue mass does not stick to the GI mucosa and is not always detectable on abdominal palpation. Radiographs are recommended to confirm the presence of the "glue-ball" foreign body, and radiographic evidence of the obstruction may be seen as early as 4-6 hours following ingestion. Emesis is contraindicated owing to the risk of aspiration of the glue into the respiratory tree or the subsequent lodging of the expanding glue mass in the esophagus. Likewise, efforts to dilute the glue and prevent the formation of the foreign body through administration of liquids, activated charcoal, or bulk-forming products to push the foreign body through the GI tract have proven ineffective. Even endoscopy performed to remove the foreign body has

  3. The Exploration Portable Electrostatic Detector (xPED)

    NASA Technical Reports Server (NTRS)

    Jackson, Telana L.; Farrell, William M.

    2012-01-01

    Astronauts and rovers, while exploring dynamic environments, can experience charge buildup through Tribo-charging (contact electrification). Charge levels can become substantially high. especially in areas where photoelectric and plasma currents are reduced (e.g. lunar polar crater). Tribo-charging in areas that have little to no charge dissipative path can be severe, leaving an astronaut or roving object to remain charged for extended periods of time. Charge buildup on space suits and/or rovers is expected to present significant hazards to missions, such as electrostatic discharge and arcing, dust adhesion to space suits/equipment, and destruction of equipment. The avoidance of hazards associated with charge buildup is critical for future NASA missions to near earth objects, the Moon and Mars. The Exploration Portable Electrostatic Device (xPED) will allow astronauts to determine their charge state, and also characterize the electrical environment from their excursions. xPED would benefit manned, as well as robotic missions.

  4. Effects of the electrostatic environment on the Majorana nanowire devices

    NASA Astrophysics Data System (ADS)

    Vuik, A.; Eeltink, D.; Akhmerov, A. R.; Wimmer, M.

    2016-03-01

    One of the promising platforms for creating Majorana bound states is a hybrid nanostructure consisting of a semiconducting nanowire covered by a superconductor. We analyze the previously disregarded role of electrostatic interaction in these devices. Our main result is that Coulomb interaction causes the chemical potential to respond to an applied magnetic field, while spin-orbit interaction and screening by the superconducting lead suppress this response. Consequently, the electrostatic environment influences two properties of Majorana devices: the shape of the topological phase boundary and the oscillations of the Majorana splitting energy. We demonstrate that both properties show a non-universal behavior, and depend on the details of the electrostatic environment. We show that when the wire only contains a single electron mode, the experimentally accessible inverse self-capacitance of this mode fully captures the interplay between electrostatics and Zeeman field. This offers a way to compare theoretical predictions with experiments.

  5. Adhesion as a weapon in microbial competition

    PubMed Central

    Schluter, Jonas; Nadell, Carey D; Bassler, Bonnie L; Foster, Kevin R

    2015-01-01

    Microbes attach to surfaces and form dense communities known as biofilms, which are central to how microbes live and influence humans. The key defining feature of biofilms is adhesion, whereby cells attach to one another and to surfaces, via attachment factors and extracellular polymers. While adhesion is known to be important for the initial stages of biofilm formation, its function within biofilm communities has not been studied. Here we utilise an individual-based model of microbial groups to study the evolution of adhesion. While adhering to a surface can enable cells to remain in a biofilm, consideration of within-biofilm competition reveals a potential cost to adhesion: immobility. Highly adhesive cells that are resistant to movement face being buried and starved at the base of the biofilm. However, we find that when growth occurs at the base of a biofilm, adhesion allows cells to capture substratum territory and force less adhesive, competing cells out of the system. This process may be particularly important when cells grow on a host epithelial surface. We test the predictions of our model using the enteric pathogen Vibrio cholerae, which produces an extracellular matrix important for biofilm formation. Flow cell experiments indicate that matrix-secreting cells are highly adhesive and form expanding clusters that remove non-secreting cells from the population, as predicted by our simulations. Our study shows how simple physical properties, such as adhesion, can be critical to understanding evolution and competition within microbial communities. PMID:25290505

  6. Analysis of the effect of LRP-1 silencing on the invasive potential of cancer cells by nanomechanical probing and adhesion force measurements using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Le Cigne, A.; Chièze, L.; Beaussart, A.; El-Kirat-Chatel, S.; Dufrêne, Y. F.; Dedieu, S.; Schneider, C.; Martiny, L.; Devy, J.; Molinari, M.

    2016-03-01

    Low-density lipoprotein receptor-related protein 1 (LRP-1) can internalize proteases involved in cancer progression and is thus considered a promising therapeutic target. However, it has been demonstrated that LRP-1 is also able to regulate the endocytosis of membrane-anchored proteins. Thus, strategies that target LRP-1 to modulate proteolysis could also affect adhesion and cytoskeleton dynamics. Here, we investigated the effect of LRP-1 silencing on parameters reflecting cancer cells' invasiveness by atomic force microscopy (AFM). The results show that LRP-1 silencing induces changes in the cells' adhesion behavior, particularly the dynamics of cell attachment. Clear alterations in morphology, such as more pronounced stress fibers and increased spreading, leading to increased area and circularity, were also observed. The determination of the cells' mechanical properties by AFM showed that these differences are correlated with an increase in Young's modulus. Moreover, the measurements show an overall decrease in cell motility and modifications of directional persistence. An overall increase in the adhesion force between the LRP-1-silenced cells and a gelatin-coated bead was also observed. Ultimately, our AFM-based force spectroscopy data, recorded using an antibody directed against the β1 integrin subunit, provide evidence that LRP-1 silencing modifies the rupture force distribution. Together, our results show that techniques traditionally used for the investigation of cancer cells can be coupled with AFM to gain access to complementary phenotypic parameters that can help discriminate between specific phenotypes associated with different degrees of invasiveness.Low-density lipoprotein receptor-related protein 1 (LRP-1) can internalize proteases involved in cancer progression and is thus considered a promising therapeutic target. However, it has been demonstrated that LRP-1 is also able to regulate the endocytosis of membrane-anchored proteins. Thus, strategies

  7. Electrostatic Surface Modifications to Improve Gene Delivery

    PubMed Central

    Shmueli, Ron B.; Anderson, Daniel G.

    2010-01-01

    Importance of the field Gene therapy has the potential to treat a wide variety of diseases including genetic diseases and cancer. Areas covered in this review This review introduces biomaterials used for gene delivery and then focuses on the use of electrostatic surface modifications to improve gene delivery materials. These modifications have been used to stabilize therapeutics in vivo, add cell-specific targeting ligands, and promote controlled release. Coatings of nanoparticles and microparticles as well as non-particulate surface coatings are covered in this review. Electrostatic principles are crucial for the development of multilayer delivery structures fabricated by the layer-by-layer method. What the reader will gain The reader will gain knowledge about the composition of biomaterials used for surface modifications and how these coatings and multilayers can be utilized to improve spatial control and efficiency of delivery. Examples are shown for the delivery of nucleic acids, including DNA and siRNA, to in vitro and in vivo systems. Take home message The versatile and powerful approach of electrostatic coatings and multilayers will lead to the development of enhanced gene therapies. PMID:20201712

  8. PH dependent adhesive peptides

    DOEpatents

    Tomich, John; Iwamoto, Takeo; Shen, Xinchun; Sun, Xiuzhi Susan

    2010-06-29

    A novel peptide adhesive motif is described that requires no receptor or cross-links to achieve maximal adhesive strength. Several peptides with different degrees of adhesive strength have been designed and synthesized using solid phase chemistries. All peptides contain a common hydrophobic core sequence flanked by positively or negatively charged amino acids sequences.

  9. Thermal Characterization of Epoxy Adhesive by Hotfire Testing

    NASA Technical Reports Server (NTRS)

    Spomer, Ken A.; Haddock, M. Reed; McCool, Alex (Technical Monitor)

    2001-01-01

    This paper describes subscale solid-rocket motor hot-fire testing of epoxy adhesives in flame surface bondlines to evaluate heat-affected depth, char depth and ablation rate. Hot-fire testing is part of an adhesive down-selection program on the Space Shuttle Solid Rocket Motor Nozzle to provide additional confidence in the down-selected adhesives. The current nozzle structural adhesive bond system is being replaced due to obsolescence. Prior to hot-fire testing, adhesives were tested for chemical, physical and mechanical properties, which resulted in the selection of two potential replacement adhesives, Resin Technology Group's TIGA 321 and 3M's EC2615XLW. Hot-fire testing consisted of four forty-pound charge (FPC) motors fabricated in configurations that would allow side-by-side comparison testing of the candidate replacement adhesives with the current RSRM adhesives. Results of the FPC motor testing show that: 1) the phenolic char depths on radial bondlines is approximately the same and vary depending on the position in the blast tube regardless of which adhesive was used, 2) the replacement candidate adhesive char depths are equivalent to the char depths of the current adhesives, 3) the heat-affected depths of the candidate and current adhesives are equivalent, and 4) the ablation rates for both replacement adhesives were equivalent to the current adhesives.

  10. Spatiotemporal distribution of different extracellular polymeric substances and filamentation mediate Xylella fastidiosa adhesion and biofilm formation

    PubMed Central

    Janissen, Richard; Murillo, Duber M.; Niza, Barbara; Sahoo, Prasana K.; Nobrega, Marcelo M.; Cesar, Carlos L.; Temperini, Marcia L. A.; Carvalho, Hernandes F.; de Souza, Alessandra A.; Cotta, Monica A.

    2015-01-01

    Microorganism pathogenicity strongly relies on the generation of multicellular assemblies, called biofilms. Understanding their organization can unveil vulnerabilities leading to potential treatments; spatially and temporally-resolved comprehensive experimental characterization can provide new details of biofilm formation, and possibly new targets for disease control. Here, biofilm formation of economically important phytopathogen Xylella fastidiosa was analyzed at single-cell resolution using nanometer-resolution spectro-microscopy techniques, addressing the role of different types of extracellular polymeric substances (EPS) at each stage of the entire bacterial life cycle. Single cell adhesion is caused by unspecific electrostatic interactions through proteins at the cell polar region, where EPS accumulation is required for more firmly-attached, irreversibly adhered cells. Subsequently, bacteria form clusters, which are embedded in secreted loosely-bound EPS, and bridged by up to ten-fold elongated cells that form the biofilm framework. During biofilm maturation, soluble EPS forms a filamentous matrix that facilitates cell adhesion and provides mechanical support, while the biofilm keeps anchored by few cells. This floating architecture maximizes nutrient distribution while allowing detachment upon larger shear stresses; it thus complies with biological requirements of the bacteria life cycle. Using new approaches, our findings provide insights regarding different aspects of the adhesion process of X. fastidiosa and biofilm formation. PMID:25891045

  11. Spatiotemporal distribution of different extracellular polymeric substances and filamentation mediate Xylella fastidiosa adhesion and biofilm formation.

    PubMed

    Janissen, Richard; Murillo, Duber M; Niza, Barbara; Sahoo, Prasana K; Nobrega, Marcelo M; Cesar, Carlos L; Temperini, Marcia L A; Carvalho, Hernandes F; de Souza, Alessandra A; Cotta, Monica A

    2015-01-01

    Microorganism pathogenicity strongly relies on the generation of multicellular assemblies, called biofilms. Understanding their organization can unveil vulnerabilities leading to potential treatments; spatially and temporally-resolved comprehensive experimental characterization can provide new details of biofilm formation, and possibly new targets for disease control. Here, biofilm formation of economically important phytopathogen Xylella fastidiosa was analyzed at single-cell resolution using nanometer-resolution spectro-microscopy techniques, addressing the role of different types of extracellular polymeric substances (EPS) at each stage of the entire bacterial life cycle. Single cell adhesion is caused by unspecific electrostatic interactions through proteins at the cell polar region, where EPS accumulation is required for more firmly-attached, irreversibly adhered cells. Subsequently, bacteria form clusters, which are embedded in secreted loosely-bound EPS, and bridged by up to ten-fold elongated cells that form the biofilm framework. During biofilm maturation, soluble EPS forms a filamentous matrix that facilitates cell adhesion and provides mechanical support, while the biofilm keeps anchored by few cells. This floating architecture maximizes nutrient distribution while allowing detachment upon larger shear stresses; it thus complies with biological requirements of the bacteria life cycle. Using new approaches, our findings provide insights regarding different aspects of the adhesion process of X. fastidiosa and biofilm formation. PMID:25891045

  12. TOWARD MINIMALLY ADHESIVE SURFACES UTILIZING SILOXANES

    EPA Science Inventory

    Three types of siloxane-based network polymers have been investigated for their surface properties towards potential applications as minimally adhesive coatings. A filled poly(dimethylsiloxane) (PDMS) elastomer, RTV it, has been studied to determine surface weldability and stabil...

  13. Theoretical studies of "stabilizing" behavior about carbon nanotubes under the electrostatic force.

    PubMed

    Zhao, Hong-Wei; Hu, Li-Chun; Chang, Chun-Rui

    2013-04-01

    We study the dispersion and stability of carbon nanotube (CNT) suspensions under the electrostatic interactions. The potential energies of van der Waals (vdW) attractions between the CNT themselves are obtained on the continuum Lennard-Jones (LJ) model. The potential energies of electrostatic repulsions are based upon the Yukawa-segment model. We explore the overall interactions mediated by the vdW force and the electrostatic force between two identical, parallel CNTs. Consequently, we preliminarily confirm the accuracy and reliability of the electrostatic model. PMID:23763212

  14. Engineering scale electrostatic enclosure demonstration

    SciTech Connect

    Meyer, L.C.

    1993-09-01

    This report presents results from an engineering scale electrostatic enclosure demonstration test. The electrostatic enclosure is part of an overall in-depth contamination control strategy for transuranic (TRU) waste recovery operations. TRU contaminants include small particles of plutonium compounds associated with defense-related waste recovery operations. Demonstration test items consisted of an outer Perma-con enclosure, an inner tent enclosure, and a ventilation system test section for testing electrostatic curtain devices. Three interchangeable test fixtures that could remove plutonium from the contaminated dust were tested in the test section. These were an electret filter, a CRT as an electrostatic field source, and an electrically charged parallel plate separator. Enclosure materials tested included polyethylene, anti-static construction fabric, and stainless steel. The soil size distribution was determined using an eight stage cascade impactor. Photographs of particles containing plutonium were obtained with a scanning electron microscope (SEM). The SEM also provided a second method of getting the size distribution. The amount of plutonium removed from the aerosol by the electrostatic devices was determined by radiochemistry from input and output aerosol samplers. The inner and outer enclosures performed adequately for plutonium handling operations and could be used for full scale operations.

  15. Miniature Bipolar Electrostatic Ion Thruster

    NASA Technical Reports Server (NTRS)

    Hartley, Frank T.

    2006-01-01

    The figure presents a concept of a bipolar miniature electrostatic ion thruster for maneuvering a small spacecraft. The ionization device in the proposed thruster would be a 0.1-micron-thick dielectric membrane with metal electrodes on both sides. Small conical holes would be micromachined through the membrane and electrodes. An electric potential of the order of a volt applied between the membrane electrodes would give rise to an electric field of the order of several mega-volts per meter in the submicron gap between the electrodes. An electric field of this magnitude would be sufficient to ionize all the molecules that enter the holes. In a thruster-based on this concept, one or more propellant gases would be introduced into such a membrane ionizer. Unlike in larger prior ion thrusters, all of the propellant molecules would be ionized. This thruster would be capable of bipolar operation. There would be two accelerator grids - one located forward and one located aft of the membrane ionizer. In one mode of operation, which one could denote the forward mode, positive ions leaving the ionizer on the backside would be accelerated to high momentum by an electric field between the ionizer and an accelerator grid. Electrons leaving the ionizer on the front side would be ejected into free space by a smaller accelerating field. The equality of the ion and electron currents would eliminate the need for an additional electron- or ion-emitting device to keep the spacecraft charge-neutral. In another mode of operation, which could denote the reverse mode, the polarities of the voltages applied to the accelerator grids and to the electrodes of the membrane ionizer would be the reverse of those of the forward mode. The reversal of electric fields would cause the ion and electrons to be ejected in the reverse of their forward mode directions, thereby giving rise to thrust in the direction opposite that of the forward mode.

  16. SPARCLE: Electrostatic Tool for Lunar Dust Control

    SciTech Connect

    Clark, P. E.; Curtis, S. A.; Minetto, F.; Cheung, C. Y.; Keller, J. F.; Moore, M.; Calle, C. I.

    2009-03-16

    Successful exploration of most planetary surfaces, with their impact-generated dusty regoliths, will depend on the capabilities to keep surfaces free of the dust which could compromise performance and to collect dust for characterization. Solving the dust problem is essential before we return to the Moon. During the Apollo missions, the discovery was made that regolith fines, or dust, behaved like abrasive velcro, coating surfaces, clogging mechanisms, and making movement progressively more difficult as it was mechanically stirred up during surface operations, and abrading surfaces, including spacesuits, when attempts were made to remove it manually. In addition, some of the astronauts experienced breathing difficulties when exposed to dust that got into the crew compartment. The successful strategy will deal with dust dynamics resulting from interaction between mechanical and electrostatic forces. Here we will describe the surface properties of dust particles, the basis for their behavior, and an electrostatically-based approach and methodology for addressing this issue confirmed by our preliminary results. Our device concept utilizes a focused electron beam to control the electrostatic potential of the surface. A plate of the opposite potential is then used to induce dust migration in the presence of an electrical field. Our goal is a compact device of <5 kg mass and using <5 watts of power to be operational in <5 years with heritage from ionic sweepers for active spacecraft potential control (e.g., on POLAR). Rovers could be fitted with devices that could harness the removal of dust for sampling as part of the extended exploration process on Mercury, Mars, asteroids or outer solar system satellites, as well as the Moon.

  17. A Solvatochromic Model Calibrates Nitriles’ Vibrational Frequencies to Electrostatic Fields

    PubMed Central

    Bagchi, Sayan; Fried, Stephen D.; Boxer, Steven G.

    2012-01-01

    Electrostatic interactions provide a primary connection between a protein’s three-dimensional structure and its function. Infrared (IR) probes are useful because vibrational frequencies of certain chemical groups, such as nitriles, are linearly sensitive to local electrostatic field, and can serve as a molecular electric field meter. IR spectroscopy has been used to study electrostatic changes or fluctuations in proteins, but measured peak frequencies have not been previously mapped to total electric fields, because of the absence of a field-frequency calibration and the complication of local chemical effects such as H-bonds. We report a solvatochromic model that provides a means to assess the H-bonding status of aromatic nitrile vibrational probes, and calibrates their vibrational frequencies to electrostatic field. The analysis involves correlations between the nitrile’s IR frequency and its 13C chemical shift, whose observation is facilitated by a robust method for introducing isotopes into aromatic nitriles. The method is tested on the model protein Ribonuclease S (RNase S) containing a labeled p-CN-Phe near the active site. Comparison of the measurements in RNase S against solvatochromic data gives an estimate of the average total electrostatic field at this location. The value determined agrees quantitatively with MD simulations, suggesting broader potential for the use of IR probes in the study of protein electrostatics. PMID:22694663

  18. Magnetic Insulation for Electrostatic Accelerators

    SciTech Connect

    Grisham, L. R.

    2011-09-26

    The voltage gradient which can be sustained between electrodes without electrical breakdowns is usually one of the most important parameters in determining the performance which can be obtained in an electrostatic accelerator. We have recently proposed a technique which might permit reliable operation of electrostatic accelerators at higher electric field gradients, perhaps also with less time required for the conditioning process in such accelerators. The idea is to run an electric current through each accelerator stage so as to produce a magnetic field which envelopes each electrode and its electrically conducting support structures. Having the magnetic field everywhere parallel to the conducting surfaces in the accelerator should impede the emission of electrons, and inhibit their ability to acquire energy from the electric field, thus reducing the chance that local electron emission will initiate an arc. A relatively simple experiment to assess this technique is being planned. If successful, this technique might eventually find applicability in electrostatic accelerators for fusion and other applications.

  19. Surface electrostatics: theory and computations

    PubMed Central

    Chatzigeorgiou, G.; Javili, A.; Steinmann, P.

    2014-01-01

    The objective of this work is to study the electrostatic response of materials accounting for boundary surfaces with their own (electrostatic) constitutive behaviour. The electric response of materials with (electrostatic) energetic boundary surfaces (surfaces that possess material properties and constitutive structures different from those of the bulk) is formulated in a consistent manner using a variational framework. The forces and moments that appear due to bulk and surface electric fields are also expressed in a consistent manner. The theory is accompanied by numerical examples on porous materials using the finite-element method, where the influence of the surface electric permittivity on the electric displacement, the polarization stress and the Maxwell stress is examined. PMID:24711720

  20. Turbulence in electrostatic ion acoustic shocks

    NASA Technical Reports Server (NTRS)

    Means, R. W.; Coroniti, F. V.; Wong, A. Y.; White, R. B.

    1973-01-01

    Three types of collisionless electrostatic ion acoustic shocks are investigated using a double plasma (DP) device: (1) laminar shocks; (2) small amplitude turbulent shocks in which the turbulence is confined to be upstream of the shock potential jump; and (3) large amplitude turbulent shocks in which the wave turbulence occurs throughout the shock transition. The wave turbulence is generated by ions which are reflected from the shock potential; linear theory spatial growth increments agree with experimental values. The experimental relationship between the shock Mach number and the shock potential is shown to be inconsistent with theoretical shock models which assume that the electrons are isothermal. Theoretical calculations which assume a trapped electron equation of a state and a turbulently flattened velocity distrubution function for the reflected ions yields a Mach number vs potential relationship in agreement with experiment.

  1. Electrostatic model of radial pn junction nanowires

    NASA Astrophysics Data System (ADS)

    Chia, A. C. E.; LaPierre, R. R.

    2013-08-01

    Poisson's equation is solved for a radial pn junction nanowire (NW) with surface depletion. This resulted in a model capable of giving radial energy band and electric field profiles for any arbitrary core/shell doping density, core/shell dimensions, and surface state density. Specific cases were analyzed to extract pertinent underlying physics, while the relationship between NW specifications and the depletion of the NW were examined to optimize the built-in potential across the junction. Additionally, the model results were compared with experimental results in literature to good agreement. Finally, an optimum device design is proposed to satisfy material, optical, and electrostatic constraints in high efficiency NW solar cells.

  2. Critical length scale controls adhesive wear mechanisms

    PubMed Central

    Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois

    2016-01-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270

  3. Critical length scale controls adhesive wear mechanisms.

    PubMed

    Aghababaei, Ramin; Warner, Derek H; Molinari, Jean-Francois

    2016-01-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270

  4. Critical length scale controls adhesive wear mechanisms

    NASA Astrophysics Data System (ADS)

    Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois

    2016-06-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients.

  5. Outer Membrane Remodeling: The Structural Dynamics and Electrostatics of Rough Lipopolysaccharide Chemotypes.

    PubMed

    Dias, Roberta P; da Hora, Gabriel C A; Ramstedt, Madeleine; Soares, Thereza A

    2014-06-10

    Lipopolysaccharides (LPS) are the primary constituent of the outer membrane of Gram-negative bacteria such as Pseudomonas aeruginosa. Gram-negative bacteria can synthesize modified forms of LPS in response to environmental stimuli or due to genetic mutations, a process known as outer membrane remodeling. Chemical modifications of the LPS modulate the integrity and antibiotic susceptibility of bacterial outer membranes. It also governs microbial adhesion to tissues and artificial material surfaces. We have extended a previous model of the rough LPS to include four novel chemotypes rmlC, galU, LPS Re, and Lipid-A. Atomistic molecular dynamics (MD) simulations were performed for outer membrane models constituted of each LPS chemotypes and 1,2-dipalmitoyl-3-phosphatidylethanolamine. It is shown that the decrease in the LPS polysaccharide chain length leads to a significant increase in the diffusion coefficients for the Ca(2+) counterions, increase in acyl chain packing (decrease in membrane fluidity), and attenuation of the negative potential across the LPS surface as positive counterions becomes more exposed to the solvent. The electrostatic potential on the LPS surfaces reflects heterogeneous charge distributions with increasingly larger patches of positive and negative potentials as the polysaccharide chain length decreases. Such a pattern originates from the spatial arrangement of charged phosphate-Ca(2+) clusters in the LPS inner-core that becomes exposed in the membrane surface as monosaccharide units are lost in the shortest chemotypes LPS Re and Lipid-A. These MD-derived conformational ensembles reproduce experimental trends and provide atom-level structural information on the rough LPS chemotypes that can help to rationalize antibiotic resistance and bacterial adhesion processes. PMID:26580769

  6. Polarizable multipolar electrostatics for cholesterol

    NASA Astrophysics Data System (ADS)

    Fletcher, Timothy L.; Popelier, Paul L. A.

    2016-08-01

    FFLUX is a novel force field under development for biomolecular modelling, and is based on topological atoms and the machine learning method kriging. Successful kriging models have been obtained for realistic electrostatics of amino acids, small peptides, and some carbohydrates but here, for the first time, we construct kriging models for a sizeable ligand of great importance, which is cholesterol. Cholesterol's mean total (internal) electrostatic energy prediction error amounts to 3.9 kJ mol-1, which pleasingly falls below the threshold of 1 kcal mol-1 often cited for accurate biomolecular modelling. We present a detailed analysis of the error distributions.

  7. Charge sniffer for electrostatics demonstrations

    NASA Astrophysics Data System (ADS)

    Dinca, Mihai P.

    2011-02-01

    An electronic electroscope with a special design for demonstrations and experiments on static electricity is described. It operates as an electric charge sniffer by detecting slightly charged objects when they are brought to the front of its sensing electrode. The sniffer has the advantage of combining high directional sensitivity with a logarithmic bar display. It allows for the identification of electric charge polarity during charge separation by friction, peeling, electrostatic induction, batteries, or secondary coils of power transformers. Other experiments in electrostatics, such as observing the electric field of an oscillating dipole and the distance dependence of the electric field generated by simple charge configurations, are also described.

  8. Electrostatically actuatable light modulating device

    DOEpatents

    Koehler, Dale R.

    1991-01-01

    The electrostatically actuatable light modulator utilizes an opaque substrate plate patterned with an array of aperture cells, the cells comprised of physically positionable dielectric shutters and electrostatic actuators. With incorporation of a light source and a viewing screen, a projection display system is effected. Inclusion of a color filter array aligned with the aperture cells accomplishes a color display. The system is realized in terms of a silicon based manufacturing technology allowing fabrication of a high resolution capability in a physically small device which with the utilization of included magnification optics allows both large and small projection displays.

  9. Analyzing electrostatic induced damage risk to reticles with an in situ e-reticle system

    NASA Astrophysics Data System (ADS)

    Tu, Richard; Sebald, Thomas

    2009-12-01

    E-Reticle system is an electrostatic field test device, which has the form factor of a conventional six inch quartz production reticle. The E-Reticle was used to assess the ESD damage risks in a mask cleaning tool. Test results indicate that a reticle may see higher than ITRS recommended electrostatic potential specifications when mechanical operations and cold DIW rinse start and in progress, hence seeing increased probability of electrostatic induced damages.

  10. Enteral n-3 fatty acids and micronutrients enhance percentage of positive neutrophil and lymphocyte adhesion molecules: a potential mediator of pressure ulcer healing in critically ill patients.

    PubMed

    Theilla, Miriam; Schwartz, Betty; Zimra, Yael; Shapiro, Haim; Anbar, Ronit; Rabizadeh, Esther; Cohen, Jonathan; Singer, Pierre

    2012-04-01

    n-3 Fatty acids are recognised as influencing both wound healing and immunity. We assessed the impact of a fish oil- and micronutrient-enriched formula (study formula) on the healing of pressure ulcers and on immune function in critically ill patients in an intensive care unit. A total of forty patients with pressure ulcers and receiving nutritional support were enrolled (intervention group, n 20, received study formula; and a control group, n 20, received an isoenergetic formula). Total and differential leucocyte count and percentage of adhesion molecule positive granulocyte and lymphocyte cells (CD11a, CD11b, CD18 and CD49b) were measured on days 0, 7 and 14. Percentage of positive lymphocytes for CD54, CD49b, CD49d and CD8 were also measured on days 0, 7 and 14. The state of pressure ulcers was assessed by using the pressure ulcer scale for healing tool score on days 7, 14 and 28 of treatment. No between-group differences in patient demographics, anthropometry or diagnostic class were observed. Patients who received the study formula showed significant increases in the percentage of positive CD18 and CD11a lymphocytes and of CD49b granulocytes as compared to controls (P < 0·05). While the severity of pressure ulcers was not significantly different between the two groups on admission, severity increased significantly over time for the control group (P < 0·05), but not for the study group. The present study suggests that a fish oil- and micronutrient-enriched formula may prevent worsening of pressure ulcers and that this effect may be mediated by an effect on adhesion molecule expression. PMID:22040465

  11. Bridging implicit and explicit solvent approaches for membrane electrostatics.

    PubMed Central

    Lin, Jung-Hsin; Baker, Nathan A; McCammon, J Andrew

    2002-01-01

    Conformations of a zwitterionic bilayer were sampled from a molecular dynamics simulation and their electrostatic properties analyzed by solution of the Poisson equation. These traditionally implicit electrostatic calculations were performed in the presence of varying amounts of explicit solvent to assess the magnitude of error introduced by a uniform dielectric description of water surrounding the bilayer. It was observed that membrane dipole potential calculations in the presence of explicit water were significantly different than wholly implicit solvent calculations with the calculated dipole potential converging to a reasonable value when four or more hydration layers were included explicitly. PMID:12202363

  12. Ion beam probing of electrostatic fields

    NASA Technical Reports Server (NTRS)

    Persson, H.

    1979-01-01

    The determination of a cylindrically symmetric, time-independent electrostatic potential V in a magnetic field B with the same symmetry by measurements of the deflection of a primary beam of ions is analyzed and substantiated by examples. Special attention is given to the requirements on canonical angular momentum and total energy set by an arbitrary, nonmonotone V, to scaling laws obtained by normalization, and to the analogy with ionospheric sounding. The inversion procedure with the Abel analysis of an equivalent problem with a one-dimensional fictitious potential is used in a numerical experiment with application to the NASA Lewis Modified Penning Discharge. The determination of V from a study of secondary beams of ions with increased charge produced by hot plasma electrons is also analyzed, both from a general point of view and with application to the NASA Lewis SUMMA experiment. Simple formulas and geometrical constructions are given for the minimum energy necessary to reach the axis, the whole plasma, and any point in the magnetic field. The common, simplifying assumption that V is a small perturbation is critically and constructively analyzed; an iteration scheme for successively correcting the orbits and points of ionization for the electrostatic potential is suggested.

  13. Evaluation of high temperature structural adhesives for extended service

    NASA Technical Reports Server (NTRS)

    Hendricks, C. L.; Hill, S. G.

    1984-01-01

    High temperature stable adhesive systems were evaluated for potential Supersonic Cruise Research (SCR) vehicle applications. The program was divided into two major phases: Phase I 'Adhesive Screening' evaluated eleven selected polyimide (PI) and polyphenylquinoxaline (PPQ) adhesive resins using eight different titanium (6Al-4V) adherend surface preparations; Phase II 'Adhesive Optimization and Characterization' extensively evaluated two adhesive systems, selected from Phase I studies, for chemical characterization and environmental durability. The adhesive systems which exhibited superior thermal and environmental bond properties were LARC-TPI polyimide and polyphenylquinoxaline both developed at NASA Langley. The latter adhesive system did develop bond failures at extended thermal aging due primarily to incompatibility between the surface preparation and the polymer. However, this study did demonstrate that suitable adhesive systems are available for extended supersonic cruise vehicle design applications.

  14. Discriminatory bio-adhesion over nano-patterned polymer brushes

    NASA Astrophysics Data System (ADS)

    Gon, Saugata

    1000/mum 2) was required for fibrinogen adsorption while a greater density comprised the adhesion threshold for albumin. Surface compositions between these two thresholds discriminated binding of the two proteins. The binding behavior of the two proteins from a mixture was well anticipated by the single- protein binding behaviors of the individual proteins. The mechanism for protein capture was shown to be multivalent: protein adhesion always occurred for averages spacings of the adhesive patches smaller than the dimensions of the protein of interest. For some backfill brush architectures, the spacing between the patches at the threshold for protein capture clearly corresponded to the major dimension of the target protein. For more dense PEG brush backfills however, larger adhesion thresholds were observed, corresponding to greater numbers of patches involved with the adhesion of each protein molecule. . The thesis demonstrates the tuning of the position of the adhesion thresholds, using fibrinogen as a model protein, using variations in brush properties and ionic strength. The directions of the trends indicate that the brushes do indeed exert steric repulsions toward the proteins while the attractions are electrostatic in nature. The surfaces also demonstrated sharp adhesion thresholds for S. Aureus bacteria, at smaller concentrations of adhesive surfaces elements than those needed for the protein capture. The results suggest that bacteria may be captured while proteins are rejected from these surfaces, and there may be potential to discriminate different bacterial types. Such discrimination from protein-containing bacterial suspensions was investigated briefly in this thesis using S. Aureus and fibrinogen as a model mixture. However, due to binding of fibrinogen to the bacterial surface, the separation did not succeed. It is still expected, however, that these surfaces could be used to selectively capture bacteria in the presence of non-interacting proteins. The

  15. Adhesion force studies of nanofibers and nanoparticles.

    PubMed

    Xing, Malcolm; Zhong, Wen; Xu, Xiuling; Thomson, Douglas

    2010-07-20

    Surface adhesion between nanofibers and nanoparticles has attracted attention for potential biomedical applications, but the measurement has not been reported. Adhesion forces were measured using a polystyrene (PS) nanoparticle attached to an atomic force microscopy (AFM) tip/probe. Electrospun PS nanofibers of different diameters were tapped with the probe to study the effect of fiber diameters on adhesion force. Both AFM experiments and numerical models suggest that the adhesion force increases with increased fiber diameters. Numerical models further demonstrated that local deformation of the fiber surface, including the flattening of surface asperities and the nanofiber wrapping around the particle during contact, may have a significant impact on the adhesion force. The adhesion forces are in the order of 100 nN, much smaller than the adhesion forces of the gecko foot hair, but much larger than that of the receptor-ligand pair, antibody-antigen pair, and single-stranded DNA from a substrate. Adhesion forces of nanofibers with roughness were predicted by numerical analysis. This study is expected to provide approaches and information useful in the design of nanomedicine and scaffold based on nanofibers for tissue engineering and regenerative medicine. PMID:20552953

  16. Adhesions and Adhesiolysis: The Role of Laparoscopy

    PubMed Central

    Kavic, Suzanne M.

    2002-01-01

    Background: Adhesions commonly result from abdominal and pelvic surgical procedures and may result in intestinal obstruction, infertility, chronic pain, or complicate subsequent operations. Laparoscopy produces less peritoneal trauma than does conventional laparotomy and may result in decreased adhesion formation. We present a review of the available data on laparoscopy and adhesion formation, as well as laparoscopic adhesiolysis. We also review current adjuvant techniques that may be used by practicing laparoscopists to prevent adhesion formation. Database: A Medline search using “adhesions,” “adhesiolysis,” and “laparoscopy” as key words was performed for English-language articles. Further references were obtained through cross-referencing the bibliography cited in each work. Discussion: The majority of studies indicate that laparoscopy may reduce postoperative adhesion formation relative to laparotomy. However, laparoscopy by itself does not appear to eliminate adhesions completely. A variety of adjuvant materials are available to surgeons, and the most recent investigation has demonstrated significant potential for intraperitoneal barriers. Newer technologies continue to evolve and should result in clinically relevant reductions in adhesion formation. PMID:12113430

  17. Nature of the adhesion bond between epoxy adhesive and steel

    NASA Astrophysics Data System (ADS)

    Vettegren', V. I.; Mamalimov, R. I.; Savitskii, A. V.; Shcherbakov, I. P.; Sytov, V. V.; Sytov, V. A.

    2014-03-01

    The potential difference that appears in the epoxy resin located between two grade 3 steel plates is studied. One of them is stored in epoxy resin to reach equilibrium, and the second plate is coated with an asprepared mixture of epoxy resin with a hardener. It is found that the potential difference decreases in time because of charge transfer by Fe2+ ions through epoxy resin. The luminescence and infrared absorption spectra of the epoxy adhesive on the grade 3 steel surface are recorded. An analysis of these spectra shows that Fe2+ ions penetrate into the as-prepared mixture of epoxy resin with the hardener, and interact with CN groups in the mixture, and form coordination compounds. As a result, a diffusion layer saturated by the coordination compounds forms at the interface between the steel and the adhesive.

  18. Electrostatic properties of two porin channels from Escherichia coli.

    PubMed

    Karshikoff, A; Spassov, V; Cowan, S W; Ladenstein, R; Schirmer, T

    1994-07-22

    The electrostatic interactions in the channels of OmpF and PhoE porins from Escherichia coli were analysed on the basis of a macroscopic multi-dielectric model of the protein-membrane complex derived from the respective porin X-ray structures. The membrane was represented as layers of distinct dielectric constants corresponding to the aliphatic core and the polar head groups of the lipids. The pKa values of the titratable groups and the electrostatic field in the region of the channel were calculated by the finite difference technique. In spite of the differences in sequences and charge constellations, the calculated electrostatic properties of the two porins are similar in several aspects: (1) unusual titration behaviour (pKa below 7) was found for some groups of the cluster of basic residues at the constriction of the pore; (2) a number of acidic groups buried between the internal loop and the barrel wall are stabilized in their protonated forms at neutral pH; (3) there is a strong transverse electrostatic field in the channel characterized by a screw-like form. The strength of the field is greatest at the region of the constriction zone. This would facilitate the diffusion of solutes with a large dipole moment such as free amino acids. Differences between the electrostatic fields of OmpF and PhoE are mainly confined to that end of the pore that faces the cell exterior in vivo. In OmpF the electrostatic potential is close to zero in this region of the channel, whereas a positive potential was found in PhoE. It was shown that the experimentally observed difference in ion selectivity of the two porins can largely be attributed to this distinct electrostatic property. PMID:8035460

  19. Atomic processes in Inertial Electrostatic Confinement (IEC) devices

    SciTech Connect

    Nebel, R.A.; Turner, L.; Tiouririne, T.N.; Barnes, D.C.; Nystrom, W.D.; Bussard, R.W.

    1993-12-31

    Inertial Electrostatic Confinement (IEC) is one of the earliest plasma confinement concepts, having first been suggested by P. T. Farnsworth in the 1950s. The concept involves a simple apparatus of concentric spherical electrostatic grids or a combination of grids and magnetic fields. An electrostatic structure is formed from the confluence of electron or ion beams. Gridded IEC systems have demonstrated neutron yields as high as 2*10{sup 10} neutrons/sec. These systems have considerable potential as small, inexpensive, portable neutron sources for assaying applications. Neutron tomography is also a potential application. Atomic physics effects strongly influence the performance of all of these systems. Important atomic effects include elastic scattering, ionization, excitation, and charge exchange. This paper discusses how an IEC system is influenced by these effects and how to design around them. Theoretical modeling and experimental results are presented.

  20. Inertial electrostatic confinement I(IEC) neutron sources

    SciTech Connect

    Nebel, R.A.; Barnes, D.C.; Caramana, E.J.; Janssen, R.D.; Nystrom, W.D.; Tiouririne, T.N.; Trent, B.C.; Miley, G.H.; Javedani, J.

    1995-12-01

    Inertial Electrostatic Confinement (IEC) is one of the earliest plasma confinement concepts, having first been suggested by P.T. Farnsworth in the 1950s. The concept involves a simple apparatus of concentric spherical electrostatic grids or a combination of grids and magnetic fields. An electrostatic structure is formed from the confluence of electron or ion beams. Gridded IEC systems have demonstrated neutron yields as high as 2*10 [10]. neutrons/sec in steady state. These systems have considerable potential as small, inexpensive, portable neutron sources for assaying applications. Neutron tomography is also a potential application. This paper discusses the IEC concept and how it can be adapted to a steady-state assaying source and an intense pulsed neutron source. Theoretical modeling and experimental results are presented.

  1. First-principles simulations of electrostatic interactions between dust grains

    SciTech Connect

    Itou, H. Amano, T.; Hoshino, M.

    2014-12-15

    We investigated the electrostatic interaction between two identical dust grains of an infinite mass immersed in homogeneous plasma by employing first-principles N-body simulations combined with the Ewald method. We specifically tested the possibility of an attractive force due to overlapping Debye spheres (ODSs), as was suggested by Resendes et al. [Phys. Lett. A 239, 181–186 (1998)]. Our simulation results demonstrate that the electrostatic interaction is repulsive and even stronger than the standard Yukawa potential. We showed that the measured electric field acting on the grain is highly consistent with a model electrostatic potential around a single isolated grain that takes into account a correction due to the orbital motion limited theory. Our result is qualitatively consistent with the counterargument suggested by Markes and Williams [Phys. Lett. A 278, 152–158 (2000)], indicating the absence of the ODS attractive force.

  2. Electrostatic Precipitator (ESP) TRAINING MANUAL

    EPA Science Inventory

    The manual assists engineers in using a computer program, the ESPVI 4.0W, that models all elements of an electrostatic precipitator (ESP). The program is a product of the Electric Power Research Institute and runs in the Windows environment. Once an ESP is accurately modeled, the...

  3. ELECTROSTATIC STIMULATION OF FABRIC FILTRATION

    EPA Science Inventory

    The paper gives results of an investigation of the concept of electrostatic stimulation of fabric filtration (ESFF) at pilot scale. The pilot unit consisted of a conventional baghouse in parallel with an ESFF baghouse, allowing direct comparison. Reported results are for pulse-cl...

  4. Resistivity Problems in Electrostatic Precipitation

    ERIC Educational Resources Information Center

    White, Harry J.

    1974-01-01

    The process of electrostatic precipitation has ever-increasing application in more efficient collection of fine particles from industrial air emissions. This article details a large number of new developments in the field. The emphasis is on high resistivity particles which are a common cause of poor precipitator performance. (LS)

  5. Electrostatic Charging of the Pathfinder Rover

    NASA Technical Reports Server (NTRS)

    Siebert, Mark W.; Kolecki, Joseph C.

    1996-01-01

    The Mars Pathfinder mission will send a lander and a rover to the martian surface. Because of the extremely dry conditions on Mars, electrostatic charging of the rover is expected to occur as it moves about. Charge accumulation may result in high electrical potentials and discharge through the martian atmosphere. Such discharge could interfere with the operation of electrical elements on the rover. A strategy was sought to mitigate this charge accumulation as a precautionary measure. Ground tests were performed to demonstrate charging in laboratory conditions simulating the surface conditions expected at Mars. Tests showed that a rover wheel, driven at typical rover speeds, will accumulate electrical charge and develop significant electrical potentials (average observed, 110 volts). Measurements were made of wheel electrical potential, and wheel capacitance. From these quantities, the amount of absolute charge was estimated. An engineering solution was developed and recommended to mitigate charge accumulation. That solution has been implemented on the actual rover.

  6. Reversible Thermoset Adhesives

    NASA Technical Reports Server (NTRS)

    Mac Murray, Benjamin C. (Inventor); Tong, Tat H. (Inventor); Hreha, Richard D. (Inventor)

    2016-01-01

    Embodiments of a reversible thermoset adhesive formed by incorporating thermally-reversible cross-linking units and a method for making the reversible thermoset adhesive are provided. One approach to formulating reversible thermoset adhesives includes incorporating dienes, such as furans, and dienophiles, such as maleimides, into a polymer network as reversible covalent cross-links using Diels Alder cross-link formation between the diene and dienophile. The chemical components may be selected based on their compatibility with adhesive chemistry as well as their ability to undergo controlled, reversible cross-linking chemistry.

  7. Adhesion at metal interfaces

    NASA Technical Reports Server (NTRS)

    Banerjea, Amitava; Ferrante, John; Smith, John R.

    1991-01-01

    A basic adhesion process is defined, the theory of the properties influencing metallic adhesion is outlined, and theoretical approaches to the interface problem are presented, with emphasis on first-principle calculations as well as jellium-model calculations. The computation of the energies of adhesion as a function of the interfacial separation is performed; fully three-dimensional calculations are presented, and universality in the shapes of the binding energy curves is considered. An embedded-atom method and equivalent-crystal theory are covered in the framework of issues involved in practical adhesion.

  8. Planar geometry inertial electrostatic confinement fusion device

    NASA Astrophysics Data System (ADS)

    Knapp, Daniel R.

    2015-03-01

    In the classic gridded inertial electrostatic confinement (IEC) fusion reactor, ion bombardment of the grid leads to heating, thermionic electron emission, significant power loss, and ultimately melting of the grid. Gridless IEC devices have sought to overcome these limitations. Klein reported a gridless device in which ions are circulated as a linear beam in an electrostatic analogue of an optical resonator. To overcome limits of stored ions due to space charge effects at the turning regions, the device employed multiple overlapping traps. The work reported here seeks to further increase the turning region space in a gridless trap by employing a planar geometry. Ion trapping in the planar device was examined by simulating trajectories of 2H+ ions with SIMION 8.1 software. Simulations were carried out using multiple potentials as in Klein's device and for a single potential trap as a planar analogue of the anharmonic ion trap. Scattering by background gas was simulated using a hard sphere collision model, and the results suggested the device will require operation at low pressure with a separate ion source.

  9. Design considerations in the creation and maintenance of electrostatic cleanliness for solar electrically propelled spacecraft

    NASA Technical Reports Server (NTRS)

    Sellen, J. M., Jr.; Fitzgerald, D. J.

    1975-01-01

    Charge build-up on spacecraft surfaces and resulting zones of electrostatic contamination have been examined for electrically active and electrically passive spacecraft with both conducting and dielectric surface materials, illuminated and nonilluminated surface conditions, and for both inclusion and neglect of free charge effects from photocurrents and ambient space plasma particles. Techniques for measurement and reduction of electrostatic contamination zone extent have been developed for spacecraft with charge release capability. Indicated limitations for contamination cleanup are about 1 volt potential variation from spacecraft to ambient plasma. Bandwidths of electrostatic monitoring and clamping devices extend to several hundred kilohertz for both DC and 'broadband' AC electrostatic cleanliness.

  10. Electrostatically stricted polymers (ESSP)

    NASA Astrophysics Data System (ADS)

    Liu, Chang; Bar-Cohen, Yoseph; Leary, Sean P.

    1999-05-01

    Miniature, lightweight, miser actuators that operate similar to biological muscles can be used to develop robotic devices with unmatched capabilities and impact many technology areas. Electroactive polymers (EAP) offer the potential to producing such actuators and their main attractive feature is their ability to induce relatively large bending or longitudinal strain. Generally, these materials produce a relatively low force and the applications that can be considered at the current state of the art are relatively limited. While improved material are being developed there is a need for methods to develop longitudinal actuators that can contract similar to muscles. In addition, it is desirable to have these actuators in a fiber form that can be bundled to provide the necessary characteristics of stiffness, fracture toughness, resilience and large force actuation. To address this need efforts were made to develop both the material basis as well as the electromechanical modeling of the actuator.

  11. Sticky Matrix: Adhesion Mechanism of the Staphylococcal Polysaccharide Intercellular Adhesin.

    PubMed

    Formosa-Dague, Cécile; Feuillie, Cécile; Beaussart, Audrey; Derclaye, Sylvie; Kucharíková, Soňa; Lasa, Iñigo; Van Dijck, Patrick; Dufrêne, Yves F

    2016-03-22

    The development of bacterial biofilms on surfaces leads to hospital-acquired infections that are difficult to fight. In Staphylococci, the cationic polysaccharide intercellular adhesin (PIA) forms an extracellular matrix that connects the cells together during biofilm formation, but the molecular forces involved are unknown. Here, we use advanced force nanoscopy techniques to unravel the mechanism of PIA-mediated adhesion in a clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) strain. Nanoscale multiparametric imaging of the structure, adhesion, and elasticity of bacteria expressing PIA shows that the cells are surrounded by a soft and adhesive matrix of extracellular polymers. Cell surface softness and adhesion are dramatically reduced in mutant cells deficient for the synthesis of PIA or under unfavorable growth conditions. Single-cell force spectroscopy demonstrates that PIA promotes cell-cell adhesion via the multivalent electrostatic interaction with polyanionic teichoic acids on the S. aureus cell surface. This binding mechanism rationalizes, at the nanoscale, the well-known ability of PIA to strengthen intercellular adhesion in staphylococcal biofilms. Force nanoscopy offers promising prospects for understanding the fundamental forces in antibiotic-resistant biofilms and for designing anti-adhesion compounds targeting matrix polymers. PMID:26908275

  12. Peritoneal adhesions after laparoscopic gastrointestinal surgery

    PubMed Central

    Mais, Valerio

    2014-01-01

    Although laparoscopy has the potential to reduce peritoneal trauma and post-operative peritoneal adhesion formation, only one randomized controlled trial and a few comparative retrospective clinical studies have addressed this issue. Laparoscopy reduces de novo adhesion formation but has no efficacy in reducing adhesion reformation after adhesiolysis. Moreover, several studies have suggested that the reduction of de novo post-operative adhesions does not seem to have a significant clinical impact. Experimental data in animal models have suggested that CO2 pneumoperitoneum can cause acute peritoneal inflammation during laparoscopy depending on the insufflation pressure and the surgery duration. Broad peritoneal cavity protection by the insufflation of a low-temperature humidified gas mixture of CO2, N2O and O2 seems to represent the best approach for reducing peritoneal inflammation due to pneumoperitoneum. However, these experimental data have not had a significant impact on the modification of laparoscopic instrumentation. In contrast, surgeons should train themselves to perform laparoscopy quickly, and they should complete their learning curves before testing chemical anti-adhesive agents and anti-adhesion barriers. Chemical anti-adhesive agents have the potential to exert broad peritoneal cavity protection against adhesion formation, but when these agents are used alone, the concentrations needed to prevent adhesions are too high and could cause major post-operative side effects. Anti-adhesion barriers have been used mainly in open surgery, but some clinical data from laparoscopic surgeries are already available. Sprays, gels, and fluid barriers are easier to apply in laparoscopic surgery than solid barriers. Results have been encouraging with solid barriers, spray barriers, and gel barriers, but they have been ambiguous with fluid barriers. Moreover, when barriers have been used alone, the maximum protection against adhesion formation has been no greater than

  13. Quantitative nanoscale electrostatics of viruses

    NASA Astrophysics Data System (ADS)

    Hernando-Pérez, M.; Cartagena-Rivera, A. X.; Lošdorfer Božič, A.; Carrillo, P. J. P.; San Martín, C.; Mateu, M. G.; Raman, A.; Podgornik, R.; de Pablo, P. J.

    2015-10-01

    Electrostatics is one of the fundamental driving forces of the interaction between biomolecules in solution. In particular, the recognition events between viruses and host cells are dominated by both specific and non-specific interactions and the electric charge of viral particles determines the electrostatic force component of the latter. Here we probe the charge of individual viruses in liquid milieu by measuring the electrostatic force between a viral particle and the Atomic Force Microscope tip. The force spectroscopy data of co-adsorbed φ29 bacteriophage proheads and mature virions, adenovirus and minute virus of mice capsids is utilized for obtaining the corresponding density of charge for each virus. The systematic differences of the density of charge between the viral particles are consistent with the theoretical predictions obtained from X-ray structural data. Our results show that the density of charge is a distinguishing characteristic of each virus, depending crucially on the nature of the viral capsid and the presence/absence of the genetic material.Electrostatics is one of the fundamental driving forces of the interaction between biomolecules in solution. In particular, the recognition events between viruses and host cells are dominated by both specific and non-specific interactions and the electric charge of viral particles determines the electrostatic force component of the latter. Here we probe the charge of individual viruses in liquid milieu by measuring the electrostatic force between a viral particle and the Atomic Force Microscope tip. The force spectroscopy data of co-adsorbed φ29 bacteriophage proheads and mature virions, adenovirus and minute virus of mice capsids is utilized for obtaining the corresponding density of charge for each virus. The systematic differences of the density of charge between the viral particles are consistent with the theoretical predictions obtained from X-ray structural data. Our results show that the density of

  14. Using 2,6-dichlorobenzamide (BAM) degrading Aminobacter sp. MSH1 in flow through biofilters--initial adhesion and BAM degradation potentials.

    PubMed

    Albers, Christian Nyrop; Jacobsen, Ole Stig; Aamand, Jens

    2014-01-01

    Micropollutants in groundwater are given significant attention by water companies and authorities due to an increasing awareness that they might be present even above the legal threshold values. As part of our investigations of the possibility to remove the common groundwater pollutant 2,6-dichlorobenzamide (BAM) by introducing the efficient BAM degrader Aminobacter sp. MSH1 into biologically active sand filters, we investigated if the strain adheres to filters containing various filter materials and if the initial adherence and subsequent degradation of BAM could be optimized. We found that most of the inoculated MSH1 cells adhered fast and that parameters like pH and ionic strength had only a minor influence on the adhesion despite huge influence on cell surface hydrophobicity. At the given growth protocol, the MSH1 strain apparently developed a subpopulation that had lost its ability to adhere to the filter materials, which was supported by attempted reinoculation of non-adhered cells. Analysis by quantitative PCR showed that most cells adhered in the top of the filters and that some of these were lost from the filters during initial operation, while insignificant losses occurred after 1 day of operation. The inoculated filters were found to degrade 2.7 μg/L BAM to below 0.1 μg/L at a 1.1-h residence time with insignificant formation of known degradation products. In conclusion, most filter materials and water types should be feasible for inoculation with the MSH1 strain, while more research into degradation at low concentrations and temperatures is needed before this technology is ready for use at actual waterworks. PMID:23670436

  15. Potential of mZD7349-conjugated PLGA nanoparticles for selective targeting of vascular cell-adhesion molecule-1 in inflamed endothelium.

    PubMed

    Imanparast, Fatemeh; Paknejad, Maliheh; Faramarzi, Mohammad Ali; Kobarfard, Farzad; Amani, Amir; Doosti, Mahmood

    2016-07-01

    Early diagnosis and restoring normal function of dysfunctional endothelium is an attractive strategy for prevention of inflammatory diseases such as atherosclerosis. Inhibition of cell adhesion in the process of atherosclerosis plaque formation, mediated by peptide antagonists of very late antigen-4 (VLA-4) has already been developed and evaluated both in vitro and in vivo. In this study, for the first time, modified ZD7349 (mZD7349) peptide, as an antagonist for VLA-4, was used for targeting fluorescein isothiocyanate-loaded poly (DL-lactic-co-glycolic acid) nanoparticles (FITC-PLGA NPs). Rate of binding and internalization of mZD7349-NPs to activated human umbilical vein endothelial cells (HUVECs) were compared with that of untargeted. Effects of temperature reduction and clathrin-mediated endocytosis inhibitor (0.45M sucrose) were also studied on the binding and internalization of mZD7349-NPs and NPs. Results showed that binding of the conjugated NPs could be significantly blocked by pre-incubating cells with the free peptide, suggesting that the binding of NPs is mediated by attaching the surface peptide to VCAM-1 on HUVECs. Also, conjugated FITC-loaded NPs were shown to be rapidly endocytosized to a greater extent than the unconjugated ones. The binding and internalization of mZD7349-NPs and NPs were slowed down at low temperature and in the presence of sucrose with greater reductions for mZD7349-NPs. To conclude, the peptide-NPs targeting the VCAM-1 is suggested as a theranostic carrier for lesions upregulating VCAM-1. PMID:27105996

  16. PILOT SCALE EXPERIMENTS TO IMPROVE PERFORMANCE OF ELECTROSTATIC PRECIPITATORS

    EPA Science Inventory

    The paper describes pilot plant experience with techniques with a potential for improving the performance of electrostatic precipitators (ESPs) by using a novel rapping reentrainment collector and flexible steel cable (in place of solid large-diameter discharge electrodes) for bo...

  17. Test instrumentation evaluates electrostatic hazards in fluid system

    NASA Technical Reports Server (NTRS)

    Collins, L. H.; Henry, R.; Krebs, D.

    1967-01-01

    RJ-1 fuel surface potential is measured with a probe to determine the degree of hazard originating from static electricity buildup in the hydraulic fluid. The probe is mounted in contact with the fluid surface and connected to an electrostatic voltmeter.

  18. Postoperative Peritoneal Adhesions

    PubMed Central

    Ryan, Graeme B.; Grobéty, Jocelyne; Majno, Guido

    1971-01-01

    This paper describes an experimental model of peritoneal adhesions, in the rat, based on two relatively minor accidents that may occur during abdominal surgery in man: drying of the serosa, and bleeding. Drying alone had little effect; drying plus bleeding consistently produced adhesions to the dried area. Fresh blood alone produced adhesions between the three membranous structures [omentum and pelvic fat bodies (PFBs)]. The formation of persistent adhesions required whole blood. Preformed clots above a critical size induced adhesions even without previous serosal injury; they were usually captured by the omentum and PFBs. If all three membranous structures were excised, the clots caused visceral adhesions. The protective role of the omentum, its structure, and the mechanism of omental adhesions, are discussed. These findings are relevant to the pathogenesis of post-operative adhesions in man. ImagesFig 3Fig 4Fig 5Fig 6Fig 7Fig 12Fig 13Fig 1Fig 2Fig 14Fig 15Fig 8Fig 9Fig 10Fig 11 PMID:5315369

  19. Adhesion of colloidal particles on modified electrodes.

    PubMed

    Kuznetsov, Volodymyr; Papastavrou, Georg

    2012-12-01

    The adhesion between colloidal silica particles and modified electrodes has been studied by direct force measurements with the colloidal probe technique based on the atomic force microscope (AFM). The combination of potentiostatic control of gold electrodes and chemical modification of their surface with self-assembled monolayers (SAMs) allows for the decoupling of forces due to the electrical double layers and functional groups at the solid/liquid interface. Adhesion on such electrodes can be tuned over a large range using the externally applied potential and the aqueous solution's ionic strength. By utilizing cantilevers with a high force constant, it is possible to separate the various contributions to adhesion in an unambiguous manner. These contributions comprise diffuse-layer overlap, van der Waals forces, solvent exclusion, and electrocapillarity. A quantitative description of the observed adhesion forces is obtained by taking into account the surface roughness of the silica particle. The main component of the adhesion forces originates from the overlap of the electrical double layers, which is tuned by the external potential. By contrast, effects due to electrocapillarity are of only minor importance. Based on our quantitative analysis, a new approach is proposed that allows tuning of the adhesion force as a function of the externally applied potential. We expect this approach to have important applications for the design of microelectromechanical systems (MEMS), the development of electrochemical sensors, and the application of micro- and nanomanipulation. PMID:23072548

  20. Electrostatic properties of two-dimensional WSe2 nanostructures

    NASA Astrophysics Data System (ADS)

    Hao, Guolin; Kou, Liangzhi; Lu, Donglin; Peng, Jie; Li, Jin; Tang, Chao; Zhong, Jianxin

    2016-01-01

    Recently, two-dimensional transition metal dichalcogenides have intrigued much attention due to their promising applications in optoelectronics. The electrostatic property investigation of WSe2 nanostructures is essential for device application. Here, the interlayer screening effects of WSe2 nanoplates with different thicknesses were investigated by measuring surface potential employing Kelvin probe force microscopy. Simultaneously, charges can be injected into WSe2 nanoplate by means of conducting atomic force microscopy to tune the electrostatic properties of WSe2 nanostructures. Our experimental results have some important implications for improving performance of WSe2-based optoelectronic devices through interface or surface engineering.

  1. Electrostatic mirror objective with eliminated spherical and axial chromatic aberrations.

    PubMed

    Bimurzaev, Seitkerim B; Serikbaeva, Gulnur S; Yakushev, Evgeniy M

    2003-01-01

    Computational formulae for the coefficients of the third-order spherical aberration and the second-order axial chromatic aberration are presented for an axially symmetric electrostatic electron mirror. A technique for eliminating the high-order derivatives of the potential axial distribution in mirror systems from the integrands is described. Conditions for elimination of spherical and axial chromatic aberrations, either separately or simultaneously, are found for a three-electrode axially symmetric mirror composed of coaxial cylinders of the same diameter. A principal scheme of the transmission electron microscope, where an electrostatic electron mirror serves as its objective, is presented. PMID:14599097

  2. Electrostatic actuators for portable microfluidic systems

    NASA Astrophysics Data System (ADS)

    Tice, Joshua

    minimize actuation potentials while eliminating stiction. Two strategies were developed to overcome challenges with electrode screening in the presence of aqueous fluids. First, instead of using the electrostatic actuators to interact directly with aqueous solutions, the actuators were used to regulate pressurized control lines for pneumatic microvalves. Secondly, by adopting a normally-closed architecture, the actuators were converted into microvalves capable of directly interacting with aqueous solutions. The two strategies are complementary, and together should enable sophisticated microfluidic systems for applications ranging from point-of-care diagnostics to portable chemical detection. To conclude the dissertation, I demonstrate a proof-of-principle microfluidic system that contained sixteen independently-operated electrostatic valves, operated with battery-operated electrical ancillaries in a hand-held format.

  3. Electrostatic Spraying With Conductive Liquids

    NASA Technical Reports Server (NTRS)

    Kosmo, Joseph J.; Dawn, Frederic S.; Erlandson, Robert E.; Atkins, Loren E.

    1989-01-01

    Thin, uniform polymer coatings applied in water base normally impossible to charge. Electrostatic sprayer modified so applies coatings suspended or dissolved in electrically conductive liquids. Nozzle and gun constructed of nonconductive molded plastic. Liquid passageway made long enough electrical leakage through it low. Coaxial hose for liquid built of polytetrafluoroethylene tube, insulating sleeve, and polyurethane jacket. Sprayer provided with insulated seal at gun-to-hose connection, nonconductive airhose, pressure tank electrically isolated from ground, and special nozzle electrode. Supply of atomizing air reduced so particle momentum controlled by electrostatic field more effectively. Developed to apply water-base polyurethane coating to woven, shaped polyester fabric. Coating provides pressure seal for fabric, which is part of spacesuit. Also useful for applying waterproof, decorative, or protective coatings to fabrics for use on Earth.

  4. Electrostatic chucking of EUVL reticles

    NASA Astrophysics Data System (ADS)

    Nataraju, Madhura; Sohn, Jaewoong; Mikkelson, Andrew R.; Engelstad, Roxann L.; Turner, Kevin T.; Van Peski, Chris K.; Orvek, Kevin J.

    2007-03-01

    Characterizing the effect of electrostatic chucking on the flatness of Extreme Ultraviolet Lithography (EUVL) reticles is necessary for the implementation of EUVL for the sub-32 nm node. In this research, finite element (FE) models have been developed to predict the flatness of reticles when clamped by a bipolar Coulombic pin chuck. Nonflatness measurements of the reticle and chuck surfaces were used to create the model geometry. Chucking was then simulated by applying forces consistent with the pin chuck under consideration. The effect of the nonuniformity of electrostatic forces due to the presence of gaps between the chuck and reticle backside surfaces was also included. The model predictions of the final pattern surface shape of the chucked reticle have been verified with chucking experiments and the results have established the validity of the models. Parametric studies with varying reticle shape, chuck shape, chuck geometry, and chucking pressure performed using FE modeling techniques are extremely useful in the development of SEMI standards for EUVL.

  5. Frontier applications of electrostatic accelerators

    NASA Astrophysics Data System (ADS)

    Liu, Ke-Xin; Wang, Yu-Gang; Fan, Tie-Shuan; Zhang, Guo-Hui; Chen, Jia-Er

    2013-10-01

    Electrostatic accelerator is a powerful tool in many research fields, such as nuclear physics, radiation biology, material science, archaeology and earth sciences. Two electrostatic accelerators, one is the single stage Van de Graaff with terminal voltage of 4.5 MV and another one is the EN tandem with terminal voltage of 6 MV, were installed in 1980s and had been put into operation since the early 1990s at the Institute of Heavy Ion Physics. Many applications have been carried out since then. These two accelerators are described and summaries of the most important applications on neutron physics and technology, radiation biology and material science, as well as accelerator mass spectrometry (AMS) are presented.

  6. A spectral canonical electrostatic algorithm

    NASA Astrophysics Data System (ADS)

    Webb, Stephen D.

    2016-03-01

    Studying single-particle dynamics over many periods of oscillations is a well-understood problem solved using symplectic integration. Such integration schemes derive their update sequence from an approximate Hamiltonian, guaranteeing that the geometric structure of the underlying problem is preserved. Simulating a self-consistent system over many oscillations can introduce numerical artifacts such as grid heating. This unphysical heating stems from using non-symplectic methods on Hamiltonian systems. With this guidance, we derive an electrostatic algorithm using a discrete form of Hamilton’s principle. The resulting algorithm, a gridless spectral electrostatic macroparticle model, does not exhibit the unphysical heating typical of most particle-in-cell methods. We present results of this using a two-body problem as an example of the algorithm’s energy- and momentum-conserving properties.

  7. Electrostatic waves in the magnetosphere.

    NASA Technical Reports Server (NTRS)

    Scarf, F. L.; Fredricks, R. W.

    1972-01-01

    Electric dipole antennas on magnetospheric spacecraft measure E field components of many kinds of electromagnetic waves. In addition, lower hybrid resonance emissions are frequently observed well above the ionosphere. The Ogo 5 plasma wave experiment has also detected new forms of electrostatic emissions that appear to interact very strongly with the local plasma particles. Greatly enhanced wave amplitudes have been found during the expansion phases of substorms, and analysis indicates that these emissions produce strong pitch angle diffusion. Intense broadband electrostatic turbulence is also detected at current layers containing steep magnetic field gradients. This current-driven instability is operative at the bow shock and also at field null regions just within the magnetosheath, and at the magnetopause near the dayside polar cusp. The plasma turbulence appears to involve ion acoustic waves, and the wave particle scattering provides an important collisionless dissipation mechanism for field merging.

  8. A model study of sequential enzyme reactions and electrostatic channeling

    NASA Astrophysics Data System (ADS)

    Eun, Changsun; Kekenes-Huskey, Peter M.; Metzger, Vincent T.; McCammon, J. Andrew

    2014-03-01

    We study models of two sequential enzyme-catalyzed reactions as a basic functional building block for coupled biochemical networks. We investigate the influence of enzyme distributions and long-range molecular interactions on reaction kinetics, which have been exploited in biological systems to maximize metabolic efficiency and signaling effects. Specifically, we examine how the maximal rate of product generation in a series of sequential reactions is dependent on the enzyme distribution and the electrostatic composition of its participant enzymes and substrates. We find that close proximity between enzymes does not guarantee optimal reaction rates, as the benefit of decreasing enzyme separation is countered by the volume excluded by adjacent enzymes. We further quantify the extent to which the electrostatic potential increases the efficiency of transferring substrate between enzymes, which supports the existence of electrostatic channeling in nature. Here, a major finding is that the role of attractive electrostatic interactions in confining intermediate substrates in the vicinity of the enzymes can contribute more to net reactive throughput than the directional properties of the electrostatic fields. These findings shed light on the interplay of long-range interactions and enzyme distributions in coupled enzyme-catalyzed reactions, and their influence on signaling in biological systems.

  9. Electrostatic structure of a magnetized laser-produced plasma.

    PubMed

    Bonde, Jeffrey; Vincena, Stephen; Gekelman, Walter

    2015-11-01

    Measurements of the structure of the electrostatic fields produced by the expansion of a laser-produced plasma into a background magnetized plasma are presented. The three-dimensional measurements of the electrostatic field are made using an emissive probe that measures the time-varying plasma potential on two orthogonal planes, one across and one containing the background magnetic field. The inductive electric field is also calculated from probe measurements of the time-varying magnetic fields. Deviations from local charge neutrality at the level of 10(-4) generate a radial electrostatic field with peak strength an order of magnitude larger than the corresponding inductive field. The electrostatic energy density near full expansion is over an order of magnitude larger than that of the induced azimuthal electric field. These measurements show that electrostatic fields must be included in theoretical and computational models of collisionless coupling in magnetized point explosions of laser-produced plasmas and their relation to similar phenomena such as magnetospheric chemical releases. PMID:26651639

  10. CATALOG OF MATERIALS AS POTENTIAL SOURCES OF INDOOR AIR EMISSIONS - VOLUME 1. INSULATION, WALLCOVERINGS, RESI- LIENT FLOOR COVERINGS, CARPET, ADHESIVES, SEALANTS AND CAULKS, AND PESTICIDES

    EPA Science Inventory

    The report discusses and presents data on constituents and emissions from products that have the potential to impact the indoor air environment. t is a tool to be used by researchers to help organize the study of materials as potential sources of indoor air emissions. ncluded are...

  11. Strategies to Minimize Adhesion Formation After Surgery

    PubMed Central

    Lazarou, George; Mondesir, Carlene; Wei, Kai; Khullar, Poonan; Ogden, Lorna

    2011-01-01

    Objectives: To compare the potential for postoperative laparoscopic adhesion formation utilizing either monopolar cautery or ultrasonic energy and to determine whether there is added benefit with the addition of a suspension of hyaluronate/carboxymethylcellulose in saline versus saline alone. Methods: Injuries were induced in rabbits by using monopolar cautery on 1 uterine horn and adjacent sidewall and ultrasonic energy on the opposite. Hyaluronate/ carboxymethylcellulose or saline was added to every other animal. Autopsies were performed after 3 weeks. Clinical and pathologic scoring of adhesions was performed by blinded investigators. Results: A very significant difference occurred in pathologic adhesion scores favoring the ultrasonic scalpel when the animals were treated with saline. However, a borderline significant difference was found in pathologic scores favoring the ultrasonic scalpel compared to the monopolar cautery. There was no significant difference in clinical adhesion scores between the 2 modalities. No significant difference in either score was found with the addition of hyaluronate/carboxymethylcellulose or saline with either instrument. Conclusion: No benefit was found for adhesion prevention with hyaluronate/carboxymethylcellulose. Although no reduction was achieved in clinical adhesions, the ultrasonic scalpel resulted in fewer histologic signs of tissue inflammation in the early postoperative period, suggesting that further clinical adhesions might develop over time with cautery. PMID:21985723

  12. Electrostatic generator/motor configurations

    SciTech Connect

    Post, Richard F

    2014-02-04

    Electrostatic generators/motors designs are provided that generally may include a first cylindrical stator centered about a longitudinal axis; a second cylindrical stator centered about the axis, a first cylindrical rotor centered about the axis and located between the first cylindrical stator and the second cylindrical stator. The first cylindrical stator, the second cylindrical stator and the first cylindrical rotor may be concentrically aligned. A magnetic field having field lines about parallel with the longitudinal axis is provided.

  13. Electrostatics interactions in classical simulations.

    PubMed

    Cisneros, G Andrés; Babin, Volodymyr; Sagui, Celeste

    2013-01-01

    Electrostatic interactions are crucial for both the accuracy and performance of atomistic biomolecular simulations. In this chapter we review well-established methods and current developments aiming at efficiency and accuracy. Specifically, we review the classical Ewald summations, particle-particle particle-method particle-method Ewald algorithms, multigrid, fast multipole, and local methods. We also highlight some recent developments targeting more accurate, yet classical, representation of the molecular charge distribution. PMID:23034752

  14. Effect of "helper lipid" on lipoplex electrostatics.

    PubMed

    Hirsch-Lerner, Danielle; Zhang, Ming; Eliyahu, Hagit; Ferrari, Marylin E; Wheeler, Carl J; Barenholz, Yechezkel

    2005-08-15

    Lipoplexes, which are complexes between cationic liposomes (L+) and nucleic acids, are commonly used as a nucleic acid delivery system in vitro and in vivo. This study aimed to better characterize cationic liposome and lipoplex electrostatics, which seems to play a major role in the formation and the performance of lipoplexes in vitro and in vivo. We characterized lipoplexes based on two commonly used monocationic lipids, DOTAP and DMRIE, and one polycationic lipid, DOSPA--each with and without helper lipid (cholesterol or DOPE). Electrical surface potential (Psi0) and surface pH were determined using several surface pH-sensitive fluorophores attached either to a one-chain lipid (4-heptadecyl hydroxycoumarin (C17HC)) or to the primary amino group of the two-chain lipids (1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-carboxyfluorescein (CFPE) and 1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-7-hydroxycoumarin) (HC-DOPE). Zeta potentials of the DOTAP-based cationic liposomes and lipoplexes were compared with Psi0 determined using C17HC. The location and relatively low sensitivity of fluorescein to pH changes explains why CFPE is the least efficient in quantifying the differences between the various cationic liposomes and lipoplexes used in this study. The fact that, for all cationic liposomes studied, those containing DOPE as helper lipid have the least positive Psi0 indicates neutralization of the cationic charge by the negatively-charged phosphodiester of the DOPE. Zeta potential is much less positively charged than Psi0 determined by C17HC. The electrostatics affects size changes that occurred to the cationic liposomes upon lipoplex formation. The largest size increase (based on static light scattering measurements) for all formulations occurred at DNA-/L+ charge ratios 0.5-1. Comparing the use of the one-chain C17HC and the two-chain HC-DOPE for monitoring lipoplex electrostatics reveals that both are suitable, as long as there is no serum (or other lipidic

  15. Quantitative nanoscale electrostatics of viruses.

    PubMed

    Hernando-Pérez, M; Cartagena-Rivera, A X; Lošdorfer Božič, A; Carrillo, P J P; San Martín, C; Mateu, M G; Raman, A; Podgornik, R; de Pablo, P J

    2015-11-01

    Electrostatics is one of the fundamental driving forces of the interaction between biomolecules in solution. In particular, the recognition events between viruses and host cells are dominated by both specific and non-specific interactions and the electric charge of viral particles determines the electrostatic force component of the latter. Here we probe the charge of individual viruses in liquid milieu by measuring the electrostatic force between a viral particle and the Atomic Force Microscope tip. The force spectroscopy data of co-adsorbed ϕ29 bacteriophage proheads and mature virions, adenovirus and minute virus of mice capsids is utilized for obtaining the corresponding density of charge for each virus. The systematic differences of the density of charge between the viral particles are consistent with the theoretical predictions obtained from X-ray structural data. Our results show that the density of charge is a distinguishing characteristic of each virus, depending crucially on the nature of the viral capsid and the presence/absence of the genetic material. PMID:26228582

  16. KSC Electrostatic Discharge (ESD) Issues

    NASA Technical Reports Server (NTRS)

    Buhler, Charles

    2008-01-01

    Discussion of key electrostatic issues that have arisen during the past few years at KSC that the Electrostatics Laboratory has studied. The lab has studied in depth the Space Shuttle's Thermal Control System Blankets, the International Space Station Thermal Blanket, the Pan/Tilt Camera Blankets, the Kapton Purge Barrier Curtain, the Aclar Purge Barrier Curtain, the Thrust Vector Controller Blankets, the Tyvek Reaction Control System covers, the AID-PAK and FLU-9 pyro inflatable devices, the Velostat Solid Rocket Booster mats, and the SCAPE suits. In many cases these materials are insulating meaning that they might be a source of unsafe levels of electrostatic discharge (ESD). For each, the lab provided in-depth testing of each material within its current configuration to ensure that it does not cause an ESD concern that may violate the safety of the astronauts, the workers and equipment for NASA. For example the lab provides unique solutions and testing such as Spark Incendivity Testing that checks whether a material is capable of generating a spark strong enough to ignite a flammable gas. The lab makes recommendations to changes in specifications, procedures, and material if necessary. The lab also consults with a variety of non-safety related ESD issues for the agency.

  17. Voltage limitations of electrostatic accelerators

    SciTech Connect

    Hyder, H. R. McK.

    1999-04-26

    The history of electrostatic accelerators has been punctuated by a series of projects in which innovative designs have failed to meet the expectations of their designers. From the early, air-insulated Van de Graaffs at Round Hill to certain of the large pressurized heavy ion accelerators of the 1970s and 1980s, increases in size or changes in design and materials have not always led to the maximum voltages expected or extrapolated. Since these failures have continued beyond childhood into a mature technology, it is reasonable to assume that the causes of voltage limitation are varied and complex. They have remained poorly understood for a number of reasons: resources for an extended program of research into breakdown and failure of electrostatic generators have always been meager, especially for large machines devoted to nuclear research; the inaccessibility of pressurized generators makes instrumentation difficult and testing slow; the calculation of transient and dynamic effects is laborious and the results difficult to verify; voltage test experiments on operating accelerators are inhibited by the significant risk of damage due to energy release on breakdown: and the total voltages (though not the local fields) achieved in many electrostatic accelerators exceed those produced in any other man-made environment. In this review, the behavior of several generators of different designs is examined in order to assess the importance of the various design features and operating conditions that control the maximum voltage achievable in a working machine.

  18. Voltage limitations of electrostatic accelerators

    SciTech Connect

    Hyder, H.R. )

    1999-04-01

    The history of electrostatic accelerators has been punctuated by a series of projects in which innovative designs have failed to meet the expectations of their designers. From the early, air-insulated Van de Graaffs at Round Hill to certain of the large pressurized heavy ion accelerators of the 1970s and 1980s, increases in size or changes in design and materials have not always led to the maximum voltages expected or extrapolated. Since these failures have continued beyond childhood into a mature technology, it is reasonable to assume that the causes of voltage limitation are varied and complex. They have remained poorly understood for a number of reasons: resources for an extended program of research into breakdown and failure of electrostatic generators have always been meager, especially for large machines devoted to nuclear research; the inaccessibility of pressurized generators makes instrumentation difficult and testing slow; the calculation of transient and dynamic effects is laborious and the results difficult to verify; voltage test experiments on operating accelerators are inhibited by the significant risk of damage due to energy release on breakdown: and the total voltages (though not the local fields) achieved in many electrostatic accelerators exceed those produced in any other man-made environment. In this review, the behavior of several generators of different designs is examined in order to assess the importance of the various design features and operating conditions that control the maximum voltage achievable in a working machine. [copyright] [ital 1999 American Institute of Physics.

  19. Monitoring Mars for Electrostatic Disturbances

    NASA Technical Reports Server (NTRS)

    Compton, D.

    2011-01-01

    The DSN radio telescope DSS-13 was used to monitor Mars for electrostatic discharges from 17 February to 11 April, 2010, and from 19 April to 4 May, 2011, over a total of 72 sessions. Of these sessions, few showed noteworthy results and no outstanding electrostatic disturbances were observed on Mars from analyzing the kurtosis of radio emission from Mars. Electrostatic discharges on mars were originally detected in June of 2006 by Ruf et al. using DSS-13. he kurtosis (normalized fourth moment of the electrical field strength) is sensitive to non-thermal radiation. Two frequencies bands, either 2.4 and 8.4 GHz or 8.4 and 32 GHz were used. The non-thermal radiation spectrum should have peaks at the lowest three modes of the theoretical Schumann Resonances of Mars. The telescope was pointed away from Mars every 5 minutes for 45 seconds to confirm if Mars was indeed the sources of any events. It was shown that by including a down-link signal in one channel and by observing when the kurtosis changed as the telescope was pointed away from the source that the procedure can monitor Mars without the need of extra equipment monitoring a control source.

  20. Electrostatic control of thermoelectricity in molecular junctions.

    PubMed

    Kim, Youngsang; Jeong, Wonho; Kim, Kyeongtae; Lee, Woochul; Reddy, Pramod

    2014-11-01

    Molecular junctions hold significant promise for efficient and high-power-output thermoelectric energy conversion. Recent experiments have probed the thermoelectric properties of molecular junctions. However, electrostatic control of thermoelectric properties via a gate electrode has not been possible due to technical challenges in creating temperature differentials in three-terminal devices. Here, we show that extremely large temperature gradients (exceeding 1 × 10(9) K m(-1)) can be established in nanoscale gaps bridged by molecules, while simultaneously controlling their electronic structure via a gate electrode. Using this platform, we study prototypical Au-biphenyl-4,4'-dithiol-Au and Au-fullerene-Au junctions to demonstrate that the Seebeck coefficient and the electrical conductance of molecular junctions can be simultaneously increased by electrostatic control. Moreover, from our studies of fullerene junctions, we show that thermoelectric properties can be significantly enhanced when the dominant transport orbital is located close to the chemical potential (Fermi level) of the electrodes. These results illustrate the intimate relationship between the thermoelectric properties and charge transmission characteristics of molecular junctions and should enable systematic exploration of the recent computational predictions that promise extremely efficient thermoelectric energy conversion in molecular junctions. PMID:25282046